Science Lab Special: Resurrection Plant

Selaginella lepidophylla 

To protect crops from rising droughts, scientists are looking to the genes of a small group of plants that can survive months of drought then regreen within hours.

It was as a child growing up in South Africa in the 1970s that Jill Farrant first noticed several plants around her apparently coming back from the dead.

These plants, she later learned, can survive six months or more without water. Their leaves turn brown and brittle to the touch but, given water, they will regreen within hours. Within a day, they've returned to their former self and can continue to photosynthesise.

While such a Lazarus-like ability is common among mosses, ferns and other non-flowering plants, these "resurrection plants" belonged to the angiosperms, or flowering plants, the group that includes every blossoming tree and fruit-bearing, seed-carrying crop. But out of the 352,000 known species of flowering plants only 240 are resurrection plants. Scattered across this branch of the tree of life, they are often unrelated, each having independently evolved the ability to live without water. Primarily found growing on the rocky slopes or gravelly soils of South Africa, Australia and South America, the tactics used for this zombie-like trick are surprisingly similar – almost as if an ancestral toolkit can be retrieved from deep inside their DNA to deal with the problem of drought.

Farrant, now a professor of desiccation tolerance at the University of Cape Town, has been studying these unusual plants for over three decades. Along with several other researchers, she believes the drought-resistant powers found in their genes may be key to adapting agriculture to a future of climate change.

For plants to survive for months without water may seem like science-fiction. The vast majority of plants do indeed die when they experience water loss of 10-30%. But resurrection plants are able to tolerate over 95% water loss.

But it's not just the ability to survive drought that is important for these species, says Carlos Messina, a maize scientist at the University of Florida. It's also how resurrection plants regrow following drought.

Maize plants might also survive after a drought, he says, "but when they rehydrate, they don't go back to the same leaf architecture they had before, and the flow of CO2 and water is all messed up". Drought therefore compromises their growth long after the rains have returned.

But resurrection plants "seem to come back to the form that they had before the drought," he says. "If we can create maize that does that, that's fantastic, because we can regain that productivity."

Resurrection plants have evolved this essential skill by replacing disappearing water with sugars such as sucrose, turning the inside of their cells into a viscous, glass-like substance that slows down any chemical reactions. Known as vitrification, the same tactic is used by desiccation-tolerant animals such as tardigrades (also known as water bears) and the eggs of Artemia shrimp (sea monkeys).

As they turn to glass, these plants also deconstruct their photosynthetic machinery (such as chloroplasts), switching off their primary source of food as they turn to a state of dormancy. To hold their assembly of proteins and cell membranes together, they secrete a suite of protective proteins known as "chaperones", since they guide the cell through dangerous times. 

"How they preserve their tissue is quite a miracle," Farrant says.

- Author: Alex Riley, BBC