PHYSIOLOGICAL-RESPONSES OF GRAPEVINE CALLUS-CULTURES TO IRON-DEFICIENCY

Grapevine is considered a 'Strategy I' plant because it performs some peculiar biochemical and physiological responses when grown under iron (Fe) deficiency stress conditions. Callus cultures were started from leaf and internode cuts of micropropagated plantlets of two grapevine genotypes well known for their Fe-chlorosis characteristic: Vitis ripa ria a very susceptible genotype and Vitis berlandieri a resistant one. Modification of NADH: ferric (Fe3+) reductase activity was spectropho tometrically evaluated by following the formation of the complex ferro us (Fe2+)-(BPDS)(3), while the malic and citric acid production were d etermined in callus cultures grown both in the presence (+Fe) and abse nce (-Fe) of Fe. Moreover, a microsomal fraction was isolated from the calli to evaluate the H+-ATPase and the Fe3+-EDTA reductase activitie s. As expected, calli of the Fe-efficient genotype (V. berlandieri) wa s able to enhance Fe3+-EDTA reductase activity when growing under Fe d eficiency while the Fe-chlorosis susceptible V. riparia could not or d id it with lower efficiency. Therefore, the H+-ATPase assay showed a h igher enzymatic activity in the microsomal fraction isolated from Viti s berlandieri grown without Fe with respect to its control(+Fe). Organ ic acid determination gave quite contradictory results, specially rega rding malic acid which, under our study conditions, seemed not to be l inked with the strategies of response to Fe deficiency.