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

Abstract

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 (ΔA460–665) 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 × 10−2 g) 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 × 10−2 g, 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 × time) of about 3 × 10−3 g 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.

Gravireception in <i>Phycomyces</i>: Threshold Determination on the Sounding Rocket TEXUS 50

“…The total length of the rocket is about 13 m, the length of the payload 5.189 m. from the Northern Regional Research Laboratory, USDA, Peoria, IL, USA. Sporangiophores of Phycomyces were raised as described previously [15]. For short, they were grown in glass shell vials (1 cm diameter × 4 cm height; Flachbodengläser, AR Klarglas, Münnerstädter Glaswarenfabrik, Münnerstadt, Germany) on a synthetic solid medium with glucose.…”

“…Sporangiophores that are exposed to sudden acceleration changes display nearly instantaneous absorption changes, so-called GIACs [15]. In highly scattering samples such as SPPHs absorbance and reflection of light are intimately correlated [16] justifying the term "GIAC", even if reflection is measured.…”

Gravireception in Phycomyces Blakesleeanus and Arabidopsis Thaliana: Hysteretic Behavior of Primary Reactions

“…During the phases of hypergravity the g-vector is perpendicular to the floor of the airplane such that persons and objects can stand "normally" as on ground or during horizontal flight. The airplane, airbus A300-ZERO-G located at the international airport of Bordeaux-Merignac and serviced by the company Novespace, is flying the parabolas depending on the weather conditions either over the Mediterranean Sea or over the Atlantic Ocean near the coast of the Bretagne (details in Schmidt and Galland 2004).…”

Gravity Induced Absorption Changes in Phycomyces blakesleanus and Coleoptiles of Zea mays as Measured on the Drop Tower in Bremen (FRG)

“…Until the appearance of stage-4b sporangiophores (i.e. with sporangium) of 2.5 cm length the material was kept in transparent plastic boxes at ambient temperature (19-21 • C) under white incandescent light fluence rate (0.5 W m −2 ) (Schmidt and Galland 2004).…”