Accumulation of phosphorus, magnesium and potassium in developing rice grains: followed by electron microprobe X-ray analysis focusing on the aleurone layer

The levels of P, Mg and K and their distributions in rice grains were followed during the ripening period. These elements were rapidly translocated into the grains between the 10th and 20th day after flowering and thence their amounts remained constant until maturation. The ratio of the electric charges K++Mg2+ to −PO42− (monoester-P) became 1 with maturation. Electron microprobe X-ray analysis of transverse sections of grains indicated that P and Mg began to concentrate in the aleurone layer about the 12 th day after flowering. The accumulation processes and the distribution patterns of P and Mg were very similar throughout the ripening period. In contrast, K was not concentrated in the aleurone layer until the 19th day and its distribution pattern differed from that of P and Mg.