Physiological effects of lepidimoic acid (a stimulatory allelochemical) on cucumber cotyledons

A novel disaccharide lepidimoic acid was isolated from the mucilage of Arabidopsis (Arabidopsis thaliana L.) germinating seeds and was found to be a stimulatory allelochemical. Its effect was investigated on the detached cucumber (Cucumis sativus L.) cotyledons at transcription level of a gene encoding glutamyltRNA reductase 1 (HEMA1), which is a key enzyme in chlorophyll biosynthesis. Under light conditions, the level of transcription of HEMA1 increased with treatment of lepidimoic acid and cytokinin in a dose-dependent manner. In contrast, no significant increase occurred in dark conditions. These results are consistent with the hypothesis that lepidimoic acid might generate its promoting activity through a signaling pathway similar to cytokinin in chlorophyll biosynthesis. Besides in light, lepidimoic acid promoted the adventitious root emergence from the cutting end of cotyledons. We conclude that lepidimoic acid may exhibit multiple physiological effects in plants, interacting with phytohormones such as cytokinin and auxin.