Evolution du contenu en DNA nucléaire dans les gamétophytes mâles du Datura innoxia au cours de la période favorable à l'androgenèse

The nuclear DNA content was estimated by densitometry for six stages during the maturation of male gamétophytes of Datura innoxia Mill. Changes in nucleus size and structure (distribution of chromatin) were analysed simultaneously. The following were found. (a) After the tetrad stage, DNA synthesis preceding the first haploid mitosis took place progressively and slowly. Once this division was terminated, the pollen nuclei had the same DNA content (1C). When the period favoring embryogenesis was completed, the DNA content of the reproductive nuclei approached 2C while there was a tendency for the vegetative nuclei to undergo endomitosis. (b) A direct correlation between DNA content and size of pollen nuclei was only noted for the stages having identical nuclear structures. (c) The stage during which the pollen grain had the greatest embryological potential was a period of complete change in the DNA content (change from postsynthetic to presynthetic). (d) The fusion of the 2C reproductive nucleus with the 4C vegetative nucleus could lead to the formation, after a normal mitosis, of a 3C pollen nucleus; that would explain the formation of androgenic triploid seedlings found in Datura innoxia. [Translated by the Journal]