Table of contentsSummaryIntroductionDrought stressPlant physiologyEffect of drought stress on plants1. Crop growth and yield2. Plant-water relationships3. Nutritional relationships4. Photosynthesis5. Oxidative damageDrought symptoms in plantsPlant response to drought stress1. Escape2. Avoidance3. ToleranceConclusionSummaryDrought stress is one of the most threatened environmental stresses facing humanity. It is the most serious stress limiting agricultural growth and development and furthermore poses a serious threat to global food security. Drought stress occurs mainly in arid and semi-arid regions, under conditions of low precipitation, high and low temperatures, salinity and high light intensity. The dry spell over a certain period of time can lead to water stress conditions in plants that negatively affect the growth and total yield of plants. Plants have evolved different morphological, biochemical and physiological response mechanisms to cope with these environmental stresses, but they are different depending on the plant species. Plants respond to drought stress through various mechanisms such as escape, avoidance, tolerance, use of growth regulators and certain molecules that help them survive high and low temperatures. In this review, we study the effect, mechanism and management of drought stress in plants. Here we discuss various morphological, physiological and biochemical mechanisms that help tolerate drought stress in plants and promote their survival under stressful conditions. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essayIntroductionPlants are generally exposed to various environmental stresses under varying weather and climatic conditions under natural and agricultural influences. Various environmental stresses such as heat, cold, drought, high and low temperatures, salinity, cold, frost and molecular stress affect plants from seed germination to maturity. Water represents approximately 80 to 95% of fresh plant biomass. It plays a very important role in most aspects of growth, development, metabolism, biochemical activities, etc. plants. In the current scenario, water stress constitutes a major environmental stress for plants. Drought stress is one of the most important environmental stresses that limits plant growth, inhibits crop production and distribution worldwide, especially in arid and semi-arid areas. Over the coming decades, with continued increases in dry periods or high temperatures, a drastic increase in drought conditions is expected (IPCC, 2007). Drought stress negatively affects plant growth and limits their total yield potential. It inhibits plant growth, decreases photosynthetic activity, damages the structure and function of organelles, degrades chlorophyll content, includes water loss in leaves and accelerates the aging process in the early stages of plant. Drought stress induces oxidative stresses through the accumulation of reactive oxygen species (ROS) in plant cells. The main target of relative oxygen species (ROS) are membrane phospholipids which preventmembrane damage and increase its permeability and also influence lipid peroxidation (Sharma et al., 2012). Tolerance to drought stress is found in almost all plants, but varies from plant to plant and species to species. Drought stress in plants can be alleviated by different strategies. Plants have various mechanisms to tolerate drought stress. They have the ability to withstand drought to some extent. Certain molecules, proteins, and growth regulators serve as osmolytes to protect the structure and function of cellular components within the cell membrane. Molecules like melatonin regulate different physiological, biochemical and molecular processes in plants and further help the plant to cope with drought stress or to survive under drought stress conditions. Drought stress is an ordinary loss of water, which causes stomata to close and limits gas exchange in plant species. Dehydration is much more serious and can lead to a breakdown in metabolism and cellular structure. To develop or create a new variety of crops to achieve good productivity under water stress conditions, a better understanding of morphological and physiological changes in plants is necessary. Understanding the response of plants to drought is one of the most important and fundamental elements in making plants stress tolerant. Plants can execute various mechanisms such as escape, drought avoidance, and drought tolerance in response to drought stress. Drought escape is defined as the ability of plants to complete their life cycle before the entry of severe stress. Drought avoidance is described as maintaining high tissue water potential instead of soil water deficit. Drought tolerance is the ability of the plant to perform drought stress tolerance functions. Plant Physiology under Drought Stress Under drought stress, plants face many challenges in the physicochemical and molecular functioning of plants, which can ultimately affect the growth, development and yield quality of plants. plants. During drought stress, light mechanization of harvesting leads to a significant decrease in the photosynthetic activity of plants, which ultimately decreases the functioning of the Rubisco enzyme. Photosynthetic performance also decreased due to the dysfunction of the chloroplast structure. Drought conditions also influence the level of carbon dioxide in plants, which is involved in the generation of photosynthetic electron transport. This leads to increased degeneration of ROS activity which directly affects the photosynthetic apparatus and damages the apparatus, thereby decreasing the level of photosynthesis. Due to the dysfunction of the photosynthetic apparatus under drought stress, there is a decrease in photosynthetic rate, stomatal conductance, transpiration rate, photochemical efficiency of PSII and photosynthetic electron transport rate. In the event of drought or water deficit, the closure of the stomata is regulated by the increase in the level of abscisic acid (ABA). This acts as a signaling molecule that regulates the functioning of various physiological and molecular processes. Drought causes a decrease in water potential as well as a decrease in the relative water content of plants. With the decrease in water potential, there is a reduction in the absorption ofmany different macro and microelements, nitrogen transport and metabolism, reduction of compounds such as ammonium transporter, nitrate reductase, nitrite reductase and glutamine synthetase. During water stress at the root zone, there is a significant decline in root tissue growth, which affects nutrient uptake by roots and their translocation to target sites. Effect of Drought Stress on Plants Drought stress affects the range of plant species from their morphological to molecular levels and inhibits the growth and development of plants. The various effects of drought stress on plants are described as follows: 1. Crop Growth and YieldDrought significantly affects the growth and development of crops and limits their yield quality or yield potential. The first effect of drought is that it causes poor germination and poor establishment of the plant population. Drought stress significantly decreases the germination rate and seedling density of various crops. Cell division, elongation and maturation are the overall growth processes of the plant. It also includes physical, chemical, genetic and molecular growth functions. Water deficit conditions, i.e. drought stress, affect these growth functions and result in significant loss in both quality and quantity of produce. Under conditions of severe drought, by decreasing the level of water flow from the xylem to elongating stem cells, cell elongation of higher plants may be reduced and there is a decline in growth rate (Nonami, 1998). During the grain filling phase, starch and carbohydrates are formed. Due to lack of water at the grain filling stage, there is a reduction in the synthesis of sucrose and carbohydrates and a decrease in qualitative yield.2. Plant-water relationshipsPlant-water relationships in plants are influenced by certain factors named as follows: relative water content, leaf water potential, stomatal resistance, transpiration rate, leaf temperature and canopy temperature. During the initial phase of wheat, i.e. the leaf development stage, the relative water content of the leaves is higher and reduces the dry matter accumulated during leaf maturation (Siddique et al., 2001 ). Wheat and rice plants subjected to water stress in the initial stages have lower relative water content than non-stressed plants. When these plants are subjected to drought stress, they exhibit a subsequent decrease in relative leaf water potential, relative water content, and transpiration rate, as well as a significant increase in leaf temperature. The conservative influence of decreased stomatal conductance in non-irrigated plants was overridden by a leaf-air vapor pressure difference caused by the associated higher leaf temperature. Transpiration rates also increase and occur at a high rate due to high temperature during drought stress.3. Nutrient relationships Drought stress limits the availability of total nutrient uptake by plants and the concentration of minerals and nutrients in crop plants is limited. Cellular tissues shrink or eventually become damaged due to severe fluid deficits. There is a limitation in the accumulation and absorption of nutrients in the root zone and their translocation from the.