Changes of metabolic responses to direct and induced Fe deficiency of two Pisum sativum cultivars

The aim of this work was to investigate the effect of Fe deficiency (whether direct or bicarbonate-induced) on the glucose metabolism, by determining the activities of several enzymes (PK, PFK, G3PDH and G6PDH), together with other enzymes involved in the organic acids metabolism (PEPC, MDH, CS and ICDH) in two cultivars of Pisum sativum (Kelvedon and Lincoln, respectively tolerant and sensitive to Fe deficiency). Moreover, we studied the effects of Fe deficiency on iron reduction mechanism and proton extrusion (FCR and H+-ATPase activity, respectively), in addition to the concentrations in roots and exudates of some organic compounds (malate, citrate and phenols). Three treatments were used: (+Fe), complete medium (CM) containing 30 μM Fe; (-Fe), direct deficiency, CM without iron; (+Bic.), indirect deficiency, CM containing 30 μM Fe + lime. Our results showed that all glycolytic enzymes activities increased in the extracts of Fe-deficient roots of both cultivars when compared to the control. The above increases in the activity were particularly evident for Fe-deficient roots of Kelvedon. FCR and H+-ATPase activity was stimulated by Fe deficiency in both cultivars. PEPC activity increased by 254% in root extracts of Kelvedon particularly when grown in the absence of Fe. MDH, CS and ICDH activities showed a marked increase in the -Fe treated roots of both cultivars. The bicarbonate treatment resulted in a significant induction of root MDH and CS activities only in Kelvedon cultivar. In leaves, CS activity increased significantly in Fe deficient plants of both cultivars. However, Fe deficiency (whether direct or indirect) had no effect on the leaf activity of MDH and ICDH. Citrate concentration increased in both cultivars, particularly in Kelvedon (187% and 50% of the control, respectively in the -Fe and +bicarbonate treatments). Higher concentrations of phenols were observed in Fe-deficient roots of both cultivars than in the control plants. The increase in phenol concentration in roots was greater in Kelvedon than in Lincoln. We demonstrate that the metabolic responses of the two cultivars are differently affected by Fe deficiency both direct and induced by bicarbonate supply. The effective modulation of glycolytic and organic acid metabolisms may account for the better tolerance of Kelvedon when compared to Lincoln.