continuously, which could even result in the complete disintegration of the polar
structural organization of the statocytes after hours of clinorotation (Hensel and
Sievers 1980; Hoson et al. 1997). Therefore, research focusing on specific molecular
and cellular components of gravity sensing mechanisms and on the role of second
messengers like cytoplasmic free calcium, InsP3, and pH in gravity signaling
pathways are best performed under real-microgravity conditions in space. Recently,
experiments on the ISS have provided evidence that the establishment of the auxingradient system, the prerequisite for the curvature response, is gravity independent.
The cytokinin distribution, however, was different in space-grown and control roots
suggesting that cytokinin-associated process involved in gravitropism might be
affected (Ferl and Paul 2016).
Further research on the ISS and other microgravity platforms is currently planned
to increase our knowledge on the hormone-associated components of gravitropic
responses. In particular future research on mutants in the stimulus-free microgravity
environment promises to further contribute to the unravelling of the fascinating
processes of gravity sensing and gravitropic orientation in higher plants.
References
Andreeva Z, Barton D, Armour WJ et al (2010) Inhibition of phospholipase C disrupts cytoskeletal
organization and gravitropic growth in Arabidopsis roots. Planta 232:1263–1279. https://doi.
org/10.1007/s00425-010-1256-0
Audus L (1979) Plant geosensors. J Exp Bot 8:235–249
Baldwin KL, Strohm AK, Masson PH (2013) Gravity sensing and signal transduction in vascular
plant primary roots. Am J Bot 100:126–142. https://doi.org/10.3732/ajb.1200318
Baluška F, Kreibaum A, Vitha S et al (1997) Central root cap cells are depleted of endoplasmic
microtubules and actin microfilament bundles: implications for their role as gravity-sensing
statocytes. Protoplasma 196:212–223. https://doi.org/10.1007/BF01279569
Band LR, Wells DM, Larrieu A et al (2012) Root gravitropism is regulated by a transient lateral
auxin gradient controlled by a tipping-point mechanism. Proc Natl Acad Sci 109:4668–4673.
https://doi.org/10.1073/pnas.1201498109
Behrens HM, Gradmann D, Sievers A (1985) Membrane-potential responses following
gravistimulation in roots of Lepidium sativum L. Planta 163:463–472. https://doi.org/10.1007/
BF00392703
Bennett MJ, Marchant A, Green HG et al (1996) Arabidopsis AUX1 gene: a permease-like
regulator of root gravitropism. Science 273:948–950. https://doi.org/10.1126/science.273.
5277.948
Berridge MJ (2009) Inositol trisphosphate and calcium signalling mechanisms. Biochim Biophys
Acta, Mol Cell Res 1793:933–940
Blancaflor EB (2002) The cytoskeleton and gravitropism in higher plants. J Plant Growth Regul
21:120–136. https://doi.org/10.1007/s003440010041
Blancaflor EB, Fasano JM, Gilroy S (1998) Mapping the functional roles of cap cells in the response
of Arabidopsis primary roots to gravity. Plant Physiol 116:213–222. https://doi.org/10.1104/pp.
116.1.213
Boonsirichai K, Sedbrook JC, Chen R et al (2003) ALTERED RESPONSE TO GRAVITY is a
peripheral membrane protein that modulates gravity-induced cytoplasmic alkalinization and
lateral auxin transport in plant statocytes. Plant Cell 15:2612–2625
88
6 Gravitropism in Higher Plants: Cellular Aspects
structural organization of the statocytes after hours of clinorotation (Hensel and
Sievers 1980; Hoson et al. 1997). Therefore, research focusing on specific molecular
and cellular components of gravity sensing mechanisms and on the role of second
messengers like cytoplasmic free calcium, InsP3, and pH in gravity signaling
pathways are best performed under real-microgravity conditions in space. Recently,
experiments on the ISS have provided evidence that the establishment of the auxingradient system, the prerequisite for the curvature response, is gravity independent.
The cytokinin distribution, however, was different in space-grown and control roots
suggesting that cytokinin-associated process involved in gravitropism might be
affected (Ferl and Paul 2016).
Further research on the ISS and other microgravity platforms is currently planned
to increase our knowledge on the hormone-associated components of gravitropic
responses. In particular future research on mutants in the stimulus-free microgravity
environment promises to further contribute to the unravelling of the fascinating
processes of gravity sensing and gravitropic orientation in higher plants.
References
Andreeva Z, Barton D, Armour WJ et al (2010) Inhibition of phospholipase C disrupts cytoskeletal
organization and gravitropic growth in Arabidopsis roots. Planta 232:1263–1279. https://doi.
org/10.1007/s00425-010-1256-0
Audus L (1979) Plant geosensors. J Exp Bot 8:235–249
Baldwin KL, Strohm AK, Masson PH (2013) Gravity sensing and signal transduction in vascular
plant primary roots. Am J Bot 100:126–142. https://doi.org/10.3732/ajb.1200318
Baluška F, Kreibaum A, Vitha S et al (1997) Central root cap cells are depleted of endoplasmic
microtubules and actin microfilament bundles: implications for their role as gravity-sensing
statocytes. Protoplasma 196:212–223. https://doi.org/10.1007/BF01279569
Band LR, Wells DM, Larrieu A et al (2012) Root gravitropism is regulated by a transient lateral
auxin gradient controlled by a tipping-point mechanism. Proc Natl Acad Sci 109:4668–4673.
https://doi.org/10.1073/pnas.1201498109
Behrens HM, Gradmann D, Sievers A (1985) Membrane-potential responses following
gravistimulation in roots of Lepidium sativum L. Planta 163:463–472. https://doi.org/10.1007/
BF00392703
Bennett MJ, Marchant A, Green HG et al (1996) Arabidopsis AUX1 gene: a permease-like
regulator of root gravitropism. Science 273:948–950. https://doi.org/10.1126/science.273.
5277.948
Berridge MJ (2009) Inositol trisphosphate and calcium signalling mechanisms. Biochim Biophys
Acta, Mol Cell Res 1793:933–940
Blancaflor EB (2002) The cytoskeleton and gravitropism in higher plants. J Plant Growth Regul
21:120–136. https://doi.org/10.1007/s003440010041
Blancaflor EB, Fasano JM, Gilroy S (1998) Mapping the functional roles of cap cells in the response
of Arabidopsis primary roots to gravity. Plant Physiol 116:213–222. https://doi.org/10.1104/pp.
116.1.213
Boonsirichai K, Sedbrook JC, Chen R et al (2003) ALTERED RESPONSE TO GRAVITY is a
peripheral membrane protein that modulates gravity-induced cytoplasmic alkalinization and
lateral auxin transport in plant statocytes. Plant Cell 15:2612–2625
88
6 Gravitropism in Higher Plants: Cellular Aspects