Transgenic barley expressing the Arabidopsis AKR4C9 aldo-keto reductase enzyme exhibits enhanced freezing tolerance and regenerative capacity

Aldo-keto reductase (AKR) enzymes contribute to reactive aldehyde detoxifying capacity and to osmotic stress protection of various plant species. The protective effects of these enzymes have already been well characterised but only limited information has been gained on the role of AKRs in frost tolerance. The approach to study frost tolerance was based on transgenic barley (Hordeum vulgare L.) carrying and expressing the Arabidopsis thaliana At2g37770.2 gene (coding AKR4C9) under constitutive regulation. We demonstrated that the osmoprotective sugar alcohol sorbitol was present in both non-transgenic (WT) and transgenic barley plants. The increase of the sorbitol concentration was around 2- and 4-fold higher in the low (line C2) and in the high (line C1) AKR4C9-expressing transgenic line, respectively, compared to WT. Furthermore by applying three subsequent, identical − 20 °C treatments 94.7% of all the leaves of WT plants had died, but only 80% in the case of transgenic line C1. The average electrolyte leakage of the transgenic plants (line C1) was lower than that of WT plants. Line C1 plant also had significantly higher fresh weight than the WT after 6 days of recovery following frost-treatment. Transgenic line C2 had an intermediate freezing tolerance based on the same physiological parameters. The results indicate that AKR-overexpression may lead to higher frost tolerance and higher post-frost regenerative capacity.