Review Article Relevance of Proteomic Investigations in Plant Abiotic Stress Physiology Khalid Rehman Hakeem, 1 Ruby Chandna, 1 Parvaiz Ahmad, 2 Muhammad Iqbal, 1 and Munir Ozturk 3 Abstract Plant growth and productivity are influenced by various abiotic stresses. Stressful conditions may lead to delays in seed germination, reduced seedling growth, and decreased crop yields. Plants respond to environmental stresses via differential expression of a subset of genes, which results in changes in omic compositions, such as transcriptome, proteome, and metabolome. Since the development of modern biotechnology, various research projects have been carried out to understand the approaches that plants have adopted to overcome environ- mental stresses. Advancements in omics have made functional genomics easy to understand. Since the funda- mentals of classical genomics were unable to clear up confusion related to the functional aspects of the metabolic processes taking place during stress conditions, new fields have been designed and are known as omics. Proteomics, the analysis of genomic complements of proteins, has caused a flurry of activity in the past few years. It defines protein functions in cells and explains how those protein functions respond to changing environmental conditions. The ability of crop plants to cope up with the variety of environmental stresses depends on a number of changes in their proteins, which may be up- and downregulated as a result of altered gene expression. Most of these molecules display an essential function, either in the regulation of the response (e.g., components of the signal transduction pathway), or in the adaptation process (e.g., enzymes involved in stress repair and degradation of damaged cellular contents), allowing plants to recover and survive the stress. Many of these proteins are constitutively expressed under normal conditions, but when under stress, they undergo a modification of their expression levels. This review will explain how proteomics can help in eluci- dating important plant processes in response to various abiotic stresses. Introduction T he potentially adverse abiotic stress conditions commonly encountered by plants include extreme tem- peratures, low water availability (drought), waterlogging (flooding), and high salinity and mineral deficiency, which result in significant reductions in the yield of economically important crops (Ahmad and Prasad, 2012a, 2012b; Ahmad and Umar, 2011). These unfavorable conditions bring about alterations in plant metabolism, growth, and development, ultimately leading to plant death (Ahmad et al., 2010a, 2012a; Ashraf, 2010; Manavalan et al., 2009; Tester and Langridge, 2010; Tran and Mochida, 2010a). Being sessile in nature, plants lack mechanisms to escape from adverse conditions. A notable feature of plants to adapt to abiotic stresses is the activation of multiple responses involving complex networks that are interconnected at many levels (Sarwat et al., 2012; Shinozaki and Yamaguchi-Shinozaki, 2007; Tran et al., 2007a, 2007b, 2010b). These complex responses initiated by the signal transduction pathways, via which plants perceive and re- spond to environmental stresses, are not well understood. In many cases, several types of abiotic stress collectively chal- lenge plants (Hadiarto and Tran, 2011; Manavalan et al., 2009; Shinozaki and Yamaguchi-Shinozaki, 2007; Tran and Mochida, 2010a). Proteomics has appeared as an important tool in the field of plant science, enabling us to interpret the stress responses occurring in plants. The vast range of applications of pro- teomics in biological fields has greatly increased its use over the last decade (Bindschedler et al., 2008; Chen et al., 2011; Evers et al., 2012; Kaufmann et al., 2011; Nanjo et al., 2011; Thelen and Peck, 2007; Yang et al., 2011; Yokthongwattana et al., 2012; Zhang et al., 2012; Zheng et al., 2012). The term ‘‘proteome’’ (PROTEins expressed by genOME) represents the survey of the expression of all proteins in a given time and condition. Proteomics is also described as the study of the 1 Molecular Ecology Laboratory, Department of Botany, Jamia Hamdard, New Delhi, India. 2 Department of Botany, Amar Singh College, University of Kashmir, Srinagar, India. 3 Department of Botany, Ege University, Bornova, Izmir, Turkey. OMICS A Journal of Integrative Biology Volume 16, Number 11, 2012 ª Mary Ann Liebert, Inc. DOI: 10.1089/omi.2012.0041 621