Exogenous Ca enhances antioxidant defense in rice to simulated acid rain by regulating ascorbate peroxidase and glutathione reductase.

Exogenous calcium enhances rice tolerance to acid rain stress by regulating isozymes composition and transcriptional expression of ascorbate peroxidase and glutathione reductase. Calcium (Ca) participates in signal transduction in plants under abiotic stress, and addition of Ca is beneficial to alleviate damage of plants caused by acid rain. To clarify the effect of exogenous Ca on tolerance of plants to acid rain stress, we investigated regulation of Ca (5 mM) on activities, isozymes composition and transcriptional expression of ascorbate peroxidase (APX) and glutathione reductase (GR), redox state, and HO concentration and growth in rice leaves and roots under simulated acid rain (SAR) stress. SAR (pH 3.5/2.5) decreased the total activities of APX and GR in rice by decreasing the concentration of APX isoforms (APXII in leaves and APXIII in roots) as well as activation degree of GR isozymes and transcription level of GR1, indicating that SAR (pH 3.5/2.5) destroyed the redox state in rice cells and induced HO excessive accumulation, and inhibited growth of rice. Exogenous Ca alleviated SAR-induced inhibition on activities of APX and GR by regulating the concentration, activation, and transcription of their isozymes, and then maintained the redox level of cells and protected cells from oxidative damage, being beneficial to the growth of rice. Therefore, the promotion of exogenous Ca on activities of APX and GR can be important to enhance rice tolerance to acid rain by maintaining redox state and avoiding oxidative damage.