A Nicotiana plumbaginifolia protein labeled with an azido cytokinin agonist is a glutathione S-transferase

• Published in: Physiologia plantarum 1998-05, Vol.103 (1), p.114-124
• Main Authors: Gonneau, M. (INRA, Versailles (France). Lab. de Biologie Cellulaire), Mornet, R, Laloue, M
• Format: Article
• Language: English
• Subjects: ACIDE AMINE; Agronomy. Soil science and plant productions; AMINO ACIDS; AMINOACIDOS; BIOCHEMICAL PATHWAYS; Biological and medical sciences; Chemical agents; CITOQUININAS; Cytokinin; cytokinin-binding; CYTOKININE; CYTOKININS; Economic plant physiology; FEUILLE; Fundamental and applied biological sciences. Psychology; GLUTATHION; GLUTATHIONE; glutathione S-transferase; GLUTATION; Growth and development; Growth regulators; HOJAS; LEAVES; Life Sciences; NICOTIANA PLUMBAGINIFOLIA; photoaffinity labeling; PLANT GROWTH SUBSTANCES; Plant physiology and development; PROTEINAS; PROTEINE; PROTEINS; SUBSTANCE DE CROISSANCE VEGETALE; SUSTANCIAS DE CRECIMIENTO VEGETAL; Vegetal Biology; Vegetative apparatus, growth and morphogenesis. Senescence; VIA BIOQUIMICA DEL METABOLISMO; VOIE BIOCHIMIQUE DU METABOLISME
• ISSN: 0031-9317; 1399-3054
• DOI: 10.1034/j.1399-3054.1998.1030114.x

The mechanisms of reception/transduction of cytokinins still remain largely unknown. We used 1‐(2‐azido‐6‐chloropyrid‐4‐yl)‐3‐(4‐[3H])phenylurea ([3H]azido‐CPPU), a new photoaffinity probe to search for cytokinin‐binding proteins. A soluble protein that binds phenylurea‐type cytokinins has been specifically photolabeled in Nicotiana plumbaginifolia (cv. Viviani line pbH1D) leaf extracts. The protein was purified to homogeneity by affinity chromatography. Its N‐terminal amino acid sequence, as well as four internal peptidic sequences are highly homologous with the theta class of the glutathione S‐transferase superfamily (GST, EC 2.5.1.18) including Hyoscyamus muticus and Arabidopsis GSTs identified as auxin‐binding proteins. The purified N. plumbaginifolia protein also possesses GST enzymatic activity. To test the possible involvement of this GST in the mechanism of action of cytokinin, we studied the binding of tritiated‐CPPU to the purified GST in the presence of various compounds, cytokinin agonists, cytokinin antagonists, or inactive molecules. Thidiazuron is a poor competitor, and neither zeatin nor the active optical isomer R‐MeBA is able to inhibit the binding of CPPU. There is no correlation between the cytokinin activity and the binding properties of the molecules tested. Our results confirmed that plant GSTs bind different compounds, especially plant hormones but probably have no specific role in the mode of action of cytokinins.