Phytohormones are chemicals used by plants to regulate growth. Since we all want our plants to grow, phytohormones are pretty important. Let’s learn how we can use phytohormones to our advantage in the garden.
Unlike our glandular bodies, each cell within a plant is able to produce its own hormones. These hormones dictate flower, leaf, and stem formation, the timing of leaf drop, seed growth, flowering, flower gender, and, the really Bog One, fruit development and ripening. These chemicals also tell which tissues to grow down (roots) and which tissues to grow up (stems), and even how long a plant will live.
Appropriately enough, the word hormone comes from a Greek word that means to set in motion. Phytohormones, more commonly known as plant growth regulators, or PGRs, trigger certain cells to respond only at certain stages of the cell’s life. New, undifferentiated meristem tissue produces a lot of phytohormones. After the cells have used all that they need, any remaining phytohormones are moved to other locations within the plant where they are needed, or they can be inactivated and stored for later use. In some cases, phytohormones are cannibalized for their various parts, or chemically destroyed within the plant.
What do plant hormones have to do with gardening?
For one thing, it means that every time you prune out a branch or stem, you are altering the hormonal activity within your plant. The auxins that prohibit bud development further down a stem are mostly found at a growing tip. Remove that tip and hormone levels change, allowing more buds (read fruit) to develop further down the stem.
Secondly, upright, vertical stems tend to produce leaves over buds, because they contain a phytohormone called auxin. Bending a vertical stem into a horizontal position suppresses auxin development, allowing several flower-bearing buds to develop that otherwise would have remained dormant. Bottom line: more fruit.
Also, some bacteria create the plant hormones auxin and cytokinin, which can result in tumor-like crown galls.
Classes of phytohormones
There five basic classes of PGRs. Please don’t let the chemistry scare you off. After reading the descriptions, you will find a handy poem at the bottom to help you remember:
See if the poem below can help you sort all this information out:
Germinate with gibberellins, then ethylenes break ground
Auxins push them higher, abscisic acid slows things down
Cytokinins make them longer, keep them young and stronger
Always working in the garden, in flowers, shrubs and trees
I wish there was a cytokinin made especially for me!
Okay, so it doesn’t exactly roll off the tongue. How about trying your hand at creating an easy pneumonic and share it with the rest of us in the comments section!
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