Abstract
Changes of phenylalanine ammonia-lyase (PAL) activity in 1-year-old twigs of D. taitoensis and D. kaki were investigated with reference to the cold acclimation from autumn to winter. Low temperature exotherms (LTE) of twig pieces in D. taitoensis were found by differential thermal analysis (DTA) at -14.5--15.5°C in Aug. to Nov., and at -18°C in early Jan. While in 4 cultivars of D. kaki, LTE occurred at -16--19°C in early Sept., and found at -29.2°C for ‘Mapang, ’ at -26.4--27.5°C for other Japanese cultivars in early Jan. PAL activities in bud, cortex and xylem of D. kaki (‘Fuyu’) twigs gradually increased from Oct., and the highest activity was found in Dec. In D. taitoensis, PAL activity was relatively lower than in D. kaki, however, the peak activities were found in the bud and cortical tissues during the coldest part of the season. PAL activities in cortical and xylem tissues of both species increased under chilling treatment (4°C, 8h photoperiod) in early autumn. Particularly the higher activities were found in cortical tissues of kaki at 7th day and the chilling treatment lowered electrolite leakage of twigs by more than 20% in Sept. and 10% in Oct. Thus, an apparent difference was found in the ability of cold acclimation between 2 Diospyros species. D. kaki seems to have evolved the ability of cold acclimation by controlling the enzyme systems related with production of phenolic substances according to the environmental temperatures.
