Mitotic cycles in Triticum species

Abstract

The duration of the mitotic cycle at 20°C was estimated in meristems of roots averaging 12 mm long in six species of the Triticinae. They include two diploids, Aegilops squarrosa and Triticum monococcum; two tetraploids, Triticum dicoccoides and Triticum timopheevi and two hexaploids, Triticum aestivum and Triticum spelta. The average duration of the cycle increased in the order 2x (11 to 12 hours) to 4x (15–16 hours) to 6x (19–20 hours). In relation to nuclear DNA amount the duration of the cycle increased by c. 0·31 hours per picogram. This rate of increase corresponds closely with that established for diploid monocotyledons by Evans et al. (1972). The mean duration of mitotic cycles also corresponds closely with that for diploid monocotyledons with the same DNA amount. The increase in the duration of the mitotic cycle with increasing DNA is accounted for by increase in all the component phases i.e. in Division, G1, S and G2. There is some indication of a disproportionately long G2 and a shorter G1 in the wild, uncultivated species viz. Ae. squarrosa and the two tetraploids. With few exceptions it appears that the duration of the mitotic cycle, as in the six species investigated here, is closely dependent upon and constrained by the nuclear DNA quantity per se.