Abstract
Brown algae (Phaeophyceae) are multicellular photoautrophic organisms and the largest biomass producers in coastal regions. A variety of observations indicate that their extracellular matrix (ECM) is involved with screening of salts, development, cell fate selection, and defense responses. It is likely that these functionalities are related to its constitutive structures. The major components of the ECM of brown algae are β-glucans, alginates, and fucose-containing sulfated polysaccharides. The genus Ectocarpus comprises a wide range of species that have adapted to different environments, including isolates of Ectocarpus subulatus, a species highly resistant to low salinity. Previous studies on a freshwater strain of E. subulatus indicated that the sulfate remodeling of fucans is related to the external salt concentration. Here we show that the sulfate content of the surrounding medium is a key parameter influencing both the patterning of the alga and the occurrence of the BAM4 sulfated fucan epitope in walls of apical cells. These results indicate that sulfate uptake and incorporation in the sulfated fucans from apical cells is an essential parameter to sustain tip growth, and we discuss its influence on the architectural plasticity of Ectocarpus.
Highlights
The molecular mechanisms determining apical growth have been studied in details in fungi and land plants
We confirm that the branching activity of E. subulatus filaments depends on the salinity of seawater. It is the presence of sulfate in the culture medium, and not its overall ionic strength, which triggers growth of the primary filaments as well at the emergence of secondary filaments. We show that this developmental pattern correlates with the incorporation of sulfated fucans at the dome of apical cells, and we discuss the underlying mechanisms likely to affect the viscoelasticity of the extracellular matrix
These results indicate that the salinity of the culture medium impacts the pattern of SF emergence in E. subulatus (Supplementary Figure S4B), with a higher branching activity when the strain was cultivated at 100% NSW compared to 10% NSW
Summary
The molecular mechanisms determining apical growth have been studied in details in fungi and land plants (i.e., pollen tube, root hairs, moss protenemata). The tip is devoid of callose and the degree of pectin methyl-esterification from tip-to-flank correlates with an increase in the degree of cell wall rigidity and a decrease in viscoelasticity. This affects extensibility of the cell wall and growth of the pollen tube (Parre and Geitmann, 2005; Chebli et al, 2012).
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