Poster: Clocks

Abs # 773: Leaf Gibberellins Control Diurnal Expression of the Gene Encoding a Xylem Sap Lectin in Cucumber Root

Presenter:	Oda, Atsushi , astushi@sakura.cc.tsukuba.ac.jp
Authors	Oda, Atsushi  (A)   Mizoguchi, Tsuyoshi  (A)   Sakuta, Chiyoko  (A)   Masuda, Susumu  (B)   Kamada, Hiroshi  (A)   Satoh, Shinobu  (A)
Affiliations:	(A): Institute of Biological Sciences, University of Tsukuba (B): Noda Institute for Scientific Reserch

Xylem sap contains macromolecules such as proteins and oligo- and polysaccharides. Recently biochemical approaches have revealed identities of some of the xylem sap proteins, but biological functions and regulation of the production of xylem sap proteins have not been fully understood. XSP30 ( XYLEM SAP PROTEIN 30-kDa) is specifically expressed in pericycle and xylem parenchyma of cucumber (Cucumis sativus L.) roots, encodes a N-acetylglucosamine-specific lectin and is proposed to be one of the xylem sap macromolecules which may affect development of the organs of aerial part. Here we demonstrate that the XSP30 gene expression and its protein level show diurnal rhythm in cucumber roots. The rhythmic gene expression continues at least two cycles even under continuous light or dark conditions, demonstrating that the gene expression is controlled by a circadian clock. Removal of mature leaves or treatment of shoots with uniconazole-P (an inhibitor of GA biosynthesis) lowers amplitude of the rhythmic expression, and application of GA to the shoots restores these effects. These results suggest that light signal, perceived by organs of aerial part and GA, possibly produced in mature leaves, are quite important for the rhythmic expression of the XSP30 in roots. This is the first demonstration of a possibility that expression of a clock-controlled gene is regulated by GA.