[Biology Class Notes] on Stress Hormones Pdf for Exam

Stress hormones modulate many aspects of body functioning (plants and animals) in a genomic fashion. To understand the mechanisms that underlie stress hormone-mediated effects, profiling stress-responsive gene patterns may be useful to generate new hypotheses.

Stress hormones definition: As the human body perceives stress, certain glands produce and release specific hormones into the bloodstream for a response. These hormones are often called stress hormones and they cause various physical effects that increase your heart rate and blood pressure. They can also be found in the plant body.

In general, stress hormones can be categorised into: 

1. Human stress hormones

2. Plant stress hormones

The following is a summary of both stress hormones.

Human Stress Hormones

These are hormones that secrete in response to stress or an emergency and are responsible for a reaction known as fight or flight:

There are Three Types of Human Stress Hormones:

1. Epinephrine or adrenaline

2. Nor-adrenaline or nor-epinephrine

3. Glucocorticoids

Epinephrines and Norepinephrines (Called Together as Catecholamine)

Epinephrine (adrenalin) and Nor-epinephrine (noradrenaline) create an immediate reaction under stress. They increase the rate of respiration, increased alertness, heartbeat, pupillary, sweating, dilation and piloerection (raising of hairs. 

• Catecholamines stimulate the breakdown of glycogen thus increasing blood glucose levels. The surge of energy that might be required to run away from a dangerous or harmful situation.

• Catecholamine also stimulates the breakdown of proteins and lipids.

• These hormones shift the blood flow away from areas that are less crucial under stress conditions to areas such as muscles which need it more during stress.

• Depending on the situation, it may take half an hour to two days to return to the normal resting state.

• Epinephrine acts on adipose tissue and releases free fatty acids into the circulation.

• Epinephrine is an effective stimulant of heart action. It increases the irritability and the rate and strength of contraction of car­diac muscle and increases cardiac output. It causes vasodilatation of the arterioles of the skin and mucous membranes. Nor­epinephrine has less effect on cardiac output.

• Epinephrine causes relaxation of the smooth muscles of the stomach, intestine, bronchioles and urinary bladder. This hormone is valuable in the treatment of asth­matic attacks.

Glucocorticoids or Cortisol

• Cortisol increases glucose, amino acids and fatty acid levels in the blood.

• In the muscle and adipose tissues, they cause protein depletion.

• In the adipose tissue, cortisol increases lipolysis and in muscle, they cause depletion of stored protein.

• Glucocorticoids increase the levels of alanine-α-ketoglutarate and tyrosine transaminases as well as tryp­tophan pyrrolase.

• They increase the key enzymes in the regulation of gluconeogenesis (Phosphoenolpyruvate carboxykinase, Pyruvate car­boxylase, glucose-6- phosphatase and Fructose-1 6-di-phosphatase).

• In the liver, cortisol acts on the fixation of carbon dioxide at the level of pyruvate carboxylase which is the key enzyme in gluconeogenesis.

• This group of hormones is inactive on red cells, heart and the brain.

• They have immune-suppressive and anti-inflammatory effects.

• They have effects on bone, exocrine se­cretion, cyclic AMP and stress.

Plant Stress Hormones:

When plants are exposed to different types of stress such as salinity, heat, cold and drought etc. Phytohormones play an integral role during stressful conditions and assist the plant body in adapting to adverse environmental conditions. 

Several phytohormones like Salicylates, Jasmonates and ABA interact together and act in hormone signal transduction cascade or “crosstalk” between hormones to form a defence network against environmental stresses. An important plan for stress hormone is Abscisic acid.

Abscisic Acid (ABA)

(ABA) acts as a plant growth inhibitor and regulates dormancy and abscission. It is called a stress hormone because the synthesis of ABA is stimulated by stressful environmental conditions such as waterlogging, drought etc. It plays a critical role in tolerating abiotic stress. The functions of ABA are mentioned below: 

• This hormone stimulates the closure of stomata during high salinity and reduces the loss of water by transpiration. ABA interacts with other phytohormones such as nitric oxide, Jasmonates and signalling molecules to induce stomatal closure.

• Abscisic acid induces seed dormancy and thereby helps seeds to withstand unfavourable conditions such as desiccation for the growth. 

• ABA also plays a role in the growth and modification of the root system during nitrogen deficiency and drought. It regulates gene expression that’s required for water uptake and root growth maintenance.

• The hormone regulates protein-encoding genes and biosynthesis of fats (lipids) and storage proteins.

• ABA plays a critical role during signal transduction pathway during a stress response.

• This hormone is involved in the synthesis of osmoprotectants, dehydrins and protective proteins.