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How plants say 'no' to fungus.

How plants say 'no' to fungus

Although you never hear them complaining, plants hae a tough life. If bacteria, viruses, worms, locusts, other plants, wind, sun or air pollutants aren't harassing them, fungus might very well be bringing plants to a brown, wilted end. But despite their inability to run away from their oppressors, plants make defensive stands in ways that are only partially understood.

Now, a quartet of Swiss scientists reports direct evidence that some plants defend themselves against fungus by producing an enzyme called chitinase that potently inhibits fungal growth. Not only is this the first time a biological function has been associated with the enzyme, according to the scientists, but chitinase also could have agricultural applications.

Chitin--a tough biological polymer--is the major constituent of the exoskeletons of lobsters, crabs and many insects. It is also one of the major building materials of the fungal cell wall. Several research groups have observed that when chitinase and certain other enzymes are present, tiny chunks of fungal cell walls break off. But this is only indirect evidence and does not pinpoint chitinase as the fungus fighter, says Angela Schlumbaum, who authored the report with Felix Mauch, Urs Vogeli and Thomas Boller, all from the Botanical Institute of the University of Basel. The report appears in the Nov. 27 NATURE.

To catch chitinase red-handed, the scientists purified it from bean plants and tested its effect on the fungus Trichoderma viride, which they had cultured in petri dishes. They found that chitinase inhibits fungal growth in proportion to the amount of the enzyme present. The Swiss scientists also found that if they denatured the chitinase by boiling it, or if they added antibodies that bind to it, antifungal activity was blocked.

In addition, chitinase from crude protein extracts of bean leaves showed antifungal activity that increased if the leaves were first treated with ethylene, which is known to induce plants to manufacture chitinase. If the researchers added antibodies against chitinase to the crude protein extracts, antifungal activity was blocked.

The newly reported work "is the first time that anyone has demonstrated that chitinase has the possibility to inhibit the fungus," Schlumbaum told SCIENCE NEWS. By itself, chitinase inhibits Trichoderma viride, she adds, but to inhibit many other fungi, other natural enzymes such as [BETA]-1,3-glucanase must be present.

Plant pathologist Richard M. Bostock of the University of California at Davis says the Swiss findings describe for the first time a possible defensive function for the enzyme. Bostock told SCIENCE NEWS that further understanding of how chitinase activity is controlled by the plant genes could enable scientists to manipulate it either by using techniques of genetic engineering or by learning how to turn the gene on or off with well-designed molecules.
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Title Annotation:by producing enzyme called chitinase
Author:Amato, Ivan
Publication:Science News
Date:Dec 6, 1986
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