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Abstract. The role of cis-abscisic acid (ABA) and gibberellins (GAs) in the induction of cell-cycle activities has been studied during imbibition and subsequent germination of tomato seeds. Using flow cytometry, nuclear replication activity was investigated in embryo root tips isolated from seeds of the ABA-deficient mutant sit w, the GA-deficient mutant gib-1, and the wild-type (MM) tomato (Lycopersicon esculentum Mill. cv. Moneymaker) upon imbibition in water, 10 gM GA4+7, 5 gM ABA or 5 gM ABA+ 10 gM GA4+ 7. The nuclei of fully matured dry MM, sit W and gib-1 seeds predominantly showed 2C DNA signals, indicating that the celt-cycle activity of most root-tip cells had been arrested at the G~ phase of nuclear division. However, ABA-deficient sit w seeds contained a significantly higher amount of G z cells (4C DNA) compared with the other genotypes, suggesting that, during maturation, cell-cycle activity in sit" seeds is less efficiently arrested in G1. Upon imbibition in water, an induction of the 4C signal, indicating nuclear replication, was observed in the root tip cells of both MM and sit w embroys. The augmentation in the 4C signal occurred before visible germination. Gib-1 seeds did not show cell-cycle activity and did not germinate in water.Upon imbibition in GA4+7, both cell-cycle activity and subsequent germination were enhanced in MM and sit w seeds, and were induced in gib-1. In ABA, the germination of MM and sit w seeds was inhibited while nuclear replication of these seeds was not affected. It is concluded that GA influences germination by acting upon processes that precede celt-cycle activation, while ABA affects growth by acting upon processes that follow cell-cycle activation.

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1994). The effects of priming on nuclear replication activity and germination of pepper ( Capsicum annuum) and tomato ( Lycopersicon esculentum) seeds. AbstractUsing flow cytometry, we determined relative DNA amounts expressed as C-values, of large numbers of nuclei isolated from embryo root tips in three seed lots of pepper (Capsicum annuum) and tomato (Lycopersicon esculentum) The nuclei in embryos of fully matured dry pepper and tomato seeds predominantly revealed 2C signals, which indicates that the cells of maturing seeds have arrested at G, phase of the cell cycle Priming of pepper and tomato seeds in -1 1 , -1 3 or -1 5 M P a polyethylene glycol (PEG) for 14 days reduced the mean time to germination. In all seed lots an induction of 4C signals was found after priming, indicating that during priming the cells of the embryonic root tip had replicated their DNA and arrested at the G 2 phase of the cell cycle For both tomato and pepper, the frequency of 4C signals was highest at the lowest PEG concentration (osmotic potential of -1 . 1 MPa). A significant inverse correlation was found between the frequency of root tip cells expressing 4C DNA signals and the mean time to germination for each individual pepper and tomato seed lot However, the effect of a specific osmotic treatment differed between seed lots of the same cultivar, with regard to both the decrease in the mean time to germination and to the percentage of 4C cells, suggesting specific differences among seed lots in the response to priming The present results indicate that flow cytometry can be used to follow the progress in nuclear replication activities during priming. The advancement in DNA synthesis can thus be used to measure the efficiency of a priming treatment with regard to enhancement of seed lot germination rate ""Correspondence