Interactions between plant hormones and heavy metals …

ver recent years, mounting evidence led to the widely accepted concept that plant hormone action is not the read-out of linear pathways, but determined by the extensive combinatorial activity of the signaling molecules and the integration of their signaling pathways, both in terms of regulating growth and development and in adapting to external stimuli. Further complicating the scenario, the triggered physiological processes are not only dependent on the perceived stimulus, but also on the specific properties of the responding tissue in terms of sensitivity and responsiveness to a given signaling molecule class. The plant hormone network can affect plant development and physiological responses on several different levels involving for example, control of mRNA and protein synthesis, configuration, modification, and turnover of proteins, as well as by hormone transport and reversible or irreversible inactivation of active signaling molecules (Fig. 1). For instance, directed polar auxin transport and spatiotemporally defined auxin maxima, and the therewith coupled control of gene expression and gene signaling hierarchies, coordinate organogenesis and axis formation during embryogenesis and patrol plant development. Another example is the modification of plant hormones by, e.g., glycosylation, methylation, or amino acid conjugation, which either serve to reversibly modulate their activity or confer the first step in their irreversible metabolism. In addition, plant hormones can also directly impact the synthesis or degradation of other signaling molecules, as has been shown, amongst other relationships, for ethylene production, which is induced both by auxin and brassinosteroids. Also, posttranslational modifications of proteins can be a target modulated by plant hormones, as is the case in cytokinin, abscisic acid, and ethylene signaling that involve phosphorylation of downstream components of the signal transduction machinery.

The BR is biosynthesised from . Thebiosynthetic pathway was elucidated by Japanese researchers andlater shown to be correct through the analysis of BR biosynthesismutants in , tomatoes and peas. Thesites for BR synthesis in plants have not been experimentallydemonstrated. One well-supported hypothesis is that all tissuesproduce BRs, since BR biosynthetic and signal transduction genesare expressed in a wide range of plant organs, and short distanceactivity of the hormones also supports this.Experiments have shown that long distance transport is possible andthat flow is in an acropetal direction, but it is not known if thismovement is biologically relevant.Brassinosteroids are recognized at the cell membrane, although theyare membrane soluble.

Divergent regulation of Arabidopsis SAUR genes: a …

Selective interaction of triazole derivatives with DWF4, a cytochrome p450 monooxygenase of the brassinosteroid biosynthetic pathway, correlates with brassinosteroid deficiency in planta.

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