Abstract
Biologically formed amorphous silica (biosilica) is widely found in diatoms, marine sponges, terrestrial plants, and bacteria, some of which have been well characterized. Although rice plants produce large amounts of biosilica (plant opal) in their leaf blades and rice husks, the molecular mechanism of biomineralization is still poorly understood. In the present study, we investigated the fundamental properties of plant opal in leaf blades of the rice plants (Oryza sativa) by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy. The number of fan-shaped plant opal increases in the motor cells (bubble-shaped epidermal cells) during heading time. High-resolution SEM analysis revealed that the plant opals are composed of nanoparticles, as is the case with diatom silica and siliceous spicule of sponge. Organic matrices in biominerals have been considered to control mineralization. Biosilicas in diatom and marine sponge are formed under ambient conditions using organic matrices, unique proteins, and long-chain polyamines. In this study, we report the establishment of purification method of plant opals from rice leaf blades. Finally, we succeeded in extracting organic matrices from the purified plant opal.
Highlights
Biomineralization is widespread phenomenon by which organisms produce minerals by using organic matrices under ambient conditions (Lowenstam and Weiner 1989)
Biosilica is widely observed in skeleton of diatoms, spicules of marine sponges, spore coats of bacteria, and epicuticles of certain higher plants
In diatoms, glass sponges, and certain facultative bacteria, several organic matrices involved in silica formation have previously been identified, such as unique proteins and long-chain polyamines (LCPAs) (Sumper and Kröger 2004; Shimizu et al 2015; Matsunaga et al 2007; Motomura et al 2016)
Summary
Biomineralization is widespread phenomenon by which organisms produce minerals by using organic matrices under ambient conditions (Lowenstam and Weiner 1989). As in the case of other biominerals, organic matrices in biosilicas are thought to be associated with silica formation. In diatoms, glass sponges, and certain facultative bacteria, several organic matrices involved in silica formation have previously been identified, such as unique proteins (silaffin, glassin, and CotB1) and long-chain polyamines (LCPAs) (Sumper and Kröger 2004; Shimizu et al 2015; Matsunaga et al 2007; Motomura et al 2016). These matrices are highly charged and have been shown to promote silica formation from monosilicic acid solution near a neutral pH. We have investigated the fundamental properties of plant opals by microscopic analyses and extracted an organic matrix from fan-shaped plant opals
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