Protective effect of silicon on phenolic biosynthesis and ultraviolet spectral stress in rice crop Masakazu Goto a, *, Hiroshi Ehara a , Shyuichi Karita a , Keiji Takabe b , Natsumi Ogawa a , Yutaka Yamada a , Satoru Ogawa c , Mohammed Sani Yahaya a , Osamu Morita a a Faculty of Bioresources, Mie University, 1515 Kamihama-cho, Tsu 514-8507, Japan b Faculty of Agriculture, Kyoto University, Kyoto 606-01, Japan c Faculty of Medicine, Mie University, 1515 Kamihama-cho, Tsu 514-8507, Japan Received 7 May 2002; received in revised form 25 October 2002; accepted 1 November 2002 Abstract A work of ultraviolet microspectrometry and immuno light microscopy of cinnamyl alcohol hydrogenase (CAD) in the cells of leaf blades was carried out on rice plants grown in a paddy field with ( /Si) or without ( /Si) application of a silicate fertilizer. The pattern of silicon distribution on the longitudinal surface of leaf blades by X-ray microanalyzer, morphological characteristics, and gross composition such as silica, other major mineral elements, cellulose, non-cellulosic polysaccharides, lignin and phenolic acids were also compared between both rice plants. The X-ray microanalysis of silicon indicated the higher deposit on dumbbell bodies and other surface area in the  /Si rice plants compared with those of the  /Si rice plants. The  /Si rice plants also showed the lower immuno-reaction of antiserum of the CAD in the cell walls of sclerenchyma, vascular bundle sheath and metaxylem vessel cells. The  /Si rice plants had the lower UV absorbance around 280 and 320 nm in the leaf blades compared with those of the  /Si rice plants. Microscopic observations of leaf blades in both sets of rice plants were also consistent with results of phenolic acids examined. This study suggests that silica fertilization and/or silicate accumulation in the leaves can be associated with decreases of the phenolic biosynthesis in rice plants. # 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Cinnamyl alcohol dehydrogenase; Phenolic biosynthesis; Rice plant; Silica; Ultraviolet microspectrometry 1. Introduction Silica application can improve the growth and yield of various crops, including rice (Oryza sativa L.) [1], sugarcane (Saccharum officinarum L.) [2,3], barley (Hordeum vulgare L.), oats (Avena sativa L.), wheat (Triticum aestivum (L.) Thell.), rye (Secale cereale L.) [4], cucumber (Cucumis sativus L.), and tomato (Lyco- persicon esculentum Mill) [5  /7]. It plays a significant role in the improvements of light intercepting structure, resistance against lodging and pathogenic infection in cereal [8]. As well as reduces the excessive toxicity of some minerals such as manganese (Mg) and iron (Fe) [8]. Similarly, the applications of silica fertilizer have been reported to lower electrolyte leakage in leaves and promote greater photosynthetic activity in rice plant grown under water deficit or heat stress, compared with that treated without silica fertilizer [9]. Also silica deficiency have been observed for spikelet fertility of rice plants at reproductive stage [10], as well as lower chlorophyll content and photosynthetic activity in young leaves of rice plants [11]. Silica in the glumes of rice plants has the important role of protecting their kernel from damage by ultra vio- let (UV) radiation. Kernels in the rice plants were strongly damaged when the plant glumes were artifi- cially removed and exposed to sunlight, but developed normally when covered by an UV-absorbing film [12]. Low molecular UV-absorbing compounds, including hydroxycinnamic acids in Arabidopsis , ascorbic acid * Corresponding author. Tel./fax:  /81-59-231-9494. E-mail address: goto@bio.mie-u.ac.jp (M. Goto). Plant Science 164 (2003) 349  /356 www.elsevier.com/locate/plantsci 0168-9452/02/$ - see front matter # 2002 Elsevier Science Ireland Ltd. All rights reserved. PII:S0168-9452(02)00419-3