Chromosome Studies and Nuclear DNA in Relation to Sex Difference and Plant Habit in Two Species of Cucurbitaceae.

Abstract

Analyses of the structure and behaviour of chromosomes and estimation of 4C nuclear DNA in both male and female plants of Coccinia indica and Trichosanthes dioica were made. In male and female plants of T. dioica had identical chromosome numbers. There was remarkable similarity between sexes in chromosome morphology, number of secondary constrictions and total chromosome length, as well as the amount of 4C DNA. In absence of any detectable chromosomal differences it may be argued that the sex determination in this species is principally controlled at the autosomal level. The karyotypes of male and female individuals were not markedly different in C. indica, except for the sex chromosomes. The total chromosome length was slightly more in male as compared to female plant. There was a corresponding difference in 4C DNA values. The differences in chromosome size between sexes of C. indica reflected additional chromatin rather than differential condensation. The heterochromatic nature of long sex chromosome was also indicated in its staining behaviour. The total chromosome length, average chromosome length and the 4C nuclear DNA values of both males and females of annual T. dioica were comparatively higher than those of the related perennial, C. indica.