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EXPERIMENTAL CONTROL OF DNA SYNTHESIZING AND DIVIDING CELLS IN EXCISED ROOT TIPS OF PISUM
Author(s) -
Hof Jack Van't
Publication year - 1966
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1966.tb06860.x
Subject(s) - biology , dna synthesis , interphase , mitosis , sucrose , dna , cell division , thymidine , pisum , carbohydrate , cell cycle , biochemistry , microbiology and biotechnology , cell , botany
The number of dividing and DNA‐synthesizing cells in excised pea roots can be regulated by eliminating the carbohydrate normally supplied in the culture medium. When the excised roots were allowed to remain for 24 hr in a medium lacking carbohydrate, the number of mitotic figures and tritiated thymidine (H 3 ‐T) labeled cells was reduced almost to zero. After an additional 24 hr in the incomplete culture medium, 15% of the interphase cells were H 3 ‐T labeled, the percentage of the cells that were dividing never exceeded 1.4, and 30% of these were H 3 ‐T labeled. When the roots remained in the deficient medium for 72 hr, neither cell division nor cells synthesizing DNA were observed. Upon addition of 2% sucrose, cell division and DNA synthesis were resumed in the roots that were maintained for 24 or 72 hr without an exogenous carbohydrate supply. It has been hypothesized that some proliferative systems consist of two cellular subpopulations which selectively stop or remain in either the pre‐DNA synthetic (G 1 ) or post‐DNA synthetic (G 2 ) periods of the mitotic cycle. The addition of sucrose, H 3 ‐T, and 5‐aminouracil to the medium, after the roots had been maintained for 24 hr without a carbohydrate, indicated that most of the proliferative cells in the roots had accumulated in either G 1 , a quasi‐G 1 condition, i.e., DNA synthesis stopped sometime before completion, or G 2 periods of interphase; the majority, however, were in G 1 or quasi‐G 1 conditions. The results suggested that DNA synthesis (S period) and mitosis or the onset of these processes have the highest metabolic requirements in the mitotic cycle and that G 1 and G 2 were the most probable states for proliferative cells in a meristem with a low metabolic level.