Sexual differences in cold acclimation and freezing tolerance development in sea buckthorn (Hippophae rhamnoides L.) ecotypes

Sexual differences in cold acclimation and freezing tolerance development of two contrasting sea buckthorn (Hippophae rhamnoides L.) ecotypes from northern and southern regions in China were recorded after exposure to short day photoperiod (SD) and low temperature (LT). The results demonstrated that cold acclimation could be triggered by exposing the plants to SD or LT alone, and that a combination of both treatments had an additive effect on freezing tolerance in all plants tested. However, development of freezing tolerance was dependent on the sex of plants under SD and LT, the males were clearly more responsive to SD and LT than the females in both ecotypes studied. On the other hand, development of freezing tolerance was also ecotype-dependent, the northern ecotype was more responsive to SD and LT than the southern ecotype, resulting in earlier cold acclimation under SD and higher freezing tolerance under LT. Moreover, development of freezing tolerance induced by SD and LT was accompanied by changes in ABA levels. These alterations in ABA levels were different in different treatments, ecotypes and sexes. Therefore, the differences in SD and LT-induced physiological responses showed that the different ecotypes and the different sexes might employ different survival strategies under environmental stress.