Early land plant adaptations to terrestrial stress

Proc. Natl. Acad. Sci. U.S.A.

Wilcox

Cook

et al. 2004

Absence of a substantial pretracheophyte fossil record for bryophytes (otherwise predicted by molecular systematics) poses a major problem in our understanding of earliest land-plant structure. In contrast, there exist enigmatic Cambrian-Devonian microfossils (aggregations of tubes or sheets of cells or possibly a combination of both) controversially interpreted as an extinct group of early land plants known as nematophytes. We used an innovative approach to explore these issues: comparison of tube and cell-sheet microfossils with experimentally degraded modern liverworts as analogues of ancient early land plants. Lower epidermal surface tissues, including rhizoids, of Marchantia polymorpha and Conocephalum conicum were resistant to breakdown after rotting for extended periods or high-temperature acid treatment (acetolysis), suggesting fossilization potential. Cell-sheet and rhizoid remains occurred separately or together depending on the degree of body degradation. Rhizoid break-off at the lower epidermal surface left rimmed pores at the centers of cell rosettes; these were similar in structure, diameter, and distribution to pores characterizing nematophyte cell-sheet microfossils known as Cosmochlaina. The range of Marchantia rhizoid diameters overlapped that of Cosmochlaina pores. Approximately 14% of dry biomass of Marchantia vegetative thalli and 40% of gametangiophores was resistant to acetolysis. Pre-and posttreatment cell-wall autofluorescence suggested the presence of phenolic compounds that likely protect lower epidermal tissues from soil microbe attack and provide dimensional stability to gametangiophores. Our results suggest that at least some microfossils identified as nematophytes may be the remains of early marchantioid liverworts similar in some ways to modern Marchantia and Conocephalum.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Resistant tissues of modern marchantioid liverworts resemble enigmatic Early Paleozoic microfossils

Proc. Natl. Acad. Sci. U.S.A.

Wilcox

Cook

et al. 2004

“…Biomass was determined using a Sartorius analytical weight type 1872 (Brinkman Instruments, Westbury, NY) and then utilized for quantitative acetolysis (Graham et al 2004(Graham et al , 2010 to determine the relative amount of hydrolysis-resistant biomass. Plants from three replicate culture dishes per treatment were dried and weighed, and cellulose was extracted and quantified.…”

Section: Harvesting and Biomass Assessmentmentioning

confidence: 99%

“…Such acidification influences peatland community composition and fosters peat accumulation in the ecosystem by slowing the decomposition process (Clymo 1965;Coulson and Butterfield 1978;Johnson and Damman 1993;Aerts et al 2001;Rydin and Jeglum 2006;Pankratov et al 2011). Cell wall polysaccharides are known to reduce decay processes (Hájek et al 2011), and hydrolysisresistant, phenolic cell wall polymers not only foster formation of peat by nonliving tissues but also confer to living plant tissues resistance to microbial attack, desiccation, and cellular damage from UV originating from solar emissions (Kroken et al 1996;Graham et al 2004). …”

mentioning

confidence: 97%

Anatomical Effects of Temperature and UV-A + UV-B Treatments and Temperature-UV Interactions in the Peatmoss Sphagnum compactum

Cardona-Correa

International Journal of Plant Sciences

2015

Premise of research. Sphagnum peatmosses strongly influence local and regional hydrology and biotic communities and based on high abundance at high latitudes also play a global environmental role in maintaining atmospheric chemistry and climate homeostasis. Previous field research suggests that elevated temperature linked to global climate change or elevated UV related to ozone depletion at high latitudes affects aspects of peatmoss productivity or external morphology hypothesized to influence environmental roles. However, changes in microscopic anatomy or potential temperature-UV interaction effects have not previously been investigated. Controlled environments offer advantages for assessing anatomical impacts of temperature and UV variation and detecting temperature-UV interactions.Methodology. Clonal cultures of experimentally tractable Sphagnum compactum were treated for a 2-mo period with environmentally relevant temperature levels (107, 207, and 307C) and two levels of UV-A 1 UV-B found in a pilot study to produce contrasting structural effects, in a factorial experimental design. Proportions of hydrolysis-resistant and cellulosic biomass and numerous features of microscopic anatomy having potential ecological significance were assessed and analyzed using two-way ANOVA.Pivotal results. Elevated temperature, the higher level of UV treatment, or temperature-UV interaction significantly influenced survival, biomass, cell wall biochemistry, or anatomical features of ecological significance. Plants grown at 107 or 207C and under the higher level of UV treatment displayed increased proportion of hydrolysis-resistant cell wall material. Elevated temperature was associated with reduction in stem width and reduced numbers of supportive fibrils in branch and stem leaf hyaline cells. Plants exposed to 307C and the higher level of UV treatment died during the treatment period.Conclusions. Elevated temperature, UV, and temperature-UV interactions affect peatmoss biomass, wall chemistry, and anatomy in ways that could influence environmental roles. Functionally important traits affected by temperature or UV are recommended for assessment in field studies.

“…1,2 Early gametophytedominant streptophytes, thought to have had ecological roles and biogeochemical impacts much like those of modern streptophyte algae and bryophytes, likely contributed to soil formation and stability, provided nutritional resources for early terrestrial heterotrophs, and influenced atmospheric chemistry for tens of millions of years prior to the rise of vascular plants. 3,4 Because the latest-diverging modern streptophyte algae and the earliestdiverging modern embryophytes display prostrate dorsiventral or erect axial bodies, these growth forms are also inferred for earliest terrestrial vegetation. 5,6 Even so, the particular environmental influences that determine dorsiventral or axial gametophytic body orientation in modern seedless plants are largely unknown.…”

Section: Introductionmentioning

confidence: 99%

Direction of illumination controls gametophyte orientation in seedless plants and related algae

Cardona-Correa

Ecker

Plant Signaling & Behavior

2015

Self Cite

The environmental influences that determine dorsiventral or axial gametophyte orientation are unknown for most modern seedless plants. To fill this gap, an experimental laboratory system was employed to evaluate the relative effects of light direction and gravity on body orientation of the dorsiventral green alga Coleochaete orbicularis, and gametophytes of liverworts Blasia pusilla and Marchantia polymorpha, early-diverging moss Sphagnum compactum, and fern Ceratopteris richardii, the latter functioning as experimental control. Replicate clonal cultures were experimentally illuminated only from above, only from below, or from multiple directions, with the same near-saturation PAR level for periods brief enough to minimize nutrient limitation effects, and orientation of new growth was evaluated. For all species tested, direction of illumination exerted stronger control over gametophyte body orientation than gravity. When illuminated only from below: 1) axial Sphagnum gametophores that had initially grown into an overlying air space inverted growth by 180, burrowing into the substrate; 2) new growth of dorsiventral Blasia, Marchantia, and Ceratopteris gametophytes-whose ventral rhizoids initially penetrated agar substrate and dorsal surfaces initially faced overlying airspace-twisted 180 so that ventral surfaces bearing rhizoids faced overlying air space and rhizoids extended into the air; and 3) Coleochaete lost typical dorsiventral organization and diagnostic dorsal hairs. Direction of illumination also exerted stronger control over orientation of liverwort new growth than surface contact did. These results indicate that early land plants likely inherited light-directed gametophyte body orientation from ancestral streptophyte algae and suggest a mechanism for reorientation of gametophyte-dominant land plants after spatial disturbance.