Abstract. The change in polyphenol content in the primed leaves of burley, flue-cured, and Turkish tobaccos during air-curing was related to the activities and isozymes of polyphenol oxidase and peroxidase. The quantity of chlorogenic acid was rapidly reduced during the first week of curing. The decrease in rutin content during curing was less significant, especially when the concentration of chlorogenic acid was high in leaf tissues. This result was further confirmed by in vitro assays with partially purified tobacco polyphenol oxidase.The polyphenol oxidase activity did not differ at any stage of curing in the 3 tobaccos. When the activity was measured by the oxidation of 3,4-dihydroxyphenylalanine it rose rapidly during the first day of curing and then decreased sharply so that in the fully cured leaf only 15 %/c activity remained. The increase in activity was not observed when chlorogenic acid was used as the substrate. A similar level of peroxidase activity was found in the 3 tobaccos before curing. Peroxidase activities increased rapidly during the first 24 hr of curing. declined thereafter, and remained highest in the flue-cured tobacco, less in the Turkish line, and least in the burley at the end of curing process.By polyacrylamide gel block electrophoresis, 10 peroxidase isozyme bands, 2 cationic and 8 anionic, appeared identical in all 3 tobaccos. When catechol replaced benzidine-2 HCI as the electron donor, 1 cationic and 2 anionic peroxidase isozvmes did not form. Of interest is that the same 10 peroxidase isozyme bands also exhibited polyphenol oxidese activities when treated with 3,4-dihydroxyphenylalanine or chlorogenic acid.
Ten tobacco cultivars representing various tobacco types were directly seeded in the field at 70 to 80 plants per square meter and were harvested when 50 to 60 cm high. Biomass yield ranged from 44 to 70 metric tons per hectare, with Ky16 Mammoth having the highest yield. The Mammoth variety, however, had the lowest leaf/stalk ratio (1.77), whereas Coker 139 bad the highest (4.04). One metric ton of wet biomass produced about 6 to 8 kg of soluble protein, which is independent of the leaf/stalk ratio. Analyses of the deproteinized fibrous residues revealed that the levels of neutral detergent fiber, acid detergent fiber, cellulose, and apparent hemicellulose were comparable among the ten cultivars. A large variation of lignin content was observed among the dark green tobaccos. Burley, in general, had lower concentrations of starch and protein in the fibrous residue than the dark green tobacco. When compared with the deproteinized alfalfa fibrous residue, the low concentrations of lipids, lignin, and cellulose and a greater amount of apparent hemicellulose in the tobacco residue show its suitability as animal feed. The present results also indicate that the selection of tobacco genotypes is of importance for high density cultivation in the production of soluble protein and fibrous residue.
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