Cadmium stress related to root-to-shoot communication depends on ethylene and auxin in tomato plants

Abstract

Stress perception and signalling pathways between plant organs involve complex mechanisms and remain a major focus of interest. To further address the role of phytohormones in the modulation of stress perception from root-to-shoot signalling, we used ethylene-insensitive Never ripe (Nr) and auxin-insensitive diageotropica (dgt) tomato mutants combined with the grafting technique. Lipid peroxidation, H2O2, chlorophyll and proline contents, and activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) in non-grafted and grafted tomato mutants subjected to cadmium (Cd) were analysed. The results revealed different responses according to genotype, grafting combination and Cd application. Non-grafted hormonal mutants exhibited higher Cd content in roots than MT plants, being 39.9% in Nr and 17.7% in dgt plants, whereas in leaves, the Cd content was higher in Nr plants. In grafted plants, where the rootstocks were exposed to Cd before grafting, the MT rootstock exhibited the highest Cd content. In non-grafted plants following Cd application, roots of Nr also exhibited a decrease in Ca concentration, whilst Mg, S, Cu and Zn decreased in Nr leaves. In grafted plants, it was possible to notice peculiar differences in nutrient concentration patterns according to grafting combination and Cd application. The proline and chlorophyll contents were less affected in the hormonal mutants. In the presence of Cd, the scions of grafted plants exhibited increased antioxidant enzymes activities in response to a signal from the rootstocks. However, it was possible to associate the involvement of ethylene and auxin with the antioxidant responses because the Nr and dgt genotypes were less affected by Cd stress than their wild-type counterpart, MT.