Physio-biochemical Mechanisms of Acetic Acid Involved in Cold and Freezing Tolerance in Mexican Lime Plants (Citrus aurantifolia Swingle)

Abstract

Cold stress is one of the abiotic stresses that leads to most losses in citrus. ‘Mexican’ lime is one of the commercial citrus cultivars in the world, which is commonly used as a citrus rootstock. This study aimed to investigate the effect of acetic acid (0 and 15 mM) as a cost-effective agent on the cold tolerance of ‘Mexican’ lime plants at 0 and −6 °C. The results showed that at 0 °C, the increase of both enzymatic and non-enzymatic antioxidant system significantly increased the cold tolerance of ‘Mexican’ lime plants, while at −6 °C, the non-enzymatic antioxidant system played a more effective role. Plants treated with acetic acid exhibited lower electrolyte leakage, malondialdehyde, absorption flux per active reaction center (ABS/RC), and DI0/RC at both stress levels. On the other hand, higher levels of total soluble carbohydrate, pigments, Fv/Fm (maximum quantum yield of PSII [photosystem II] photochemistry), Fv/F0, PIABS (performance index of PSII based to absorption), antioxidant capacity, and total phenol were found in acetic acid treated plants. At 0 °C, peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) enzymes increased in the treated plants, but a different trend was observed at −6 °C. This study provides strong evidence that acetic acid could moderate cold and freezing stresses in ‘Mexican’ lime plants.