Traits of tolerance in Vitis rootstocks submitted to iron chlorosis

Vitis ssp. frequently grow under Fe deficiency conditions that limit Fe absorption and cause a typical yellowing of young leaves and a dramatic decrease in productivity. This nutritional disorder is particularly common in the Mediterranean area and can be a matter of concern for the development of orchards and vineyards. To identify traits of tolerance useful in breeding programs, we have analyzed two rootstocks, characterized by different degrees of tolerance to Fe deficiency (M1, tolerant and 101.14, susceptible), grown in a hydroponic culture with (+Fe) or without (-Fe) Fe(III)–NaEDTA and with NaHCO3 added to +Fe medium (+FeBic). After 10 d, –Fe leaves of both genotypes and leaves of 101.14 grown in the presence of bicarbonate, showed visible symptoms of chlorosis. As a preliminary analysis we have investigated some of the main physiological parameters linked to leaf gas exchanges and determined the macro-and microelement content through ICP-MS. In general, while M1 grown in +FeBic exhibited a behavior similar to the control, in 101.14 the presence of bicarbonate exerted the same effects on the analyzed traits as those found in the absence of Fe. The main mechanisms induced by Fe deficiency in Strategy I species (FC-R, H+-ATPase, IRT1, PEPC) and some key enzymes of glycolysis and PPP pathway were investigated by enzymatic assay and western blotting. M1 roots showed a greater increase in all the tested activities both in the absence of Fe and in the presence of bicarbonate, while 101.14 ones exhibited a not significant increase in all growth conditions. We propose that in a calcareous soil, the major activation of the plasma membrane-located H+-ATPase, as found in the M1, could provide better conditions for Fe uptake (i. e. lower pH in apoplast and rhizosphere). By using an antibody against H+-ATPase, we observed in Fe-deficient M1 root PM extracts, the presence of a band lower than 112 kDa. Through nHPLC-ESI-MS/MS analysis this band was identified as a form of PM H+-ATPase probably deleted at the N terminus. Immunological analysis carried out with antibodies against the C and N termini of the H+-ATPase other than the PM-bound 14.3.3 proteins revealed substantial differences between M1 and 101.14 rootstocks. In M1 the results allow to foresee a model in which both termini are presumably involved in the interaction between 14.3.3 proteins and the H+-ATPase itself, determining the transition to the high-activity state of the enzyme. The work is supported by Progetto AGER- SERRES 2010-2105