単細胞緑藻 Chlorella vulgaris IAM C-27 株の耐凍性獲得に及ぼすルヌラリン酸の効果

Many plants acquire freezing tolerance through cold acclimation, a prolonged exposure to low but non-freezing temperatures. We have studied the development of freezing tolerance in plant using Chlorella vulgaris IAM C-27 strain as a convenient model. Chlorella vulgaris IAM C-27 is known to develop its freezing tolerance during the treatment of 3℃ for 24 hours, called hardening. It was demonstrated that exogenous treatment of ABA increased in freezing tolerance in various higher plants. Lunularic acid (LA) was first isolated from the liverwort Lunularia cruciata as a growth-inhibiting and dormancy-inducing factor. It has also been reported that LA is an endogenous growth regulator in the lower plants. We have found that the treatment of LA during hardening at 3℃, 24 hours inhibits the growth of chlorella cells after freezing at -20℃. On the other hand, the treatments of LA at 10℃ accelerate their recovery in growth. To examine the mechanism of developing in freezing tolerance via LA, we researched the hiC (hardening-induced chlorella) gene expressions with LA treatments at 10℃. It was reported that the HIC6 and HIC12 protein were homologous to late embryogenesis abundant (LEA) proteins. The result of Real time RT-PCR suggested that mechanism of the freezing tolerance induction via LA was different from that involved in expression hiC genes.