Investigation of cold stress tolerance in seedlings of pepper (Capsicum annuum) following application of meta-topolin.

This study investigated the anatomical and physiological effects of exogenous meta-topolin (mT) at different concentrations (0, 0.25, 0.50 mM) on the leaves of cold-susceptible cultivar Kahramanmaraş-1 (KM-1) and cold-tolerant cultivar Çoban F1 (ÇF1) of pepper (Capsicum annuum) before cold stress (4°C). Leaf thickness of ÇF1 was higher than KM-1 at optimum (25°C) and low temperatures. Long-term cold stress reduced stomatal density while increasing leaf thickness in KM-1. At 48 and 60 h of stress, both cultivars showed increased malondialdehyde (MDA) and ion leakage, while FW, actual water content (AWC), and relative water content (RWC) decreased. Under cold stress, 0.25 mM mT increased RWC, AWC, and FW in KM-1 at 48 and 60 h, and at 60 h in ÇF1, without changing DW. It decreased the upper stomatal density of ÇF1 and index ratio at 60 h. At 24 h of stress, all mT concentrations increased ferric-reducing antioxidant power (FRAP), peroxidase (POD) activity, protein, phenolic compounds, H2O2, MDA, and leaf thickness. At 48 h, ÇF1 showed higher flavonoid, FRAP, and POD activity when compared with KM-1. All mT applications increased total protein content and decreased MDA levels at 48 and 60 hcompared with stress alone. mT positively supported tolerance to cold stress in pepper through anatomical and physiological mechanisms.