How do plants grow towards the sun?

[daniel_i_l]

How do plants grow towards the sun?
Thanks.

 

[baywax]

How do plants grow towards the sun?
Thanks.

Gravitropism is the term for the plant's tendency to "know" which way is up. Phototropism is the plant's tendency to "know" which way the source of light is... which is utilized by its photosynthetic properties.

The Light Side
Negative gravitropism leads plants to grow up out of the Earth but growth of the shoot directly toward the sun is even more advantageous to a photosynthetic organism. This response (photot- ropism) is apparently mediated by the shoot tip and has been mostly studied in coleoptiles (the sheath around cereal grain shoots). Unequal auxin distribution also seems to be involved, with auxin apparently transported away from the lighted side toward the darker side of the shoot. Since auxin stimulates cel elongation in shoots, this produces unequal growth on the two sides of the shoot and the shoot bends toward the light. Research has shown phototropism to be a re- sponse to blue light but the receptor is not wel established. The receptor is not a phytochrome, and experiments indicate that a likely candidate is a flavoprotein. Phototropic and gravitropic responses share several properties. A stimulus (light or gravity) leads to unequal distribution

http://www.carolina.com/fastplants/pdfs/Physiology/plantsknowtheway.pdf

Pretty cool mechanism of nature.

 

[daniel_i_l]

Thanks for the explanation.

 

[K.J.Healey]

Does anyone know if there are plants that do not do this? It seems to be one of the "survival of the fittest" tests. Plants that have this property have a better chance of thriving, and thus take over. But it seems like there could be sections of the world that do not have this ability, either due to their location under the sun (equatorial), or some other reason.

 

[baywax]

Thanks for the explanation.

You are most welcome. I learned as much as you from this.

Auxin (in plants) is like a hormone but it isn't one. Perhaps a precursor. As it is explained here it acts as a growth agent much like a growth hormone in animals.

 

[Ouabache]

Yes the phototropic effect is an interesting phenomena. We used to demonstrate it by planting a seed that will easily germinate (bean) in a small pot, cover the pot with a large box and poke a single hole in one of the sides of the box. As the seedling emerges, it's only source of light, comes from that hole and proceeds to bend in that direction.

If you have ever passed a field of sunflowers or jerusalem artichokes at different times of the day, it is fun to notice the flowers follow the position of the sun across the sky.

I was taught "auxin" is a plant hormone. http://hcs.osu.edu/hcs300/hormone.htm

 

[Astronuc]

Does anyone know if there are plants that do not do this? It seems to be one of the "survival of the fittest" tests. Plants that have this property have a better chance of thriving, and thus take over. But it seems like there could be sections of the world that do not have this ability, either due to their location under the sun (equatorial), or some other reason.

I have noticed that the canes of my blackberries tend to grow away from the sun. They seem to prefer shade, which perhaps means an adaptation for growing in the direction toward moist soil, which would be out of the sun.

http://img521.imageshack.us/img521/8426/blackberriesawayfromsunmt5.jpg

Interestingly though, in contrast, the wild blackberry brambles tend to grow toward the sun!