“Lignified” seaweeds: mechanical consequences of cell wall elaboration in a red alga

PATRICK T. MARTONE AND JOSÉ M. ESTEVEZ

USA

Congreso; Phycological Society of America; 2009

Phycological Society of America

The recent discovery of secondary cell walls and lignin in the intertidal red alga Calliarthron cheilosporioides has raised many questions about the adaptive significance and evolutionary history of these traits.  In land plants, lignified cell walls mechanically stabilize upright growth and facilitate hydraulic transport.  In Calliarthron, thick lignified cell walls strengthen tissues, helping fronds resist breaking under waves crashing on the shore.  In this study, we performed standard material testing techniques to further explore the mechanical properties of this unique algal tissue.  Engineering stress-strain analyses reveal that Calliarthron tissue is stronger and stiffer than other algal tissues, but not as stiff as terrestrial plant tissues.  Calliarthron tissues are also highly extensible – able to stretch more than twice their original length – unlike lignified terrestrial tissues which generally cannot stretch more than 1-3%.  The addition of secondary walls makes Calliarthron tissues stronger and tougher, absorbing more than ten-times the energy per volume as most woody or algal tissues before breaking.  This mechanical augmentation coincides with a doubling of cellulose content within the walls and may be unrelated to lignin content.  Surprisingly, as Calliarthron cell walls get thicker, they also get weaker per unit area, suggesting that either primary walls deteriorate over time or that secondary walls are made of weaker materials than primary walls.