Some plants may have an easier time "waking up" than many people do, thanks to a built-in biological clock that causes them to open their leaves in the morning and fold them at night. Now a Weizmann Institute researcher has discovered a biochemical "switch" that appears to control this opening and closing action.
Leaf movements are produced by changes in the volume of motor cells on opposite sides of the pulvinus, a thickened area at the base of each leaf stalk that acts as the leaf-moving organ. At dawn, cells in the lower half of the pulvinus swell and those in the upper half shrink, opening the leaves, while at dusk the reverse process occurs.
The swelling and shrinking are made possible by the flow of charged salt particles called ions through special channels in the motor cell membrane. Dr. Nava Moran of the Neurobiology Department has shown that certain ion channels open up only if they, or other nearby proteins, acquire phosphate.
In a study reported in the August issue of Plant Physiology, she was able to use this biological "switch" to control the opening and closing of the channels. Borrowing a technique known as the patch clamp from neurobiological research, Moran immersed a tiny strip of membrane in a solution where phosphate could be added or removed, and observed the opening and closing of the channels.
Since ion channels probably underlie not only leaf movements, including those produced in response to light or touch, but also other vital processes in plants, the improved understanding of the movement-control mechanism may one day have such diverse applications as preventing the wilting of crops during drought, or altering the time of flowering and fruition.
Funding for Dr. Moran's work was provided by the Israel Science Foundation administered by the Israel Academy of Sciences and Humanities; the U.S.-Israel Binational Science Foundation, Jerusalem, Israel; the U.S.-Israel Binational Agricultural Research and Development Fund; and the Helen and Milton A. Kimmelman Center for Biomolecular Structure and Assembly at the Weizmann Institute.
The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel.