There are two basic starting points for plants to take up carbon dioxide from the air to start photosynthesis. The dominant way among plants nowadays is called C3 because the first product of the biochemistry is a 3-carbon sugar phosphate. The other way, C4, makes a 4-carbon acid. That acid is moved to cells in the interior, where a set of biochemical reactions take the acid apart. This frees CO2, where it can build up to a higher level. The CO2 then gets passed to the rest of the C3 path, which operates more efficiently at the higher CO2 level.
C4 plants such as corn use water, nitrogen, and light more efficiently than do C3 plants. (They don’t do as well in the cold, however, with a few exceptions.) For decades plant researchers have been working at altering C3 plants to make them C4. That entails moving structures and enzymes around in the leaf. Very tricky, except that species of plants have evolved that switch at least 60 times!
Now, the December 5th issue of the journal Nature has an exciting report. Joseph Swift and 10 colleagues in the US and UK report find that a switch in a single gene in C3 plants changes where the photosynthetic enzymes are located. It has the pattern of a C4 plant. Evolution is amazing, and so it our growing ability to trace it.
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
Source: Nature 5 December, pp. 143 ff.
