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Vol 57 No. 2 | Jan. 2005
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Professor Receives NSF Grant to Study Plant Adaptation to Light

As any gardener knows, placing a shade-tolerant plant in full sun or putting a sun-loving plant in a shady place usually causes the plant to eventually wither.

The process of photosynthesis, in which plants turn light into energy, is well known, but how plants genetically adapt to different light levels is still not fully understood. With a $452,000 grant over three years from the National Science Foundation, Judy Brusslan, an associate professor of biological sciences at CSULB, is looking at how genes within the plant Arabidopsis thaliana, or mouse ear cress, enable the plant to react to different light intensities, called photoacclimation.

"The reason there is life on earth is because plants do photosynthesis," Brusslan explained. Plants absorb carbon dioxide, create oxygen and are a vital part of the food chain. "We're interested in how plants grow in different light intensities. Since plants need light energy, they have to be able to deal with different amounts of light. Too little light is going to make it hard for them to grow--they don't have enough energy--and too much light is actually damaging, too. It produces extra photon energy that they need to dissipate in some way."

In her lab, she found that if a normal plant was moved from a low to a moderate light intensity, there was a gene whose level of expression went down. "But when we moved mutants that can't harvest light efficiently -- it's missing a certain pigment so it can't harvest light effectively -- into moderate light, we don't see a decrease in the expression of this gene.

"It seems the expression of the gene is dependent on light harvesting. If you harvest enough light, then you turn down the expression of this gene. If you can't harvest enough light, then the expression of this gene stays high," she said. "What turned out to be interesting is when we looked at the sequence of this gene, it turns out to be a protease, which means it degrades other proteins. It is similar to proteins that have a specific activity; that is, they remove the first two amino acids from the protein. Proteins are long chains of amino acids. This will occur only if the second amino acid is a proline." The positions of amino acids within a protein help determine its biological function.

She is working with a particular type of protease called dipeptidyl aminopeptidase (DAP). By creating and studying mutant plants that lack DAP, she hopes to better understand the chemical and biological means that help plants gather photons of light and convert them to energy.

"It can have agricultural implications. We still don't know if this protease could be involved in signaling. It could cleave some specific protein and that's really important for signaling, or it could be something much more general, where it's sort of the garbage disposal of the chloroplast," Brusslan said. Chloroplasts are the bodies within a plant cell that contain chlorophyll, the green pigment essential to photosynthesis. "We still don't know if our proteases have specific functions or more general functions. That's hopefully something we're going to tease out through the mutants."

"This work will be done by undergraduate and graduate students, and I'm also hiring a postdoctoral fellow," she said, noting additional benefits of the grant. Cal State Long Beach is recognized by the National Science Foundation as the master's level university with the largest number of students who go on to earn doctoral degrees in science.


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