Wednesday, January 24, 2018

Genetic engineering and chlorophyll

One of the interesting discussions in The Wizard and the Prophet was what the wizards are trying to get up to next in terms of trying to increase food production.  One idea goes to the fundamentals of photosynthesis.

The most important protein in photosynthesis is affectionately known as RuBisCO and makes up about half the protein in a leaf.  Photosynthesis seems to be pretty hard and so RuBisCO doesn't work as well as most other catalyst proteins.  It's supposed to grab the carbon in carbon dioxide from the air but frequently grabs plain oxygen instead.  I suppose it worked a lot better before the Great Oxygen Catastrophe.  Some plants have versions that are a bit more selective but they work more slowly.  Some are faster but they mess up which to grab more frequently.  Biologists hoped they could improve RuBisCO but it seems that evolution did about as good a job as could be done.

There are some plants, though, that do have method of photosynthesis that's often better than the run of the mill one.  They spend a little energy to concentrate carbon dioxide in cells where the RuBisCO is and so when RuBisCO grabs a random air molecule its more likely to be CO2 instead of O2, speeding up photosynthesis.  The extra energy means this isn't always a benefit, but it usually is.

Many plant species have developed this C4 carbon fixation process, as it's known, in nature.  Notably corn does it this way.  But researchers are hoping that you could develop a strain of rice that works that way too.  That is very ambitious.  Changing a single protein like RuBisCO is easy but this would involve growing whole new structures in the leaves to channel the CO2 and that doesn't involve just new proteins but new development paths.

That's very nifty but when I was reading the chapter my mind was going somewhere else.  The Great Oxygen Catastrophe was very good to use oxygen breathing creatures but it really sucked for plants.  Wouldn't the kind thing, for plants, be to let them live in a high CO2, low O2 environment?  And you could give the plants a high speed, low specificity version of RuBisCO that would work really well in that environment.

I'm mostly thinking of this in terms of growing plants in outer space but it could be applied in greenhouses too.  Enclosed environments also reduce the need for pesticides and herbicides though obviously the enclosures are expensive and have their own environmental impact.  And certainly there would be an energy cost in getting the oxygen the plants produce out of these buildings.

Oxygen free environments are dangerous.  But ones filled with CO2 less so.  Normally when you aren't getting any oxygen you feel perfectly fine as you get stupider and more lethargic until you die.  Here's a video from Smarter Every Day showing someone in a low pressure environment similar to a depressurized airplane and how he acts until given a breath mask.  When you hold your breath and feel like you're running out of air that sensation is caused by the buildup of CO2 rather than the lack of O2.  These always went together in our ancestral environment so there was no need for us to distinguish.  So at least in these greenhouses people with mask trouble could at least notice something wrong and leave.

I'm sure that some of you are thinking, "wait, how does this relate to all the CO2 we're pumping into the atmosphere?"   Well, plants will like the extra CO2 but the extra heat will make RuBisCO even less selective so for moderate warming it depends on the plant in question and for high global warming its generally bad.  Plus there are all those other very hard to predict changes in rainfall, etc, which would almost certainly be painful.  So lets not forget to work on better renewable energy too.

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