Calcium compounds in cell walls of rice shoots were investigated by molecular sieve chromatography and compared with silicon compounds. The phenolcarbohydrate complexes (PCC) obtained by eellulase action, and the lignincarbohydrate complexes (LCC) extracted by dimethylsulfoxide (DMSO) were loaded onto a Sephacryl S-400 column. Then calcium, silicon, phenolic acids, or lignin, and carbohydrate of both complexes were detected in the void volume. These results indicate that calcium and silicon may combine with the phenol-or lignin-earbohydrate complexes in cell walls of rice shoots.Key Words: calcium, cell wall, lignin-earbohydrate complexes, phenolic acids, silicon.Calcium is an essential element and plays an important role in many physiological functions of higher plants. The maintenance of the cell wall structure depends upon calcium cross-linkages, particularly with pectin components of the middle lamella (Bangerth 1979). In a previous paper (Inanaga et al. 1988), we indicated that calcium may play an important role in the stability of the cell wall of the peanut shell through the formation of a calciumcomplex not only with pectin substances but also with the caffeic acid moiety in the LCC or PCC. Ito and Fujiwara (1968) reported that when the cell wall of rice leaf was fractionated, calcium was associated with ligneous substances. In addition to the cell wall of the peanut shell, calcium may also combine with the PCC and LCC of rice.Although silicon is an essential element for the development of rice (Lewin 1969), its physiological role is far from clear. Lewin (1969) reported that silicon is depositted in the form of silica gel in the epidermal cells and cell walls of many plants, and that very often it occurs as special morphological skeletal structure. As silicic acid can be readily formed with polyhydric alcohols and organic acids (Lewin 1969), silicon may also bind with the LCC and PCC of rice plant in a similar way as calcium.Attempts were made to determine whether calcium and silicon combine with the PCC or with the LCC in cell walls of rice shoots. MATERIALS AND METHODSPlant culture. In a greenhouse, rice (Oryza sativa L. cv. Koshijiwase) seedlings transplanted on June 25 were grown for 40 d in tap water with 100 mg L -1 silicon, to which nutrients (40 mg L -1 nitrogen as NH4NO3, 8.7 mg L -1 phosphorus as Na2HPO4, 25 mg L -~ potassium as KC1, 6 mg L -1 magnesium as MgSO4, 7 mg L -~ calcium as CaC12, 3 mg L -~
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