Thursday, December 6, 2012

Apical Dominance, Symmetry, and Christmas Tree Genomics?

Yesterday's New York Times featured an article on breeding the perfect Christmas tree using RNA sequencing. The perfect (dead) tree would presumably retain its needles for longer than the ones we see now in our living rooms. Probably it would have more idealized proportions (perfectly obconical) and other traits that we consider desirable in holiday icons. You've gotta wonder.

Plants have evolved for the past several hundred million years through the interaction of their genetically-controlled anatomy and the challenges of a harsh terrestrial environment. One feature of plants that I always teach my students is apical dominance. Apical dominance describes a primary feature of plant growth---the tips grow toward sunlight. Apical dominance is apparent in our "typical" Christmas tree-like conifers. The tip of the tree, its highest point, is also its narrowest point. 

The phenomenon of apical dominance is mediated by the release of hormones by cells at the tip. The hormones quiet growth in regions closest to the tip so that the tree can focus its energy and resources on growing upward. This enables the individual tree to out-compete others in the forest that might otherwise block its sunlight, vital for photosynthesis.

As a result of apical dominance the conifers we use for Christmas trees present with a nice symmetrical shape where branches radiate outward in increasingly wide whorls as they gain distance from the apex and its "do not grow" hormonal messages. While this phenomenon is most apparent in "christmas trees" we can detect it in all kinds of trees and woody shrubs. It just takes a little bit of looking at.

"Looking" is what I'm thinking about here. It is an unusual feature of our visual culture that stresses unwavering symmetry as a signal of beauty. I wonder why that is. If we consider the arts of east Asia, particularly China and Japan, we see a completely different approach. There, natural beauty is seen in plants, rocks, and landscapes whose symmetry is slightly (or a lot) perturbed by interferences. Holes, bends, reversals, crookedness. These are the features that make a rock or a bonsai or a tea bowl special.

Would our steroid-injected visual culture benefit from an appreciation of the crooked, the stunted, and the asymmetrical? I think so. For one thing it might give us a little more appreciation for those imperfections that lie just beneath the surface of our supercharged lifestyle.

I know that aesthetics is big business all around the world, not just in the United States. But I wonder whether we should re-assess our mass-produced approach to Christmas tree beauty. Instead of pouring resources into developing a "perfect" (dead) tree for our living rooms over the holiday season, maybe we should plant some trees that will live into the future. Some more greenery in all its imperfection might go far toward preserving our soil, our climate, and our sanity. 

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