METABOLISM OF RESERVE PRODUCTS DURING DEVELOPMENT OF SOMATIC EMBRYOS AND GERMINATION OF ZYGOTIC EMBRYOS IN GRAPEVINE

Accumulation and utilization of triacylglycerols and starch were studi ed during the development of Vitis vinifera 'Grenache noir' somatic em bryos and during germination of their zygotic counterparts. Somatic em bryos accumulate storage compounds normally and, at the torpedo stage, both types of embryos (somatic and zygotic) were very rich in lipid b odies and very poor in starch. Following the torpedo stage, germinatio n and conversion into plantlets of zygotic embryos was accompanied by a transient starch and triacylglycerol accumulation in the cotyledon f ollowed by hydrolysis and utilization of these same reserves. By contr ast, in somatic embryos an important accumulation of starch and lipids was observed following the torpedo stage but these storage compounds were not used. This inability was partially due to the absence of isoc itrate lyase activity necessary to the glyoxylate cycle. The abnormal and teratological development of grapevine somatic embryos is discusse d and this behaviour is compared with the precocious germination obser ved in in vitro cultured immature zygotic embryos.