Hormones and Growth

Wednesday, April 18, 2012
Anybody who was ever a teenager knows about hormones. We produce them naturally and in differing amounts throughout life, but it is the adolescent years that get most of the attention. Yes, we all know about mood swings and body development because these hormone-influenced conditions hit close to home. Plants produce hormones, too, and their role in plant growth and especially propagation cannot be underestimated. The naturally-occurring plant hormones are auxins, cytokinins, gibberellins, and ethylene. The latter is important in fruit ripening, as when we put a cut apple into a plastic bag with a pineapple or green bananas to speed them to the table. Gibberillins are noted for their impact on cell division and elongation. You may know someone who ‘gibbs’, applies the auxin to their camellias to increase bloom size. Cytokinins influence cell division, lateral bud development, and leaf longevity. Auxins are the hormones used to promote rooting, but they are also promote uniform flowering and fruit set and, in some cases, forestall early fruit drop. The auxin known as IBA (indole-3-butyric acid) contributes to the formation and growth of healthy roots and is the substance in Hormex Rooting Powders of various strengths. Vitamin B-1 (thiamine) is the additional active ingredient in Hormex Liquid Concentrate. B-1 is produced naturally in leaves and moves into the roots to assist their growth and is always beneficial to plants. By adding the hormone B-1 to liquid auxin, Hormex Liquid Concentrate promotes thrifty growth at all stages in a plant’s development. How fast and how well cuttings take root and begin to grow depends on the condition of the plant material, the media you choose to root in, and the temperature of the media, air, and water used in the process. But in the end, we are dependent on the amount of IBA available to the plants for roots to be stimulated. The role of IBA in plant growth is to regulate and direct growth by working in relation to other hormones like cytokinins. For example, the ratio of auxin to cytokinin in some plants can determine whether cells differentiate into roots or shoots. By adding Hormex products to the process, we increase the auxin influence towards roots. How this influence occurs can be attributed to the nifty ability of auxin molecules to move from cell to cell, to marshal their influence where it is needed. It’s a talent we mere mortals do not share which imparts to the plants the ability to shift growth patterns right down at the cellular level. It even allows them to react to some external threats. We take advantage of this quality when we expose some kinds of cuttings to the air so that they form callus on the cut surface before rooting them. The injury of an open wound on the stem stimulates cells to adapt and become thicker to block further fluid loss. Fortunately for us, this layer also develops roots more quickly than the fresh cut stem. All auxins are hormones, but not all hormones are auxins. Chemically, each auxin consists of an aromatic ring and carboxylic acid group in quite elegant molecular arrangements of carbon and hydrogen. When I was a teenager, we didn’t talk much about hormones, human or plant, but a good biology teacher offered extra credit for a report on plant anatomy and I stumbled into a curiosity about how growth happens. In college, I learned about plant hormones in class but really first observed their power when I tried to root bougainvillea and lollipop plant, aka golden shrimp plant. Both are rather woody, tropical plants then in consideration for greenhouse production schedules. My first task was to determine whether tip cuttings or stem cuttings would root better and to compare cuttings rooted using IBA with those that had no hormone applied. I used a single blade knife to make clean cuts from healthy stems on the stock plants. I made labels, filled flats with a damp perlite/peat media, and tapped out a little rooting hormone onto a brown paper towel laid on the bench in the head house. I stuck the untreated groups and then rolled each remaining stem base in rooting powder and shook off the excess before sticking it. Virtually every tip cutting died before roots could form, but the 2 that survived were from the treated group. The stem cuttings were much more successful overall. Some of the untreated made a few roots, but nearly all the treated stem cuttings rooted and rooted very well in the same length of time. The proof of the pudding, as they say, was in the hormone.
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