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

Abstract

Under parabolic flight conditions microgravity is not lower than 3 to 5 times 10 -2 g. In contrast to parabolic flights, sounding rocket flights are virtually vibrational-free allowing microgravity as low as 10 -5 g. Thus, a rotating platform serving as centrifuge allows the precise generation of gravitational forces ranging from 5 to 100 mg (not possible during parabolic flights). On this basis we determined the threshold 1 for optical reflection/absorption changes in Phycomyces to be lower than 25 × 10 -3 g. This compares well with the threshold determination of gravitropism in Phycomyces on a clinostat centrifuge. Kinetics of gravity-induced absorption changes and gravity as generated by the on-board centrifuge do not coincide but show a distinctive hysteresis with a latency of 4 s (75 mg-ramp, pull-up).