Calcium Ascorbate Attenuates Chilling Injury of Tomato Seedlings by Altering the Bioactivity of Phenolic Compounds

The present investigation focused on the role of calcium ascorbate (CaAsc) on tomato seedlings under low-temperature stress. Study was conducted by spraying aqueous solution of CaAsc at 0, 50, and 100 mM, on tomato seedlings with 5-7 true leaves in order to counteract the adverse impacts of chilling stress. One week after foliar application of CaAsc, all seedlings were exposed to a chilling temperature of 3±0.5 °C for six days (six hours per day) in a growth chamber. Loss of membrane integrity due to chilling stress led to oxidation of phenolic compounds by activation of peroxides (POD) and polyphenol oxidase (PPO) enzymes. Higher phenylalanine ammonia-lyase (PAL) activity, which is responsible for phenolic compounds accumulation, due to chilling temperature, has been considered as defense mechanism of chilling stress. The results revealed that application of 50 mM CaAsc ameliorated chilling injury of tomato seedling, which was associated with lower electrolyte leakage (16.2 %) and malondialdehyde (1.54 nmol g-1 FW) accumulation. Also, CaAsc-treated seedlings with 50 and 100 mM of CaAsc exhibited higher total phenols accumulation (36.2 and 28.4 mg pyrogallol g-1 FW, Respectively) which results from higher PAL enzyme activity concurrent with lower POD and PPO enzymes activity. Enhancing chilling tolerance in tomato seedling treated with 50 mM CaAsc by triggering phenols metabolism was associated with better seedling growth rate.