Small, Thick-Walled Cells Help Mangroves Thrive in Saltwater

Saltwater is typically lethal for plants. As sea levels rise, agricultural crops in coastal regions are especially susceptible to damage, so scientists are racing to find solutions to this problem.

One strategy is to look for ways to engineer plants to be more resilient against saltwater. To this end, Adam Roddy, a plant biologist at New York University, seeks to better understand what allows mangroves—the only plants that can live in saltwater—to thrive in that environment.

In a new study, Roddy and his colleagues discovered that compared to the cells of their inland relatives, mangrove cells are smaller and have thicker walls, and these traits likely help mangroves survive in saltwater.¹ These findings, published in Current Biology, may offer a path to improve salt tolerance in other plants.

“The work reveals that just a few simple cell traits are critical to tolerating the extreme conditions experienced by some of the most distinctive and resilient plants in the world,” said Roddy in a statement.

Guo-Feng Jiang, a plant biologist at Guanxi University and a coauthor of the study, added, “Nature offers simple solutions to complex challenges.”

Researchers typically group mangroves based on their physiological traits rather than genetic ties—there are about 80 species of mangroves spanning nearly 20 plant families. These trees have independently evolved characteristics that help them survive in saltwater, which can kill plants by severely dehydrating them. The accumulation of salt itself can also be toxic to plant tissues.

Many mangroves have developed special abilities to exclude or pump salt out of their systems, but Roddy and his team wondered if other traits, such as the size and shape of cells that make up the leaves’ outer layer, called the epidermal pavement cells, might contribute to mangroves’ ability to withstand salty waters as well.

To test this hypothesis, the researchers viewed the leaves of 34 mangrove species and 33 of their inland relatives under the microscope. They measured several properties, such as the size of the epidermal pavement cells and the stomata (openings on leaves that plants use for gas exchange) as well as the thickness of the cell walls. Then, they analyzed whether any of these characteristics were statistically distinct between mangroves and their relatives that live farther from the coast.

The team discovered that mangroves’ epidermal pavement cells were significantly smaller and had thicker cell walls, supporting the researchers’ hypothesis. In contrast, there was no difference in stomatal size, suggesting that mangrove leaves likely rely more on their cells’ mechanical strength than on gas exchange capacity to adapt. This solution contrasts with the more complex and specialized strategy that mangrove roots adopt: Many mangroves have aerial roots that shoot above the water to help them “breathe” in oxygen-poor saltwater environments.

Roddy said, “These results point to a promising strategy [for] engineering salt-tolerant plants: manipulating cell size and cell wall properties.”