This seeming contradiction is explained by the secondary need of drought-tolerant plants to protect their dehydrating cells from shrinking as they lose turgor pressure, the researchers said.
“While a stiff wall doesn’t maintain the cell turgor, it prevents the cells from shrinking as the turgor decreases and holds in water so that cells are still large and hydrated, even at turgor loss point,” Bartlett explained. “So the ideal combination for a plant is to have a high solute concentration to keep turgor pressure and a stiff cell wall to prevent it from losing too much water and shrinking as the leaf water pressure drops. But even drought-sensitive plants often have thick cell walls because the tough leaves are also good protection against herbivores and everyday wear and tear.”
Even though the team showed that turgor loss point and salty cell sap have exceptional power to predict a plant’s drought tolerance, some of the most famous and diverse desert plants – including cacti, yuccas and agaves – exhibit the opposite design, with many flexible-walled cells that hold dilute sap and would lose turgor rapidly, Sack said.
“These succulents are actually terrible at tolerating drought, and instead they avoid it,” he said. “Because much of their tissue is water storage cells, they can open their stomata minimally during the day or at night and survive with their stored water until it rains. Flexible cell walls help them release water to the rest of the plant.”
This new study showed that the saltiness of cells in plant leaves can explain where plants live and the kinds of plants that dominate ecosystems around the world. The team is working with collaborators at the Xishuangbanna Tropical Botanical Gardens in Yunnan, China, to develop a new method for rapidly measuring turgor loss point across a large number of species and make possible the critical assessment of drought tolerance for thousands of species for the first time.
“We’re excited to have such a powerful drought indicator that we can measure easily,” Bartlett said. “We can apply this across entire ecosystems or plant families to see how plants have adapted to their environment and to develop better strategies for their conservation in the face of climate change.”
Details of the Study:
Source: By Stuart Wolpert, UCLA.
