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University of California - Davis

Tomato grafts show how plants control growth

Genes in one part of a plant can override the genetic program in a distant part of the same plant and change how the plant grows, according to researchers at the University of California, Davis.

"This forces us to look at plant growth and development a little differently," said UC Davis plant biologist Neelima Sinha, who supervised the research team. The system could act like the hormonal system or nervous system in animals, taking orders from one part of the organism to another. For example, environmental signals might switch on genes in the leaves of a plant. Messenger RNA made from these genes would travel to other parts of the plant and change how it grows.

Short pieces of messenger RNA are the blueprints for making proteins from genes encoded by DNA. Conventionally, the process of transcription from DNA to RNA and then translation from RNA to protein is supposed to take place within the same cell.

However, scientists have found that messenger RNA moves throughout plants using a network of tubes called the phloem, said Sinha.

Biologists did not know whether this long-distance movement of messenger RNA had a real function in plants.

Sinha's team grafted shoots from normal tomato plants onto tomato plants with a genetic change that causes abnormally shaped leaves. They found that new leaves on the normal part of the plant began to develop the abnormal leaf pattern.

When they looked at cells from the plants, they found that RNA specific to the genetic change had traveled from the abnormal leaves to the normal part of the plant. The RNA accumulated in the meristems -- the growing tips of the shoots.

"This is the first study to show that long-distance transported RNA is functional," said graduate student Minsung Kim, who is lead author on the study. Because the RNA accumulated in cells of the meristem, it must carry within it an address to take it to that location.

The study is published in the July 13 issue of the journal Science. The other authors on the paper are graduate student Sharon Kessler and undergraduate student Wynnelena Canio.

Editor's note: Electronic images of the grafted tomato plants are available. Contact Andy Fell for details.

Media contacts: Neelima Sinha, 530-754-8441, nrsinha@ucdavis.edu (not available until July 23); Andy Fell, News Service, 530-752-4533, ahfell@ucdavis.edu.

Infinitely sticky antibodies deliver cancer treatment

Using antibodies as "smart bombs" to carry doses of radiation straight to tumor cells is the aim of research by University of California, Davis, chemistry professor Claude Meares. The team has developed a new method to permanently bind radioactivity to antibodies.

Antibodies are proteins made by the immune system that fight disease by sticking to bacteria, viruses and cancerous cells. They are highly specific to one target. In theory, an antibody directed against a tumor cell could carry a toxin or a dose of radiation straight to the tumor.

Some clinical trials of these treatments are beginning, for example in ovarian cancer, said Meares.

To make these smart-bomb antibodies more effective, Meare's lab looked for ways to get tighter binding between the antibody and the radioactive element indium-111, contained in a small carrier molecule. In the experimental treatments currently in trials, antibodies are tagged with radioactivity using two natural molecules, biotin and streptavidin, that stick together but can pull apart again.

Instead, graduate student Albert Chmura, research assistant Molly Orton and Meares made an antibody that recognized and stuck to the radioactive carrier. Then they engineered the binding region of the antibody protein, so that when it meets the carrier molecule it not only binds to it, but forms a permanent chemical bond. It's rather like replacing Velcro with welding.

To treat cancer with this approach, you would need a double-headed antibody. One end would recognize the tumor, and the other would grab the radioactive carrier. The antibody would go into the body first and find it's way to the tumor. Then the radioactive carrier would be injected. Because this is a small molecule, it would reach the tumor quickly and stick to the antibody, delivering the maximum amount of radiation to the tumor cell while avoiding healthy tissues.

The research on permanent binding of antibodies and radioactive carriers is described in a paper by Chmura, Orton and Meares in the July 10 issue of Proceedings of the National Academy of Sciences of the U.S.A. Meares has licensed the patented discovery from the University of California, and has founded a company, Lexrite Labs of Dixon, Calif., to commercialize the invention.

Media contacts: Claude Meares, Chemistry, 530-752-0936, cfmeares@ucdavis.edu; Andy Fell, 530-752-4533, ahfell@ucdavis.edu.

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