Biological activity of some conjugated gibberellins

The biological activity of several gibberellin (GA) conjugates was studied and compared with that of the corresponding free GAs. The following conjugates were included: O(3)-β-D-glucopyranosides of GA1, GA3 and GA4; O(13)-β-D-glucopyranosides of GA1, GA3 and GA5; O(13)-β-D-glucopyranosyl-GA5-β-D-glucopyranosyl ester; GA3-β-D-glucopyranosyl ester and GA3-α-D-glucopyranosyl ester; N-GA3-oyl-glycine, its methyl ester, N-GA3-oyl-glycylglycine, and N-GA3-oyl-proline. All compounds were synthesized chemically but some of them are known to occur as endogenous plant products, or to be formed in plants upon application of a free GA. Activity was determined in the dwarf pea, dwarf corn, dwarf rice, and lettuce hypocotyl bioassays. The GA conjugates were found to posses different relative activities depending on the chemical structure, the bioassay system, and the site of application (shoot or roots). It is concluded that the activity of GA conjugates as measured in different bioassays is based upon the ability of plant enzymes and possibly of certain microorganisms to hydrolyze glucosidic, glucosyl ester, and amide-like linkages.