Revolutionary look at how plants use light may help improve crops

Dina Mandoli can lay claim to a feat that's relatively rare among doctoral candidates.

Not only has she tossed out the interpretation of 40 years of botanical research, but she's made a major contribution to the understanding of how plants use light.

First, she discovered that ''safe'' lights - lamps commonly used by botanists to see during experiments where plants are supposed to ''think'' it's dark - weren't fooling the plants. Plants, she found, will react even to the low level of light emitted by these safe lamps. This error has resulted in the collection of incorrect data in thousands of experiments.

Then she discovered that plants have a highly sophisticated fiber-optical system for passing light from one part of the plant to the other. Light can travel along plant fibers in much the same way that the telephone company sends it through bundles of thin glass rods, she reports.

''It's brilliant work,'' says Washington University plant physiologist Barbara Picard. Ms. Mandoli's fiber-optics discovery, she says, is a ''critical'' step toward understanding of how plants grow. The understanding of the plant growth cycle, she adds, is necessary to improve crop strains in agriculture and other applications.

''It's going to be a boon to the basic research people,'' says Stanley Roux, a biochemist at the University of Texas, Austin. ''It will change the way they design their research.'' Researchers, he says, knowing how plants carry light through their system and where they're most sensitive to light, will be able to separate the most light-sensitive parts for study. Then they can accurately measure the light efficiency of plants, looking for plants that use light the most efficiently. This could lead to increased productivity per acre.

''We may be able to forget about genetically engineering plants - the strains we're looking for may already exist,'' Roux said.

Initially, Ms. Mandoli, a graduate student at Stanford University, set out on a sort of trial run to reproduce many of the classical experiments of the last 60 years dealing with phytochrome, a blue-green pigment controlling growth in plants.

''But I couldn't reproduce them.'' Rather than being daunted, she found her curiosity was piqued.''

Ms. Mandoli was investigating the sensitivity to light of oat seedlings growing in darkness. Tiny amounts of light were known to affect plant growth even while the plant was almost entirely in the seedling stage. But Ms. Mandoli, working with her dissertation adviser, Winslow W. Briggs, found that only a very brief encounter of oat seedlings with the lab's ''safe'' lights initiated plant growth.

There were, she allows, hints in the scientific literature that safe lights were not as safe as believed. ''But no one ever took them really seriously,'' she says. ''Since this oat test system is used as a classic test system for light responses, I think that's awfully peculiar.''

She spent the rest of her dissertation sealed in a steaming, pitch-black botany lab about the size of a meat locker.

The plants, she determined, were so sensitive to light that dark curtains over the metal door and seamless walls weren't enough. Ms. Mandoli prevented static electricity from being generated on her hair and clothing by pulling her hair back and wearing heavy cotton garments. She tried infrared Army night vision equipment but found, even when covering the eyepieces, that this gave off too much light. Only then, targeting laser beams on the fibers of plants grown in the dark, were she and Briggs able to make their discovery about their optical properties.

Through total internal reflection, the mechanism of an optical fiber, Ms. Mandoli found that plants are 10 percent as efficient in transmitting light as their synthetic counterparts - not good enough for the phone company but fine for a plant. More significantly, rather than merely distributing a hazy glow through their tissues, plants can transmit light coherently. A laser-generated Roman character ''E'' shown in one end was clearly readable coming out the other.

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