COMPARISON OF STARCH, ADP-GLUCOSE PYROPHOSPHORYLASE AND STARCH SYNTHASE LEVELS IN NONEMBRYOGENIC CELLS AND DEVELOPING EMBRYOS IN HEVEA-BRASILIENSIS

Sucrose, glucose, fructose and starch levels, and ADP-glucose pyrophos phorylase (EC 2.7.7.27) and starch synthase (EC 2.4.1.21) activities w ere studied in an embryogenic strain of Hevea brasiliensis during the periods of multiplication of proembryogenic clusters and development o f somatic embryos. For comparison, a non-embryogenic strain was also i nvestigated. The development of somatic embryos was studied on a mediu m containing polyethylene glycol and abscisic acid and a medium devoid of both. First, a correlation between ADP-glucose pyrophosphorylase a ctivity and starch accumulation was shown during the multiplication pe riod of proembryogenic clusters. Second, starch accumulation in somati c embryos was observed at the end of the developmental period on the m edium containing polyethylene glycol and abscisic acid but not on the medium devoid of these substances. In non-embryogenic cells, starch le vels were similar whatever the culture conditions. However, this diffe rence in starch content was not reflected in the starch biosynthetic c apacity inferred from the ADP-glucose pyrophosphorylase and starch syn thase activities, which were similar in the two culture conditions and in somatic embryos and non-embryogenic cells. Also, somatic embryos w ere more numerous, especially at the torpedo stage, on the medium cont aining polyethylene glycol and abscisic acid than on the medium devoid of these substances.