Category Archives: super photosynthesizer

Superphotosynthesizer: Cat Island Baldcypress

Today May 18, 2015 is ‘Fascination of Plants Day,’ an initiative organized by the European Plant Science Organisation with other events organized by the American Society of Plant Biology. On this blog, there’s no shortage of reasons why plants are fascinating, but to most they are still just the scenery. Take some time today to consider all that these primary producers do for you. Here are just a few things plants do for us- food, forestry products, paper, pharmaceuticals, energy, and beauty.

Of course, I am partial to the oxygen that they provide for us. In that spirit, today’s post will feature another superphotosynthesizer: the Cat Island Baldcypress located on the Cat Island National Wildlife Refuge in West Feliciana Parish, LA. This tree is the national champion of its species and also noted as the largest tree of any species east of the Sierra Nevada range.

It is located at the end of an easy walking trail (0.75 mile round-trip), but it only accessible for part of the year. Access to portions of the Cat Island NWR is prevented by levels of the Mississippi River since at least a couple of low bridges must be traversed to get you from the main road to the trailhead. If the river stage at Baton Rouge is greater than 20 feet, which is usually between February and June, there is no vehicle access to the trail. I was able to make a trip there in early February just before the river restricted access. It’s not quite clear whether the base of the tree itself is submerged at any point during the spring flooding because there is a really nice decking just before the tree at the end of the trail. As of today, the river stage at Baton Rouge is 27.8 feet, so it may still be another month before access is regained.


The tree is impressive. At 96 feet it is taller than all the other trees around, but it’s certainly not the tallest tree east of the Sierra Nevada. However, its girth is undeniably impressive. It has the characteristic buttressed-base of all baldcypress trees, which measures 17 feet in diameter and 56 feet in circumference.  It has knees as tall as me. Well, for those of you who know me in real life maybe that’s not so impressive, but for a random root outgrowth that is still significant.


This brings me to one of the real secrets of the swamp- cypress knees. These strange growths at the base of cypress trees have been puzzling botanists and plant biologists for centuries since Francois Andre Michaux wrote in 1819, “No cause can be assigned for their existence.” Many people have had theories as to how they contribute to cypress biology- increased aeration capability for growing in inundated swamps, methane (swamp gas) emission conduits, vegetative reproduction, mechanical support, nutrient acquisition, and carbohydrate storage. None of these hypotheses have really held up to analysis and the biological function* of these root outgrowths are still fascinating plant biologists today.


This is just one local fascinating plant example. Check out the links below for more information about Fascination of Plants Day or follow #FOPD on social media.



*These expendable appendages are painted and carved for folk art projects. They are also fairly proficient at disemboweling lawnmowers of homeowners with cypress trees in their yards and capsizing careless motorboat operators in the swamps. Perhaps this is a plant defense mechanism ahead of its time.

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Corpse Flower: The Living Dead

Corpse Flower Credit: U.S. Botanic Garden via Wikipedia

Today’s plant costume is an odiferous disguise instead of a visual one. Its common name is also appropriate for the Halloween season- The Corpse Flower. It only pretends to be dead by giving off a rank odor of rotting flesh when it blooms. Again the reason is pollination. This horrible smell to us calls to every beetle and fly around that supper’s on. While they root around in the tight dark spaces of the bloom trying to find a decent place to feed and lay their eggs, they become covered in pollen. These pollen-covered insects then fly off to another bloom to pollinate another plant.

This species, Amorphophallus titanum*, is also a superphotosynthesizer in the plant world. As you may have noticed from the pictures and videos, the blooms can be as large as 10 feet tall. This makes the corpse flower the world’s largest inflorescence. Notice I didn’t say flower. Ah, botanical anatomy semantics! The images may look like a giant flower with burgundy petals surrounding a central stigma on steroids. Not so. The ‘petal’ portion of the flower is actually a bract structure called a spathe (plant biology word of the day). The tall central feature is called a spadix (bonus plant biology word of the day), and it is this structure on which the true flowers of the plant (separate male and female flowers) are arranged. The entirety of this plant reproductive structure is the inflorescence and there isn’t a bigger one in the plant world. The world’s record for a corpse flower bloom is nearly 11 feet tall. After flowering, the plant then makes the world’s largest leaf structure. It may look a tree in its own right, but developmentally, it’s just a compound leaf.


* Grossly translated as giant misshapen penis. Yeah. Well, you’ve seen the pictures. Stay classy readers!

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Adamantium, for plants!

Researchers have basically created the plant equivalent of Wolverine

Researchers have basically created the plant equivalent of Wolverine

One of the goals of photosynthesis research is to improve plants’ productivity to a level adequate for human food and energy needs. As of now, plants are currently doing a good enough job to reproduce themselves and mostly sustain our biosphere, but we would still like to kick this up a notch. Scientists are using a variety of tools to tackle this problem. The most notable is using genetics- either by breeding new varieties or genetically engineering new traits by manipulating specific genes sometimes between different organisms. Today’s post features another type of engineering to improve plants ability to photosynthesize- nanotechnology.

Researchers at MIT report that plant chloroplasts can be infused with carbon nanotubes to impart increased photosynthetic capacity (as much as 49% greater than unaltered chloroplasts and 30% in whole plants). Much like the X-Men character Wolverine was infused with the metal alloy adamantium to render his skeleton indestructible and give him those awesome retractable claws, plant chloroplasts can be infused with special materials to give them what amounts to photosynthetic superpowers. No, they didn’t use adamantium. The material used in their study was carbon nanotubes fused to cerium oxide nanoparticles aka nanoceria.*

You may be wondering to yourself, “What exactly are photosynthetic superpowers?”**

The nanoceria are able to absorb infrared light, which no native plant pigments can do. Plant pigments like chlorophylls and carotenoids do a good job of covering the visible light spectrum, but this is only half of the incident solar energy beaming down on them all day. The researchers in this study conclude that the boost in photosynthetic capacity is in part due to the fact that the nanotubes absorb light energy beyond the visible range and can then transfer this energy to the photosynthetic machinery. In this way, the nanotubes are acting like an antenna- a giant antenna that doesn’t just boost the signals you’re already getting, but allows access to a whole set of new premium channels.

The nanotubes have a couple of other advantageous side effects as well. The cerium oxide nanoparticles are quite effective radical oxygen species (ROS) scavengers. Remember when I told you photosynthetic organisms have a complicated relationship with light? They need enough of it to live, but too much can be extremely damaging. This is why blasting plants with bright light at all times isn’t necessarily the best way of improving their growth and productivity. Likewise, improving their ability to capture light can also be dangerous. This is all due to the fact that overloading the photosynthetic circuitry with too many electrons can start to generate ROS which in turn irreversibly damage proteins, pigments and DNA they encounter. Since the nanoceria are quite good at scavenging or capturing and inactivating ROS, they also boost photosynthesis by helping out plants’ innate systems for dealing with this problem. Again, like Wolverine, plants have some level of ‘healing powers’ when it comes to dealing with light, but the nanotubes help kick it up a notch. Wolverine’s adamantium doesn’t really help with his healing powers, but coating his skeleton with it means it doesn’t get broken as easily and he doesn’t have to use his healing powers to mend broken bones. In the same way, the nanoceria prevent some damage before it happens so the plants don’t have to waste their resources on repairing damage caused by ROS.

In true superhero style, the nanotube-infused chloroplasts’ powers don’t stop there. They also confer the ability to detect certain chemicals in the environment. Yes, just like Wolverine has heightened senses (if he twitches is nose, he’s knows you’re there!), chloroplasts containing nanotubes do too. Different types of nanoparticles have been developed to detect toxins and pollutants like nitric oxide, sarin gas, and TNT. Integrating this technology into a photosynthetic organism may allow plants to become stealthy biodetectors of these chemicals. No longer would they be merely scenery, but solar-powered secret agents (green-ops?) with skills no training could ever provide.***

These super powers may not be indestructible retractable claws, but it’s a good start down the path to lots of useful applications.

Conclusion: Plants infused with nanoceria definitely qualify as super photosynthesizers, but we still have some work to do to put this into useful practice beyond the lab.

How do nanoparticles and enhanced photosynthesis affect plants over their entire lifespan vs. short experiments in the lab? Does this kind of boost in the light reactions translate into an increase in biomass? Sure, the light reactions could always use some help when sunlight is less than its brightest, but the real rate-limiting pathway is the dark reactions. (I’m looking at you Rubisco!).

How can this technology be translated into field agriculture to boost productivity of crops? Is it worth it? It’s not like you can propagate the nanotubes biologically, but who knows, maybe in the future tractors will be outfitted with attachments to infuse or spray seedlings with nanoparticles. In terms of calculating potential for improving plant productivity, photosynthetic energy conversion remains a variable in the equation that has yet to be thoroughly tapped when it comes to improving crop plants. Using carbon nanotubes to extend the spectrum of useful light into the infrared would definitely help plants breakthrough some yield ceilings we are seeing.

How can we turn our scenery into useful biosensors for pollutants? What kinds of chemicals can they detect and how can that be cheaply and easily measured? Sure, everyone and their grandma has a satellite and a drone these days, but are we really going to have to laser scan our environment every hour? How about a nice color change or wi-fi signal that NORAD can detect?

Speaking of wi-fi, why can’t we engineer plants with nanotechnology that allows them to have other superpowers, like transmitting wi-fi signals? Solar-powered free internet anywhere! Finally, getting plants to release something useful besides oxygen****, and it would go a long way to keep me from going over my monthly data plan limits.

These are all questions and exciting possibilities that will keep photosynthesis researchers like the Strano lab busy for years to come.


*IMHO, ‘nanoceria’ is itself a name worthy of comic book lore. Maybe DC Comics can do a series where Swamp Thing is infused with nanoceria boosting his plant-like powers.

** You must be new here. Welcome.

***K-9 units may be relegated to history. SWAT, move over for SWNTs. (You’ll get it if you read the paper).

****It’s important to me that you catch the sarcasm in that phrase. If you’ve been breathing today, thank a photosynthetic organism.

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Mass out of Thin Air

“True, I talk of dreams,

Which are the children of an idle brain,

Begot of nothing but vain fantasy,

Which is as thin of substance as the air…”

Romeo and Juliet, William Shakespeare

It’s true the atmosphere around us is invisible, but is it really as insubstantial as Mercutio thinks? For humans perhaps, but not for photosynthetic organisms. Sure, plants may appear to be firmly rooted in the ground, but this tether to substance is only a deception. They really make a living knitting mass out of thin air by pulling carbon dioxide from the atmosphere and fixing it into useful biological molecules.*

General Sherman Tree via Wikipedia

This feat is most obvious in the world’s most massive organisms- the Sequoias. These giants are experts at silently converting air into substance. Tree size can be measured in different ways like height or girth, but the true measure of mass is trunk volume. Based on this measure, the largest tree ever reported was the Lindsey Creek tree. It was felled by a storm in 1905, and the local paper published some details on its measurements to give an estimated trunk volume of 90,000 cubic feet. The Crannell Giant was discovered in 1926 and more precise measurements calculated a minimum trunk volume of 61,573 cubic feet. It was logged in the late 1940s.

The most massive living tree (single stem) is the giant sequoia (Sequoiadendron giganteum) General Sherman in the Giant Forest of Sequoia National Park with an estimated trunk volume of 52,508 cubic feet. It soars to a respectable 274.9 feet in height with a base circumference of 102.6 feet and is estimated to be more than 2,000 years old. It is truly the biological manifestation of majesty.

Of course, even this mighty giant has humble beginnings. Check out this video that documents the growth of sequoia seedlings over the first five years of their lives. You may still doubt how those young trees could grow into a giant the size of the General Sherman, but over the course of ~2300 years the area corresponding to the base of the General Sherman received 341 Gigawatt hours-worth of incident solar energy.** What would you do with that much energy? Well, you could power New York City for about a month. If you are a sequoia, you could use photosynthesis to turn it into ~50,000 cubic feet of tree.

Don’t think that an older tree like the General Sherman is going to sit on its laurels when it comes to gaining mass. As I mentioned yesterday, new research has shown that this kind of older tree is increasing its growth rate when it comes to adding mass. The statement can seem quite intangible when juxtaposing the most massive living organism and a substance as thin as air. How much mass are we talking about? The 40 cubic feet of growth General Sherman adds annually at 13.42 pounds of carbon per cubic foot corresponds to 537 pounds of carbon. That’s just over a quarter ton of carbon extracted from the air each year by a single tree.

With those numbers, I’ll have to disagree with Shakespeare. It seems that air has more substance than Mercutio would lead you to believe. Perhaps there is more to that dream as well.


* Remember the equation for photosynthesis? No? You must be new here.

**∏(5.5 m)2 = 123 m2 x 4.2 kWh/day x 365 days/yr x 2300 yrs = 341GWh

The incident solar radiation on the area of the size of the base of the General Sherman. Sure, the size of the base would be changing over the course of those 2300 years, but the canopy area is much larger and the error bars on the age are on the order of centuries, so I’m calling it close. If anyone else would like to come up with a better algorithm that takes into account the changing area over the course of the tree’s lifetime, please show your work in the comments section below.

References and Links:

Even microbial marriages are more than they seem

I wrote a guest post for the American Society of Microbiology blog Small Things Considered. Click the link to read more about the intimate relationship between a hardworking photosynthesizer and its motile heterotrophic partner. What do these two species see in one another? Has a metabolically lazy flagellate found biochemical sugar daddies? Have green sulfur bacteria engineered a way to steer a motile bacterium to their favorite places? Don’t be so quick to judge… the answers will surprise you.

How do they make it work? Genomic Revelations on a Microbial Consortium in Small Things Considered


Original journal article:

Cyanobacteria Shed

Here’s something new under the sun… cyanobacteria shed in the ocean.


Most people are well aware of the fact that dogs and cats shed, but did you know that oceanic cyanobacteria also shed?* OK, so the cyanobacteria don’t shed hair, and you won’t need a lint brush. In a report in this week’s Science, researchers from the Chisholm lab show that cyanobacteria living in the world’s open oceans are shedding zillions of membrane vesicles. Before you accuse them of pollution, allow me to explain why they are the most important bacteria you’ve never heard of– the Prochlorococci. Don’t worry about being too late to this fountain of knowledge, scientists only discovered them about 25 years ago.

Prochlorococcus species are cyanobacteria that live in the oligotrophic ocean, areas of the world’s open oceans that are nutrient poor when it comes to sources of nitrogen, phosphorous and bioavailable forms of essential metals like iron. These bacteria dominate these otherwise ocean deserts and are possibly the Earth’s most populous species by sheer numbers of individuals. Remember about half of the world’s primary productivity comes from aquatic sources. Prochlorococci are a major contributor to global nutrient cycles and a significant number of the oxygen molecules you are constantly breathing in and out were produced by a Prochlorococcus.

You may be curious as to why scientists have only recently discovered these numerous and critically important photosynthetic organisms. The answer is because of their other trademark- their size.  Measuring in with widths and lengths well under a micrometer, they are the world’s smallest photosynthesizers. Prochlorococci pass through many of the standard filters used for trapping microbes from aquatic samples. They were detected using a cell-sorting technique that could just detect their faint chlorophyll fluorescence signal. These fascinating microbes have been studied in the ocean as well as the laboratory for the last couple of decades, but it is a labor of love. Since Prochlorococci live in such a nutrient-limiting environment, they don’t have much competition. Consequently, these cyanobacteria don’t have to grow very fast, and their small size is another way of conserving their resources. In the laboratory, they don’t grow as fast as the other model cyanobacteria and their extremely small size means scientists have to wait quite a while before significant biomass is achieved for experiments.

So, it is quite a remarkable discovery that something so tiny that has toiled so diligently to fix carbon dioxide into biological molecules would just shed them as tiny vesicles into the ocean. The vesicles released by the Prochlorococci and Synechococci** are small membrane-closed vesicles that contain proteins and even small fragments of DNA and RNA. Surely, the bacteria are not just throwing away precious resources. It’s unlikely that science has stumbled upon the first eating disorder among primary producers, so the obvious question arising from this observation is why the bacteria shed these vesicles.  The authors offer some hypotheses to justify this seemingly wasteful phenomenon.

It could be an example of the cyanobacteria ‘casting their bread upon the waters.’ Preliminary results suggest that- as the saying goes- they find it again. The open ocean environment is a hard place to live, but cyanobacteria are not the only organisms living there. Heterotrophic microbes are also part of the biological community and previous reports have demonstrated that they can stimulate the growth of Prochlorococcus strains. Perhaps the vesicles are a way for the cyanobacteria to feed their beneficial heterotrophic neighbors without putting their cells on the menu.

The vesicles could also serve as bacterial countermeasures against cyanophages, viruses that infect cyanobacteria. For all intents and purposes, the vesicles look like miniature bacteria complete with receptor proteins the phages use to recognize their bacterial victims. The authors were able to observe ‘fooled phages’ that had bound and injected their genetic material into vesicles. In this way, the shed vesicles would be a good defense against these oceanic pathogens. From the phage perspective, an ocean filled with zillions of vesicles, each appearing like a potential host would seem like a lottery they can’t lose. However, the cyanobacteria have ensured the odds are in their favor by shedding many, many more vesicles into the environment relative to the susceptible cells.

Finally, the vesicles could just be the clichéd ‘message in bottles’ of seafaring lore. Even an ocean teeming with trillions and trillions of other Prochlorococci is isolating when reproduction is asexual. For microbes, setting your genetic material adrift on the ocean swells is a hopelessly romantic gesture. That DNA may eventually make its way to another cyanobacterial cell that will find it useful and incorporate the DNA into its genome. It is also possible that the messages are not necessarily genetic. The vesicles could also be used to store and transport specialized metabolites as a defensive or offensive strategy. For now, only the cyanobacteria seem to be able to decipher the messages.


* Hopefully, you weren’t unwittingly gifted any pet cyanobacteria for Christmas.

**larger cyanobacteria than the Prochlorococci, but still not in a position to freely give away hard won nutrients

Fun fact: Dr. Chisholm has also co-authored a couple of children’s books on photosynthesis. Check them out here.


About those solar-powered sea slugs…

Elysia chlorotica,Credit: Patrick Krug Cataloging Diversity in the Sacoglossa LifeDesk via Wikipedia

About those ‘solar powered sea slugs’… a new study has given me reason to change their status from super photosynthesizer to plain heterotroph. It seemed too good to be true: sea slugs that can slurp on algae, digesting all but their chloroplasts which are retained in an active state inside the digestive tract conferring a photosynthetic lifestyle to the sea slug hosts. With such an elaborate mechanism for retaining these photosynthetically active chloroplasts, of course it must be to the nutritional advantage of the sea slugs. The early studies on the sea slugs suggested as much. The community of photosynthesis researchers, including myself, was taken with the idea of heterotrophs becoming photosynthetic. Not that we really wanted to convert the human race to autotrophy, but if some organism had figured out a way to enslave chloroplasts, then we should be researching those animals. Was it possible that slugs knew more than humans about the complexities of chloroplast exploitation?

Photosynthesis in plants and algae involves an elaborate exchange of proteins and signals between the chloroplasts and the cell nucleus for proper function. Hundreds of genes are involved and the system acutely senses the needs of the cell and the primary inputs of photosynthesis (light, water, carbon dioxide). Harnessing the chloroplast for the biochemical benefit of a cell is no small feat. Researchers have been looking for answers as to how the slugs might accomplish this. While there have been some instances of an algal gene present in the sea slugs, these are few and far between.

At this point, scientists had to reconsider the hypothesis that the stolen chloroplasts were conferring some kind of autotrophy to the slugs. A recent report in Proceedings of the Royal Society B addresses this assumption. Previous work had established that the presence of kleptoplasts offered an advantage to the slugs during starvation studies, but was it because they were photosynthetically active? Christa and co-authors were able to make more carefully-controlled weight measurements during starvation experiments of different kinds of kleptoplast-containing sea slugs. They compared weight loss of sea slugs starved (1) in the light, (2) in the dark, and (3) in the light in the presence of an inhibitor of photosynthesis. It turns out that there was no difference in the rate of weight loss among these conditions. This means that it doesn’t matter whether the chloroplasts are photosynthetically active or not. Consequently, the slugs are not gaining any autotrophic advantage, but are likely just holding onto them as a food reserve.

The sea slugs and the algal chloroplasts still have an odd relationship that begs for a deeper meaning. The overwhelming majority of the Earth’s biosphere depends on heterotrophs eating photosynthetic organisms, but I can’t think of another example of another heterotroph that saves organelles in specialized structures within its digestive tract (biochemically active or not). It seems like an over-engineered way to stash a midnight snack.

As an omnivore myself, I can’t be too condemning of these sea slugs for feasting on algae. However, given this new information, Elysia chlorotica is the herbivore equivalent of Buffalo Bill* saving parts of its victims as an ornate garment. This revelation definitely gives a creepy vibe to heterotrophy. Are the ‘kleptoplasts’ decorative? Maybe we are on the brink of photosynthetic fashion, remember these guys?

Why chloroplasts and why not some other organelle like mitochondria? Do the sea slugs use some elaborate form of communication based on chlorophyll fluorescence signals? Elysia chlorotica may not need the stolen chloroplasts to be photosynthetically active, but they still need something from them. Researchers have shown that the slugs cannot continue through development past a certain point without ingesting the algae and simultaneously stealing the chloroplasts. For their diet and development to be so tightly linked, there must be some intimate connection between these two species (or species and organelle) that scientists haven’t identified yet. There may be something special about chloroplasts,**but for Elysia chlorotica it isn’t photosynthesis.

This is one strange relationship that doesn’t fit nicely into our typical interspecies interaction categories. It’s not a symbiosis. I would call either organism a parasite. It’s more than an herbivore and its lunch. One thing that is safe to say about it, Elysia chlorotica and its stolen chloroplasts will keep researchers busy for quite some time into the future.


* I’m talking about this guy from the Silence of the Lambs and not this guy from American Wild West history.

**Of course there’s something special about chloroplasts, haven’t you been reading the blog? But I guess Elysia and I will have to agree to disagree on the importance of photosynthesis.

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