Tomasz Góral

Stomatal differentiation and abnormal stomata in hornworts

Abstract This light and electron microscope study reveals considerable uniformity in hornwort stomata morphology and density in contrast to common spatial and developmental abnormalities in tracheophytes and mosses. Stomata arise from a median longitudinal division of sporophyte epidermal cells morphologically indistinguishable from their neighbours apart from the retention of a single chloroplast whilst those in the other epidermal cells fragment. Chloroplast division and side-by-side repositioning of the two daughter chloroplasts determines the division plane in the stomatal mother cell. The nascent guard cells contain giant, starch-filled chloroplasts which subsequently divide and, post aperture opening, regain their spherical shape. Accumulation of wall material over the guard cells and of wax rodlets lining the pores follows opening. While the majority of stomata are bilaterally symmetrical those lining the dehiscence furrows display dextral and sinistral asymmetry due to differential expansion of the adjacent epidermal cells. The ubiquity of open stomata suggests that these never close with the maturational wall changes rendering movement extremely unlikely. These structural limitations, a liquid-filled stage in the ontogeny of the intercellular spaces, and spores already at the tetrad stage when stomata open, suggest that their primary role is facilitating sporophyte desiccation leading to dehiscence and spore dispersal rather than gaseous exchange. Stomata ontogeny and very low densities, like those in Devonian fossils, suggest either ancient origins at a time when atmospheric carbon dioxide levels were much greater than today or a function other than gaseous exchange regulation. We found no evidence for stomatal homology between hornworts, mosses and tracheophytes.

A New Chytridiomycete Fungus Intermixed with Crustacean Resting Eggs in a 407-Million-Year-Old Continental Freshwater Environment

The 407-million-year-old Rhynie Chert (Scotland) contains the most intact fossilised remains of an early land-based ecosystem including plants, arthropods, fungi and other microorganisms. Although most studies have focused on the terrestrial component, fossilised freshwater environments provide critical insights into fungal-algal interactions and the earliest continental branchiopod crustaceans. Here we report interactions between an enigmatic organism and an exquisitely preserved fungus. The fungal reproductive structures are intermixed with exceptionally well-preserved globular spiny structures interpreted as branchiopod resting eggs. Confocal laser scanning microscopy enabled us to reconstruct the fungus and its possible mode of nutrition, the affinity of the resting eggs, and their spatial associations. The new fungus (Cultoraquaticus trewini gen. et sp. nov) is attributed to Chytridiomycota based on its size, consistent formation of papillae, and the presence of an internal rhizoidal system. It is the most pristine fossil Chytridiomycota known, especially in terms of rhizoidal development and closely resembles living species in the Rhizophydiales. The spiny resting eggs are attributed to the crustacean Lepidocaris rhyniensis, dating branchiopod adaptation to life in ephemeral pools to the Early Devonian. The new fungal interaction suggests that, as in modern freshwater environments, chytrids were important to the mobilisation of nutrients in early aquatic foodwebs.

New insights into the evolutionary history of Fungi from a 407 Ma Blastocladiomycota fossil showing a complex hyphal thallus

Zoosporic fungi are key saprotrophs and parasites of plants, animals and other fungi, playing important roles in ecosystems. They comprise at least three phyla, of which two, Chytridiomycota and Blastocladiomycota, developed a range of thallus morphologies including branching hyphae. Here we describe Retesporangicus lyonii gen. et sp. nov., an exceptionally well preserved fossil, which is the earliest known to produce multiple sporangia on an expanded hyphal network. To better characterize the fungus we develop a new method to render surfaces from image stacks generated by confocal laser scanning microscopy. Here, the method helps to reveal thallus structure. Comparisons with cultures of living species and character state reconstructions analysed against recent molecular phylogenies of 24 modern zoosporic fungi indicate an affinity with Blastocladiomycota. We argue that in zoosporic fungi, kinds of filaments such as hyphae, rhizoids and rhizomycelium are developmentally similar structures adapted for varied functions including nutrient absorption and anchorage. The fossil is the earliest known type to develop hyphae which likely served as a saprotrophic adaptation to patchy resource availability. Evidence from the Rhynie chert provides our earliest insights into the biology of fungi and their roles in the environment. It demonstrates that zoosporic fungi were already diverse in 407 million-year-old terrestrial ecosystems. This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.

Relationships between Genetic Diversity and Fusarium Toxin Profiles of Winter Wheat Cultivars.

Fusarium head blight is one of the most important and most common diseases of winter wheat. In order to better understanding this disease and to assess the correlations between different factors, 30 cultivars of this cereal were evaluated in a two-year period. Fusarium head blight resistance was evaluated and the concentration of trichothecene mycotoxins was analysed. Grain samples originated from plants inoculated with Fusarium culmorum and naturally infected with Fusarium species. The genetic distance between the tested cultivars was determined and data were analysed using multivariate data analysis methods. Genetic dissimilarity of wheat cultivars ranged between 0.06 and 0.78. They were grouped into three distinct groups after cluster analysis of genetic distance. Wheat cultivars differed in resistance to spike and kernel infection and in resistance to spread of Fusarium within a spike (type II). Only B trichothecenes (deoxynivalenol, 3-acetyldeoxynivalenol and nivalenol) produced by F. culmorum in grain samples from inoculated plots were present. In control samples trichothecenes of groups A (H-2 toxin, T-2 toxin, T-2 tetraol, T-2 triol, scirpentriol, diacetoxyscirpenol) and B were detected. On the basis of Fusarium head blight assessment and analysis of trichothecene concentration in the grain relationships between morphological characters, Fusarium head blight resistance and mycotoxins in grain of wheat cultivars were examined. The results were used to create of matrices of distance between cultivars – for trichothecene concentration in inoculated and naturally infected grain as well as for FHB resistance Correlations between genetic distance versus resistance/mycotoxin profiles were calculated using the Mantel test. A highly significant correlation between genetic distance and mycotoxin distance was found for the samples inoculated with Fusarium culmorum. Significant but weak relationships were found between genetic distance matrix and FHB resistance or trichothecene concentration in naturally infected grain matrices.

Identification of Kernel Proteins Associated with the Resistance to Fusarium Head Blight in Winter Wheat (Triticum aestivum L.)

Numerous potential components involved in the resistance to Fusarium head blight (FHB) in cereals have been indicated, however, our knowledge regarding this process is still limited and further work is required. Two winter wheat (Triticum aestivum L.) lines differing in their levels of resistance to FHB were analyzed to identify the most crucial proteins associated with resistance in this species. The presented work involved analysis of protein abundance in the kernel bulks of more resistant and more susceptible wheat lines using two-dimensional gel electrophoresis and mass spectrometry identification of proteins, which were differentially accumulated between the analyzed lines, after inoculation with F. culmorum under field conditions. All the obtained two-dimensional patterns were demonstrated to be well-resolved protein maps of kernel proteomes. Although, 11 proteins were shown to have significantly different abundance between these two groups of plants, only two are likely to be crucial and have a potential role in resistance to FHB. Monomeric alpha-amylase and dimeric alpha-amylase inhibitors, both highly accumulated in the more resistant line, after inoculation and in the control conditions. Fusarium pathogens can use hydrolytic enzymes, including amylases to colonize kernels and acquire nitrogen and carbon from the endosperm and we suggest that the inhibition of pathogen amylase activity could be one of the most crucial mechanisms to prevent infection progress in the analyzed wheat line with a higher resistance. Alpha-amylase activity assays confirmed this suggestion as it revealed the highest level of enzyme activity, after F. culmorum infection, in the line more susceptible to FHB.

Alterations in Kernel Proteome after Infection with Fusarium culmorum in Two Triticale Cultivars with Contrasting Resistance to Fusarium Head Blight

Highlight: The level of pathogen alpha-amylase and plant beta-amylase activities could be components of plant-pathogen interaction associated with the resistance of triticale to Fusarium head blight. Triticale was used here as a model to recognize new components of molecular mechanism of resistance to Fusarium head blight (FHB) in cereals. Fusarium-damaged kernels (FDK) of two lines distinct in levels of resistance to FHB were applied into a proteome profiling using two-dimensional gel electrophoresis (2-DE) to create protein maps and mass spectrometry (MS) to identify the proteins differentially accumulated between the analyzed lines. This proteomic research was supported by a measurement of alpha- and beta-amylase activities, mycotoxin content, and fungal biomass in the analyzed kernels. The 2-DE analysis indicated a total of 23 spots with clear differences in a protein content between the more resistant and more susceptible triticale lines after infection with Fusarium culmorum. A majority of the proteins were involved in a cell carbohydrate metabolism, stressing the importance of this protein group in a plant response to Fusarium infection. The increased accumulation levels of different isoforms of plant beta-amylase were observed for a more susceptible triticale line after inoculation but these were not supported by a total level of beta-amylase activity, showing the highest value in the control conditions. The more resistant line was characterized by a higher abundance of alpha-amylase inhibitor CM2 subunit and simultaneously a lower activity of alpha-amylase after inoculation. We suggest that the level of pathogen alpha-amylase and plant beta-amylase activities could be components of plant-pathogen interaction associated with the resistance of triticale to FHB.

Simultaneous selection for yield-related traits and susceptibility to Fusarium head blight in spring wheat RIL population

Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium, is a fungal disease that occurs in wheat and can cause significant yield and grain quality losses. The present paper examines variation in the resistance of spring wheat lines derived from a cross between Zebra and Saar cultivars. Experiments covering 198 lines and parental cultivars were conducted in three years, in which inoculation with Fusarium culmorum was applied. Resistance levels were estimated by scoring disease symptoms on kernels. In spite of a similar reaction of parents to F. culmorum infection, significant differentiation between lines was found in all the analyzed traits. Seven molecular markers selected as linked to FHB resistance QTLs gave polymorphic products for Zebra and Saar: Xgwm566, Xgwm46, Xgwm389, Xgwm533, Xgwm156, Xwmc238, and Xgwm341. Markers Xgwm389 and Xgwm533 were associated with the rate of Fusarium-damaged kernels (FDK) as well as with kernel weight per spike and thousand kernel weight in control plants. Zebra allele of marker Xwmc238 increased kernel weight per spike and thousand kernel weight both in control and infected plants, whereas Zebra allele of marker Xgwm566 reduced the percentage of FDK and simultaneously reduced the thousand kernel weight in control and infected plants.

Micro-CT 3D imaging reveals the internal structure of three abyssal xenophyophore species (Protista, Foraminifera) from the eastern equatorial Pacific Ocean

Xenophyophores, giant foraminifera, are distinctive members of the deep-sea megafauna that accumulate large masses of waste material (‘stercomare’) within their agglutinated tests, and organise their cells as branching strands enclosed within an organic tube (the ‘granellare’ system). Using non-destructive, three-dimensional micro-CT imaging we explored these structures in three species from the abyssal eastern Pacific Clarion-Clipperton Zone (CCZ). In Psammina spp., the low-density stercomare occupied much of the test interior, while high-density granellare strands branched throughout the structure. In Galatheammina sp. the test comprised a mixture of stercomare and test particles, with the granellare forming a web-like system of filaments. The granellare occupied 2.8–5.1%, the stercomare 72.4–82.4%, and test particles 14.7–22.5%, of the ‘body’ volume in the two Psammina species. The corresponding proportions in Galatheammina sp. were 1.7% (granellare), 39.5% (stercomare) and 58.8% (test particles). These data provide a potential basis for estimating the contribution of xenophyophores to seafloor biomass in areas like the CCZ where they dominate the megafauna. As in most xenophyophore species, the granellare hosted huge numbers of tiny barite crystals. We speculate that these help to support the extensive granellare system, as well as reducing the cell volume and lightening the metabolic burden required to maintain it.