Novel insights into orchid mycorrhiza functioning from stable isotope signatures of fungal pelotons.

Stable isotope signatures of fungal sporocarps have been instrumental in identifying carbon gains of chlorophyllous orchids from a fungal source. Yet, not all mycorrhizal fungi produce macroscopic sporocarps and frequently fungi of different taxa occur in parallel in orchid roots. To overcome this obstacle, we investigated stable isotope signatures of fungal pelotons extracted from orchid roots and compared these data to the respective orchid and reference plant tissues. Anoectochilus sandvicensis and Epipactis palustris represented specialized or unspecialized rhizoctonia-associated orchids. Epipactis atrorubens and Epipactis leptochila are orchids considered ectomycorrhiza-associated with different preferences for Basidio- and Ascomycota. 13 C enrichment of rhizoctonia pelotons was minor compared with plant tissues and significantly lower than enrichments of pelotons from ectomycorrhizal Epipactis species. 15 N values of pelotons from E. leptochila and E. atrorubens showed similar patterns as known for respective sporocarps of ectomycorrhizal Ascomycota and Basidiomycota, however, with an offset towards lower 15 N enrichments and nitrogen concentrations. Our results suggest an explicit fungal nutrition source of orchids associated with ectomycorrhizal fungi, whereas the low 13 C enrichment in rhizoctonia-associated orchids and fungal pelotons hamper the detection of carbon gains from fungal partners. 15 N isotopic pattern of orchids further suggests a selective transfer of 15 N-enriched protein-nitrogen into orchids.

At the core of the endomycorrhizal symbioses: intracellular fungal structures in orchid and arbuscular mycorrhiza.

Arbuscular (AM) and orchid (OrM) mycorrhiza are the most widespread mycorrhizal symbioses among flowering plants, formed by distinct fungal and plant species. They are both endosymbioses because the fungal hyphae can enter inside the plant cell to develop intracellular fungal structures that are surrounded by the plant membrane. The symbiotic plant-fungus interface is considered to be the major site of nutrient transfer to the host plant. We summarize recent data on nutrient transfer in OrM and compare the development and function of the arbuscules formed in AM and the pelotons formed in OrM in order to outline differences and conserved traits. We further describe the unexpected similarities in the form and function of the intracellular mycorrhizal fungal structures observed in orchids and in the roots of mycoheterotrophic plants forming AM. We speculate that these similarities may be the result of convergent evolution of mycorrhizal types in mycoheterotrophic plants and highlight knowledge gaps and new research directions to explore this scenario.

Cell pelotons: A model of early evolutionary cell sorting, with application to slime mold Dictyostelium discoideum.

A theoretical model is presented for early evolutionary cell sorting within cellular aggregates. The model involves an energy-saving mechanism and principles of collective self-organization analogous to those observed in bicycle pelotons (groups of cyclists). The theoretical framework is applied to slime-mold slugs (Dictyostelium discoideum) and incorporated into a computer simulation which demonstrates principally the sorting of cells between the anterior and posterior slug regions. The simulation relies on an existing simulation of bicycle peloton dynamics which is modified to incorporate a limited range of cell metabolic capacities among heterogeneous cells, along with a tunable energy-expenditure parameter, referred to as an "output-level" or "starvation-level" to reflect diminishing energetic supply. Proto-cellular dynamics are modeled for three output phases: "active", "suffering", and "dying or dead." Adjusting the starvation parameter causes cell differentiation and sorting into sub-groups within the cellular aggregate. Tuning of the starvation parameter demonstrates how weak or expired cells shuffle backward within the cellular aggregate.

Fusarium oxysporum KB-3 from Bletilla striata: an orchid mycorrhizal fungus.

Orchid mycorrhizal fungi are essential for the seed germination and vegetative growth of orchids. The orchid Bletilla striata has great medical value in China because its tuber is rich in mannan. Some endophytic fungi were isolated from the roots of B. striata. The isolate KB-3 was selected for experiments because it could promote the germination of B. striata seeds. Based on morphological characters and phylogenetic analysis, the isolate KB-3 was identified as Fusarium oxysporum. Co-cultivation experiments of KB-3 with B. striata and Dendrobium candidum were performed to demonstrate orchid mycorrhizal structures. Microscopic examination showed that KB-3 established colonization and produced coiled hyphal structures known as pelotons within the cortical cells of both orchid roots. The results confirm that F. oxysporum KB-3 can behave as an orchid mycorrhizal fungus.

The Relationship Between Exercise Habits and Stress Among Individuals With Access to Internet-Connected Home Fitness Equipment: Single-Group Prospective Analysis.

BACKGROUND: Physical activity (PA) confers numerous benefits to health and health care costs, yet most adults are not meeting recommended PA guidelines. Stress may be a factor that influences PA behavior. Research investigating the impact of stress on PA has yielded inconsistent findings. Most studies find that stress negatively impacts PA, but there is some evidence that habitual exercising buffers this association. OBJECTIVE: This study aims to examine the relationship between stress and exercise habits among habitual exercisers with internet-connected home fitness equipment (Peloton Bike) during the COVID-19 lockdown. METHODS: Participants were recruited through Facebook (N=146) and asked to complete an internet-based survey that assessed COVID-19-related stressors, perceived stress associated with those stressors, and general perceived stress. Self-reported exercise was assessed on the survey using the Godin Leisure-time Exercise Questionnaire (GLTEQ). Participants were also asked for consent to access their Peloton usage data through the Peloton platform. From their usage data, the frequency and duration of cycling classes was calculated for 4 weeks prior to and 12 weeks following the survey. Hierarchical regression equations tested the association between stress reported on the survey and subsequent exercise participation. Exercise participation was quantified both as the frequency and duration of Peloton cycling over the 12 weeks following the survey and as self-reported moderate to vigorous activity on a second survey completed by a subset of participants 12 weeks after the initial survey. RESULTS: There were 146 participants in our Peloton analysis sample and 66 in the self-reported exercise analysis. Peloton user data showed that study participants cycled frequently (mean 5.9 times per week) in the month prior to the initial survey, and that presurvey Peloton use was a strong predictor of exercise frequency (R2=0.57; F2,143=95.27; P<.001) and duration (R2=0.58; F2,143=102.58; P<.001) for the 12 subsequent weeks. Self-reported overall exercise likewise showed that this sample was very active, with an average of more than 8 times per week of moderate to vigorous exercise at the initial survey. Self-reported exercise on the initial survey was a strong predictor of self-reported exercise 12 weeks later (R2=0.31; F1,64=29.03; P<.001). Perceived stress did not impact Peloton cycling duration or frequency (P=.81 and .76, respectively) or self-reported exercise (P=.28). CONCLUSIONS: The results suggest that stress did not negatively impact exercise participation among habitually active adults with access to internet-connected home fitness equipment. Habitual exercise may buffer the impact of stress on participation in regular moderate to vigorous activity. Future research should examine the role that the availability of home-based internet-connected exercise equipment may play in this buffering.

Energy saving mechanisms, collective behavior and the variation range hypothesis in biological systems: A review.

Energy saving mechanisms are ubiquitous in nature. Aerodynamic and hydrodynamic drafting, vortice uplift, Bernoulli suction, thermoregulatory coupling, path following, physical hooks, synchronization, and cooperation are only some of the better-known examples. While drafting mechanisms also appear in non-biological systems such as sedimentation and particle vortices, the broad spectrum of these mechanisms appears more diversely in biological systems that include bacteria, spermatozoa, various aquatic species, birds, land animals, semi-fluid dwellers like turtle hatchlings, as well as human systems. We present the thermodynamic framework for energy saving mechanisms, and we review evidence in favor of the variation range hypothesis. This hypothesis posits that, as an evolutionary process, the variation range between strongest and weakest group members converges on the equivalent energy saving quantity that is generated by the energy saving mechanism. We also review self-organized structures that emerge due to energy saving mechanisms, including convective processes that can be observed in many systems over both short and long time scales, as well as high collective output processes in which a form of collective position locking occurs.