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Stomata are openings, or pores, on the surfaces of leaves that allow plants to take in carbon dioxide, which they use to form organic molecules in photosynthesis. They consist of two epidermal guard cells that allow the pore between them to open and close. Every time a stoma is open, carbon dioxide enters a leaf and water and oxygen (one of the by-products of photosynthesis) escape. Plants regulate the opening and closing of stomata to ensure a balance between carbon dioxide intake and water loss. The basic structure of stomata (two guard cells flanking a central pore) has been conserved throughout the 400-million-year history of land plants, but with some variations. For example, in the grass family, which evolved in the late Cretaceous, the guard cells are flanked by two support cells that help fine tune the regulation of pore opening and closing. Such fine tuning may have enabled grasses to more easily adapt to changing environments. Scientists are now exploring the effects of such changes by studying the grass Brachypodium distachyon. In this example, they produced stomata with the usual two guard cells (center of the image) and many support cells (surrounding the guard cells). Such studies may have practical applications for producing crops with improved carbon assimilation and water use, which could more easily adapt to our rapidly warming climate.
The documents supporting the classroom implementation using this image as an anchoring phenomenon can be found with the Root Movement image here.
Technical Details:To generate this image, the grass tissue was stained with a fluorescent dye that reveals cell outlines (in magenta) and a fluorescent protein attached to a factor involved with the control of gene expression (in yellow), and imaged using laser scanning confocal microscopy.
Michael Raissig, PhD and HHMI Investigator Dominique Bergmann, PhD, Department of Biology, Stanford University, Stanford, CA