Using the atomic force microscope, we have investigated the nanoscale mechanical response of the attachment adhesive of the terrestrial alga Prasiola linearis (Prasiolales, Chlorophyta). We were able to locate and extend highly ordered mechanical structures directly from the natural adhesive matrix of the living plant. The in vivo mechanical response of the structured biopolymer often displayed the repetitive sawtooth force-extension characteristics of a material exhibiting high mechanical strength at the molecular level. Mechanical and histological evidence leads us to propose a mechanism for mechanical strength in our sample based on amyloid fibrils. These proteinaceous, pleated β-sheet complexes are usually associated with neurodegenerative diseases. However, we now conclude that the amyloid protein quaternary structures detected in our material should be considered as a possible generic mechanism for mechanical strength in natural adhesives.

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While biological systems are notorious for their complexity, nature sometimes displays mechanisms that are elegant in their simplicity. We have recently identified such a mechanism at work to enhance the mechanical properties of certain natural adhesives. The mechanism is simple because it utilizes a non-specific protein folding and subsequent aggregation process, now thought to be generic for any polypeptide under appropriate conditions. This non-specific folding forms proteinaceous crossed β-sheet amyloid fibrils, which are usually associated with neurodegenerative diseases. Here we show evidence for the beneficial mechanical characteristics of these fibrils discovered in natural adhesives. We suggest that amyloid protein quaternary structures should be considered as a possible generic mechanism for mechanical strength in a range of natural adhesives and other natural materials due to their many beneficial mechanical features and apparent ease of self-assembly.

SUMMARY The patterns of occurrence of photosynthetic pigments and fatty acids among seven available species (11 strains) of marine raphidophytes were determined and used as chemotaxonomic markers. All currently recognized genera of marine raphidophytes were included for analysis: that is, Chattonella, Fibrocapsa, Heterosigma, Olisthodiscus and Haramonas. The characteristic pigment composition was shown to be chlorophyll a, chlorophylls c1 and/or c2, fucoxanthin as the major carot‐enoid, β,β‐carotene and any or all of zeaxanthin, violaxanthin and an auroxanthin‐like pigment as the minor carotenoids. The carotenoid composition of all marine raphidophyte genera investigated was virtually the same, except in Fibrocapsa and Haramonas, which differed due to the occurrence of fucoxanthinol and 19′‐butanoyloxyfucoxanthin, respectively. These fucoxanthin derivatives, in addition to fucoxanthin, have potential chemotaxonomic use for differentiating the two species. In all 11 strains, 15 fatty acids (saturated, mono‐unsaturated and polyunsaturated) were determined. Significant taxonomic distinctions between genera were reflected by their fatty acid profiles. A rapid key for the differentiation of genera, in addition to morphological features, may be the absence of the 18:4 fatty acid in Olisthodiscus; presence of 18:5 in Heterosigma; the presence of fucoxanthinol in Fibrocapsa and presence of 19′‐butanoyloxyfucoxanthin in Haramonas.

The presence of ''proteinaceous b-sheet rich fibrillar structures'' and amyloidogenic material, has been alluded to extensively in the literature, in association with natural materials exhibiting superior mechanical strength per unit volume. Here we provide a clear experimental demonstration and explanation for why individual amyloid quaternary structures themselves have beneficial mechanical characteristics.