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

Using flow cytometric analyses of the nuclear DNA content, we studied the e ffects of various conditions of osmopriming on the activation of the cell c ycle 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 s eeds transferred onto water at 15 degrees C. This was associated with an in crease in 4C signals when priming was carried out at -1.0 and -1.5 MPa. Pri ming at -2.0 MPa enhanced subsequent germination but had no effect on DNA r eplication. For temperatures during priming up to 25 degrees C, a positive linear correlation existed between the efficiency of the treatment, evaluat ed by the reciprocal of time to obtain 50% germination at 15 degrees 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% oxyge n in the atmosphere was required during priming for the induction of DNA re plication and for the enhancement of subsequent germination. In the presenc e 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 o n 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 p riming. However, in suboptimal conditions of priming (-2.0 MPa or temperatu res higher than 25 degrees C), the improvement of seed germination was not associated with the onset of DNA replication. (C) 1999 Annals of Botany Com pany.