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 productivit y of some Cactaceae under cultivation suggest that relatively low grow th 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) i n the root apical meristem of seedlings of three sympatric species fro m the Sonoran Desert [Ferocactus peninsulae (F. A. C. Weber) Britton B Rose 'Townsendianus' (Britton & Rose) N. P. Taylor, stat, nov., Steno cereus 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 appli ed during the steady-state growth phase, which was relatively short in the first two species because of the determinate pattern of root grow th. 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 thes e species and was within the same range as T determined by the RCP met hod. 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 corr ect, indicating that these species can be more productive under cultiv ation than in the wild due to the relatively short duration of the cel l division cycle. Adaptive features of these findings are also conside red. (C) 1998 Annals of Botany Company.