Genotype-dependent effect of exogenous 24-epibrassinolide on chromium-induced changes in ultrastructure and physicochemical traits in tobacco seedlings

Greenhouse hydroponic experiments were carried out using three different heavy metal accumulation tobacco genotypes to evaluate how different genotypes responded to chromium (Cr) toxicity in the presence of 24-epibrassinolide (EBR; a biologically active brassinosteroid). The results showed that Cr stress caused a marked reduction in plant biomass, chlorophyll content, chlorophyll fluorescence, and photosynthesis parameters but induced malondialdehyde accumulation and ultrastructure damage, with 2010-38 (L) less affected. Foliar application of 24-epibrassinolide (0.1 μM) on Cr-stressed plants greatly alleviated Cr-induced inhibition of growth and photosynthesis, oxidative stress and ultrastructure damage, decreased Cr accumulation in different parts of leaves and roots, with the exception of the upper and lower of leaves of genotype L, and maintained ion homeostasis. Regarding genotypes, L was more tolerant than M and H, as it absorbed less Cr and also performed better in all of the studied parameters. These findings suggest a potential role for 24-epibrassinolide in Cr stress alleviation and the utilization of elite genetic resources in future breeding programs to develop low Cr accumulation genotypes. These results advocate a positive role for 24-epibrassinolide in reducing pollutant residues from health point of view.