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Global warming has reportedly made much of the planet hotter and hotter.
High temperatures can lead to drought because plants need to regulate their growth and development through metabolism. One of the main functions of plant metabolism is carbon metabolism, which plays a key role in regulating plant growth, development, and adaptation to the environment.
Studies have shown that high temperatures can negatively affect plant metabolism, including carbon absorption, carbon breakdown, and respiration. Over the past few decades, we have identified many of the effects of climate change on plant metabolism.
Recently, we have identified some important mechanisms that may further improve our understanding of how future climate change affects plant metabolic processes.
Therefore, this paper reviews the known mechanisms associated with high temperature and drought stress and their effects on carbon metabolism, and highlights the importance of these mechanisms in future research.
Carbon absorption, carbon decomposition and respiration in plants
Plants are the most important carbon reservoir on the planet because it produces all the carbon on the planet. During plant growth, the photosynthesis of plants releases large amounts of carbon dioxide, which is stored in the xylem.
In wood, this stored carbon dioxide is converted into organic compounds (such as sugars), which are then used by plants. Through photosynthesis, plants are able to convert their stored carbon dioxide into usable glucose and other organic matter.
The xylem is the main site of lignin accumulation. In soil, carbon is fixed in soil pores and soil organic matter and exists in the form of organic compounds such as cellulose and hemicellulose.
Plants can regulate their metabolic processes by altering their carbon absorption, carbon breakdown, and respiration. Carbon uptake refers to the process by which plants absorb carbon dioxide, glucose, or other organic compounds from the environment.
Carbon decomposition refers to the process by which plants break down organic compounds stored in the xylem into small molecules such as carbon dioxide, water, and glucose.
Respiration refers to the process by which plants oxidize organic compounds stored in the xylem to carbon dioxide or produce oxygen and release them into the atmosphere.
However, in most cases, carbon uptake and carbon decomposition are closely related to respiration. Cellular respiration, photosynthetic electron transport, mineral nutrition, respiratory enzyme activity, and endogenous hormones (e.g., auxin, ethylene, abscisic acid) are all key regulators of carbon uptake and carbon decomposition.
Under drought stress, plants reduce their impact on carbon uptake and carbon decomposition by reducing the moisture content in the leaves and the surface temperature of the leaves, thereby limiting their growth and development.
In addition, under drought stress, plants reduce the content of carbohydrates in leaves by inhibiting auxin synthesis, thereby limiting the carbon decomposition process.
Drought stress reduces the sensitivity of plants to changes in CO2 and CO2 concentration, thereby increasing their sensitivity to respiration.
However, drought stress promotes carbon uptake, carbon decomposition and respiration processes as higher temperatures increase the moisture content in the leaves and increase the leaf surface temperature.
Carbon metabolism plays an important role in the growth and development of plants
One of the main functions of plant metabolism is carbon metabolism. Carbon metabolism is mainly composed of three parts: photosynthesis, respiration and starch formation, of which the synthesis of starch is realized in the process of photosynthesis.
Starch synthase in plant leaves catalyzes the breakdown of starch molecules into glucose under light, which is converted into glycogen (a polysaccharide containing 3 carbon atoms), and these products form starch in plants.
Plants produce energy through these processes. Although carbon metabolism plays an important role in plant growth and development, it is also closely related to plant stress tolerance.
Carbohydrates enter the leaf through the stomata on the leaf, accumulate on the leaf, and photosynthesize through chloroplast photochemistry. Plants convert carbohydrates into organic matter through respiration.
Photosynthesis is the main source of energy for plants, and it is also the main way for plants to grow, develop and adapt to the environment.
In addition to photosynthesis, carbon metabolism is involved in many other physiological processes. Carbon metabolism is also involved in cellular respiration. Although carbon metabolism plays a key role in photosynthesis, it is also involved in other metabolic processes by influencing cellular respiration.
Plant cell respiration refers to the redox reactions that take place in plant cells that involve multiple enzyme activities and ATP production while producing large amounts of energy. Plants obtain energy in this way to support their growth and development.
Moreover, plants need a lot of nutrients to meet the needs of their life activities during the period of vegetative growth; During reproductive growth, more nutrients are needed to maintain seed and fruit development.
Unlike other metabolic processes, carbon metabolism does not require energy expenditure or ATP production to produce energy as compensation, so it has a high degree of autohomeostasis.
In addition, carbon metabolism has a high degree of adaptability and plasticity. When the temperature rises, the carbon metabolism process may be negatively affected, and when the temperature decreases, the carbon metabolism process may be positively affected.
Carbon metabolism is the main site for a series of physiological reactions in plants. Therefore, although carbon metabolism is one of the important physiological processes, we do not know enough about its mechanism.
Carbon metabolism in response to temperature changes
The function of carbon metabolism in plants is to convert carbohydrates (sugars) into energy within the cells while releasing carbon dioxide from respiration. One of the main functions of carbon metabolism is the production of organic acids from plants, which are one of the most important hormones during plant growth and development.
There are two types of responses of carbon metabolism to temperature changes: direct and indirect. Direct responses include synthesis pathways and decomposition pathways; Indirect responses include processes related to energy supply, such as respiration, photosynthetic electron transport, and photosynthesis.
Carbohydrates are an important part of plant growth and can play a regulating role between carbon absorption, carbon decomposition, carbohydrate conversion, and respiration.
Carbon in carbohydrates can be absorbed by plants in three main ways: directly by the leaves, transported through the phloem, and transported through the xylem.
This carbon transport is determined by the activity of key enzymes during carbohydrate synthesis, including starch synthetase, sucrose phosphosynthase, and amylgranule/glycogen synthetase.
Plants can assimilate carbon in a variety of ways. In the most basic case, plants produce energy through photosynthesis. Therefore, photosynthesis is the main pathway for plant carbon assimilation.
Since photosynthesis is a very complex process, many other factors must be considered when studying plant carbon assimilation, including light, temperature, carbon dioxide concentration, and moisture.
Depending on the temperature, plants can undergo carbon assimilation in a variety of ways: the energy produced by photosynthesis is first stored in the plastid (e.g. starch); Most of the energy is fixed in the phloem in the form of carbon dioxide; Part of the energy is used for respiration.
Whether the plant is absorbed directly or transported through the phloem, carbohydrates are used as an energy source. In addition, carbohydrates can infiltrate into the soil through xylem to improve soil fertility and water use efficiency.
The main difference between carbon assimilation pathways in plants is whether the carbon metabolism pathways are actively or passively regulated.
Summary and outlook
Although the effects of global warming on plant metabolism have been extensively studied, there are still many unanswered questions in this field.
In the future, we can continue to study the following aspects: explore the effects of high temperature and drought stress on plant metabolism, including carbon accumulation, metabolism and carbohydrate transport in plant tissues;
Explore the interaction between carbon metabolism and other metabolic processes such as osmoregulation and ion transport; Explore the effects of high temperature and drought on hormone levels, signaling and protein expression in plants; To study the effects of high temperatures and drought on plant transcriptomics.