Réactivation du bourgeon cotylédonnaire du Pois en réponse à la kinétine

Abstract

For three components (apical meristem, subapical internodes, and foliar apparatus) of Pisum sativum (cv. nain hâtif d'Annonay) cotyledonary buds, DNA microdensitometry, mitotic indices, and release of growth have been used to detect changes produced by kinetin applications (50 μg/mL). One kinetin treatment is sufficient to release the cell cycle, but continuous kinetin supply is necessary to maintain bud elongation. At the apical, subapical, and foliar levels, inhibited cotyledonary buds contain a majority of nuclei with 2C DNA content, in the G1 phase of the cell cycle. Following hormonal treatment, the prereplicative phase of the noncycling cells is at least 6 h in the whole bud. The lag period for the release of bud growth is between 15 and 23 h in subapical regions (first and second internodes) and between 23 and 38 h at the foliar level. At subapical and foliar levels, a few mitoses precede and then follow the elongation process. The first mitoses are from G2 nuclei of the inhibited bud. The following ones, more numerous, are from noncycling cells of inhibited buds, which have entered the S phase in response to kinetin application. The degree of inhibition of an axillary bud, estimated by the distribution of the DNA content in its three components, conditions the events induced by hormonal treatment or decapitation. The discussion shows how the knowledge of the original nuclear states of inhibited buds is necessary to understand axillary bud reactivation.