ROLE OF HIGH SUGAR CONCENTRATIONS IN INDUCING SOMATIC EMBRYOGENESIS FROM CUCUMBER COTYLEDONS

We examined the effects of sucrose concentrations in initiation media with a constant carbohydrate molarity, and of osmotic potential provided by glucose or mannitol, on somatic embryogenesis from cotyledon explants of Cucumis sativus L. cv. 'Shimoshirazu'. In constant carbohydrate molarity (0.25 M), the percentage embryo formation and the yield of embryos were enhanced by increasing sucrose concentrations. Sucrose (0.25 or 0.50 M) and glucose (0.50 M) both gave high frequencies of somatic embryogenesis; no embryos were formed when mannitol was the sole carbon source. When initiation media contained 0.25 M sucrose, raising the osmotic potential with either mannitol or glucose increased embryo yield and significantly promoted direct embryo formation. The percentage of bipolar embryos was also enhanced by increasing the molarity of carbohydrates in the initiation medium by the addition of glucose or mannitol. Glucose was a more effective sugar supplement than mannitol in inducing somatic embryos. Addition of 0.15 M glucose to the initiation medium containing 0.25 M sucrose resulted in the highest number of somatic embryos. Glucose had a specific carbon effect as well as an osmotic role. The specific carbon effect plays a major role and osmotic potential a minor and supplementary role in cucumber embryogenesis.