Fluctuations in Protein Levels of Tobacco Leaves and Consequences for Extractability

Abstract

Greenhouse and field experiments were conducted to evaluate the effect of time, cultural conditions and genetic factors on protein extractability from tobacco leaves. Leaf protein was periodically extracted from green tobacco from time of transplanting through early senescence. Intensive sampling revealed substantial fluctuations in protein concentrations superimposed upon an age-related decline in protein levels with approaching plant maturity. Predictably, these oscillations affected the degree of protein extractability. Combined totals of the three major soluble protein fractions, viz. the green chlorophyll/protein complex, the white Fraction I protein (cryoprecipitate), and the white Fraction II protein (thermoprecipitate), deviated occasionally from protein values in unfractionated homogenates, but the fluctuation trends were similar. Investigations of variations in protein extractability among greenhouse-grown tobacco and selected genotypes grown under field conditions revealed that protein fluctuations during plant development are a common phenomenon. It is concluded that the occurrence of periodic fluctuations in total protein concentration and in the amount of extractable protein can severely distort estimates of leaf protein yields that are based upon insufficient numbers of samples and prolonged intervals between sampling.

Tobacco Leaf Protein: I. An Evaluation of the Use of Putative Chemical Growth Enhancers for Tobacco Leaf Protein Production

“…After stripping the leaves from the stalk of five representative plants, 1.5 kg to 2.0 kg of homogenate were prepared by maceration in an extrusion grinder. No process water was added but a mixture of dry NaOH (at 0.6 g/kg) and sodium metabisulfite (at 3 g/kg) was metered into the hopper to retard browning and to maintain the pH above 5.5 (1 ). Protein extraction was conducted for the first four weeks although yield data were collected for an additional two weeks thereafter.…”

“…Protein yield variability has been a major impediment to the development of reliable methods for commercializing protein production from tobacco leaves. Earlier work from this laboratory showed that total protein concentrations in freshly harvested green leaves from tobacco fluctuate in a saw-tooth pattern during plant development (1). Other investigators have commented on the lower than expected yields of leaf protein when laboratory procedures are upscaled to preparative operations (2).…”