The human version of nocturnal shutdowns has absolutely nothing on plants. When we sleep, our bodies continue doing a lot of the functions they do when we're awake. But when darkness sets in over the plant kingdom, at least the very large portion that derives its energy from sunlight, it's like an off-switch: no germination, flowering, growing, food production, or even aging. Nothing, and no arguments.
Once the sun comes back out, signals within the plant get the whole process started again, hopefully persisting for long enough to keep that plant alive and, crucially, completing its reproductive tasks.
This on/off cycle traces back to molecules called phytochromes, which detect light and send along the various chemical signals that tell plants to wake up. That the manipulation of this molecule is of great interest to botanists should come as no surprise, and the phytochrome protein was first purified some three decades ago.
Now, the same researcher behind that initial work, the University of Wisconsin's Richard Vierstra, has fully described the crystalline structure of the actual photosensing element. The new paper is published in the June 30 edition of the Proceedings of the National Academy of Sciences.
You can already see the potential for agriculture and, in particular, the study highlights the potential for increasing the density of farm plots.
"It's the molecule that tells plants when to flower," says Vierstra in a UW statement. "Plants use the molecule to sense where they are in the canopy; they use the phytochromes for color vision—to sense whether they are above, next to or under other plants."
When plants sense that they're under a canopy, shaded by the leaves of neighboring plants, they stop flowering, instead expending energy on new stalks and stems rather than fruits and seeds.
For phytochromes, it's not simply a matter of telling the difference between light and no light; the task is differentiating between the red light of full sun and the far-red bandwidths of the "leftover" light one finds underneath a canopy, while communicating to the rest of the plant whether or not it should be in either an active or passive mode.
The red light-detecting portion of the phytochrome was described in a 2010 paper from researchers at Brookhaven labs, but we now have the full picture, including far-red, which means being able to trace how the structure changes its signals in response to changes in light conditions.
"Photoconversion between the active and inactive states of phytochromes is arguably the most important twitch on this planet, as it tells plants to become photosynthetic and consequently make the food we eat and the oxygen we breathe," Vierstra said. "By mutating the phytochromes, we created plants that think they're in full sun, even when they're not."
The potential goes beyond crop density and into the realm of growing seasons. Another recent study examined the role of phytochromes in the flowering of wheat plants, finding that the structure has potential as "an additional entry point to modify wheat flowering and to accelerate the development of wheat varieties better adapted to new and changing environments."
And of course there's the underground corn plantations of the near-future, but that has a bit more to do with relative air concentrations of carbon dioxide. Still, the future of agriculture is becoming a very strange and bafflingly productive place, even without the drone farmers.