Both plant and animal cells have mitochondria. Every textbook-standard plant cell and animal cell contains these organelles, which serve as the primary site where the cell converts nutrients into usable chemical energy. The interesting part of this question is not whether both cell types have them, but how differently mitochondria behave in the two kingdoms and why plants need mitochondria at all when they already have chloroplasts to harvest sunlight.
Why Mitochondria Are Universal in Complex Life
Mitochondria are present in nearly all eukaryotic cells, a category that includes plants, animals, fungi, and protists. Their central job is producing ATP, the molecule cells use as energy currency. In animal mitochondria, energy for making ATP comes from a force generated by moving protons across the organelle’s inner membrane during respiration.1PubMed Central. Bioenergetic cost of making an adenosine triphosphate molecule in animal mitochondria Plant mitochondria do the same thing. But energy production is only part of the story. Mitochondria also handle iron and calcium balance and help produce hormones and signaling molecules like melatonin.2PubMed Central. Mitochondria: It is all about energy These functions are so deeply wired into complex cell biology that losing mitochondria entirely is almost unheard of.
The reason for this universality traces back roughly two billion years. All mitochondria descend from a single ancient event in which a bacterium related to modern alphaproteobacteria was absorbed by a host cell related to a group of archaea called Asgard Archaea.3Current Biology. The origin and evolution of mitochondria That merger happened before the lineages leading to plants, animals, and fungi split apart, which is why all three kingdoms inherited the organelle. Plants later picked up a second endosymbiont, the ancestor of chloroplasts, but they kept their mitochondria throughout.
Why Plants Still Need Mitochondria When They Have Chloroplasts
This is the question that catches most people off guard. If chloroplasts harvest sunlight and make ATP through photosynthesis, why would a plant bother maintaining a second energy-producing organelle? The answer is that chloroplasts alone cannot meet all of a plant cell’s energy demands, even in broad daylight.
Research using a moss called Physcomitrium patens showed that when plants were depleted of a key respiratory component in their mitochondria (Complex I), the amount of ATP available in the cytosol dropped even during active photosynthesis. Mitochondrial respiration turns out to be critical for supplying ATP to the rest of the cell while chloroplasts are working.4PubMed. Mitochondrial respiration is essential for photosynthesis-dependent ATP supply of the plant cytosol Chloroplasts generate ATP inside their own membranes primarily for carbon fixation, but they are not great at exporting that ATP to the rest of the cell. Mitochondria fill the gap.
Chloroplasts and mitochondria are also metabolically intertwined in ways that go beyond simple energy budgets. Mitochondria stay active during daylight and are essential for sustaining photosynthetic carbon fixation itself. Disrupting mitochondrial function does not just cut the cell’s nighttime power supply; it also impairs the chloroplast’s ability to do its job during the day.5Trends in Plant Science. Interactions between chloroplasts and mitochondria in plant cells The two organelles, along with peroxisomes and the cytosol, exist in a metabolic equilibrium where upsetting any one compartment throws the others off balance. And at night, when there is no sunlight to drive photosynthesis, mitochondria are the sole source of ATP. A plant without mitochondria would starve in the dark.
A Plant-Specific Trick Called Photorespiration
One of the more surprising jobs plant mitochondria perform is a process called photorespiration. When the enzyme responsible for fixing carbon dioxide occasionally grabs an oxygen molecule instead, it produces a waste product that the cell has to recycle. Part of that recycling happens in mitochondria, where the amino acid glycine is converted to serine.
Experiments with barley leaf cells showed that this recycling step is coupled to ATP production. Under conditions where photorespiration was active, mitochondria produced extra ATP that was exported to the cytosol, boosting energy levels there. When an inhibitor blocked the glycine-to-serine conversion, mitochondrial and cytosolic ATP levels dropped.6Plant Physiology. Influence of Photorespiration on ATP/ADP Ratios in the Chloroplasts, Mitochondria, and Cytosol, Studied by Rapid Fractionation of Barley (Hordeum vulgare) Protoplasts In other words, plant mitochondria take what is essentially a photosynthesis mistake and salvage useful energy from it. Animal cells do not perform photorespiration because they do not photosynthesize, so this entire branch of mitochondrial work is unique to plants.
What Mitochondria Do Differently in Animal Cells
Animal mitochondria share the core ATP-generating machinery with plant mitochondria, but they have some roles that matter more in animal biology. One of the best-studied is controlling programmed cell death, known as apoptosis. A protein called cytochrome c normally sits inside the mitochondrion, helping shuttle electrons to keep ATP production running. But when a cell receives signals to self-destruct, cytochrome c is released from the mitochondria into the surrounding cytosol, where it triggers a cascade of enzymes that dismantle the cell from the inside.7PubMed Central. Cytochrome c: the Achilles’ heel in apoptosis
The release of cytochrome c is not a simple on-off switch. Research with isolated liver mitochondria demonstrated that it takes two distinct steps. Cytochrome c is normally anchored to the inner membrane by a lipid called cardiolipin. First, that bond has to be disrupted to free the protein. Then the outer membrane has to be punctured by a protein called Bax to allow cytochrome c out. Neither step alone is enough; both have to occur.8PubMed Central. Cytochrome c release from mitochondria proceeds by a two-step process This two-step mechanism acts as a safety check, preventing accidental cell death from a single molecular hiccup. When the system goes wrong, though, it can contribute to disease: too little apoptosis lets damaged cells survive (a hallmark of cancer), while too much kills healthy tissue (as happens in neurodegenerative conditions).
Shape, Size, and How They Move Around the Cell
If you looked at mitochondria under a microscope, you would notice a visual difference between the two kingdoms. Plant mitochondria tend to be more numerous per cell and more grain-shaped, while animal mitochondria often form longer, tubular networks.9PubMed Central. Frequent fusion and fission of plant mitochondria with unequal nucleoid distribution In both kingdoms, mitochondria constantly divide and fuse with each other. This dynamic reshaping lets cells redistribute their energy supply and mix mitochondrial contents to keep everything functioning well.
The machinery driving these dynamics differs, though. In animal cells and yeast, specific proteins (with names like Mfn and Opa1) handle the merging of mitochondrial membranes. Plants clearly fuse their mitochondria too, as demonstrated by elegant experiments in onion cells where researchers color-coded individual mitochondria and watched green and red ones merge into yellow. Yet despite years of searching the genome of the model plant Arabidopsis, no one has found functional equivalents of the fusion proteins used by animals and yeast.10PubMed Central. Fission and Fusion of Plant Mitochondria, and Genome Maintenance Plants apparently evolved a completely different molecular toolbox for mitochondrial fusion, one that researchers have not yet fully identified. It is a reminder that even when two kingdoms perform the same basic cellular task, they may have arrived at different solutions.
The DNA Inside Is Vastly Different
Mitochondria carry their own small genomes, a remnant of their bacterial ancestry. In animals, this genome is remarkably uniform: nearly all animal mitochondrial genomes run about 16,500 base pairs. Plant mitochondrial genomes, by contrast, are enormous by comparison, ranging from roughly 200,000 to 2,000,000 base pairs. Most of that extra DNA consists of large introns, repeated sequences, and non-coding regions rather than additional genes. The physical structure differs as well: animal mitochondrial DNA is a tidy circle, while plant mitochondrial DNA exists as a messy collection of linear molecules mixed with smaller circular and branched forms.11Front Biosci (Landmark Ed). Plant mitochondrial DNA
Inheritance patterns are another area where the textbook version is oversimplified. The standard teaching is that mitochondrial DNA passes exclusively from one parent, typically the mother. While that is the general trend, it is far from absolute. Plants, animals, and fungi all show episodes of biparental inheritance, where mitochondria come from both parents, and even recombination between genetically distinct mitochondrial genomes. The extent varies across species, but the assumption that mitochondrial DNA is always strictly maternal and never recombines draws largely from early animal studies and does not hold up well across the tree of life.12PubMed. Inheritance and recombination of mitochondrial genomes in plants, fungi and animals
How Plants Import Proteins Into Their Mitochondria
Most mitochondrial proteins are encoded in the cell’s nuclear DNA, made in the cytosol, and then imported into the mitochondria through a set of molecular gatekeepers. The basic import system was established in early eukaryotes and is shared across kingdoms, but plants have layered on unique modifications that animals lack.
The most striking example involves a receptor protein called Tom20, which sits on the outer mitochondrial membrane and helps recognize incoming proteins. Both plants and animals have a Tom20, and structurally the two look similar, folding into comparable shapes. But they are not related by direct descent. They evolved independently, arriving at the same structural solution from different starting points.13PubMed. Mitochondrial protein import: convergent solutions for receptor structure Plants have also evolved a second unique receptor called OM64 and modified other components of the import system, changes thought to have been driven by the arrival of chloroplasts. Once plant cells had two organelles that needed protein deliveries from the nucleus, the import system had to become more specific to avoid sending the wrong proteins to the wrong address.14PubMed. Unique components of the plant mitochondrial protein import apparatus
Even within the plant kingdom, the import machinery is not uniform. The receptor OM64 is found in flowering plants like rice and Arabidopsis but appears absent in more ancient plant lineages like lycophytes and gymnosperms. Different plant groups have also evolved distinctive motifs in another import component called Metaxin that are not found in red algae.15PubMed Central. An in silico analysis of the mitochondrial protein import apparatus of plants
Plant Mitochondria Can Generate Heat
Animals generate body heat primarily through metabolism in tissues like brown fat and muscle. Plants are generally considered cold-blooded, but some species use their mitochondria to produce significant warmth. Certain flowering plants in the Araceae family, which includes species like skunk cabbage and the voodoo lily, can heat their flower structures to temperatures well above the surrounding air. This heat vaporizes smelly compounds that attract pollinating insects.
The heat comes from a respiratory pathway involving a protein called alternative oxidase, or AOX, which is found in plant mitochondria but absent from animal ones. The standard electron transport chain in mitochondria captures energy and stores it as ATP. AOX provides a shortcut that lets electrons bypass the energy-capturing steps, dissipating the energy as heat instead. Research on thermogenic plants shows that as temperature rises, control of respiration shifts progressively toward AOX, creating a self-regulating heating system.16PubMed. Regulation of thermogenesis in flowering Araceae: the role of the alternative oxidase Beyond heat production, AOX also helps plants cope with environmental stress, including cold, drought, nutrient shortages, and bacterial infection, by keeping the electron transport chain from backing up and generating harmful reactive oxygen species.17PubMed Central. Alternative oxidase: a mitochondrial respiratory pathway to maintain metabolic and signaling homeostasis during abiotic and biotic stress in plants
Day Versus Night in a Plant Cell
Plant mitochondria do not just plod along at the same rate around the clock. Their protein composition and metabolic activity shift substantially between light and dark periods. Proteomic studies of Arabidopsis mitochondria revealed clear diurnal changes in their capacity to run the main energy-producing cycle, as well as in functions related to nitrogen and sulfur metabolism, cellular redox balance, and antioxidant defense.18PubMed Central. Diurnal changes in mitochondrial function reveal daily optimization of light and dark respiratory metabolism in Arabidopsis During the day, when chloroplasts are active, mitochondria adjust their activity to complement what the chloroplasts are doing. At night, they ramp up as the sole ATP supplier. This daily retuning is something animal mitochondria do not face, since animal cells lack chloroplasts and run on a more constant metabolic baseline.
Reactive Oxygen Species in Both Kingdoms
Mitochondria are a major source of reactive oxygen species (ROS) in both plant and animal cells. These molecules are a normal byproduct of the electron transport chain, and in small amounts they serve as signaling molecules. In excess, they damage DNA, proteins, and membranes.
Both kingdoms share a phenomenon in which ROS production in one organelle can trigger a burst of ROS in another, a chain reaction called ROS-induced ROS release. In animal cells, this process was originally described as a way for one mitochondrion to communicate with neighboring mitochondria within the same cell. In plants, the concept has expanded to include cell-to-cell signaling: ROS produced by one cell trigger enhanced ROS production in the next cell, creating a wave that can travel across long distances through the plant as a rapid stress signal.19PubMed. ROS-induced ROS release in plant and animal cells So while the basic chemistry is similar, plants have repurposed mitochondrial ROS as part of a long-distance alarm system that has no real counterpart in animal biology.
When Mitochondrial Mutations Cause Trouble
Defects in mitochondrial genes cause disease in both kingdoms, and the parallels can be remarkably specific. In humans, point mutations in a mitochondrial gene called atp6 cause severe neurological conditions. In sorghum, the loss of a normal editing process in the same gene’s RNA results in equivalent amino acid changes and causes cytoplasmic male sterility, meaning the plant cannot produce viable pollen. The molecular lesions in the plant effectively mimic the mutations that cause human disease.20PubMed. Mutations at specific atp6 codons which cause human mitochondrial diseases also lead to male sterility in a plant This cross-kingdom parallel underscores how deeply conserved mitochondrial function is, and it has practical implications for agriculture: cytoplasmic male sterility is widely exploited in crop breeding to produce hybrid seeds without hand-pollination.
The One Eukaryote That Lost Its Mitochondria Entirely
Given how universal mitochondria are, researchers spent decades debating whether any eukaryote could survive without them. The answer finally came from Monocercomonoides exilis, a tiny single-celled organism that lives inside the guts of chinchillas. Genome sequencing revealed that it lacks every known mitochondrial protein. The one pathway that was thought to be universally retained in all eukaryotes, a system for assembling iron-sulfur clusters, has been completely replaced in Monocercomonoides by a bacterial system acquired through horizontal gene transfer.21PubMed. A Eukaryote without a Mitochondrial Organelle Phylogenetic analysis makes clear this organism is not a primitive holdout that never had mitochondria. Its ancestors had them and lost them secondarily, probably because the nutrient-rich, oxygen-poor environment inside a chinchilla gut made the organelle dispensable.22PubMed Central. The Oxymonad Genome Displays Canonical Eukaryotic Complexity in the Absence of a Mitochondrion
Other organisms have gone partway. Some anaerobic protists have converted their mitochondria into hydrogenosomes, organelles that produce hydrogen gas instead of running the full electron transport chain.23Molecular Biology and Evolution. Convergent Evolution of Hydrogenosomes from Mitochondria by Gene Transfer and Loss These are still mitochondria in an evolutionary sense, just stripped down and repurposed. No multicellular animal or plant has ever been found without functional mitochondria. For organisms with the metabolic demands of an animal body or a photosynthesizing plant, these organelles remain indispensable.