Reduction in amounts of mitochondrial DNA in the sperm cells as a mechanism for maternal inheritance in Hordeum vulgare.

It is known that extranuclear organelle DNA is inherited maternally in the majority of angiosperms. The mechanisms for maternal inheritance have been well studied in plastids but not in mitochondria. In the present study we examined the mitochondrial DNA in the male reproductive cells of Hordeum vulgare L. by immunoelectron microscopy. Our results show that the number of anti-DNA gold particles on sections of sperm cell mitochondria decreased by 97% during pollen development. The reduction occurred rapidly in the generative cells and subsequently in the sperm cells, concomitant with a remarkable reduction in mitochondrial volume. It seems that the copy numbers of mitochondrial DNA were reduced in the male reproductive cells, which may be a possible mechanism by which paternal transmission is inhibited. Unlike mitochondria, plastids are excluded from the generative cells during the first pollen mitosis. These data suggest a mechanism for maternal inheritance of mitochondria in angiosperms and for independent control of inheritance of mitochondria and plastids in H. vulgare.