What, How, Who & Why of 5 types Plant Hormones?
May 19, 2023
We know hormones cause a lot of changes in humans but did you know that plant hormones serve different functions too?
As plants require sunlight, water, oxygen and nutrition to grow and develop, they also need plant hormones which are naturally produced by the plant itself for proper growth and development.
Plant hormones are simple organic molecules that have several chemical compositions. These plant hormones aid in the plant functioning under stress which helps the plant to tolerate different environmental stresses. Other than that, they also help in ripening of fruit, wilting of leaves, formation of leaves, flowers and stems, etc.
There are five types of plant hormones. Let’s look at each one of them.
Plant Homones: Auxin
The term Auxin is derived from the Greek language whose meaning is ‘to grow’. It is a plant growth promoter and was discovered by the biologist Charles Darwin.
It is one of the most important plant hormones.
If you have ever wondered to yourself, “How does a plant bend towards sunlight?”, it has to do with auxin in the stem.
Auxin plays various roles depending on the place it is produced. It is produced primarily in the parts that are actively growing like the stem. When Auxin is produced by apical buds, root growth and development is promoted.
Auxin is the only plant hormones where transportation happens in one direction. It is transported from the top to the bottom which is why the concentration of auxin is the highest at the top of the plant and decreases once you get closer towards the roots.
The naturally occurring members of this group include IAA (Indole-3-Acetic Acid), IBA (Indole-3-Butyric Acid), 4-Cl-IAA (4-Chloro-Indole-3-Acetic Acid)
The concentration of Auxin is very important for spraying on plants and it should be 5 to 15 ppm. Auxin-based rooting products can be applied at 500-1500 ppm for herbaceous and softwood cuttings.
For woodier tissue, 1000-3000 ppm and not more than 5000 and 10,000 ppm for semi-hardwood and hardwood cuttings respectively.
You can apply this plant hormones by dipping, using powders and quick-dip solutions and post-planting sprays.
Plant Homones: Gibberellin
Gibberellin was originally discovered in Japan and it causes some similar effects that Auxin has on plants but it is in effect a very different hormone.
It is effective in germination, flowering, stem elongation, enzyme induction, etc.
While gibberellins Plant hormones help plants in many areas like leaf expansion, acceleration of the malting process, delaying senescence in fruits, they play the most important role when it comes to stem elongation. Even if applied in low concentration to a bush, the stem starts to grow dramatically.
Knowing about stem elongation is important. For example if you’re a farmer whose business comes from the stem of the plant like sugarcane, it would make sense to apply gibberellins. But if you’re just concerned with plants in a greenhouse, you might want to restrict more gibberellin induction.
The concentration of gibberellin acid should generally range from 0.1 mg/mL to 1 mg/mL. You can apply it using methods like drenching, drip irrigation or by foliar spray.
The best period to apply it is during June through September. Utkarsh Bhim Plus is the go-to product for gibberellins.
Plant Homones: Cytokinin
Cytokinin is involved in cell division and in the making of new plant organs like a shoot or a root. This Plant hormones is produced in the tip of the roots and it travels up the stem.
They delay senescence or the ageing process that leads to death of plants. They also help to heal if the plant gets wounded. Not only that, it regulates immunity by modulating salicylic acid and defending against insects and pathogens. Cytokinin also builds tolerance to drought stress.
Cytokinin and auxin affect plants in several ways. If the concentration of both is equal, normal cell division takes place. If concentration of auxin is more, roots will form whereas if concentration of cytokinin is more, shoots will form.
The other different ways cytokinin helps plants is by promoting the growth of the lateral bud, keeping flowers fresh for a longer time, facilitating adventitious shoot formation and promoting nutrient mobilization that assists delaying leaf senescence.
Plant Homones: Abscisic Acid
Abscisic acid is a growth inhibitor which was discovered in the 1960s.
When our bodies need water, we feel thirsty. This response leads us to taking a break from our work or from the things we are doing and get ourselves a glass of water. The same is not possible for plants, especially during droughts.
This is when plants produce a chemical messenger named as “abscisic acid” that alerts the rest of the plant that it is feeling water stressed. When this message is sent, the guard cells spring to attention and alerts the stomata to close. No more water is then able to exit the plant and thus it can increase the plant tolerance to water stress and other types of stress.
This abscisic acid – Plant hormones is made in droughted roots, droughted leaves and developing seeds and it has the ability to travel both up and down in a plant stem.
The various functions of abscisic acid are inhibiting plant metabolism and germination, regulating abscission and dormancy, helping in the maturation and development of seeds and inducing seed dormancy that helps in withstanding desiccation and various undesired growth factors.
Plant Homones: Ethylene
Ethylene is a gaseous plant hormones that affects ripening and rotting in plants. No other plant hormone except ethylene is gaseous.
Another interesting fact about ethylene is that it can be produced in almost any part of the plant and can diffuse through the plant’s tissue and go outside of the plant and travel to a totally different plant. Isn’t that amazing?
Ethylene is an unsaturated hydrocarbon which has double covalent bonds between and adjacent to carbon atoms. It can be used both as a plant growth promoter and plant growth inhibitor.
The many different functions of ethylene are that they promote sprouting of potato tubers, induce flowering in the mango tree, break the dormancy of seeds and buds, facilitate senescence and abscission of both leaves and flowers and stimulate the ripening of fruits like tomatoes and citrus fruits.
You can apply it in gaseous form or by spraying and dipping.
The formation of ethylene requires oxygen. The agriculture industry controls the partial pressure of oxygen and carbon dioxide while the produce is in the truck to prevent ethylene synthesis and thus slowing down the ripening process. This becomes important when the produce has to be transported miles away and growers don’t want their produce to go bad even before it is sold.
Plant Homones: Conclusion
There is so much interesting that goes on behind the mechanisms of the way a plant functions. Plant hormones is one such important mechanism. It not only aids in proper growth and development but it also acts as a growth inhibitor when required.
Knowing about plant hormones, their functions and the proper time to use them can be really beneficial to your agriculture business and can aid in having a healthy and proper yield.
To know more about plant hormones, you can see the detailed video: https://youtu.be/DnHWSdMzt00
Feel free to contact Utkarsh for any doubts and advice on Plant hormones.
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