Lead exposure dose-dependently affects oxidative stress, AsA-GSH system, photosynthesis, and mineral element content in pakchoi (Brassica Chinensis L.)

Abstract

Abstract Lead (Pb) stress can cause oxidative stress and abnormal plant growth. The ascorbic acid-glutathione (AsA-GSH) cycle mainly exists in the chloroplast and is involved in resisting oxidative stress, scavenging reactive oxygen radicals in the chloroplast, and maintaining normal photosynthesis. However, whether Pb can affect the photosynthesis of pakchoi in a dose-dependent manner through the oxidative stress and AsA-GSH system is unclear. In this study, the low-dose (300 mg/kg), medium-dose (600 mg/kg) and high-dose (900 mg/kg) Pb stress models were established. In this experiment, methods such as ICP-MS, detection of photosynthetic characteristics and fluorescence characteristics, qRT-PCR, principal component analysis and correlation analysis were used. The results showed that Pb stress induced a dose-dependent increase in Pb content in pakchoi leaves. Principal component analysis discovered that Se, B and Pb were significantly negatively correlated. Pb stress caused an increase in MDA content and the decrease in SOD, GSH-Px and T-AOC activities. We also found that the Vc content and the GSH/GSSG ratio decreased. In addition, Pb stress resulted in the decreases of Pn, Tr, Gs, Ci, and VPD, and attenuated Fv/Fm and Fv/Fo. In the high-dose group, the contents of chlorophyll a, chlorophyll b and carotenoids were significantly decreased, and the expression of chloroplast development genes (GLK, GLN2) were abnormal. Taken together, our data suggests that Pb stress leads to aberrant photosynthesis in a dose-dependent manner by inhibiting the AsA-GSH system in pakchoi. The study expands the field of Pb toxicology research and provides indications for screening antagonists.