A comparative analysis of photosynthetic function and reactive oxygen species metabolism responses in two hibiscus cultivars under saline conditions

Abstract

Hibiscus (Hibiscus syriacus Linn.) is considered to be an important flowering shrub in Asia, and has high medicinal value. However, there are few studies on its cultivation and application in salinity soils. To understand the photosynthetic adaptive strategies employed by hibiscus to deal with saline conditions, the potential tolerant [H. syriacus ‘Duede Brabaul’ (DB)] and sensitive [H. syriacus ‘Blueberry Smoothie’ (BS)] cultivars were grown under 0–200 mM NaCl concentrations followed by a comprehensive assessment of their photosynthetic function and reactive oxygen species (ROS) metabolism. NaCl treatment significantly reduced the chlorophyll content of the two hibiscus cultivars, and the photosynthetic carbon assimilation capacity of the hibiscus leaves decreased, which was a result of stomatal and nonstomatal limiting factors. With the extension of NaCl stress days, nonphotochemical quenching (NPQ) can be significantly increased, which can effectively activate the nonradiant heat energy dissipation mechanism to release excess excitation energy to reduce the damage from the stressful environment and protect itself. Moreover, DB showed high antioxidant activities of reduced glutathione, and lower accumulation of ROS compared to BS. Taken together, this work suggests that the greater oxidative damage of the sensitive cultivar BS leaves is an important reason for its higher degree of photoinhibition to PSII than those of the tolerant cultivar DB leaves under NaCl stress.