Cellulose-rich secondary walls in wave-swept red macroalgae fortify flexible tissues

Area of Science:

• Evolutionary Biology
• Plant Cell Biology
• Biomechanics

Background:

• Cellulose-enriched secondary cell walls are characteristic of woody vascular plants, aiding terrestrial support.
• Coralline red algae, non-vascular marine organisms, also exhibit cellulosic secondary walls.
• The function and evolution of these walls in algae, particularly against wave forces, remain under investigation.

Purpose of the Study:

• To investigate the presence and convergent evolution of cellulosic secondary walls in coralline red algae.
• To compare the structure and biomechanical properties of these secondary walls with those in land plants.
• To understand the role of secondary walls in enabling coralline algae to withstand wave-induced stress.

Main Methods:

• Field emission scanning electron microscopy (FESEM) to visualize cell wall structure.
• Use of His-tagged recombinant carbohydrate-binding module to differentiate cellulose types.
• Mechanical testing of coralline algal tissues to assess strength, toughness, and extensibility.

Main Results:

• Coralline red algae possess cellulosic secondary walls with approximately 22% cellulose content, significantly increasing cell wall thickness.
• Cellulose bundles in algal secondary walls lack a predominant orientation, differing from some land plants.
• Secondary walls enhance tissue strength and toughness while maintaining remarkable extensibility, allowing tissues to double in length before breaking.

Conclusions:

• Cellulosic secondary walls evolved convergently in coralline red algae, reinforcing tissues against wave-induced breakage.
• Despite similarities, algal secondary walls exhibit differences in cellulose abundance, microfibril orientation, and wall structure compared to vascular plants.
• The development of these strong-yet-flexible secondary walls is crucial for coralline algae survival in wave-battered coastal environments.