Increasing media pH contribute to the absorption of boron via roots to promote the growth of citrus.

Low pH is an important limiting factor for plant development in the south of China due to problems of acid red soil and boron (B) deficiency. Whereas, there is very limited information on the relationship between media pH and B distribution in plant, the physiological process changed by the interaction of pH and B in citrus growth also unclear. This experiment was conducted on trifoliate rootstock by employing two different concentrations of B (0 or 10 μM B) under three pH levels: pH 4, pH 5, and pH 6. Our results illustrate that low pH inhibite plant growth and cause oxidative stress in the roots, resulting in cell membrane injury. The increase of pH and B addition reduce the accumulation of ROS (O and HO) by regulating the activity of Class Ⅲ peroxidases (CIII Prxs). Moreover, increased pH improves the internal circulation of B in plants and decrease the content of lignin and cellulose in cell wall (CW). In summary, our investigation demonstrated that the increase of pH in nutrient solution can accelerate the re-distribution of B by roots to promote citrus growth. The accumulation of B in roots can protect plants from the damage of ROS by regulating the activity of CIII Prxs as well as decrease the content of lignin and cellulose are to promotes roots elongation.