Among the specialized cells in corn leaves are the stomata. Each stomate consists of two guard cells and two companion cells. Corn, being a monocot, has these specialized cells organized parallel to the length of the leaf at a rate of about 36000 stomata per square inch on the top of the leaf and about 50000 per square inch on the bottom to the leaf.
Blue light wavelengths detected by a carotenoid activates a process in which potassium ions flow into the guard cells. Thus, the water concentration in the cell drops, resulting in osmotic pressure for water to enter the guard cells. The shape of the guard cells allows uneven swelling and a pore opening up between the two guard cells. Photosynthesis produces sucrose that then contributes to the osmotic pressure in the cells. At the end of the daylight, starch is synthesized from the sucrose and potassium ion concentration is reduced and the opening between the two guard cells closes. Other compounds within these cells also contribute to this phenomenon. https://academic.oup.com/jxb/article/57/2/381/489968.
This is essential, of course, to allow diffusion of CO2 into leaves for photosynthesis in other leaf cells. Open stomates allows O2 to be released to the atmosphere but also water loss. Water evaporation through stomates (transpiration) is affected by the relative humidity in surrounding atmosphere as the water concentration within the leaf spaces is nearly 100%. Cohesiveness of water molecules ‘pulls’ water up to the leaves so that essentially every molecule of water that goes out the stomata is replaced by one from the root tissue.
During the day, stomata are open, carbon dioxide moves into the leaf, oxygen moves out and so does water. At night, photosynthesis in the guard cells stops, water moves out of the guard cells causing the swelling to be reduced and the pore is closed. We will discuss more about this phenomenon later as the plants grow.
Stomata are essential to corn and have a dramatic affect on productivity as import of carbon dioxide and export of water occurs through the stomata. This topic is covered in Corn Journal 5/10/16.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.