Arrested Development

Plants need boron to develop properly. Now we know why.

soil-based compounds of boron — a chemical element that resides near the top of the periodic table — are essential to healthy plant development. Crops in boron-deficient fields, especially those stressed by dry conditions, struggle to flower and pollinate properly. Boron-starved plants become withered and discolored. They yield poorly, if at all.

Plant scientists have long shared with farmers the knowledge that boron additives can compensate for deficiencies. What scientists hadn’t figured out was why boron-related stunting occurred in the first place. Now, thanks to a recent finding by a team of MU researchers, they’re closing in on an answer.

“Our study showed that a lack of boron actually causes a problem in the meristems, or the stem cells of the plant,” said Paula McSteen, an associate professor of biological sciences. “That was completely unknown before. Through a series of experiments involving scientists from several disciplines at MU, we were able to piece together the puzzle and reach a new conclusion.”

Meristems are tissues in plants that contain “undifferentiated” cells, those that have not yet grown into cells with a specific structure or function. Every organ in plants develops from meristem tissue, but insufficient boron torpedoes the process.

Corn is a crop that often suffers from boron deficiencies, making it a cereal of interest. Symptoms typically include problems with tassel development and subsequent kernel formation. For their study, the researchers evaluated a group of plants, called tassel-less, that were similarly stunted.

Kim Phillips, a graduate student in McSteen’s lab, mapped the corn plant’s genome and found a genetic mutation that rendered it unable to transport boron across the plant membranes, inhibiting further growth in the plants.

Amanda Durbak, a post-doctoral fellow, treated two groups of tassel-less corn, one with a boron fertilizer and the other with only water. The group treated with boron grew normally, while the group treated with water withered. Further testing revealed that, at the cellular level, the affected plants’ meristems had altered pectin, a biological polymer that is strengthened with boron and helps stabilize plants’ cell walls. Without the pectin, plant meristems disintegrate. These insights, McSteen says, are a strong first step toward developing new ways of dealing with boron-related crop losses.

“By using various techniques and expertise at MU, including genomics, translational experiments with frog eggs, research in the field, cellular testing, and evaluations at the MU Research Reactor and at MU’s Plant and Soil Analysis Facility, the study team drew conclusions that will help corn producers make informed decisions about raising crops in boron deficient zones,” says McSteen.

Researchers at the University of Georgia and at California State University, Long Beach also contributed to this study. The paper was published in the July 2014 issue of the journal, The Plant Cell.

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