AGRICULTURAL RESEARCH COMMUNICATION CENTRE www.arccjournals.com *Corresponding author’s e-mail: srngsapre27@gmail.com. 1 Department of Biochemistry, College of Agriculture, Junagadh Agricultural University, Junagadh- 362001. Gujarat. India. Agricultural Reviews, 37 (2) 2016 : 109-116 Print ISSN:0253-1496 / Online ISSN:0976-0539 Role of silicon under water deficit stress in wheat: (Biochemical perspective): A review Sarang S. Sapre* and Dinesh N. Vakharia 1 College of Agriculture, Junagadh Agricultural University, Amreli-365 601, Gujarat, India. Received: 16-09-2015 Accepted: 11-05-2016 DOI: 10.18805/ar.v37i2.10736 ABSTRACT Silicon’s role in mediating resistance against various stresses has been a matter of focus in the past decade. Poaeceae family plants are known as high accumulators of silicon. Wheat shows rapid absorption, the optimum accumulation of silicon occurring at around 20 days. Silicon plays a role as a mechanical and a physiological barrier. It also alters the levels of osmolytes and antioxidant enzymes which are a first line of defense in the water deficit stress; also reducing the levels of oxidative stress factors such as hydrogen peroxide. But the results vary with respect to the modes of stress application and its duration. Nowadays, foliar mode of silicon application is carried out compared to the traditional soil application yielding some promising results. Further studies are needed to confirm the mechanisms governing protection which can be done with the comparison of the transcriptome analysis of the stressed plants and also microscopic studies revealing the site of deposition. Key words: Antioxidant enzymes, Osmolytes, Silicon, Wheat, Water deficit stress. Many compounds (resistance elicitors) have been shown to increase the resistance of plants to pests and pathogens by priming the resistance response prior to infection. The concept of induced disease resistance to reduce subsequent infection is well established. Fewer compounds have so far been tested for their ability to induce resistance to abiotic stress e.g. drought and the molecular mechanisms of such induced resistance to abiotic stress are still poorly understood. Compounds such as abscisic acid, aminoalcohols, ascorbic acid,  -amino butyric acid, cytokinin, glycine betaine, nitric oxide, paclobutrazol, putrescine, salicylic acid, silicon (Si), triazoles are a few of the examples which are able to confer drought resistance. Silicon- An outline: Role of silicon with regards to plant nutrition was speculated quite earlier as cited by Lewin and Reimann (1968); but during that phase there was a lack of physiological studies governing the metabolic and biochemical events resulting in silica deposition in higher plants (Epstein, 1965). Silicon comprising 28% in mass is the second most abundant element after oxygen in the earth’s crust (Ahmed et al., 2014; Ma and Yamaji, 2008; Epstein, 1994). Due to weathering, silicon goes into soil solution. Its chemical form in soil solution is silicic acid (H 4 SiO 4 ) at the concentration 0.1-0.6 mM, at pH levels (below 9) found in most agricultural soils (Knight and Kinrade, 2001). This concentration is equivalent to some of the macro elements viz. potassium, calcium etc. and even higher than phosphorus in soil solutions (Epistein, 1994). Silicon is not considered as an essential element for higher plants even though it is accumulated in large amounts by plants of many species (Epistein, 1999; Guntzer, 2012). According to Epstein and Bloom (2005), element is essential if it fulfils either one or both of the following criteria: (1) The element is the part of a molecule which is an intrinsic component of the structure or metabolism of the plant and (2) the plant can be so severely deficient in the element that it exhibits abnormalities in growth, development or reproduction i.e. performance compared to the plants with lower deficiency. Silicon may fit into this criterion of essentiality in the coming future (Liang et al., 2007). Silicon status and its distribution in plants: The silicon content in plant shoot varies from 0.1 to 10% on dry weight basis (Epstein, 1999). Plants can be classified as Si accumulators, intermediates and non-accumulators on the basis of their Si content. Plants of the families Poaceae, Equisetaceae and Cyperaceae show higher Si accumulation (>4%), the Cucurbitales, Urticales and Commelinaceae show intermediate Si accumulation (2-4% Si), while most other species demonstrate little accumulation. Si concentrations of shoot tend to decline in the order liverworts> horsetails> clubmoss> mosses> angiosperms> gymnosperms> fern (Hodson et al., 2005; Currie and Perry, 2007). The silicon concentration in some of the major crops is depicted in Table 1. There is also a genotypic variation in the Si concentration in the shoot within a species, although the variation is usually not as large as the one among species. For example, japonica