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Name: carol
Status: other
Grade: other
Location: N/A
Country: N/A
Date: 5/13/2005


Question:
If you cover just the leaves on a plant the stem will elongate rapidly and eventually the leaves will fall off. What plant hormones/chemicals will cause the rapid growth in the stem?


Replies:
This effect is known as etiolation.

To be perfectly honest, we don't have a good understanding of the hormonal regulation of this phenomenon. We do understand the biochemical mechanism by which the light level is sensed. Higher plants have a pigment known as phytochrome which senses the relative proportions of red (660nm) and far-red (730nm) light in their environment. This allows plant seedlings to sense, firstly, whether there is any light present and secondly, the degree to which they are shaded by neighboring plants. Unfortunately, we don't really have a clear understanding of how phytochrome brings about different growth responses. I personally suspect that the hormones auxin (indole acetic acid, or IAA) and cytokinin (a variety of different related compounds) may be involved. A few years ago I did some experiments looking at hormone levels in plants that were shaded compared to those in full sun. I'm sorry to say that I never managed to find anything conclusive. Plant hormone work is notoriously difficult, although a lot of progress has been made fairly recently. This is one of those areas of biology where researchers are still scratching their heads.

C. Perkins


Auxins are plant hormones that cause stem elongation.

Perhaps helpful:

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookPLANTHORM.html#Auxins

http://www.cnr.vt.edu/dendro/forestbiology/htmltext/chapter5.htm

http://www.hcs.ohio-state.edu/hort/biology/pplandeve.html

Anthony Brach Ph.D.



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