RECOVERY FROM DORMANCY IN ROOTS

Abstract

S ummary Seedlings of Zea mays have been grown at 5° C to induce dormancy in their root apices. Recovery has been studied when the plants were returned to 21° C by observing the changes in cell patterns, in the labelling of nuclei with [6‐ 3 H]thymidine and in rates of mitosis measured by metaphase accumulation. Recovery involves stimulation into division of the cells of the quiescent centre and the consequent repopulation of other regions of the meristem from the quiescent centre. We suggest that the reason for this behaviour is that the quiescent centre cells are less badly injured during the cold because their nuclei, which are normally at G 1 , rest there. By contrast, in the surrounding meristem, many of the cells being at S or G 2 at the onset of cold, proceed through mitosis to the following G 1 and, in so doing, suffer chromosomal damage and impairment of reproductive potential. This view is supported by the hypersensitivity found in the cap initials, which normally have no G 1 phase. Some previous work on dormancy and on the organization of meristems is discussed in the light of this theory.