Abstract
Secondary salinization caused by the overaccumulation of calcium nitrate [Ca(NO3)2] in soils due to excessive fertilization has become one of the major handicaps of protected vegetable production. Brassinolide, a bioactive plant steroid hormone, plays an important role in improving abiotic stress tolerance in plants. However, whether and how brassinolide (BR) can alleviate Ca(NO3)2 stress remains elusive. Here, we investigated the effects of exogenous BR on hydroponically grown tomato (Solanum lycopersicum L.) plants under Ca(NO3)2 stress through proteomics combined with physiological studies. Proteomics analysis revealed that Ca(NO3)2 stress affected the accumulation of proteins involved in photosynthesis, stress responses, and antioxidant defense, however, exogenous BR increased the accumulation of proteins involved in chlorophyll metabolism and altered the osmotic stress responses in tomatoes under Ca(NO3)2 stress. Further physiological studies supported the results of proteomics and showed that the exogenous BR-induced alleviation of Ca(NO3)2 stress was associated with the improvement of photosynthetic efficiency, levels of soluble sugars and proteins, chlorophyll contents, and antioxidant enzyme activities, leading to the reduction in the levels of reactive oxygen species and membrane lipid peroxidation, and promotion of the recovery of photosynthetic performance, energy metabolism, and plant growth under Ca(NO3)2 stress. These results show the importance of applying BR in protected agriculture as a means for the effective management of secondary salinization.
Highlights
The development of protected agriculture has made crop production possible beyond the seasonal barriers (Henry, 2019)
Observations of the microstructure of the tomato leaves showed that Ca(NO3)2 stress disrupted the arrangement of the epidermis, palisade mesophyll, and spongy mesophyll in tomato leaves (Figure 1C)
Exogenous BRinduced the differential regulation of Pro, soluble sugar, and soluble protein contents from 1 to 5 days of Ca(NO3)2 stress, indicating the more complex role of BR action in the production of antioxidant and osmotic adjustment substances, which appears to be specific to the temporal context, but increased the soluble sugar content and decreased the MDA content after 5 days which signified the role of BR in protecting plants from long-term osmotic stress and oxidative damage
Summary
The development of protected agriculture has made crop production possible beyond the seasonal barriers (Henry, 2019). With the fast-growing development of protected agriculture, secondary salinization in the continuous cropping soil has become increasingly common, which is attributed to excessive fertilization and intensive farming. BR Improves Ca(NO3) Stress Tolerance adverse effect on crop production in protected agriculture (Zhu et al, 2021). As it is different from open-field cultivation, the amount of nitrogen fertilizer used in greenhouse vegetable farming is large, with the main anion being nitrate (NO3−) and the cation being calcium cation (Ca2+) in the soils (Shu et al, 2016; Zhu et al, 2021). The genes encoding glutathione S-transferase and glutathione POD are up-regulated to protect plants from salinization (Poonam et al, 2015)
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