Grapevine Hormones

Yes, plants have them too! I am reading (reading is not exactly the word, it's more like studying each paragraph by dissecting every word) a deceptively thin book written by Prof. Markus Keller called The Science of Grapevines Anatomy and Physiology. I am only on the first chapter which is about Botany and Anatomy. One thing that our online Viticulture class did not go over was about the various hormones that regulate the growth of plants and the grapevine in particular. Prof. Keller devotes about 27 pages on the morphology and anatomy of the grapevines beginning with the root, trunk and shoots, nodes and buds, leaves, tendrils and clusters and finally, flowers and grape berries. He also discusses the various hormones that are present in these plant structures.
Hormone: a definition
Hormones are defined as extracellular signaling molecules that act on target cells distant from their site of production.
Cytokinin and abscisic acid are the main root hormones.

• Cytokinin is the cell division hormone produced in the root tips.
• Absicisic acid is the dormancy hormone acts to keep the lateral root production in a dormant state under conditions of water stress or high nitrogen availability.

Auxin and gibberellin are the main shoot hormones.

• Auxin stimulates cell division and is delivered from the shoot tips via the phloem. Shoot derived auxin can initiate lateral root growth.
• Gibberellins promotes cell elongation and differentiation upon stimulation by auxin in tissues with rapidly expanding cells.

There is a lot to know and learn about the influence of hormones on vine growth which I will continue in other blog posts. But, I'll end this post with something to think about. Prof. Keller, mentions on page 38 that the herbicide 2,4-dichlorophenoxyacetic acid better known as 2,4-D is a synthetic, nontransportable auxin that stimulates cell division but inhitibits cell expansion and differentiation. 2,4-D has the following deceptively innocuous looking chemical structure:

I recalled reading about 2,4-D spray drift in a book written by Geoff Heinricks called A Fool and Forty Acres. In this book, Heinricks writes:
As I walked along the western hedgerow of our Pinot Noir plot one summer I checked for phylloxera galls on the wild vines a dozen yards away. The galls can be found every year, but what stood out this time was the number of them. I looked closer and noticed something strange: many of the wild-grape leaves were deformed. Some were growing extremely long teeth, almost like long strands of green hair. Others mimicked a gingko leaf shape, with veins arrayed like fans.
I knew it was herbicide damage. There must have been 2,4-D drift from fields on the other side of our hedgerow, for the deformations were clear symptoms of the herbicide hitting new grape tissue.
1. The structure was found on Wikipedia: 2,4-dichlorophenoxyacetic acid
2. All structures were drawn by the freely available drawing program from ACD Labs called ACD/ChemSketch Freeware.
The information contained in this blogpost was exerpted from:
The Science of Grapevines Anatomy and Physiology, Markus Keller, 2010, Academic Press, pg. 20-47.
To see a larger representation of the structure, simply click on the image. To get back to the blogpost, click on the upper right hand "close x".