Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/12/1999
Publication Date: N/A
Citation: Interpretive Summary: Broccoli and related vegetables contain a series of compounds known as glucosinolates that give the characteristic flavor, provide resistance to certain plant infections and are thought to decrease the rate of cancer when consumed in the human diet. Few systems are available, however, to discover how these compounds are made, to determine how their levels are controlled and to do careful analysis of the effects of individual compounds. We have produced a series of plants with genetic modifications in Arabidopsis that have allowed us to study the relationship between clubroot disease (a disease that alters the shape of the roots such that growth is restricted), the glucosinolate content and the metabolism of the growth hormone indoleacetic acid. These studies show that clubroot symptom development is related to the glucosinolate content and that reduced glucoinolate to indoleacetic acid conversion decreases the development of club roots. These studies will be of interest to plant pathologists and plant physiologists interested in the relationship between plant hormones and disease symptoms. The genetic system in Arabidopsis should also be useful to those interested in studies of dietary glucosinolates and the development of animal/human cancer.
Technical Abstract: Mutants of Arabidopsis thaliana with altered glucosinolate accumulation patterns were compared to study indole glucosinolate and IAA biosynthesis. Only the line TU8 seemed to be affected in phenotype (shorter stems, reduced apical dominance), whereas the other mutants with altered aliphatic glucosinolate patterns did not have a different phenotype. The activity of tryptophan oxidizing enzyme (TrpOxE) was decreased in 5-day-old seedlings. Nitrilase mRNA was slightly decreased in TU8 seedlings, but was at wild type levels in 4-week-old plants. By feeding labeled putative IAA precursors it was shown that a) a tryptophan-independent pathway is present in Arabidopsis seedlings grown in liquid shaking culture, b) the tryptophan-dependent and -independent pathways seem to be present at the same time and c) no differences in these two pathways were detectable between the mutant TU8 and the wild type. In TU8 plants tryptophan turnover was slower than in the wild type. Only line TU3 had a lower clubroot infection rate than the wild type, and lines TU3 and TU8 showed reduced symptom development.