Accumulation of dehydrins and osmolytes and functioning of the antioxidant system in etiolated wheat seedlings during cold hardening: differences in adaptation strategies between tolerant and sensitive genotypes.

Winter cereals at the etiolated seedling stage possess the ability to undergo cold hardening, after which they develop varying levels of frost tolerance depending on their genotype. However, the functioning of stress-protective systems in etiolated wheat seedlings at the biochemical and cellular levels remains poorly understood. We investigated the contribution of dehydrins, osmoprotective and antioxidant systems to cold adaptation in six Triticum aestivum (L.) cultivars differing in frost resistance. The seedlings were subjected to a 6-day hardening treatment at 3 °C, followed by freezing at - 9 °C. The survival rate of the most frost-tolerant cultivars after 5 h of freezing was 54-73%, while that of the most sensitive cultivars was 17-22%. During the hardening process, soluble carbohydrates accumulated in the shoots of tolerant cultivars. Also in tolerant cultivars, the soluble protein content remained stable after exposure to the hardening temperature, whereas in sensitive cultivars it decreased. Unhardened seedlings of all studied cultivars contained virtually no dehydrins. Meanwhile, following hardening, an accumulation of dehydrins with molecular weights ranging from 14 to 68 kDa was observed. In frost-tolerant cultivars, the total dehydrins content was higher. Additionally, only frost-tolerant cultivars produced significant amounts of low-molecular-weight dehydrins with molecular weights of 14-16 kDa. Superoxide dismutase activity increased significantly after hardening only in the most sensitive cultivar. The activity of catalase and guaiacol peroxidase after hardening remained stable in tolerant cultivars, while it increased in all sensitive ones. The hydrogen peroxide content after hardening varied among seedlings of different genotypes, although it remained at a stable, higher level in frost-tolerant cultivars. It was concluded that there are differences in the cold adaptation strategies of wheat seedlings of different genotypes. Tolerant cultivars are characterized by an increase in dehydrins content, especially low-molecular-weight dehydrins, the preservation of a large pool of soluble proteins, and the accumulation of soluble carbohydrates. At the same time, sensitive cultivars undergoing cold hardening are characterized by increased antioxidant enzyme activity.