Land plants' ability to sprout upward through the air, unsupported except by their own woody tissues, has long been considered one of the characteristics separating them from aquatic plants, which rely on water to support them. Now lignin, one of the chemical underpinnings vital to the self-supporting nature of land plants – and thought unique to them – has been found in marine algae.From the press release:
"All land plants evolved from aquatic green algae and scientists have long believed that lignin evolved after plants took to land as a mechanical adaptation for stabilizing upright growth and transporting water from the root," says Martone.
"Because red and green algae likely diverged more than a billion years ago, the discovery of lignin in red algae suggests that the basic machinery for producing lignin may have existed long before algae moved to land."
Alternatively, algae and land plants may have evolved the identical compound independently, after they diverged.
"The pathways, enzymes and genes that go into making this stuff are pretty complicated, so to come up with all those separately would be really, really amazing," says Denny. "Anything is possible, but that would be one hell of a coincidence."
The team's finding provides a new perspective on the early evolution of lignified support tissues – such as wood – on land, since the seaweed tissues that are most stressed by waves crashing on shore appear to contain the most lignin, possibly contributing to mechanical support, says Martone.