Plants don’t grow well when always on high alert | Science News for Students

Plants don’t grow well when always on high alert

Scientists bred a weed to make insect-repelling chemicals all the time
Nov 14, 2018 — 6:45 am EST
a photo of thale cress, a bioengineered plant, with small white flowers

Scientists engineered a plant called thale cress (above) to be nearly always on alert to leaf-eating predators. In the lab, these plants grew smaller and made fewer viable seeds than normal.

ROBERT VIDÉKI, DORONICUM KFT./BUGWOOD.ORG (CC BY-NC 3.0 US)

Plants make sacrifices to protect themselves from pests. Now a tiny weed that squeezes through sidewalk cracks is helping scientists understand those costs of always being on guard.

Nature's greenery often fights insects and other plant-eaters by releasing bitter chemicals into their leaves. If a plant tastes bad, hungry bugs will avoid it. Arabidopsis (Ah-rab-ih-DOP-sis) is a commonly found member of the mustard family. Scientists often turn to it as the “lab rat” of the plant world. In the new study, researchers studied thale cress (Arabidopsis thaliana) to learn what this bitter defense costs the plant.

Putting extra energy into pumping protective chemicals through a plant’s veins leaves a plant less able to grow and reproduce, they now report.

All plants have a bundle of what are called JAZ genes in their DNA. Those genes provide the instructions to make JAZ proteins. These proteins help plants control how they use defensive chemicals. Over a 10-year span, the team bred together Arabidopsis plants that had been engineered to possess mutated JAZ genes. (Mutations are altered forms of some gene.) These plants ended up with 10 of its 13 JAZ genes disrupted, so they made less of those JAZ proteins.

Such plants were in defensive mode nearly all of the time. And they paid a price. They grew shorter than normal and were weaker. These plants also made fewer seeds that were viable (able to sprout). The plants also developed brown and withered leaves. This showed that the engineered plants were being starved of the carbon they need for growth. Carbon starvation happens when plants close up the tiny holes in their leaves known as stomata (Stoh-MAH-tah). Those holes let leaves breathe in the carbon dioxide they need to make food.

The scientists reported their findings online October 22 in the Proceedings of the National Academy of Sciences.

When plants keep their defenses turned on all the time, they use up energy. This leaves them with less energy to power growth and reproduction, the scientists explain.

“When plants use those resources for defense — in this case, a defense against insects — there is a major trade-off,” says Gregg Howe. An author of the new study, he’s a plant biologist at Michigan State University in East Lansing.

It’s not yet clear how the lessons learned from this plant might apply to other species, including the grains farmers grow for food, notes Georg Jander. He’s a chemical ecologist at Cornell University who was not involved in the new work.

Howe’s team hopes, however, that research like this will reveal new ways to protect crops from bugs without harming the plants or needing to douse fields in pesticides.

Power Words

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Arabidopsis thaliana     A weedy mustard plant frequently used to study the growth and behavior of plants. It is so commonly used by plant scientists that it has come to be called the “lab rat” of green-plant studies.

biology     The study of living things. The scientists who study them are known as biologists.

bug     The slang term for an insect. Sometimes it’s even used to refer to a germ.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon dioxide (or CO2)     A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

crop     (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers. 

defense     (in biology) A natural protective action taken or chemical response that occurs when a species confront predators or agents that might harm it. (adj. defensive)

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

ecology    See  A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

insect     A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

mutation     (v. mutate) Some change that occurs to a gene in an organism’s DNA. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet. A gene with this change is referred to as a mutant.

pesticide     A chemical or mix of compounds used to kill insects, rodents or other organisms harmful to cultivated plants, pets or livestock; or unwanted organisms that infest homes, offices, farm buildings and other protected structures.

Proceedings of the National Academy of Sciences     A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

vein     Part of the body’s circulation system, these tubes usually carrying blood toward the heart.

viable     Able to live and survive. (in biology) Able to survive and/or live a normal lifespan. (in engineering) Something that should work or operate according to plan, as in a “viable concept.”

weed     (in botany) A plant growing wild in, around — and sometimes smothering over — valued plants, such as crops or landscape species (including lawn grasses, flowers and shrubs). Often a plant becomes such a botanical bully when it enters a new environment with no natural predators or controlling conditions, such as hard frosts.

Citation

Q. Guo et alJAZ repressors of metabolic defense promote growth and reproductive fitness in ArabidopsisProceedings of the National Academy of the Sciences. Published online October 22, 2018. doi: 10.1073/pnas.1811828115.