Betaine Improves Freezing Tolerance in Wheat

The accumulation of the osmolyte betaine was found to be correlated with the development of freezing tolerance (FT) of two wheat cultivars where it increases by about three fold during the cold' acclimation period. Exogenous betaine application resulted in a large increase in total osmolality mostly due to betaine accumulation. Plants that accumulated betaine are more tolerant to freezing stress since a four day exposure to 250 mM betaine resulted in a LT50 of -8° C (in spring wheat Glenlea) and -9° C (in winter wheat Fredrick) compared to — 3°C (Glenlea) and — 4°C (Fredrick) for control non-exposed plants. Betaine treatment (250 mM) during cold acclimation increased FT in an additive manner since the LT50 reached — 14°C (Glenlea) and -22° C (Fredrick) compared to -8° C (Glenlea) and — 16°C (Fredrick) for plants that are cold acclimated in the absence of betaine. These results show that betaine treatment can improve FT by more than 5°C in both non-acclimated and cold-acclimated plants. The betaine treatment resulted in the induction of a subset of low temperature responsive genes, such as the wcor410, and wcor413, that are also induced by salinity or drought stresses. In addition to these genetic responses, betaine treatment was also able to improve the tolerance to photoinhibition of PSII and the steady-state yield of electron transport over PSII in a manner that mimicked cold-acclimated plants. These data also suggest that betaine improves FT by eliciting some of the genetic and physiological responses associated with cold acclimation.