Sunday, September 6, 2009

Rural Delivery: Sacrificial Cells

by Michael Hofferber. Copyright © 1996. All rights reserved.

Plants get sick. They develop soft rot and leaf spot and cankers of all sorts. They suffer ulcerous lesions, mildews, and various wilts and scabs.

Apple trees get fire blight, which blackens their leaves and twigs and is sometimes fatal. Potatoes are susceptible to late blight, as 19th century Ireland learned too well, and grapes are vulnerable to powdery mildew, which nearly wrecked the French wine industry.

In the U.S. alone, there are more than 25,000 known plant diseases causing crop losses of several billion dollars annually.

Figuring out how plants defend themselves against disease and bolstering those defenses has been a priority for agricultural researchers.

Much study has been done on the activation of the "defense genes" which encode the proteins of plant cells with protective functions. Using gene splicing techniques, scientists have learned how to activate the cell's defenses before a pathogen attacks, an important breakthrough in crop protection.

Yet, while scientists have looked closely at the cells of plants and figured out how they protect against disease, until lately they passed over one peculair aspect of resistance: cell suicide.

When a disease appears on a plant the cells at the front lines often collapse and die. This has been called a "hypersensitive response" because it happens before the cells have actually been attacked.

At the Salk Institute for Biological Studies scientists closely observing the hypersenitive response noticed a buildup of hydrogen peroxide inside the cells.

The scientists watched as the hydrogen peroxide caused a cross-linking of structural polymers in the cell wall, making it tougher and harder to penetrate, much like a self-sealing tire. The chemical also triggered the pre-programmed death of the suicide cells, if you will, and alerted other nearby cells to the presence of an invader.

By checking the advance of the disease and alerting other defense cells, suicide cells give the plant a chance to produce antibiotics and raise other defenses. Their sacrifice, in some cases, makes a life-or-death difference to the plant.

Knowing how the hypersensitive response works will lead to techniques for stimulating it artificially. Plants will soon be genetically engineered to produce hydrogen peroxide in their suicide cells more readily after a pathogen attack.

How this will effect crop protection efforts and food supplies remains to be seen. But unlike attempts to control disease by attacking pathogens, this approach delivers its prescription directly to the plant: Get well soon.

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