Gravisensitivity of cress roots.

The minimum dose (stimulus x time [gs]) eliciting a visible gravitropic response, has been determined using continuous and intermittent stimulation and two different accelerations at 1 g and 0.l g. The minimum dose of 20-30 gs estimated for microgravity roots and of 50-60 gs for roots grown on a 1 g-centrifuge indicated a higher sensitivity of microgravity roots.

Statocyte polarity and gravisensitivity in seedling roots grown in microgravity.

Space experiments have offered a unique opportunity to analyse the mechanism of gravisensing in plant roots. It has been shown that the strict structural polarity of statocytes observed on the ground is perturbed in microgravity: the amyloplasts move towards the proximal half of the cell and, at least in some cases, the nucleus becomes located further away from the (proximal) plasma membrane. It has thus been demonstrated that the amyloplasts do not move freely in the cytoplasm.

Gravisensitivity of cress roots: investigations of threshold values under specific conditions of sensor physiology in microgravity.

The minimum dose (dose = stimulus x time), one of three threshold values related to gravity, was determined under microgravity conditions for cress roots. Seedlings were cultivated on a 1g centrifuge in orbit and under microgravity, respectively. After continuous stimulation on a threshold centrifuge, minimum doses of 20-30 gs for microgravity roots and 50-60 gs for roots grown on a 1g centrifuge were estimated, which indicated that microgravity roots have a higher sensitivity than 1g roots.

Graviresponse of cress roots under varying gravitational forces.

During the spacelab mission IML-2 threshold values concerning gravity controlled growth processes have been estimated in order to test the reciprocity law (dose = stimulus x time = constant) for the first time under exact physiological conditions. Cress seedlings have been cultivated from dry seeds under conditions of microgravity and on a 1 x g-centrifuge in the ESA-BIORACK. With the help of NIZEMI--the slow rotating centrifuge microscope--these seedlings have been stimulated by different doses ranging from 12 to 60 x g x s.

Automatic fixation facility for plant seedlings in the TEXUS Sounding Rocket Programme.

Automatic chemical fixation of plant seedlings within a 6 min period of reduced gravity (10(-4)g) was performed on three ballistic rocket flights provided by the German Sounding Rocket Programme TEXUS (Technologische Experimente unter Schwerelosigkeit = Technological Experiments in Microgravity). The described TEXUS experiment module consists of a standard experiment housing with batteries, cooling and heating systems, timer, and a data recording unit. Typically, 60 min before launch an experiment plug-in unit containing chambers with the plant material, the fixation system, and the temperature sensors is installed into the module which is already integrated in the payload section of the sounding rocket (late access).