Blue-light-induced phosphorylation of a plasma-membrane protein from phototropically sensitive tips of maize coleoptiles

• Published in: Planta Vol. 189; no. 4; pp. 567 - 576
• Main Authors: Hager, A. (Tuebingen Univ. (Germany). Botanisches Inst.), Brich, M
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-04-1993; Springer
• Subjects: Autoradiography; Auxins; Biological and medical sciences; Cell biochemistry; CELL MEMBRANES; Cell physiology; COLEOPTILE; COLEOPTILES; COLEOPTILOS; Corn; FOSFORILACION; Fundamental and applied biological sciences. Psychology; Koleoptyle; Lichtfarbe; LIGHT REGIMES; MEMBRANAS CELULARES; MEMBRANE CELLULAIRE; Membrane proteins; Peas; PHOSPHORYLATION; Phosphorylierung; Photons; Phototropism; Phototropismus; Plant physiology and development; Plasmamembran; Protein; PROTEIN KINASE; PROTEINA QUINASA; PROTEINAS; PROTEINE; PROTEINE KINASE; Proteinkinase; PROTEINS; REGIME LUMINEUX; REGIMENES DE LUZ; TROPISME; TROPISMO; TROPISMS; Zea; ZEA MAYS; Light effect; Monocotyledones; Phosphorylation; Membrane protein; Zea mays; Enzyme; Photoreceptor; Phototropism; Cereal crop; Gramineae; Protein kinase; Angiospermae; Plasma membrane; Spermatophyta; Blue light
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/bf00198221

Tips of maize coleoptiles, which function as esential light sensors for the phototropic growth reaction, exhibit a rapid blue-light-induced phosphorylation of a plasma-membrane-associated 100-kDa protein. Characteristics of this reaction are as follows: (i) The functional unit involved in the light-dependent phosphorylation consists of a photoreceptor, a protein kinase and the 100-kDa protein. This complex is only localized in the plasma membrane of tips but not in other parts of the seedling. (ii) The photoreceptor is a cryptochrome-like compound. (iii) The pH optimum of the light-dependent phosphorylation on isolated plasma membranes is around pH 7.8 whereas the light-independent phosphorylation of other membrane proteins occurs at lower values (pH 6.2). (iv) The light-induced in-vitro phosphorylation of the 100-kDa protein is strongly inhibited by the protein-kinase inhibitor staurosporine (IC50 = 4 nM). (v) The 32P-moiety of a 32P—[100 kDa]-protein complex generated after a light pulse with the aid of a membrane-associated protein kinase in the presence of [γ-32P]ATP cannot be removed by a 100-fold higher level of (unlabelled) ATP. This fact indicates that protein and phosphate are covalently connected and that the complex is not a short-lived intermediate. (vi) The 100-kDa protein is not identical to the plasma-membrane H+-ATPase, as shown by immunostaining on Western blots. (vii) Irradiation-dependent in-vivo phosphorylation of the 100-kDa protein in tips is already saturated by a light pulse of 5 s. In contrast, the de-phosphorylation of the protein in the dark is a slow reaction lasting about 30 min. It is suggested that the blue-light-triggered phosphorylated status of the 100-kDa protein is an early step in phototropism of the coleoptile, affecting the transport of auxin primarily in the irradiated flank.