Effects of Epibrassinolide on Sugar Transport and Allocation to the Epicotyl in Cucumber Seedlings

Abstract

Epibrassinolide (EBR, 24-epibrassinolide), one of the brassinosteroids (BRs), promotes elongation and sugar accumulation in the epicotyl of cucumber (Cucumis sativus L.) seedlings. In the seedlings with the primary leaf removed, such effects of EBR were not observed. On the other hand, in the seedlings with cotyledons removed, EBR promoted epicotyl elongation as in intact seedlings, and also promoted sugar accumulation in the epicotyl although the promotion was weaker than in intact seedlings. To examine the sugar transport to the epicotyl from the primary leaf, cotyledon, and hypocotyl, we applied [¹⁴C]-labeled sucrose to each organ, and examined the distribution of radioactivity 18 hr later. Allocation to the epicotyl of [¹⁴C]-sucrose applied to the primary leaf was enhanced by EBR, but that of [¹⁴C]-sucrose applied to the cotyledon or hypocotyl was not. This suggests that EBR specifically promotes the transport of sugar from the primary leaf to the epicotyl, and enhances sugar accumulation in the epicotyl.

Key words:

• Brassinosteroids
• Cucumber
• Distribution of [¹⁴C]-labeled sucrose
• Epibrassinolide
• Sugar transport