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Gravisensitivity of cress roots: investigations of threshold values under specific conditions of sensor physiology in microgravity *
Author(s) -
VOLKMANN D.,
TEWINKEL M.
Publication year - 1996
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1996.tb00435.x
Subject(s) - clinostat , chemistry , stimulus (psychology) , biophysics , hypergravity , botany , stimulation , weightlessness , centrifuge , physics , biology , neuroscience , nuclear physics , psychology , astrobiology , psychotherapist , astronomy
The minimum dose (dose = stimulus × time), one of three threshold values related to gravity, was determined under microgravity conditions for cress roots. Seedlings were cultivated on a 1 g centrifuge in orbit and under microgravity, respectively. After continous stimulation on a threshold centrifuge, minimum doses of 20–30 g s for microgravity roots and 50–60 g s for roots grown on a 1 g centrifuge were estimated, which indicated that micro‐gravity roots have a higher sensitivity than 1 g roots. These results do not confirm the threshold value of 12 g s which was determined for cress roots using the slow rotating clinostat. Following application of intermittent stimuli to microgravity‐grown roots, gravitropic responses were observed after two stimuli of 13‐5 g s separated by a stimulus‐free interval of 118 s. Generally, this demonstrates that higher plants are able to ‘sum up’ stimuli which are below the threshold value. Microscopic investigations of the cellular structure corresponding to stimulations in the range of the threshold value demonstrated a small displacement of statoliths in root statocytes. No significant correlation was observed between gravitropic curvature and statolith displacement. If the statolith theory is accepted, it can be concluded that stimulus transformation must occur in the cytoplasm in the near vicinity of the statoliths and that this transformation system – probably involving cytoskeletal elements – must have been affected during microgravity seedling cultivation.