~ 290 ~    Journal of Pharmacognosy and Phytochemistry 2017; 6(6): 290-293 E-ISSN: 2278-4136 P-ISSN: 2349-8234 JPP 2017; 6(6): 290-293 Received: 06-09-2017 Accepted: 07-10-2017 Guntamukkala Babu Rao PhD. Scholar. Department of Agronomy. Assam Agricultural University, Jorhat, Assam, India Pusarla Susmitha PhD. Scholar. Department of Seed Science and Technology, Anand Agricultural University, Gujarat, India Correspondence Guntamukkala Babu Rao PhD. Scholar. Department of Agronomy. Assam Agricultural University, Jorhat, Assam, India Silicon uptake, transportation and accumulation in Rice Guntamukkala Babu Rao and Pusarla Susmitha Abstract Silicon (Si) is the important nutrient for sustainable production of rice. Rice is a typical silicon accumulating plant and it benefits from silicon nutrition. In the soil, silicon is present as monosilicic acid and polysilicic acid as well as complexes with organic and inorganic compounds such as aluminium oxides and hydroxides. Silicon is absorbed by plant roots as monosilicic acid. Silicon transportation in rice is governed by three genes i.e. LSi1, LSi2 and LSi6. Among these, LSi1 and LSi2 are responsible for transport of silicon from root cells to the apoplast, whereas LSi6 is involved in transfer of Si from the large vascular bundles to the panicles. When the concentration of monosilicic acid exceeds, it gets polymerized to form silica gel (SiO2.nH2O). Silicon is deposited beneath the cuticle as cuticle-silicon double layer in the form of silicic acid. Amorphous silica particles that precipitate in plant cells are called Phytoliths or Plant opal. Phytoliths can be assembled without any energy by polymerization of silicic acid, when its concentration exceeds 2 mM. Phytoliths are found in specific cells called silica cells located on vascular bundles and/or are present as silica bodies in bulliform cells, fusoid cells or prickle hairs in rice. The silica accumulation of plant is higher during the reproductive period. Keywords: silicon, low silica genes, phytoliths, rice, silicic acid Introduction Silicon is the second most abundant element in the earth's crust. The average concentration of Si in the lithosphere is about 28 per cent and in soils normally ranges between 23-35 per cent. It is a principal soil component lost during weathering and the conversions of silicon to secondary minerals are most important mechanisms of soil formation. It is well known that silicon is present in primary silicate minerals, secondary aluminosilicates and various forms of Si02. The amount of silicon present in soils varies with the type of soils, climatic conditions, geological materials, nature of rocks and minerals forming soils etc. However, sandy soils contain more than 40 per cent silicon as compared to 9 per cent silicon in highly weathered tropical soils. Si is a tetravalent Si +4 element, which is not found in free-state. In soil solutions, the prevailing form is monosilicic acid Si(OH)4, which is in equilibrium with quartz (SiO2) and the concentrations in the soil solution is usually ranging from 14 to 20 mg l -1 Si. All soil-grown plants contain Si. However, the Si concentration of plant shoots varies greatly among plant species, ranging from 0.1 to 10% Si on a dry weight basis. It has been estimated that in excess of 200 million tons of silicon are removed annually from arable soils globally when crops are harvested (Matichenkov et al., 2002) [8] . Silicon is not considered as an essential element, but is a beneficial element for crop growth, especially for Poaceae crops. Silicon has been officially designated as a “beneficial substance” by the Association of American Plant Food Control Officials and plant-available Si may now be listed on fertilizer labels. Silicon plays a crucial role in amino acid and protein metabolism. Silica strengthens the plant, protects the plant against disease, insect, and fungi, increases crop production and quality, stimulates active immune systems of plants, increases plant nutrition, increase plant salt resistance and neutralizes heavy metal toxicity in acid soils. Numerous laboratory, greenhouse, and field experiments have shown benefits of application of silicon fertilizer for rice, corn, wheat, barley, and sugar cane. Silicon fertilizer has a double effect on the soil-plant system. First, improved plant-silicon nutrition reinforces plant-protective properties against diseases, insect attack, and unfavorable climatic conditions. Second, soil treatment with bio-geochemically active silicon substances optimizes soil fertility through improved water, physical and chemical soil properties and maintenance of nutrients in plant- available forms. Plants vary widely in their capacity to take up silicon. In accumulating plants, silicon uptake largely exceeds water uptake and in silicon non-accumulating plants silicon uptake is similar to or less than water uptake. In soil, silicon is not a much mobile element to plants. Therefore, a continued supply of this element would be required particularly for the healthy and productive development of plant during all growth stages.