MECHANISMS OF FE-EFFICIENCY IN ROOTS OF VITIS SPP. IN RESPONSE TO IRON-DEFICIENCY STRESS

Iron chlorosis induced by Fe-deficiency is a widespread nutritional di sorder in many woody plants and in particular in grapevine. This pheno menon results from different environmental, nutritional and varietal f actors. Strategy I plants respond to Fe-deficiency by inducing physiol ogical and biochemical modifications in order to increase Fe uptake. A mong these, acidification of the rhizosphere, membrane redox activitie s and synthesis of organic acids are greatly enhanced during Fe-defici ency. Grapevine is a strategy I plant but the knowledge on the physiol ogical and biochemical responses to this iron stress deficiency in thi s plant is still very poor. In this work four different genotypes of g rapevine were assayed for these parameters. It was found that there is a good correlation between genotypes which are known to be chlorosis- resistant and increase in both rhizosphere acidification and Fe-III re ductase activity. In particular, when grown in the absence of iron, Vi tis berlandieri and Vitis vinifera cv Cabernet sauvignon and cv Pinot blanc show a higher capacity to acidify the culture medium (pH was dec reased by 2 units), a higher concentration of organic acids, a higher resting transmembrane electrical potential and a greater capacity to r educe Fe-III-chelates. On the contrary, Vitis riparia, well known for its susceptibility to iran chlorosis, fails to decrease the pH of the medium and shows a lower concentration in organic acids, lower capacit y to reduce Fe-III and no difference in the resting transmembrane elec trical potential.