No, stomata themselves are not typically green. However, the guard cells, which are the cells surrounding and controlling the opening and closing of the stomata, can be green in some plant species. This green color is due to the presence of chlorophyll, the pigment responsible for photosynthesis.
Guard Cell Chlorophyll Content
The presence of chlorophyll in guard cells varies depending on the plant species. For example, the reference mentions that in Tradescantia zebrina, the guard cells of the stomata are green because they contain chlorophyll. [^1] This means they can photosynthesize to some degree. However, many other plant species have guard cells that lack chlorophyll and appear colorless.
Several references highlight stomata's role in plant function, such as regulating gas exchange and water loss, and their interaction with light (blue, red and green)[^2, ^3, ^4, ^5, ^6]. These functions are independent of whether the guard cells themselves contain chlorophyll or not.
- Example: The image in a news article shows many stomata on a green begonia leaf; however, this doesn't necessarily indicate that the guard cells themselves are green. [^7] The green color is likely from the leaf's chloroplasts in the surrounding cells.
- Another Example: Research on the transport of green leaf volatiles (GLVs) through xylem mentions stomatal closure and its effects.[^8, ^9] This research focuses on stomata's function and not the color of the guard cells.
Conclusion
While the guard cells surrounding the stomata can contain chlorophyll and appear green in certain plants, it's inaccurate to say that stomata are inherently green. Their color depends on the presence of chlorophyll in the guard cells, which is species-specific.
[^1]: Wikipedia: Stoma - https://en.wikipedia.org/wiki/Stoma (In this species (Tradescantia zebrina) the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigments.)
[^2]: NSF: Scientists discover mechanism plants use to control 'mouths' - https://new.nsf.gov/science-matters/scientists-discover-mechanism-plants-use-control
[^3]: Stomatal closure prevents xylem transport of green leaf volatiles and impairs their systemic function in plants. - https://pubmed.ncbi.nlm.nih.gov/37828776/
[^4]: Stomata: gatekeepers of uptake and defense signaling by green leaf ... - https://dx.doi.org/10.1093/jxb/erae401
[^5]: Reversal by green light of blue light-stimulated stomatal opening in ... - https://pubmed.ncbi.nlm.nih.gov/16418232/
[^6]: Photosynthesis-Dependent and -Independent Responses of ... - https://dx.doi.org/10.1093/pcp/pcr005
[^7]: NSF: Scientists discover mechanism plants use to control 'mouths' - https://new.nsf.gov/science-matters/scientists-discover-mechanism-plants-use-control (A magnified view of many tiny plant stomata on a green begonia leaf.)
[^8]: Stomatal closure prevents xylem transport of green leaf volatiles and ... - https://pure.psu.edu/en/publications/stomatal-closure-prevents-xylem-transport-of-green-leaf-volatiles
[^9]: Stomata: Gatekeepers of Uptake and Defense Priming by Green ... - https://www.biorxiv.org/content/10.1101/2024.05.22.595386v1
