Does Chelated Copper Ameliorate the Greening of Iron-deficient Cucumber Plants through Nitric Oxide Signaling? Comparison with Chemical Forms of Zinc

Recently the role of nitrogen monoxide (NO) in iron homeostasis has been proved by means of exogenously-applied different NO donors that can provoke leaf re-greening under conditions of iron deficiency. It was also supposed, that Fe-deficiency itself could stimulate the endogenous production of NO in stressed plants (Graziano and Lamattina, 2007). In this study, the comparison between effects of NO-donor sodium nitroprusside (SNP and related structural compounds) and chelated forms of copper and zinc [Cu(II)HEDTA and Zn(II)HEDTA, all applied at equimicromolar concentrations in the nutrient solution] towards leaf chlorosis of Fe-deficient cucumber plants was investigated. Plant variants (–Fe+2 µM Cu 2+) and (–Fe+ 20 µM Zn 2+) with very strong chlorosis were chosen for experiments to follow the recovery of leaf greening after treatment with substances or inhibitors of NO production and action. Treatment with SNP, Fe(II)CN and Cu(II)HEDTA produced leaf greening in both variants, especially strong for the newly developed leaf, as it was shown with chlorophyll measurements. KCN, Fe(III)CN and Zn(II)HEDTA were without greening effect. Using specific NO-inhibitor cPTIO it was shown that Cu(II)HEDTA treatment of iron-deficient cucumber plants could provoke leaf greening by means of endogenous