Poster: Membrane Transport

Abs # 1199: Si uptake mechanism in higher plants

Presenter:	Ma, Jian Feng , maj@ag.kagawa-u.ac.jp
Authors	Ma, Jian Feng  (A)   Mitani, Namiki  (A)   Tamai, Kazunori  (A)
Affiliations:	(A): Faculty of Agriculture, Kagawa University

Silicon is a beneficial element for higher plants and the effect is characterized by conferring resistance of plants to multiple stresses including abiotic and biotic stress. Si is taken up in the form of uncharged molecule, silicic acid, and the uptake capacity differs greatly with plant species. However, the mechanism of Si uptake is less understood. We first compared Si uptake by rice, cucumber and tomato, which have great difference in the Si content of the top. A short-term uptake experiment showed that uptake by rice resulted in a rapid decrease in Si concentration in the solution, while that by tomato resulted in an increase in the Si concentration. The Si concentration remained unchanged with uptake by cucumber. However, in the presence of a metabolic inhibitor, 2.4-dinitrophenol, no changes in the Si concentration were observed in all three species, suggesting that different mechanisms for Si uptake are involved in different species. Further study with rice showed that the Si uptake by rice roots is mediated by a kind of transporter on the plasma membrane. The transporter has a low affinity for silicic acid (Km value, 0.32 mM) and contained Cys residue, but not Lys residue. The putative transporter was not inducible. To clone the gene encoding the Si transporter, a rice mutant which is defective in Si uptake was isolated and molecular work using this mutant is currently being carried out.