Abstract
In order to consider characteristic chromosomal evolution, agamatoploidy in genus Carex, nuclear DNA content of metaphase plates in root tip of 50 cytologically stable strains belonging to 26 species of Carex collected in Japan was measured Feulgen cytophotometrically. Considerably large variation was observed in six species with rather high chromosome number. There was 7.7 times variation in DNA content among species analyzed in the present study. As assumed by earlier reports, it is presumed that C. siderosticta 4x and C. humilis were derived from C, siderosticta 2x and C. humilis ssp. nana, respectively. Among diploid species, 4.66 times but continuous variation was observed. There were no significant differences in nuclear DNA among four aneuploid of C. oxyandra and five of C. conica, respectively. Neither of five couples of strains, each belonging to a single species and having the same chromosome number but collected at different sites revealed any differences, indicating intraspecific aneuploid resulted from simple change of chromosome number. Three pairs of close relatives, C. foliosissima vs. C. morrowii, C. paxii vs. C. nubigera and C. pumila vs. C. kobomugi, were similar to each other in DNA content. It is clear that the increase in chromosome number is accompanied by the decrease in nuclear DNA content; negative correlation and regression between DNA content and chromosome number were confirmed to be highly significant in 45 diploid species. Based on the evidence of various kinds of earlier investigrtions and the present study, it is suggested that species with many small chromosomes would be derived from species having small number of large chromosomes by means of fragmentation followed by slight reduction of DNA.
