We've talked about how water moves through a plant and introduced the idea that gas exchange happens through the stomata. Most people look at plants and see non-moving things; but plants actually have many moving parts. One of these is the stomata. Stomata are holes in the plant leaf that are surrounded by guard cells. Plants regulate the size of this opening by osmotically swelling or shrinking the guard cells.
What gases pass through stomata?
- Carbon dioxide (in during the day, out during night)
- Oxygen (out during the day, in during the night)
- Water (out at all times)
Plants typically close their stomata at night--not all the way closed of course since they still need to get rid of carbon dioxide from respiration. The receptor turns out to respond to blue wavelengths of light. When you shine blue light onto the plant, the receptor triggers a signal cascade that results in the guard cells becoming turgid and the stomata open.
The mechanism for opening relies on a proton pump setting up a concentration gradient of H+ across the cell membrane.
It uses this proton gradient to drive a K+ into the cell. This lowers water potential in the guard cell causing water to enter. The cells swell, opening the stomata. Closing them seems to be a result of simply releasing the K+ by facilitated diffusion. The exact signaling pathways that control stomata are an area of active research. In any case, here is a fun demonstration of how stomata open and close.
No comments:
Post a Comment