Cell wall components affect mechanical properties: studies with thistle flowers

Pollen presentation of Cirsium horridulum depends partially on the thigmonastic contraction of staminal filaments. Although the elastic cuticle is a major component in filament elasticity, it is not clear how the cell wall copes with the shape change. Based on mechanical studies, FT-IR spectroscopy and biochemical analyses we investigated the relationship between cell wall composition and elastic properties using thistle floral tissues as a model. EDTA-extractable pectin correlated with the increased elasticity of the filament and the basal style, suggesting that pectin plays a major role in the elastic behavior of soft tissues. In contrast, covalently linked pectin contributes to the stiffness of the upper style and corolla. Mechanical tests contrasting the soft basal and rigid apical parts of the style after incubation in solutions designed to alter the pectin network confirmed these results. The rigid corolla contained more cellulose than the softer style and filaments. The cellulose-associated xyloglucan of the style and filament cell walls increase the flexibility of cell walls.