Plant Hormones | Turf Dietitian

Written by Mike Hamilton, CCA

At Turf Dietitian we continually educate ourselves on plant and soil health in order to be the best resource possible for turf professionals. Coming from a long line of Farmers and Teachers, I feel it’s in my DNA to share everything we learn, with anyone who has a desire to understand the amazing natural balances and reactions in carbon-based life forms.

Plant hormones are bio-chemicals in plants that regulate almost all aspects of plant growth and development. Plant hormones are produced by plants with the help of enzymes. It has been common knowledge for centuries that hormones assist and regulate plant growth, development, longevity, and even cellular death. Hormones derive from secondary metabolites such as organic acids amino acids, carbohydrates, nitrogen compounds, sulfur compounds, just to name a few.

However, the comprehension of the role of hormones plays assisting plants to survive and even thrive under both abiotic (freezing, heat stress, drought, flooding, ultra-violet radiation, soil salinity, nutrient deficiency, air pollution and soil contamination), and biotic stress (viruses, bacteria, fungi, nematodes, insects, weeds, and free radical oxygen compounds) comes from relatively new scientific research.

Through modern research scientists have discovered that hormones are also a primary signaling stimuli excreted through the plant roots, which has the ability to communicate the plant needs to microbes in the soil, on the leaf, and inside the plant.

I’m confident that this new wisdom gained from modern research will lead to the development of more precise biological controls as an option to chemical controls.

Hormones are responsible for plant growth and also as a plant growth regulator. If the environment is ideal for growth, and the plant is producing sufficient amounts of carbohydrates, the structural hormones (Auxins, Gibberellins, and Cytokines) will form an ideal balance, which allow plant to grow to its maximum genetic potential and to actively reproduce.

If the plant is under stress the stress adaptation hormones (Abscisic Acid, Salicylic acid, Ethylene, and Jasmonates Acid), will speed up, slow down, stop or even kill live cells to adjust to the particular stresses of a plant.

Here is just one of thousands of examples. If a plant is in drought stress, abscisic acid will be produced by stressed leaves and roots to protect the whole plant. The build-up of abscisic acid will kill older roots and leaves. Why? Because sacrificing older leaves and roots allows for more water and food to be available for younger plant parts. If the drought continues the abscisic acid will close the cell stomata to prevent any water from evaporating out of the plant. The closure of the stomata brings all plant growth to a stop, and preserves any water and food left in the plant. Interestingly enough, abscisic acid is the only thing other than sunlight that can open and close the stomata, it’s overriding the natural laws of plant growth.

Have you ever seen sod planted on a road shoulder or a bank, that in a drought goes completely brown for months? With the first good rain the dead looking sod greens up and comes back to life. You can thank abscisic acid for that.

Golf Course Superintendents are one of the only plant growers who want to slow down or stop growth. The use of plant growth regulators is widely used, and in many cases on a weekly basis.

One of my recommendations for Superintendents that see turf thinning, is to use Gibberellins to push lateral growth. It works great, but what kind of damage are we doing to our plants when we override the natural growth patterns of turf. According to research articles I have read, they can do great harm to a plant if over applied. So how do we know what rate is harmful and what rate is safe?

According to research that’s a difficult question to answer because every plant and probably every species of turfgrass has different levels and balances of hormones for healthy growth. A plant with a perfect balance of hormones may be a deadly balance for another species of plant.

You would think that with only 7 or 8 different groups of hormones it wouldn’t take that much research to identify natural levels for plants. However, like anything that happens in nature, things are much more complex than they may appear. Each individual hormone group has multiple numbers of unlike hormones in the group. Auxins for example have over 200 individual hormones in the group and gibberellins have over 100.

WHAT WE KNOW ABOUT THE ROLE OF EACH HORMONE GROUP IN PLANTS TO DATE?

Why do I say to date? Because every plant function is being researched at an accelerated pace. What scientists have learned in the past 5 years is more than they did with all the research from the previous 500 years. And I don’t anticipate the pace at which mankind is acquiring knowledge slowing down. What makes these achievements possible? Super computers (Al).

Let’s break down what we know.

Auxins

Auxin is a growth hormone that causes responses in plants, but mostly promotes cell growth and elongation of plants. But sometimes, its overproduction or application causes toxicity or accelerated plant growth which kills the plants. An overdose of auxin within the plant stimulates ethylene. Ethylene is a gaseous hormone that impedes the root and shoot elongation and gradually kills the whole plant.

Auxin are produced in the tips of plant leaves and move downward through the plant. Because auxins are produced in the leaf tip, the highest concentration of them are in the above ground part of the plant.

2,4D and glyphosate are synthetically made auxins, that kill many types of broad-leaved plants. These herbicide work by causing the cells in the tissues that carry water and nutrients, to divide and grow without stopping, causing plants to literally grow themselves to death.

Other Auxin Responses

Promotes the suppression
Flower
Fruit set and
Formation of adventitious
Promote cell
Promotes stem
Promotes root
Increases plant
Directly links growth regulation with stress adaptation responses through interactions with salicylic acid (SA} and abscisic acid (ABA}
Regulates growth and development through signaling
Adaptive responses to biotic and abiotic
There are over 200 separate and different hormones in the auxin

Cytokinin

Cytokinin’s are involved in cell division and in the formation of roots and shoots. Cytokinin’s are produced in the root tips of plants, and they travel upward through the xylem along with water. Cytokinin’s help in increasing cell division in the plant with the help of a specific protein.

Other Cytokinin responses

Cell
Trigger a response to various biotic and abiotic stresses in
Induce the formation of young leaves, chloroplasts, and lateral
Involved in leaf and root shaping along with a balance amount of
Slows leaf senescence and other organs by mobilization of nutrients towards
Induce bud
High cytokinin/auxin ratios favor the formation of
Low cytokinin/auxin ratios favor the formation of

Intermediate cytokinin/auxin ratios favor balance
Cytokinin acts antagonistically to
Cytokinin’s suppresses apical dominance, whereas auxins promote
Increases disease resistance and high and low-temperature resistance in
Speed up seed
Plays an important role in bacterial disease
Repair wounded

Gibberellins

Gibberellins like all the other plant growth hormones play an essential role in several plant formation stages in plants. However, the primary function of gibberellins is to make stems and limbs longer on plants. Gibberellins promote stem elongation and increase the space between internodes. The level of gibberellins in dwarf plants is low in comparison to other plants.

Other Gibberellins responses

Early seed production
Increases vegetative
Delay
Promotes flowering.
Speed up recovery from
Promotes fruit
Speed up vertical growth of
There are some 100 different types of

Abscisic Acid

Abscisic Acid is a general plant-growth inhibitor. It induces dormancy and prevents seeds from germinating; causes dead leaves, fruits, and flowers to fall off of plants. Abscisic is the only biological chemical that can initiate closure of cell stomata. Abscisic Acid is always in high concentrations in guard cells during periods of drought stress. It is believed that abscisic acid is the primary signaling hormone for abiotic stress. Abscisic acid is the only hormone that is produced in droughted leaves, droughted roots, and developing seeds. Abscisic acid, unlike the structural hormones, travels both up and down in a plant stem, xylem, or phloem. This unrestricted movement enables abscisic acid to message microbes to assist the plant in abiotic stress.

Other Abscisic Acid Responses

Plays a key role in signaling to soil
Promotes root growth during periods of low
Desensitizes the enzymes needed for

Helps to regulate water movement in the plant to prevent growth of roots when exposed to salty conditions.
Promotion of plant antiviral
Reduces stress intensity in plants by triggering defense
Increasing a once affected plant’s tolerance to environmental
Teams up with other hormones to play a dule role in protecting plants in

Salicylic Acid

Salicylic acid has important regulatory functions in plant growth, particularly under adverse stressful conditions Salicylic acid has roles in flower induction, general growth and development, various enzyme biosynthesis, stomata movements, membrane protections, and cell respiration. Salicylic acid also plays a major role in ion absorption, nutrient transfer, increasing the representation of CO2 gas, controlling the movement of stomata, photo materials, gas exchange, and protein synthesis.

Other Salicylic Acid Responses

Stimulates the production of antioxidants within the
Increase plants’ growth rates and
Increases salt
Increases chlorophyll
Increases plants immunity to pathogen
Creates signaling pathways that enhance defensive
Enhances antioxidative
Improves nutrient and water uptake when plants are
Regulates the activities of many
Relieves heavy metal stress on
Contributes to plant energy savings by increasing the levels of nucleic and amino

Ethylene

Ethylene is the only hormone found that exists in a gaseous form. Ethylene is involved in the dormancy process of plants. Ethylene induces ripening of fruit, plant drooping, senescence, and the dropping of leaves. It is frequently found to be high in concentrations with plant cells at the time of their death. Longer-term exposure to high concentrations of ethylene can result in stunted growth, deformed or chlorotic leaves, delayed flowering, and plant death.

Other Ethylene Responses

Breaks the bud and seed
Facilitates rapid elongation of internodes and
Raises the absorption surface by inducing root growth and root hair
Helps in the root

Forces the root to grow downwards in the
Increase the capability of water and mineral
Stimulates plant bending toward the
Interference with auxin

In Turf, hormonal products have been available and widely used for the past 30 years with much success. The majority of the products currently being used are derived from seaweed or animals and consist of mainly the three structural hormones: auxin, cytokinin, and gibberellin. However, given the modern research and the potential from what has been discovered, I see the potential for great breakthroughs in natural plant defense products to be at your disposal in the next 10 years.

With that being said, I do see the potential for some of these products being very tricky to apply. Simply because plants produce and use only an infinitesimal quantity of hormones. Also, each species of turfgrass may require different amounts and balances.

Because of the unknown we are adding the 6 major groups of plant growth hormones onto our tissue testing equipment. I believe the data we accumulate will give us and you the ability to monitor the levels of hormones in the plant, see how hormonal applications affect the balance in the plant, the plant response to current levels, and if the products are doing what they claim to do.

If you are currently using our service, you know we have added 20 amino acids, and 8 carbohydrates over the past year. We are in the process of adding the 6 groups of plant growth hormones we discussed in this article. That process should be finished by mid-March. We won’t add another metabolite until we’ve established target ranges for the last thing we added.

From what I understand labs typically will create target ranges after they have tested 50 to 200 samples. We establish target ranges after 1,000 samples, because we feel they are more accurate with that quantity. In our busy season we will test that many samples in 3 to 4 weeks. Also, every sample we test is added to a master sheet that adds to the overall data, and constantly adjusts the ranges. We’ve found that once we have 5,000 samples in the database, the target ranges rarely change after that.

Once we get the ball rolling to add another metabolite to our testing equipment, it typically takes 6 to 8 weeks before we can start testing for that metabolite. Below is a list and time frame for us to add other metabolites to our equipment.

Enzymes – June 2024
Chlorophyll – September 2024
Proteins – January 2025

Our promise to you is that we will do our best to keep up with the vast amounts of research and comprehension of the results. Please call if you have any questions or feedback.

Mike Hamilton, CCA
Turf Dietitian, Inc
239-707-9974