Physiological and biochemical responses to low temperature stress in hybrid clones of Populus ussuriensis Kom. × P. deltoides Bartr
Cuttings of three hybrid clones of P. ussuriensis × P. deltoides were exposed to different low temperatures (cold and freezing) for 24 h, or consecutive low temperatures (5°C, 0 to 120 h), to determine physiological and biochemical responses to cold stress in these woody plants. Soluble sugar and protein contents increased in the three clones under cold (10, 5°C) stress, malondialdehyde (MDA) concentrations, electrolytes leak and activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) also variously increased at 10, 5, and 0°C. While under lower temperatures (-5, -10, and -15°C) treatment, levels of all except electrolytes leak and MDA gradually decreased relatively. During consecutive low temperature (5°C) treatment, concentrations of soluble protein and MDA, electrolytes leak and activities of CAT, APX and GR increased immediately or after 3 h, however, soluble sugar concentrations and SOD and POD activities slightly decreased at the beginning of the treatment; subsequently increased quickly, and then declined. When exposed to different (10, 5, 0, -5, and -10°C) and consecutive (5°C, after 12 or 24h) low temperature stresses, there were significant differences between the three clones. Levels of soluble sugar and soluble protein, and SOD, CAT, POD, APX and GR activities were relatively higher in clone UD183 than in UD189 or UD191. Levels of electrolyte leak and MDA were lower than in UD189 or UD191. Poplar hybrid clones thus employ various physiological and biochemical responses and mechanisms for coping with low temperature stress. According to the results of this study, we presume that clone UD183 may acquire much more freezing- tolerance than clones UD189 and UD191. Our research will promote understanding of cold acclimation and freezing-tolerance in poplars, and encourage selection of the best clones for the cold regions of northern China.
Key words: Osmotic adjustment, electrolyte leakage, malondialdehyde, antioxidant enzymes, low temperaturestress, hybrid clones, populus.