Cytological, Cytochemical and Electrophoretic Distinction of a Dioecious Cucurbit, Coccinia indica

Abstract

Summary Chromosome studies, in situ estimation of 4C nuclear DNA content and isoesterase profiles of vegetative propagules were carried out in dioecious Coccinia indica Wight and Arn. Somatic chromosome number 2nϭ24 though recorded in both sexes, a distinct heteromorphic pair of sex chromosome is found in male plants. Diploid males are heterogametic with 22ϩXY and females are homogametic with 22ϩXX. The somatic chromosomes are generally short with median and submedian constrictions except the metacentric Y chromosome which is conspicuously large. The relative size differences of chromosomes indicate a tendency towards progressive asymmetry. 4C nuclear DNA content shows marked variation in relation to sex and a positive linear relationship between the amount of the DNA and the total chromosome length is recorded. The average packing ratio (APR) of male and female plants differs which suggests a differential organisation of mitotic chromosome in relation to sex. Differences in the isoesterase pattern obtained in the vegetative reproductive structure indicate that it could also be used as an important biochemical marker for identification of sexes.Coccinia indica, a dioecious vegetatively propagated species of cucurbitaceae, shows a wide spread distribution in the tropical and subtropical regions of the world (Chakrabarty 1959) and in particular in Tripura state, India (Deb 1981). Earlier workers have found that a series of polyploidy (2nϭ24, 36, 48) exists in C. indica with distinct heteromorphic pairs of sex chromosomes (Bhaduri and Bose 1947, Chakravarty 1948, D'cruz et al. 1972, Kumar and Vishveswaraiah 1952, Roy and Roy 1971, Sen and Datta 1977, in which, Y chromosome plays a decisive role in the differentiation of male sex (Kumar and Vishveshwariah 1952). Interspecific and intraspecific variation and constancy in the amout of nuclear DNA content of flowering plants have been reported by several authors (Bennett 1985, Bennett and Smith 1976, Chattopadhyay and Sharma 1990, Riana and Rees 1983, Sinha et al. 1997. Data on nuclear DNA content was meagre in the sex forms of C. indica (Chattopadhyay and Sharma 1991) and no comparative analysis of the karyotype in relation to DNA content was done in this species. The overall compaction of DNA molecules into the somatic chromosome complements described as average packing ratio (Lewin 1994) could be estimated (Sinha et al. 1996) to find out the measure of condensation at mitotic metaphase of the sex forms of the taxon. Moreover, the male and female plants strictly maintain their respective sexual phenotype and as dioecism exist in this taxon, the specialized reproductive structure i.e. the tuberous roots of the two sex forms could be analyzed electrophoretiacelly to detect distinction between them. The present work deals with chromosome studies, 4C nucler DNA content and isoesterase pattern of the sex forms of C. indica. The differential rate of average packing ratio (APR) in relation to sex has been analyzed as well. Materials and methodsTuberous roots of male and fe...