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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.

A chromatographic method was developed for the separation and quantification of chloroplast pigments from tobacco (Nicotiana tabacum L.) leaves. The apparatus consisted of a low-pressure pumping system, a sealed silica gel column, and a recording spectrophotometer. Pigments were eluted with a stepped gradient solvent mixture containing heptane, diethyl ether, and acetone. The rapidity and accuracy of the technique provided a convenient means for individually measuring and collecting each of the chlorophyll and carotenoid components in leaf extracts from selected yellow mutant and green tobacco genotypes. The pattern of pheophytin a distribution in leaves harvested from different levels on the stalk showed no correlation with chlorophyll a content. It is suggested that pheophytin a is not necessarily an extraction artifact but could have a physiological role in photosynthesis.

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