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Transcript abundance, enzyme activity and metabolite concentration regulates differential carboxylate efflux in soybean under low phosphorus stress

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Low phosphorus (P) availability in soil owing to adsorption, precipitation and conversion of organic forms drastically limits plant growth and yield. Among several strategies adopted by plants to cope with P starvation, research on root carboxylate exudation to release fixed P in soil is gaining impetus. Since the rate of exudation is a function of carboxylate synthesis and expression of efflux transporters, our objective was to analyse the expression and activity of genes influencing carboxylate exudation in soybean and the effect of P starvation on biomass and P acquisition efficiency. The relative expression levels and enzyme activity of phosphoenolpyruvate carboxylase, malate dehydrogenase and citrate synthase in soybean roots increased during low-P stress, particularly in genotypes exhibiting higher carboxylate efflux. With the exception of two genotypes (G-2656 and HIMSO-1521), the relative expression of efflux transporters for malate and citrate did not correspond to carboxylate exudation. Carboxylates in root apices were higher in NRC-7, HIMSO-1521 and EC-232019 under low-P as compared to sufficient P. P-efficient soybean genotypes (EC-232019 and HIMSO-1521) exhibiting higher carboxylate exudation showed better P acquisition and biomass under low-P stress. Down regulation of pyruvate kinase at the transcript- and enzyme-level was observed under low-P stress in P-efficient genotypes suggesting an effective glycolytic bypass mechanism to facilitate continued carbon flux from glycolytic pathway to the tricarboxylic acid cycle. Hence, transcript abundance, enzyme activity and internal carboxylate concentration in the root tissues govern carboxylate efflux in soybean, in turn, influencing biomass and P uptake.

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This work was funded by the Extra Mural Research Division [Grant number 38(1354)/13/EMR-II] of Council of Scientific and Industrial Research, New Delhi, India. Senior Research Fellowship provided by ICAR-IARI, New Delhi to VK is sincerely acknowledged.

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Correspondence to Renu Pandey.

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Vengavasi, K., Kumar, A. & Pandey, R. Transcript abundance, enzyme activity and metabolite concentration regulates differential carboxylate efflux in soybean under low phosphorus stress. Ind J Plant Physiol. 21, 179–188 (2016).

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