MATURATION AND GERMINATION OF SOMATIC EMBRYOS AS AFFECTED BY SUCROSE AND PLANT-GROWTH REGULATORS IN SOYBEANS GLYCINE-GRACILIS SKVORTZ AND GLYCINE-MAX (L) MERR

The effects of sucrose on maturation and of plant growth regulators on germination of soybean somatic embryos were investigated for the purpose of developing an efficient culture method for plant recovery. Somatic embryos produced on medium with a low sucrose concentration (5 g l-1), less than 1 mm in length, 0.6 mg in fresh weight, and green in color, were grown for 2 weeks on MS medium containing 5 g l-1 or 30 g l-1 sucrose and then for another 5 weeks on MS medium containing 5 - 90 g l-1 sucrose. The highest increase in fresh weight of somatic embryos was obtained in the treatment of transferring from 30 g l-1 sucrose (2 weeks) to 60 g l-1 (5 weeks). With the increase in fresh weight, the somatic embryos gradually changed color from green to yellow, and finally to white, when they stopped growth. Soybean seed storage proteins (beta--conglycinin and glycinin) were accumulated in somatic embryos under tissue specific and stage specific control analogous to that in zygotic embryos. Exogenous gibberellic acid was effective in promoting precocious germination of premature soybean somatic embryos, but was not necessary for the germination of mature somatic embryos. The efficiency of somatic embryo germination was as high as 77% from semi-wild soybean and 60-64% from cultivated soybeans, showing that the plant regeneration system developed in this study was efficient and practical.