Cell wall physicochemical properties determine the thallus biomineralization pattern of Padina gymnospora (Phaeophyceae)

Abstract

Approximately half of the Padina (Dictyotales, Phaeophyceae) species mineralize aragonite needles over the adaxial thallus surface, where mineral bands are interspersed with nonmineralized regions along the thallus from the apical to basal end. However, this calcification pattern and the related algal properties are not well understood. Therefore, this work was performed to elucidate a potential role of cell walls in the inhibition/induction of mineralization in the brown alga Padina gymnospora. In a comparison of specific thallus regions, differences were identified in the cellulose distribution, microfibrils arrangement and thickness, distribution and abundance of phenolic substances, and physical differences among the surfaces of the thallus (deformation, adhesion, topography, and nano-rugosity). In vitro mineralization assays indicated that phenolic substances are strong modulators of calcium carbonate crystals growth. In addition, de novo mineralization assays over cell wall surfaces that were used as templates, even without cellular activity, indicated that the cell wall remains a key factor in the induction/inhibition of mineralization. Overall, the current findings indicate a strong correlation between the physico-chemical and structural properties of the cell wall and the alternation pattern of the mineralization bands over the thallus of P. gymnospora.

Chemical Defense against Herbivory in the Brown Marine Macroalga Padina gymnospora Could Be Attributed to a New Hydrocarbon Compound

“…Feeding assays have also revealed that the methanolic extract (ME) of P. gymonospora was the most consumed by L. variegatus and contained low amounts of phlorotannins (PH). Our data showed that a low PH content in the P. gymnospora ME extract (0.23% ± 0.03 DW) used in feeding assays and from samples of the natural populations (0.11% ± 0.01 to 0.38% ± 0.02 DW) agree with the literature for tropical brown macroalgae (<0.5%) [35,46,47]. That said, these amounts are very low to inhibit herbivory [47].…”

“…After collection, living macroalgal samples were stored in filtered seawater inside a dark isothermal chamber and transported to the laboratory. Thereafter, P. gymnospora individuals were maintained inside an 8 L aquarium with seawater enriched with Provasoli medium [63], under controlled conditions as already described elsewhere [35].…”

“…For the second bioassay-type (2), mineralized (MIN) pieces of P. gymnospora tissues were treated with HNO 3 5% (3 × 30 min) for obtaining demineralized tissue (DEM) according to the usual method [35]. Both tissues (MIN and DEM) were washed in filtered seawater, inserted in Petri dishes and inspected with a stereomicroscope (Olympus SZX7, Tokyo, Japan) [35]. Afterwards, the water excess in MIN and DEM tissues of P. gymnospora and respective control (Ulva sp.)…”

“…The normal force required to remove tissue by the limpet species Collisella tranquebarica, Tectura elegans and Tectura albicosta decreases as the calcification increases, but secondary metabolites or other attributes probably influence the algae consumption [34]. Chemical and microscopic analyses have evidenced that mineralized and non-mineralized regions of P. gymnospora possess different contents of phlorotannins and physical properties, such as deformation, adhesion, topography and nano-rugosity [35], which presupposes a possible distinct relationship of these parts of the thallus of Padina with consumers.…”