Xerophytes Stomata Distribution

[_Mayday_]

Hey all you Biologists out there!I've been studying http://en.wikipedia.org/wiki/Xerophytes" and how they are adapted to their environment. I have talked about things like them having minimal/no leaves to decrease the rate of water loss through transpiration, CAM photosynthesis, where the Stomata remain open at night to take in Carbon Dioxide which is then used for photosynthesis in the day when there is light. (The Carbon Dioxide is stored as a sugar if I am correct, but don't take my word for it)

I wanted to do some extra work though. I have read that some cacti have gooves to minimise the rate of transpiration or water loss from air movement and sunlight, this happens dueto a continuous water potential gradient being maintained by a continuous flow of air sweeping the diffusion shells away and resulting in a lower water potential outside of the leaf/stomata. I would have thought that there would be a higher density of stomata in these grooves and less outside the grooves, now I say this simply for the reason that it would probably be more efficient in terms of water loss. There is however the argument that they should remain constant, as Gaseous exchange is also important.

I took leaf prints (with good old nail varnish) and found that there seemed to be more stomata outside the grooves! Now I only did this once so it may be an anomoly. In a given sample I found 20 stomata in the groove and 22 outside the groove, this is hardly any evidence to base a solid conclusion on though!

Can anyone provide either an explanation or a source for this idea? Not necessarily agreeing with my results but some information on the distribution of stomata in these grooved cacti. Any help would be great! If I have made any mistakes in this post or if there is a possible missunderstanding of an idea please feel free to correct me, this has really captured my imagination and I'd love to know a bit more about it!

_Mayday_EDIT: By grooves I mean how it is ribbed, or in other, non-scientific words, the green sticky out bits.

Here is a picture to help show what I am talking about:

http://thump01.pbase.com/u37/jwalk/small/24138755.cactuscloseup.jpg

 

[_Mayday_]

I hope nobody minds if I bump this thread, as I have a lesson tomorrow and although it is not set work it would be nice to have some information to back my findings. My teachers says he doesn't know, so it would be great to get some information.

 

[Moonbear]

20 vs 22 doesn't really sound different enough to me to think it's going to hold up as consistent if you did more sampling. Why don't you gather up a few more samples and find out if there's any consistent pattern before banging your head on the wall trying to explain it?

 

[_Mayday_]

I will do, another person from England has been in contact with me, and has said that he has actually conducted a similar experiment within the same few days! What are the chances ey? Anyway he said he took a few samples and has similar mixed results, he has said after talking to his teacher they concluded that there was no obvious conclusion to be drawn from the results.

 

[NoTime]

Purely a guess on my part
The grooves may be a way to increase surface area while retaining strength.
Vaguely in the line of corrugated cardboard.

Did you count the stomata on unit surface area or just in and out of groove?
That could make a difference.

edit: I can't see your jpg - says "You don't have permission to access /u37/jwalk/small/24138755.cactuscloseup.jpg on this server."

 

[_Mayday_]

The grooves are primarily used as a way of preventing a diffusion gradient from forming through air movement, I have also read from some sources that it prevents excessive amounts of sunlight causing an increase in the rate of transpiration.

Moonbear: I have done some replicatesv and have found an even distribution of stomata in a given area.

I cannot think of any reasons for uneven distribution, would anyone be able to suggest an idea? I think in making a conclusion we would need to take into account:

a) Gaseous Exchange - Why would the cacti need a variance in distribution for Gaseous Exchange?
b) Transpiration - Why would the cacti need a variance in stomata distribution for transpiration?
c) If there would be any variance in the distribution due to "in classroom" conditions. The cacti is straight, and there is no variance in growth which I cannot see any noticeable change in the girth. Would the cacti be able to adapt by changing the distibution of stomata. Has this environment effected my results?

Here is how I would answer them.

a) I would guess that these grooves would not effect the rate of gaseous exchange and so could say that the grooves are there primarily as a way of restricting water loss through transpiration.
b) A higher density of stomata in the grooves would allow an increase in the rate of gaseous enchange without effecting the rate of water loss. Though I cannot think of any reasons why it wouldn't be evenly distributed.
c) This is a question to you!


Please give your knowledge/opinions on this. Thank you!

_Mayday_