Introduction
Stress is any external condition that negatively affects the growth, development, or productivity of plants. Stresses are generally categorized as abiotic and biotic stresses. Abiotic stress refers to any stress caused by non-living units. These include drought, salinity, temperature, rain, heavy metals, etc. While biotic stress is a type of stress due to biological units like bacteria, viruses, fungi, and insects, etc. Under stress, plant triggers a variety of responses such as alteration in gene expression, change in cellular metabolism and growth as well as in crop yield. Due to the stresses, the world faces a huge reduction in the productivity of crops every year.
Drought Stress
Drought stress is one of the most severe stresses affecting plants. The majority of a plant’s fresh biomass consists of water which is very important in carrying out different physiological functions. So, some consider this drought stress the main environmental stress for various plants particularly those present in drought prone areas. However, in case of pseudo drought, plants are unable to take water even though moisture is available in root zones.
Causes of Drought Stress
1: Global warming
2: Rainfall Anomalies
3: Shift in Monsoon Patterns
Effect of Drought Stress on Plants
Decrease water availability to plants effects its growth and development. The degree and duration of drought-related symptoms in plants are significantly influenced by environmental factors such as plant species, growth conditions and stages, soil properties, drought length, intensity, and frequency. The most prominent symptoms in plants under drought stress include increase in rate of senescence in leaf, leaf rolling, wilting, premature fall, yellowing and senescence of leaves etiolation, turgidity, etiolation, premature fall, drooping, closed flowers, scorching of limp leaves, and flower sagging.
Sometimes, plants may die under extreme drought stress condition. But mostly, water deficiency effect the plant growth and development. However, excessive amount of water also effect the growth and development of plants.
Plant Responses to Drought Stress
When plant encounter drought stress, plant adapt different mechanisms to counter the stress. Plant adopt three strategies when exposed to stress. These are stress avoidance, escape and tolerance.
1: Escape Mechanisms
Plants adapt to drought stress by utilizing mechanisms such as rapid development, shortening life cycles, self-reproduction, and seasonal growth. Early flowering is a key escape mechanism, but may reduce growth duration and productivity in some cases.
2: Avoidance and Tolerance
Plant water potential is maintained through stomatal transpiration losses and increased water uptake from established root systems. Overdevelopment of xeromorphic structures like hairy leaves and cuticles can reduce productivity and plant size. Adaptive tolerance mechanisms at the photosynthetic machinery level include reduced leaf area and limited leaf expansion. Exomorphic attributes like trichomes reduce leaf temperature and water loss. Changes in root system, osmotic adjustment, antioxidant defense, solute accumulation, metabolic and biochemical dynamics, and root shoot ratio are common strategies for drought-tolerant plants.
Alleviation of the harmful effects of Drought Stress
Climate change poses a significant threat to global food security and plant production sustainability, particularly drought stress. This stress affects plant growth, development, yield, and biomass, leading to food insecurity. To combat this, plants adopt adaptations that enhance drought tolerance.Using best management practices which are related to plant population, sowing time, soil and nutrient management and plant genotype can help in reducing grain yield losses in crops fields under drought stress. Breeding technologies, molecular and genomics approaches, and practices like seed priming, growth hormones, osmoprotectants, silicon, selenium, and potassium application are being explored. Microbes, hydrogel, nanoparticles, and metabolic engineering techniques can also improve plant tolerance and cell homeostasis. These innovative strategies can potentially increase plant productivity in dry environments, reducing the threat to global food security.
