The Exogenous Application of Brassinosteroids Confers Tolerance to Heat Stress by Increasing Antioxidant Capacity in Soybeans

Abstract

Heat stress is an important factor affecting soybean yield. Brassinosteroids (BRs) play a crucial role in plant growth, development, and defense. In the present study, the regulatory effects of 24-epibrassinolide (EBR, one of the bioactive BRs) on heat tolerance in soybeans, and its underlying physiological mechanisms were investigated. The results show that foliar spraying with EBR significantly alleviate heat stress–induced water loss and oxidative damage in soybean leaves. The activities of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) and the contents of antioxidant substances (ascorbic acid and reduced glutathione) were markedly increased in EBR–treated leaves compared with water–treated leaves, which contributed to maintaining reactive oxygen species homeostasis and relieving oxidative injury under heat stress. However, EBR–treated leaves showed a significant decrease in free proline and total soluble sugar content under heat stress compared to water–treated leaves. In addition, EBR treatment showed obviously higher photosystem II activity under heat stress, and higher net photosynthetic rate and biomass accumulation after recovery from heat stress compared to water treatment. Collectively, these results indicated that EBR could significantly improve the capacity of antioxidant defense systems to protect photosynthetic apparatus under heat stress, thereby effectively alleviating heat stress-induced growth inhibition in soybean plants.

Brassinosteroid modulates ethylene synthesis and antioxidant metabolism to protect rice (Oryza sativa) against heat stress-induced inhibition of source‒sink capacity and photosynthetic and growth attributes

“…The prevailing study speculates that an enhancement in relative leaf water content implies a stable plant-water relationship, favoring PDM accumulation in BR-and ethylene-treated plants under heat stress. Our results are consistent with those obtained by Wang et al (2022), who reported that BR (0.05-1 μM) treatment effectively alleviated the heat stress-induced decrease in relative water content and significantly increased the leaf net photosynthesis rate and plant dry mass production in soybeans (Glycine max) under heat stress conditions.…”

“…Notably, previous studies have also highlighted the positive effects of BR and ethylene on AsA-GSH levels, as well as their involvement in enhancing stress tolerance (Mazorra et al, 2014;Kaya et al, 2020;Fatma et al, 2021). Wang et al (2022) also found that BR had a significant regulatory effect on the antioxidant system in soybeans under heat stress. Previous studies showed that BR could upregulate the expression of genes encoding antioxidant enzymes, such as Cu/Zn-SOD, CAT1, cAPX and GR1, in tomato and cucumber seedlings (Xia et al, 2009;Zhou et al, 2014)., This transcriptional regulation suggests that BR plays a crucial role in enhancing antioxidant capacity.…”

The Role of Heat Acclimation in Thermotolerance of Chickpea Cultivars: Changes in Photochemical and Biochemical Responses

“…Heat stress leads to lipid peroxidation of cell membranes and membrane injury in numerous plants [ 5 , 19 , 22 , 53 ]. The heat stress treatments led to a marked increase in RLR and MDA results of the cultivars, but this increase remained lower increase due to heat acclimation.…”

“…However, the increase in H 2 O 2 levels was lower in acclimated cultivars than in non-acclimated cultivars. Although H 2 O 2 is a stimulant to increase antioxidant capacity under stress conditions, its presence in cellular components above a threshold level is an indicator of oxidative stress [ 19 ]. Plants have antioxidant defense mechanisms to prevent excessive ROS production and improve tolerance to oxidative stress.…”

“…Subsequently, the presence of excessive amounts of ROS leads to oxidative stress and oxidative stress damages all cellular structures, especially membranes [ 9 ]. To alleviate the ROS-induced oxidative injury, plants generate antioxidant defense systems (enzymatic and non-enzymatic) to scavenge the overproduced ROS [ 19 ]. The enzymatic antioxidant defense system includes several antioxidant enzymes: superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), catalase, etc.…”