Does plant have a defense system?

  Sichuan experts researched and confirmed the hypothesis: there are not only "weapons" but also "call for help"

  A hypothesis

  Phytophagous insects and their natural enemies participate in driving the evolution of leaf volatiles so that plants have defensive functions?

  After the hypothesis in the field of plant research was put forward, an ideal plant population and its corresponding insect taxa have not been successfully found to verify.

  One time verification

  Sichuan Agricultural University, Zhejiang University, Leiden University in the Netherlands and Neuchâtel University in Switzerland have jointly carried out an experiment called to verify the evolution of plant "fangs", confirming that plants will not be "slaughtered" by insects as we thought. -Hundreds of millions of years of evolution, so that plants also have their own smart "armor."

  What's the point

  “An autonomous defense system can be formed in the field to reduce pest damage to crops. There is no need to spray pesticides manually, which saves time, effort and money, and is more environmentally friendly.” said Lin Tiantian, an associate professor at the College of Forestry of Sichuan Agricultural University. The components of volatile substances, through chemical synthesis, become new and safe "insect repellents" and "inducing agents".

  Do you have any doubts that plants that will not run away can only be "ravaged" in vain when the leaves are eaten by insects?

As a "low-rank" player in the food chain, are plants really so humble?

  There has always been a hot hypothesis in the field of plant research: herbivorous insects and their natural enemies participate in driving the evolution of leaf volatiles so that plants have defensive functions.

  On August 9, Lin Tiantian, associate professor of Forestry College of Sichuan Agricultural University, published a research paper titled "The evolution of an invasive plant proves the defensive function of plant leaf volatiles" in Contemporary Biology as the first author, confirming Plants will not be "slaughtered" by insects as we imagined-hundreds of millions of years of evolution have given plants their own clever "armor".

  Does plants have defensive functions?

  This hypothesis has not been verified

  There has always been a hot hypothesis in the field of plant research: herbivorous insects and their natural enemies participate in driving the evolution of leaf volatiles so that plants have defensive functions.

  It seems to be beyond ordinary people's understanding of plants that are "submissive".

  In the field of plant research, it has not been successful to find an ideal plant population and its corresponding insect taxa to verify this hypothesis. Therefore, whether this hypothesis is true or not has been a lot of controversy in the academic circles.

  "If you rely solely on the laboratory for experiments, you need to place a plant population in an environment where there are no insects and their natural enemies to evolve for more than 100 years, which is obviously unrealistic." Lin Tiantian explained.

  It just so happens that the research group of Dr. Klaas Vrieling of Leiden University in the Netherlands is studying invasive plants.

  Senecio, a perennial plant native to Eurasia, was brought to the United States, Canada, Australia, New Zealand and other places by human activities about 150 years ago. It became a local "invasive plant" and became the ideal of this experiment. Plant populations.

"In the'territory' where plants have invaded, there are no insects and their natural enemies." Lin Tiantian explained. This means that in the past 150 years, Senecio has "brutally grown" in a "free" environment, and it will still Does it produce substances that resist insects?

  The discovery of a transnational cooperation:

  Plants also have "weapons" and "seek help"

  Beginning in 2015, experiments to verify the evolution of plant "fangs" were carried out in cooperation with Sichuan Agricultural University, Zhejiang University, Leiden University in the Netherlands, and Neuchâtel University in Switzerland.

  "The Leiden University group in the Netherlands mainly collects and cultivates plants, and does insect measurement in Neuchâtel, Switzerland, because they have an insect olfactory tester and a professional volatiles tester." Lin Tiantian said, the experimental team is in the local environment of Senecio For example, the Netherlands, France and other places have collected more than 20 populations from different distribution areas, and 20 populations have also been collected in "invasive environments" such as the United States, Canada, Australia, and New Zealand.

"Put them under the same experimental conditions for comparative verification."

  In the selection of herbivorous insects, the experimental team selected Senecio’s monophasic insect-Cinnabaridae, and the obligate parasitic wasp of Cinnabaridae. At the same time, it also chose another general feeding insect-Brassica oleracea.

  "Senecio leaves produce two volatile substances, one is constitutive volatiles and the other is induced volatiles." Lin Tiantian said.

  Constitutive volatiles refer to substances produced by the continuous release of Senecio leaves themselves, which can be used as a direct defense to prevent them from being eaten by common feeding insects, which is equivalent to "insect repellent".

  Inducible volatiles refer to the rapid secretion of ingredients that can attract insects’ natural enemies after being gnawed by the monophagous insects. Adhering to the strategy of “the enemy’s enemy is a friend”, it sends out a “help” signal and summons the insect’s natural enemy. Coming to "rescue" is equivalent to "inducing agent".

  In the experiment, two control groups of native population and invasive population were set up. First, the selection preference of "universal insects", "special feeding insects" and "parasitic wasps of special feeding insects" was tested by using an insect olfactory tester in a laboratory environment.

  "Simply put, we put Senecio plants from two different populations of indigenous and invasive species in an insect olfactory device to see which plant the three types of insects prefer." Lin Tiantian said, and also collected two in the experiment. The constitutive volatiles and inducible volatiles of the population of plants, and the composition and content of different volatiles are analyzed with detection equipment.

  In addition to drawing conclusions in the experimental environment, the team also returned to the natural environment, planted native and invasive species of Senecio in the experimental field, and placed the larvae of monophagous insects on the leaves. The parasitism of the parasitic wasp, and compare which Senecio population has higher egg production." Lin Tiantian said.

  The study found that compared with the local population, the constitutive volatile content released by the invasive Senecio population was higher, while the inducible volatile content released by the monophagous insects was significantly reduced.

The results of insect olfactory and oviposition experiments show that, compared with local populations, the constitutive volatiles released by invading populations have a stronger attracting effect on monophagous insects, and a stronger repellent effect on phagophagous insects.

At the same time, the inducible volatiles released by local populations caused by the damage of monophagous insects are more attractive to parasitic wasps than invasive populations.

This result is corroborated by the field experiment of natural parasitism.

  That is to say, in the invading environment of "barbaric growth", because it does not specifically eat its own natural enemy insects, Senecio does not have to laboriously grow "armor" to resist natural enemies. Inducible volatiles have no "useful place" and function " Degradation".

But other "omnivorous" insects may also regard the invading Senecio as a "Chinese meal". As an "outside visitor" Senecio should be careful to use constituent volatiles to "invisible" and "protect from poisoning." ".

  The future uses are exciting:

  Or it will allow crops to grow their own "armor"

  From 2015 to August 2021, the experiment and data analysis work lasted 6 years.

"Because the insects used in the experiment only appear in May and June each year, we have to spend a lot of time collecting insects. We did experiments in the laboratory the previous year, and we have to wait until the next year before we can do field experiments." Lin Tiantian said. Part of the time is also doing preliminary preparations, coupled with cross-border cooperation, it takes a long time.

  Such smart behaviors of plants are discovered by humans, and naturally they cannot be wasted in vain.

  "In the future, we may be able to use other plant materials, such as corn, rice and other crops, to find the regulatory genes for plant volatiles, and use gene editing to increase constitutive volatiles and insect-inducible volatiles. Lin Tiantian said, so as to form an autonomous defense system in the field to reduce the pests suffered by crops, there is no need to spray pesticides manually, which saves time, effort and money, and is more environmentally friendly.

  Another possibility is to find the components of volatile substances, through chemical synthesis, to become a new and safe "insect repellent" and "inducing agent."

"But these all require further research by scientists, especially verification by field experiments." Lin Tiantian said.

  Chengdu Commercial Daily-Red Star News reporter Yu Zunsu internship Cheng Jiachi