低温对油桐种子萌发和幼苗生长的影响

油桐种子和幼苗在低温下内部生理生化过程发生明显变化。随着温度的下降和胁迫时间的延长,其K+外渗率明显增加,细胞TTC还原率显著下降,超氧物歧化酶活性和抗坏血酸含量下降,膜脂过氧化产物丙二醛含量增加,过氧化氢酶、过氧化物酶和抗坏血酸氧化酶活性也发生明显变化。低温下,油桐幼苗叶片叶绿素含量下降,光合作用明显降低。冷害初期,幼苗呼吸即有增强的表现,特别是从低温转入暖温后呼吸速率大大增加,随着冷害的发展,呼吸又明显下降;冻害则使幼苗呼吸逐渐降低,但从低温转入暖温后仍出现呼吸高峰。不同品种或不同器官对低温的反应不同。外源脱落酸和抗坏血酸预处理能明显地提高油桐幼苗抗冷性。

MECHANISM OF THE AFFECTING LOW TEMPERATURE STRESS ON SEED GERMINATION AND SEEDLING GROWTH OF TUNG OIL TREES

The physiological and biochemical process inside the seed and seedling of tung oil trees (Vernicia fordii ) were observed to remarkably change with the low temperature stress. As the temperature fell and the chilling stress time lengthened, the following changes took place: i ) the rate of potassium ion leakage obviously increased; ii) the rate of cell triphenyl tetrazolium chloride (TTC ) reduction decreased markedly; iii ) the superoxide dismutase ( SOD ) became less active and the content of ascorbic acid ( ASA ) lowered; iv ) the content of malondiald-ehyde(MDA), a product of membrane lipid peroxidation, went up; and v ) there was notable variance in the activity of catalase ( CAT ) , pero-xidase ( POX ) and ascorbic acid oxidase ( AOD ) .The marked decrease of content of chlorophyll and the rate of photosynthesis of tung oil tree leaves was also observed under chilling stress.At the initial stage the respiratory intensity of the seedlings was noted to go up; especially when the low temperature was changed over to a warm one, the seedlings' respiratory rate rose greatly, although their respiratory intensity would go on decreasing as the coldness further injured the plant. And despite the declining tendency the respiratory peak was still present between the two temperatures.Besides, the effects of low temperature on the seedling differed with variety and organ of the tree.And it was revealed that the pretreatme-nt with external abscisic acid ( ABA ) and ASA could considerably promote the seedling's cold resistance.