Contrasting effect of silicon on iron, zinc and manganese status and accumulation of metal-mobilizing compounds in micronutrient-deficient cucumber

Although the beneficial role of silicon (Si) in alleviation of abiotic stress is well established, little is known of the relevance of Si nutrition under microelement deficiency. The aim of our work was to investigate the physiological role of Si in relation to micronutrient (Fe, Zn and Mn) deficiencies in cucumber (Cucumis sativus L). Cucumber (cv. Semkross) plants were grown hydroponically in a complete nutrient solution (control) and in nutrient solutions free from Fe, Zn or Mn, with or without Si supply. Plant tissue concentrations of microelements, organic acids and phenolics were measured. Si supply effectively mitigated the symptoms of Fe deficiency, but only in part, the symptoms of Zn- or Mn deficiency. Leaf Fe concentration significantly increased in plants deprived of Fe but treated with Si, whereas the concentrations of other microelements were not affected by Si supply. The effects of Si supply in increasing accumulation of both organic acids and phenolic compounds in cucumber tissues were exclusively related to Fe nutrition. Enhancement of Fe distribution towards apical shoot parts, along with the tissue accumulation of Fe-mobilizing compounds such as citrate (in leaves and roots) or cathechin (in roots) appears to be the major alleviating effect of Si. Si nutrition, however, was without effect on the mobility and tissue distribution of either Zn or Mn

Fullerenol changes metabolite responses differently depending on the iron status of cucumber plants.

The unique properties of carbon-based nanomaterials, including fullerenol, have attracted great interest in agricultural and environmental applications. Iron (Fe) is an essential micronutrient for major metabolic processes, for which a shortage causes chlorosis and reduces the yield of many crops cultivated worldwide. In the current study, the metabolic responses of Cucumis sativus (a Strategy I plant) to fullerenol treatments were investigated depending on the Fe status of plants. Cucumber plants were grown hydroponically, either with [+FeII (ferrous) and +FeIII (ferric)] or in Fe-free (-FeII and -FeIII) nutrient solution, with (+F) or without (-F) a fullerenol supply. Iron species-dependent effects were observed in either Fe-fed or Fe-starved plants, with alteration of metabolites involved in the metabolism of carbohydrates, amino acids, organic acids, lipophilic compounds. Metabolic perturbations triggered by fullerenol in the FeIII-treated plants were in the opposite kind from those in the FeII-treated plants. Whereas in the FeIII-fed plants, fullerenol activated the metabolisation of carbohydrates and amino acids, in the FeII-fed plants, fullerenol activated the metabolisation of lipophilic compounds and repressed the metabolisation of carbohydrates and amino acids. In FeIII-deficient plants, fullerenol stimulated the metabolism of C3 carboxylates and lipophilic compounds while repressing the metabolism of amino acids, hexoses and dicarboxylates, while in FeII-deficient plants, activations of the metabolism of amino acids and dicarboxylates and repression of sterol metabolism by fullerenol were observed. The results indicated that the valence state of Fe sources is of importance for re-programming metabolome responses in cucumber to fullerenol either in Fe-sufficient or Fe-deficient conditions. These investigations are significant for understanding fullerenol interactions and risk assessment in plants with different Fe statuses