A New Finding on Evolution of Superhydrophobictiy from bacteria to land plants
Post: 2022-05-28 17:46  View:212

The group of Prof. Wilhelm Barthlott from University of Bonn has discovered the Evolution of Superhydrophobictiy from bacteria to land plants, and this has been published on Front. Plant Sci. in the May, 2022 entitled "Superhydrophobic Terrestrial Cyanobacteria and Land Plant Transition" . It is believed that this will provide a new aspect of the very early evolution and importance of bionic relevant structures since more than one billion years.

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【Abstract】Plants and other organisms have evolved structures and mechanisms for colonizing land since the Early Ordovician. In this context, their surfaces, the crucial physical interface with the environment, are mainly considered barriers against water loss. It is suggested that extreme water repellency (superhydrophobicity) was an additional key innovation for the transition of algae from water to land some 400 mya. Superhydrophobicity enhances gas exchange on land and excludes aquatic competitors in water films. In a different context, in material science and surface technology, superhydrophobicity has also become one of the most important bioinspired innovations enabling the avoidance of water films and contamination. Here, we present data for an extremely water-repellent cyanobacterial biofilm of the desiccation tolerant Hassallia byssoidea providing evidence for a much earlier prokaryotic Precambrian (ca. 1–2 bya) origin of superhydrophobicity and chemical heterogeneities associated with land transition. The multicellular cyanobacterium is functionally differentiated in a submerged basal hydrophilic absorbing portion like a “rhizoid” and an upright emersed superhydrophobic “phyllocauloid” filament for assimilation, nitrogen fixation, and splash dispersed diaspores. Additional data are provided for superhydrophobic surfaces in terrestrial green algae and in virtually all ancestral land plants (Bryophytes, ferns and allies, AmborellaNelumbo), slime molds, and fungi. Rethinking of superhydrophobicity as an essential first step for life in terrestrial environments is suggested.


Figure 1. Hassallia byssoidea (Cyanobacteria). (A) Water droplets on the superhydrophobic biofilm. (B) Single droplet with a high contact angle and fragmented Hassallia filaments attached for splash dispersal.


Figure 2. Hassallia byssoidea (Cyanobacteria). (A) Emersed superhydrophobic filaments showing false branching under a light microscope. (B) Single filament; the SEM image reveals the granular microstructure of the sheet. (C) Filament in cross section. (D) AFM image of the filament surface showing the system of semiglobular nanostructures (diameter 50–100 nm) arranged in a larger cluster of approximately 250–400 nm diameter.


Figure 3. Surface structure of Hassallia byssoidea (Cyanobacteria). (A) SEM image of an air dried H. byssoidea fragment sputtered with a thin gold layer. (B) Topography (Height signal) of an H. byssoidea fragment measured by AFM. In comparison with the SEM image, the AFM image shows exactly the same structures and dimensions. The surface shows clusters of semi globular nanostructures. (C) Phase signal of the same AFM measurement as shown in (B). Different colors represent different phase angles and indicate different attractive forces in these areas. This is a first hint for a chemical heterogeneity of the surface.


Figure 4. Superhydrophobic biological surfaces. (A,B) Stemonitis sp. (Mycetozoa); superhydrophobic reproductive structures of the slime mold. (A) Capillitium with water droplet. (B) Structured capillitium fibers and attached spinulose spore. (C) Desmococcus olivaceus (Chlorophyta); ornamented hydrophobic cells from a terrestrial biofilm. (D) The bonfire moss Funaria hygrometrica (Bryophyta) produces wax crystals only on its reproductive structures (peristome). Wax crystals are characteristic of the water repellency of all hydrophobic green plants.


Figure 5. Wax crystals causing superhydrophobicity in vascular plants. (A) The hydrophilic tropical fern ally Tmesipteris (Psilotales). Similar to Psilotum and some Selaginella species, only the guard cells of the stomata are superhydrophobic to guarantee gas exchange under humid conditions. (B) The same phenomenon can be observed in the ancestral angiosperm Amborella trichopoda (Amborellaceae). In modern angiosperms, a high diversity of wax patterns and epidermal cell shapes can be observed, such as (C) the “electromagnetic field line” wax crystal pattern surrounding each stoma of the lily-of-the-valley Convallaria majalis (Monocots) or (D) the water- and dirt-repelling surface of the lotus Nelumbo nucifera (Eudicots), entirely covered by wax crystals; the sunken stoma in the center of the image is hardly recognizable.

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