Dependence of Gravity Induced Absorption Changes on the Earth’s Magnetic Field as Measured during Parabolic Flight Campaigns ()
1. Introduction
Working several years on the measurement and analysis of Light Induced Absorption Changes in plants and fungi (LIACs), we expanded this idea to gravisensing, searching for (minute) Gravity Induced Absorption Changes (GIACs). The basic idea is that any stimulus such as light or gravity which is discerned by an organism, consequently causes some kinds of molecular change which could be spectroscopically detectable. For this purpose, we designed a novel, highly sensitive micro dual wavelength spectrophotometer [1,2] and we detected the first GIACs in laboratory bound experiments simply by tilting gravisensitive specimen (Phycomyces, coleoptiles of maize, oat and Arabidopsis [2]) into the horizontal position (a crude test for GIAC-activity). This was the starting point of our activities between 2000 and 2012 to come: eleven parabolic flight campaigns (PFCs, [1-5]), a drop tower campaign [6] and two sounding rocket campaigns (Nov. 2009 and a second one in March 2013, to be published).
During our recent PFCs, we observed a till then unexplainable small but significant variability of the measuring signals (GIACs). As discussed here, these discrepancies could be finally traced back to the various flight directions, because these, in turn, are inevitably associated with changes of the earth’s magnetic field. The ability to respond to magnetic fields is ubiquitous among the five kingdoms of organisms. E.g., Palmer [7] reported that the green alga Volvox aureus swims parallel to the horizontal component of the earth’s magnetic field (Hx as discussed in the present case below). Except for the various forms of orientation of mammals, migrating birds and microorganisms, so far, no biological advantage of any other magneto response is immediately obvious. Thus, most studies as the present one remain largely on a phenomenological level and typically lack mechanistic insight. Even if ferritin has been found in Phycomyces [8], it only has been discussed in magneto reception of various other specimens such as bacteria [9], eusocial insects [10] or honey bees [11]. Besides the present study, so far no physiological and biochemical reactions in Phycomyces blakesleeanus to magnetic fields have been reported. In addition to ferrimagnetism which is well-known in bacterial magneto taxis [9] and animal navigation [12], there are two further mechanisms discussed: 1) the “radicalpair mechanism” relying on the singlet-triplet intercon-version rates of a radical by weak magnetic fields [13], or 2) the “ion cyclotron resonance” mechanism [14]. According to this, ions should circulate in a plane perpendicular to an external magnetic field with their Lamor frequenccies. This will interfere with an alternating electromagnetic field like in parabolic flight maneuvers. Both mechanisms might provide the physical basis of future investigations of biological magneto reception.
Using two three-dimensional magnetic sensors, we detected a clear-cut correlation of GIACs and particularly the Hx component of the magnetic field of the earth, i.e. as a function of flight direction, i.e. the azimuth angle. During a flight day, the AIRBUS ZERO G conducts 31 parabolas, each of which lasts about three minutes including a period just under half a minute of weightlessness.
2. Material and Methods
2.1. Strains and Culture Conditions
The wild-type strain of Phycomyces blakesleeanus (Burgeff) is NRRL1555 (-) originally obtained from the Northern Regional Research Laboratory, USDA, Peoria, IL, USA. They were grown in glass shell vials (1 cm diameter × 4 cm height; Flachbodengläser, AR Klarglas, Münnerstädter Glaswaren-fabrik, Münnerstadt, Germany) on a synthetic solid medium with glucose. 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˚C - 21˚C) under white incandescent light fluence rate (0.5 Wm−2). One remark remains to be cogent: Even if the samples are grown under well controlled conditions in a cave of Chateaux Sentoux near the airport, depending on the season the transport to the airport and finally into the plane gives rise to harsh strain (change of temperature, air pressure, humidity).
2.2. Parabolic Flights with the A300-ZERO-G
So far, GI-ACs in response to microand hypergravity were monitored during roughly 1000 parabolas and 11 campaigns organized by the DLR and ESA during the years 2002-2012 (Figure 1(a)). During a parabolic flight day 31 parabolas (counting from 0 to 30), are flown consecutively in a time period of about 180 minutes covering a distance of approximately 2200 km. Between single parabolas the airplane flies for two minutes in normal modus (1 × g). After every five parabolas an intermission of about 4 minutes of normal flight occurs before the maneuvers of another five parabolas—generally after directional change—is resumed. Each parabola consists of three phases: 1) 25 s at 1.8 × g (pull-up phase; maximal inclination angle = 47˚), 2) 22 s in microgravity (5 × 10−2 g, actual parabola), and 3) 25 s at 1.8 × g (pull-out phase, maximal inclination angle of −45˚, i.e. downward flight). 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) is located at the international airport of Bordeaux-Merignac and serviced by the company Novespace. The parabolas discussed here were flown over the Atlantic Ocean off the coast of Brittany (cf. Figures 4, 5 and 7).
Figure 1(b) shows the assignment of the three space