| Pepper and cucumber cultivars collected from different regions were used as materials to study the effect of low temperature on germination ability and the effect of low temperature and poor light on growth at their germination and seedling stage. Comprehensive evaluation methods were established to evaluate tolerance of low temperature at germination stage and tolerance of the combination low temperature and poor light at seedling stage. Cultivars with different tolerance of low temperature and poor light at seedling stage were selected to study the photosynthetic characteristics and reactive oxygen species metabolism to investigate the injury mechanisms and difference. The results are as follows.1. The germination ability of pepper and cucumber cultivars were obviously inhibited by low temperature (pepper, 18℃, cucumber, 13℃). Relative germination trend, relative germination percentage, relative germination index, relative radical length and relative vigor index of different cucumber varieties showed significant difference (p<0.05). Based on these 5 indexes, the evaluation score of different cucumber varieties was calculated by pole sorting method. According to scores of the evaluation, 108 pepper cultivars were classified into three categories. 10 cultivars were classified as low temperature tolerant materials, whereas 9 cultivars were low temperature sensitive materials and the rest cultivars were moderately low temperature sensitive materials.Except for relative germination trend, the relative germination indexes among pepper cultivars were significantly different. Based on these 4 indexes, pepper cultivars were classified into 10 cultivars low temperature tolerant materials, 9 sensitive materials and the rest moderately low temperature sensitive materials by pole sorting method. All relative indexes and evaluation scores were significantly correlated while the relative vigor index had the highest correlation coefficient in both pepper and cucumber varieties. The results indicated that the pole sorting method analysis could be used to early evaluate the low temperature tolerance of pepper and cucumber varieties by investigation of related character indexes at seed germination stage.2. Compared to control, the plant height, stem diameter, leaf length, leaf width, dry and fresh weight of the roots and the parts above and seedling index decreased obviously after being treated with low temperature and poor light. In the above indexes, seedling index had the most significant difference among cultivars. The relative indexes all reached extremely prominent in different cultivar. According to the 9 relative indexes, using pole storing method, the cucumber cultivars were classified into sensitive, tolerant and moderately sensitive materials to low temperature and poor light. The correlation among the evaluation score and the relative indexes all reached prominent or extremely prominent level.Dry and fresh weight of the roots and the parts above and seedling index decreased significantly under the treatment of low temperature and poor light and the relative indexes were significantly different among cultivars. The morphological index of different pepper cultivars showed different appearance after treated with low temperature and poor light. Compared to control, the plant height, stem diameter, leaf length and leaf width of some cultivars were decreased while others increased which might be related with the degree of the low temperature and poor light stress and different sensitive degree of cultivars to low temperature and weak light. According to the 9 relative indexes, using pole storing method, the pepper cultivars were classified into sensitive, tolerant and moderately sensitive materials to low temperature and poor light. The correlation among the evaluation score and the relative plant height, relative stem diameter reached prominent level while relative dry weight of the above parts and roots, relative seedling index were extremely correlated with the evaluation score and seedling index had the highest correlation.3. Four pepper cultivars with different tolerance of low temperature and poor light were selected to study photosynthetic characteristics and reactive oxygen species metabolism under low temperature and poor light stress. Compared to control, the activity of superoxide dismutase (SOD), glutathione peroxidase (GPX) increased and the activity of catalase (CAT) decreased while the activity of ascorbate peroxidase (APX) increased firstly and decreased when prolonging treatment time.Changing trend of the antioxidant enzyme activity are similar among different cultivars while the enzyme activity in tolerant cultivars kept higher than that in the sensitive ones. After being treated with low temperature and poor light, net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) decreased obviously and descent range of the indexes are different in the cultivars, the tolerant cultivars kept relative high Pn and Gs. Decrease in Pn under the stress condition was mainly attributed to non-stomatal limitation.The growth of cucumber seedlings were inhibited obviously by the stress of low temperature and poor light. The activity of CAT decreased and GPX increased while the activity of SOD decreased at first and then increased and the activity of APX had an opposite change. The content of MDA and permeability of cell membrane increased. Net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) decreased obviously and descent range of the indexes are different in the cultivars, the tolerant cultivars kept relative high Pn and Gs. Decrease in Pn under the stress condition was mainly attributed to non-stomatal limitation. The tolerant cultivars had higher relative growth rate, Pn and activity of antioxidant enzyme.
|
PDF Full Text Request