Physiological and biochemical characteristics and molecular-biological identification of a gigantic tobacco mutant.

A new gigantic late-flowering tobacco mutant was isolated in tobacco field in Xunyang county, Shaanxi province, in 2001. It was rescued through tissue culture and a large amount of regenerated plantlets were obtained. The results of the comparison between the regenerated plants from this mutant and the wild type plant (K346) were as follows: (1) Morphological observation showed that the leaf number of the mutant was 3.3 times as many as that of the wild type, the height of mutant was 2.2 folds that of the wild type, and the mutant had the late-flowering character. (2) Cytological examination showed that the mutant was a normal diploid, and the number of chloroplasts in a guard cell of mutant was 1.3 times that of the wild type. (3) Both chlorophyll a and b content of the mutant were larger than that of the wild type; soluble protein content of the mutant was 1.18 times as much as that of the wild type. Peroxidase isozyme and cytochrome-oxidase isozyme electrophoresis analyses indicated differences between the mutant and the wild type. The soluble protein SDS-PAGE patterns showed the absence of four bands [P1 (114.6 kD), P2 (103 kD), P3 (66.2 kD), P4 (24 kD)] in the mutant. (4) RAPD analysis showed that the similarity index of the mutant and the wild type was 0.612. This suggested that there were changes at DNA level. The mRNA of mutant leaves at flowering stage was isolated; DDRT-PCR was carried out using 10 random primers, using OligodT(15)M (M=A/G/C) as anchor primer. It has been proved that gene expression at anthesis was different between the mutant and the wild type. (5) Genetic observation showed that the mutant was homozygotic and bred true. And the mutant was a late-flowering one.