studied (sometimes simultaneously) with tropisms in spaceflight. For example, both
gravitropism and circumnutations of lentil roots were measured in an experiment on the
space shuttle (Antonsen et al. 1995; Perbal and Driss-Ecole 1994). These authors found
that roots in microgravity displayed oscillations in growth along with gravitropic re-
sponses that varied as the function of the stimulation time. Ground-based studies with
Arabidopsishave shown that roots grown on a random position machine make large
loops in the right-handed direction, whereas in 1g, roots display a wavy, right-handed
slant (Piconese et al. 2003). Similarly, nastic movements in coleoptiles of wheat
seedlings were observed in plants in microgravity (Heathcote et al. 1995b). The extent
of the interactions between oscillatory movements and gravitropism is unclear. Some ev-
idence with plants mutated in genes involved in gravity responses has suggested that the
oscillatory movements are coupled to gravitropism with auxin distribution being an
overlapping element (Piconese et al. 2003; Kitazawa et al. 2005; reviewed in Kiss 2006).
In contrast, evidence from spaceflight experiments has indicated that a variety of plants
do have circumnutations in microgravity, suggesting that gravity is not necessary for cir-
cumnutation (Brown et al. 1990; Heathcote et al. 1995b; Antonsen et al. 1995). Future
studies using microgravity may help to define the roles of gravity in these types of plant
movements.
8.8 Space flight hardware used to study tropisms
The types of hardware that have been used to study plant tropisms in microgravity are
variable since the spaceflight conditions can influence the hardware design. For example,
experiments that did not have crew available, such as experiments performed on sound-
ing rockets, biosatellites, or some space shuttle/station experiments, needed to have fully
automated hardware. Other experiments had crew interaction, which increased the com-
plexity associated with these types of studies. Some examples of the different types of
plant facilities used in microgravity to study plant tropisms are described in the next sec-
tion. In addition, hardware for plant growth studies in general has been reviewed (Lork
1988; Porterfield et al. 2003).
The use of sounding rockets or biosatellites is a relatively cost-effective way to per-
form simple experiments in microgravity. Cress plants grown in sounding rockets
(TEXUS program) were housed in containers that had temperature recording devices and
an automatic fixation system (Tewinkel et al. 1991). The fixation system automatically
flooded the containers holding the plants with chemical fixatives. Such in-flight fixation
allowed further analysis on the ground to identify plastid location during the excursion
into microgravity.
Other hardware that has been used to study gravity effects on plant tropisms and
growth is the Biological Research in Canister (BRIC) system. The canisters are basically
light-tight cylinders that are placed aboard the Space Shuttle for experiments that have
little or no crew involvement. One such experiment with the BRIC system studied pho-
totropism and gravitropism interactions in moss. This hardware incorporated LEDs (light
emitting diodes) (STS-87) for unilateral illumination and a chemical fixation system for
moss plants grown in Petri dishes (Kern et al. 1999).