Molecular Plant Breeding 2025, Vol.16, No.1, 44-54 http://genbreedpublisher.com/index.php/mpb 51 temperature stress, but the accumulation of heat resistant ‘Sark’ and moderately heat resistant ‘Ingelise’ was significantly lower than that of heat sensitive ‘Golden Ivalace’ and ‘Wonder’ throughout the entire high temperature stress process (Figure 4A). Plants under environmental stress also accumulate large amounts of metabolites, especially amino acids. There is a large amount of data indicating that proline can accumulate as a cell osmoprotectant when plants are under stress, to maintain cell expansion or osmotic balance, enhance plant stress resistance, stabilize cell membranes to prevent electrolyte leakage, and coordinate the balance of ROS in the body (Tu et al., 2013; Gosavi et al., 2014). In addition, when plants respond to various stress responses, proline can also play a beneficial role as a metal chelating agent, antioxidant defense molecule, and signaling molecule. When low concentrations of proline are applied in vitro, it can enhance plant tolerance (Hayat et al., 2012). Studies have shown a positive correlation between proline content and plant stress resistance (Kumar et al., 2012), and similar results were also found in this study. When ivy is subjected to high temperature stress, proline accumulates to varying degrees in different varieties. On the third or fifth day of heat treatment, proline accumulation reaches its peak and then begins to decline. During the entire process of high temperature stress, the accumulation of proline in heat-resistant ‘Sark’ and moderately heat-resistant ‘Ingelise’ was higher than that in thermosensitive ‘Golden Ivalace’ and ‘Wonder’, and there was a significant difference (P<0.05) (Figure 4B). High temperature can generate ROS accumulation, thereby triggering oxidative stress response in plants. High temperature can disrupt the balance between the generation and elimination of ROS within cells, leading to a significant accumulation of reactive oxygen species and affecting plant growth and development. Usually, plants induce an increase in antioxidant enzymes in response to high temperature stress, thereby initiating antioxidant protection mechanisms to maintain their own redox balance (Hameed et al., 2012). In the experiment, the activities of SOD and CAT in ivy under high temperature stress were analyzed. The results showed that the heat-resistant variety ‘Sark’ reacted the most rapidly and the activities of SOD and CAT increased the fastest when ivy was subjected to high temperature stress. There was a significant increase on the first day of high temperature treatment, followed by the moderately heat-resistant variety ‘Ingelise’, with a smaller increase. On the third day of heat treatment, all tested ivy SOD and CAT enzyme activities showed significant improvement compared to the control group. Afterwards, the SOD and CAT activities of heat resistant ‘Sark’ and moderate heat resistant ‘Ingelis’ decreased slowly, while those of heat sensitive ‘Golden Ivalace’ and ‘Wonder’ decreased rapidly. This indicates that high temperatures can stimulate the antioxidant enzyme activity of ivy. Compared with thermosensitive ivy, heat-resistant materials have a faster increase in SOD and CAT enzymes and a slower decrease. It is speculated that thermosensitive ivy may have a stronger ability to counteract the harmful effects of ROS and achieve the goal of heat resistance. This experiment conducted a comprehensive analysis of the heat damage index, chlorophyll content, Fv/Fm, MAD, proline, SOD, and CAT activities of four ivy varieties under artificial high temperature stress using membership functions to determine their heat tolerance: ‘Sark’> ‘Ingelis’> ‘Wonder’> ‘Golden Ivalace’. Artificial high temperature stress seriously affects the structure and function of the light system in ivy leaves, resulting in varying degrees of decrease in chlorophyll content, Fv/Fm values, ETR, and increase in MDA content in four ivy species. Proline content, SOD and CAT activities show an initial increase followed by a decrease with increasing stress duration. After high temperature stress, the Fv/Fm values, Proline content, SOD and CAT activities of heat-resistant varieties ‘Sark’ and ‘Ingelise’ were higher than those of thermosensitive varieties ‘Golden Ivalace’ and ‘Wonder’, while the MDA content was lower than that of thermosensitive varieties. This study analyzed the morphological, physiological, and biochemical indicators of ‘Sark’, ‘Ingelise’, ‘Golden Ivalace’, and ‘Wonder’ ivy under artificial high temperature stress, which will contribute to the screening or cultivation of heat-resistant ivy in the future.
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