A cytological study of Podocarpus macrophyllus with special reference to sex chromosomes

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Female and male plants of Podocarpus macrophyllus (Thunb.) Lamb. were cytologically investigated. The chromosome numbers were 2n=38 in the female plants, and 2n=37 in the male plants. The chromosome complement in female was composed of 38 telocentric chromosomes, and that in male was composed of one large submetacentric chromosome and 36 telocentric chromosomes. Bright chromomycin A3 bands appeared at the proximally interstitial region of two middle-sized telocentric chromosomes in both the female and male plants and coincided with secondary constriction in position. DAPI-bands appeared at proximal regions of about two-third the large telocentric chromosomes, but did not in the large submetacentric chromosome and the small telocentric chromosomes. Seventeen bivalents and one trivalent were constantly formed at meiotic metaphase I in the pollen mother cells (PMCs). The trivalent displayed a conspicuous shape with one free chromosomal end. These chromosomes were segregated into an anaphase I group of n=18 with a large submetacentric chromosome, and the other anaphase I group of n=19. These observations on mitotic and meiotic chromosomes strongly suggest that sex of P. macrophyllus could be determined by the XXY type of the sex chromosome system.