"Review of literatureassociated with a decline in the cell enlargement and more leaf senescence in A.esculentus under water stress (Bhatt and Srinivasarao, 2005). Development of optimalleaf area is important to photosynthesis and dry matter yield. Water deficit stressresulted reduced leaf growth and leaf areas in many species of plant-like Populus(Wullschleger et al., 2005), soybean (Zhang et al., 2004) and many other species(Farooq et al., 2012). Significant interspecific differences between two sympatricPopulus species were found in a total number of leaves, total leaf area and total leafbiomass under drought stress (Wullschleger et al., 2005). The leaf growth was moresensitive to water stress in wheat than in maize (Sacks et al., 1997) and Vignaunguiculata (Manivannan et al., 2007).The importance of root systems in acquiring water has long been recognized.The development of root system increases the water uptake and maintains requisiteosmotic pressure through higher proline levels in Phoenix dactylifera (Djibril et al.,2005). An increased root growth due to water stress was reported in sunflower (Tahir etal., 2002) and Catharanthus roseus (Jaleel et al., 2008). Greater plant fresh and dry weights under water-limited conditions are desirablecharacters. A common adverse effect of water stress on crop plants is the reduction infresh and dry biomass production (Farooq et al., 2012). Plant productivity underdrought stress is strongly related to the processes of dry matter partitioning andtemporal biomass distribution (Kage et al., 2004). Diminished biomass due to waterstress was observed in genotypes of sunflower (Tahir and Mehid, 2001). However,some genotypes showed better stress tolerance than the others. Mild water stressaffected the shoot dry weight, while shoot dry weight was greater than root dry weightloss under severe stress in sugar beet genotypes (Mohammadian et al., 2005). Reducedbiomass was seen in water-stressed soybean (Specht et al., 2001).10 Review of literatureAnatomical and cytological responses of plants to drought stress In the majority of the plant species, water stress is linked to changes in leafanatomy and ultrastructure. Shrinkage in the size of leaves, decrease in the number ofstomata; thickening of leaf cell walls, cutinization of leaf surface, andunderdevelopment of the conductive system, increase in the number of large vessels,submersion of stomata in succulent plants and in xerophytes, formation of tube leavesin cereals induction of early senescence are the other reported morphological changes(Shao et al., 2008). The root to shoot ratio increases under water-stress conditions tofacilitate water absorption and to maintain osmotic pressure, although the root dryweight and length decrease as reported in sugar beet and Populus (Lisar et al., 2012). AHigher root-to-shoot ratio under the drought conditions has been linked to the ABAcontent of roots and shoots. Water stress is linked to decreasing in stem length in plantssuch as Albizzia (Chaves et al., 2002). Decreased leaf growth, total leaf area and leafarea plasticity were observed under the drought conditions in many plant species, suchas peanut and Oryza sativa (Lisar et al., 2012). Biochemical responses of plants to drought stress To reduce the adverse effects of drought stress, plants have evolvedmultifaceted strategies, including morphological, physiological, and biochemicaladaptations (Ingram and Bartels, 1996; Bohnert et al., 2006). The adaptive response todrought must be coordinated at the molecular, cellular, and whole-plant levels (Yu etal., 2008). Water stress tolerance appears to be the result of production and/oraccumulation of compatible osmotic solutes. By lowering water potential theaccumulation of compatible solutes involved in osmoregulation allows additional waterto be taken up from the environment. Accumulation compatible solutes seem to beinvolved in the process of adaptation to osmotic stress (Hare and cress 1998). The11 Review of literatureaccumulation of osmolytes plays important roles in stress adaptation in addition toosmotic adjustments.Novel roles for some of the osmolytes may include free radicalquenching, the use of reducing power or methyl donor groups during their synthesis(Bohnert and Jensen, 1996).Osmolytes In the process of osmotic adjustment during stress adaptation of plants,osmolytes such as amines (polyamines and glycine betaine), amino acids (proline),sugars (trehalose, fructan), and sugar alcohols (trehalose, mannitol and galactitol) aresynthesized to maintain the osmotic equilibrium and ensure resistance against droughtand cellular dehydration. In principle, the hydroxyl group of sugar alcohols substitutes- the OH group of water to maintain the hydrophilic interactions with the membranelipids and proteins. Thus, these molecules help to maintain the structural integrity of themembranes (Hoekstra et al., 2001; Ramanjulu and Bartles, 2002). Synthesis ofosmolytes in accordance to stress is considered as the crucial event in plant adaptationto stresses. The accumulation of compatible solutes involved in osmoregulation thatallows the plant roots to absorb water from the drying soil. Proline Proline is an imino acid that accumulates in larger quantities and contributes toosmo-protection in various plant species when exposed to osmotic stress (Deuschle etal., 2001). Proline has been known as a compatible osmolyte and a way to storecarbon and nitrogen (Hare and Cress, 1997). Accumulation of proline in plants understress is caused either by increases in the biosynthesis of proline synthesizing enzymesor by preventing or repressing proline degradation (McNeil et al., 1999).Proline alsoacts as a potent antioxidant and inhibitor of programmed cell death (Rejeb et al., 2014).Other functions of proline include a protein stabilizer, a metal chelator, an inhibitor of12 "