Adaptive responses to iron-deficiency in callus cultures of two cultivars ofVitisspp.

The correlation between iron chlorosis resistance and induction of adaptive mechanisms in grapevine calli belonging to cultivars with different susceptibility to iron chlorosis has been investigated. Fe(III)-chelate reductase was clearly linked to the Fe-efficiency status of the genotype. When growing on iron deprived medium (-Fe) calli of the Fe-efficient genotype ‘Cabernet sauvignon’ showed a remarkable increase in enzyme activity, up to five times higher, with respect to +Fe cultures. Moreover, 31P-NMR revealed that in -Fe medium the increase of vacuolar Pi content of the Fe-efficient cultures was more pronounced than that recorded for the Fe-inefficient Vitis riparia. Furthermore, Fe starvation also enhanced the production of phenolic compounds in calli of ‘Cabernet sauvignon’ with respect to those of Vitis riparia. The role of H+-ATPase as a marker of Fe-efficiency in tissue culture remains ambiguous in the case of grapevines.