Foliar-applied 24-epibrassinolide systemically triggers tolerance to magnesium stress in soybean plants: plausible responses focused on root and leaf structures

Abstract

ABSTRACT The adverse effects caused by inadequate magnesium (Mg) supplies (deficiency or toxicity) cause disorders in root and leaf structures, compromising the uptake and transport of nutrients and gas exchange. However, 24-epibrassinolide (EBR) is a biodegradable and ecologically viable steroid that exhibits benefits on cell division and vascular differentiation. This study aimed to evaluate whether exogenous EBR application can attenuate the deleterious effects linked to inadequate Mg supplies on the anatomical structures of roots and leaves in soybean plants. The experiment followed a completely randomized factorial design with two concentrations of 24-Epibrassinolide (0 and 100 nM EBR, described as - EBR and + EBR, respectively) and three Mg supplies (0.0225, 2.25 and 225 mM Mg, described as low, control and high supplies of Mg). In general, low and high Mg supplies promoted negative changes in the anatomical variables evaluated. In root tissue, pretreatment with 100 nM EBR stimulated the root structures, confirming the systemic action of EBR and benefits related to the differentiation of these structures. Treatment with low Mg + EBR promoted increases in epidermis thickness from the abaxial leaf side (ETAb) and spongy parenchyma thickness (SPT) in 20% and 13%, respectively. High Mg and EBR were increased in ETAb (31%) and SPT (15%) compared with equal treatment without steroids, improving protection and CO2 fixation. Our results indicate that the foliar application of EBR mitigated the deleterious effects linked to inadequate Mg supply in the anatomical structures of the root and leaf, confirming the systemic action of this steroid.