Abstract
Reversible phosphorylation of proteins and the assembly of thylakoid complexes are the important protective mechanism against environmental stresses in plants. This research was aimed to investigate the different responses of the antioxidant defense system and photosystem II (PSII) to osmotic stress between drought-resistant and drought-susceptible wheat cultivars. Results showed that the decrease in PSII photochemistry and six enzyme activities was observed in drought-susceptible wheat compared with drought-resistant wheat under osmotic stress. In addition, a lower accumulation of reactive oxygen species (ROS) and cell death were found in the resistant wheat compared with the susceptible wheat under osmotic stress. Western blot analysis revealed that osmotic stress led to a remarkable decline in the steady state level of D1 protein in drought-susceptible wheat. However, the CP29 protein was strongly phosphorylated in drought-resistant wheat compared with the susceptible wheat under osmotic stress. Our results also showed that drought-resistant wheat presented higher phosphorylated levels of the light-harvesting complex II (LHCII), D1, and D2 proteins and a more rapid dephosphorylated rate than drought-susceptible wheat under osmotic stress. Furthermore, the PSII-LHCII supercomplexes and LHCII trimers were more rapidly disassembled in drought-susceptible wheat than the drought-resistant wheat under osmotic stress. These findings provide that reversible phosphorylation of thylakoid membrane proteins and assembly of thylakoid membrane complexes play important roles in plant adaptation to environmental stresses.
Highlights
Wheat (Triticumae stivum L.) is one of the most important food crops planted in the world and a staple food for 35–40% of the world population[1,2]
It is well known that water stress is one of the most important environmental stresses and a major limitation for plant growth, development and yield[33,38]
Many studies have showed that osmotic stress affected gas exchange parameters, chlorophyll content, lipid peroxidation, the activities of antioxidant enzymes, photosystem II (PSII) photochemistry, and the structure of thylakoid[11,33,38,39,40]
Summary
Wheat (Triticumae stivum L.) is one of the most important food crops planted in the world and a staple food for 35–40% of the world population[1,2]. Photochemical activity, phosphorylation of PSII proteins, thylakoid ultrastructure, and stomatal conductance are classically measured to evaluate the structural and functional changes in the photosynthetic apparatus of plants under environment stress[20,21,22,23]. There was still few studies on the comprehensive comparisons of the photosynthetic characteristics and the antioxidant system between two wheat cultivars with different drought resistance under osmotic stress[35,36]. We compared the difference in chlorophyll fluorescence, ROS generation, activities of antioxidant enzymes, amounts of thylakoid proteins, phosphorylation of thylakoid membrane proteins and the structure of thylakoid between drought-susceptible and drought-resistant wheat cultivars exposed to osmotic stress. We expected to elucidate the regulatory role of the reversible phosphorylation of PSII proteins and thylakoid membrane complexes in the drought resistance of plants and provide a better understanding of stress resistant mechanisms in plants
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