Chloroplast damage induced by simulated acid rain is delayed in soybean plants pretreated with 24- epibrassinolide: Evidence connected to photosynthesis and biomass

Acid rain (AR) is a major climate change-related factor that adversely affects plant metabolism and reduces crop and cereal yield. The natural, biodegradable plant growth regulator 24-epibrassinolide (EBR) has multiple effects on plant performance, including enhancing photosynthesis, antioxidant defences, and growth. In this study, we investigated whether pre-treatment with EBR can protect soybean plants exposed to simulated acid rain (SAR), with a focus on its impact on chloroplast pigments, photosynthetic apparatus, and biomass. The experiment was designed with four treatments, namely, two SAR (0 and 0.5 M H ₂ SO ₄ , designated – SAR and + SAR, respectively) and two brassinosteroid concentrations (0 and 100 nM EBR, defined as – EBR and + EBR, respectively). Five replicates for each of the four treatments were conducted, yielding 20 experimental units used in the experiment, with one plant in each. SAR adversely affected plant metabolism and growth; however, plants pretreated with EBR exhibited less damage to leaf structures and higher biomass under SAR conditions. Chloroplastic pigment degradation was delayed, and was detected as increased chlorophyll a (23%), chlorophyll b (29%), and total chlorophyll (24%) compared to plants receiving similar treatment without EBR. Regarding gas exchange, increments in net photosynthetic rate and water-use efficiency of 44% and 41%, respectively, were observed. These results can be explained by the stimulating effects of EBR pretreatment on stomatal characteristics, including stomatal density. Therefore, this study revealed that exogenous EBR application delayed SAR-induced deleterious effects in soybean plants.