Embryons somatiques de Vitis rupestris et embryons zygotiques de Vitis sp. : morphologie, histologie, histochimie et développement

Abstract

The problem of the development of grapevine somatic embryos into plantlets was examined through a morphological, histological, and histochemical comparison of zygotic and somatic embryos. Only 3% of somatic embryos were capable of developing into plantlets. However, 27% of these embryos had shoot and root apices showing a histological pattern similar to that observed in zygotic embryos; other embryos had root apex but no shoot apex. In comparison with zygotic embryos, somatic embryos showed the following characteristics: acquisition of giant, and often teratologic, organs, retention of a high proliferative capacity among superficial cells, starch and tannin accumulation, important suberization and slight lignification of superficial cells, differentiation of tracheids in the vascular system, and preservation of a high embryogenic potential in the absence of exogenous growth regulators. The water-saturated atmosphere to which grapevine somatic embryos were submitted during in vitro culture could be unfavourable to germination. Under these conditions, embryos built impermeable suberized superficial layers. Key words: somatic embryos, zygotic embryos, Vitis sp., histochemistry, development.