THE CYTOLOGICAL CHIMERAS IN ORIGINAL REGENERATES FROM TOBACCO TISSUE CULTURES AND IN THEIR OFFSPRINGS

Abstract

A cytological analysis was made with root-tip meristematic cells of regenerated plants and their offspring originated from tissue cultures of Nicotiana tabacum cv. ''Wisconsin No. 38''. Each original regenerate showed a wide range of variation in chromosome number, irrespective of combinations or concentrations of growth regulators used for regeneration. Two regenerates designated 1 and 2 were used for analysis of further generations. In the 1st selfed generation (S1), all the progenies of 1 and 2 exhibited variable chromosome numbers. Five plants derived from 1 had 43.0 .+-. 1.0 chromosomes on the average, while 2 plants from 2, 63.7 .+-. 1.9. The majority of S1 plants of 1 showed normal or hypoploid chromosome numbers, whereas hyperploid numbers were common in S1 plants of 2. In the 2nd selfed generation (S2), the chromosome number of all the progeny plants of 1 stabilized to 48, whereas all the S2 plants of 2 still exhibited highly variable chromosome numbers. All the plants belonging to the 1 lineage were almost normal physiologically (pollen and seed fertility, plant height, leaf color, leaf form, inflorescence shape, etc.). In the 2 lineage, in contrast, these characteristics segregated frequently and most of the plants exhibited some anomalies. Observations of mitotic anaphase revealed that there exist considerable irregularities such as anaphase bridges. The lineage of 2 possesses some genetical and/or physiological factor(s) leading to the cytological instability. From the reciprocal crosses between 1 and normal plants, existence of a cytoplasmic effect on the cytological stabilization was also presumed. To determine the existence of the gene(s) involved in the present cytological chimerism, further studies on the crosses involving the 1 lineage are required.