Shulou(Shulou.com)11/24 Report--

In our impression, when the wheat and rice are ripe, the heavy ears bend their "waist".

But you may not have thought about such a question: why do mature seeds hang on the matrix and not fall?

The answer to this question may surprise you, that is, the millet that falls will run away.

The seeds of the ancestors of many weeds ran away. Let's first take a look at one of the most "able"-- oat's close relative, Avena sterilis.

Wild oats (photo: wikimedia) Oats are common weeds in wheat and barley fields. They are so adaptable that they can be mixed on any continent except Antarctica. Its seeds may have spread from the Middle East to Europe and elsewhere with the cultivation of wheat and barley three to four thousand years ago.

As you can see, when the seeds of wild oats fall off from the mother and fall to the ground, they show innate kung fu--

Unreal wild oats (photo source: see watermark) A carp beat up, and then a Ling Bo micro step, it will be a long way off. No wonder wild oats are also called animated oat.

False wild oats (photo source: see watermark) you may have noticed that two dull hairs keep turning when the wild oats run away. Does its movement have anything to do with the dull hairs?

Yes, this kind of sport does rely on dull hair-- awn. However, it does not move consciously, and its driving force for running away does not come from itself, but from the air.

The specific process is this: the spikelets of wild oats can easily fall off and fall to the ground before ripening.

Wild oats (photo source: see watermark) these two long awn parts close to the seed have asymmetric water absorption, one side can absorb water and expand, while the other side remains dry all the time.

The base of the wild oat awn is curled with the change of humidity. (photo Source: DOI: 10.1016 / j.actbio.2021.08.048) Heat and moisture accumulate on the long awn surface during the day and cool and dry at night. In the process of constant wetting and dehydration, this asymmetrically absorbent awn keeps the seeds spinning in one direction. In this way, the seed can roll farther and farther through the night to achieve expansion.

The autonomous movement of wild oats. (photo source: GRU Information Resource) when the seed falls into the crack, the dull machine also allows the seed to continue to make holes, ensuring that it touches the soil and germinates smoothly.

Wild oats drill into the soil. (photo Source: GRU Information Resource) look, "Antenna full Bud" dived under the stone to lie down.

In other words, the seed of wild oat is a moisture-driven biological engine. This autonomous movement through moisture is called hygroscopic movement (Hygroscopic movement).

Unreal oats hide from the ground. (photo Source: BYUI Applied Plant Science Department) of course, not only wild oats have this ability, but our staple foods basically have the ability to roll all over the floor. Because with the exception of buckwheat and quinoa, almost all human staple foods (such as rice and wheat) are Gramineae, and as early as 1979, researchers found that many Gramineae plants can run away.

That year, Martyn H. Peart, a botanical researcher at the University of Queensland in Australia, proved for the first time that many seeds of the Graminea family could "walk".

This is because the seeds of Gramineae usually have dull hair-awn. He collected six different varieties of grasses with dull hair and found that they all ran away. After getting rid of the dull hair, they will not move, they can only lie flat on the ground, and the germination rate decreases sharply.

Rivka Elbaum and Abraham Yael, botanists at the Hebrew University, point out that the spread of all plant seeds depends on moisture absorption, except that some plants roll like grasses, some fry like sesame seeds, and some dig holes in the ground.

Let's take a look at the wheat roll.

Wheat (photo source: wikimedia) the awn of wheat is also a biological engine. In order to ensure that the wheat will not slip when rolling, the dull hair of the wheat is siliceous and has a lot of friction. The hard composition of the soil also contains silicon compounds, silicon-silicon collision can not be eliminated, can only increase friction.

The dull hair of wheat also has the ability to prevent "backing up". Do you see the burr in the picture below? This burr is similar to the anti-reverse ratchet on a gear and prevents the seed from moving in the opposite direction. So the wheat seeds have to roll all the way out.

The burr on the wheat awn prevents it from reversing as it rolls. (photo source: doi:10.1126 / science.1140097) in addition to rolling, the wheat awn also has the ability to eject.

A study published in Science in 2007 compared the movement of wheat seeds to frog legs, and changes in humidity could drive the seeds to eject.

How is this achieved? Once the dull hairs of the wheat cross and cannot move, the stress builds up, making the dull hairs look like compressed springs. Once the stress accumulates to a certain extent, the dull hair will cause the seed to eject outward.

The Science study points out that this setting of wheat makes perfect use of the natural environment.

(photo: wikimedia) because in the hometown of wheat, the crescent fertile soil in the Lianghe River Valley (near present-day Israel, Syria, Iraq and Turkey), summer is dry and long, while winter is a short rainy season. The season of wheat seed ripening coincides with the dry season, but the humidity is slightly higher at night. The seeds of wheat happen to take advantage of the diurnal changes of the natural climate, so that they can happily run all night, and achieve extensive automation and long-distance unmanned transmission.

This kind of rolling and crawling skill is naturally good for plants, but humans won't like it. What else do people eat when all the seeds are gone?

Rice (Oryza sativa). (photo Source: wikimedia) so our ancestors chose grains that were fatter, could not run, or even fell to the ground.

Elbaum and colleagues point out that wheat was domesticated about 10,000 years ago, and humans deliberately selected fat seeds that could not run; some varieties of domesticated wheat had no awn, and the rest of the fat cubs could not run not because of their short legs, but because they could not get into the field.

Elbaum they further pointed out that, in fact, another important thing that human ancestors did to prevent wheat from running away was what was mentioned at the beginning of the article: to prevent seeds from falling to the ground in the first place.

The behavior of seeds falling to the ground after maturity is called shattering by biologists. In fact, a big part of agricultural research is to find the genes that control threshing so that wild grains with special skills can be domesticated.

Comparison between non-threshing red rice (left 1) and threshed red rice. (photo source: FAO) Wild wheat is easy to thresh because it is controlled by dominant genes. However, in the process of wheat domestication, the threshing wheat was deliberately eliminated by human beings. However, the restless genes of domesticated and awned wheat are still preserved, and their seeds are still beaten according to changes in ambient humidity.

The awn of wheat moves with the change of air humidity. (photo source: doi:10.1126 / science.1140097) the gramineous rice (Oryza sativa) and oats (Avena sativa) we eat now is another story. In the process of domestication, rice and oats not only do not shed grains, but also lose the dull hairs that can run away.

Oats that have lost their hair after being domesticated by humans. (photo source: wikimedia) but also because they no longer have dull hair, rice and oats cannot drill their own holes into the soil and need to be sown artificially. So now they are completely dependent on human beings to survive, and they will not survive if they are released into the wild.

From this point of view, the wild is more independent, the well-behaved is more clingy, and it is also suitable for plants.

If you are fat and don't like sports, it may be that someone doesn't want you to get out.

Reference:

Https://docs.qq.com/doc/DVGtBSlhsSUhrUXZl

This article comes from the official Wechat account: take Science Home (ID:steamforkids), author: Qijun

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