12 replies to this topic

[Primarygun]

Sometimes, it would say that stomata rarely open or even close at night.
If plants close the stomata at night, how can the plants get oxygen? Are all the stomata fully closed?
If not, the problem is simple because oxygen can still diffuse into the plants in a low rate.

[Sorcerer]

Oxygen for respiration is produced by photosynthesis and abosorbed from the air during the day, I think plants have some kind of storage system, for oxygen, there are 2 different ways plants assimilate carbon through C4 and C3 pathways, I think the difference here may have something to do with their oxygen or water requirements.

My plant physiology is rusty.

[Skye]

I beleive the stomata stay open to some extent at night. There is a small intake of oxygen and release of carbon dioxide.

[Drabav]

Most plants use the C3 photosynthetic pathway. Stomates usually only close for these plants during dry periods to conserve water, not at night. In fact, where did you hear that plants close their stoma at night? I believe that is false information.

There are some plants, mostly living in desert environments, that follow the CAM pathway. They ONLY open their stomates at night. During that time they take in CO2 and release O2, which is used during the day for photosynthetic processes while the stomates are closed.

Yes, it is inefficient, but it seems to work in places where not much else can grow.

Draba v.

...a postscript of the hope of spring.

Edit: Since when do plants take in Oxegen and release CO2 anyway? Where ARE you getting this info?

[Sorcerer]

Ahhh thanx drab, thats what I was getting at, yeah, I didnt think plants closed their stomata at anytime unless the turgor pressure drops.... ie dehydration.

Edit: Plants take in oxygen and release carbon dioxide like every other living eukaryotic organism, they have mitochondria, perhaps the thing is though they take in water which contains oxygen, then convert this to 6CO2+6H20---> C6H12O6 + 602

But then they release it when they respire, so the equation is balanced, however flucuations in homeostasis would most efficiently be corrected by the diffusion of oxygen from the air.

[Drabav]

Actually, I think that a better way to say this would be that they intake both CO2 and O2 through the stoma. The oxygen is then used for cellular respiration (oxidation, crebs cycle, etc) and the CO2 is used in the grana of the cloroplasts to produce "food"(much more than just glucose is produced, including ammino acids, nucleotides and lipids). I think my problem is that I was looking primarily at the Photosynthetic side of plant respiration, and took the cellular or mitochondrial side (O2) to be supplied mostly by the Photosynthesis reation. I don't know if that is true, and I don't know where I could go to verify that statement.

[Skye]

Most plants use the C3 photosynthetic pathway. Stomates usually only close for these plants during dry periods to conserve water, not at night. In fact, where did you hear that plants close their stoma at night? I believe that is false information.

Here's a few sites that are spreading the blasphemy.
http://www.tiscali.c...n/m0007013.html
http://www.mun.ca/bi...ortinPlants.htm
http://www.utoronto....ah/B101lc06.htm

[Drabav]

Other than the part about closing at night, I don't think anything is that bad about these sites. How would you even test such a think, as most light tends to make a plant photosynthesis, and electron scanning can only be done with dead tissue? I think that this is just a statement in the blue, like an urban legend with no proof to back it up.

Please, if someone can offer proof that stomates close for any other reason than dehydration or CAM cycling, I would like to see it.

Draba v.

...a postscript to a hope of spring.

[Skye]

Similarly stomata predict dusk and start to close many hours before the onset of darkness, reducing water loss.

From:

Webb, Alex A. R. (2003)
The physiology of circadian rhythms in plants.
New Phytologist 160 (2), 281-303.

[Primarygun]

Ok. Thank you guys.

[Drabav]

Interesting. I didn't realize that plants have circadian clocks for stoma opening and closing. Hmmm, did that article also talkabout the mechanism that causes this particular closing? A hormone, possibly?

Draba v.

....a postscript to the hope of spring.

[Skye]

By memory it was Ca+ ions.

Edit: The circadian rhythm is largely based on feedback loops of interacting proteins that change in concentration rhythmically. These have effects on various things in the cell that affect the turgor (greater turgor=stomata opening). Ca+ seems to be the most important of these in stomata.

[Drabav]

Hmmm...so the protien levels (possibly hormones secreated when photosynthesis is occurring or not occurring, or something like that) some how by way of a feedback loop (negative feedback?) cause these circadian rythms which open and close the stoma by way of Calcium Ions? Is this correct?

This would possibly be similar to the feedback loops that cause flowers to open at certain times of the day. Or maybe not. Pure speculation, until someone gives me evidence.

Draba v.

...a postscript to the hope of spring.