3. 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture 3

4. Drought is one of the major ecological factors limiting crop production and food quality globally, especially in the arid and semi-arid areas of the world. Among crop plants, wheat (Triticum aestivum), which often experiences water-limited conditions, is an attractive study system because of the natural genetic variation in traits related to drought tolerance (Loggini et al., 1999). 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture 4

5. Extreme environmental conditions that induce oxidative stress have been associated to an increased carbonyl groups content and to an induction in protease activity.

6. 68/5/2015 Objective: The objective of the present study was to investigate mechanisms responsible for acclimatization to drought in two wheat cultivars, Veery (drought tolerant) and Sids-1 (drought susceptible) subjected to two drought phases interrupted by 2d re-watering period. 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

7. 7 For these purposes the glutathione system of the tissue and its relation to protein synthesis was investigated in both cultivars upon dehydration and rehydration. Also to understand the role of proteolysis in the response to drought stress. 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

8. 8/5/20158 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

9. 98/5/2015 Estimation of Relative Water Content (RWC) Determination of Oxidative stress indices (protein oxidation) Glutathione determination Glutathione reductase (GR) assay Measurement of azocaseinolytic activity Two wheat (T. aestivum L.) cultivars, namely Veery (drought tolerant) and Sids-1 (drought susceptible) were used in this study for: 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

11. Fig. (1): relative water content (%) (A) and Carbonyl group content (B) of well watered and drought stressed wheat cultivars CV Sids-1 (sensitive) and CV Veery (Tolerant) subjected to two drought phases interrupted by 2d re- watering. Each value represents the mean ±SE of five replicates. Cont. Sids-1 = Control of sensitive cultivar; cv Sids-1= drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv Veery; drought stressed tolerant cultivar, 2 Rew; 2 days rewatring. Significant differences (P<0.05) between treatments according to LSD test are shown by an asterisk. 8/5/201511 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

12. Fig. (2) Changes in glutathione status, GSH, GSSG and GSG/GSSG ratio in wheat cultivars cv sids-1 and cv Veery exposed to two drought cycles interrupted by 2d re-watering (2Rew). Each value represents the mean ±SE of five replicates. Cont. Sids-1; Control of sensitive cultivar, cv Sids-1; drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv Veery; drought stressed tolerant cultivar, 2 Rew; 2 days re-watering. Significant differences (P<0.05) between treatments according to LSD test are shown by an asterisk. 12 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

13. Fig. 3 : Glutathione reductase (GR) activity of well watered and drought stressed wheat cultivars Cv Sids-1 and Cv Veery subjected to two drought phases interrupted by 2d re-watering. Each value represents the mean ±SE of five replicates. Cont. Sids-1; Control of sensitive cultivar, cv Sids-1; drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv Veery; drought stressed tolerant cultivar, 2 Rew; 2 days rewatring. Significant differences (P<0.05) between treatments according to LSD test are shown by an asterisk. 13 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

14. Fig. (4): Total protein content (A) and Azocaseinolytic activity (B) of well watered and drought stressed wheat cultivars CV Sids-1 (sensitive) and CV Veery (tolerant) subjected to two drought phases interrupted by 2d re-watering. Each value represents the mean ±SE of five replicates. Cont. Sids-1; Control of sensitive cultivar, cv Sids-1; drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv Veery; drought stressed tolerant cultivar, 2 Rew; 2 days rewatring. Significant differences (P<0.05) between treatments according to LSD test are shown by an asterisk. 14 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

15. 15 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

16. A significant increase of carbonyl concentration in response to drought stress in both cultivars tested and after prolonged drought stress, indicating the presence of oxidized protein which are selectively recognized and degraded by proteolytic enzymes (Fig.1B) The ratio of GSH to GSSG was directly related to the level of drought stress, however, after 2d re-watering, the acclimatized wheat leaves for both cultivars showed higher values at the end of the second drought phase when compared to the results obtained after the completion of the first drought phase (Fig. 2C). 8/5/201516 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

17. The high activity of GR, especially during the first drought phase, maintained glutathione pool in its reduced status. This is confirmed by the different behavior of cultivars, in which a relative low GR activity, also at high degree of drought, was associated with low GSH and high GSSG levels (Fig. 2 A, B and Fig. 3). 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture 17

18. Lower azocaseinolytic activity was referred to cultivar type in order of increasing drought stress and associated with a distinct reduction of soluble protein content in the wheat leaves. Drought has been associated with decreased protein levels, increased proteolytic activity, and the up-regulation of cysteine protease genes (reviewed in Beers et al., 2004). 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture 18

20. The recent literature confirms a central role of glutathione metabolism in plant responses to environmental stress. The results showed that antioxidant protection in both cultivars are mainly due to the enzymes and molecules involved in glutathione metabolism and re-watering regulates the timing of drought effect in part by delaying the increased proteolytic activity and subsequent protein degradation. 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture 20

21. Genetic, Physiological and Biochemical responses of some plants to interactive biotic and abiotic stress. Effect of some cumulative stress on the ultra- structure and antioxidant isozymes of some economically important plants. 218/5/2015 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture

22. 8/5/2015 This research was supported through the research center of Teachers College at King Saud University, project no. 12/1427. The author would also like to thank Dr. Salah Barakat, Professor of Plant Physiology, Botany Dept., Faculty of Science, Alexandria University for his comments and revision on the manuscript. 22 2 nd International e-Conference on Agricultural Biosciences 2009 Conference website: http://www.e-conference.elewa.org/agriculturehttp://www.e-conference.elewa.org/agriculture