ENT-KAURENE BIOSYNTHESIS IN GERMINATING BARLEY (HORDEUM-VULGARE L, CV HIMALAYA) CARYOPSES AND ITS RELATION TO ALPHA-AMYLASE PRODUCTION

ent-Kaurene biosynthesis as a prerequisite for gibberellin (GA) biosynthesis was studied in germinating Hordeum vulgare L., cv Himalaya caryopses and correlated, in time, with the appearance of alpha-amylase activity. The rate of ent-kaurene biosynthesis was estimated by inhibiting its further metabolism with plant growth retardants (triapenthenol or tetcyclacis) and measuring its accumulation by isotope dilution using combined gas chromatography-mass spectrometry. In the inhibitor-treated caryopses, ent-kaurene accumulation began approximately 24 hours after imbibition and proceeded at a rate of about 1 to 2 picomoles per hour per caryopsis, depending on the batch of seeds. In the absence of inhibitor, ent-kaurene did not accumulate, indicating that it is normally turned over rapidly, presumably to further intermediates of the GA biosynthesis pathway and eventually to GAs. ent-Kaurene accumulation occurred almost exclusively in the shoot, which is, therefore, probably the site of biosynthesis. Alpha-Amylase production began between 30 and 36 hours after imbibition and, thus, correlated well with de novo GA biosynthesis, as estimated from ent-kaurene accumulation. However, inhibition of ent-kaurene oxidation by plant growth retardants did not reduce the alpha-amylase production significantly, although it did reduce shoot elongation. We conclude that ent-kaurene is produced in the shoot and is continuously converted to GA, which is essential for normal shoot elongation, but not for the production of alpha-amylase in the aleurone layer.