INTERACTION BETWEEN CALCIUM AND SILICON IN WATER-CULTURED RICE PLANTS

The interaction between Ca and Si in water-cultured rice plants (Oryza sativa L. cv. Akebono) was investigated in terms of uptake. The effect of Ca levels in the solution on Si chemical forms and on the formation of silica bodies in the leaf blades was also examined using soft X-ray irradiation for detection of silica bodies. Si addition (1.66 mM Si) decreased both Ca content of the shoot and uptake at each Ca level. This might mainly result from a decreased transpiration rate caused by Si. Si uptake was not affected when the Ca levels were increased. The results of Si forms showed that silica sol constituted more than 90% of the total Si in the leaf blades regardless of Si and Ca levels, and soluble silica and/or polysilicic acid seems to gel physically over 8.0 mM Si within the plants. Significant difference in the numbers of silica bodies on the third leaf blade was not found between different Ca levels at the same Si level. The content of Si in the leaf blade seems to be a determining factor for the formation of silica bodies.