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

Accumulation and utilization of triacylglycerols and starch were studied during the development of Vitis vinifera 'Grenache noir' somatic embryos and during germination of their zygotic counterparts. Somatic embryos accumulate storage compounds normally and, at the torpedo stage, both types of embryos (somatic and zygotic) were very rich in lipid bodies and very poor in starch. Following the torpedo stage, germination and conversion into plantlets of zygotic embryos was accompanied by a transient starch and triacylglycerol accumulation in the cotyledon followed by hydrolysis and utilization of these same reserves. By contrast, 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 isocitrate lyase activity necessary to the glyoxylate cycle. The abnormal and teratological development of grapevine somatic embryos is discussed and this behaviour is compared with the precocious germination observed in in vitro cultured immature zygotic embryos.