Mise en évidence d'une corrélation entre la fréquence de variations somatiques sur feuilles et l'état physiologique d'un mutant chlorophyllien monogénique chez Nicotina tabacum var. samsun

After treatment with ethyl methanesulphonate (EMS), a chlorophyll mutant of Nicotiana tabacum var. Samsun has been obtained in M₁. Spontaneous somatic variations are observed as isolated areas in the pallisade cells, both on heterozygous and on homozygous plants for the semi-dominant tl gene. These variations appear either as single (green or clear), or as twin (green and clear) areas. This paper reports on the distribution of green somatic variations only, on the basis of the foliar level. The observations have been carried out on a clone homozygous for the tl gene.A highly significant correlation is evidenced between the frequency of somatic variations per leaf and/or per million of cells on the one hand and the physiological stage of the plant on the other. A consistent decrease in the number of variation, after a certain foliar level, is correlated to the transition of the shoot apex from the vegetative to the flowering stage. Modifications of the intracellular conditions caused by this transition could prevent the event responsible for the occurrence of somatic variations. It is also suggested that this event can only take place at a given stage of cell differentiation.