Abstract:

In order to examine the cold resistance function of dehydrin gene EjDHN5 from loquat （Eriobotrya japonica），it was overexpressed in tobacco plants. Two lines with relatively higher transcripts levels of the target gene，L24 and L26 were chosen for function characterization. Both of wide type（WT）and transgenic lines（L24 and L26）were treated with 0，2，4 and 8 μmol · L^-1 methyl viologen（MV）. After being exposed to 0，2，4 and 8 μmol · L^-1 MV under light，the survival rate of WT plants decreased to 73.6% and 56.9%，respectively，and the PSⅡ activity reduced dramatically，while the transgenic lines still remained a survival rate of 100% as well as a much higher PSⅡ activity. MV treatment in leaf discs from 6-leaf-stage tobaccos confirmed that transgenic lines maintained higher  chlorophyll content，accumulated less reactive oxygen species（ROS）and MDA. Moreover，compared to the WT plants，the EjDHN5- overexpressing plants exhibited a better growth status，had less ROS and suffered lighter membrane damage in leaves after cold stress. In summary，these results indicated that overexpressing EjDHN5 improved oxidative and cold tolerance in tobacco. It also provides evidence that dehydrins contribute to cold tolerance in loquat，which may be partly ascribed to its oxidative stress defense in plant.

Key words: loquat, EjDHN5, transgenic, tobacco, oxidative stress, methyl viologen, cold stress