Molecular Plant Breeding 2025, Vol.16, No.1, 44-54 http://genbreedpublisher.com/index.php/mpb 48 2.3 The effect of high temperature on SOD and CAT activities in ivy The SOD activity of four ivy varieties reached its peak on the third day of high temperature stress and decreased (Figure 4A) ‘Sark’ and ‘Ingelise’ showed a gradual increase in SOD activity from high temperature stress, reaching their highest levels on the third day of stress, which were 2.18 and 2.16 times higher than the control, respectively. ‘Wonder’ also reached its peak SOD activity on the third day after a slight decrease on the first day of high temperature stress, which was 2.33 times higher than the control. On the third day of stress, the highest peak of SOD activity reached by ‘Golden Ivalace’ was only 1.19 times that of the control, and then began to decline, reaching only 41.1% of the control on the seventh day. Its SOD activity remained at a lower level compared to the other three varieties, and the change was relatively small. The trend of CAT activity changes and SOD activity changes in the four Ivy varieties are similar, both showing an initial increase followed by a decrease (Figure 4B). On the third day, the CAT activity of ‘Sark’, ‘Ingelise’, ‘Wonder’, and ‘Golden Ivalace’ increased to their highest values, which were 2.11, 2.40, 3.02, and 1.47 times higher than the control, respectively, before gradually decreasing thereafter. On the 7th day, the CAT activity of ‘Ingelise’, ‘Wonder’, and ‘Golden Ivalace’ decreased significantly (P<0.05) to the lowest level, reaching 72.9%, 81.8%, and 61.3% of the control, respectively. Figure 4 Effect of high temperature stress on SOD activity (A) and CAT activity (B) in ivy leaves 2.4 Comprehensive evaluation of heat resistance of four types of ivy This experiment uses the average membership function values of four physiological indicators of ivy (Table 2) as the comprehensive evaluation index for the heat resistance of ivy. The results show (Table 3) that the comprehensive heat resistance of the four types of ivy is ‘Sark’> ‘Ingelise’> ‘Wonder’> ‘Golden Ivalace’. ‘Sark’ is the most heat-resistant variety, ‘Ingelis’ is a moderately heat-resistant variety, ‘Golden Ivalace’ is a thermosensitive variety, and Wonder also has poor heat resistance, but slightly stronger than ‘Golden Ivalace’. 3 Discussion Plants adopt multiple mechanisms to defend against various forms of biotic or abiotic stress they face in their living environment. The enhanced expression of various heat shock proteins and other stress-related proteins in plants, as well as the production of reactive oxygen species, constitute the main response of plants to heat stress. To cope with heat response, plants adopt many mechanisms for defense, such as maintaining membrane stability, producing antioxidants, clearing ROS, accumulating and regulating compatible solutes. A deeper understanding of the physiological and biochemical reactions and heat tolerance mechanisms of plants to high temperatures provides the possibility for improving plant heat tolerance.
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