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Plants have a finite amount of energy that must be properly allocated to ensure their growth and survival.
It has been theorized that a plant attacked by leaf-eating insects would spend more of its energy budget on defensebut as a result, growth is hampered and slows down.
Researchers from University of Michigan genetically modified a plant so that its defense systems were constantly saturated and observed the impact on growth.
A study detailing the new research was published in the journal Proceedings of the National Academy of Sciences.
The growth-defense trade-off paradigm states that a plant will allocate resources where they are most needed despite the costs.
"Our study shows that large investments in defense necessarily reduce the amount of resources that would otherwise be available for growth and reproductive capacity," said Qiang Guo, a graduate student who participated in the study.
Plants stressed by herbivores will produce toxins to keep away phytophagous insects, but when these defenses are no longer needed, a plant will use repressive proteins called JAZs to stop defense systems and conserve energy.
The researchers genetically engineered a plant so that it lacked a vast majority of its repressive JAZ proteins, which placed it in constant defense.
"He continued to produce defense compounds, even in the absence of threats. As expected, it showed great resistance to insects, "said Guo. "Unlocking this defense arsenal has also provided protection against fungi that target plant tissues."
Without the JAZ proteins, the researchers found that the growth of the genetically modified plant slowed considerably to compensate for the energy imbalance.
"They have a much slower growth rate than their wild type counterparts. We can literally see and measure the growth rate deficit per day, "said Guo.
The plants in the study also produced a third of less seeds that sprouted later than usual. The seeds were smaller and had less nutritional value than the seeds of wild plants, and the researchers found that photosynthesis did not affect the slowing of the growth rate.
"The mutated plant derives from photosynthesis the same amount of energetic compounds as its natural and wild equivalent," he said. Ian Major, member of the research team. "However, it consumes more energy than usual. We believe that the plant feeds the massive and constant production of defense compounds, which keeps resources away from growth. "
Now, thanks to this study, which has taken ten years, researchers have a better understanding of how plants affect resources and defend themselves against different threats.
"Our conclusion is that JAZ proteins help plants to grow and reproduce by taming their defenses when the threat of attack is low, which helps conserve energy," said Major . "Depending on the severity of the threat, the JAZ proteins will activate the defenses as needed, perhaps as a dimmable light switch."
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By Kay Vandette, Earth.com Editor
Image credit: MSU-DOE Plant Research Laboratory
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