Root antioxidant responses of two Pisum sativum cultivars to direct and induced Fe deficiency

The contribution of antioxidant defence systems in different tolerance to direct and bicarbonate-induced Fe deficiency was evaluated in two pea cultivars (Kelvedon, tolerant and Lincoln, susceptible). Fe deficiency enhanced lipid peroxidation and H2O2 concentration in roots of both cultivars, particularly in the sensitive one grown under bicarbonate supply. The results obtained on antioxidant activities (SOD, CAT, POD) suggest that H2O2 accumulation could be due to an overproduction of this ROS and, at the same time, to a poor capacity to detoxify it. Moreover, under bicarbonate supply the activity of POD isoforms was reduced only in the sensitive cultivar, while in the tolerant one a new isoform was detected, suggesting that POD activity might be an important contributor to pea tolerance to Fe deficiency. The presence of bicarbonate also resulted in stimulation of GR, MDHAR and DHAR activities, part of the ASC-GSH pathway, which was higher in the tolerant cultivar than in the sensitive one. Overall, while in the absence of Fe only slight differences were reported between the two cultivars, the adaptation of Kelvedon to the presence of bicarbonate seems to be related to its greater ability to enhance the antioxidant response at the root level

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 \u3bcM Fe; (-Fe), direct deficiency, CM without iron; (+Bic.), indirect deficiency, CM containing 30 \u3bcM 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

Physiological and biochemical responses for two cultivars of Pisum sativum (''Merveille de Kelvedon'' and ''Lincoln'') to iron deficiency conditions

The aim of this work was to compare the tolerance and the physiological responses to Fe deficiency of two Pisum sativum cultivars ("Merveille de kelvedon" and "Lincoln") commonly cultivated in Tunisia. We studied the effects of Fe deficiency on: (i) chlorophyll content, relative growth rate (RGR) and Fe status, (ii) rhizosphere acidification, (iii) changes under Fe-deficient conditions in the activities of two root enzymes, the first related to the proton extrusion (H+-ATPase) and the second to iron reduction mechanism (Fe(III)-chelate-reductase: FCR). Three treatments were used: C, control, complete nutrient solution (CNS) containing 30 \u3bcM Fe; DD, direct deficiency, CNS without iron; ID, indirect deficiency, CNS containing 30 \u3bcM Fe + lime. Fe deficiency led to a significant decrease of chlorophyll content in both cultivars. The below reduction was observed in Fe-deficient plants of Merveille de Kelvedon. In addition, relative growth of shoots and whole plant was not affected by Fe deficiency. H+-ATPase and FCR activities were more stimulated in Merveille de Kelvedon than in Lincoln, under DD and ID Fe deficiency. The capacity of this cultivar to maintain plant growth and to preserve adequate chlorophyll synthesis under iron-limiting conditions is related to its better Fe-use efficiency, in addition to its high acidification and root reducing capacities. This allows us to suggest that Merveille de Kelvedon is more effective in overcoming Fe deficiency than Lincoln

Micro-analytical, physiological and molecular aspects of Fe acquisition in leaves of Fe-deficient tomato plants re-supplied with natural Fe-complexes in nutrient solution

It is well known that in the rhizosphere soluble Fe sources available for plants are mainly a mixture of complexes between the micronutrient and organic ligands such as organic acids and phytosiderophores (PS) released by roots, microbial siderophores as well as fractions of humified organic matter. In the present work, mechanisms of Fe acquisition operating at the leaf level of plants fed with different Fe-complexes were investigated at the micro-analytical, physiological and molecular levels. Fe-deficient tomato plants (Solanum Lycopersicum L., cv. 'Marmande') were fed for 24 h with a solution (pH 7.5) containing 1 A mu M Fe as Fe-PS, Fe-citrate or Fe-WEHS. Thereafter, leaf tissue was used for the visualization of Fe distribution, measurements of Fe content, reduction and uptake, and evaluation of expression of Fe-chelate reductase (LeFRO1), Fe-transporter (LeIRT1) and Ferritin (Ferritin2) genes. Leaf discs isolated from Fe-deficient plants treated for 24 h with Fe-WEHS developed higher rates of translocation, Fe-chelate reduction and Fe-59 uptake as compared to plants supplied with Fe-citrate or Fe-PS. Leaves of plants treated with Fe-WEHS also showed higher transcript levels of LeFRO1, LeIRT1 and Ferritin2 genes with respect to plants fed with the other Fe-sources. Data obtained support the idea that the efficient use of Fe complexed to WEHS-like humic fractions involves, at least in part, also the activation of Fe-acquisition mechanisms operating at the leaf level