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Quantitative variation in plastid pigments and polyphenols during leaf growth and after curing have been studied with several chlorophyll-deficient genotypes of tobacco. Under culture for flue-cured tobacco, the chlorophyll-deficient pale-yellow (NC95-Py) and yellow-green (SC58-yg) lines did not differ in polyphenol accumulation from the corresponding normal green recurrent parents NC95 and SC58. A negative correlation was evident between concentrations of polyphenol and chlorophyll. Decrease of the latter during leaf growth was accompanied with a decline of PPO and PRO activities. When the chlorophyll-deficient genotypes were grown under conditions for Burley tobacco, concentrations of chlorophyll and polyphenol maintained a steady level and were positively correlated, while the oxidases tended to increase. Burley 21 contained the lowest amount of polyphenols among the chlorophyll mutants, although the low chlorophyll content of its mature leaves was comparable to that of SC58-yg. Use of cultural practices for flue-cured tobacco caused an accumulation of polyphenols in green leaves. There was a greater loss of soluble polyphenols during air-curing than during flue-curing. Results indicate that the interaction of cultural practices with chlorophyll-deficient genes affects the metabolism of chlorophylls and polyphenols during leaf growth and maturation. Introduction of these genes into tobacco cultivars may provide a means of enhancing uniformity of leaf maturity and modifying certain leaf chemical constituents.

Tobacco leaf disks were subjected to various types of lighting and chemical solutions to determine the interaction of these factors in leaf senescence. Far-red light promoted senescence more than light of lower wave-lengths. Magnesium at 50 mM was a potent inhibitor of senescence, whereas EDTA-disodium salt at 50 mM promoted senescence in the light but retarded senescence in the dark. Additional work with the effect of ethylene on detached leaves demonstrated that hydrolytic enzyme activity for amylase, peptidase and protease increased as a result of treatment but esterase activity decreased. The response differed with regard to variety and leaf maturity. Exposure to ethylene increased chlorogenic acid oxidase in lower leaves of pale yellow tobacco but decreased the enzyme in NC-95 lower leaves. These data relate to the growth behaviour of the two genotypes in that physiological maturity occurs at considerably different rates in pale yellow and NC-95 plants. The results help to explain why leaves of pale yellow plants tend to ripen within a much shorter time than leaves of conventional green tobacco cultivars.