Proceedings of ANAS (Biological Sciences), 65(5-6): 49-59 (2010) Response of Photosynthetic Apparatus and Antioxidant Defense Systems in Triticum aestivum L. Genotypes Subjected to Drought Stress Irada M. Huseynova*, Saftar Y. Suleymanov, Samira M. Rustamova Institute of Botany, Azerbaijan National Academy of Sciences, 40 Badamdar Shosse, Baku AZ 1073, Azerbaijan Two wheat (Triticum aestivum L.) genotypes contrasting in architectonics and differing in drought- resistance, Azamatli-95 (short-stemmed, with vertically oriented small leaves, drought-tolerant) and Giymatli-2/17 (short-stemmed, with broad and drooping leaves, drought-sensitive) were grown in field conditions in a wide area under normal water supply and severe water deficit. It was found out that the content of CPI (M r 115 kDa), apoprotein of P 700 with M r 63 kDa and LHCII polypeptides insignifi- cantly increases in the drought-resistant Azamatli-95 under extreme water supply condition while their content decreases in drought-sensitive Giymatli-2/17. The intensity of synthesis of α- and β- subunits of CF 1 (55 and 53.5 kDa) and 33-30.5 kDa proteins also decreases in sensitive genotype. The intensity of short wavelength peaks at 687 and 695 nm sharply increases in the fluorescence spectra (77K) of chloroplasts from Giymatli-2/17 under water deficiency and there is a stimulation of the ratio of fluorescence band intensity F687/F740. After exposure to drought Giymatli-2/17 shows a larger re- duction in the actual PSII photochemical efficiency of chloroplasts than Azamatli-95. The activitites of antioxidant enzymes such as catalase, peroxidase, glutathione reductase and superoxide dismutase dif- ferently change in wheat genotypes during ontogenesis. Keywords: drought, reactive oxygen species, relative water content, photosystem, chlorophyll, sodium do- desyl sulphate, fluorescence, activity, antioxidant enzymes, wheat genotypes INTRODUCTION Plants are subjected to a range of abiotic and bio- tic stresses that affect their growth and development. In particular, it is predicted that water deficit will con- tinue to be a major abiotic stress factor affecting glob- al crop yields (Sharma and Lavanya, 2002). One third of the world’s population resides in water-deficient regions, and with elevated CO 2 levels in the atmos- phere and climatic changes predicted in the future, drought could become more frequent and severe. Wheat is one of the widely cultivated crops in Azerbaijan, where drought is the main abiotic stress limiting its grain yield (Aliev, 2001; Aliyev, 2002). In response to stress, plants activate a number of defense mechanisms that function to increase tolerance to adverse conditions. The response to drought stress which involves a number of biochem- ical-molecular mechanisms is complex. The appli- cation of this emerging understanding to the ge- netic engineering of food crops has already led to examples of improved drought tolerance and in- creased yield under drought (Hu et al., 2008). Production of reactive oxygen species (ROS) and other radicals increases dramatically during water deficiency, and enhanced levels of reactive oxygen species are generated in various intracellular compart- ments in plants and may cause oxidative damage or act as signals (Gechev et al., 2006). The enhanced produc- tion of ROS in chloroplasts and peroxisomes has been correlated with drastic changes in nuclear gene expres- sion that reveals the transfer of 1 O 2 -derived signals from the plastid to the nucleus. Many of the 1 O 2 - responsive genes are different from those activated by superoxide (O 2 •– ) or H 2 O 2 , suggesting that O 2 •– /H 2 O 2 - and 1 O 2 -dependent signaling occurs via distinct path- ways. These pathways could act independently or may interact with each other (Baruah et al., 2009). Plants protect cellular and subcellular system from the cyto- toxic effects of active oxygen radicals with antioxida- tive enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathion re- ductase (GR) as well as metabolites like glutathione, ascorbic acid, α-tocopherol and carotenoids. In response to drought the adaptation shown by many plants could partly be due to changes in membrane composition and phase behavior, which optimizes the fluidity. Indeed, models for thylakoid membrane function require mobility of protein components and redox carriers. Membrane proteins are particularly important for the functionality of the photosynthetic apparatus (Friso et al., 2004). *E-mail: huseynova-i@botany-az.org 49