Altering the process of photosynthesis

Photosynthesis, the process by which plants turn sunlight into food, is crucial to crop production and our food systems. What if we could increase the yield of food crops by improving photosynthesis? Stephen Long, Professor of Crop Sciences and Plant Biology at the University of Illinois at Urbana-Champaign, joined Andrea Vasquez in a Google Hangout to discuss the genetic altering of plants.

TRANSCRIPT

Photosynthesis, the process by which plants turn sunlight into food, is crucial to crop production and our food systems.

What if we could increase the yield of food crops by improving photosynthesis?

Steve Long, professor of crop sciences and plant biology at the University of Illinois at Urbana-Champaign, joined Andrea Vasquez is a Google Hangout to discuss the genetic altering of plants.

Steve Long, thanks very much for being with us.

Thank you.

So, for those of us whose memory from science class is a little hazy, can you explain -- what is the process of photosynthesis?

Well, arguably, the process of photosynthesis is the most important process on the planet.

It's the source of all of our food, many of our fibers, and, indirectly or directly, most of our fuels, as well.

So, it's the process by which plants convert solar energy -- sunlight energy -- into food.

Then of course it is the source of oxygen on the planet, as well.

Okay.

So, the plant is taking in the sunlight and using that to fuel its process to feed itself.

Yes.

I mean, technically, it's taking in sunlight, using that energy to split water, which is then used to reduce carbon dioxide to carbohydrate.

Wow.

So, it's taking in carbs just like we do, more or less?

It's building carbs.

Building carbs.

So, how are you proposing to alter this process of photosynthesis?

Okay, so, we've looked at the process in a lot of detail.

And when we look at what our crops are doing, they are properly only getting about 10% of the theoretical efficiency.

We think in theory that photosynthesis should be capable of capturing about 10% of the solar energy that it receives into food.

But in practice, even our best crops are more like 1% or 2%. So, there appears to be quite a lot of headroom there to improve it.

And we've been looking at where we might be able to improve it in theory for some years now.

And now we've begun to convert some of those things to practice.

So, what are some of the things that can be getting in the way of the plants really optimizing the sunlight they're getting?

Leaves in the field are going in and out of shade.

So, they may be going in the shade of other leaves as the sun crosses the sky or wind moves leaves around.

Leaves in full sunlight are receiving more light than they can use.

And, in fact, that excess light they have to get rid of.

Otherwise, it becomes damaging to the leaf, rather like sunburn.

Oh.

They induce a process called non-photochemical quenching.

And basically what this is, is it's a change in the leaf that allows the leaf to get rid of the excess light as heat.

The problem is when the leaf goes into the shade and now it needs all the light it can get.

it carries on converting quite a lot of that limiting light to heat, and it takes many minutes, even half an hour, for the leaf to recover.

So, we mimicked a crop canopy on the computer to work out, you know, 'Well, what does this cost to plant?'

And the answer the computer came up with was, depending on the plant type and the day, something between 8% and 40%. So, it's losing a lot of potential productivity.

The next step was to then look at, 'Well, are there ways we might be able to speed this up?

What are the genes involved in this relaxation process?'

Mm-hmm.

Again, these were identified by metabolic modeling, and then we've up-regulated those in tobacco.

We've now taken that to field trials, and the field trials, over the course of the growing season, showed us that by up-regulating these genes, we could get between a 14% and 20% increase in yield.

So, would the crops that are altered in this way -- would that be considered genetically modified?

Yes, it is.

What we've done is genetic modification.

But these are genes the plant already has.

So, to speed it up, we're adding more of those same genes.

Is there the possibility that there could be other side effects of increasing the number of those genes within the plant?

There's always that possibility.

We've looked at the major photosynthetic proteins.

And it hasn't affected the levels of any of those.

The plants that were grown in the greenhouse and in the field appear perfectly normal, just bigger.

So, in times of climate change, as this is really affecting sort of seasonal highs and lows and weather, can this kind of alteration be adapted to maximize our crop yields in times of fluctuating climate?

There are definitely some changes we can make in the photosynthetic process that would adapt the plant to be able to produce more under warmer conditions.

And, in fact, what one of the colleagues in my team is doing is the process of photorespiration.

Photorespiration uses some of the carbon which has been recently fixed and releases it.

It's basically because the enzyme which takes up carbon dioxide can mistakenly take up oxygen.

We think crops like rice, wheat, soybean may lose about 30% of their productivity through photorespiration.

Those mistakes increase with temperature.

So, what my colleague here is working on is a system where photorespiration would take less energy.

And so that would certainly adapt the crop to warmer temperatures.

Steve Long, thanks very much for being with us and explaining this research that you're doing.

Thank you for your interest.