Influence of hydrodynamic environment on composition and macromolecular organization of structural polysaccharides inEgregia menziesiicell walls

摘要

To test whether secondary and tertiary structures of marine-algal structural polysaccharides may be altered during adaptive responses to hydrodynamic stresses, juvenileEgregia menziesii(Turn.) Aresch. sporophytes were cultured under three different regimes: (i) low-energy (LE) specimens were subjected to water motion produced by standard bubbling and circulation of tank water; (ii) high-energy (HE) specimens received additional movement in pumped streams of water; and (iii) stretched (STR) specimens were grown under low-energy conditions but also were subjected to constant, longitudinal tension (0.7 N). After 6–10 weeks growth, cell-wall structural polysaccharides from specimen blades were isolated by solubilizing less-ordered matrix polysaccharides. Neutral-sugar and uronic acid contents of these isolates were measured, and samples were analyzed by x-ray diffraction and by Raman and13C-nuclear magnetic resonance (NMR) spectroscopy. On average, structural polysaccharides formed about 7.2 of dry-weight biomass. The portion of isolated mass accountable to neutral sugars ranged from an average of 85 for STR sporophytes to 94 for both LE and HE specimens. For all specimens, glucose composed an average of 99 of this fraction. Uronic acids could not be detected in isolates from any treatment group. Cellulose dominance in each isolate was indicated clearly in x-ray diffraction patterns and in Raman and13C-NMR spectra. These data further demonstrated that both the cellulose I allomorph and the disordered form of the polymer were present in each isolate and that the STR isolate contained small quantities of the cellulose II allomorph. In general, the LE and HE samples had very similar crystallinity; lateral order was slightly more developed in LE samples. However, the STR treatment produced cellulose with lowest crystallinity and least lateral order. Results suggest that mechanical stress modified cellulose crystallinity in these kelps by altering levels of disordered cellulose and lateral dimensions of cellulose crystallites and, in one instance, changed the crystallinity qualitatively. Physical disturbances to cell plasma membranes may have instigated these trends. In the STR specimens in particular, such disturbances might have been supplemented by fundamental changes to kelp physiology, affecting both substantial decreases in crystallinity and production of the cellulose II allomorph. Changes in the nature of the cellulose cannot, however, account for changes in the elastic modul