H₂O₂ leaf priming improves tolerance to cold stress in pistachio rootstocks

Hydrogen peroxide (H2O2) priming is an effective strategy for alleviating the detrimental effects caused by cold stress in plants, however the underlying functional mechanisms are poorly understood. In the current study, the impact of H2O2 priming on the biochemical and physiological processes in pistachio (Pistacia vera L.) rootstocks was determined under cold stress. Overall, across the four rootstocks studied (UCB-1, Badami, Ghazvini and Kaleh-Ghouch), H2O2 priming prior to cold stress (primed condition) resulted in an increase in photosynthetic pigments (total chlorophyll and total carotenoid) and total soluble proteins compared to cold stress treatment (unprimed condition). Furthermore, the antioxidant enzymes activity (Ascorbate peroxidase (APX), Polyphenol oxidase (PPO), Catalase (CAT), and Guaiacol peroxidase (GPX)) and osmolyte levels (Proline (PRO), Total free amino acids (TFAA) and Total soluble carbohydrate (TSC)) increased under H2O2 priming + cold stress treatment compared to the unprimed condition. On the contrary, oxidative stress parameters (Electrolyte Leakage (EL), Malondialdehyde (MDA), and other aldehydes (OLD)) decreased under primed environment compared to unprimed condition. Overall, H2O2 priming improved response to cold stress in pistachio rootstocks; however, there was variations among the genotypes in the physiological and biochemical response. Cold stress in the absence of H2O2 priming revealed Badami to be the most tolerant rootstock, followed by Ghazvini, UCB-1 and Kaleh-Ghouch. However, when H2O2 priming was applied prior to cold stress exposure, UCB-1 was the most tolerant rootstock, followed by Badami, Ghazvini and Kaleh-Ghouch. Positive correlations were found between antioxidant enzyme activities and osmolytes for UCB-1, Badami and Ghazvini, while conversely, a negative correlation was found between antioxidant enzyme activities and oxidative stress parameters. The outcomes of this study indicate that priming with H2O2 can reduce the destructive effects of cold stress on pistachio rootstocks. Thus, H2O2 priming may be considered as a valuable strategy for improving the tolerance of cold-sensitive rootstocks, such as UCB-1, and implementing it as a pre-treatment could prevent economic damage resulting from cold stress in agriculture.