Stomata are the "referees" of a compromise between the admission of CO2 for photosynthesis and the loss of water by transpiration. Farmers would like their crops to transpire less, thus reducing the need for irrigation. Similarly, nurseries and gardeners would like to be able to reduce the amount of water lost by plants that are to be transplanted, because transplanting often damages the roots, causing the plant to wilt or die. What they need is a good antitranspirant: a compound that can be applied to plants, reducing water loss from the stomata without producing disastrous side effects by excessively limiting CO2 uptake.
Abscisic acid and its commercial chemical analogs have been found to work as antitranspirants in small-scale tests, but their high cost has precluded commercial use. What about making plants more sensitive to their own abscisic acid? The guard cells of transgenic plants with a mutant allele of the era gene are highly sensitive to abscisic acid and hence resistant to wilting during drought stress.
Atotally different type of antitranspirant temporarily seals off the leaves from the atmosphere. Growers use a variety of compounds, most of which form polymeric films around leaves, to form a barrier to evaporation. These compounds cause undesirable side effects, however, and can be used only for short periods of time. Their most common use is in the transplanting of nursery stock.
In the absence of antitranspirants, stomata are normally open during daylight hours, allowing CO2 to be fixed and converted to the products of photosynthesis. Next we'll see how these products are delivered to other parts of the plant, supporting growth of those parts.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.