When I teach trees and their energy transactions during our permaculture design course here at the School of Permaculture. I make note to the students that there is a lot of well documented and studied information about the botany and science of trees and of plants and how to identify the parts of them. However, if you look closer, being a soft science, it is very rare to find much of anything written about the plant’s energy transactions. This is just one of the many ways where permaculture differentiates itself from other disciplines – it is all about connections…
However, we attract, and I am sure other permaculture facilities as well, a very wide range of students with a varied set of backgrounds, skills, and understandings, especially when it comes to plants and growing them. Honestly, I knew nothing of permaculture before getting involved and barely anything about plants other than they grow in the ground and you cook them.
I have been very reluctant before now, but for this reason I am going to go ahead an make a very basic and sought after “botany series” of the permaculture tips of the day on plants. Here is one on the hormones of plants.
Plant Hormones – The Big Five
There are a wide and varying amount of plant hormones which effect plants in a variety of different ways. I am going to only focus on what is known as The Big Five below. This will help us wrap our heads around a dizzying amount of information involving plants, and especially their energy transactions, to help us make sense of it. It is also good to keep in mind that the hormones of plants often work together for all types of activity during the plant’s life and even in death and only a little hormone is needed for essential or secondary functions to be performed.
Auxins
These are the hormones responsible for cell division, cell differentiation (like when one cell becomes a root cell and another one becomes a leave cell), and for the vertical growth in a plant. It is also responsible for the leaning or bending of the plant to move towards the sun which is called phototropism. Auxins also stimulate root growth and aid in healing wounds in a plant through cell differentiation.
Gibberellin
These hormones (which over 100 have been identified) are also effecting stem elongation. However, gibberellins are important for production of fruit. Many growers will use synthetic gibberellins to stimulate fruit growth. We do not recommend that as growing your soil and soil life show much more promise for fruit production. Giberellins also play an important role in seed development and germination.
Cytokinin
What shows us how much we actually know about the world is that we have not with 100% confidence found what gene in the plant produces cytokinin. Which has raised the question if this hormone is even produced in the plant at all or is it produced by bacteria that is symbiotically living in the plant like rhizobium does in legumes. Along with auxins, cytokinins aid in cell division, plant growth, and plant repair. They are also known for stimulating lateral growth. Cytokinins also delay senescence or the plant’s natural aging processes that lead to death in plants. Working with auxin they can do this: Equal concentration of auxin and cytokinin then normal cell division will take place. If concentration of auxin is greater than cytokinin, roots will form. If concentration of auxin is less than cytokinin, shoots will form.
Ethylene
Ethylene is the only hormone that can be purchased or put into a can. It is a gas which is produced by the plant cells that help the fruit ripen. The cell will not produce much of any ethylene prematurely of the full growth of the seed. Only then do the cells produce large enough quantities to help the fruit ripen and fall to the ground or be picked to be eaten and eventually naturally sown by agents of the plants such as squirrels, mollusks, humans, and birds. If you have a very ripe fruit in a closed container with other fruits, it releases ethylene and will speed the ripening process of the other fruits up. This can be advantageous or disadvantageous depending on your scenario. This hormone is also responsible for leaf separation in autumn and especially on deciduous trees.
Abscisic acid
This hormone slows the growth of a plant. It also is responsible for a seed going into dormancy. Abscisic acid plays an important role in only allowing the seed to germinate under optimal conditions and is so good at this that it can liberally cover some seeds where the seed will go into survival mode and will not germinate until after the absicisic acid is inactivated, worn off, or leached away.
Here is a great video going over plant hormones for the auditory learners:
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