Citric acid enhances physiological and biochemical tolerance of rye (Secale cereale L.) seedlings to cadmium toxicity and repeated freeze-thaw cycles.

Crops at high altitudes often face simultaneous ecological stress from cadmium (Cd) and freeze-thaw cycles during growth. In this study, rye (Secale cereale L.) was selected as the model organism to examine the physiological impacts of exogenous CA application (19 mg/L) on rye seedlings exposed to both individual and combined stresses of freeze-thaw and cadmium (30 mg/L). Molecular docking studies revealed interactions between Cd and the active sites of CAT, chlorophyll, and POD proteins. The results demonstrated that combined stress increased malondialdehyde (MDA) by 40.95%, hydrogen peroxide (H2O2) by 28.04%, and ascorbate peroxidase (APX) by 18.45%. The results confirmed that freeze-thaw condition (FTC) and Cd stresses reduced the net photosynthetic rate (Pn) by 64.87%, stomatal conductance (gs) by 27.45%, and Water use efficiency (Wue) by 30.84% while increasing intercellular carbon dioxide concentration (Ci) of rye seedlings. CA improved resistance to these stresses in rye seedlings by increasing the activity of APX and CAT enzymes. We believe that the findings of this study will be of particular interest to readers of environmental pollution and will be crucial for formulating strategies to enhance plant adaptability and flexibility in the face of rising levels of environmental pollutants and climatic fluctuations.