Alteration of the Protein Components and other Constituents in the Tobacco Leaf by Shading.

Abstract

Studies of the protein and other constituents in leaves from sun and shade grown tobacco plants revealed distinct differences in composition. Initially, sun leaves developed more slowly biochemically and morphologically than shade leaves, but, when fully grown, sun leaves showed a more active metabolism as measured by accumulation of dry weight, reducing sugars, and protein and by the endogenous rate of O2 consumption. The concentration of certain soluble enzymes in mature sun leaves was almost twice that found in mature shade leaves. However, little difference in specific activity was found, for the concentration of soluble proteins in sun leaves was also correspondingly greater. The concentration of insoluble proteins, on the other hand, differed little. Electrophoresis on starch of the soluble proteins revealed further differences in composition. Young shade leaves exhibited only 1 major soluble fraction, whereas young sun leaves contained an additional major peak corresponding in mobility to minor shoulder components in the shade leaf extracts. No difference between the electrophoretic patterns of soluble proteins from mature sun and shade leaves was observed. The findings demonstrate that specific protein fractions in tobacco leaves can be altered selectively by experimentally imposed conditions of growth.