Plants use chloroplasts to perform photosynthesis, in which they turn sunlight into sugar that can be used by the cells. They also need mitochondria to produce ATP, the energy that plants can use for cellular functions.
Mitochondria are a major eukaryotic organelle responsible for oxidative phosphorylation and respiration. They are very similar to the eukaryotic organelles in animals and fungi, but differ substantially from higher plants.
Chloroplasts
Chloroplasts are an organelle found only in plants and photosynthetic algae (other organisms such as bacteria do not have chloroplasts). They are the major source of cellular energy, converting light into chemical energy by photosynthesis. They also provide a wide range of metabolic activities for plant cells, such as the synthesis of fatty acids and membrane lipids.
They can be distinguished from other plastids by their green color, resulting from two pigments containing chlorophyll a and b, which trap solar energy. These chlorophyll pigments are used in the photosynthesis process, a process that produces sugars from carbon dioxide.
Their structure is similar to a bacterial cell; they have double membranes, circular DNA, ribosomes, and thylakoids. This suggests that they may have evolved in eukaryotic cells from free-living cyanobacteria that had an endosymbiotic relationship with the cell, making energy in return for a safe place to live and eventually evolving into their own form.
The chloroplast has an outer membrane that encloses the cytosol, which is the liquid inside the plant cell. The outer membrane is permeable to small molecules, while the inner membrane is less permeable and studded with transport proteins. The inner membrane encloses a thick fluid called the stroma, which contains enzymes and multiple copies of the chloroplast genome.
Inside the stroma, enzymes make complex organic molecules that are used to store energy. These organic molecules can be broken down to produce glucose and other simple sugars, which are needed for photosynthesis.
In addition to their role in photosynthesis, chloroplasts are involved in plant resistance to high and low temperature stress. Under high temperature, they swell to create turgor pressure that helps prevent the cell from wilting. In low temperatures, they adapt to changes in temperature by shifting their position within the cell to increase light absorption efficiency.
Chloroplasts have also been shown to be involved in salt acclimation, a process that makes plants more resistant to harsh environments such as drought and salinity. A study on soybean revealed that when plants are exposed to salt stress, they reduce the amount of a protein known as Rubisco in their chloroplasts. This decrease in Rubisco levels was accompanied by a change in the abundance of proteins involved in cellular redox and reactive oxygen species (ROS) networks to improve salt tolerance.
Cell Respiration
Cellular respiration is a series of chemical reactions used by all living organisms to convert glucose and other sugars into a form that can be used for energy. It can be performed in the presence of oxygen, which is aerobic respiration, or in the absence of oxygen, which is anaerobic respiration.
In the case of aerobic respiration, the energy produced by the chemical reaction is stored in molecules called ATP. These molecules can then be used by other cells in other metabolic reactions. In plants, this ATP is made in the mitochondria.
The mitochondria are the organelles in the cell that perform most of the cellular respiration. They are specialized in bringing together all the necessary reactants for cellular respiration, in a small, membrane-bound space within the cell. This specialized anatomy contributes to the high efficiency of aerobic respiration and also allows it to occur in the presence of a low level of oxygen.
One of the main enzymes in a mitochondrion is an integral membrane protein called ATP synthase (Figure 8). This complex protein acts as a tiny generator, turned by the force of hydrogen ions diffusing through it down its electrochemical gradient, to bind loose phosphate groups to ADP, forming ATP.
This process generates about 90 percent of the ATP produced during aerobic glucose catabolism. This ATP is then carried to the next stage of cellular respiration, the electron transport chain.
In the electron transport chain, energy is transferred from molecules of NADH and FADH2 to ATP, using oxygen as a proton acceptor. In addition, carbon dioxide is released as a waste product and water is formed.
Another important role of the enzymes in the mitochondrion is to provide a way for hydrogen ions to diffuse through the outer membrane and enter into the intermembrane space. This is called chemiosmosis, and it is a critical component of the oxidative phosphorylation pathway in photosynthesis.
The last two stages of cellular respiration, the citric acid cycle and the electron transport chain, are performed in the mitochondria. The ATP generated during the first two stages is transported to these cells in the form of a compound called acetyl CoA, which is made from vitamin B5.
ATP Production
ATP (Adenosine Triphosphate) is the energy-storing molecule found in all living things, including plants. It consists of an adenosine base attached to a sugar ribose through three phosphate groups. It is a water soluble molecule with a high energy content because of its two phosphoanhydride bonds that link the phosphate groups. The energy held in the phosphate groups can be used by cells to do work, such as break down a food or synthesize new compounds.
When a cell needs to make more energy, the ATP molecule splits off one of its phosphate groups, forming ADP + phosphate. Then, the phosphate molecule is reattached to ADP and turned into ATP again. This process continues until the cell uses up all of its ATP. The ATP molecule is like a rechargeable battery.
It has many different reactions that are important in a plant’s metabolism. These include the Calvin-Benson cycle, the TCA cycle and redox reactions, among others. These metabolic pathways use a lot of energy, so it is important for the plant to have an efficient system to store this energy.
This is why it is so important for plants to have chloroplasts and mitochondria. These organelles can help to boost ATP production and sucrose production, which is a form of sugar that is important for growth in plants.
Interestingly, there is some evidence that mitochondria can be more efficient than chloroplasts at producing ATP. This is due to a mechanism called the mitochondrial oxidative burst.
However, this process can be disrupted if the mitochondria are infected by pathogens or if they become less resistant to drought. This can lead to lower survival and higher rates of senescence.
A better understanding of this problem can be used to help improve conservation strategies for the future. In addition, it may also provide more insight into how environmental changes affect ecologically important behaviors such as exploration and dispersal.
A recent study in Arabidopsis thaliana has shown that if chloroplasts and mitochondria cooperate to produce more ATP, plant growth will be enhanced. This is due to a protein called purple acid phosphatase 2 on the outer membranes of chloroplasts and mitochondria, which promotes the import of certain proteins into these organelles via the Toc or the Tom complexes.
Mitochondria in Plants
Mitochondria are intercellular organelles that make ATP, the cell’s main energy-carrying molecule. They break down sugars to produce ATP through cellular respiration, the process that uses chemical energy from fuels such as sugars to create a steady supply of ATP for other reactions in the cell.
They also make proteins that are required for these functions, such as adenosine diphosphate (ATPase) and thylakoids, which contain light-harvesting complexes called chlorophyll. These protein complexes are important in photosynthesis, which is how plants use the sun’s energy to make sugars and ATP.
In order to build a new mitochondria, the plant needs to synthesize different components of the organelle. This is called mitochondrial biogenesis and it requires a high level of coordination.
One way to coordinate this process is by using microRNAs, which are small, non-coding RNAs that can bind to specific mRNAs and inhibit mRNA translation or promote RNA degradation. These non-coding RNAs can affect many cellular processes, including mitochondrial biogenesis (Li et al., 2012).
Another way to coordinate mitochondrial biogenesis is to use the protein complexes that are produced by free ribosomes in the cytoplasm. These protein complexes are involved in assembling mitochondria and they have the ability to control the expression of nuclear genes that are used to make these organelles (Mahmood et al., 2011).
This type of protein coordination may be useful in regulating the activity of chloroplasts and mitochondria in plant cells. Because chloroplasts and mitochondria are closely related organelles that perform strictly coordinated actions in photosynthesis, they need to be able to communicate with each other.
For this reason, it has been shown that changes in the activity of OE mitochondria have a direct effect on the efficiency of carbon fixation, sucrose synthesis and ATP production in leaf cells. In particular, mitochondria that actively dissipate surplus reducing equivalents reduce the pressure on chloroplasts to export more of these molecules.
During growth, mitochondria in healthy plants are organized in a typical reticular structure. In contrast, when a plant goes through senescence or when a cell dies, the network disintegrates into very small mitochondria that are no longer needed for ATP synthesis.