Interaction of gibberellic acid and 24-epibrassinolide in the regulation of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> seedling scotomorphogenesis

The effects of GA₃, 24-epibrassinolide (EBL), and their combination on morphogenesis of Arabidopsis thaliana (L.) Heynh seven-day-old seedlings were studied. Four plant lines were analyzed: wild type Ler and ga4-1 mutant, belonging to the Landsberg erecta ecotype and wild type Col and det2 mutant, both of the Columbia ecotype. In ga4-1 and det2, GA_4/1-and brassinosteroid-deficient mutants, the highest hypocotyl growth response to the lack of hormones was noted. The cotyledon shape and size were dependent on EBL, and the root length was both GA₃-and EBL-regulated, indicating organ specificities in the responses to these hormones. Simultaneous treatment of dark-grown plants with GA₃ and EBL exerted an additive stimulatory effect on the root growth of det2, reduced the inhibitory effect of EBL on hypocotyl elongation of ga4-1, and enhanced the effect of EBL on hypocotyl and cotyledon elongation of det2.