Water is lost during the gas exchange that takes place in photosynthesiscarbon dioxide in, oxygen outthrough small pores in the surface of leaves that periodically open and close under the control of a biological clock. Exercising control over this clock could be a means of conserving water. "We know that these little cells on the surface of the leaf are controlled by the clock," says McClung. "It could be that different clocks regulate it slightly differently, and we would like to find the best clock, fine-tune it, and perhaps optimize the ability to get CO2 in without losing water."
Water figures prominently in another aspect of plant physiology. Water moves up through the stem to the leaves, involving proteins called aquaporins. "There is a big family of genes that encode aquaporins, and in Arabidopsis the circadian clock governs the expression cycles of about a third of those genes," says McClung. "That suggests there is mechanism to actually regulate this hydraulic conductivity over time, constituting another instance where the clock is involved in water use efficiency."
Together with colleagues in Wyoming, Wisconsin, and Missouri, McClung has been looking at another a crop, Brassica rapa, a close relative of which is the source of canola oil. With a five-year National Science Foundation grant of more than $5 million, the group is investigating Brassica's circadian patterns, looking at inheritance and water use efficiency. "We have mapped 10 genetic regions that are associated with water use efficiency," says McClung. "We have al
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