Modifying Effects of Some Plant Hormones on Zucchini Cotyledons Subjected to High Temperature and Excess Copper

Abstract The aim of the study was to investigate the potential beneficial effects of exogenous application of methyl jasmonate (MeJa) and phenylurea cytokinin (4PU-30) on zucchini (Cucurbita pepo L.) cotyledons subjected to high temperature (HT) and combined HT plus excess copper (Cu2+) stress. Compared to HT stressed zucchini cotyledons, exposure to excess Cu2+ prior to HT treatment inhibited the growth, decreased superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) activities, increased glutathione-Stransferase (GST) and peroxidase (Px) total activities, and induced new enzyme isoforms (GST4, GST8, and Px4). The effect of MeJa on the double-stressed plants was to increase SOD, GPx and Px total activities and stimulate the activity of GST8, GST9, GST10, SOD5, Px3 and Px8 isoenzymes. In addition to SOD, GPx and Px, 4PU-30 increased GST total activity, up-regulated Px1 and GR1, and had a higher stimulatory effect on SOD5, Px3, GPx3, GST9 and GST10 activities. Copper, 4PU-30 and MeJa treatments changed the abundance and pattern (MeJa) of soluble zucchini polypeptides in a specific manner. MeJa and especially 4PU-30 applied alone, or in combination, stimulated the growth of later HT-treated cotyledons. 4PU-30 counteracted better than MeJa in the HT+heavy metal-caused inhibition of the growth. The data indicated that both MeJa and 4PU- 30 may protect the zucchini plants from high temperature and combined high temperature plus excess copper stress, but 4PU-30 was more effective; the protective effect was related to the changes in the gene expression, total antioxidant enzyme activities and the activity of individual isoforms of the enzymes.