The effects of sucrose and methylglyoxal bis-(guanylhydrazone) (MGBG) on grape (Vitis vinifera L. cv. Thompson Seedless) somatic embryogenesis was examined by subculturing somatic embryos and embryogenic cells monthly to embryo maintenance medium (MMS) containing 60, 90, 120, 150, or 180 g/l sucrose; or 0, 0.1, 1, or 10 mM MGBG for three months. The growth and development of grape embryogenic cultures was inhibited by incubating them on MMS with 150 or 180 g/l sucrose compared to 60, 90, or 120 g/l. Culture dry weight was significantly greater for embryogenic cells grown on MMS with 90 or 120 g/l sucrose compared with those reared on standard MMS (60 g/l sucrose), indicating that embryogenic cells grew better on MMS with 90 or 120 g/l sucrose and were less hydrated. The number of cotyledonary-stage somatic embryos that resembled zygotic embryos was improved 10.8- to 21.3-fold by incubating grape embryogenic cells on MMS with 90 or 120 g/l sucrose, respectively. Germination-and plant development of grape somatic embryos was improved following incubation on MMS with 150 g/l sucrose before transfer to germination medium with benzyladenine. However, fewer embryos were produced on this medium compared to all other sucrose levels, suggesting that maintaining embryogenic cultures on MMS with 120 g/l sucrose followed by one transfer onto MMS with 150 g/l sucrose may improve embryo development and plant regeneration. MGBG at 1 to 10 mh I inhibited the growth and development of grape embryogenic cultures. Exposure of embryogenic cells to 10 mM MGBG inhibited their growth and development through the course of the experiment and caused their death by the third month of culture. In contrast, a 3-month exposure was required to inhibit embryo growth in the presence of 1 mM MGBG. Addition of MGBG to MMS did not improve embryo quality or plant development
