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Phytohormones & their efficacy in agriculture

Writer's picture: Josef WinterJosef Winter

Plant hormones, also known as phytohormones, play a crucial role in regulating various physiological processes in plants. In agriculture, understanding these hormones can significantly enhance crop productivity and quality. This blog explores the primary groups of phytohormones found in compost—auxins, cytokinins, gibberellins, brassinosteroids, abscisic acid, and salicylic acid—and their functions and how we can croos pollinate this knowledge into an agricultural context.


Firstly, I need to go into some detail as to what we are actually talking about. Phytohormones are chemical messengers produced in minute quantities throughout plants that regulate growth, development, and responses to environmental stimuli. Unlike animal hormones produced in specific glands, plant cells can produce hormones in various tissues. However, it's only when plants enter peak states of health, that they can actually synthesise these hormones through Plant Secondary Metabolism (PSM), critically dependent on specific microbes to support this process.


There are fungal and bacterial colonies all supporting their plant host through numerous mechanisms. But in the context of this blog I want to highlight several bacterial genera producing phytohormones in the soil and during the composting process:


• Pseudomonas, Enterobacter, Bacillus, and Azotobacter produce auxins, gibberellins, and cytokinins as secondary metabolites

• Rhizobium and Bradyrhizobium contribute to hormone production while fixing nitrogen

• Actinomycetes, particularly Streptomyces species, are involved in hormone synthesis during decomposition


Through applying this knowledge we can carry the benefits of these super charged metabolites into our cropping system to enhance the health of the plant-soil system.


Auxins

Auxins are vital for plant growth and development. They influence several processes that are essential for agricultural productivity:


1. Cell Elongation

Auxins promote cell elongation in stems and leaves by loosening cell walls. This elongation is crucial for plants to reach light sources, enhancing photosynthesis and growth.


2. Apical Dominance

Auxins produced at the apical bud suppress the growth of lateral buds, ensuring that the main stem grows more vigorously. This helps maintain a strong central structure in crops.


3. Root Initiation

Auxins stimulate root formation and growth, particularly adventitious roots. A robust root system improves water and nutrient uptake, which is essential for crop health.


4. Vascular Tissue Differentiation

Auxins are critical for developing vascular tissues (xylem and phloem), which transport water and nutrients throughout the plant.


5. Tropisms

Auxins mediate phototropism (growth towards light) and gravitropism (growth in response to gravity), ensuring optimal positioning of leaves and roots for resource acquisition.


6. Fruit Development

Auxins play a significant role in fruit growth, influencing size and shape, which can enhance marketability and yield.


7. Wound Healing

Auxins aid in the healing of damaged tissues by stimulating cell division and tissue regeneration, promoting overall plant resilience.

By applying auxin-based products found in Composts, farmers can enhance rooting in cuttings, improve crop uniformity, and prevent premature fruit drop, leading to higher yields [1][5].


Cytokinins


Cytokinins are another essential group of phytohormones that regulate various growth processes:


1. Cell Division

Cytokinins promote cell division in shoots and roots, leading to increased biomass and improved crop yield.


2. Apical Dominance Regulation

They counteract apical dominance by promoting lateral bud growth, encouraging branching and a bushier plant structure.


3. Leaf Development

Cytokinins are crucial for chloroplast development, enhancing photosynthesis efficiency. They also delay leaf senescence, allowing plants to maintain functional leaves longer.


4. Root Growth

These hormones stimulate lateral root formation and overall root biomass increase, improving nutrient uptake capabilities.


5. Stress Response


Cytokinins help plants cope with abiotic stresses such as drought by regulating water balance and enhancing stress-responsive gene expression.

Growers can utilise this knowledge to improve seed germination rates, promote branching in crops like tomatoes or peppers, and mitigate stress effects during adverse conditions [2][6].

Preparation of a Compost sample for a biomass assay. It's critical composts are composed of sufficient microbiology for the production of phytohormones and other vital metabolites.
Preparation of a Compost sample for a biomass assay. It's critical composts are composed of sufficient microbiology for the production of phytohormones and other vital metabolites.

Gibberellins


Gibberellins are crucial for promoting growth and development in various crops:


1. Stem Elongation

Gibberellins stimulate cell elongation, resulting in taller plants that can better compete for sunlight—a vital factor for crops like cereals.


2. Seed Germination

These hormones activate enzymes that break down seed reserves during germination, ensuring rapid sprouting and uniformity in crop emergence.


3. Flowering Induction

Gibberellins play a role in flowering by promoting the development of floral organs, which is particularly important for fruit-bearing plants.


4. Fruit Size Enhancement

Application of gibberellins during fruit development can increase size and improve quality—beneficial for crops like grapes and apples.

Farmers often apply gibberellins to enhance growth rates, synchronise germination times across fields, and improve fruit & seed quality, espicially within the context of arable agriculture [3][7].


Brassinosteroids


Brassinosteroids (BRs) are a class of hormones that significantly impact plant physiology:


1. Growth Promotion

BRs stimulate both cell elongation and division, leading to increased plant height and biomass—critical for maximising yield potential.


2. Stress Tolerance

These hormones enhance a plant's ability to withstand abiotic stresses such as drought or high salinity by improving water use efficiency and maintaining ion homeostasis.


3. Nutrient Uptake

BRs can increase nutrient uptake efficiency from the soil, aiding overall plant health and productivity.


4. Disease Resistance

They help induce systemic resistance against pathogens, protecting crops from diseases caused by bacteria or fungi.

Brassinosteroid applications improve seedling vigor after transplanting, enhance flowering rates, and boost overall crop resilience [4][8].


Abscisic Acid

Abscisic acid (ABA) plays a key role in managing plant responses to environmental stress:


1. Drought Response

ABA regulates stomatal closure during drought conditions to reduce water loss, helping plants conserve moisture.


2. Seed Dormancy

This hormone promotes seed dormancy until conditions are favourable for germination, ensuring successful establishment of new plants.


3. Stress Tolerance

ABA enhances tolerance to abiotic stresses such as salinity or cold temperatures by modulating gene expression related to stress responses.

Farmers can manage ABA levels through irrigation practices or soil amendments to optimise water use efficiency during dry periods [6].


Salicylic Acid

Salicylic acid (SA) is known for its role in plant defence mechanisms:


1. Disease Resistance

SA is crucial for activating defence responses against pathogens; it triggers systemic acquired resistance (SAR), enhancing overall plant immunity.


2. Stress Mitigation

This hormone helps mitigate abiotic stress effects by regulating stomatal closure and improving photosynthetic efficiency under stress conditions.


3. Growth Regulation

While primarily associated with defense responses, SA also influences growth processes such as leaf expansion and root development under certain conditions.

Farmers can leverage salicylic acid applications to bolster disease resistance in crops like tomatoes or peppers while enhancing overall plant health [6].


Conclusion

Understanding the roles of phytohormones—auxins, cytokinins, gibberellins, brassinosteroids, abscisic acid, and salicylic acid—in agriculture allows farmers to optimise their use for improved crop productivity and resilience against environmental stresses. By harnessing these natural compounds through strategic applications in farming practices, growers can enhance yields while promoting regenerative agricultural systems that benefit both the environment and food security globally.


Incorporating these insights into agricultural practices will enable farmers to make informed decisions regarding Compost extract applications in soils deprived of the micro life so essential to the plant can enhance specific crops' needs throughout their growth stages.


Sources

[1] Auxins and their roles in Growth and Development - Omex Canada https://omexcanada.com/blog/auxins-and-their-roles-in-growth-and-development/

[2] Cytokinins and their roles in Growth and development - Omex Canada https://omexcanada.com/blog/cytokinins-and-their-roles-in-growth-and-development/

[4] Brassinosteroids and their use in agriculture - Omex Canada https://omexcanada.com/blog/brassinosteroids-and-their-use-in-agriculture/

[5] Auxins: What are they used for? - Ficosterra https://www.ficosterra.com/en/auxins-what-are-they-used-for/

[6] Cytokinin and Its Key Role to Enrich the Plant Nutrients and Growth ... https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2022.883924/full

[7] Gibberellins: Key in Crop Development - Ficosterra https://www.ficosterra.com/en/gibberellins-key-in-crop-development/

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