Exploring the protective effects of proline on pepper (Capsicum annum L.) under high-temperature stress

• High-temperature stress led to a decrease in PIP1 gene expression and linoleic acid content in pepper plants. • Application of proline resulted in improved growth traits of the pepper under optimal temperature compared to the control and encapsulated proline treatments. • Under high-temperature conditions, the application of encapsulated proline enhanced the chlorophyll index, phenol, and proline concentration compared to the control treatment. Heat stress poses a significant challenge to agricultural productivity, particularly in pepper plants, by affecting their physiological and biochemical processes. Proline, an amino acid known for its role in stress mitigation, has shown potential in alleviating such impacts. However, its efficacy specifically under heat stress conditions in pepper plants has not been well established. This study aims to investigate whether exogenous application of proline and its encapsulated form can effectively reduce the adverse effects of high temperatures compared to optimal conditions. The treatments involved two temperature conditions: 25±2°C (CT) and 40±2°C (HT), along with various proline sources, including distilled water (C), proline (Pr), and encapsulated proline (N-Pr), each at a concentration of 20 mM. The findings of this study revealed that high-temperature stress led to a decrease in PIP1 gene expression which plays a crucial role in regulating water transport and maintaining cellular hydration, and linoleic acid content in pepper plants. The application of proline resulted in improved growth traits under optimal temperature in comparison with control and N-Pr. Furthermore, electrolyte leakage (EL) decreased by 45% with the application of Pr under high temperature compared to control. Under heat stress, the application of N-Pr enhanced the chlorophyll index, phenol, and proline concentration by 24%, 102%, and 147% respectively. Overall, the use of Pr under optimal temperature and N-Pr under high temperature could improve the resistance of pepper plants.