Activation of the cell cycle in tomato (Lycopersicon esculentum Mill.) seeds during osmoconditioning as related to temperature and oxygen

Abstract

Using flow cytometric analyses of the nuclear DNA content, we studied the effects of various conditions of osmopriming on the activation of the cell cycle in embryo root tips of tomato (Lycopersicon esculentum 'Elko') seeds. In dry untreated seeds, 90.7% of the nuclei revealed 2C signals. Priming of seeds in polyethylene glycol-8000 (PEG) improved the germination rate of seeds transferred onto water at 15 °C. This was associated with an increase in 4C signals when priming was carried out at -1.0 and - 1.5 MPa. Priming at -2.0 MPa enhanced subsequent germination but had no effect on DNA replication. For temperatures during priming up to 25 °C, a positive linear correlation existed between the efficiency of the treatment, evaluated by the reciprocal of time to obtain 50% germination at 15 °C, and the frequency of 4C nuclei or the 4C/2C values. Such a correlation did not exist when priming was performed at higher temperatures. At least. 5% oxygen in the atmosphere was required during priming for the induction of DNA replication and for the enhancement of subsequent germination. In the presence of 5 x 10-4 M and 10-3 M NaN3 during priming, most of the cells were maintained with 2C DNA levels and the treatment had no stimulatory effect on germination. The results show a positive linear relationship between the frequency of 4C DNA nuclei or the 4C/2C ratio and the improving effect of priming. However, in suboptimal conditions of priming (-2.0 MPa or temperatures higher than 25 °C), the improvement of seed germination was not associated with the onset of DNA replication.