Abstract
To investigate the effects of brassinosteroids on plant growth and nitrogen metabolism in pepper seedlings under chilling stress, pepper seedlings with three true leaves were foliar pretreated with 0.1 μM exogenous 24-epibrassinolide (EBR) before carrying out chilling stress for 7 days. The results showed that perapplication of EBR mitigated the chill-induced decrease in plant growth via maintenance of a high net photosynthetic rate (Anet), maximum quantum efficiency (Fv/Fm), and photochemical quenching coefficient (qP). Exogenous EBR markedly increased the levels of partial free amino acids (proline, arginine, aspartic acid, and glycine) and promoted nitrogen metabolism through increasing the activities of nitrate reductase (NR), glutamine synthase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) in the leaves of pepper seedlings under chilling stress. The effect of exogenous EBR on the content of reactive oxygen species was also investigated. Pretreatment with EBR reduced the accumulation of hydrogen peroxide (H2O2) and superoxide anion (O2−·), and concomitantly alleviated membrane lipid peroxidation of pepper leaves under chilling stress. These results suggest that foliar pretreatment of EBR has a positive effect on improving the chilling tolerance of pepper seedlings via maintaining a high photosynthetic capability and enhancing the nitrogen metabolism.
Highlights
In winter and early spring, chilling stress is a critical threat restricting the growth and nutrition quality improvement of vegetables produced in protected facilities [1,2]
The plant growth and pigment contents were significantly decreased by chilling stress compared with their respective controls
When the chilling-stressed plants were pretreated with EBR, the plant height, stem diameter, fresh weight, dry weight, and QI
Summary
In winter and early spring, chilling stress is a critical threat restricting the growth and nutrition quality improvement of vegetables produced in protected facilities [1,2]. It is well known that the damage caused by chilling stress has given rise to the disturbance of many physiological metabolic processes of plants, photosynthesis [4]. Nitrogen metabolism is another important physiological process that is sensitive to low temperature stress [5,6]. There is a closed relationship between nitrogen metabolism and photosynthetic capability [7]. Photosynthesis provides carbon skeletons and supplies reduction energy for nitrogen metabolism [8]. 25% of the energy generated by photosynthesis can be used for nitrate reduction [9]. Nitrate is mainly assimilated in plant leaves
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