Chemical agents like hormones, osmoprotectants, antioxidants, and chelating agents for abiotic stress mitigation are substances or compounds that are applied to plants to help them survive or mitigate the deleterious effects of abiotic stresses. These chemical agents work through various mechanisms to enhance the plant's stress tolerance and improve its resilience. But last few years application of these chemical agents in agriculture has increased every year, the market is filled with products formulated using chemical agents. In this blog, I try to explain in detail the mechanisms of these chemical agents and how they work in different abiotic stresses.
Phytohormones:
Plant hormones play a crucial role in regulating plant responses to abiotic
stresses. Phytohormones like ABA the most well-known hormone allied with
abiotic stress responses, predominantly drought stress. It works by inducing
stomatal closure, reducing water loss through transpiration, and conserving
water in plant tissues. ABA also induces the expression of stress-responsive
genes, stimulates the synthesis of osmoprotectants, and improves plant
tolerance to drought, salinity, and cold stress. Jasmonates, including jasmonic
acid and its derivatives signaling, activate the expression of stress-related
genes, trigger the synthesis of protective compounds (such as antioxidants),
and modulate stomatal closure and root growth to improve stress tolerance. Ethylene
is a gaseous hormone synthesis that increases under stress conditions and
regulates various adaptive responses. It promotes root growth, enhances the
synthesis of protective compounds, and stimulates senescence and leaf
abscission under stressful conditions. Cytokinins are hormones that regulate
cell division, shoot development, and nutrient mobilization. Cytokinins can
enhance root growth, delay senescence, and improve water and nutrient uptake
efficiency, thereby increasing stress tolerance. Gibberellins are involved in
regulating plant growth and development, including responses to abiotic
stresses. They influence seed germination, shoot elongation, and flowering.
Gibberellins can promote plant growth under stress conditions, help overcome
growth inhibition caused by stress
Antioxidants: Abiotic
stress can lead to the generation of reactive oxygen species (ROS) in plants,
causing oxidative damage. Antioxidants help plants by scavenging reactive
oxygen species (ROS) and protecting cellular structures from oxidative damage. Ascorbic
Acid (Vitamin C) is a well-known antioxidant compound that scavenges ROS,
including superoxide radicals and hydrogen peroxide, reducing their damaging
effects on cellular components. Tocopherols (Vitamin E) are lipid-soluble
antioxidants that act as chain-breaking antioxidants, inhibiting lipid
peroxidation and maintaining membrane integrity under abiotic stress
conditions. Glutathione is a tripeptide composed of cysteine, glutamic acid,
and glycine. It helps neutralize ROS and acts as a cofactor for
several antioxidant enzymes involved in detoxification processes. Some other
antioxidant compounds are carotenoids, anthocyanin, and flavonoids protecting
plant tissues from oxidative damage caused by abiotic stressors. Antioxidant
enzymes, like superoxide dismutase (SOD), catalase (CAT), peroxidases, and
glutathione reductase catalyze the breakdown of ROS and help maintain cellular
redox balance. These antioxidant components work together to neutralize ROS and
minimize oxidative damage in plant cells.
Osmoprotectants:
Osmoprotectants are low molecular weight compounds that accumulate in plant
cells under abiotic stress conditions, helping to maintain cellular osmotic
balance and protect cellular structures. They act as compatible solutes,
reducing water loss and stabilizing proteins and cell membranes. Common
osmoprotectants Proline is one of the most widely studied osmoprotectants that helps
maintain cellular water potential, stabilize proteins and membranes, scavenge
ROS, and act as a molecular chaperone, Glycine betaine is a quaternary ammonium
compound that accumulates in plants under osmotic stress contributes to osmotic
adjustment, protects proteins and membranes, and stabilizes the structure and
function of photosynthetic apparatus, Sugars, such as sucrose, glucose, and
fructose help maintain cellular turgor, stabilize membranes, and protect
proteins and enzymes, Sugars also serve as signaling molecules, regulating
stress-responsive gene expression and metabolic processes. Polyols,
such as mannitol and sorbitol, are sugar alcohols that maintain cellular
osmotic balance, protect cellular structures, and scavenge ROS. Proline
betaine, also known as betaine, is a quaternary ammonium compound that acts as osmoprotectant
by protecting proteins and membranes, maintaining cellular water balance, and
stabilizing enzyme activities.
Chelating Agents:
Some abiotic stresses, such as heavy metal toxicity, can disrupt plant nutrient
uptake and metabolism. Chelating agents, such as Ethylenediaminetetraacetic
Acid (EDTA) is a synthetic chelating agent that forms stable complexes with a
wide range of metal ions, including heavy metals such as lead, cadmium, and
copper. By chelating these metal ions, EDTA helps to reduce their toxicity. Citric
acid is a naturally occurring chelating agent that can form complexes with
various metal ions, including iron, aluminum, and zinc. Citric acid enhances
the solubility and availability of essential nutrients in the soil, making them
more accessible for plant uptake. Humic substances enhance nutrient
availability, improve soil structure, and promote plant growth. They also play
a role in reducing heavy metal toxicity by chelating and immobilizing the metal
ions, preventing their uptake by plants. Phytosiderophores are
organic compounds secreted by certain plant species, primarily grasses, in
response to iron deficiency. These compounds act as chelating agents for iron,
forming stable complexes that can be easily taken up by plants.
Overall, these chemical
agents can be applied as foliar sprays, seed treatments, or soil amendments to increase
plant stress tolerance and improve overall plant health. Every chemical agent
has a separate role in every plant growth stage and type of abiotic stress.
Farmers are confused with products available in the market, and several times
these products not working in field conditions. It’s our duty to provide farmers
with good quality chemical agents and educate them about the use of those
chemical agents.
