[Nanoscale silicas in oryza sativa L. and their UV absorption]

To reveal the unique microstructure of silica in rice and its absorption of ultra violet, wet digestion was chosen to isolate silica bodies from rice leaves and bract according to the fact that concentrated acid cannot destroy glass made of SiO2. A mixed solution of sulfuric and nitric acids was applied to the leaves and bract of rice, respectively. After keeping the treated samples in 60-70 "C water bath for 30 hours and times of washing and sedimentation in water, pure silica bodies were obtained. The detection by X-ray photoelectron spectroscopy(XPS) indicated that there was 35. 05% of carbon 10 nm under the surface of the silica body, much more than the amount of 5. 88% on the out surface which might be due to the contamination of the air contact with the sample. This fact showed that acid couldn't get into the silica body to oxidize the inner organic compounds to alter the structure, therefore the chemical and physical properties of the silica measured could account for the original status in the leaf and bract. Scanning electron microscopy and transmission electron microscopy observation revealed that the silica body of rice is made up of inseparable SiO2 particles of 1-2 nm, sticking slackly to form nano-scale rods of average 45 nm wide and arranging in the same direction. Besides, there were lots of pores inside the inner part of the silica body, including both micron-scale pores (< or = 1 microm) and nano interstitial pores(< or =1-2 nm). The bract silica has the greatest absorption at 285 nm of UV-B, while the leaf silica has a very low UV absorption, indicating that silica in the two organs of rice has different mechanism of radiation resistance.