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.

Identification of coiled body-like structures in meristematic cells of Pisum sativum cotyledonary buds

“…This system is particularly interesting because on the 12th day of germination the majority of nuclei are naturally blocked, by apical dominance, in the prolonged G1 state (G0±1) of the cell cycle. At this stage, the mitotic index of the whole cotyledonary bud is zero (Toupiol 1976;Nougarde et al 1981). Histological changes have been detected in cotyledonary bud nucleoli following decapitation of the main stem (Jennane et al 1987a;Nougarde et al 1990;Mineur et al 1999).…”

“…Release from apical dominance also results in starch accumulation within the bud (Nougarde and Rondet 1975), in enhancement of K + -and Mg 2+ -ATPase activity in the plasmalemma within 30 min (Nougarde et al 1983), and in a prompt increase in water content (Jennane et al 1987b;Cottignies and Jennane 1988). Decapitation further triggers DNA synthesis within 6 h, entry into G2 within 12 h, and mitoses after 24 h (Nougarde et al 1981(Nougarde et al , 1987). In the study described here we measured the abundance of nuclear bodies during the cell cycle and analysed their composition by cytochemistry and immunocytology, using several markers of animal CBs.…”

Activation of replicon origins as a possible target for cytokinins in shoot meristems of Sinapis

“…Cytokinins are natural plant growth regulators which are implicated in the control of cell division in cultured cells (Skoog et al 1965;P6aud-Lenoal 1977) as well as in meristems of intact plants (Usciati et al 1972;Bernier et al 1977;Nougar6de et al 1981). Their promotive effect on cell division in vitro has been instrumental in large-scale commercial micropropagation of desirable genotypes of agricultural and horticultural crops (Krikorian et al 1987).…”

Activités ATPasiques du nœud cotylédonaire et du bourgeon cotylédonaire du pois inhibé, réactivé ou soumis à la fusicoccine

“…Aprks ablation de l'axe principal (47,49), les CvCnements majeurs sont la reprise du cycle par passage de GI en S et 1'Clongation simultante des deux premiers entre-nceuds du bourgeon; aprks traitement par la fusicoccine (FC), toxine du Fusicoccum amygdali, les entre-nceuds subapicaux subissent jusqu'i la 15e h une forte Clongation, mais le cycle n'est pas relanct.…”

“…Lors de la levCe de dominance par dkcapitation (47,48,49), leur r6le peut Ctre capital dans la translocation a courte distance et dans le prCEvement et la distribution (26,27,28,50,51), au profit des bourgeons axillaires (39), de solutCs ou de substances nutritives qui peuvent provenir des parties basses du plant, des cotyledons ou des feuilles prksentes avant la decapitation.…”