关键词: 番茄, 酸雨, 油菜素内酯, 光合作用, 细菌性叶斑病

Abstract:

【Objective】 In the era of climate change, the acid rain deposition has become a global environmental issue, which seriously affects the yield, quality and disease incidence of vegetables and other crops. Brassinosteroids (BRs) are a group of plant hormones widely existing in plants, which regulate plant resistance to broad-spectrum environment stresses. The aim of this study was to investigate effects of BRs on plant photosynthesis and disease susceptibility in tomato under simulated acid rain conditions and its alleviation effect, so as to provide guidance for safety production of vegetable crop. 【Method】In this study, using tomato (Solanum lycopersium L.) cultivar ‘Hezuo 903’ as material, the effects of exogenous BR foliar spray on the photosynthetic characteristics and the incidence of bacterial leaf spot disease caused by Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) were studied under two levels of simulated acid rain including simulated acid rain 1 (SiAR2): NH₄NO₃ (1.3 g·L^-1),MgSO₄·7H₂O (3.1 g·L^-1),Na₂SO₄ (2.5 g·L^-1),KHCO₃ (1.3 g·L^-1),CaCl₂·2H₂O (3.1 g·L^-1), pH (3.0, adjusted by 1N H₂SO₄ ) and simulated acid rain 2 (SiAR2): rain from Hanzhou area in spring, pH (3.0, adjusted by 1N H₂SO₄), and spraying leaves with H₂O as control condition. The alleviation of exogenous BR were studied through spraying exogenous BR on tomato leaves under two levels of simulated acid rain and control conditions. To reveal the underlying mechanism of BR induced stress alleviation, the transcript abundance of photosynthesis-related genes (e.g. FBPase, SBPase, rbcS), defense-related genes (e.g. PR1 and NPR1), and the activity of antioxidant enzymes were measured. 【Result】The results showed that the phytotoxic effect of simulated acid rain on photosynthesis in tomato was mainly reflected by the decrease of net photosynthesis rate (Pn), the photosystem II photochemical efficiency (Φ_PSII), and the photochemical quenching coefficient (qP). The simulated acid rain increased tomato susceptibility to Pst DC3000, resulting in a significant increase in disease incidence and leaf bacterial population. However, the exogenous BR was able to enhance the leaf photosynthetic capacity and decrease the susceptibility of tomato to Pst DC3000 by reducing the leaf bacterial population under two levels of simulated acid rain and control conditions Furthermore, the exogenous BR treatment was able to protect plant photosynthesis and pathogen resistance from the damages caused by simulated acid rain. The BR pretreatment not only significantly increased the transcript abundance of photosynthesis-related genes (e.g. FBPase, SBPase, and rbcS) and defense-related genes (e.g. PR1 and NPR1), but also reduced the content of malondialdehyde and enhanced the activity of G-POD and CAT in tomato plants under simulated acid rain treatments. Thus, the exogenous BR alleviated the inhibition of simulated acid rain on tomato photosynthesis and disease resistance. 【Conclusion】It was concluded that exogenous BR could increase leaf photosynthesis, transcript abundance of photosynthesis, defense-related genes, and the activity of antioxidant enzymes under simulated acid rain, and could also improve the resistance of tomato plants to bacterial leaf pathogen.

Key words: tomato, acid rain, brassinosteroid, photosynthesis, bacterial leaf spot