Physiological performance of brassinolide-conditioned green soybean seeds

Factors associated to biotic and abiotic stresses, such as high temperatures and prolonged droughts, can induce premature plant maturation and, thus, lead to the formation of green seeds. This is major issue for the soybean (Glycine max (L.) Merrill) production chain, due to low physiological seed quality. Although seed conditioning can improve seed germination and vigor, little is known on the use of the brassinolide (BL) phytohormone during this process in green soybean seeds. This study, therefore, aimed to elucidate BL conditioning effects on green soybean seeds. A BL stock solution was prepared and cultivar AS 3680 IPRO seeds were conditioned at 0.0, 0.2, 0.4, 0.6 and 0.8 μM BL concentrations followed by drying until reaching original water contents. Seed conditioning effects were investigated by assessing germination and accelerated aging test results, seedling shoot, and root lengths, electrical conductivity, germination speed index and dry seedling mass. Gas exchanges and chlorophyll a fluorescence parameters were determined in seedlings 15 days after sowing. Seed germination and vigor were superior when conditioned with 0.6 and 0.8 μM BL. Photosynthetic rates, effective quantum yields of PSII photochemical energy conversion and electron transport rates were improved in seeds treated with 0.4, 0.6 and 0.8 μM BL. Brassinolide-conditioned seeds exhibited histochemical reserve tissue differences and greater lipid and protein accumulation compared to the control group. These findings demonstrate that green soybean seed BL treatment can increase the quality and subsequent physiological development in soybean seedlings.