Molecular Plant Breeding 2025, Vol.16, No.1, 44-54 http://genbreedpublisher.com/index.php/mpb 45 more resistant to freezing than young leaves near the ground. Under low concentration cadmium stress, ivy can reduce the damage caused by stress by regulating soluble protein and proline content, and regulating catalase and peroxidase activity (Cheng et al., 2019). It also has strong tolerance to lead stress (Yang et al., 2020). Li et al. (2022) used exogenous low concentration NO treatment to enhance the antioxidant enzyme activity and osmotic regulation ability of Chinese ivy, thereby improving its salt tolerance. In addition, Pandey et al. (2015) evaluated the air pollution tolerance index of British ivy, and another study found that some green leaf varieties of British ivy have higher light saturation points and lower light compensation points than some flowering leaf varieties (Zhang, 2019). Overall, there is currently no research on the physiological and biochemical responses of ivy to high temperature stress. This study used four types of ivy cuttings as test materials, and recorded their morphological changes under artificial high temperature stress. Physiological indicators such as chlorophyll content, chlorophyll fluorescence index, malondialdehyde (MDA) content, proline content, superoxide dismutase (SOD) activity, and catalase (CAT) activity in their leaves were measured to analyze and compare the differences in heat resistance among the four ivy varieties, screen ivy varieties with better heat resistance, and provide theoretical reference for the breeding and cultivation of ivy heat-resistant varieties in the later stage. 2 Results and Analysis 2.1 The effect of high temperature stress on the morphology of different ivy varieties The plants and leaves of ‘Golden Ivalace’ were most severely damaged, while ‘Sark’ performed the best. The leaves of ‘Ingelis’ and ‘Wonder’ showed significant wilting (Table 1). ‘Golden Ivalace’ is most sensitive to high temperature stress, and on the third day of heat treatment, it first shows wilting of young leaves, while ‘Sark’, ‘Ingelis’, and ‘Wonder’ do not show significant changes in morphology. On the 5th day of heat treatment, ‘Golden Ivalace’ suffered severe damage from high temperature stress, with a heat damage index of 57.2%, while ‘Sark’ did not show significant morphological damage, and the young leaves of the apical meristematic tissue of ‘Ingelis’ and ‘Wonder’ began to wilt. On the 7th day, the heat damage index of ‘Golden Ivalace’ and ‘Wonder’ reached 84.2% and 78.2% respectively. The tender leaves of ‘Ingelise’ showed obvious withering, while most of the mature leaves were healthy. However, ‘Sark’ had good growth except for a few leaves that withered, demonstrating strong resistance to high temperature stress. Table 1 Heat index of 4 species of ivy under different heat stress durations Number of heat treatment days Heat index Sark Ingelise Wonder Golden Ivalace 0 d 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00 1 d 13.99±1.56 13.15±1.26 18.08±2.36 28.12±2.63 3d 16.69±1.20 28.33±3.37 28.91±3.18 39.11±5.19 5 d 24.44±2.30 33.17±0.22 37.35±1.17 57.20±7.57 7 d 36.63±6.15 66.63±7.14 78.18±2.21 84.22±5.35 2.2 The effect of high temperature on chlorophyll content in different varieties of ivy Except for the first day of high-temperature treatment, with the increase of high-temperature stress time, the chlorophyll a and total chlorophyll content of the four ivy leaves showed an overall decreasing trend (Figure 1). On the first day of high-temperature treatment, except for ‘Golden Ivalace’, the chlorophyll a, chlorophyll b, and total chlorophyll content of the other three varieties ‘Sark’, ‘Ingelise’, and ‘Wonder’ increased slightly compared to the control. With the extension of high-temperature treatment time, the chlorophyll a content of all ivy varieties showed varying degrees of decrease. On the 7th day of high temperature stress, the chlorophyll a content in ‘Sark’ and ‘Ingelis’ decreased by 37.7% and 29.6% respectively compared to the control, while the chlorophyll a content in ‘Golden Ivalace’ and ‘Wonder’ decreased by 72% and 69.2% respectively. The chlorophyll b changes of the four varieties are irregular. The total chlorophyll content of Golden Ivalace decreased the most compared to the control, reaching 41.1%, while the total chlorophyll content of Ingelis decreased the least compared to the control, at 24.8%.
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