Nitrogen Fixation and Carbon Metabolism in Nodules of Pigeonpea (Cajanus cajan L.) Under Drought Stress

Abstract

Summary Drought stress created by withholding irrigation in pigeonpea resulted in decreased leaf water potential and nodule moisture content. Decreased leaf water potential was associated with decreased activity of nitrogenase, invertase, hexokinase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, malate dehydrogenase, and PEP carboxylase. However, the degree varied depending upon the enzyme and the level of stress. PEP carboxylase and invertase were most sensitive to drought stress followed by glucose 6-phosphate and 6-phosphogluconate dehydrogenases. Even on rewatering, the activities of these enzymes decreased further. Respiratory activity of nodules as well as dark 14CO2 fixation were also adversely affected by drought stress. To some extent, decreased N2 fixation in pigeonpea under drought stress could be due to limited supply of energy and carbon skeletons as evidenced by decreased activities of the enzymes of carbohydrate metabolism. In addition, severe stress might also affect some integral component(s) of the N2 fixing system directly.