The Effect of Exogenous Calcium Treatments on Reducing Drought Stress Damages in Pepper Grown in In Vitro Conditions

Drought stress severely limits plant growth and development. Calcium, beyond being an essential nutrient, functions as an important signaling-molecule in plant stress responses. Given its economic importance, increasing drought tolerance in Capsicum annuum L. varieties has become a priority. In this study, two pepper varieties with different drought tolerances, Hilvan and Inan, were exposed to drought stress induced by polyethylene glycol (PEG 6000; 3 mg L⁻1) and/or calcium treatments (CT) (330 and 660 mg L⁻1 CaCl₂). The seedlings were grown in a controlled growth chamber and evaluated for morphological, physiological, and biochemical responses after five weeks. PEG application promoted root growth in both varieties but significantly suppressed shoot growth, chlorophyll content, protein levels, and antioxidant capacity. These negative effects were more pronounced in Hilvan, indicating a higher sensitivity to drought. Inan exhibited relatively stable growth and metabolic response under PEG stress, indicating higher drought tolerance. CT significantly mitigated the damage caused by PEG in both varieties, with the level of mitigation differing between them. Inan exhibited marked increases in chlorophyll content, protein accumulation, root fresh weight, antioxidant enzyme activities, and phenolic compounds, accompanied by a decrease in MDA levels, indicating effective alleviation of oxidative stress. CT in Hilvan partially restored physiological balance, but the responses remained weaker compared to Inan. Overall, CT was more effective in mitigating drought-induced oxidative damage in the drought-sensitive Hilvan variety. These findings demonstrate that CT is beneficial in increasing tolerance in drought-sensitive pepper varieties, highlighting the importance of calcium-mediated signal transduction.