Developmental profile of intracellular compatments during Allium cepa root cell germination

The efflux kinetics of ⁸⁶Rb from 24 hr preloaded Allium cepacv. Evergreen Long White Bunching root tip cells through thefirst 120 hr of germination have been documented. Estimatesof the percent of isotope, the calculated amount present andthe halftime of efflux of the three root cell compartments presentwere made. Of the total isotope present the % in the vacuoledecreased from maxima of 64% to 40% with germination time, whilethe % of the isotope in the cytoplasm remained uniform near39%. The free space increased maximally throughout germinationto 20% by 120 hr. Rb content, based on specific activity calculations,of the slowest, intermediate and fastest compartments was seento rise from low levels at 52 hr germination toward maximalvalues by 96 hr. Speculation as to when a germinating root becomesfunctionally mature was attempted by comparing the times ofonset of major macromolecule synthesis (DNA, RNA, protein) tothat of maximal Rb content. Stable mitotic and DNA syntheticindices occurred at the 10 mm (72 hr) stage with the initiationof major macromolecules syntheses occurring prior to 2 mm (40hr). ⁸⁶Rb efflux data suggests that the compartments do notcontain maximal amounts until the 22 mm (96 hr) stage. (Received December 26, 1978; )