Cell cycle duration in the root meristem of Sonoran Desert Cactaceae as estimated by cell-flow and rate-of-cell-production methods

Slow rates of cactus growth in the Sonoran Desert and high productivity of some Cactaceae under cultivation suggest that relatively low growth rates are not the consequence of a long cell division cycle but of short optimal periods for growth and adverse environmental factors. To verify this hypothesis, the duration of the cell division cycle (T) in the root apical meristem of seedlings of three sympatric species from the Sonoran Desert [Ferocactus peninsulae (F. A. C. Weber) Britton B Rose 'Townsendianus' (Britton & Rose) N. P. Taylor, stat, nov., Stenocereus gummosus (Engelm.) Gibson & Horak and Pachycereus pringlei (S. Watson) Britton & Rose] was estimated with the rate-of-cell-production (RCP) and the cell-flow (colchicine) methods. Both methods were applied during the steady-state growth phase, which was relatively short in the first two species because of the determinate pattern of root growth. The RCP method permitted estimation of T in each root individually. Durations of the cell division cycle were inversely proportional to the rate of root growth (r(2) ranged from 0.42 to 0.88, P < 0.05). T, determined by the cell-flow method, ranged from 14.4 to 19.3 h in these species and was within the same range as T determined by the RCP method. The average T determined by the RCP method was 67 to 75% of that determined by the cell-flow method. Results obtained with both methods are compared and analysed. The proposed hypothesis appears to be correct, indicating that these species can be more productive under cultivation than in the wild due to the relatively short duration of the cell division cycle. Adaptive features of these findings are also considered. (C) 1998 Annals of Botany Company.