Kinetics of amyloplast sedimentation in gravistimulated maize coleoptiles.
Inner mesophyll cells from coleoptiles of Zea mays L. cv. Merit were fixed after varying periods of gravistimulation.  A statistically significant amount (17-21%) of amyloplast sedimentation occurred in these cells after 30 s of gravistimulation.  The presentation time is approx. 40 s or less.  The accumulation of amyloplasts near the new lower wall shows a linear relationship to the logarithm of the gravistimulation time (r=0.92 or higher).  The intercept of this line with the baseline value of amyloplasts in vertical coleoptiles indicates that the number of amyloplasts on the new lower wall begins increasing 11-15 s after the onset of gravistimulation.  Direct observations of living cells confirm that many amyloplasts sediment within less than 15-30 s.  These rapid kinetics are consistent with the classical statolith hypothesis of graviperception involving the sedimentation of amyloplasts to the vicinity of the new lower wall.
Sack
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Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, NY 14853, USA.
Suyemoto
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Leopold
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D018548:Cotyledon / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D006112:Gravitation; D018522:Gravitropism / Q000502:physiology; D018466:Gravity Sensing / Q000502:physiology*; D018715:Microscopy, Video; D018087:Plastids / Q000502:physiology*; D013997:Time Factors; D003313:Zea mays / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure