Changes of Catalase and Peroxidase Activity and Expression Under Cold Stress in <i>Prunus persica</i> Cultivars with Different Cold Tolerances

Peach is one of the most common stone fruit crops, but it is also the most thermophilic. One of the main problems in peach cultivation is frost up to −8 °C in spring during pollen development, budding, and flowering. The adaptation of the plant to low temperatures could be related to the activation of the antioxidant system under cold stress. The aim of this work was to test the hypothesis of distinct adaptation mechanisms to cold stress in <i>Prunus persica</i> L. cultivars with various cold tolerances. The difference between this study and the previous ones is that previously, only contrasting varieties (resistant and sensitive) were studied. For the first time, we studied the effect of cold stress on cold-resistant varieties but with different degrees of resistance, such as “Loadel” and “Springold” (medium resistant) and “Podarok Like” and “Temisovskij” (highly resistant). The experiment was designed to simulate the effects of short-term cold snaps, which are a common occurrence during February and March in the south of Crimea. A series of tests were conducted on annual shoots that were frozen at −12 °C. The activity and gene expression of two major antioxidant enzymes, catalase and peroxidase, were studied by spectrophotometry and RT-qPCR, respectively. The experiment showed that these enzymes responded differently to cold stress in varieties with different cold tolerances. Catalase responded similarly in all four varieties. After frost, there was an increase in activity (7-fold in “Temisovskij” and 3-fold in “Podarok Like”) and a decrease in expression. In contrast to catalase, peroxidase showed an opposite response to cold stress in medium-tolerant and highly tolerant cultivars. Peroxidase activity after exposure to low temperatures increased in highly tolerant cultivars (1.5-fold in “Temisovskij”), while it decreased in medium-tolerant cultivars (1.5–2 fold in “Springold” and “Loadel”, respectively). The change in peroxidase expression was the opposite. It decreased in highly resistant varieties and increased in medium-resistant varieties. Thus, our results revealed the opposite response of one of the major antioxidant enzymes (peroxidase) in moderately resistant and highly resistant cultivars. The data obtained show that varieties with a high degree of resistance could have other adaptation mechanisms involved, which may be useful for selecting resistant varieties.