FLOW CYTOMETRIC DETERMINATION OF NUCLEAR REPLICATION STAGES IN TOMATO SEEDS DURING PRIMING AND GERMINATION

Flow cytometric determination of DNA levels in embryos of fully matured dry tomato (Lycopersicon esculenium) seeds revealed large amounts of 2C DNA signals, indicating that most cells had arrested in the cell cycle at the presynthetic G1 phase of nuclear division. After imbibition in water, an augmentation of the 4C signal in the embryonic root tip region was found. This increase could be ascribed to cells entering the synthetic phase of nuclear division leading towards the doubling of chromosomal material. In the root tip cells, 4C:2C ratios increased I d after imbibition in water though radicle emergence started 2 d later. Apparently, DNA synthesis preceded germination. Only a small increase in the number of cells with 4C DNA levels was found in the rest of the embryonic tissues. In whole dry seeds, DNA histograms revealed both a 2C signal and a considerable 6C peak, the latter originating from the endoreduplicated endosperm.A priming period of 14 d in PEG-6000 considerably enhanced the rate and uniformity of germination. In the ungerminated seeds, the 4C DNA signal of root tip cells started to increase after 3 d incubation in PEG. The ratio of 4C:2C steadily increased during the 14 d priming period, though did not reach the level obtained after hydration in water. Upon priming, the 4C:2C ratio was constant after redrying the seeds towards the original moisture content, indicating that the chromosomal material in the root cells had stably ceased cell cycle activity at the G2 phase. The present results indicate that the beneficial effects of priming on seedling performance are associated with the action of replicative DNA synthetic processes prior to germination. © 1992 Annals of Botany Company.