Stress-protective effect of putrescine and spermine on wheat plants during soil drought

Polyamines are considered multifunctional stress metabolites in plants. The ability of exogenous polyamines to increase plant resistance to adverse factors of various nature is well-known. At the same time, the stress-protective effects of polyamines at the level of whole plants under conditions of dehydration close to natural have not been sufficiently studied. The aim of this work was to study the effect of foliar treatment of wheat plants with solutions of putrescine and spermine on the functioning of their protective systems during drought under laboratory soil culture conditions. In the experiments, we used young wheat plants (Triticum aestivum L.), which were subjected to a 4-day drought with a gradual decrease in the water content in the soil to 25% of the total moisture capacity. Spraying plants with putrescine in a concentration range of 0,25-5 mM significantly reduced the growth-inhibiting effect of drought; the effect of spermine was less effective, but also significant at P ≤ 0,05. Putrescine significantly reduced the manifestation of water deficit caused by drought. Under the action of spermine, only a tendency towards a decrease in the water deficit of the leaves was noted. Drought caused the effect of oxidative stress, which was manifested in an increase in the content of malondialdehyde (MDA) in leaves. During the pretreatment of plants with spermine, the increase in the MDA content was partially leveled, and under the action of putrescine it was leveled almost completely. Treatment of plants with both polyamines at concentrations of 1 and 5 mM promoted preservation of the pool of chlorophylls and carotenoids in leaves under stress conditions. Moreover, when plants were treated with putrescine and spermine under drought conditions, a close to usual ratio of chlorophylls a/b was maintained. The proline content in leaves increased significantly under the influence of drought. Pretreatment with 1 and 5 mM putrescine, and 5 mM spermine reduced effect of proline content growth in leaves, caused by drought. At the same time, the treatment of plants with both polyamines caused the accumulation of sugars in the leaves. Under the influence of drought, the content of anthocyanins and flavonoids absorbing in the UV-B region significantly decreased in the leaves. Pretreatment with spermine somewhat mitigated the negative effect of drought on the anthocyanin content. Under the action of both putrescine and spermine, the content of flavonoids absorbing in UV-B stabilized in leaves. It was concluded that the protective effect of polyamines on wheat plants under drought conditions is primarily due to the regulation of water metabolism and the prevention of oxidative damage.