Brassinosteroid alleviates chilling-induced oxidative stress in pepper by enhancing antioxidation systems and maintenance of photosystem II

Abstract

To explore regulated mechanisms of Brassinosteroids-induced chilling tolerance, we studied the involvement of foliar sprayed 24-epibrassinolide (EBR) in the growth, lipid peroxidation, distribution of absorbed energy and excitation energy, chlorophyll fluorescence characteristics and antioxidant defense system of pepper seedlings under chilling stress. We found that low temperature retarded the growth of pepper seedlings, but foliar spray of EBR solution markedly improved the photoinhibition by increasing maximum quantum efficiency of photosystem II (F v /F m ), the actual photochemical efficiency of photosystem II, photochemical quenching coefficient and the efficiency of excitation capture of open PSII center (F v 0 /F m 0 ). Likewise, EBR increased the fraction of photochemical efficiency (P) and reduced the fraction of antenna heat dissipation (D) and excess energy (E). Low temperature led the increase in end product of lipid peroxidation and the content of H 2 O 2 , O 2 -and OH -, and it caused the occurrence of oxidative stress. The activities of antioxidative enzymes including superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and contents of ascorbic acid and reduced glutathione were significantly improved by EBR during low temperature stress. The application of EBR also markedly increased the contents of proline, soluble sugar and protein under low temperature. EBR significantly reinforced antioxidant defense system, and it can be reflected through the reduced accumulation of harmful reactive oxygen species and MDA in pepper seedlings. Overall, these results suggest that EBR increases the tolerance of pepper seedlings against chilling stress largely by optimizing distribution of absorbed energy and excitation energy and enhancing antioxidant defense system.Keywords 24-epibrassinolide Á Chilling stress Á Distribution of absorbed energy and excitation energy Á Antioxidant system Á Pepper Abbreviations BRs Brassinosteroids Chl Chlorophyll D Fraction of antenna heat dissipation DAB 3,3-diaminobenzidine E Excess energy EBR 24-epibrassinolide ETR Electron transport rate F v /F m Maximum quantum efficiency of PSII F v 0 /F m 0 Efficiency of excitation capture of open PSII center FW Fresh weight GSH Reduced glutathione MDA Malondialdehyde OHHydroxyl radical O 2 -

Effects of Brassinosteroids on Photosynthetic Performance and Nitrogen Metabolism in Pepper Seedlings under Chilling Stress

“…Brassinosteroids (BRs), as polyhydroxylated steroidal plant hormones, are involved in plant physiological processes [14,48]. This present study extends our previous work on EBR in the regulation of chilling tolerance from hormone metabolism, calcium signaling transduction, and cellular redox homeostasis [19,49]. Here, we have demonstrated the positive role of EBR in enhancing plant growth and development through maintaining higher photosynthetic capability and nitrogen metabolism (Figure 8).…”

“…Exogenous application of 24-epibrassinolide (EBR) could alleviate the inhibition of photosynthesis induced by drought [16], salty stress [17], and low temperature stress [18]. We previously reported that exogenous EBR mitigates chilling stress by enhancing the autoxidation system [19]. Furthermore, exogenous EBR reduces the content of ROS in suspension cells of alpine mustard under chilling stress, protects the integrity of the cytoplasmic membrane, and mitigates the damage caused by chilling stress [20,21].…”

Brassinosteroids increase electron transport and photosynthesis in soybean plants under water deficit

“…The increases in qP and ETR promoted by the EBR reveals the positive interference on the activation of the PSII reaction centres, inducing the oxidation of QA, the primary quinone molecule responsible for receiving and transferring electrons between PSII and PSI (Maxwell and Johnson 2000, Singh and Prasad 2014, Jia et al 2015. Li et al (2015) found benefits for PSII after EBR application in seedlings of Capsicum annuum subjected to oxidative stress by low temperature, in which plants exposed to low temperature + 0.l μM EBR exhibited significant increases of 13.2 and 5.6% in ΦPSII and qP, respectively, compared to the treatment under low temperature without EBR.…”

Brassinosteroids improve photosystem II efficiency, gas exchange, antioxidant enzymes and growth of cowpea plants exposed to water deficit

“…Thussagunpanit et al (2015a) studied the action mechanisms of EBR in Oryza sativa plants and reported increases in U PSII after EBR application. Research conducted by Li et al (2015) showed that EBR increases the proportion of open PSII reaction centres, improving the efficiency of the capture of light energy for the electron transport chain. Rivas et al (2016) observed reductions in q P and ETR in V. unguiculata exposed to a water deficit due to lower activation of enzymes linked to carboxylation as well as limited extinction of fluorescence during photochemical processes.…”