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First published online April 30, 2004; 10.1104/pp.103.033282

Plant Physiology 135:183-192 (2004)
© 2004 American Society of Plant Biologists

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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Optospectroscopic Detection of Primary Reactions Associated with the Graviperception of Phycomyces. Effects of Micro- and Hypergravity1

Werner Schmidt and Paul Galland*

Fachbereich Biologie, Philipps-Universität, D–35032 Marburg, Germany

The graviperception of sporangiophores of the fungus Phycomyces blakesleeanus involves gravity-induced absorbance changes (GIACs) that represent primary responses of gravitropism (Schmidt and Galland, 2000). GIACs ({Delta}A460–665) of sporangiophores were measured in vivo with a micro-dual wavelength spectrometer at 460 and 665 nm. Sporangiophores that were placed horizontally displayed an instant increase of the GIACs while the return to the vertical position elicited an instant decrease. The GIACs are specific for graviperception, because they were absent in a gravitropism mutant with a defective madJ gene. During parabola flights hypergravity (1.8g) elicited a decrease of the GIACs, while microgravity (0 ± 3 x 10–2g) elicited an instant increase. Hypergravity that was generated in a centrifuge (1.5–6.5g) elicited also a decrease of the GIACs that saturated at about 5g. The GIACs have a latency of about 20 ms or shorter and are thus the fastest graviresponses ever measured for fungi, protists, and plants. The threshold for eliciting the GIACs is near 3 x 10–2g, which coincides numerically with the threshold for gravitropic bending. In contrast to gravitropic bending, which requires long-term stimulation, GIACs can be elicited by stimuli as short as 20 to 100 ms, leading to an extremely low threshold dose (acceleration x time) of about 3 x 10–3g s, a value, which is four orders of magnitude below the ones described for other organisms and which makes the GIACs of Phycomyces blakesleeanus the most sensitive gravi-response in literature.

1 This work was supported by a grant from the DLR/BMBF (Deutsches Zentrum für Luft- und Raumfahrt, and Bundesministerium für Bildung und Forschung). The parabola flights were financed by the ESA (European Space Agency) and by the DLR. The DLR financed and supported the experiments involving the usage of the human centrifuge at the DLR in Köln-Porz.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.033282.

* Corresponding author; e-mail galland{at}staff.uni-marburg.de; fax 49–6421–2822057.

Received September 13, 2003; returned for revision December 28, 2003; accepted January 21, 2004.

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