Light and electron microscopic and energy dispersive X-ray microanalysis studies of globoids in protein bodies of embryo tissues and the aleurone layer of rice (Otyza sativa L.) grains

Abstract

To understand the differences in mineral nutrient storage within tissues and organs of rice (Oryza sativa L.) grains, the distribution of globoids in rice embryo and endosperm tissues was examined using light and transmission electron microscopy and energy dispersive X-ray microanalysis was used to study globoid composition. Globoids were found in most embryo tissues, including provascular cells, and their location and size in sections of protein bodies is described. While P, Mg, and K were commonly detected in all globoids, other elements such as Ca, Mn, Fe, and Zn were sometimes detected in globoids of specific tissues and (or) regions. High peak-to-background ratios for P were obtained in globoids of scutellar and aleurone cells, and moderately high values were detected in ground meristem regions of the mesocotyl and coleoptile. Relatively high K levels were found in globoids in parenchyma cells of the scutellum and coleorhiza; in provascular cells of the radicle; and in ground meristem cells from the mesocotyl, coleoptile, and plumule. Calcium was mainly detected in globoids of the aleurone layer. Iron was mostly found in radicle tissue globoids. Zinc was commonly found in globoids of the scutellar epithelium and in provascular tissues of the mesocotyl, coleoptile, and radicle. Manganese was distributed throughout most of the tissues examined, but the highest levels of Mn were detected in globoids from the coleoptile tip regions and the plumule. A novel finding was that, in the provascular tissues of the coleoptile tip, distinctive differences were found in Mn, Fe, and Zn storage between globoids in the future xylem and the future phloem. Key words: EDX analysis, embryos, globoids, mineral storage, phytate, Oryza sativa, rice.