RESPONSE MECHANISMS OF GRAPEVINE ROOTSTOCKS TO SEVERE IRON DEFICIENCY

In many important viticultural areas of the Mediterranean basin, plants often face prolonged periods of scarce iron (Fe) availability in the soil. The main objective of the present work was to compare physiological and biochemical response mechanisms to severe Fe-deficiency in Vitis genotypes. A hydroponic experiment was conducted, in which three rootstocks characterized by a different susceptibility degree to Fe chlorosis have been submitted to two Fe levels. The Fe chlorosis susceptible rootstock 101-14 (Vitis riparia x Vitis rupestris) reacted to a prolonged Fe-deficiency reducing the root activity of phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH). Noteworthy, it accumulated high levels of citric acid in roots. In contrast, the Fe chlorosis tolerant rootstock 110 Richter (Vitis berlandieri x Vitis rupestris) was capable of maintaining an active metabolism of organic acids in roots, accumulating them to a lesser extent than 101-14. Similarly to 101-14, SO4 genotype (Vitis berlandieri x Vitis riparia) displayed a strong decrease of PEPC and MDH enzyme activities. Nevertheless it was able to avoid excessive accumulation of citric acid in roots, similarly to 110 Richter. In conclusion, root PEPC and MDH activities represent an important tool for screening Fe chlorosis tolerance. After a prolonged exposure to Fe-deficiency, the accumulation of organic acids in the roots may not represent a reliable indicator of Fe chlorosis tolerance.