Favorable climate of the earth created by plants

Carbon dioxide in the atmosphere works as a so-called greenhouse gas and has protected our planet from freezing in Earth’s history. Artificial emission of carbon dioxide from fossil fuels exceeding the capacity of I wonder if this should be “the planet’s” carbon sink is now the origin of global warming.

Therefore, efforts are being made around the world to reduce the amount of carbon dioxide. Among these efforts, I would like to pay attention to the actions and functions of plants.

As you know, the major function of plants is photosynthesis. It means that plants convert carbon dioxide into sugar and produce oxygen by using water and solar energy. In fact, this function of plants has made the earth an environment in which many creatures can evolve and live.

The primitive earth had little oxygen in the atmosphere, the ground was extremely hot, and tiny forms of life originated in the sea.

However, about 2.7 billion years ago, organisms performing photosynthesis emerged and they began to proliferate. As a result, carbon dioxide decreased and oxygen increased in the atmosphere, and the temperature dropped. Then, various kinds of life including our ancestral animals appeared on the earth.

When plants die, they become buried in the ground with carbon fixed in the body. Humans dig up the fossils from hundreds of millions of years ago as coal and petroleum oil and utilize them as energy by burning them.

In other words, we have released the fixed carbon into the atmosphere and have disturbed the fine balance of atmospheric components brought by plants. This has led to the global warming we now face.

It has been reported that sea levels will rise as a result of water expansion and melting ice in the polar regions, and the extreme weather events will increase due to global warming. This is now coming true, unfortunately, but the biggest impact is the possibility of the extinction of various species.

For example, it is often reported that the flowering time of cherry blossoms is moving forward owing to global warming, while the number of plant species whose flowering and germination is delayed or disturbed is increasing.

If we have no seed germination, as we can see from the food chain, many animals cannot survive. Human beings are on the top of the pyramid, yet are, in fact, weak among animals. If the number of plants and animals that serve as food decreased to a certain level, we would not be able to survive.

In recent years, interest in considering the realization of a sustainable world is growing. We, human beings, and other animals cannot live without plants; however, we have not yet understood many of the mechanisms involved in how plants grow in response to the environment.

In order for living things including ourselves to survive on the earth, we need to know more about plants.

Plants have amazing temperature-sensing systems

Why can each plant sprout or bloom in a regular season? This mechanism has remained unknown for a long time.

Probably, plants have something like a temperature sensor, but we don’t know what it is. However, when we conduct experiments to examine the responses of plants, we can see that they can sense the difference of 1°C.

About five years ago (in 2016 and 2017), three papers stating that light sensors in plants also function as temperature sensors was published. Last summer (in 2020), another paper stating that a protein with the properties of a “prion” is related to temperature response was also presented.

The prion is known as a pathogenic substance of mad cow disease and human prion disease, and it has been found that it accumulates in the brains of Alzheimer’s disease patients, so it has been drawing increasing attention. It is a protein that we originally have, but its three-dimensional conformation changes to show pathogenicity. On the other hand, the possibility that it works not only harmfully but for the formation and retention of long-term memory has also been shown.

We mainly study the seeds of plants to learn how they determine the season of germination. As seeds are in the soil, they may not be able to sense light. However, the temperature of the soil changes depending on the exposure to sunlight. The plants are thought to be sensing it.

It means that temperature sensors different from light sensors are also working. In other words, it is considered that there is not only one mechanism for temperature sensing in plants but there are many.

For example, the temperature of the ground changes depending on the angle of sunlight and the length of time the ground is exposed to sunlight, so the temperature sensor of the seed may detect them and decide whether or not it should germinate.

But it is not possible for seeds to know whether it is spring or autumn now by only sensing the temperature of the time. However, when the temperature rises after a low temperature continues, seeds can know it is now spring, and when the temperature falls after a high temperature continues, they can know it is now autumn.

In other words, they can store or accumulate the temperature data. Therefore, plants that grow in summer can sprout in spring, and plants that have a low tolerance for heat can sprout in autumn.

In addition, some plants utilize the temperature difference between day and night. The ground directly exposed to sunlight warms during the day and cools at night, so the temperature difference in the ground becomes large. On ground where the sunlight is blocked by something, the temperature does not rise much during the day, so the temperature difference between day and night is not so large.

In this case, the seeds do not germinate even in the germinating season and remain dormant. Some seeds remain dormant for decades and keep living.

On the other hand, in soil where the temperature difference between day and night is large, seeds germinate properly in the season when they should germinate. This is because the area is exposed to a lot of sunlight, so photosynthesis can be carried out sufficiently after sprouting to grow up.

Otherwise, the seeds remain dormant without germinating until conditions are good for them.

In this way, not only the seeds know the season when they can sprout through the temperature sensor, but also they can choose whether to germinate or not by counting back the time when they are guaranteed to grow after germination.

We aim to find out the sequence of mechanisms that plants have. Then we may be able to find a way to support the recovery of normal growth of plants whose germination and flowering times are disturbed owing to the worsening of global warming.

This will increase the number of healthy plants and thereby increase the amount of carbon dioxide in the atmosphere fixed in the plants.

This will not only control global warming and climate change, which causes stress for plants, but also lead to sustainable food production. In other words, plants are at the core of this virtuous cycle.

Human beings are kept alive by plants

While research on plants is progressing, research on artificial photosynthesis is also progressing. The aim is to obtain energy (hydrogen, formic acid, alcohol, etc.) that can be stored by physicochemically absorbing and fixing carbon dioxide in the atmosphere using sunlight as an energy source, following the inherent system of plants.

At present, artificial photosynthesis using only natural energy such as sunlight is being developed. On the other hand, there are still problems to be solved, so expectations for future research and development are rising.

Momentum for decarbonization is growing, and, for example, a shift from gasoline-powered vehicles to electric vehicles is progressing rapidly. However, even if it looks clean, it will not mean zero carbon dioxide emissions as long as the energy required for production and transportation is derived from fossil fuels. There are still many things we can learn from plants.

Recently, plants sprouting from the gaps in asphalt in urban cities have become a topic. While plants are delicate, they also have such resilience. We still have not fully discovered the mechanism of plants to live.

However, if you look at the history of the earth and living things, you can see that plants are its basis. I think that if human beings continue to exist on the earth, it will be when we understand plants and learn from them.

Everyone, please look around. You can see that plants are around you.

Some plants are sprouting from the gaps in concrete, and some trees give shade in a park. In the countryside, there are some places where deep forests remain. Of course, some people grow plants in their rooms or gardens. We live with plants.

People not only eat plants directly as food, but also receive various benefits from them. But they are invisible and so natural that we tend to forget about them. Even so, we may be trying to live with plants because we know these benefits deep down in our hearts as living things.

In other words, we are kept alive by plants. We researchers are working to make these benefits visible.

* The information contained herein is current as of August 2021.
* The contents of articles on Meiji.net are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.

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