Temporal Changes in Putrescine-Induced Protective Mechanisms at Metabolite and Gene Expression Levels in Wheat and Maize Against Osmotic Stress

Polyamine treatments are beneficial against various stress factors due to direct protective effects and the regulation of metabolite remodelling and gene expression. However, their protective, specific effects as priming under stress conditions remain not fully understood. We hypothesised that the positive effect of priming decreases even shortly after priming. To investigate the duration of action of putrescine treatment against osmotic stress, and to reveal species- and time-dependent differences, the effects of putrescine seed-soaking were monitored in wheat and maize during osmotic stress. The putrescine pre-treatment was effective in both species against osmotic stress during three trials ran in parallel, even when the stress was applied 7 days after seed-soaking. Leaves and roots responded differently, and putrescine induced certain unique changes under control and osmotic stress conditions. The effects of the treatments at the metabolite level changed between the sub-experiments and differed between the two species. Putrescine alone had an increasing effect on jasmonic acid-isoleucine level in the roots of both wheat and maize, and it induced the expression of WRKY97 in both the leaves and roots of maize plants throughout the experiment. These results highlight that different hormonal and transcriptional changes induced by putrescine were associated with the observed positive effects.