Discovery of secondary cell walls and lignin precursors in the joints of the articulated coralline Calliarthron

MARTONE, P., ESTEVEZ, J, RALPH, J., LU, F., RUEL, K., DENNY, M., AND C. SOMERVILLE

USA

Congreso; Phycological Society of America; 2007

Phycological Society of America

Joints (genicula) in the wave-swept articulated coralline Calliarthron (Rhodophyta, Corallinaceae) lend flexibility to calcified fronds, helping them resist forces imposed by breaking waves.  Genicular tissue is stronger and stiffer than other algal tissues.  Previous studies demonstrated that tissue strength results from thickened genicular cell walls, while tissue stiffness is likely a consequence of distinct material composition.  Stiff, thickened cell walls are characteristic of the vessel and fiber elements of terrestrial plant xylem, which produce secondary cell walls fortified with lignin.  Transmission electron micrographs revealed the presence of secondary cell walls in genicular cells that develop after cell elongation ceases.  Mass spectrum analyses demonstrated that Calliarthron genicula contain three distinct monolignols, which polymerize to form P-, G-, and S-lignins in terrestrial plants.  Secondary cell walls and monolignols are known only from terrestrial plant tissues and have never been described in marine algae.  Lignin histochemistry and lignin-specific antibodies corroborated mass spectra results, suggesting that G-monolignols are concentrated in secondary cell walls, while P-, G- and S-monolignols may be present at lower levels in primary walls.  Data presented here suggest the need to re-examine the evolutionary history of lignified cell walls.  Developmental pathways for both secondary cell walls and monolignols may have evolved in a common ancestor of red and green algae more than 1 billion years ago or may have evolved convergently in coralline algae and land plants as adaptations to mechanical stress.