Newswise — Pressing on the gas and the brakes at the same time hardly sounds like a good driving technique, but Weizmann Institute of Science researchers have discovered that plants drive some of their key processes precisely in such a manner.
A team headed by Prof. Avihai Danon of the Department of Plant and Environmental Sciences, along with postdoctoral fellow Dr. Erez Eliyahu and then graduate students Ido Rog and Inbal Dangoor, studied the mechanisms controlling the plant production of starch, the most common carbohydrate in the human diet. The plant starts making starch as soon as the morning light turns on photosynthesis, and stops when photosynthesis subsides at night.
About 50 years ago, scientists discovered the “on” switch for starch production: a launch enzyme that is activated, via a series of regulatory proteins, by the flow of electrons generated in photosynthesis. Now, as reported in the Proceedings of the National Academy of Sciences, Weizmann Institute scientists have discovered the “off” switch for starch production. Working with a mustard-like plant called Arabidopsis, they figured out the chain of biochemical events leading to its shutdown at night. The decrease in light causes a small signaling protein called ACTH4 to lose electrons and become oxidized, which, in turn, quickly prompts it to transmit the “take a break” message to the starch production enzyme.
The scientists further realized that this mechanism remains active at a low level throughout the day. It’s as if the plant drives its starch production by pressing on the gas pedal and the brakes simultaneously: turning the production on while at the same time keeping it in check. When the scientists genetically engineered the plants to eliminate the “brakes,” starch production shot up by nearly 20 percent. This suggests that, in general, production efficiency stands at only about 80 percent because this brake pedal is on all the time. In the future, this research may make it possible to increase starch production in agricultural crops.
Why do plants naturally produce starch in such an inefficient manner?
Since light intensity, and with it the rate of photosynthesis, often fluctuates rapidly throughout the day, the plant needs to adjust its metabolism on an ongoing basis. Starch synthesis in particular needs to be closely attuned to photosynthesis so that the compounds created in photosynthetic reactions are promptly taken up – otherwise reactive oxygen molecules called free radicals, generated as a byproduct of photosynthesis, can build up in excess and harm the plant.
Pressing the “gas” and the “brake” pedals simultaneously enables plants to control their starch production rapidly and effectively via adjusting the relative strengths of the two. Keeping the brake pedal slightly pressed most of the time leaves room for a potential increase, should sunlight suddenly become extremely intense. Keeping one foot on the brakes is therefore part of the sophisticated set of control mechanisms that has helped plants survive over hundreds of millions of years.
Prof. Avihai Danon’s research is supported by the Raymond Burton Plant Genome Research Fund; the Lerner Family Plant Science Research Fund; the Leona M. and Harry B. Helmsley Charitable Trust; the Jacob and Charlotte Lehrman Foundation; Mr. Jack N. Halpern, New York, NY; and Adolfo Eric Labi, Italy. Prof. Danon is the incumbent of the Henry and Bertha Benson Professorial Chair.
The Weizmann Institute of Science in Rehovot, Israel, is one of the world’s top-ranking multidisciplinary research institutions. The Institute’s 3,800-strong scientific community engages in research addressing crucial problems in medicine and health, energy, technology, agriculture, and the environment. Outstanding young scientists from around the world pursue advanced degrees at the Weizmann Institute’s Feinberg Graduate School. The discoveries and theories of Weizmann Institute scientists have had a major impact on the wider scientific community, as well as on the quality of life of millions of people worldwide.
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