Plants and Drought

There are essentially two ways societies can respond to drought.

One is societal adaption – stored water and food (or water and food trading), limits on growth during wet times, or mobility to move from dry places to wet places.

The other is to just ignore reality (or not understand the reality) and then get screwed when things dry up.

Mobility seems to have been the preferred option in pre-Anasazi Four Corners cultures, for example – moving to higher, wetter country when things got dry. The growing season was shorter, so it was sub-optimal, but the tradeoff worked. Populations tended to stay small, as well. The Anasazi opted for food trading, spreading their risk across a larger area. This worked , but failed when drought hit the whole region simultaneously. The population was too large for the mobility option to work – they already lived everywhere.

The post-Anasazi Puebloans followed by the Spanish and Mormon immigrants, followed by Arthur Powell Davis and the U.S. government, developed ever more sophistiticated water storage and diversion technologies. Today, we live (and farm) essentially everywhere and we have stored water and we have complex food trading networks.

All this is rambling prelude to a great plant metaphor in a new paper by a team of geneticists led by Patrick Achard at the John Innes Centre in Norwich, UK.

Obviously, mobility is not an option for individual plants. Over the long term, the range of a species will change in response to changing ecological conditions. You can see that in the mountains of northern New Mexico, for example, in the way the boundary between piñon-juniper and ponderosa woodlands has shifted in response to changing climate. But an individual plant is stuck where it is.

So do plants just suffer when the water supply is shut off, growing stunted and gnarly because they have no choice? Or do they have more sophisticated self-regulatory mechanisms to restrict their own growth in response to increased salinity or drought?

The answer is the latter, Achard and his colleagues found.

Arabidopsis, a small flowering plant used as a model organism by geneticists, was found to release a protein called DELLA in response to high salinity conditions. DELLA is a protein that acts as a sort of central governor on growth, keeping the plants small in the face of adverse conditions:

Perhaps growth restraint enables the redirection of resources to support mechanisms that promote survival of adversity. Alternatively, smaller plants may be less vulnerable to stress because they have less surface area. Although the nature of these underlying mechanisms remains unknown, it is nevertheless clear that DELLA restraint permits a flexible growth response to environmental variability, thus promoting survival.

In other words, “sustainability” is biologically built into Arabidopsis.