Genetic, Physiological and Biochemical Analysis of the Formation of Yellow-green Leaf Color of Burley Tobacco (Nicotiana tabacum)

To investigate the formation of the yellow-green leaf color of burley tobacco, the inheritance of leaf color, the contents of plastid pigments and the characteristics of chlorophyll metabolism in burley tobacco leaves were determined with burley tobacco cv. Burley21 and normal green Maryland tobacco cv. Maryland609 as the experimental plants. Field genetic populations of the reciprocal Fl generation, inbred F2 generation and the backcrossed BC1 generation of Burley21 and Maryland609 were constructed and the statistical analysis revealed that the inheritance of the yellow-green leaf color of burley tobacco was controlled by a double recessive gene. Chlorophyll content and carotenoid content were measured using spectrophotometric method and the results found that chlorophyll contents in the leaves of Burley21 were always lower than in that of Maryland609 during the whole growth period; the content ratios of chlorophyll to carotenoid showed a decreasing trend in Burley21, while in normal green Maryland609, it maintained at about 5. Further researches on the characteristics of chlorophyll metabolism indicated that the precursors of 6-aminolevulinic acid (ALA), porphobilinogen (PBG), uropmphyrinogen III (Urogen III), copropmphyrinogen III (Coprogen III), protopmphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX) and protochlorophyllide (Pchlide) in chlorophyll biosynthesis in Burley21 were lower than in Maryland609 at vigorous growing period; the activity of 6-aminolevulinate dehydratase (ALAD) in Burley21 was 0.43% as compared to Maryland609, but the activity of chlorophyllase in Burley21 was 2.04 times as high as in that of Maryland609. In conclusion, the yellow-green leaf color of burley tobacco was caused by low chlorophyll content, which might due to the combination of inhibited biosynthesis and accelerated degradation of chlorophyll regulated by key enzymes of ALAD and chlorophyllase, respectively. (C) 2016 Friends Science Publishers