it is wrong to turn plants around

Kipp McMichael
Tue, 14 Feb 2012 17:52:47 PST


  I think a few different things are at issue when it comes to moving plants and maintaining allignment to the sun (cardinal directions aren't really relevant except to the extent that they correlate to exposure).

  Other have mentioned chloroplast alignment & migration in plant tissue (google "Halimeda chloroplast migration" for a really neat example). Were this the only issue, the worst we would expect for improperly moved plants would be a temporary setback. A much worse problem is sunburn.

  Many plants - both herbs and woody plants - have photosynthetic tissue in the surface layers of their branches/twigs/trunk. In woody species without thick bark (like Manzanita) the conductive tissue that carries food and water is also very near the surface. When a plant is re-oriented toward the sun, surfaces that previously did not receive direct sunlight are suddenly exposed. Just like a pale sunbather in spring, the newly exposed tissue can get sunburned. The structure of plant tissue makes sunburn much more damaging to plants than to animals.

  Plant cells are surrounded by a cell wall and this constrains the way they can recover from sun damage. Even if a plant cell dies, the rigid cell wall still occupies the same space in the tissue where it resided (more or less - the empty cell can get squeezed by it's still-living neighbors). In animals, a cell killed by sun exposure is wholly re-absorbed and neighboring cells can grow/move into the gap. The photosynthetic and conductive tissue in a plant damaged by sunburn cannot "make way" for fresh cells. Thus, if you burn (kill) the conductive or photosynthetic tissue on a given section of trunk or branch, the damage is permanent.

  Additionally, sunburn can kill meristematic cells (the tissue that gives rise to buds & new branches) and thus prevent a plant from growing new branches or leaves from sun-damaged tissue. 

  After a sunburn, annuals and/or deciduous plants can always try with new branches or leaves. For non-deciduous plants like cacti or bromeliads, however, sunburn can be permanently disfiguring and/or lethal.



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