PLOIDY VARIATION OF PRONAMIDE-TREATED MAIZE CALLI DURING LONG-TERM CULTURE

Anther-derived calli of com were treated with 10 muM pronamide for 2, 3 and 4 days. The ploidy level of the calli was then evaluated using f low cytometry, at different times after the treatment. Untreated haplo id calli did not change in ploidy level for 97 days but by 466 days, t here were up to 50% diploid or higher ploidy cells thus showing that s pontaneous doubling may occur during com calli subculture with this ge notype. Pronamide treatment did increase the percentage of diploid and tetraploid cells and by 466 days, all of the lines showed an addition al change toward higher ploidy levels. This change may be due to spont aneous chromosome doubling or to differential cell cycle times of cell s with different ploidy levels. The ploidy level of plants regenerated from the cultures was determined by counting the guard cell chloropla st numbers and the correlation with the ploidy level of the cultures w as r2=0.84. These studies show that pronamide treatments can increase haploid maize callus chromosome numbers and that spontaneous chromosom e doubling can occur with time in maize callus.