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 riparia a very susceptible genotype and Vitis berlandieri a resistant one. Modification of NADH: ferric (Fe3+) reductase activity was spectrophotometrically evaluated by following the formation of the complex ferrous (Fe2+)-(BPDS)(3), while the malic and citric acid production were determined in callus cultures grown both in the presence (+Fe) and absence (-Fe) of Fe. Moreover, a microsomal fraction was isolated from the calli to evaluate the H+-ATPase and the Fe3+-EDTA reductase activities. As expected, calli of the Fe-efficient genotype (V. berlandieri) was able to enhance Fe3+-EDTA reductase activity when growing under Fe deficiency while the Fe-chlorosis susceptible V. riparia could not or did it with lower efficiency. Therefore, the H+-ATPase assay showed a higher enzymatic activity in the microsomal fraction isolated from Vitis berlandieri grown without Fe with respect to its control(+Fe). Organic acid determination gave quite contradictory results, specially regarding malic acid which, under our study conditions, seemed not to be linked with the strategies of response to Fe deficiency.