March 2, 2021 at 9:38 am | Updated February 28, 2023 at 9:20 pm | 8 min read
Photosynthesis is undoubtedly one of the most important physiological processes on earth. It is how plants, algae, and bacteria produce food. Photosynthesis makes these organisms the primary producers of the earth, as all other organisms feed on them for their energy source. People depend on this important process for most of their needs: food, fiber, fuel, timber, etc. Thus, many scientists are considering how photosynthesis can be used to combat climate change and increase productivity for a growing population. Read on to discover how researchers are finding new photosynthesis measurement methods in 2023.
What is Photosynthesis?
Photosynthesis is the process by which organisms with chlorophyll capture light and use its energy to combine water and carbon dioxide (CO2) to produce simple carbohydrates and oxygen. There are two stages in the process:
- The first step, CO2 fixation, is a light-dependent stage.
- The second step is the light-independent stage, where NADPH and ATP produced in the first stage is used to form carbohydrates in the Calvin Cycle.
Three kinds of plants depend on photosynthesis: C3, C4, and crassulacean acid metabolism (CAM).
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If the end product is a three-carbon compound, the plants are called C3. Both stages of photosynthesis occur in the same chloroplast. During hot or dry weather, photorespiration occurs when the stomata remain closed. Oxygen produced by photosynthesis reacts with the photosynthetic enzyme, Rubisco, hindering the production of C3 carbohydrates. Thus, water use and photosynthesis efficiency can be low in C3 plants. Examples of C3 plants are rice, wheat, soybeans, and all trees; 85% of plants are C3.
In hot and dry places, plants, which often keep stomata closed, have evolved a different system to use the limited amount of CO2 coming in. CO2 is fixed in the stomata of the mesophyll to produce C4 carbohydrates, which is transported to the chloroplast of another cell in the sheath for the Calvin Cycle to escape photorespiration. Examples of C4 plants are sorghum, maize, ragi, switchgrass, etc.
In places with extreme heat and drought, like deserts, plants open their stomata only at night, when CO2 can enter. So, in these plants, CO2 is fixed at night and stored in a vacuole. During the day, the Calvin Cycle occurs in the same chloroplast, avoiding photorespiration. Examples are succulents such as cacti.
Bacteria have no organelles but do have chlorophyll that aids the two steps of photosynthesis. Also, some sulfur bacteria use hydrogen sulfide as the hydrogen source for their photosynthesis.
although photosynthesis is important, many aspects and reactions are still unknown. Not surprisingly, scientists are trying to learn more about it to solve today’s many challenges.
New Kind of Photosynthesis
Photosynthesis in many cyanobacteria (blue-green algae) uses near-infrared light by chloroplast instead of red of the visible light and can occur in dark or shaded places. Light beyond the red spectrum of light can damage plants. A deeper study into how cyanobacteria avoid this damage can help produce new crop plants.
Knowledge of this new photosynthesis can widen the scope of places to search for alien life on distant planets.
Scientists are using the chemicals associated with photosynthesis and charging them with electrical energy in a solar cell. The cells fix CO2 to produce fuels like methanol at micro-levels. Attempts are being made to scale up carbon capture through this novel method.
Understanding Photosynthesis Reactions
Earlier photo-inhibition of photosystem-I or damage due to excessive exposure to sunlight was considered harmful to plant productivity and crop yield. A Finnish group has shown that photo-inhibition of photosystem-I can lessen damage to photosystem II and also contain further damage to itself. A better understanding of processes helps target future research to boost crop yield.
The function of Plant Rubisco
Rubisco is the main CO2-fixing enzyme and is vital for plant productivity. Yet, according to leading plant science Lecturer Amanda Cavanagh, even 75 years after Rubisco was first isolated from spinach leaves, we do not know much about their functioning.
Rubisco is made up of eight small subunits that interact in heretofore unknown ways. In 2020, Khumsupan et al. created mutants of four subunits using gene engineering. With the help of the mutants, the scientists found how the subunits influenced Rubisco’s functioning, thereby advancing knowledge of photosynthesis.
Photosynthesis for Energy Production
Scientists are working to utilize the intricate mechanisms of plant energy production for use in human systems. They are doing this by using natural and artificial photosynthesis.
Optimizing Photosynthesis for Energy Production by Algae
Research is being conducted on the use of microalgae for the production of next-generation solar biotechnologies. Photosynthesis uses a linear or cyclic electron flow (CEF) depending on changing light conditions. A large compound has now been identified as the CEF complex that plays a major role in fine-tuning the balance of these two processes. The complex found in microalgae and plants has remained unchanged for millions of years and has been used to adapt to varying light and energy levels. Understanding how microalgae optimize photosynthesis can increase production to supply more energy and food.
Artificial Photosynthesis for Energy Production by Algae
Scientists from the University of Cambridge have tested a laboratory prototype of novel solar cells that can conduct artificial photosynthesis to produce solar energy. They used a mixture of photocatalysts in a sheet of semiconductors. These solar cells produce formic acid in the presence of sunlight and water. This product can be easily stored and converted to produce hydrogen fuel.
The advantage of the prototype is that it is being produced cheaply and easily. Hence, scaling the prototype to produce regular-sized panels should not be a problem.
Research groups in Germany and France have produced artificial cell-sized chloroplasts that use greenhouse carbon dioxide and light. The semi-synthetic membranes were encapsulated in cell-like droplets. The artificial chloroplasts contain novel enzymes, and their reactions fix CO2 100 times faster than natural photosynthesis.
Scientists think this new product has material science, medicine, and biotechnology applications.
Improving Crop Yield
With the human population rising steeply, scientists are looking for ways to improve plant yield besides experimenting with fertilizer and irrigation use efficiency. They are looking deeper into plants, especially at photosynthesis. Some new approaches to increasing crop growth and yield are covered below.
Improving Light Storage
Plants use only 1% of the sunlight that falls on them. Photosystems I and II, which are involved in light absorption, are subsets of photosynthetic reactions that are of great interest. Scientists aim to understand these complex and little-known processes to increase light storage by just another 1% to produce enough food, fuel, and energy for all people.
C3 plants that suffer from photorespiration can be improved to increase growth and produce more. Scientists are trying many approaches at the genetic level to achieve this aim, including a shortcut and finding C4 enzymes.
- A shortcut: One is through genetic engineering in a new variety of tobacco. Toxins produced during photosynthesis must be broken down, so the plant is not harmed. If plants could use this energy for growing, it could boost yields. Therefore, researchers used genetic engineering in a new variety of tobacco to avoid this step. The shortcut resulted in a 40% increase in plant growth due to increased photosynthesis. Rice and wheat could see similar applications shortly.
- Finding C4 enzymes: C3 plants conduct both steps of photosynthesis in the mesophyll. C4 plants produce vital enzymes in bundle sheath cells, which allows them to use a second location in the leaf to avoid photorespiration effects. A project called “Realizing Increased Photosynthetic Efficiency” (RIPE) at Essex compared the genetic control of these enzymes in C3 and C4 plants. They found the DNA regions which control the production of four such enzymes in C4 plants. Introducing these codes into C3 plants could make them function like C4 plants and increase crop yield.
Improving Greenhouse Production
Growers of fruits, vegetables, and flowers seek to improve the rate of photosynthesis in greenhouses by using LEDs with customized light color and intensity for each species. Combinations of red and blue lights are primarily used to improve light absorption and plant growth.
Increasing Rubisco Content
One method that increases the amount of the enzyme Rubisco in C4 plants to raise CO2 fixation and improve plant growth and yield has proved successful in maize.
Predicting Climate Change Effect on Food Production
Many people associate increasing CO2 levels due to climate change with the potential for increased food yield, but it is not that simple. Since C4 is already adapted to use more CO2, increased gas levels will not affect them or increase their yield. However, under conditions of higher CO2, higher rates of photosynthesis will occur in C3 plants such as rice and wheat.
Impact of Climate Change on Photosynthesis
The many important components and environmental factors for photosynthesis come into play during climate change and its ability to fix carbon.
- The optimum range of temperature for photosynthesis is 10 – 35°С. Beyond this range, all photosynthetic reactions are affected, and the assimilation of CO2 decreases. Since many subsets of reactions and compounds are involved, it will be hard to find ways to reverse adverse effects on photosynthesis caused by the rise in temperatures.
- The intensity of photosynthesis is expected to peak when CO2 levels are 0.8 -1.0%. As the current atmospheric CO2 level is ≈ 0.038%, plants are expected to absorb and fix more CO2. However, the CO2 fertilization effect (CFE) is weaker than earlier thought. A recent 2020 study notes that the deficiency of nutrients, such as nitrogen and phosphorus, does not allow plants to benefit fully from the rise in carbon levels.
- The accompanying drought stress occurring with climate change must also be considered. Drought destroys the total chlorophyll content in leaves and other leaf organelles. It also changes biochemical processes and shuts stomata to cause a reduction in photosynthesis; see Figure 3.
- When temperatures and CO2 levels increase simultaneously, there is more respiration than photosynthesis. Therefore, forests and crops will act as carbon sinks only in wet years and seasons. In drier periods of the year, they would produce more CO2.
How to Measure Photosynthesis
The increased interest in photosynthesis to improve crop yield and mitigate climate change requires precise measurement of this important physiological process. The CI-340 Handheld Photosynthesis System from CID Bio-Science provides instant and accurate readings. They can measure all kinds of leaves in farms, laboratories, and natural ecosystems, from conifers to broadleaves.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
Feature Photo by Andrey Tikhonovskiy.
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