Identification of auxins by a chemical genomics approach

Thirteen auxenic compounds were discovered in a screen of 10 000 compounds for auxin-like activity in Arabidopsis roots. One of the most potent substances was 2-(4-chloro-2-methylphenoxy)-N-(4-H-1,2,4-triazol-3-yl)acetamide (WH7) which shares similar structure to the known auxenic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). A selected set of 20 analogues of WH7 was used to provide detailed information about the structure–activity relationship based on their efficacy at inhibiting and stimulating root and shoot growth, respectively, and at induction of gene expression. It was shown that WH7 acts in a genetically defined auxin pathway. These small molecules will extend the arsenal of substances that can be used to define auxin perception site(s) and to dissect subsequent signalling events

A high-throughput imaging auxanometer for roots and hypocotyls of Arabidopsis using a 2D skeletonizing algorithm

Next generation phenotyping of auxin response mutants will be greatly facilitated by the ability to record rapid growth responses in roots and hypocotyls at high throughput and at high temporal resolution. As Arabidopsis seedlings are very tiny and fragile, imaging is the only adequate way for data acquisition. As camera-based systems described before have a limited throughput, we used commercial flatbed scanners to record a large number of simultaneous experiments. We developed Hansa Trace, software for automatically detecting and measuring hypocotyl segments and roots in the images. We validated this system by measuring some well-characterized growth responses to auxins, non-auxins, ATPase activators and apoplastic acidification. The method can be shared on a cooperation basis and is able to perform measurements with minimal user intervention

Rapid Auxin-Induced Cell Expansion and Gene Expression: A Four-Decade-Old Question Revisited1[C][W]

The classical effect of the plant hormone auxin is very rapid stimulation of cell expansion followed by sustained growth over a longer time period. However, auxins are also important in other responses, such as cell division and differentiation. Recently, the TRANSPORT INHIBITOR RESPONSE1/AUXIN

Cytokinin Inhibits a Subset of Diageotropica-Dependent Primary Auxin Responses in Tomato

Many aspects of plant development are regulated by antagonistic interactions between the plant hormones auxin and cytokinin, but the molecular mechanisms of this interaction are not understood. To test whether cytokinin controls plant development through inhibiting an early step in the auxin response pathway, we compared the effects of cytokinin with those of the dgt (diageotropica) mutation, which is known to block rapid auxin reactions of tomato (Lycopersicon esculentum) hypocotyls. Long-term cytokinin treatment of wild-type seedlings phenocopied morphological traits of dgt plants such as stunting of root and shoot growth, reduced elongation of internodes, reduced apical dominance, and reduced leaf size and complexity. Cytokinin treatment also inhibited rapid auxin responses in hypocotyl segments: auxin-stimulated elongation, H(+) secretion, and ethylene synthesis were all inhibited by cytokinin in wild-type hypocotyl segments, and thus mimicked the impaired auxin responsiveness found in dgt hypocotyls. However, cytokinin failed to inhibit auxin-induced LeSAUR gene expression, an auxin response that is affected by the dgt mutation. In addition, cytokinin treatment inhibited the auxin induction of only one of two 1-aminocyclopropane-1-carboxylic acid synthase genes that exhibited impaired auxin inducibility in dgt hypocotyls. Thus, cytokinin inhibited a subset of the auxin responses impaired in dgt hypocotyls, suggesting that cytokinin blocks at least one branch of the DGT-dependent auxin response pathway

Dose–response kinetics of mutants resistant to primary root growth inhibition elicited by WH7 and 2,4-D, respectively

(A) Four mutant lines, designated , , , and , were identified in a screen for mutations that confer resistance to WH7. (B) The mutant (open symbols) is resistant to both WH7 and 2,4-D. Data indicate means ±SE of five to nine individual measurements.<p><b>Copyright information:</b></p><p>Taken from "Identification of auxins by a chemical genomics approach"</p><p></p><p>Journal of Experimental Botany 2008;59(10):2757-2767.</p><p>Published online 31 May 2008</p><p>PMCID:PMC2486469.</p><p></p

Time courses of growth responses induced in maize coleoptiles by WH7, WH7E, WH7G, and IAA (from top to bottom), as measured with an angular transducer

The substances were applied at the time indicated by the arrows. The control shows the typical onset of elongation growth after a few hours caused by restoration of internal auxin production. Data points indicate the growth rate of five stacked coleoptiles, measured simultaneously. Typical results are shown.<p><b>Copyright information:</b></p><p>Taken from "Identification of auxins by a chemical genomics approach"</p><p></p><p>Journal of Experimental Botany 2008;59(10):2757-2767.</p><p>Published online 31 May 2008</p><p>PMCID:PMC2486469.</p><p></p