No effect of preferential digestion of chloroplast genome of male origin on chloroplast genome of female origin in young zygotes of Chlamydomon as reinhardtii as revealed by a video-intensified microscope photon counting system.

Abstract

It has been examined using a video-intensified microscope photon counting system (VIMPCS) whether preferential digestion of chloroplast gemone of male origin in young zygotes of Chlamydomonas reinhardtii affects the chloroplast genomes of female origins in number. To distinguish between the chloroplasts of male origin and the chloroplasts of female origin in young zygotes, a cross, that is, mt+ (gametes with normal chlorophyll, 137c wild type)×mt- (gametes with diminished chlorophyll, ac29a mutant) was prepared. The timing of initiation of the digestion of the male chloroplast genome differs among zygotes but usually occurs during 50-120min. The degrees of the preferential destruction of male chloroplast genomes in young zygotes were quantitatively examined using VIMPCS after 4′-6-diamidino-2-phenyindole (DAPI) staining. The results show that each gamete (mt+, mt-) has a cu-pshaped chloroplast including 7-8 chloroplast nuclei (ct-nuclei). Each ct-nucleus (mt-, mt+) is composed of 1-43 copies of the chloroplast genome (mean number, 10 copies) and female and male chloroplasts contain about 83 and 86 copies, respectively. In most zygotes, all copies of the chloroplast genome from the male gamete are completely digested during the first 40-180min after mating, while all copies from the female gamete persit till at least 4 days later when 7ct-nuclei have fused together to form one large ct-nucleus. This suggests that the preferential digestion of the chloroplast genome of male origin does not affect the chloroplast genome of female origin in zygotes.