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Hi Reddit! Tanai, Thomas, Anthony and Andrea here and we’re researchers at Imperial College London exploring photosynthesis! You’ll likely remember from school that photosynthesis is the process in plants and other organisms that harnesses sunlight to turn CO2 and water into energy and oxygen.

More than 99% of life on Earth is dependent one way or another on oxygenic photosynthesis. It's been a central engine of life and has influenced Earth’s ecosystem since the dawn of life itself. However, when exactly it first appears in that story has proved controversial.

Some of our work, aims to understand photosynthesis at an atomic level and is helping us to travel back in time to piece together this story of early life on Earth and how nature’s own solar panels first came into being. It is work that is overturning what we thought we knew. It was previously thought that life first emerged in the dark and photosynthesis using sunlight only came along much later. But our studies suggest photosynthesis could be as old as life itself.

At the same time as looking to the distant past, we are bringing photosynthesis into the future – hoping to evolve its machinery in the lab and go beyond what biology can do. The aim is to power new chemistry to meet global challenges such as climate change, global hunger and disease.

We look forward to discussing photosynthesis from its origins in the fossil record to its future applications. We are keen to answer your questions on how photosynthesis works, how it evolved and how it could play an important role in:

  • Protecting the environment through carbon sequestration and pollution clean-up
  • Addressing food security concerns by improving crop yields
  • Replacing fossil-fuel-based industrial chemical reactions that produce a lot of today’s commercial products for greener ones


  • Thomas Oliver is a final year PhD student working on the molecular evolution and function of photosystems.
  • Anthony Cheuk is a final year PhD student working on structure and function of some of the key enzymes of photosynthesis, ATP synthase.
  • Andrea Fantuzzi is a Research Fellow working on the structure and function of photosynthesis, but also expert on solar fuels technologies, policy regarding bioenergy, and other applied aspects of photosynthesis.
  • Tanai Cardona is a UKRI Future Leaders Fellow and the leader of the Molecular Evolution Lab and has been interested in photosynthesis since he was a teenager! His specialty is the evolution of Photosystem II - the water oxidizing enzyme of oxygenic photosynthesis.

Furth info / interesting links:

Comments: 57 • Responses: 21  • Date: 

Cat_inabox8 karma

Houseplant question. Living in the UK I struggle to get enough sunlight to keep my houseplants alive. Hypothetically, would it be possible to develop plants with more efficient photosynthesis to better tolerate low light levels?

ImperialCollege3 karma

Hi Anthony here, great question. I also struggle keeping houseplants alive. Yes this is definitely possible, in fact, evolution has already done this many times already. We have such a biodiverse planet with plants, algae and cyanobacteria thriving in all sorts of environments. For example, photosynthesis can even occur deep in the ocean where very little light reaches.

Studying the many enzymes and pathways involved in photosynthesis can shed some light on how these organisms have adapted and manage to live in low-light conditions. And maybe one day, we can apply that to our houseplants.

Odd_Transportation124 karma

Could a person in a coma survive through synthetically induced photosynthesis?

If that were possible, could we induce said coma for say astronauts on long-term flights to perhaps Mars to preserve energy instead of the (fan-favorite) cryo-sleep that is observed by certain organisms other than plants?

ImperialCollege3 karma

Hi, Tanai here. Interesting question… assuming that all the medical aspects of going into coma are taken care of, then I suppose it would be theoretically possible but perhaps not very convenient, if what it is needed is oxygen. The problem is that to produce enough amounts of oxygen from photosynthesis, a lot of surface area is needed. So, the space-ship on its way to Mars will need to accommodate a lot of plants. For example, to power a human directly with photosynthesis, the person would need to have a surface area the size of a football field. I think there are already other ways developed, perhaps more convenient’ to produce large quantities of oxygen.

ImperialCollege3 karma

Hi, Andrea chipping in. As Tanai mentions photosynthesis could provide both oxygen and energy for the metabolic need of the sleeping/coma person. The question is how much energy the sleeping person needs to survive. I seem to remember that if you do not move you will still need plants to cover the surface of a bowling alley. On the other hand there is that cool sea slug that eats algae and stores the chloroplast for then to change its shape to look like a leaf and then survive with the power of photosynthesis. Not sure the astronauts would like that though. Here is the link to the sea slug that becomes a leaf (

On-mountain-time3 karma

If it was possible for your body to photosynthesize for energy with only minimal nutrient supplementation instead of having to eat every day, would you make the switch? And what "flavor" would you make sunlight taste like? Thank you for your time.

ImperialCollege3 karma

Tom here. I would definitely make the switch, my chef skills are lacking and if I didn’t have to bother with making food, then my life would be a lot easier. I would make sunlight taste like oranges maybe? Difficult to answer, I’ve not really thought too much about this before.

Anthony here. Yes absolutely! Think of all the time and money you could save, and all the research you could do on yourself. For me, I’d hope sunlight tastes like lychees or chocolate, possibly both.

ImperialCollege3 karma

Tanai here. I would make the switch, for sure! I don’t like the biological business of daily waste disposal and would not mind a dark green skin tone. I do wonder what it would feel like to burp oxygen. :D haha. I think I would make light taste like katsu curry or Colombian “Bandeja Paisa”.

ImperialCollege2 karma

Andrea here. I would probably do the switch though I really like food. Could I really do without my Italian mamma’s food? As for the flavour, I would like something refreshing and citrus that goes well with the sun and summer. It would be great if the flavour would change with the hour of the day. In that case, you could pop out at different times and enjoy the variety.

Puzzleheaded_Peak1403 karma

How does the efficiency of photosynthesis as a process compare to the efficiency of something like solar panels? What are some ways you could improve the efficiency of photosynthesis?

ImperialCollege6 karma

Hi Anthony here. For your second question, I’ll have a go at giving an example of how we could improve photosynthesis because there are many. So the first thing to bear in mind is that photosynthesis involves many different reactions and each is catalysed by enzymes that help the reaction occur at “life-friendly” temperatures and time-scales. And each enzyme has potential to be more efficient and the important thing would be to identify which ones are most rate-limiting to the overall process. The first inefficient enzyme that springs to mind is called RuBisCO and this enzyme is the one responsible for fixing CO2 into sugar molecules. Unfortunately, RuBisCO doesn’t always distinguish between CO2 and O2 very well so sometimes the unwanted reaction with oxygen takes place instead. There are currently attempts at reducing this inefficiency by adding other enzymes that can surround RuBisCO enzymes with more CO2 than O2. These other enzymes that concentrate CO2 around RuBisCO are already found in photosynthesising bacteria called cyanobacteria.

ImperialCollege3 karma

Tom here. Like Anthony says, there are many approaches to tackling the ‘improvement’ of photosynthesis efficiency. Generally improving photosynthesis from the perspective of humans is related to improvements in crop yields because providing food for all of the inhabitants of our planet will become increasingly more difficult over the next 100 years. One approach that has been taken by the Long Lab in Illinois is to genetically modify the tobacco plant’s photoprotective response to high light conditions. When the plants are naturally shaded by clouds or other leaves, this photoprotective response reduces the amount of photosynthesis that can take place. By modifying this response, they showed that the plants had greater productivity under fluctuating light conditions. As the molecular mechanisms for this response are present in all plants, it is possible that this approach could be applied to crop plants in the future.

ImperialCollege2 karma

Andrea here chiming in too... a deceivingly short question but quite hard to answer. The short answer is that photosynthesis is very inefficient when compared with solar panels. Solar panels are about 20% efficient while photosynthesis is way below 1%. Nevertheless, they do not produce the same product as solar panels produce electricity, with all the difficulties associated with storage, while photosynthesis stores the energy in chemical bonds. The comparison is also complicated by the fact that solar panels have only one job to do while a plant is a living organism that grows, reproduces, interacts with other plants, fights for a spot in the sun and defends itself from predators and parasites. Many of the inefficiencies that reduce the overall photosynthetic efficiency is the results of redundancies and protection mechanisms in the system. These are there because the environment where the plants live is not static and the plants have to be able to respond rapidly to any change. Eliminating these protection mechanisms in order to make photosynthesis more efficient could result in the plant becoming more fragile and dying. If you have to invest energy to protect a more fragile plant that is more photosynthetically efficient it would in the end defeat the purpose to make it more efficient in the first place.

ConflictBrave5812 karma

Are there any pharmaceutical companies currently using photosynthesis to manufacture drugs? What are the advantages of such an approach over traditional methods?

ImperialCollege2 karma

Anthony here, yes there are companies doing this for drugs, antibody therapeutics and vaccines. While some are still in an early research phase others are being trialled. One advantage over traditional methods is that some drugs may be difficult to synthesise chemically due to their complexity, fortunately, in some cases nature has already optimised a biochemical pathway for that particular product.

Another advantage is if the drug or vaccine is stored in a plant then you avoid having to keep it cold through the whole supply chain. This would be especially helpful for developing countries where the infrastructure may not be available to keep a precious medicine at -80C for weeks at a time.

Brinsley992 karma

Are there any ethical considerations or concerns around 'evolving' photosynthesis or meddling in these natural processes?

ImperialCollege2 karma

Anthony here. Great question. Over the course of human civilisation and agriculture, we have already “meddled” in these natural processes. We have selectively bred many species of plants to produce bigger and tastier leaves, fruits and roots. And now, with an improved understanding of the biochemistry and genetics of these plants and an improved toolbox of precise genetic engineering we have the potential to unlock further improvements that were not possible in traditional breeding.

However, we should definitely keep asking these ethical questions and monitoring how these changes can affect the environment and other species in the ecosystem. And generally, make agriculture more sustainable as a whole. There are also ethical considerations of not taking action when we can. For example, vitamin A deficiency affects around 127 million preschool children each year, with about 250,000 - 500,000 becoming blind because of it. We now have the technology to genetically enrich rice with a vitamin A precursor that could help reduce these cases.

Clarko902 karma

Hi! What is still needed for artificial photosynthesis to be a reality in today's world and technology?

ImperialCollege2 karma

Tom here. A lot of artificial photosynthesis approaches generally split the problem into 3 parts. Firstly you have antenna molecules that harvest photons and funnel the absorbed energy to a photosensitizer. Secondly, the photosensitizer performs charge separation (moving oppositely charged species apart, spatially). Thirdly, redox catalysts then perform chemistry using these charged species. These approaches take inspiration from the photosystems found in photosynthetic organisms. Often the hardest part is the redox catalysis. For example, photosystem II performs water oxidation, removing electrons so that they can eventually be used to reduce carbon dioxide into sugars. This water oxidation chemistry is very difficult to imitate. Firstly, the oxidative power required to remove the electrons is very large. In Photosystem II this leads to harmful side reactions which damage the protein scaffold and lead to very high turnover rates of the enzyme. Secondly, the oxidation of water occurs in 4 separate steps, and synchronizing the movement of protons and electrons away from the catalytic site is a very complex process that requires many different components. Applying this complexity to an artificial system is something that we aren’t capable of right now but research in this field is growing all the time and I wouldn’t be surprised if this problem is solved in the near future.

LongShore-Drift2 karma

Hi there, Is there a reasonable priced type of mirror or glass that reflects/permits the transmission of the vital UV waves for (human) Vitamin D production and other wellbeing?

ImperialCollege3 karma

Thomas here - As I understand it, Vitamin D is produced by UV-B, which has a wavelength range of 280-315 nm. The glass in your windows will block most UV-B because of its amorphous structure. If you changed this glass into quartz, you would let UVB through into your house. But this will probably be pretty expensive and it’s cheaper just to buy vitamin D supplements.

sinkingsand2 karma

We all learn that mitochrondria are the power house of animal cells, but no one talks about chloroplasts which I guess are the plant equivalent?

Do you have any cool chloroplast facts and is it possible to bio-engineer them to be super photosynthesisers?

ImperialCollege1 karma

Tanai here. One of the big differences between mitochondria and chloroplasts is where the energy of light is transformed into sugars. That is the only way there is for energy to enter the living world. So the chloroplast is like an energy factory. The mitochondria then uses the sugars (that originally came from a plant) as fuel to power the cell.

Interestingly, plants use both chloroplasts and mitochondria!

Some interesting facts about chloroplasts… I like the fact that they originally came from bacteria (cyanobacteria) and inside it, you can find a tiny genome with genes encoding photosynthesis but that are nearly identical to those of the bacteria they came from nearly 2.0 billion years ago!

There are currently huge efforts by research teams around the world attempting to enhance photosynthesis one way or another. There are also some interesting ideas to attempt to make the chloroplast use photons of light that are beyond the current range of photosynthesis. For example, most photosynthesis uses colors from 400 nanometers (blue) to 700 nm (red), but it may be possible to extend this range up to 750 nm or more, which could result in an additional boost. Such kind of ideas are in the pipeline, and some research efforts are ongoing from several labs trying to accomplish it, but it is too early to say whether such an approach will result in better or enhanced chloroplast.

I personally think that one day, with enough advancements, we will have super-photosynthetizers!

aseakins2 karma

How do you go about researching photosynthesis so far back in time - what kinds of data do you use and what are you looking for?

ImperialCollege3 karma

Tanai here, thanks for this question. Exactly what I have spent the last 10 years of my life doing! :) There are different approaches. You could say that there is the approach of the biologist, and the approach of the geologist. The biologist would look at the record found in genomes and by comparing the known diversity of photosynthetic organisms; and the geologists would look for traces or past signatures of photosynthesis, either direct or indirect ones, in the rock record.

I study the evolution of the molecular machines that actually do photosynthesis. And it turns out that they have changed little, and predictably, over billions of years… so I can compare for example, two of these molecular machines, known as photosystems, from two different types of photosynthetic organisms: say a plant, and a bacterium, and then see what has remained unchanged and what has changed. Then we can start formulating testable hypotheses.

Photosystems take the energy of light and convert it into chemical energy that can be used by the cell. They are huge molecular complexes that bind chlorophylls… those are what make plants green, and they come in different types with interesting variations. We find them in plants, but also in bacteria across the tree of life.

Fortunately, today we understand photosynthesis at an unprecedented level of atomic detail… and have a pretty good understanding of how all of these molecular machines work. And structure and function is evolutionary information! So we can compare them and try to understand how they relate to each other, and what steps and conditions were necessary for photosynthesis to evolve. In a similar way that a paleontologist would compare the skeleton of a dinosaur and a bird, I can compare the molecular structures of photosystems, or other molecules, from distantly related organisms.

From the rock record, there is good evidence that there were photosynthetic bacteria by about 3.4 billion years ago. Possibly even 3.8 billion years ago… and these are the oldest rocks on earth that survive and can be studied in the lab. There is also good evidence for oxygen, from photosynthesis, at about 3.0 billion years ago, even perhaps before that.

But because photosynthesis is so old, we work in spans of times of billions of years!

Brinsley991 karma

Hi all - did photosynthesis evolve independently more than once on Earth, or does all photosynthesis related to one species that evolved the trait billions of years ago?

ImperialCollege2 karma

Thomas here. Cool question but one that is quite hard to answer. Photosynthesis is not a single reaction but is a term for the many different processes that are catalysed by many different enzymes. In ‘oxygenic’ photosynthesis, the common theme is that water is oxidised, removing its electrons so that they can eventually be used to reduce carbon dioxide into more complex carbon molecules like sugars. It just so happens that the byproduct of this initial reaction is molecular oxygen which we breathe!

The enzyme responsible for catalysing this water oxidation reaction is called Photosystem II. It is one of the most interesting and complex enzymes that we are aware of. Photosystem II is present in certain bacteria (cyanobacteria), algae and plants but we know that all of the genes present in different organisms originated from a common ancestor - i.e Photosystem II only evolved once. This water oxidation chemistry is actually quite a difficult reaction to catalyse and requires a large oxidation potential - this is something that humans find difficult to imitate in their quest for artificial photosynthesis and one of the reasons why we don’t have unlimited energy via this technique.

As part of Tanai and my most recent work, we have argued that Photosystem II evolved very early in the history of our planet, close to the origin of life itself, 3.7 billion years ago.

Ok_Race91631 karma

So, I can see how photosynthesis might be harnessed to tackle climate change - it literally turns a greenhouse gas into oxygen - and has a role to play in crop yield to tackle hunger, but what's the link to disease?

ImperialCollege1 karma

Andrea here. Well spotted point. Plant biotechnology is a fast-growing field of research where plants have been proven to be expression vectors for compounds of biological importance. In particular, chloroplasts are self-contained powerhouses capable of working as tiny bioreactors for the production of biopharmaceuticals, bioproducts or vaccines. A few years ago, the breakthrough in the hyperexpression of biopharmaceuticals in edible leaves has opened this field of research and promises to reduce the cost of production of protein-based drugs, currently not affordable to a large portion of the global population. Vaccines expressed in edible leaves could be targeted to both animal and human diseases.

Tanai here chipping in. Other complex drugs that could be produced in a similar way are protein-based (monoclonal antibodies) chemotherapy drugs, like this for example:

In addition, both plants, algae, and other photosynthetic microorganisms could be engineered to specifically produce any range of chemical compounds, like pharmaceuticals. Currently, many pharmaceuticals and drugs are actually produced using non-photosynthetic organisms used in industry like yeast, or E. coli, and to grow these, they need to be fed with sugars and other nutrients that most of the time come from crops. So, it may be as well possible to produce them directly in the photosynthetic organisms, although the technology is still being developed.

Neutrinos_Discussion1 karma

Could an algae or microrganism ever be developed that could feed on oil spill pollutants?

ImperialCollege1 karma

Tanai here. Thank you for your question. The interesting thing that photosynthetic organisms do is that they use the energy of light to fix carbon and build the cells, right? By doing so, they first make sugars, and they can then transform the sugars into natural oils, like vegetable oil. Algae can also do the same. So, in practice, algae and other photosynthetizers are actually oil producers! What you need to clean up oil spills is not a photosynthetizer, but an organism that will use the oil as a source of food.

It turns out however that at oil spill sites, microbial communities have already evolved to degrade these oils and those are currently being studied by research labs. I’m not very familiar with their research though, and I don’t know how intensive these research efforts are today. However, using those naturally occurring microbial communities as starting points, it may be possible to enhance the process of oil degradation with genetic engineering. It may also be possible, with a technique called “directed evolution” to enhance the activity of the molecules that do the degradation. I’m not sure if there is anyone trying to do that at the moment since the topic is outside my expertise! :)

ConflictBrave5811 karma

Great answers so far everyone! I wondered if there are any common agricultural crops that are notoriously bad / inefficient photosynthesisers? Or have they all been selectively bred to be pretty good? Which crop is the low hanging fruit in terms of evolving their photosynthesising machinery?

ImperialCollege1 karma

Thank you. Tanai here! In all of the years as part of the photosynthesis research community I have never heard of a crop that is particularly bad at photosynthesis or with comparably less efficient photosynthesis. Interestingly, crops have never been bred for improving or enhancing photosynthesis, and all of the yield improvement made in the past half-a-century, have come from breeding for other things. The reason for this is that most of the breeding that have been done, focuses on traits that are “evident to the eye”. Is the fruit larger? Does it have more grain? Thus, selecting for enhanced or improved photosynthesis has not been done yet in a concerted effort, because it is a bit more complicated to prove for enhanced photosynthesis. In fact, the concept of what “improved photosynthesis” or “enhanced photosynthesis” is, might be also up for debate.

However, I understand that there are currently major projects in different continents aimed at enhancing photosynthesis one way or another. See this for example: ( or something like this in Australia:

I also know that some scientists think you cannot really enhance photosynthesis, and that it is an unlikely solution to solve the world food problem, as there are other environmental and physiological factors that can limit crop yields.

Regarding your last question... there are two types of plant photosynthesis called C3 and C4. The differences between these types have to do with how carbon is fixed and transiently stored in the cell during photosynthesis. It is thought that C4 plants are a bit more efficient, but over 80% of plants are C3, including many important crops like rice and wheat. So, there are efforts and research attempted to engineer C4 photosynthesis in C3 plants! A hard challenge as it involves different types of cells and complex regulation. However, it is known that C4 photosynthesis has evolved several times independently in different plants, so perhaps there is potential!

Purple-Plus-Green1 karma

Has anoxygenic photosynthesis evolved vertically or has it been transferred laterally? What about the Alphaproteobacteria? Are they ancestrally photosynthetic? I believe all possible scenarios have been proposed in the past for the evolution of anoxygenic photosynthesis in the Proteobacteria. What does most evidence point to nowadays?

ImperialCollege1 karma

Tanai here. Thank you for the interesting questions! Right down my alley. Regarding your first question, the answer is both. I think there is good evidence for anoxygenic photosynthesis to have been inherited both vertically and laterally. And there is also evidence for anoxygenic photosynthesis being lost in bacteria. In Alphaproteobacteria in particular, there are gene clusters that are relatively easily transferable, both within Alphaproteobacteria, and from them to other groups of bacteria. There is also evidence for a lot of exchange of photosynthesis enzymes and compounds between different groups of photosynthetic organisms, say for example some cyanobacteria exchanging some of their enzymes needed to make chlorophylls for those of Alphaproteobacteria, and also the other way around!

I don’t think there is a consensus on whether Alphaproteobacteria were ancestrally photosynthetic, and I don’t think this question has been discussed much recently, in the particular case of the Alphaproteobacteria. In addition, I don’t think anyone has tried to answer this question recently with a dedicated project.

From my own research, I would say that Alphaproteobacteria were ancestrally photosynthetic. In 2007 a new group of photosynthetic bacteria was discovered known as Acidobacteria, and only a few species are known from this group. However, several of the photosynthesis proteins seem to be the closest in evolutionary terms, to those of Proteobacteria. When we then compare with the tree of life, Proteobacteria and Acidobacteria appear to be closest to each other among those groups that have photosynthesis. I interpreted that as evidence of them sharing a common ancestor that was indeed photosynthetic. However, I don’t think that evidence is hugely conclusive. In addition, Acidobacteria have a different type of photosystem than Alphaproteobacteria! Acidobacteria use a “type I” and Alphaproteobacteria a “type II”! So, it is plausible that some exchange of photosynthetic components occurred, or that their ancestor had both types.

Based on my own research, I have come to conclude that the evolution of photosynthesis suggests that nearly all, if not all, bacteria were ancestrally photosynthetic. Not only that… but I have also come to challenge the idea that anoxygenic photosynthesis came first and gave rise to oxygenic photosynthesis. But that is another story!

I’m currently entertaining the idea that there was never a discrete origin of photosynthesis, but that the process traces back to light-powered reactions going back to the origin of life itself :)

Brinsley991 karma

How would the quality or type of sunlight received on other planet affect how life there might harness it chemically? How about the sunlight from red dwarf stars?

ImperialCollege1 karma

Andrea here, this is a very interesting and intriguing question. The colour and quality of the light on another planet would define the amount of energy available for the chemical reaction. The nature of the chemical reaction will therefore also depend on that but in our planet water turns out to be an excellent source of electrons also because of its abundance. In terms of energy in the light, more blue light will give the organisms on that planet more energy but that would also mean the need for more protection mechanisms because more energy also means more damage. More red light would give less energy. When we investigated the organisms capable of using far-red light to do photosynthesis we also suggested that since there are more M class stars (red dwarf and red giants) in our galaxy than G class (our sun) life on other planets would likely be using more far-red light photosynthesis than visible light. What would be the consequences of that is, is what we are trying to investigate at the moment. Part of our current research is directed at understanding if far-red photosynthesis carries a penalty in terms of efficiency or stability and to try to answer the question on why far red photosynthesis is not more widespread on our planet. On the other hand, the search for life on other planets should certainly extend the spectrum of light from the visible to include the far-red.