ARS | Publication request: Biochemical responses to Fe deficiency in Pisum sativum L., cv. Sparkle and dgl mutant: Is the PM H+-ATPase the sole activity involved in H+ extrusion?

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2010
Publication Date: June 26, 2010
Citation: Dell'Orto, M., Vigani, G., Grusak, M.A., Zocchi, G. 2010. Biochemical responses to Fe deficiency in Pisum sativum L., cv. Sparkle and dgl mutant: Is the PM H+-ATPase the sole activity involved in H+ extrusion [abstract]? 15th International Symposium on Iron Nutrition and Interactions in Plants. p. 150.

Technical Abstract: The study of processes regulating Fe acquisition by plants provides useful knowledge for breeding programs aimed to obtain Fe-efficient and/or biofortified varieties. In fact, total Fe uptake is an important, though not sufficient prerequisite to increase Fe density in plant tissues. Like the majority of plant species, Pisum sativum L. reduces soil Fe3+ to Fe2+ through a plasma membrane (PM), Fe(III)-chelate reductase (FCR), and takes up Fe2+ through a specific transporter (RIT1). Such activities are induced under Fe deficiency, and with the net H+ extrusion that increases Fe solubility in the rhizosphere and apoplast, these processes favour Fe acquisition. The pea mutant dgl is defective in the regulation of Fe uptake owing to constitutively high Fe-reducing and H+ extrusion activities, leading to Fe accumulation in plant tissues. While the former activity had previously been attributed to a constitutive expression of FRO1 in roots, no data are available up to now about the nature of high H+ extrusion in dgl. Here, the biochemical characterization of FCR and H+-ATPase activities was performed by enzymatic assays and immunoblotting of H+-ATPase on PM enriched fractions extracted from roots of dgl and the corresponding parent line (cv. “Sparkle”). FCR activity is increased in dgl grown both in the presence and in the absence of Fe and in Fe-deficient Sparkle, in agreement with findings published on in vivo Fe-reducing capacity and expression pattern of FRO1 in roots. Contrarily, neither H+-ATPase activity nor its protein accumulation in dgl fully reflect the high H+ extrusion shown in vivo in both growth conditions; this evidence is confirmed by root agar-embedding experiments performed in the presence of orthovanadate (a specific inhibitor of P type H+-ATPase), showing no inhibition of root acidification. This leads to hypothesize that other mechanisms, other than PM H+-ATPase induction, may contribute to H+ extrusion in pea, especially in dgl. Fe deficiency responses imply changes in the metabolic pathways involved in sustaining the supply of NAD(P)H, H+ and ATP and the activation of pH-stat mechanisms, thus the different aptitude among species to efficiently face with Fe constraint should be related also to the ability to up-regulate these processes. In view of this, the activity of several cytosolic enzymes involved in glycolysis, pentose phosphate pathway and anapleurotic reactions (PEPC) have been examined in both the parent line and the dgl mutant.