Effects of exogenous salicylic acid and abscisic acid on growth, photosynthesis and antioxidant system of rice

The key function of plant growth regulators is to adjust the growth and development of plants to adapt to the changing environment, which plays a vital role in the growth and yield of crops. This study was aimed to evaluate the ability of foliar application of salicylic acid (SA) and abscisic acid (ABA) to regulate rice (Oryza sativa L.) growth quality at seedling stage and reproductive stage. The two rice cultivars Wanshengyoutianhong-4 (W4) and Huanghuazhan (HZ) were sprayed foliar with SA (100 mg [L.sup.-1]) and ABA (4 mg [L.sup.-1]) at two-leaf stage, and their effects on morphological growth, physiological characteristics, malondialdehyde (MDA), osmotic substances, protective enzyme activities, photosynthesis and yield components were studied. Results indicated that SA and ABA significantly increased morphological growth, osmotic substances, antioxidant enzyme activities; MDA content dropped significantly (p < 0.05) in W4. While the two regulators inhibited morphological growth and physiological characteristics in HZ. Additionally, net photosynthesis, stomatal conductance, transpiration rate, water use efficiency and apparent mesophyll conductance were improved in both of rice cultivars at heading stage as well as grain weight. In conclusion, foliar spray of SA and ABA enhanced plant growth, induced an increase in protective enzyme activities and reduced the oxidative damage of the hybrid rice cultivar but not of the conventional rice cultivar at seedling stage. Meanwhile, photosynthetic parameters and grain weight were slightly enhanced at reproductive stage. These results served as a theoretical basis and technical support for the chemical regulation and cultivation practices of rice. Key words: Abscisic acid, antioxidant enzyme activities, photosynthesis, salicylic acid, yield components.