Image: Mariana Ruiz Villarreal/Wikimedia Commons.
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Feel the force!

Image: Mariana Ruiz Villarreal/Wikimedia Commons.
Image: Mariana Ruiz Villarreal/Wikimedia Commons.

Plants are remarkably sensitive to their environment, responding by appropriate growth and development to a wide range of environmental stimuli. In the case of gravity, the appropriate response is for stems to grow upwards (‘away from the source of gravity’; negative geotropism), and for roots to grow downwards (‘towards the source of gravity’; positive geotropism – for examples, see reviews by Elison Blancaflor and Patrick Masson  and by Miyo Morita). Although the details of the full pathway involved are still the subject of intense research efforts, a role for gravity-stimulated repositioning of cell-located statoliths (starch-bearing amyloplasts) in the gravity-detection side of things has long been proposed. However, the dynamic – rather than settled – nature of such amyloplasts has cast doubt on their effectiveness to act in this way. Now, elegant work by Masatsugu Toyota et al. has demonstrated that amyloplast displacement is necessary for gravisensing (in arabidopsis shoots). Using a custom-built centrifuge microscope they show that ‘sedimentary movements of amyloplasts under hypergravity conditions are linearly correlated with gravitropic curvature in wild-type stems’. Furthermore, and using a range of gravitropic mutants that do not exhibit a normal response under the Earth’s usual 1 g gravity field,  they demonstrate that their ‘hypergravity-induced amyloplast sedimentation and gravitropic curvature… was identical to that of wild-type plants’. Such work supports the view that arabidopsis shoots do have a gravisensing mechanism that converts the number of gravity-settling amyloplasts into gravitropic signals. And restoration of the gravitropic response by hypergravity in the gravitropic mutants examined indicates that those plants probably also have a functional gravisensing mechanism, albeit one that is not triggered at 1 g. Nice work. But in view of recent upsets (see previous ‘Ouch! That must hurt…’ post), I wonder if it also applies to non-arabidopsis plants…? Still, it is good to have the odd positive story about arabidopsis (I suppose…!).

[For more on the tangled web that is plant gravity-sensing and involvement of the actin cytoskeleton, check out the recent review by Elison Blancaflor  – Ed.]

Nigel Chaffey

I am a Botanist and former Senior Lecturer in Botany at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany I contributed the monthly Plant Cuttings column to that international plant science journal for almost 10 years. As a freelance plant science communicator I continue to share my Cuttingsesque items - and appraisals of books with a plant focus - with a plant-curious audience at Plant Cuttings [] (and formerly at Botany One []). In that guise my main goal is to inform (hopefully, in an educational, and entertaining way) others about plants and plant-people interactions, and thereby improve humankind's botanical literacy. I'm happy to be contacted to discuss potential writing - or talking - projects and opportunities.
[ORCID: 0000-0002-4231-9082]

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