Seeds of Arabidopsis thaliana were exposed to hypergravity environments (2g and 6g) and germinated during centrifugation.
Seedlings grew for 2 and 4 days before fixation. In all cases, comparisons were performed against an internal (subjected to
rotational vibrations and other factors of the machine) and an external control at 1g. On seedlings grown in hypergravity
the total length and the root length were measured. The cortical root meristematic cells were analyzed to investigate the
alterations in cell proliferation, which were quantified by counting the number of cells per millimeter in the specific cell
files, and cell growth, which were appraised through the rate of ribosome biogenesis, assessed by morphological and morphometrical
parameters of the nucleolus. The expression of cyclin B1, a key regulator of entry in mitosis, was assessed by the use of
a CYCB1:GUS genetic construction. The results showed significant differences in some of these parameters when comparing the
1g internal rotational control with the 1g external control, indicating that the machine by itself was a source of alterations.
When the effect of hypergravity was isolated from other environmental factors, by comparing the experimental conditions with
the rotational control, cell proliferation appeared depleted, cell growth was increased and there was an enhanced expression
of cyclin B1. The functional meaning of these effects is that cell proliferation and cell growth, which are strictly associated
functions under normal 1g ground conditions, are uncoupled under hypergravity. This uncoupling was also described by us in
previous experiments as an effect of microgravity, but in an opposite way. Furthermore, root meristems appear thicker in hypergravity-treated
than in control samples, which can be related to changes in the cell wall induced by altered gravity.