The Unstable Behavior of a Chromosomal Fragment of NICOTIANA PLUMBAGINIFOLIA Responsible for Chlorophyll Variegation in N. TABACUM.

HE origin of chromosome instability and subsequent chlorophyll variegation Tin hybrid derivatives of Nicotiana tabacum (n=24) and N . plumbaginifolia (n=10) has been described by MOAV (1961) and GUPTA (1965, 1968b). It was demonstrated by (GUPTA 1968b) that the alien chromosome of N . plumbaginifolia (pbg) carrying a Ws gene (chlorophyll factor) showed instability in association with the N . tabacum (tbc) genome (homozygous for the white seedling loci, ws,, ws,, ws,, us,), and formed somatic anaphase bridges which after breakage led to loss of the W s gene. Somatic loss of Ws from the pbg chromosome was found to be responsible for chlorophyll variegation. A pbg chromosome which frequently formed mitotic anaphase bridges (more than 5 % ) was termed unstable in comparison to the stable one which formed less than 5% mitotic bridges ( GUPTA 1968). The investigation reported here revealed that even a chromosomal fragment of N . plumbaginifolia carrying the gene Ws, could cause chlorophyll variegation in tbc-pbg hybrid derivativles without forming somatic bridges.