Two sensitive cultivars were examined, Vittoria and Italia, grafted on a tolerant rootstock (140 Ruggeri). Two levels of iron chlorosis in scions were selected, initial and evident, and compared to the healthy rootstock (control). The fractions of extracellular and cytoplasmatic cations, chloroplastic mobile, loosely linked, strongly linked and residual cations as well as the active fraction were extracted from the fresh matter. In the chlorotic the plant inability to use Fe2+ uptaken by the rootstock was highlighted, with a different response from Vittoria and Italia, as evidenced by the decrease in the available fraction of Fe2+, particularly in the case of evident chlorosis. The increase in leaf content of the active forms of K+ and Ca2+ resulted directly correlated to the intensity of iron deficiency, since they bring about a higher pH and a destabilization of membranes, respectively, both hindering iron utilization. The modified response in terms of reduced photosynthetic activity in chlorotic scions was evidenced through the decrease in the active form of Mg2+and consequently in chlorophyll content.
Key words: Fe and nutrition unbalance, active Fe fraction, iron chlorosis.
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