Stoma and chloroplasts of maize leaf

This image shows the mesophyll (middle cell layers) of a maize leaf. It shows a living - but closed - stoma and surrounding cells in the epidermis of the leaf. It has been imaged using a confocal microscope and lasers of two different wavelengths. Each wavelength excites a different chemical within the cells. The chemical that fluoresces green is ferulic acid found within the cell walls, whilst the red highlights chlorophyll within the chloroplasts. Chlorophyll is the chemical that gives plants their green colour and is important in photosynthesis, hence why the chloroplasts are often called the 'energy centres' of the plant cells. The stomata (Greek for mouths; stoma is the singular) are tiny holes present within the epidermis, the external layer of cells, and are found commonly on the leaves and stems of plants. They are the main routes through which the plant exchange gases with the environment. The two guard cells are such named because they control the orifice, or pore, that comprises the stomata and regulates the mechanisms of opening and closing. The guard cells are shown in this image spanning vertically across the stoma with red blobs at their ends. By uptake of water the guard cells expand and open the pore; by losing water they 'relax' and the hole closes. Using this mechanism plants can control their uptake of gases (notably oxygen for respiration and carbon dioxide for photosynthesis) and loss of water vapour. Therefore, carbon dioxide levels can influence the degree of opening of the stomata, and as this gas is essential to photosynthesis stomas have become the subject of intense research by scientists in relation to our changing environment.