10 Continental J. Agricultural Science 5 (1): 10 - 25, 2011 ISSN: 2141 - 4203 © Wilolud Journals, 2011 http://www.wiloludjournal.com ` Printed in Nigeria MECHANISM OF DROUGHT TOLERANCE IN PLANT AND ITS MANAGEMENT THROUGH DIFFERENT METHODS Muhammad Waseem 1 , Asghar Ali 1 , M.Tahir 1 , M. A. Nadeem 1 , M. Ayub 1 , Asif Tanveer 1 ,R. Ahmad 2 and M.Hussain 3 1 Department of Agronomy , University of Agriculture, Faisalabad, 38040, Pakistan, 2 Department of Crop Physiology , University of Agriculture, Faisalabad, 38040, Pakistan, 3 Department of Botany University of Agriculture, Faisalabad, 38040, Pakistan ABSTRACT Control of drought stress in plant is not only very complex, but is also highly influenced by other environmental factors and by the developmental stage of the plant. Here we review certain physiological responses of plants to a deficit of water include leaf wilting, a reduction in leaf area, leaf abscission, and thereby reducing water loss through transpiration, and increasing the rate of photosynthesis in relation to drought. Critical global scenarios related to water availability for human consumption and crop production anticipated to arise in the near future, and intensive research is currently being conducted on basic and applied issues, from molecular to ecological approaches. Considering that up to 70-80% of the fresh water is utilized for irrigation of field crops, development of plants with less water requirements can contribute much to alleviate the problem of excessive water consumption in agriculture. These responses improve the water-use efficiency of the plant on the short term and we can also improve the resistance in plant against certain stress by genetic manipulation for increased drought tolerance in plants, developing drought tolerant plants by traditional breeding and transgenic approaches. KEYWORDS: Drought stress; photosynthesis; physiological responses; respiration; tolerances mechanism INTRODUCTION Although some of the effects of a rapidly imposed water deficit might be common to those when the deficit is imposed slowly, reproduction of slowly imposed water deficits under field conditions is required when considering a crop’s response to drought. This type of study will allow the evaluation of acclimation processes in mature plants as well as plant resistance to a multistress situation that often is the cause of dramatic losses in agricultural production. Recent studies revealed that molecular and metabolic responses of plants to a combination of stresses are unique and cannot be extrapolated from the separate study of individual stresses (Mittler, 2006). Moreover, from an agricultural perspective, drought is ultimately defined in terms of its effects on yield, since this is the relevant issue when addressing the improvement of crop production under water- limited environments. Consequently, the timing of water deficits during the season (e.g. sowing, crop establishment, flowering, or grain filling) may have a much larger impact on yield than the intensity of drought Aranjuelo et al.,(2011), Pinheiron and Chaves (2011). Adaptation to drought is undoubtedly one of the most complex biological processes. It involves numerous changes including reduced growth, transcriptional activation/inactivation of specific genes, transient increases in ABA levels, accumulation of compatible solutes and protective enzymes, increased levels of antioxidants and suppression of energy-consuming pathways. Drought reduces plant productivity by inhibiting growth and photosynthesis (Taiz, et al.,1998). A positive correlation between photosynthesis rate and crop yield is commonly found (Pooter and Remkes, 1990), but factors changing assimilate partitioning and utilization can reduce this association (Guo et al., 2002). Alteration of growth patterns in plants contributes to survival under water depletion conditions. An increase in root to shoot ratio is found commonly in physiological studies on the effects of drought on plants. Growth arrest can be considered as a medium by which plants can preserve carbohydrates for sustained metabolism, prolong energy supply and recovery faster after stress relief. On the other hand, continuation of root growth increases the exploratory capacity of plants in deeper more humid soil layers. Reduction of photosynthesis under restricted