VOL. 8, NO. 4, APRIL 2013 ISSN 1990-6145 ARPN Journal of Agricultural and Biological Science © 2006-2013 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 291 ANTIOXIDATIVE AND BIOCHEMICAL RESPONSES OF WHEAT TO DROUGHT STRESS Mohammad Reza Amirjani and Majid Mahdiyeh Department of Biology, Faculty of Sciences, Arak University, Arak, Iran E-Mail: m-amirjani@araku.ac.ir ABSTRACT Drought stress is considered as an effective parameter in decreasing crop production. Present study was investigated to understand the effect of drought stress on wheat (Triticum aestivum) seedlings under controlled condition. The seeds of wheat were subjected to five levels of water potential. 0 MPa (as control) and -2, -4, -6 and -8 MPa (as treatments) and germination percentage, mean germination time, proline and sugar amounts, chlorophyll contents, maximum photochemical efficiency of PSII and electron transport rate (ETR) have been examined. In addition enzymatic and non-enzymatic response of wheat seedlings to drought have been explored. Germination percentage and mean germination time were affected by different osmotic potentials. The least germination percentage and MGT were obtained from -8 osmotic potential. Drought caused significant losses in relative water content. Total chlorophyll content was reduced in all studied treatments. Drought levels higher than -2 MPa resulted in significant decrease of F V /F M value. ETR, however, observed no significant changes in drought treated seedlings. MDA, AsA and GSH contents increased in relation to the drought period. Activities of enzymatic antioxidants, such as SOD, CAT, APX, POD and GR increased to manage the oxidative stress. Keywords: antioxidant; drought stress; triticum aestivum; wheat INTRODUCTION Regarding to the FAO organization the wheat (Triticum aestivum) crop accounts for about 21% of food and 200 million hectares of farmland worldwide (available from: http://www.fao.org). Developing countries produce and utilize 81% of wheat they consume. In the period leading up to 2020, demand for wheat for human consumption in developing countries is expected to grow at 1.6% each year. The global average wheat yield must be increase during the coming 25 years from 2.6 to 3.5 tones ha -1 . Plants in nature are continuously exposed to many biotic and abiotic stresses. Among these stresses, drought stress is one of the most adverse factors of plant growth and productivity and considered a severe threat for sustainable crop production in the conditions on changing climate. Future climate scenarios suggest that global warming may be beneficial for the wheat crop in some regions, but could reduce productivity in zones where optimal temperatures already exist. Global warming, however, may negatively affect wheat grain yields which potentially increasing food insecurity [1]. High temperature is often accompanied with low water supply, so the primary aim of cereal breeding must be to develop cultivars tolerating both types of stresses [2]. Drought, the result of low precipitation or high temperature, is one of the most important factor limiting yield by restricting most stages of crop growth in arid and semiarid areas [3]. Drought affects about 32% of 99 million hectares under wheat cultivation in developing countries and at least 60 million hectares under wheat cultivation in developed countries [4]. Drought stress can reduce grain yield, therefore, it has been estimated that average yield loss of 17 to 70% in grain yield is due to drought stress [5]. Wheat yields are reduced by 50-90% of their irrigated potential by drought on at least 60 million hectare in the developing world [6]. Drought triggers a wide variety of plant responses, ranging from cellular metabolism to changes in growth rates and crop yields. Understanding the biochemical and molecular responses to drought is essential for a holistic of perception plant resistance mechanisms to water-limited conditions [7]. Chlorophyll which is one of the major chloroplast components for photosynthesis, and relative chlorophyll content has a positive relationship with photosynthetic rate. The decrease in chlorophyll content under drought stress has been considered a typical symptom of oxidative stress and may be the result of pigment photo-oxidation and chlorophyll degradation [7]. Photosynthesis is one of the most sensitive processes to drought stress [8]. The inhibitory effects of drought on photosynthesis may be associated with low CO 2 availability due to low stomatal and mesophyll conductances [9] and/or impairments in carbon assimilation metabolism [10]. Stomatal closure is an early response to drought and an efficient way to reduce water loss in water-limiting environments. Biochemical limitation of photosynthesis also plays an important role under prolonged periods of drought stress [9]. Relative water content (RWC), leaf water potential, stomatal resistance, rate of transpiration, leaf temperature and canopy temperature are important characteristics that influence plant water relations. Relative water content is considered a measure of plant water status, reflecting the metabolic activity in tissues and used as a most meaningful index for dehydration tolerance. RWC of leaves is higher in the initial stages of leaf development and declines as the dry matter accumulates and leaf matures. RWC related to water