Amounts of Nuclear DNA and Internal Morphology of Gibberellin- and Abscisic Acid-deficient Tomato (Lycopersicon esculentumMill.) Seeds During Maturation, Imbibition and Germination

Abstract

Using X-ray photography and flow cytometry, the internal morphology and DNA replication activity of wild type (wt), GA- (gib-1) and ABA-deficient (sitw) tomato (Lycopersicon esculentumMill. cv. Moneymaker) mutant seeds were studied. During seed formation, from 30 to 45 d after pollination (DAP) the endosperm becomes solid and the seed starts to gain desiccation tolerance. At this time significant changes occur in the amounts of DNA in radicle tip cells. At 30 DAP, radicle tip cells of the three genotypes manifest about 60% of 2C, 30% of 4C and 10% of 8C amounts of DNA. Upon maturation (45 DAP onwards), most cells in the seeds of the three genotypes arrest in the G1phase of the cell-cycle with 2C amounts of DNA. However, a relatively high proportion of cells with 4C amounts of DNA was detected in the radicle tip cells ofsitwcompared with wild type andgib-1. At the well-matured stage (60 DAP), there were about 2% of seeds with free space in wild type andgib-1, and about 13% insitw. At the over-matured stage (75 DAP), even more seeds with free space were found insitw, whereas no increase in the proportion of the seeds with free space was detected in the other two genotypes. In −1.0 MPa PEG-6000 with or without 10 μMGA4+7, no germination occurred in well-matured wild type andgib-1seeds, whether or not they were dried after harvest. However,sitwseeds were able to germinate both in over-mature fruit and in −1.0 MPa PEG-6000. Priming of dried seeds in −1.0 MPa PEG induced a large amount of free space in almost all seeds of the three genotypes, and nuclear DNA synthesis in the radicle tip cells of wild type andsitwseeds. However, PEG priming of fresh (non-dried) seeds had no effect on the amount of free space and 2C/4C DNA ratios in wild type orgib-1seeds, but did induce free space in about 20–25% ofsitwseeds and provoked 4C signals insitwseeds. Removal of the endosperm and testa opposite the radicle tip of seeds resulted in root protrusion, the induction of free space and an increase of 4C DNA signals in the three genotypes. It is concluded that ABA is crucial for the efficient arrest of tomato embryo radicle tip cells in G1phase upon maturation, whereas GAs play an important role in re-initiating 4C DNA levels upon germination.