Dobra, Jana , Storchova, Helena , Havlova, Marie , Haisel, Daniel , Libus, Jiri , Vankova, Radomira .
Putative link between cytokinins and proline degradation and its potential involvement in plant response to drought stress.
The level of free proline, important osmoprotectant, is controlled by regulation of expression of genes for its biosynthesis and conversion back to glutamate (coding for pyrroline-5-carboxylate synthetase and proline dehydrogenase, respectively). Exogenous cytokinins (CK) were reported to induce expression of a gene homologous to proline dehydrogenase (cig1). We compared the impact of constitutive and inducible elevation of total CKs on cig1 expression. In watered wild type (WT) plants cig1 expression was low in the youngest leaves and gradually elevated in middle and lower ones. In drought stressed WT plants, cig1 expression was strongly suppressed with the exception of 2 - 3 lowest leaves, in which a sharp increase of cig1 mRNA was found. Uniform elevation of total CK levels achieved by constitutive expression of the gene for trans-zeatin O-glucosyltransferase (ZOG1) led to a mild decrease of cig1 expression, significant especially in lower leaves. As proline levels were lower in 35S::ZOG1 transgenics at moderate stress, diminished cig1 expression might reflect lesser demand for proline catabolism. Expression studies on SAG12::ZOG1 plants indicated transient stimulation of cig1 expression coinciding with the early onset of SAG promoter activity. In lower, progressively senescing leaves cig1 expression was inhibited, especially under stress conditions. The results indicate that cig1 expression is under strong environmental control. Its stimulation after rehydration might be connected with elevation of CK content in leaves after enhancement of the transpiration stream. Significant differences in drought response of 35S::ZOG1 and SAG12::ZOG1 plants, especially in stress sensing, will be discussed.
This work was supported by Ministry of Education of CR, project no. ME868.
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1 - Institute of Experimental Botany AS CR, v.v.i.
2 - Institute of Experimental Botany AS CR, v.v.i., Laboratory of Hormonal Regulations in Plants, Rozvojova 263, Prague 6, CZ 165 02, Czech Republic
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM