Nuclear DNA content of somatic and zygotic embryos ofVitis vinifera cv. Grenache noir at the torpedo stage

Abstract

A flow cytometric analysis and an in situ DNA microspectrophotometric study were made concomitantly to establish why somatic grapevine (Vitis viniferacv. Grenache noir) embryos showed a low level of conversion into plantlets. In somatic embryos at the torpedo stage and in zygotic embryos at the same stage of development, ploidy level, DNA content per 2 C nucleus, and the cell-cycle state of the shoot apical meristem were examined. The frequency distribution histograms of nuclear DNA values were similar in the two types of embryos. At the torpedo stage both types of embryos had a majority of nuclei with 2 C DNA content equal to 1.6pg. In the shoot apices of somatic and zygotic embryos, DNA microspectrophotometry showed preferential blockage of the cell cycle at the G0–1 stage; however, 20% of somatic embryo shoot apices were blocked at the G0–2 stage. Analogies between somatic embryos and their zygotic homologues were shown. The genetical and environmental causes of the low level of conversion of grapevine somatic embryos into plantlets are discussed. Our work suggests that the in vitro culture conditions which were used could be incompatible with normal morphogenesis from the torpedo stage.