Format: ORAL

Jeffrey G Duckett Silvia Pressel

Life Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK

The 1950s to the early 21st century was the Golden Age of biological electron microscopy: almost every university Biology department had both transmission (TEM) and scanning electron microscopes (SEM). The benefits to bryology have been enormous. In 1952, Manton and Clarke discovered the compound nature of the sperm flagella in Sphagnum and suggested it was the same as in algae, ferns and humans. Sectioning then revealed the sperm cytoskeleton, the microtubule spline and multilayered structure. Consequent on meticulous reconstructions, initiated by Carothers spermatozoid ultrastructure now provides a suite of features key to defining the different lineages of land plants and their algal ancestors. Manton was also the first to observe the ultrastructure of hornworts: though disappointed that their cells are basically the same as other bryophytes she illustrated their unique channelled thylakoids. Decades later immunogold labelling confirmed pyrenoids as crystalline arrays of RUBISCO. The same technique has then been used to unravel the unexpected complexities of bryophyte cell walls particularly those of conducting cells, whose unique features had been well documented by Hbant, and stomata. Though TEM has revealed that the structure and biogenesis of oil bodies are unique to liverworts, we have still to solve the mystery of their function. The biggest contributions of SEM have been to illustrating surface and spore ornamentation and the unrivalled beauty of peristomes. Cryo-SEM from the late 1990s added an extra dimension in enabling the observation of bryophytes in different stages of cytorrhytic dehydration and rehydration. In vascular plants intercellular spaces are gas-filled from the outset whereas in bryophytes they are liquid-filled. They remain in this condition in the gametophytes but become gas-filled following stomatal opening in mosses and liverworts. Except for hydroids, bryophyte cells are highly resistant to cavitation. Cryo-SEM also demonstrates that bryophytes have a mixture of hydrophilic and hydrophobic surfaces.