Shirley M. Norman

Cytokinins Inhibit Abscisic Acid Biosynthesis in Cercospora Rosicola

Summary The fungus Cercospora rosicola produces the plant hormone, abscisic acid (ABA), as a secondary metabolite. We developed C. rosicola into a convenient system to determine the effects of compounds on the biosynthesis of ABA. Another important group of plant hormones, the cytokinins, inhibited ABA biosynthesis in C. rosicola. The inhibition of ABA biosynthesis was concentration dependent and, in studies using farnesyl-[1-14C]pyrophosphate, appeared to be specific rather than resulting from a general blocking of terpenoid biosynthesis. Inhibitors of ABA biosynthesis have not previously been reported. Knowledge that cytokinins have the ability to inhibit ABA biosynthesis in this fungal system indicates the need for further studies to determine if cytokinin inhibition of ABA biosynthesis occurs in plants and is an element of the hormonal action of cytokinins.

Biosynthesis of abscisic acid from [1,2-13C2]acetate in Cercospora rosicola

Abstract [1,2- 13 C 2 ]Sodium acetate was converted to abscisic acid (ABA) by Cerospora rosicola . The labelling pattern, determined by NMR spectroscopy,

β-carotene from the abscisic acid producing strain of Cercospora rosicola

Abstractβ-carotene was isolated from an extract of Cercospora rosicola mycelia and identified on the basis of chromatographic properties and UV-visible spectroscopic evidence. The accumulation of β-carotene was inhibited 71 and 52% by 10 μM amounts of decylimidazole and fluridone, resepectively. Abscisic acid accumulation was inhibited 63% by decylimidazole and enhanced about 10% by fluridone. Several other inhibitors of carotenoid synthesis failed to inhibit ABA biosynthesis.

Reversed-Phase Cleanup and High Performance Liquid Chromatographic Analysis of Abscisic Acid in Cercospora rosicola, Liquid Culture Media

Abstract A high performance liquid chromatographic method is described for measuring abscisic acid produced by the mold Cercospora rosicola Passerini in liquid culture media. The acidified liquid medium was passed through a Cis reversed-phase cartridge, impurities and ABA were eluted separately, and the ABA fraction was chromatographed on a reversed-phase column. Detection was by UV absorbance at 268 nm. No significant difference was found between ABA recoveries obtained by solvent partition and reversed-phase cartridge cleanup.