Influence of Arsenate and Phosphate on the Regulation of Growth and TCA Cycle in the Rice (Oryza sativa L.) Cultivars IR64 and Nayanmani

摘要

The influence of arsenate and phosphate on the growth and respiration of 21 days old seedlings in two cultivars of rice, viz., IR64 and Nayanmani was studied. As arsenate and phosphate are similar in their chemical configuration and the latter is preferentially taken up by the phosphate transporters, it results in a competitive inhibition of arsenate uptake in presence of phosphate. Increasing concentrations of sodium arsenate (25 μM, 50 μM and 100 μM) hindered the growth in both the cultivars, with cv. IR64 being more severely affected than cv. Nayanmani. There was an elevation in the levels of organic acids measured in both the cultivars, accompanied by a reduction in the activities of the dehydrogenases of the TCA cycle, viz., pyruvate dehydrogenase, isocitrate dehydrogenase, succinate dehydrogenase and malate dedrogenase under arsenic treatment alone. Also, an elevation in the activities of citrate synthase and fumarase enzymes was noticed in both test seedlings with increasing concentrations of arsenic. These alterations were more prominent in cv. IR64 than in cv. Nayanmani. On joint application of phosphate along with arsenate, amelioration of the toxic effects of arsenate was observed to some extent, resulting in an overall revival of respiration leading to improved growth and metabolism.