Scientists Aim To Improve Photosynthesis

vasanth writes "Two new initiatives at the University of Cambridge aim to address the growing demand on the Earth's resources for food and fuel by improving the process of photosynthesis. Four transatlantic research teams – two of which include academics from Cambridge's Department of Plant Sciences – will explore ways to overcome limitations in photosynthesis which could then lead to ways of significantly increasing the yield of important crops for food production or sustainable bioenergy. Despite the fact that photosynthesis is the basis of energy capture from the sun in plants, algae and other organisms, it has some fundamental limitations. There are trade-offs in nature which mean that photosynthesis is not as efficient as it could be – for many important crops such as wheat, barley, potatoes and sugar beet, the theoretical maximum is only 5%, depending on how it is measured. There is scope to improve it for processes useful to us, for example increasing the amount of food crop or energy biomass a plant can produce from the same amount of sunlight."

Comments

New Pigments!

[NFN_NLN]

They should work on a pigment that absorbs useful light in the yellow-green band of the spectrum. Some of the inefficiency of photosynthesis comes from the fact that it only absorbs visible light in two narrow bands of the spectrum.

Re:New Pigments!

[Anonymous Coward]

Disclaimer: My group is collaborating with one of the guys from the FA.

It is not so simple as you think. But I see the same type of misunderstanding in many people in the field (especially the kind that is good at getting grants and bad at doing science, there are many of them...).

Leaves are pretty well designed (I mean that not in the intelligent way), and being green is one of them. The pigments that absorb the majority of the light (chlorophylls) have absorption peaks in the blue and red, and the absorption for green is indeed quite low. However, if you look at the total absorption spectrum of a whole leaf you will see the dip in the green is only 10-20% for most leaves. It is even less if you consider the whole canopy. Nevertheless our eyes pick up this small difference so that leaves look green.

The problem with having black leaves (i.e. absorbing all light, some seeweeds do that) is that you get too much energy in the upper most layer of your leaf (a leaf is several hundred micrometers thick), giving you plenty of energy, but other things (enzyme capacity, CO2 levels, etc) become limiting. Thus, this absorbed energy is wasted, or even starts to damage things (lots of electrons flying around is not always a good thing).

Thus, the green "window" allows part of the light to travel into deeper layers of the leaf, which is also often more porous, resulting in more scattering (longer pathlength, thus increasing chance of absorption) of the light. In this way, the green light drives much of the photosynthesis in the lower part of a leaf. Spreading out the light energy over several 100 micrometers makes the leaves much more efficient, but this would not work if the pigments absorbed green light equally well.

That is not to say that nothing in the pigments can be optimized. Crops are often large stands of genetically identical organisms. We want to optimize the growth of the whole group. This is different from what might have been selected for by evolution (in a mixed canopy, a good survival strategy is to overshadow your competitors, i.e. become tall and allocate more pigments to the top). Big increases in grain yields were realized by breeding for shorter plants (little stem, mostly leaves). This would not work in nature because if one genotype starts to cheat (become bigger), the others will be starved of light. A similar gain might be possible by optimizing pigment allocation to allow a better distribution of the light (most plants still put too much in the top).

Re:New Pigments!

[Anonymous Coward]

The photosystem is pretty good at capturing photons! It's after that initial step that the tough bits of chemistry come in.

First up, whenever you capture energy, you will heat up, hence plants have to manage that, and they do that with radiating out the excess energy captured (it is a lot!). There are a bunch of publications on reducing chlorophyll quantity in algae, which led to an improvement in photosynthetic efficiency and a drop in the excess energy radiated out (I think it was in the red region).

After that, the captured energy is used to split water, generating rather damaging radicals/ions (I forget which one) in the process - one changes your pH, the other causes redox stress. Either way, both are bad. The photo-system can't take a lot of that either, hence there are a ridiculous number of processes to effectively convert the split water back to water! (Refer Dynamics of Photosynthesis - Annual Review by Eberhard et al... Hah, luckily remember one paper from my thesis work!)

It doesn't get much better by the time the Hydrogen ion travels across the membranes, creating the much wanted NADPH, and some ATPs in the process. Now, depending on the chemicals wanted by the cells, the ratio of NADPH/ATP need to be tweaked, losing some energy there too.

And then come in the enzymes which start to use this simple energy to climb up the rather hard entropy ladder to create ordered polymers from the ridiculously simple water and carbon dioxide. Not the easiest of tasks in my opinion... and my un-calculated and un-verified bias is that the free energy change needed to accomplish this must be pretty high. Thermodynamics didn't like me very much... Nonetheless, the often abused number of 5% or 10% or 1% (yes, you can find all of these numbers in literature) photosynthetic efficiency means little as people always compare sunlight received to the calorific value of the biomass, completely missing out all the effort it took to build up that complexity against the rather real forces of disorder. Burning it is a complete waste!

Which is why my money (when I will have money!) will be on chemically simpler fuels - higher efficiencies are possible. But unfortunately, none of our alternatives to biomass have the self-replicating chemistry awesomeness of Biology. Hence it's not very cheap to manufacture and maintain. Plants kind of grow... You don't have to do much. Except, of course, if you're a corn ethanol producer, where you're doing too much! ;)

So basically, the problems are not at the pigments... The quantum yield of photon capture is near 100%. The complexity is after that. It's a mix of matching rates of various processes along the way, and losing energy working against entropy. And we're not even *close* to figuring out this system. Long shot.

Sayash

Re:New Pigments!

[uniquename72]

You're being deliberately obtuse, but I'll explain anyway. Your argument is identical to people in the Middle Ages who refused to look through a telescope because it showed them things that God didn't want them to see. Those people also argued against eye-glasses -- after all, humans were created by God, and man couldn't (and shouldn't) improve upon God's creation.

The only difference is that you're substituting God with evolution.

There no reason to think that photosynthesis can't be improved, just like there's no reason to think that human anatomy can be improved. Evolution chose to leave humans with all sorts of imperfections. How many people need glasses (from a very young age), need to have their wisdom teeth or appendix removed, or rely on medication for various chronic -- but not life-threatening -- conditions?

OP mentioned a few things that we've created or mastered to improve our environment, but I think we've gone beyond that and actually improved ourselves biologically in a number of ways. Certainly that's true from an evolutionary standpoint (I can have many, many more children than my ancestors of only a hundred years ago, even though I choose not to).

What could possibly go wrong?

[eln]

This is a horrible, horrible idea. If you make photosynthesis more efficient, plants won't have to spend all their time generating food. A few hours a day, and they'll have all they need. Soon enough, plants will have more free time than they know what to do with. They'll wake up in the morning, spend a couple of hours making sugar, and spend the rest of the day sitting in coffee shops and arguing about the finer points of whatever passes for philosophy among the members of the plant kingdom.

Eventually, various collectives will form based on commonalities of ideas and who is rooted near what coffee shop. Sure, most of these collectives will concern themselves primarily with taking drugs and producing regrettable artworks, but eventually some of them will start to ponder their lot in life at the constant mercy of mankind. This will lead to the writing of lengthy treatises on the Rights of Plants and how they are constantly being trod upon (often quite literally) by man. After that, it's only a matter of time before they rise up under the banner of the Glorious Plant Revolution and kill us all.

Honestly, the last thing we can afford to do is make plants more efficient.

how about using the plants we have efficiently?

[nido]

Feeding grain to animals in concentrated animal feeding operations is stupid. Farms should be run by farmers, NOT "absentee landlords" (like my dad & his two siblings, who inherited some ~200 acres from their parents. Grandma grew up on her farm, while Grandpa's parents owned their farm but never worked it). From the second link:

And yet it is not impossible to imagine a far different food and farming system than the one we have today, beginning with a long-term commitment to pasture-based farming. Many have been advocating for some time for an ambitious transformation in U.S. agriculture: away from soil-eroding feed grains toward deep-rooted perennial pastures; converting large-areas of the High Plains back to grass and grazing operations; diversifying the corn and soybean dominated Midwest. In fact, thousands of family farmers are managing appropriately-scaled, grass-fed meat, dairy and egg farms without raising animals in vile and sordid conditions. A smart pasture operation (SPO)—to pick up on a new phrase—is one of the easiest entry points for beginning farmers in current U.S. agriculture. Start-up costs are relatively modest and markets for healthfully raised animal products are underserved and growing rapidly. These pasture-based rotational grazing systems can be extremely resource efficient, and often have the advantage of not needing the energy- and capital-intensive inputs such as heating, ventilation, and cooling systems, housing construction, imported industrial feeds, and mechanized manure management systems. They rely on sound animal husbandry techniques and integrate farm animals into a healthy landscape, using manure as a source of soil fertility. But this will require whole new generations of farmers willing to join the ranks of this noble profession, and legions of consumers and an financial and production infrastructure to support them.

Many of humanity's health problems stem from the inappropriate use of grain crops. Grain-finished cattle have a fraction of the beta carotene and vitamin A as grass-finished beef.

Feeding cattle directly on land currently used to grow soybeans & corn would be a lot more productive. But I don't think all the "farmers" (who really just hire tenants to plant crops) would approve.

Re:how about using the plants we have efficiently?

[SuricouRaven]

Sorry, but there is no way that pasture systems can be as efficient as ithe modern intensive farming system. That's exactly why we use the intensive system - it can produce so much more food from a given area, and for such a low cost, that it's almost impossible for anything else to compete in the market. The only possible way is to target the premium market of customers who will pay extra, such as by labeling the food as organic.

Re:how about using the plants we have efficiently?

[Lorien_the_first_one]

You're right. This isn't about quantity, it's about sustainable quality.

Re:how about using the plants we have efficiently?

[dkleinsc]

Sorry, but there is no way that pasture systems can be as efficient as the modern intensive farming system.

Sure it can, once you factor in all the costs, rather than the costs that the farmer pays directly. The kinds of costs I'm thinking of here:
- Environmental damage caused by fertilizer runoff
- The wars to secure the oil to create the chemical fertilizers that the farmers depend on
- The depletion of the arable land, so that in a couple more generations the land that's currently used for growing feed corn will be able to grow nothing at all, ending up with another Dust Bowl
- The CO2 emissions from the more intensive farming methods, which are higher for modern agriculture than the entire US transportation system

I could go on. The point is that modern farming appears cheaper because it's effectively convinced everyone else to pay much of the bill in the form of taxes or inflation or deferred costs.

One word of warning:

[justsomecomputerguy]

Kudzu!

Re:I have this vague recollection

[angiasaa]

A Déjà vu is usually a glitch in the Matrix. It happens when they change something....

Re:We already have the tech

[marjancek]

Don't call it birth control; it's better called 'family planning'.

A family is less poor not only if wisely chooses its number of children, but also the moment in time when they have it.

In countries with high birth rates (children per woman) couples get their first child so early that usually they don't finish school, before getting any working experience that would grant them a safe monthly income, nor any time at those job positions to save some money while they could have.

That's why I prefer the term Family Planning, it makes more sense.