The Open Plant Science Journal




ISSN: 1874-2947 ― Volume 11, 2018
RESEARCH ARTICLE

Acid Phosphatases Activity and Growth of Barley, Oat, Rye and Wheat Plants as Affected by Pi Deficiency



Iwona Ciereszko*, Honorata Balwicka, Ewa Żebrowska
Institute of Biology, The University of Bialystok, K. Ciolkowskiego 1J, 15-245 Bialystok, Poland

Abstract

Objective:

The influence of phosphorus deficit on the growth of plants and acid phosphatases activity in leaves and roots of barley seedlings (Hordeum vulgare L.), as well as oat (Avena sativa L.), rye (Secale cereale L.) and wheat plants (Triticum vulgare L.) was studied.

Method:

Plants were cultured three weeks in a nutrient media: complete (control, +P) or without phosphorus (-P). The growth on -P medium significantly affected the inorganic phosphate (Pi) content in plants tissues. Pi deficit decreased shoots growth but ratio of root/shoot was higher for -P plants when compared to control. The root elongation was enhanced under Pi deficiency - in -P oat and barley more intensive elongation was observed than in other plants. On the other hand, inhibition of shoot growth was more pronounced for -P rye and wheat. Pi-deficient plants showed higher activity of acid phosphatases in tissue extracts and in exudates from roots than +P plants.

Result:

Extracellular acid phosphatases activity increased the most for -P rye and wheat plants. Acid phosphatases secretion was intensive in growing parts of Pi-deficient roots. The activity of enzymes secreted by -P roots of all studied plants was higher than intracellular acid phosphatases.

Conclusion:

Our results indicated that wheat is more sensitive to the Pi deficiency at the early stage of growth than other plants, whereas oat is rather resistant to Pi deficit. The results suggested that acid phosphatases played an important role in acclimation of studied crop plants to moderate Pi deficiency.

Keywords: Extracellular phosphatase, Low Pi nutrition, Root, Secretion, Pi mobilization, Phosphate deficiency.


Article Information


Identifiers and Pagination:

Year: 2017
Volume: 10
First Page: 110
Last Page: 122
Publisher Id: TOPSJ-10-110
DOI: 10.2174/1874294701710010110

Article History:

Received Date: 28/02/2017
Revision Received Date: 11/05/2017
Acceptance Date: 22/05/2017
Electronic publication date: 30/09/2017
Collection year: 2017

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© 2017 Ciereszko et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence to this author at the The University of Bialystok, Institute of Biology, K. Ciolkowskiego 1J, 15-245 Bialystok, Poland; Tel: +48 85 7387028; Fax: +48 85 7457302; E-mail: icier@uwb.edu.pl




1. INTRODUCTION

Phosphate-limiting condition is common in the soils because phosphorus-containing compounds are mainly insoluble and thus unavailable for plants. Phosphorus is an essential nutrient important in metabolism, plant growth, development and productivity. Plants respond to phosphorus starvation by developing various mechanisms that can increase the Pi availability and uptake from soil as well as Pi mobilization/recycling and transport in plant cells and tissues [1Schachtman DP, Reid RJ, Ayling SM. Phosphorus uptake by plants: From soil to cell. Plant Physiol 1998; 116(2): 447-53.
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-5Raghothama KG, Karthikeyan AS. Phosphate acquisition. Plant Soil 2005; 274: 37-49.
[http://dx.doi.org/10.1007/s11104-004-2005-6]
]. Plants acclimate to Pi deficiency by modifications of growth parameters and metabolism or genes expression and protein production [6Lynch JP, Brown KM. Regulation of root architecture by phosphorus availability. Current Topics in Plant Physiology 1998; 19: 148-56.-11Ciereszko I, Kleczkowski LA. Expression of several genes involved in sucrose/starch metabolism as affected by different strategies to induce phosphate deficiency in Arabidopsis. Acta Physiol Plant 2005; 27: 147-55.
[http://dx.doi.org/10.1007/s11738-005-0018-2]
]. One of the common symptoms of phosphate deficiency is the increase of root/shoot ratios which is usually the result of reduction of shoot growth and/or stimulation of root growth [7Hermans C, Hammond JP, White PJ, Verbruggen N. How do plants respond to nutrient shortage by biomass allocation? Trends Plant Sci 2006; 11(12): 610-7.
[http://dx.doi.org/10.1016/j.tplants.2006.10.007] [PMID: 17092760]
, 12Mollier A, Pellerin S. Maize root system growth and development as influenced by phosphorus deficiency. J Exp Bot 1999; 50: 487-97.
[http://dx.doi.org/10.1093/jxb/50.333.487]
-14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
]. Low Pi availability in the soil often affected the root elongation, increase development of lateral roots as well as the number and length of root hairs [15Hajabbasi MA, Schumacher TE. Phosphorus effects on root growth and development in two maize genotypes. Plant Soil 1994; 158: 39-46.
[http://dx.doi.org/10.1007/BF00007915]
-17Williamson LC, Ribrioux SP, Fitter AH, Leyser HM. Phosphate availability regulates root system architecture in Arabidopsis. Plant Physiol 2001; 126(2): 875-82.
[http://dx.doi.org/10.1104/pp.126.2.875] [PMID: 11402214]
]. Pi deficiency can regulate many features of anatomy of roots, or root architecture, e.g., aerenchyma formation (via ethylene mediation), higher root hair density, different lateral branching or cluster root formation and the total surface area enhance [6Lynch JP, Brown KM. Regulation of root architecture by phosphorus availability. Current Topics in Plant Physiology 1998; 19: 148-56., 7Hermans C, Hammond JP, White PJ, Verbruggen N. How do plants respond to nutrient shortage by biomass allocation? Trends Plant Sci 2006; 11(12): 610-7.
[http://dx.doi.org/10.1016/j.tplants.2006.10.007] [PMID: 17092760]
, 16Borch K, Bouma TJ, Lynch JP, Brown KM. Ethylene: a regulator of root architectural responses to soil phosphorus availability. Plant Cell Environ 1999; 22: 425-31.
[http://dx.doi.org/10.1046/j.1365-3040.1999.00405.x]
, 18Fan M, Zhu J, Richards C, Brown KM, Lynch JP. Physiological roles for aerenchyma in phosphorus-stressed roots. Funct Plant Biol 2003; 30: 493-506.
[http://dx.doi.org/10.1071/FP03046]
]. In response to Pi deficit many plants activate root colonization by mycorrhizal fungi or interaction with rhizosphere bacteria [5Raghothama KG, Karthikeyan AS. Phosphate acquisition. Plant Soil 2005; 274: 37-49.
[http://dx.doi.org/10.1007/s11104-004-2005-6]
, 9Rausch C, Bucher M. Molecular mechanisms of phosphate transport in plants. Planta 2002; 216(1): 23-37.
[http://dx.doi.org/10.1007/s00425-002-0921-3] [PMID: 12430011]
, 19Karandashov V, Bucher M. Symbiotic phosphate transport in arbuscular mycorrhizas. Trends Plant Sci 2005; 10(1): 22-9.
[http://dx.doi.org/10.1016/j.tplants.2004.12.003] [PMID: 15642520]
]. Probably, all of these changes result in a better opportunity for soil exploration and are under strictly genetic control [20Schiefelbein JW. Constructing a plant cell. The genetic control of root hair development. Plant Physiol 2000; 124(4): 1525-31.
[http://dx.doi.org/10.1104/pp.124.4.1525] [PMID: 11115870]
, 21Wissuwa M. How do plants achieve tolerance to phosphorus deficiency? Small causes with big effects. Plant Physiol 2003; 133(4): 1947-58.
[http://dx.doi.org/10.1104/pp.103.029306] [PMID: 14605228]
]. Differences in Pi uptake from soil may be due to better growth of roots or high external root efficiency, the simulations indicated that even very small changes in parameters related to the root growth could have significant effects on Pi uptake [21Wissuwa M. How do plants achieve tolerance to phosphorus deficiency? Small causes with big effects. Plant Physiol 2003; 133(4): 1947-58.
[http://dx.doi.org/10.1104/pp.103.029306] [PMID: 14605228]
]. In addition, low Pi supply often induces exudation of organic acids and protons from roots to increase Pi availability from insoluble mineral forms of phosphorus in the rhizosphere, or secretion of enzymes hydrolyzing organic esters of phosphorus [4Vance CP, Uhde-Stone C, Allan DL. Phosphorus acquisition and use: Critical adaptations by plants for securing a nonrenewable resource. New Phytol 2003; 157: 423-47.
[http://dx.doi.org/10.1046/j.1469-8137.2003.00695.x]
, 5Raghothama KG, Karthikeyan AS. Phosphate acquisition. Plant Soil 2005; 274: 37-49.
[http://dx.doi.org/10.1007/s11104-004-2005-6]
, 22Wang Y-L, Almvik M, Clarke N, et al. Contrasting responses of root morphology and root-exuded organic acids to low phosphorus availability in three important food crops with divergent root traits. AoB Plants 2015; 7: plv097.
[http://dx.doi.org/10.1093/aobpla/plv097] [PMID: 26286222]
, 23Duff SM, Sarath G, Plaxton WC. The role of acid phosphatases in plant phosphorus metabolism. Plant Physiol 1994; 90: 791-800.
[http://dx.doi.org/10.1111/j.1399-3054.1994.tb02539.x]
].

Acid phosphatases (EC 3.1.3.2) are important components of the response of plants to Pi limitation [23Duff SM, Sarath G, Plaxton WC. The role of acid phosphatases in plant phosphorus metabolism. Plant Physiol 1994; 90: 791-800.
[http://dx.doi.org/10.1111/j.1399-3054.1994.tb02539.x]
-25Tran HT, Hurley BA, Plaxton WC. Feeding hungry plants: the role of purple acid phosphatases in phosphate nutrition. Plant Sci 2010; 179: 14-27.
[http://dx.doi.org/10.1016/j.plantsci.2010.04.005]
]. Acid phosphatases, mainly extracellular isoforms, catalyze the hydrolysis of Pi from phosphate monoesters (present both in soil and plant tissues) and function in the processes of uptake, transport and recycling of Pi. Intracellular acid phosphatases are important for phosphorus scavenging processes and Pi remobilization in plant cells and tissues [4Vance CP, Uhde-Stone C, Allan DL. Phosphorus acquisition and use: Critical adaptations by plants for securing a nonrenewable resource. New Phytol 2003; 157: 423-47.
[http://dx.doi.org/10.1046/j.1469-8137.2003.00695.x]
, 14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
, 23Duff SM, Sarath G, Plaxton WC. The role of acid phosphatases in plant phosphorus metabolism. Plant Physiol 1994; 90: 791-800.
[http://dx.doi.org/10.1111/j.1399-3054.1994.tb02539.x]
, 25Tran HT, Hurley BA, Plaxton WC. Feeding hungry plants: the role of purple acid phosphatases in phosphate nutrition. Plant Sci 2010; 179: 14-27.
[http://dx.doi.org/10.1016/j.plantsci.2010.04.005]
], but their role in plant acclimation to low Pi availability is not always clear [26Yan X, Liao H, Trull MC, Beebe SE, Lynch JP. Induction of a major leaf acid phosphatase does not confer adaptation to low phosphorus availability in common bean. Plant Physiol 2001; 125(4): 1901-11.
[http://dx.doi.org/10.1104/pp.125.4.1901] [PMID: 11299369]
]. Acid phosphatases are found in intracellular spaces, cell walls and inside cell: in amyloplast, mitochondrium, nucleus, Golgi body and endoplasmic reticulum [23Duff SM, Sarath G, Plaxton WC. The role of acid phosphatases in plant phosphorus metabolism. Plant Physiol 1994; 90: 791-800.
[http://dx.doi.org/10.1111/j.1399-3054.1994.tb02539.x]
, 25Tran HT, Hurley BA, Plaxton WC. Feeding hungry plants: the role of purple acid phosphatases in phosphate nutrition. Plant Sci 2010; 179: 14-27.
[http://dx.doi.org/10.1016/j.plantsci.2010.04.005]
, 27Sujkowska M, Borucki W, Golinowski W. Localization of acid phosphatase activity in the apoplast of root nodules of pea (Pisum sativum). Acta Soc Bot Pol 2006; 75: 33-8.
[http://dx.doi.org/10.5586/asbp.2006.006]
]. Acid phosphatase activity increase under Pi-deficient conditions have been documented for various crop plants, including lupine and clover, barley, oat, rice or wheat [28Hunter DA, McManus MT. Comparison of acid phosphatases in two genotypes of white clover with different responses to applied phosphate. J Plant Nutr 1999; 22: 679-92.
[http://dx.doi.org/10.1080/01904169909365663]
-32Mc Lachlan KD. Acid phosphatase activity of intact roots and phosphorus nutrition in plants: II. Variations among wheat roots. Aust J Agric Res 1980; 31: 441-8.
[http://dx.doi.org/10.1071/AR9800441]
]. Some of the genes encoding acid phosphatases, both intra- and extracellular, were found to be upregulated by Pi-deficient condition, and correlated with higher proteins content [5Raghothama KG, Karthikeyan AS. Phosphate acquisition. Plant Soil 2005; 274: 37-49.
[http://dx.doi.org/10.1007/s11104-004-2005-6]
, 14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
, 29Wasaki J, Yamamura T, Shinano T, Osaki M. Secreted acid phosphatase is expressed in cluster roots of lupin in response to phosphorus deficiency. Plant Soil 2003; 248: 129-36.
[http://dx.doi.org/10.1023/A:1022332320384]
, 33Tomscha JL, Trull MC, Deikman J, Lynch JP, Guiltinan MJ. Phosphatase under-producer mutants have altered phosphorus relations. Plant Physiol 2004; 135(1): 334-45.
[http://dx.doi.org/10.1104/pp.103.036459] [PMID: 15122033]
]. Extracellular acid phosphatases, including those secreted by plant roots, can efficiently acquire Pi from organic sources of phosphorus - several studies have demonstrated that Pi deficiency in the soil (or growth medium) increased secretion of acid phosphatases from the roots [29Wasaki J, Yamamura T, Shinano T, Osaki M. Secreted acid phosphatase is expressed in cluster roots of lupin in response to phosphorus deficiency. Plant Soil 2003; 248: 129-36.
[http://dx.doi.org/10.1023/A:1022332320384]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
, 33Tomscha JL, Trull MC, Deikman J, Lynch JP, Guiltinan MJ. Phosphatase under-producer mutants have altered phosphorus relations. Plant Physiol 2004; 135(1): 334-45.
[http://dx.doi.org/10.1104/pp.103.036459] [PMID: 15122033]
-36Lu L, Qiu W, Gao W, Tyerman SD, Shou H, Wang C. OsPAP10c, a novel secreted acid phosphatase in rice, plays an important role in the utilization of external organic phosphorus. Plant Cell Environ 2016; 39(10): 2247-59.
[http://dx.doi.org/10.1111/pce.12794] [PMID: 27411391]
]. On the other hand, some experiments showed no significant changes in acid phosphatase activities in plants grown under Pi deficiency [26Yan X, Liao H, Trull MC, Beebe SE, Lynch JP. Induction of a major leaf acid phosphatase does not confer adaptation to low phosphorus availability in common bean. Plant Physiol 2001; 125(4): 1901-11.
[http://dx.doi.org/10.1104/pp.125.4.1901] [PMID: 11299369]
, 28Hunter DA, McManus MT. Comparison of acid phosphatases in two genotypes of white clover with different responses to applied phosphate. J Plant Nutr 1999; 22: 679-92.
[http://dx.doi.org/10.1080/01904169909365663]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
], or indicated that root acid phosphatases are poor indicator of growth of crop plants under low Pi nutrition in different soils [37George TS, Gregory PJ, Hocking PJ, Richardson AE. Variation in root associated phosphatase activities in wheat contributes to the utilization of organic P substrates in-vitro, but does not explain differences in the P-nutrition when grown in soils. Environ Exp Bot 2008; 64: 239-49.
[http://dx.doi.org/10.1016/j.envexpbot.2008.05.002]
]. Genotypic variations in activity of acid phosphatases (or secretion) and morphological features under Pi deficiency has been reported for various crop species and cultivars [14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
, 28Hunter DA, McManus MT. Comparison of acid phosphatases in two genotypes of white clover with different responses to applied phosphate. J Plant Nutr 1999; 22: 679-92.
[http://dx.doi.org/10.1080/01904169909365663]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
, 32Mc Lachlan KD. Acid phosphatase activity of intact roots and phosphorus nutrition in plants: II. Variations among wheat roots. Aust J Agric Res 1980; 31: 441-8.
[http://dx.doi.org/10.1071/AR9800441]
, 38Ciereszko I, Szczygła A, Żebrowska E. Phosphate deficiency affects acid phosphatases activity and growth of two wheat varieties. J Plant Nutr 2011; 34: 815-29.
[http://dx.doi.org/10.1080/01904167.2011.544351]
, 39Asmar F, Gahoonia TS, Nielsen NE. Barley genotypes differ in activity of soluble extracellular phosphatase and depletion of organic phosphorus in the rhizosphere soil. Plant Soil 1995; 172: 117-22.
[http://dx.doi.org/10.1007/BF00020865]
].

The aim of the study was to compare responses of common cereal plants (barley, oat, rye, wheat) to early phosphate deficiency during growth period important to tiller formation and further productivity. Due to the variability in responses of plant species/cultivars to Pi deficiency, such studies are still necessary. The examination of the intensity of growth and activity of acid phosphatases in different plant tissues could be helpful to estimate the role of these enzymes in acclimation of studied crop plants to Pi deficit.

2. MATERIAL AND METHODS

2.1. Plant Growth Conditions

Seeds of barley (Hordeum vulgare L., cv. Rodos) and oat plants (Avena sativa L., cv. Bajka), rye (Secale cereale L., cv. Dankowskie Zlote) as well as wheat (Triticum vulgare L., cv. Henrika) were germination (7 days), after that transferred to separate containers filled with control nutrient medium (+P) or medium without Pi (-P), similar to that described by Ciereszko et al. [40Ciereszko I, Gniazdowska A, Mikulska M, Rychter AM. Assimilate translocation in bean plants (Phaseolus vulgaris L.) during phosphate deficiency. J Plant Physiol 1996; 149: 343-8.
[http://dx.doi.org/10.1016/S0176-1617(96)80132-5]
]. Pi-sufficient nutrient medium contained: Ca(NO3)2 (4.4 mM), MgSO4 (2.7 mM), KNO3 (1.5 mM), KH2PO4 (1 mM), Fe-EDTA (76 μM), H3BO3 (43 μM), MnCl2 (9 μM), CuSO4 (0.3 μM), ZnSO4 (0.8 μM), H2MoO4 (0.1 μM); to the -P medium KCl (2 mM) (instead KH2PO4) was added. Plants were cultured in different containers (15 seedlings per about 5 l of nutrient medium). The culture medium was adjusted to pH 5.7 (by adding drops of 1N NaOH), aerated and changed every 4 days. Plants were cultured for one to three weeks in growth chamber under 16 h light period, photon flux density of 130 μmol m-2 s-1, temperature of 23/19 °C (day/night), and air humidity about 70%. Cereal plants were cultured 7, 14 and 21 days on various nutrient media (14-, 21- and 28-day old plants, respectively). Samples of tissues (leaves or roots) were collected 4-5 hours after the beginning of photoperiod. Fresh mass and length of shoots and roots were measured after plant harvest, dry mass-after at least 24 h tissue drying at 900C; root diameters were estimated according to [15Hajabbasi MA, Schumacher TE. Phosphorus effects on root growth and development in two maize genotypes. Plant Soil 1994; 158: 39-46.
[http://dx.doi.org/10.1007/BF00007915]
].

2.2. Phosphate Content Measurements

Inorganic phosphate (Pi) content was determined after homogenization and extraction of tissues (leaves or roots) of barley, oat, rye and wheat plants (0.5 g samples), cultured 1, 2 and 3 weeks on +P and –P nutrient media, with cold 10% trichloroacetic acid. The phosphomolybdate colorimetric assay, described by Ames [41Ames BN. Assay of inorganic phosphate, total phosphate and phosphatases. Methods Enzymol 1966; 8: 115-8.
[http://dx.doi.org/10.1016/0076-6879(66)08014-5]
], was used to Pi determination.

2.3. Extracellular Acid Phosphatases Activity Measurements

Root surface acid phosphatases activity measurements were described before by Ciereszko et al. [13Ciereszko I, Janonis A, Kociakowska M. Growth and metabolism of cucumber in phosphate-deficient conditions. J Plant Nutr 2002; 25: 1115-27.
[http://dx.doi.org/10.1081/PLN-120003943]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
]. The whole roots or root “tips” (around 20 mm) were washed in distilled water, blot dried and placed into 10 ml (or 30 ml for larger roots) of substrate (6 mM p-nitrophenyl phosphate in 100 mM sodium acetate buffer, pH 5.0) and incubated at 20°C. To ensure linearity, 100 μl aliquots of medium were removed at different intervals for above 2 hours, to each sample 100 μl of 4N NaOH was immediately added (to terminate the reaction) and the absorbancies were read at 410 nm (Cecil CE 2501) and compared to a standard curve with p-nitrophenol. Enzymes activity, after 15 min incubations, was presented, as μmol p-nitrophenol h-1 g-1 of fresh weight (FW).

2.4. Intracellular Acid Phosphatases Activity Measurements

For intracellular acid phosphatase activity assay, tissues samples (0.2 g, leaves or roots) were homogenized and extracted in 5 ml of 50 mM Na-acetate buffer, pH 5.0, with 1 mM DTT (dithiothreitol), centrifuged at 12000 g for 10 min at 4°C. Enzyme activities were determined in supernatants (100 μl) after 10 min incubations at 37°C with 6 mM p-nitrophenyl phosphate in 100 mM Na-acetate buffer, pH 5.0; reaction was terminated of as described above. The results after 15 min of incubations are presented. The protein content in media for measurements of surface acid phosphatase activity was extremely low, thus both intra- and extracellular enzymes activity was expressed per g FW (μmol p-nitrophenol h-1g-1FW), similar to Żebrowska et al. [14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
].

2.5. Soluble Proteins Content Determination

The soluble proteins content was determined by the method described by Bradford [42Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 1976; 72: 248-54.
[http://dx.doi.org/10.1016/0003-2697(76)90527-3] [PMID: 942051]
]. The absorbance at 595 nm was measured in enzymatic extract (0.2 ml) after 15 min incubation with the Bradford reagent (Sigma) (2 ml) and compared to a standard curve with BSA.

2.6. Statistical Analysis

All measurements were performed in at least three replicates in four to five series, independent, of experiments and standard deviation (SD) was calculated. The treatments effects were tested by one way analysis of variance. Means were compared between the treatments at the 0.05 probability level (SPSS Statistics).

3. RESULTS

Inorganic phosphate content in leaves and roots of all studied plants decreased significantly already after one week of culture without Pi (Fig. 1). After 2 weeks culture on nutrient media the Pi content in -P leaves (21-days-old plants) was between 6-13% of that found in control (+P plants). Pi content in root of P-deficient barley and rye was about 7% of control but in -P roots of oat and wheat was about 16% and 14%, respectively, of control. After three weeks of culture in -P conditions, Pi level in leaves of studied plants was about 8-9% of the control. In the -P roots of barley, Pi content decreased to about 4% of control, however in roots of oat and wheat was 7% or in rye - 11% of that found in +P plants (Fig. 1).

The growth of studied plants was significantly affected by Pi deficiency, especially after three weeks of growth (Fig. 2). The fresh mass of shoots after one week growth on -P nutrient medium was between 73%-82% of control plants; the fresh mass of +P and -P roots after one week culture was similar, with exception of barley (64% of control) (Table 1). Shoot mass of Pi-deficient cereals decreased significantly after two weeks of culture and was 70%, 58%, 35% and 51% of control for -P barley, oat, rye and wheat, respectively; however root fresh mass of -P and +P plants was similar (Tables 1-4). The differences in growth parameters were higher after three weeks of culture when the shoot fresh weight was about 54%, 26%, 13% and 23% of control, respectively, for -P barley, oat, rye and wheat. Additionally, the reduction of -P root mass was observed and was 67%, 69% and 49% of control, respectively, for -P oat, rye and wheat (Tables 2-4). However, the ratio of root/shoot for fresh mass was always significantly higher in -P plants than in +P plants, e.g. up to 3-5-fold for rye (Table 3). The shoot dry masses of Pi-deficient cereal plants were lower when compared to phosphate-sufficient plant, in a similar way like fresh weight of shoots (Tables 1-4). The dry masses of roots were similar in younger +P and -P plants, however after 3 weeks of culture under Pi-deficient condition the root dry weight of rye and wheat was about 65% of the control (Tables 3, 4). The decrease in shoot mass of -P crop plants was accompanied by a decrease in shoot height; on the other hand, root length of Pi-deficient plants increased by about 20% (for 21 days old barley and 28 days old wheat), by 28 and 38% (for 14- and 21 days old rye) or even by 39% (for 28 days old oat) when compared to control, even despite mass drop (Tables 1-4). The increase of root length of studied -P plants was probably at the cost of decrease of root diameters. The ratio of root/shoot length was always higher in -P plants than in +P plants, especially after 2-3 weeks of culture (Tables 1-4).

Fig. (1)
Pi content in shoots and roots of barley, oat, rye and wheat plants grown for 1, 2 and 3 weeks in phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium (means ± SD); all differences between treatments are statistically important at p<0.05.


Table 1
Growth parameters of barley plants (Hordeum vulgare L.) cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Table 2
Growth parameters of oat (Avena sativa L.) plants cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Table 3
Growth parameters of rye (Secale cereale L.) plants cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Table 4
Growth parameters of wheat (Triticum vulgare L.) plants cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Fig. (2)
Barley, oat, rye and wheat plants after 3 weeks of culture on complete phosphate-sufficient nutrient medium (+P), and phosphate-deficient (-P) nutrient medium.


The activity of intracellular acid phosphatases in shoots and roots generally increased in all studied plants under Pi deficiency, especially after 2-3 weeks of culture on nutrient medium; however, this occurred to a lesser extent than increase of extracellular phosphatases activity (Tables 5-8). After three weeks of culture the activity of acid phosphatase in extracts from leaves of -P barley and oat plants was higher by about 20% and 50%, respectively, as compared with +P plants (Tables 5, 6). However, the activity of internal acid phosphatases in -P shoots of rye and wheat increased significantly already after 2 weeks culture by about 1.9 and 1.3-fold, whereas after 3 weeks - by 2.5-fold and 2.3-fold, respectively, when compared to control plants (Tables 7, 8). After 14 days of plant growth on nutrient media, the activity of internal acid phosphatases in -P root of rye increased by about 85%, but in wheat and barley roots - by 35% and 27%, respectively, as compared to +P plants (Tables 6-8). After 21 days of culture, intracellular acid phosphatases activity was enhanced by about 1.4-fold for -P roots of barley and oat (Tables 5-6), and even 2.7-fold for -P rye (Table 7), but was similar in -P and +P roots of wheat (Table 8). Soluble proteins content in enzymatic extracts from leaves and roots was generally not affected by Pi deficit, except that found in shoots of barley and wheat plants, grown 1-2 weeks on –P medium and shoots of oat and rye cultured 3 weeks (Table 9); in all experimental conditions soluble proteins content in roots was much lower than in leaves.

Table 5
Intracellular and extracellular acid phosphatase activities in leaves and roots of barley (Hordeum vulgare L.) plants cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Table 6
Intracellular and extracellular acid phosphatase activities in leaves and roots of oat (Avena sativa L.) plants cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Table 7
Intracellular and extracellular acid phosphatase activities in leaves and roots of rye (Secale cereale L.) plants cultured 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Table 8
Intracellular and extracellular acid phosphatase activities in leaves and roots of wheat (Triticum vulgare L.) plants cultured 1-3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD.


Extracellular acid phosphatase activity increased already after one week of culture on -P nutrient medium in intact roots of barley, rye and wheat, by about 50% or 80% when compared to +P roots (Tables 5, 7, 8). The increase of enzyme activity, secreted by intact -P roots after 2 week-culture, was about 1.5- and 1.4-fold for barley and oat (Tables 5, 6), 2.4-fold for rye (Table 7), 2.8-fold for wheat (Table 8), as compared to control. After 3 weeks of culture the increase of extracellular phosphatase activity in -P roots was: 2.4-fold for barley, 2.3-fold for oat, 4.8-fold for rye and 3.5-fold for wheat as compared to the control (Tables 5-8). The acid phosphatases activity (and secretion) was intensive in young, growing parts of -P roots of all crop plants (e.g., even up to 4-5 times more, for rye and wheat) whereas activity of extracellular phosphatases in the mature parts of roots was lower (Tables 5-8 and data not shown). When compared the studied plants, the highest activity of root surface enzymes was observed for wheat and rye, after 21 days of culture on -P medium (especially in root tips of plants).

Table 9
Soluble protein content in extracts from leaves and roots of barley, oat, rye and wheat plants grown for 3 weeks on phosphate-sufficient (+P) or phosphate-deficient (-P) nutrient medium. Means ± SD values are indicated. *Differences statistically important at 0.05.


4. DISCUSSION

The growth of barley, oat, rye and wheat plants for three weeks on Pi-deficient nutrient media resulted in lower Pi content in tissues, changed characteristics of growth (mainly root to shoot ratios increase) and had significant effect on acid phosphatases activity increase in tissues and root exudates.

Pi deficiency significantly reduced shoots growth of all studied plants, especially after 3-weeks culture, the –P plants were also characterized by lower formation of tillers. When compared the growth parameters of studied cereal plants, some conclusion could be made, e.g. the inhibition of shoot growth was more pronounced for rye and wheat, cultured on Pi-deficient medium than other crop plants (Tables 1-4). Our other experiments indicated that Pi deficiency, after 2-3 weeks culture, affected also leaves area and intensity of photosynthesis and assimilate production in crop plants [13, 40 and data not published]. Generally, the early Pi-deficiency had no significant effect on fresh and dry mass of roots but a tendency to enhanced elongation of roots was observed for all studied plants. More intensive elongation of the roots was observed for -P oat (and barley) than other plants, especially after 3 weeks growth on nutrient medium. The length of roots of –P plants increased, compared with control, already after one week of culture on nutrient media without Pi and differences were similar (or higher - for rye) until about 14-days-culture; however after that the root growth was relatively slower and after 21 days of culture the root length was similar (for barley, rye) or lower (for wheat) (Tables 1-4).

Our previous results indicated that transfer of -P cucumber plants to full nutrient media did not change the slope of curve of root growth, the elongation of roots after such transfer was more similar to Pi-deficient plants than to +P plants, which might indicate that a signal coming from Pi starvation caused nonreversible reaction of plant, in this case - the initial increase of root length [13Ciereszko I, Janonis A, Kociakowska M. Growth and metabolism of cucumber in phosphate-deficient conditions. J Plant Nutr 2002; 25: 1115-27.
[http://dx.doi.org/10.1081/PLN-120003943]
]. The stimulation of root elongation is one of plant responses to low Pi level, important for exploring and searching of available Pi, mainly at the beginning of stress condition. However, as an effect of prolonged Pi starvation the significant reduction of root growth was also observed [6Lynch JP, Brown KM. Regulation of root architecture by phosphorus availability. Current Topics in Plant Physiology 1998; 19: 148-56., 7Hermans C, Hammond JP, White PJ, Verbruggen N. How do plants respond to nutrient shortage by biomass allocation? Trends Plant Sci 2006; 11(12): 610-7.
[http://dx.doi.org/10.1016/j.tplants.2006.10.007] [PMID: 17092760]
, 12Mollier A, Pellerin S. Maize root system growth and development as influenced by phosphorus deficiency. J Exp Bot 1999; 50: 487-97.
[http://dx.doi.org/10.1093/jxb/50.333.487]
, 13Ciereszko I, Janonis A, Kociakowska M. Growth and metabolism of cucumber in phosphate-deficient conditions. J Plant Nutr 2002; 25: 1115-27.
[http://dx.doi.org/10.1081/PLN-120003943]
, 43Gniazdowska A, Mikulska M, Rychter AM. Growth, nitrate uptake and respiration rate in bean roots under phosphate deficiency. Biol Plant 1998; 41: 217-26.
[http://dx.doi.org/10.1023/A:1001862513105]
]. It was indicated that growth of maize root was also enhanced shortly after beginning of Pi deficit, although it was reduced when low-Pi conditions were prolonged [12Mollier A, Pellerin S. Maize root system growth and development as influenced by phosphorus deficiency. J Exp Bot 1999; 50: 487-97.
[http://dx.doi.org/10.1093/jxb/50.333.487]
, 15Hajabbasi MA, Schumacher TE. Phosphorus effects on root growth and development in two maize genotypes. Plant Soil 1994; 158: 39-46.
[http://dx.doi.org/10.1007/BF00007915]
]. The elongation rate of axial roots was maintained but density of some laterals was not affected, however the emergence of new axial roots was drastically reduced, probably due to lower availability of carbohydrates [7Hermans C, Hammond JP, White PJ, Verbruggen N. How do plants respond to nutrient shortage by biomass allocation? Trends Plant Sci 2006; 11(12): 610-7.
[http://dx.doi.org/10.1016/j.tplants.2006.10.007] [PMID: 17092760]
, 17Williamson LC, Ribrioux SP, Fitter AH, Leyser HM. Phosphate availability regulates root system architecture in Arabidopsis. Plant Physiol 2001; 126(2): 875-82.
[http://dx.doi.org/10.1104/pp.126.2.875] [PMID: 11402214]
]. It was suggested that, under Pi starvation, a decrease of ATP content might be a limiting factor for plant biomass production and that the increase of root mass or length of -P plants was the result of better relative growth rate but only at the beginning of culture [43Gniazdowska A, Mikulska M, Rychter AM. Growth, nitrate uptake and respiration rate in bean roots under phosphate deficiency. Biol Plant 1998; 41: 217-26.
[http://dx.doi.org/10.1023/A:1001862513105]
]. In addition, Pi deficiency could regulate other features of root architecture/ anatomy of crop plants, similar to those reported by [6Lynch JP, Brown KM. Regulation of root architecture by phosphorus availability. Current Topics in Plant Physiology 1998; 19: 148-56., 7Hermans C, Hammond JP, White PJ, Verbruggen N. How do plants respond to nutrient shortage by biomass allocation? Trends Plant Sci 2006; 11(12): 610-7.
[http://dx.doi.org/10.1016/j.tplants.2006.10.007] [PMID: 17092760]
, 16Borch K, Bouma TJ, Lynch JP, Brown KM. Ethylene: a regulator of root architectural responses to soil phosphorus availability. Plant Cell Environ 1999; 22: 425-31.
[http://dx.doi.org/10.1046/j.1365-3040.1999.00405.x]
, 18Fan M, Zhu J, Richards C, Brown KM, Lynch JP. Physiological roles for aerenchyma in phosphorus-stressed roots. Funct Plant Biol 2003; 30: 493-506.
[http://dx.doi.org/10.1071/FP03046]
, 21Wissuwa M. How do plants achieve tolerance to phosphorus deficiency? Small causes with big effects. Plant Physiol 2003; 133(4): 1947-58.
[http://dx.doi.org/10.1104/pp.103.029306] [PMID: 14605228]
], often resulted in a greater exploration of the soil and better root efficiency and higher Pi uptake, however we did not observed such features in our studies.

Change in acid phosphatases activity is rather a common reaction of plant on phosphorus starvation, facilitated Pi availability by hydrolyses of organic sources of phosphorus in soil or inside plant cell [5Raghothama KG, Karthikeyan AS. Phosphate acquisition. Plant Soil 2005; 274: 37-49.
[http://dx.doi.org/10.1007/s11104-004-2005-6]
, 23Duff SM, Sarath G, Plaxton WC. The role of acid phosphatases in plant phosphorus metabolism. Plant Physiol 1994; 90: 791-800.
[http://dx.doi.org/10.1111/j.1399-3054.1994.tb02539.x]
]. Intracellular acid phosphatases are probably involved in greater recycling of organic P, mainly in the vacuole; whereas acid phosphatases secreted from roots have a role in breakdown of organic forms of phosphorus in the rhizosphere [23Duff SM, Sarath G, Plaxton WC. The role of acid phosphatases in plant phosphorus metabolism. Plant Physiol 1994; 90: 791-800.
[http://dx.doi.org/10.1111/j.1399-3054.1994.tb02539.x]
-25Tran HT, Hurley BA, Plaxton WC. Feeding hungry plants: the role of purple acid phosphatases in phosphate nutrition. Plant Sci 2010; 179: 14-27.
[http://dx.doi.org/10.1016/j.plantsci.2010.04.005]
]. The increase of root surface phosphatases activity was often correlated with the decrease of phosphorus level in leaves, as observed for white clover genotypes [28Hunter DA, McManus MT. Comparison of acid phosphatases in two genotypes of white clover with different responses to applied phosphate. J Plant Nutr 1999; 22: 679-92.
[http://dx.doi.org/10.1080/01904169909365663]
]. However, other experiments showed negative relationship between acid phosphatase activity and efficiency of Pi uptake under phosphate deficit [26Yan X, Liao H, Trull MC, Beebe SE, Lynch JP. Induction of a major leaf acid phosphatase does not confer adaptation to low phosphorus availability in common bean. Plant Physiol 2001; 125(4): 1901-11.
[http://dx.doi.org/10.1104/pp.125.4.1901] [PMID: 11299369]
, 32Mc Lachlan KD. Acid phosphatase activity of intact roots and phosphorus nutrition in plants: II. Variations among wheat roots. Aust J Agric Res 1980; 31: 441-8.
[http://dx.doi.org/10.1071/AR9800441]
]. Enzyme activity is dependent on the plant species, duration of Pi deficiency and may differ, even between crop cultivars, e.g. barley, rice, maize or oat genotypes [14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
, 15Hajabbasi MA, Schumacher TE. Phosphorus effects on root growth and development in two maize genotypes. Plant Soil 1994; 158: 39-46.
[http://dx.doi.org/10.1007/BF00007915]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
, 31Ming F, Mi G, Zhang F, Zhu L. Differential response of rice plants to low-phosphorus stress and its physiological adaptive mechanism. J Plant Nutr 2002; 25: 1213-24.
[http://dx.doi.org/10.1081/PLN-120004383]
, 39Asmar F, Gahoonia TS, Nielsen NE. Barley genotypes differ in activity of soluble extracellular phosphatase and depletion of organic phosphorus in the rhizosphere soil. Plant Soil 1995; 172: 117-22.
[http://dx.doi.org/10.1007/BF00020865]
]. Significant differences were found, e.g., in activity of soil acid phosphatases under low-Pi availability in the rhizosphere of roots of five barley cultivars [39Asmar F, Gahoonia TS, Nielsen NE. Barley genotypes differ in activity of soluble extracellular phosphatase and depletion of organic phosphorus in the rhizosphere soil. Plant Soil 1995; 172: 117-22.
[http://dx.doi.org/10.1007/BF00020865]
], however study with other cultivars have shown more similar responses to Pi depletion [30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
]. As indicated by our previous results, oat varieties may use different forms of acid phosphatases to acquire Pi from the soil or internal sources under Pi starvation [14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
]. When compared the studied cereal plants, the increase of extracellular acid phosphatases activity was the highest for Pi-deficient rye and wheat, after 2-3 weeks of culture and enzymes secretion was the most intensive in young, growing zones of -P roots (Tables 5-8). In addition, the increase of activity of extracellular acid phosphatases was higher than intracellular enzymes (Tables 5-8). Histochemical visualization of acid phosphatases in oat and barley roots demonstrated the highest enzymes activity in the rhizodermis and vascular tissue of -P plants [14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
]. In the present study we used in experiments the older cereal varieties, plants which are currently not in use in intensive agriculture. However, the important traits like the ability to increase acid phosphatase production and activity might be useful in breeding and selection of the future-plants. Especially the ability of rye (wheat and perhaps oat) to increase acid phosphatase activity/secretion and better growth under low-Pi conditions are interesting and should be investigated more in details. The knowledge of acclimation mechanism to Pi deficit may be useful to culture the chosen varieties of crop plants, especially when lack of inexpensive phosphorus will cause a potential crisis in agriculture [44Abelson PH. A potential phosphate crisis. Science 1999; 283(5410): 2015.
[http://dx.doi.org/10.1126/science.283.5410.2015] [PMID: 10206902]
, 45Ramaekers L, Remans RM, Rao IM, Blair MW, Vanderleyden J. Strategies for improving phosphorus acquisition. Field Crops Res 2010; 117(2-3): 169-76.
[http://dx.doi.org/10.1016/j.fcr.2010.03.001]
].

The induction of acid phosphatase production in roots and secretion could be huge, e.g., under Pi-deficient conditions enzyme secretion from roots of lupine increased up to 20 times, when compared to Pi-sufficient conditions [46Tadano T, Sakai H. Secretion of acid phosphatase by the roots of several crop species under phosphorus deficient conditions. Soil Sci Plant Nutr 1991; 37: 129-40.
[http://dx.doi.org/10.1080/00380768.1991.10415018]
]. The increase of acid phosphatases activity in root extracts and exudates of Pi-deficient white lupine was most pronounced in the proteoid region and proteoid-root-specific phosphatases secretion often coincided with organic acids exudation as well as root development [47Gilbert GA, Knight JD, Vance CP, Allan DL. Acid phosphatase activity in phosphorus-deficient white lupin roots. Plant Cell Environ 1999; 22: 801-10.
[http://dx.doi.org/10.1046/j.1365-3040.1999.00441.x]
]. However, in our experimental conditions not observed changes of pH in the -P nutrient media indicated, that studied cereal plants not respond to Pi starvation via increased exudation of protons or organic acids from roots (data not shown). Recent studies by [48Wang Y, Krogstad T, Clarke JL, et al. Rhizosphere organic anions play a minor role in improving crop species’ ability to take up residual phosphorus (P) in agricultural soils low in P availability. Front Plant Sci 2016; 7: 1664.
[http://dx.doi.org/10.3389/fpls.2016.01664] [PMID: 27872635]
] indicated that the effects of organic anions in the rhizosphere could be varied among plant species and they play minor roles in improving phosphorus availability and Pi uptake.

The root-associated acid phosphatases pool increased when Pi was limiting and several enzyme isoforms were secreted from roots of Arabidopsis; however, as an activity, only one of them increased specifically as response to low external phosphorus level [33Tomscha JL, Trull MC, Deikman J, Lynch JP, Guiltinan MJ. Phosphatase under-producer mutants have altered phosphorus relations. Plant Physiol 2004; 135(1): 334-45.
[http://dx.doi.org/10.1104/pp.103.036459] [PMID: 15122033]
]. Three to four acid phosphatase isoforms were detected in oat and barley tissues but only one unique isoform was strongly induced by moderate Pi deficiency [14Żebrowska E, Bujnowska E, Ciereszko I. Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities. Acta Physiol Plant 2012; 34: 1251-60.
[http://dx.doi.org/10.1007/s11738-011-0918-2]
, 30Ciereszko I, Żebrowska E, Ruminowicz M. Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition. Acta Physiol Plant 2011; 33: 2355-68.
[http://dx.doi.org/10.1007/s11738-011-0776-y]
]. In rice, several acid phosphatase isoforms were identified corresponding to novel secreted purple phosphatase, OsPAP10c overexpression increased the accumulation of four isoforms of acid phosphatases in transgenic plants [49Lu L, Qiu W, Gao W, Tyerman SD, Shou H, Wang C. OsPAP10c, a novel secreted acid phosphatase in rice, plays an important role in the utilization of external organic phosphorus. Plant Cell Environ 2016; 39(10): 2247-59.
[http://dx.doi.org/10.1111/pce.12794] [PMID: 27411391]
]. Recently, several studies demonstrated that transgenic plants with higher expression of acid phosphatase genes, including a purple phosphatase genes, had improved Pi acquisition and better biomass production [45Ramaekers L, Remans RM, Rao IM, Blair MW, Vanderleyden J. Strategies for improving phosphorus acquisition. Field Crops Res 2010; 117(2-3): 169-76.
[http://dx.doi.org/10.1016/j.fcr.2010.03.001]
, 49Lu L, Qiu W, Gao W, Tyerman SD, Shou H, Wang C. OsPAP10c, a novel secreted acid phosphatase in rice, plays an important role in the utilization of external organic phosphorus. Plant Cell Environ 2016; 39(10): 2247-59.
[http://dx.doi.org/10.1111/pce.12794] [PMID: 27411391]
-51Tian J, Wang C, Zhang Q, He X, Whelan J, Shou H. Overexpression of OsPAP10a, a root-associated acid phosphatase, increased extracellular organic phosphorus utilization in rice. J Integr Plant Biol 2012; 54(9): 631-9.
[http://dx.doi.org/10.1111/j.1744-7909.2012.01143.x] [PMID: 22805094]
], thus contribute to a better understanding of acid phosphatases function in plants.

CONCLUSION

The responses of rye, wheat, oat and barley to phosphorus starvation were similar to those observed for other crop plants. Pi deficiency, at a moderate level, significantly affected the growth of shoots of the studied crop plants, this was followed by enhanced activity of acid phosphatases both in -P root extracts and those secreted by roots. More prolonged low Pi-stress strongly reduced shoot growth of all studied plants, however root elongation growth was not affected or even enhanced. The crop plant acclimation to Pi deficit is dependent both on duration of stress condition, and plant species/cultivar ability, e.g., wheat is more sensitive to lack of Pi than oat or barley. The efficient acclimation of growth and metabolic processes of cereal plants to moderate Pi deficiency conditions are necessary to appropriately respond to changes of environment and survive on low-Pi soil.

LIST OF ABBREVIATIONS

Pi  = Inorganic phosphate
+P  = Plants phosphate-sufficient plants (control)
-P  = Plants - phosphate-deficient plants

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

Not applicable.

HUMAN AND ANIMAL RIGHTS

No Animals/Humans were used for studies that are base of this research.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

This work was supported by the Grant DEC-2012/07/N/NZ9/00972 from the National Science Center (NCN), Poland (given to EZ). We wish to thank PODR (Szepietowo, Poland) and DANKO (Choryn, Poland) for cereal seeds used in the experiments.

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