Polyamine metabolism and S-adenosylmethionine decarboxylase gene expression during the cytokinin-stimulated greening process

This report deals with the effect of kinetin on the greening process, in relation to endogenous free polyamine levels and their metabolism in cucumber cotyledons. The kinetin response on free polyamine levels was found to be accompanied by an increase in free putrescine throughout the greening process. There was no significant difference in spermidine and spermine levels between control (water-treated) and kinetin-treated cotyledons; however, a slight increase in spermidine level, which was higher in control was observed at 4 h. In order to examine the action of kinetin on polyamine metabolism, particularly spermidine synthesis, the effect of kinetin on the level of S-adenosylmethionine decarboxylase mRNA and its enzyme activity were studied. First, an increase in the S-adenosylmethionine decarboxylase transcript level was observed at 30 min of illumination in water and kinetin-treated cotyledons, and next, the transcript decreased and was restored again at 2 h in kinetin-treated cotyledons and at 4 h in the control. This is the first report that demonstrates the light and kinetin regulation of S-adenosylmethionine decarboxylase transcript level. The highest S-adenosylmethionine decarboxylase activity was observed at 2 h of illumination, and it was higher in control when compared to kinetin-treated cotyledons. Spermidine and spermine levels observed in kinetin-treated cotyledons at 4 h of illumination may partly be a result of: lower S-adenosylmethionine decarboxylase activity inhibited by kinetin and/or higher by about 35% on kinetin polyamine oxidase activity. Experiments with methylglyoxal-bis (guanylhydrazone) and dicyclohexylamine showed that both spermidine synthesis inhibitors depressed chlorophyll accumulation in the greening cucumber cotyledons. Additionally, these results, indirectly confirm that polyamines may play some role in the greening process stimulated by kinetin.