Leaf Proteins and Chemical Constituents in Tobacco Chlorophyll Genotypes

Bright and Burley tobacco breeding lines carrying the chlorophyll-deficiency genes Py and yg were compared with the corresponding normal genotypes and dark fire-cured and Maryland tobacco types during the growing season for the quantity of proteins and chemical constituents affecting the quality of homogenized cured leaves. Varietal difference in soluble leaf protein content was not observed in the immature plant stage but became evident upon approach to leaf maturation. Fraction I protein (F I protein) accumulated to a maximum level of about 130 mg / g dry weight in all tobaccos analysed before topping. The greatest quantity of Fraction II protein (F II protein), ranging from 100 to 160 mg / g dry weight, occurred one to two weeks after maximum F I protein accumulation. F I protein concentration decreased at a faster rate than F II protein during leaf maturation and senescence. Among the chlorophyll genotypes, Ky14 and Burley 21-yg had the highest amounts of soluble leaf proteins and the lowest levels of plastid pigments and/or chlorogenic acid. These characteristics are desirable for the homogenized leaf curing (HLC) process, which yields smoking material as a main product and heat-denatured protein as a by-product. The present results also suggest that tobacco can be grown for the production of both water-soluble and insoluble proteins as main products and deproteinized fibers as a by-product. In this regard, protein production would be affected by the yield of leaf biomass since the concentrations of soluble and insoluble proteins were similar in plants of the different tobacco types and chlorophyll genotypes under comparison.