Water Stress - Types, Causes And Response Of Plants To Water Stress
It has been discovered that water stress is the most significant limiting factor that plays a role in controlling primary production in terrestrial environments.
The rate of transpiration in plants will slow down when there is less water available to the roots of the plant, which is what we mean when we talk about water stress.
It is most commonly brought on by a lack of water, which may be due to conditions of drought or the salinity of the soil.
The disruption of agricultural production that results from water stress ultimately leads to a decrease in the amount of food that is produced globally, which in turn causes starvation.
One of the most common environmental factors that affect plant growth is stress caused by an insufficient supply of water.
COPYRIGHT_WI: Published on https://washingtonindependent.com/water-stress/ by Katya Ryder on 2022-08-15T01:05:26.089Z
Types And Causes Of Water Stress
A study found that aspen seeds under stress showed a decline in shoot water potential after 17 hours.
After 20 hours of stress, shoot water potential fell rapidly. Here are a few plant water stress types and their contributing factors.
Drought stress affects plants earlier than you think. (Infrared time-lapse)
Mild Water Deficit Stress
When applied to pea plants, mild water stress increases leaf senescence by 15 days compared to well-watered pots.
It has been estimated that leaves have a lifespan of 25 days on average.
Mild stress conditions in trembling aspen include increased root hydraulic conductivity and decreased apoplastic tracer dye, indicating increased apoplastic activity.
Mild water stress increases water use efficiency and degrades sugar relative to starch in leaf blades, leading to carbohydrate accumulation.
It has been discovered that the moderate stress leads to a reduction in the total leaf area and leaf biomass that each plant possesses.
This is as a result of fewer new leaves being produced, more leaves being shed, and smaller average leaves.
The two processes most susceptible to water stress are leaf production and leaf expansion.
Severe Water Deficit Stress
When plants are under severe water deficit stress, root volume flux density and hydraulic conductivity decrease, increasing the apoplastic root flow pathway.
Severe drought downregulates metabolic processes, reducing RuBP and inhibiting photosynthesis and CO2 assimilation.
In trembling aspen, severe stress reduces root hydraulic conductivity and increases apoplastic tracer dye.
Severely water-stressed plants increase osmolality in sap and proline in leaves.
Assimilation of carbon dioxide and stomatal conductance decrease, increasing water use efficiency. Stomatal index increases in stress, but not severe stress.
Moderate Water Deficit Stress
Moderate water deficit stress doesn't harm plants and can be reversed.
In bean plants under moderate stress, stomatal conductance and net photosynthetic rate decrease. There was no evidence of photoinhibition.
Reduced electron transport in stressed plants can be reversed.
Moderate water stress causes barley root dehydration and leaf dehydration under prolonged stress.
Effect Of Water Stress On Plants
Plants respond differently to water stress.
Mild water deficit stress has the same effect on all plants.
Under stress, switchgrass leaf dry matter is high.
Water stress on chickpea and soybean plants showed that soybeans are more susceptible to damage.
Under stress, chickpea root water content rises.
Drought-induced activation of lignin enzymes reduces forage growth and digestibility.
Biostimulants & Abiotic stress
Assimilation Of Carbon Dioxide
The photosynthetic assimilation of carbon dioxide is reduced when there is water stress.
Two factors account for this decline.
The stomatal closure restricts carbon dioxide diffusion in the leaf, and water stress inhibits carbon dioxide metabolism.
This stress affects carbon dioxide assimilation more than oxygen evolution, so the increase in carbon dioxide does not affect assimilation.
Experiments on cowpea show that stomatal closure reduces internal carbon dioxide and restricts water loss through transpiration.
Effects On Photosynthesis
Cowpea experiments revealed that photochemical activity is unaffected in the early stages of water stress.
In advanced stress, photosystem II activity and maximum quantum yield decrease.
Water stress has no impact on the overall efficiency of photosynthesis.
It takes three days for the plant to fully recover after re-watering.
If drought stress is mild, Rubisco activity and RuBP content won't limit photosynthesis.
Water stress shifts electrons from cytochrome to alternative pathways.
In drought-stressed plants, electron partitioning increases by 40%.
Under water stress, photosynthesis inhibition affects plant growth, survival, and yield.
In response to water stress, photosynthetic potential decreases due to impaired metabolism.
As a result, both the assimilation of carbon dioxide and the relative water content decrease.
As photosynthetic potential and ATP synthesis decline, ribulose bisphosphate synthesis is limited.
Reduction Of Growth Rate
Hydraulic signaling includes reduced root growth, water uptake, water potential, turgidity, and leaf enlargement.
Water stress causes the plant's water potential and transpiration rate to decrease.
As a result, the plant cell is harmed due to a decrease in cell turgor and relative water content.
A maize study found that drought affects plant height, leaf area index, grain yield per hectare, number of ears per plant, grain yield per cob, and 1000-kernel weight.
Drought reduces plant dry weight by 28–32 percent.
Long-term water stress reduces grapevine stomatal conductance and CO2 assimilation.
Reduced CO2 absorption reduces ribulose bisphosphate activity.
Stomatal conductance and photosynthesis are found to be highly correlated. Under water stress, cell growth is inhibited and root growth is favored.
When applied to plants, water stress can have a variety of effects on both the roots and the leaves.
With root water stress, osmotic adjustment occurs quickly, allowing partial turgor recovery and re-establishment of the osmotic gradient for water uptake.
Additionally, the cell wall's capacity to loosen also declines.
This enables the root to continue growing even when under stress.
Under the same water stress, leaves show slow osmotic adjustment and wall-loosening ability, inhibiting growth.
Reduced plant height, total fresh weight, and total dry weight are all effects of water stress in plants.
The rate at which soybean plants exchange carbon is decreased by ongoing water stress. As a result, the yield is 39% lower and the seeds are 23–33% smaller.
In the initial stress revealing phase, an increase in the carbon exchange rate is observed.
By relieving the plant of its stress, senescence brought on by water stress cannot be stopped. Short bursts of stress during seed filling have significant consequences.
Another crucial element of water stress in plants is water use efficiency (WUE).
Through the use of agricultural practices, the WUE can be increased by lowering the amount of water lost through evaporation from the soil surface.
Metabolic Changes
Recent trends and techniques like proteomics, transcriptomics, and metabolomics reveal plant stress response mechanisms.
In water-stressed cowpea leaves, soluble sugars accumulate.
Water stress on oil-producing plants causes an increase in oil accumulation, primarily carvacrol and gamma terpinene.
When under moderate stress, carvacrol concentration rises while terpinene concentration falls.
Early Water Stress Response And Signal Transduction Pathways
Through catalytic processes like phosphorylation, membrane-localized receptor and sensor proteins communicate information to cytoplasmic target proteins.
The first step in determining the water status of the environment outside may involve signaling at the plasma membrane.
Osmotic-stress signaling in prokaryotes is mediated by AHK1, an Arabidopsis plasma membrane HK.
AHK1 also functions as an osmosensor.
Arabidopsis developed drought resistance due to AHK1 overexpression.
AHK1 is an osmosensor and a positive regulator of osmotic-stress signaling, as shown by the decreased abscisic acid (ABA) sensitivity and downregulation of ABA and/or stress-responsive genes in AHK1 mutants.
As a multiple His-Asp phosphorelay, it appears that AHPs and ARRs regulate the downstream AHK1 cascades.
It is unclear which components make up signaling cascades or which factors are affected by AHK1 signals.
According to research on Arabidopsis, the ABA and drought signaling are negatively regulated by the cytokinin (CK) receptor HKs, AHK2, AHK3, and AHK4.
Numerous ahk2, ahk3, and ahk4 mutants are ABA-sensitive and drought-resistant.
These findings imply that there is cross-talk between the ABA, CK, and stress signaling pathways.
In Arabidopsis, there are more than 600 members of the receptor-like kinase (RLK) family, with LRR-RLKs constituting the largest subgroup.
The plasma membrane-localized RLKs are the first step in the osmotic-stress signaling pathway in many plant species.
It is possible that environmental stimuli can activate RLK-mediated signaling pathways and transmit external osmotic conditions because these stress-related RLKs have a variety of extracellular domains (such as an LRR domain, an extensin-like domain, or a cysteine-rich domain).
Recent studies suggest that RLKs that bind to cell walls, such as CrRLKs (Catharanthus roseus RLK1-like family), proline-rich extensin-like receptor kinases (PERKs), and WAKs, may play a role in the perception of turgor pressure.
An association between RLKs and cell-wall binding, ABA biosynthesis, and the water stress response may be discovered by examining the roles of RLKs in signaling systems linked to mechanosensing pathways activated by water stress.
This finding may contribute to our understanding of the early signaling mechanism that regulates growth and tolerance to water stress.
Protecting Photosynthesis During Water Stress
Plant photosynthesis is impacted by the reduced carbon dioxide (CO2) availability caused by stomatal closure and/or photosynthetic metabolism.
Excess light (EL) reduces photosynthesis when water stress lowers rates of photosynthesis.
An estimated 70% of the genes activated by EL are also activated by drought. EL promotes the production of reactive oxygen species (ROS), such as H2O2, superoxide (O2-), and singlet oxygen (1O2), which also inhibits photosynthesis, through photochemical and biochemical processes.
Several genes are up-regulated by H2O2, some of which overlap with genes that are also up-regulated in response to methyl viologen, extremely cold or hot temperatures, or protracted drought.
Cytosolic ascorbate peroxidase (APX)-encoding genes (cytosolic APXs) transcription is induced by light stress and the plastoquinone redox state. These genes help remove hydrogen peroxide from cytosol.
Degraded chloroplast proteins accumulated in APX loss-of-function mutants, indicating that APXs shield chloroplast proteins from ROS under EL conditions.
It is possible that APX mediates ROS scavenging in response to oxidative stress and nutrient limitation because AtAPX2 was also induced by drought stress and ABA.
Gain-of-function mutant altered apx2 expression 8 (alx8) with increased APX2 expression enhanced Water use efficiency (WUE) and drought resistance.
In Arabidopsis, plants exposed to EL or ROS treatment induce the zinc-finger TFs ZAT10 and ZAT12. APXs and other stress-related genes were induced by ZAT10 and ZAT12 overexpression.
Increased drought stress tolerance was seen in several transgenic lines that overexpressed ZAT10.
The regulation of ROS-mediated responses to EL and drought by ZAT10 and ZAT12 may safeguard photosynthesis under water stress.
People Also Ask
How Do You Fix A Water Stressed Plant?
Stomatal closure slows photosynthesis when there is not enough water.
Compost and other organic matter should be continuously added to your soil to help it retain moisture.
How Does Water Stress Affect Root Growth?
In all soil segments, root growth was prolific as water stress intensity increased.
Soil water in the lowest segment is used to maintain plant turgor, which supports leaf and root growth during water-stress treatment.
What Are The Types Of Water Stress?
Physical and economic scarcity are the two main categories of water scarcity.
A region experiences physical, or absolute, water scarcity when demand exceeds the region's meager water supply.
What Are Three Signs Of Water Stress In Plants?
Under long-term water stress, plants may wilt or stop growing, and they may have discolored leaves, flower buds, and flowers.
Plants may eventually die. Ground covers will start to show bare spots.
Weeds, insects, and diseases can affect water-stressed plants.
Conclusion
Presently, drought stress is a major limitation to crop expansion.
This problem is extending its tentacles to those regions where it was negligible before. This is due to the overall change in the global climate.
The crop genotypes and cultural practices for crop growth should be enhanced, especially in drought-prone areas, to combat this.
It is necessary to study plant resistance mechanisms under drought stress.
Research on genes associated with drought stress should be performed to deal with the current scenario.
Modeling techniques can be applied to plants.
Drought-tolerant transgenic plants can be generated and the quantitative trait locus (QTLs) for drought tolerance can be identified in various plant species.
There is an immediate need for a better understanding of methods and techniques that enable plants to adjust to a shortage of water as well as sustain growth and production during drought.
This will ultimately result in a better and improved selection of drought‐tolerant clones in the near future.
In the future, further studies on drought stress and photosynthesis are required, so that plants' life cycles and physiological mechanisms can be better understood.
