= B. G. Pickard
{c}
<B. G. Pickard> coauthored a 1989 test of gravity sensing in <Arabidopsis thaliana> using a starchless mutant. With <T. Caspar>, <B. G. Pickard> combined microscopic observations of <plastids> with measurements of <gravitropism> in roots and other tissues.<Gravitropism in a starchless mutant of Arabidopsis: implications for the starch-statolith theory of gravity sensing by T. Caspar and B. G. Pickard>[Original byline and Abstract]{ref}
Normal <starch>-containing plastids settled toward the lower side of the tested cells after inversion. The mutant plastids did not behave similarly, yet mutant roots retained a substantial bending response. Comparing short gravity exposures followed by <clinostat> rotation connected an initial stimulus to later curvature.<Gravitropism in a starchless mutant of Arabidopsis: implications for the starch-statolith theory of gravity sensing by T. Caspar and B. G. Pickard>[Abstract: sedimentation, induction intervals and root curvature]{ref}
The work illustrates a useful two-part test of a proposed sensor: establish that the candidate physical process was disrupted, then ask whether the biological response remains. Observing only the mutant's shape would not demonstrate that plastid sedimentation had been altered.
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