Physiological Mechanism Research Of Strengthened Low Light Tolerance Of Tomato Plants By Applying Exogenous 24-Epibrassinolide

With the demand of market and consumer, the cultivation area of off-season vegetables is gradually increasing. Among them, tomato is one of the most representative soilless cultivation crops and has the largest cultivation area at home and abroad. Due to the poor quality or aging of facility covering materials and the impact of seasonal bad weather lead to lower transmittance, the glasshouse plants are often in shading environments. The weak light stress does great damage to plant growth and development, seriously restricts the increasing production and revenue of greenhouse tomato. How to relieve the low light stress injuries has become a top priority issue. In addition to select and breed the low-light-resistant varieties, through the application of plant growth regulators to perfect plants resistance is an alternatively sensible way. Consequently, our work intend to screen a certain concentration of 24-epibrassinolide(EBR) to improve the low light tolerance of tomato plants.With low-light sensitive tomato variety’Jiersi’as the tested material, this paper was conducted to investigate the effects of exogenously sprayed of EBR on tomato plants under low light stress(80 μmol·m-2·s-1) by hydroponic culture and substrate culture in bucket. We explored the biochemistry effects that EBR regulated adaptive varieties in morphology and physiological function, further alleviated the low light stress injuries under low light from the aspects of seedling growth, antioxidant capacity, photosynthetic performance, endogenous hormones level, carbohydrate metabolism, fruits yield and quality. The main results were as follows:1. Application of 0.1 mg·L-1 EBR under low light significantly increased SOD, POD and CAT activities in leaves of tomato seedlings, and then enhanced ROS scavenging capacities and reduced the membrane lipid peroxidation injury, besides partly recovered the leaf developmental morphology and alleviated the restrictions on growth caused by low light, ultimately promoted plants growth.2. Application of 0.1 mg·L-1 EBR under low light sensibly raised net photosynthetic rate(Pn), stomatal conductance(Gs) and transpiration rate(Tr), enlarged the PSII reaction centers openness and electron transport rate(ETR), which partly alleviated the decline of maximum photochemistry efficiency(Fv/FM) and actual photochemistry efficiency(Opsn). Chlorophyll levels and chloroplast ultrastructure were also significantly improved. It was demonstrated that appropriate amount of exogenous EBR could maintain the stability of chlorophyll content or composition and the chloroplast ultrastructure, morever improve the chlorophyll fluorescence index, finally significantly strengthened the photosynthetic activity of tomato seedlings.3.Application of 0.1 mg·L-1 EBR under low light markedly promoted the apparent quantum yield(AQY), dark respiration rate(Rd) and carboxylation efficiency(CE) of the response curve parameters, reduced the light compensation point(LCP) and carbon dioxide compensation point(CCP), meanwhile the Rubisco large subunit content significantly elevated. It was illustrated that proper concentration of exogenous EBR could heighten the photosynthetic performance of tomato seedlings through keeping up the stable state of the response curve parameters and enhancing the Rubisco content.4. Application of 0.1 mg·L-1 EBR under low light noticeably enhanced the indole-3-acetic acid(IAA), zeatin riboside(ZR) and gibberellin(GA3) concentration, moreover increased the starch concentration, sucrose synthase(SS) and sucrose phosphate synthase(SPS) of the carbon metabolism key enzymes. Thus it could be seen that exogenous EBR could adjust the level of carbohydrate metabolism of tomato leaves, then alter the changes of endogenous hormones concentration, furthermore modify inner relevance of "source to pool", eventually accelerated the photosynthate allocation from leaves to fruits.5. Application of 0.1 mg·L-1 EBR under low light dramatically improved fruit weight, yield per plant, fruit diameter and peel thickness. The vitamin C, soluble solids and soluble sugar content were as well as significantly increased compared with control, whereas the titratable acid content significantly decreased. It was indicated that reasonably applying suitable concentration of exogenous EBR could improve the yield and quality of tomato...