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 -~
The content of nitrogenous compounds in the xylem saps of nodulated and non-nodulated groundnuts was determined. Asparagine and aspartic acid were the main nitrogenous compounds in the xylem saps at the ripening stage of the nodulated groundnut cultivar (PI 259747), grown without nitrogen fertilization in a pot experiment. In contrast, under combined nitrogen available conditions such as nitrogen fertilization, nitrate was a major nitrogenous compound in the xylem saps followed by asparagine and aspartic acid. This phenomenon was particularly conspicuous at the ripening stage of the non-nodulated groundnut line (Nonnod). It was assumed that asparagine was the main transport form of the nitrogen fixed in the nodules of groundnut. The 4-methyleneglutamine compound was not detected or detected only in a trace amount in the xylem saps with an ion-chromatoanalyzer.
Ca compounds combined with the cell wall of the peanut shell were investigated by molecular sieve chromatography. The supernatant centrifuged after digestion of the cell wall by cellulase and the ligneous substances extracted with dimethylsulfoxide were loaded on a Sephadex gel column, respectively. In the former a part of Ca was eluted with the phenolic acids and carbohydrates, while in the latter Ca was eluted with lignin and the carbohydrates in the void volume. The major components of the phenolic acids were p-coumaric, caffeic, and ferulic acids. In the normal shell, the molar ratio of Ca to caffeic acid of the phenol-carbohydrate complexes was approximately 1, while in the Ca deficient shell the ratio decreased to about 0.7, mainIy due to an increase in the caffeic acid moiety of the complexes. In the cell wail of the peanut shell, the presence of a Ca chelate bridge more stable than ionic bonds was suggested.
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