Nano-ZnO priming induces salt tolerance by promoting photosynthetic carbon assimilation in wheat

High salt seriously reduces plant growth in wheat by depressing photosynthetic carbon assimilation. In this study, wheat plants were firstly primed with nano-ZnO (50 mg L-1), and after 20-day recovery, the plants were then exposed to a 10-day salt stress (200 mM NaCl). The nano-ZnO priming significantly reduced Na concentration and increased leaf water potential under salt stress. In relation to the non-primed plants, the nano-ZnO primed plants possessed more effective oxygen scavenging system as exemplified by the enhanced activities of SOD, APX and CAT, leading to a better maintenance in homeostasis of ROS production under salt stress. The nano-ZnO priming benefited the tolerance of photosynthetic apparatus to subsequent salt stress, which was mainly due to the enhanced trapped energy flux and electron transport flux. The nano-ZnO priming increased the activities of phosphoglucomutase and cytoplasmic invertase, which promoted the sucrose biosynthesis in leaves under salt stress. In addition, the nano-ZnO primed plants had higher shoot dry weight than the non-primed plants under salt stress. Collectively, nano-ZnO priming activated the antioxidant system to depress the oxidative burst and enhanced the efficiency of photosynthetic electron transport and sucrose biosynthesis in leaves under salt stress, hereby improved the salt tolerance in wheat.