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Carmichael’s Concise Review


Coming Events 2018


International Microscopy Congress IMC19 September 9–14, 2018


Sydney, Australia www.imc19.com


Fatigue Damage of Structural Materials September 16–21, 2018 Cape Cod - Hyannis, MA


www.elsevier.com/events/ conferences/international- conference-on-fatigue-damage-of-structural-materials


National Society for Histotechnology Symposium


September 21–26, 2018 St. Louis, MO


www.eventsinamerica.com/events/44th-annual-nsh-annual- symposium-convention-national-society-for-histotechnology/ ev57eebaa60a3d6


Structural Biology 2018: 14th International Conference on Structural Biology September 24–26, 2018 Berlin, Germany


structuralbiology.conferenceseries.com


Microscopy: Advances, Innovation, Impact 2018 September 27, 2018 London, UK


www.rms.org.uk/discover-engage/ event-calendar/ microscopy-advances-innovation-impact-2018.html


MS&T2018: Materials Science & Technology


October 14–18, 2018


Columbus, OH www.matscitech.org


Neuroscience 2018 November 3–7, 2018 San Diego, CA


Sponsor: Society for Neuroscience www.sfn.org


2019


Microscopy & Microanalysis 2019 August 4–8, 2019


Portland, OR www.microscopy.org 2020


Microscopy & Microanalysis 2020 August 2–6, 2020


Milwaukee, WI www.microscopy.org 2021


Microscopy & Microanalysis 2021 August 1–5, 2021


Pittsburgh, PA www.microscopy.org 2022


Microscopy & Microanalysis 2022 July 31–August 4, 2022


Portland, OR www.microscopy.org 2023


Microscopy & Microanalysis 2023 July 24–28, 2023


Minneapolis, MN www.microscopy.org


More Meetings and Courses Check the complete calendar near the back of this magazine.


8


Figure 1 : (Left) Visualization of statolith piles (dark areas) sedimented under gravity at the bottom of gravisensing cells in wheat coleoptiles. (Right) Close-up of a gravisesing cell showing the individual statoliths in a pile.


doi: 10.1017/S1551929518000834 2018 September gg Plants Grow Up by Sensing “Down”


Stephen W. Carmichael Mayo Clinic , Rochester , MN 55905 carmichael.stephen@mayo.edu


T e gravity sensor of plants is unique among biological sensors in its ability to combine sensitivity and robustness to cope with a fl uctuating and noisy environment. It is found in specifi c cells, called statocytes, in which tiny assemblies of starch-rich particles, called statoliths, settle at the bottom of the cell and indicate the direction of gravity. When a shoot or root is tilted, the change in direction is detected by the statoliths within statocytes, which triggers a complex signaling pathway involving the redistribution of growth hormones within the tissue. T is in turn leads to diff erential growth of the plant organ and the bending of the organ toward vertical. A remarkable feature of this gravitropic response is that it is extremely sensitive, even to the slightest tilt. T is is key to maintaining the vertical posture of a plant on Earth. It has long been assumed that statocytes behave as a force sensor, whereby gravity is detected by sensing the weight of statoliths on the cell edges or by interaction with the cytoskeleton. However, recent experiments indicate that the gravity sensors of plants (gravisensors) function as an inclination sensor rather than a force or acceler- ation sensor. T is suggests that the position of the statoliths, not their weight, is the relevant gravitropic stimulus. In order to determine how this works Antoine Bérut, Hugo Chauvet, Valérie Legué, Bruno Moulia, Olivier Poulquen, and Yoël Forterre [ 1 ] conducted a series of experiments. One problem to be solved was that an assembly of particles such as sand does not respond to slight changes in tilt. A pile of grains remains static due to friction and other factors that keep the grains interlocked until a critical angle, the “avalanche angle,” is reached. T e sensitivity of the gravisensor in plants is not compatible with this.


Bérut et al. addressed this issue by investigating in situ the response of statolith assemblies to a wide range of inclinations over long periods of time. T ey found a peculiar fl owing behavior not observed in classical granular material where statoliths fi rst fl ow in bulk like a granular avalanche but then creep and recover a free fl at surface like a liquid. To visualize statolith dynamics in response to plant inclination they examined statocytes of wheat coleoptiles. A coleoptile is the pointed protective sheath covering the emerging shoot of wheat and other plants. Unlike leaves, the pre-emergent coleoptile does not accumulate signifi cant chlorophyll or other pigments, so it is very pale, allowing for good visualization of its interior. For this reason the wheat coleoptile


100 µm 20 µm


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