Variation of DNA content in Asian rice

Abstract

We examined the variation of DNA content in Asian rice; wild species, Oryza perennis, cultivated species, O. sativa, and the wild-cultivated intermediate Jeypore strains. DNA contents were estimated Feulgen microspectro-photometrically and chemically. In addition, nuclear volume was recorded which was known to correlate positively with DNA content. There existed strong correlations between the estimates obtained by the above three methods, showing a reliability of the present measurements.
In each species, considerably wide variation of DNA content was detected which was not due to random error of the measurements. Though variations among strains overlapped between O. perennis, Jeypore strains and O. sativa, they showed an evolutionary tendency. Oryza perennis strains generally had the higher DNA contents than O. sativa strains and the intermediate Jeypore strains had the intermediate values. Therefore, we consider that DNA content of Asian rice has decreased during evolution (domestication). In Asian rice, reduction of DNA content is parallel to the reduction of the globular period of embryo which means the decrease of developmental instability. The reductional nature of DNA content during evolution is also observed in the process of speciation of other species and as well in the evolution of monocotyledons at the order level. This suggests that many evolutionary changes in plants, if not all, are connected with the decrease of DNA content.