The Metabolism of Indole-3-acetic Acid by Geranium Stem Callus Cultures

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Abstract
Stem callus tissue from Pelargonium hortorum was grown on modified White''s medium supplemented with coconut water, casein hydrolysate, sucrose, and indoleacetic acid (IAA). When transfers were made to fresh nutrient medium, growth continued for about 300 days and ceased. At the end of this growth period, fresh weight of calluses had increased 5-fold or more. At 3-day intervals acidified culture solutions were extracted with ether, and the ether was removed under reduced pressure. Residues dissolved in ethanol were chromatographed on paper with IAA standards in 2 solvents. The IAA spot was eluted in 50% ethanol and assayed with Salkowski reagent. In duplicate experiments chromatograms were sprayed with Ehrlich'' s and Salkowski reagents. A decline in Ehrlich and Salkowski color, which became undetectable after 30 days, was observed. In cultures fed IAA-2-C14, the C14 products were investigated in both the tissue and the culture medium after 7-day intervals. Radioactivity could not be recovered from the system after 30 days. Radioautography of chromatograms revealed 2 acid-ether soluble IAA metabolites in the tissue in addition to IAA, and 5 metabolites were detected in the nutrient medium. One metabolite in the tissue had an Rf identical with that of indoleacetyl-L-aspartic acid in 2 solvents. The C14 products in the nutrient medium did not give typical indole reactions with Ehrlich''s or Salkowski reagents. Cochromatography with standards indicated the products were not anthranilic acid, o-aminoacetophenone, indole, tryptamine, tryptophan, indoleacetonitrile, or indoleacetaldehyde. Respiratory CO2 was collected in carbonate-free NaOH from callus tissue cultures and precipitated as BaCO3 with BaClo. Samples collected daily indicated the conversion of IAA-2-C14 to C14O2.