Biology subjects

Bohr, T.

Publications and source records attributed to Bohr, T..

4 recordsLinked to original sources

bioRxiv2026

Stelar starch management tailors diurnal and rehydration-related water flows in Pinus pinea needles

Pine needles contain two vascular cell types unique to gymnosperms: Transfusion parenchyma (tp) and tracheids (tt). Since they form the only connections between vascular bundles and bundle sheath, we hypothesised that they are involved in regulating the needles water import and photoassimilate export. Synchrotron-based tomography enabled us to quantify volume changes of tp and tt cells in Pinus pinea needles systematically along the needle and throughout a diurnal day cycle, as well as under rehydration. As a physiological indicator of tps carbohydrate status served their starch content. Segmentation of the comprehensive data uncovered dramatic volume changes during dehydration and showed a diurnal course of starch formation and degradation. These changes suggest a yet unknown osmotic water flux between tp and tt, balanced by the formers carbohydrate status. Confirming our hypothesis, excess of photoassimilates in tp cells went into starch synthesis during the day. Starch mobilisation during the night increased the osmotic potential in tp and led to water intake. According to the decreasing starch fraction from base to needle tip, this mechanism is predominant in the upper needle segments, particularly after rehydration of dehydrated needles. Mechanistically, osmolytes in tp cells maintain tension in tt for the needles water import. HighlightSynchrotron tomographic microscopy uncovers diurnal starch fluctuations and osmotic water pumping in inner tissues of pine needles that are utilised at night and when recovering from dehydration

plant biology↗

bioRxiv2024

Relieving the transfusion tissue traffic jam: a network model of radial transport in conifer needles

The linear geometry of conifer leaves (e.g., pine needles) imposes architectural constraints on solute transport. The needles structural solution to prevent axial stagnation, however, introduces an additional challenge to radial transport by restricting loading and unloading of sugar and water, respectively, to a narrow zone at the periphery of the vascular bundle. Moreover, a Casparian strip blocks apoplastic flow through the endodermis between the vasculature and photosynthetic tissue, forcing countercurrents of water and sugar to travel simultaneously through the cell lumen at this interface. In between these two potential bottlenecks is the transfusion tissue, a distinctive anatomical feature of conifer needles. Here we develop a network-based mathematical model to explore how the structure of the intervening transfusion tissue facilitates radial transport of sugar and water. To describe extravascular transport with cellular resolution, we construct networks from images of Pinus pinea needles obtained through X-ray CT, as well as fluorescence and electron microscopy. Our results show that the physical separation of sugar and water pathways within the transfusion tissue mitigates the consequences of constricting flow at both the vascular access points and the endodermis. SIGNIFICANCEThe efficiency with which plants transport water and sugar across many scales affects their survival and success. At the leaf scale, accommodating the opposing flows of water and sugar is a nontrivial challenge, especially when foliar geometry imposes architectural limitations (e.g., in linear leaves (needles) of conifers). The transfusion tissue is a characteristic component of the conifer needle which mediates the radial transport of sugar and water. Our network model shows that the transfusion tissue alleviates the sugar-water traffic jams that would otherwise develop between the vascular system and photosynthetic cells. Our mathematical model provides finer resolution than what is currently possible with experimental approaches.

plant biology↗

bioRxiv2022

Tracing 3D apoplasmic complexity in vascular tissue of live conifer needles by X-ray computed tomography

Architecture and conducting area of vascular elements along conifer needles are fundamentally different from broad leaves. We hypothesised that the needles unique transfusion tissue offers different mechanisms for water allocation and used multimodal imaging to dissect the critical water exchange interfaces in this xerophytic leaf type. Our study examined intact conifer needles with X-ray computed tomography (XCT) and water-soluble tracers, allowing to render the functional 3D structure of the water-filled apoplast and the complementary symplasmic domain inside the bundle sheath. Segmentation of these data, together with fluorescence and electron microscopy of axial phloem and xylem elements along the needle, enabled quantification of the dimensions of the conducting tissue complex. The transfusion tracheid system between the endodermis-type bundle sheath and the axial venation formed a sponge-like apoplast domain. Transfusion parenchyma cell chains bridged this domain not directly but as tortuous symplasmic pathways between bundle sheath and axial phloem, which is nearly exclusively accessible at flanks. The transfusion tissue extends the plasma membrane surface for phloem loading and provides a large volume space. We discuss that this unique tissue plays an important role in the subtle interplay between water uptake/storage and sugar transport that has evolved to cope with desiccation stress.

plant biology↗

bioRxiv2018

Shugoshin is essential for meiotic prophase checkpoints in C. elegans

The conserved factor Shugoshin is dispensable in C. elegans for the two-step loss of sister chromatid cohesion that directs the proper segregation of meiotic chromosomes. We show that the C. elegans ortholog of Shugoshin, SGO-1, is required for checkpoint activity in meiotic prophase. This role in checkpoint function is similar to that of the meiotic chromosomal protein, HTP-3. Null sgo-1 mutants exhibit additional phenotypes similar to that of a partial loss of function allele of HTP-3: premature synaptonemal complex disassembly, the activation of alternate DNA repair pathways and an inability to recruit a conserved effector of the DNA damage pathway, HUS-1. SGO-1 localizes to pre-meiotic nuclei, when HTP-3 is present but not yet loaded onto chromosome axes, suggesting an early role in regulating meiotic chromosome metabolism. We propose that SGO-1 acts during pre-meiotic replication to ensure fully functional meiotic chromosome architecture, rendering these chromosomes competent for checkpoint activity and normal progression of meiotic recombination. Given that most research on Shugoshin has been focused on its regulation of sister chromatid cohesion in meiosis, this novel role may be conserved but previously uncharacterized in other organisms. Further, our findings expand the repertoire of Shugoshins functions beyond coordinating regulatory activities at the centromere.

cell biology↗