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|Title:||The metabolism of dithiocarbamate fungicides by papaya (Carica papaya)|
|Authors:||Chin, Byong Han|
|Abstract:||The appearance of phytotoxic symptoms following the application of dithiocarbamate fungicides has been reported in a number of instances. Delayed phytotoxicities such as leaf spotting in peach, pear, and apple, and leaf damage to tobacco, apple, and papaya have been observed following the application of dialkyldithiocarbamates but not with the monoalkyl analogs. This suggests that the two classes of fungicides are metabolized differently by plants. Study of the metabolism of dimethyldithiocarbamates in papaya was undertaken to assess the importance of the above observations. Dimethyldithiocarbamate (DDC) labeled with 14C in the methyl groups or 35S in the dithiocarbamate function was applied either as the potassium or zinc salt to leaves and roots of papaya seedlings from 1 to 3 months old. Surface residues, volatile metabolites, and translocated materials found in root, stem, leaf, and cell sap were assayed at various times after application of labeled compound. The results of this work show that part of the fungicidal residue is hydrolyzed on the surface, presumably to carbon disulfide and dimethylamine, both of which could be recovered as volatile metabolites. This hydrolysis is more rapid with the potassium salt than with the zinc salt presumably due to insolubility of the latter. An appreciable portion of the applied 35S label has been found in sulfur amino acids (free and in proteins) and inorganic sulfate. Whether this is due to the oxidation of carbon disulfide or some dimethyldithiocarbamate metabolite is not known. In the case of methyl 14C labeled compounds, carbon dioxide was collected as a volatile metabolite and 14C was found in many plant constituents. The exact mechanism for the transformation of dimethy1amine methyl groups to carbon dioxide is unknown. Among the metabolites isolated, the largest amount of foliarly applied radioactivity (22% for 14c-KDDC and 11% for 35S-KDDC ) was recovered from the cell sap as dimethyldithiocarbamy1 glucoside, identified by paper chromatography and chemical analysis. Lesser amounts were present as dimethyldithiocarbamyl alanine and 4 other unidentified radioactive compounds. Recoveries of applied radioactivity ranged from 28% to 55% for 35S-KDDC , from 33% to 99% for 14c-KDDC , when applied to leaves. Phytotoxicity was never observed with the more rapidly decomposed KDDC whereas it was seen with Zn(DDC)2. The available data indicate that a slow but prolonged evolution of carbon disulfide and dimethylamine on the leaf surface as observed with Zn(DDC)2 may result in chronic poisoning of sensitive enzyme systems. The rapid hydrolysis and release of volatile metabolites from ICDDC does not appear to cause any phytotoxicity.|
Thesis (Ph. D.)--University of Hawaii, 1967.
Bibliography: leaves 54-58.
ix, 58 l graphs, tables
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|Appears in Collections:||Ph.D. - Horticulture|
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