Stress Reduction for Plants

What happens when a plant is under stress? Plenty, it turns out. Ruby O’Lexy, a doctoral student in biology at Penn Arts and Sciences, is examining the ways plant cells communicate, and her research may help feed the world someday.

Working in the lab of Associate Professor of Biology Kimberly Gallagher, O’Lexy is investigating plasmodesmata, which are the channels that connect adjoining plant cells to allow transport of necessary materials like proteins and nutrients. In plants almost the entire organism is connected through these channels because plant cell walls are so thick.

Though biologists used to think that these were just static holes in the cell wall, they are finding the plasmodesmata are extremely regulated for internal functions like development—during flowering, for example. But O’Lexy is much more interested by the fact that they also seem to respond to external cues. “Plasmodesmata are really, really quickly modified or regulated in response to things like pathogen infection or wounding,” she says. “When a plant is infected, it will shut down these channels to restrict its transport there.”

She is researching this communication under agricultural stresses, focusing on heavy metal toxicity. Elements like copper, zinc, and iron have leached into the soil because of industry and other human activity. These are essential nutrients for the plant, but only in small amounts. More than that and the metal becomes toxic, and even trace (or micromolar) amounts can be enough.

O’Lexy is finding that under heavy metal toxicity, plasmodesmata do seem to be modified, altering cell-cell communication and transport. Shutting down in reaction to a poison would seem to make sense, but she says the most interesting thing she is finding is that this kind of shutdown is not a general response. “Previously in the literature, everything that we knew affected plasmodesmata did so by closing them and decreasing transport,” says O’Lexy. ”But I’m finding that some stresses actually seem to increase this transport. So there may be something or some signal that needs to be propagated.”

In addition, she has discovered that different stresses seem to have tissue-specific effects, so that the plasmodesmata might be shut down in some tissues but stay normal in the rest of the plant. “This isn’t just a general response of plasmodesmata closing down. There are more nuanced things going on, which we didn’t know before. That might mean that certain tissues need to be isolated or to communicate more to respond to stress better.”

If modifying plasmodesmata is necessary for the plant’s survival and health, then scientists can look for the pathway to do so. Tolerance is just one example. O’Lexy says, “There are a few species that seem to have tolerance for specific heavy metals.  And so we’re asking how they can survive, and if we can use that and put it in other species that are not so good at that.” With about 30 percent of earth’s soils polluted with some form of heavy metal, the results might be huge.