Lee W. Wilcox

GYMNODINIUM ACIDOTUM NYGAARD (PYRROPHYTA), A DINOFLAGELLATE WITH AN ENDOSYMBIOTIC CRYPTOMONAD1

Ultrastructural examination of the freshwater, blue‐green dinoflagellate Gymnodinium acidotum Nygaard revealed the presence of an endosymbiotic cryptomonad. Features of the endosymbiont allying it with the Cryptophyceae include mitochondria with flattened cristae, paired thylakoids with electron‐dense contents, and nucleomorphs, bodies unique to the Cryptophyceae. This report is the first conclusive documentation of a symbiosis involving these two groups.

THE OCCURRENCE AND PHYLOGENETIC SIGNIFICANCE OF PUTATIVE PLACENTAL TRANSFER CELLS IN THE GREEN ALGA COLEOCHAETE

Following fertilization, zygotes of the green alga Coleochaete orbicularis, which are retained on the haploid thallus, first enlarge, then become covered with a layer of vegetative cells. Light microscopy and high-voltage electron microscopy revealed the presence of localized wall ingrowths in vegetative cells adjacent to zygotes. These covering cells resemble the gametophytic placental transfer cells of embryophytes in their morphology, location, and time of development. If Coleochaete cells with wall protuberances function as do placental transfer cells of embryophytes, their presence is evidence that photosynthates may be transported between haploid thallus cells and zygotes. Thus, a nutritional relationship between different phases of the life cycle, similar to that which occurs in embryophytes, may also have evolved in green algae. This first report of putative placental transfer cells in a green alga supports Bowers (1908) ideas concerning the origin of land plant sporophytes and alternation of generations. The presence or absence of cells with wall ingrowths in several species of Coleochaete was correlated with estimates of zygote-plant area ratios.

Genetically Distinct Populations of the Dinoflagellate Peridinium limbatum in Neighboring Northern Wisconsin Lakes

The extent to which free-living microorganisms exist in geographically isolated, genetically distinct populations is a subject of continuing debate. Some authorities contend that many microorganisms have cosmopolitan distributions, while others provide evidence that more limited geographical distribution of genetically distinct populations can occur. We report the occurrence of two morphologically similar, but genetically distinct, populations of the microbial eukaryote Peridinium limbatum (Stokes) Lemmermann from neighboring Northern Wisconsin freshwater bodies. Five strains of P. limbatum were cultured by single-cell isolation from both Crystal Lake and Crystal Bog (Oneida Co., WI). Genetic variation between the two populations encompassed 8.9% (mean of 35.4 of 397 nucleotides) of the nuclear ribosomal DNA internal transcribed spacer (ITS1 and ITS2) region. In contrast, 0.5% (mean of 2.25 of 397 nucleotides) variation was observed within the Crystal Lake population and 0.3% (mean of 1.21 of 397 nucleotides), within the Crystal Bog population. This difference between the two populations was highly statistically significant (p-value << 0.001). The extent of genetic variation between the two P. limbatum populations was greater than that reported in the literature for some morphologically distinguishable microalgal species, suggesting the occurrence of cryptic sister species. On the other hand, hybrid sequences obtained from one of the Crystal Lake strains suggest that the two populations may still be members of a single sexually compatible biological species. Our data suggest that the two neighboring P. limbatum populations may be diverging genetically under conditions of limited gene flow, suggesting a mechanism for the origin of geographically isolated, genetically distinct populations of microbial eukaryotes.

AMPHIDINIUM CRYOPHILUM SP. NOV. (DINOPHYCEAE) A NEW FRESHWATER DINOFLAGELLATE. II. ULTRASTRUCTURE1

The dinoflagellate Amphidinium cryophilum sp. nov. is one of the few gymnodinians to be studied at the ultrastructural level. It resembles other dinoflagellates in the structure of the nucleus, trichocysts, storage materials, flagella, mitochondria, and microbodies. Other features of A. cryophilum less commonly observed in related organisms include a network of small interconnected vesicles, a system of large, peripheral vacuoles, chloroplasts bound by two rather than three membranes, an accumulation body, thylakoid‐associated plastoglobuli, a vesiculated nuclear envelope, a complex tubular pusule, striated flagellar collars, collared pits, and a peduncle. The occurrence of a peduncle, a structure implicated in phagotrophy, in this autotrophic organism is noteworthy. The ultrastructure of the peduncle of A. cryophilum differs significantly from that reported in another dinoflagellate.

MICROBIOMES OF STREPTOPHYTE ALGAE AND BRYOPHYTES SUGGEST THAT A FUNCTIONAL SUITE OF MICROBIOTA FOSTERED PLANT COLONIZATION OF LAND

Premise of research. The origin of land plants catalyzed key changes in Earth’s atmosphere and biota. Microbial associations likely nurtured earliest plants and influenced their biogeochemical roles. Because angiosperm and animal microbiomes—bacteria, archaea, microbial eukaryotes, and genes that promote host survival—are known to display lineage effects, we hypothesized that microbiomes of early-diverging modern bryophytes and phylogenetically closely related green algae might likewise reveal commonalities reflecting ancestral traits. Methodology. New metagenomic sequence data were obtained for the late-diverging streptophyte algae Chaetosphaeridium globosum and Coleochaete pulvinata and the liverwort Conocephalum conicum, representing early-diverging land plants. New 16S rDNA amplicon sequences were acquired for the charalean Nitella tenuissima. Sequence data were used to infer bacterial genera and fungi for comparisons among streptophyte microbiota and with our published microbiome data for the outgroup chlorophyte Cladophora. To enhance evolutionary signal, taxa were sampled in the same time frame and from geographically close locales. Streptophyte metagenomic data were also probed for protein markers of significant physiological and biogeochemical functions: NifH indicating nitrogen fixation, particulate MMo indicating methane oxidation, and vitamin B12 (cobalamin) indicating biosynthetic pathway enzymes. Pivotal results. Microbiota of studied streptophytes consistently included diverse N-fixing cyanobacteria and/or Rhizobiales, as well as methanotrophs and early-diverging fungi, and were more similar to each other than to Cladophora microbiota. Streptophyte metagenomic data indicated diverse nifH (nitrogen fixation) and pMMo (methane oxidation) marker sequences and vitamin B12 pathway genes. Glomalean fungi occurred with Conocephalum, consistent with field studies of modern liverworts and microfossil evidence for co-occurrence of glomaleans and early land plants. Conclusions. A suite of N fixers, methanotrophs, cobalamin producers, and early-diverging fungi was consistently associated with modern streptophyte algae and bryophytes studied, suggesting features of early land plants that have played significant, previously unrecognized roles in global nitrogen and carbon cycling for hundreds of millions of years.

AMPHIDINIUM CRYOPHILUM SP. NOV. (DINOPHYCEAE) A NEW FRESHWATER DINOFLAGELLATE. I. SPECIES DESCRIPTION USING LIGHT AND SCANNING ELECTRON MICROSCOPY1

Amphidinium cryophilum sp. nov. was found in the fall of 1979 in a small pond near Madison, Wisconsin. During the ensuing winter, it became the dominant phytoplankter. Cell numbers remained high despite a thick layer of ice and snow. After the ice melted in the spring the organism disappeared from plankton samples. A successful culture of A. cryophilum was established only when isolates were incubated at 5–7° C. It is compared with two morphologically similar species, A. amphidinioides (Geitler) Schiller and Gymnodinium inversum Nygaard. Amphidinium cryophilum is distinguished from the former by its pigmentation (golden‐yellow vs. blue‐green), the location of the cingulum, and its lack of an eyespot. It differs from the latter in cell shape, the route of the sulcus and position of the nucleus.

Early land plant adaptations to terrestrial stress: A focus on phenolics

Publisher Summary This chapter maps the stress-related physiological traits onto a robust phylogeny for modern charophycean algae and bryophytes. Trait mapping suggests that early phenolics could have been preadaptive to the development of stable plant–microbe relationships. As in modern plants, phenolic compounds may have controlled microbial behavior, allowing microbes to live in close proximity to algae and early land plants without becoming pathogenic. The chapter also compares the aspects of phenolic chemistry among charophyceans, bryophytes, and pteridophytes and estimates the extent to which nonvascular plants could have contributed to carbon sequestration prior to the origin of vascular plants. Thioacidolysis was used as an assay for lignin-specific β-O-4 phenolic linkages in representative green algae and early-divergent land plants. Selected green algae and bryophytes were surveyed for the presence of resistant biomass and the percentages of resistant cell wall biomass were quantitatively determined. The amount of resistant organic carbon that might have been generated by early non-vascular land plants was also estimated. Adaptive utility for high levels of wall phenolics might include (1) resistance to attack by pathogenic bacteria, protists and fungi, (2) increased stability of cell walls, contributing to the ability to achieve increased height, (3) UV-damage resistance, and (4) desiccation resistance.

DESMID‐BACTERIAL ASSOCIATIONS IN SPHAGNUM‐DOMINATED WISCONSIN PEATLANDS1

In a survey employing epifluorescence microscopy with the DNA fluorochrome DAPI, associations between bacteria and filamentous desmids were found to be commonplace in acidic, Sphagnum‐dominated Wisconsin peat‐lands. Bacteria were associated with all genera of filamentous desmids encountered including Desmidium, Hyalotheca, Onychonema, Spondylosium, and Teilingia. Although only associations involving filamentous desmids having mucilaginous sheaths are illustrated here, bacteria were also noted on taxa lacking sheaths as well as some unicellular forms. Bacteria on Desmidium majus Lagerheim, D. grevillii (Kütz.) De Bary, and Hyalotheca dissiliens (Smith) Bréb. ex Ralfs tended to be concentrated in small pockets in the sheath material located near the isthmus and in the region between adjacent cells in the filament, whereas those associated with Spondylosium pulchrum (Bail.) Archer were more evenly distributed throughout the sheath. Most bacteria were rodshaped. Those associated with S. pulchrum, D. grevillii, and D. majus ranged from 1.1 to 11.2 μm in length. Bacteria within the sheaths of H. dissiliens and D. grevillii were Gram‐negative. A second morphologically distinct population of bacteria was found at the sheath margin in D. majus and D. grevillii. Field collections containing filamentous desmids were examined with scanning electron microscopy and bacteria associated with Desmidium majus were investigated with transmission electron microscopy.

Resistance of Filamentous Chlorophycean, Ulvophycean, and Xanthophycean Algae to Acetolysis: Testing Proterozoic and Paleozoic Microfossil Attributions

Premise of research. The taxonomic affinities of nonmarine Proterozoic and Paleozoic microfossils are often difficult to determine. Given that the preservability (degradation resistance) of cell walls displaying distinctive features is widely regarded as a key feature allowing the recognition and classification of fossil protists, we examined the retention of diagnostic cell wall features after high-temperature chemical hydrolysis of several modern filamentous algal genera previously hypothesized to be related to particular Proterozoic or Paleozoic microfossils. Methodology. We collected and in some cases cultured filamentous algae from modern terrestrial sites or freshwaters of arid locales hypothesized to model ancient nonmarine habitats. We subjected these and other samples of Vaucheria (Stramenopila, Xanthophyceae), Cladophora (Chlorophyta, Ulvophyceae), Stigeoclonium (Chlorophyta, Chlorophyceae), and Oedogonium (Chlorophyta, Chlorophyceae) to acetolysis, an extremely degradative hydrolytic process widely used in palynology to select for resistant organic materials. We imaged the remains using bright-field, polarizing, and fluorescence LM and also SEM. Pivotal results. Filaments of all xanthophycean and chlorophytan green algal genera tested resisted acetolysis and retained distinctive structural traits previously used to classify Proterozoic and Paleozoic microfossils as algae. Features of cell wall remains revealed by polarizing microscopy and SEM suggested that degradation resistance results largely from the presence in cell walls of cellulose types that are more resistant to degradation than are celluloses of land plants and streptophyte algae. In the case of Cladophora, specific autofluorescence properties also suggest the presence of a previously undetected phenolic layer in the primarily cellulosic cell wall. Conclusions. Our results are more or less consistent with previous classifications of certain ancient microfossils with genera of modern filamentous algae and explain degradation resistance of their cell walls. The results justify the use of cell wall features to classify filamentous microfossils and suggest steps that might yield even more convincing identifications.

Evolutionary and ecophysiological significance of sugar utilization by the peat moss Sphagnum compactum (Sphagnaceae) and the common charophycean associates Cylindrocystis brebissonii and Mougeotia sp. (Zygnemataceae)

UNLABELLED PREMISE OF THE STUDY The goal of this study was to illuminate the evolutionary history and ecological importance of plant mixotrophy-the uptake and utilization of exogenous organic compounds. • METHODS We quantitatively assessed the effect of sugar amendments on laboratory growth of Sphagnum compactum as a representative emergent peat moss and two species of ecologically associated zygnematalean algae, Cylindrocystis brebissonii and Mougeotia sp. • KEY RESULTS Together with observations published elsewhere, our results suggest that under carbon or light limitation, the uptake of exogenous sugars by cells of charophycean algae and peat mosses may help these organisms maintain positive carbon balance. Utilization of 1% glucose by aquatic-grown algae helped to relieve dissolved inorganic carbon limitation, enhancing photoautotrophic growth by factors of 9.0 and 1.7, respectively. After an 8-wk growth period, amendments of 1% and 2% glucose enhanced air-grown moss biomass by 28 and 39 times, respectively, that of controls lacking sugar amendments. After 9 wk, 1% fructose enhanced biomass by 21 times, and 2% sucrose enhanced biomass by 31 times. • CONCLUSION Our results indicate that plant mixotrophy is an early-evolved trait. The results also indicate that quantitative differences in sugar utilization by bryophytes and charophycean algae correlate with relative investments in protective cell-wall polyphenolics measured in previous studies, suggesting that sugar utilization may subsidize the cost of producing phenolic wall compounds in bryophytes.