Summary
Tip cells of dark-grown protonemata of the mossCeratodon purpureus are negatively gravitropic (grow upward). They possess a unique longitudinal zonation: (1) a tip group of amylochloroplasts in the apical dome, (2) a plastid-free zone, (3) a zone of significant plastid sedimentation, and (4) a zone of mostly non-sedimenting plastids. Immunofluorescence of vertical cells showed microtubules distributed throughout the cytoplasm in a mostly axial orientation extending through all zones. Optical sectioning revealed a close spatial association between microtubules and plastids. A majority (two thirds) of protonemata gravistimulated for >20 min had a higher density of microtubules near the lower flank compared to the upper flank in the plastid-free zone. This apparent enrichment of microtubules occurred just proximal to sedimented plastids and near the part of the tip that presumably elongates more to produce curvature. Fewer than 5% of gravistimulated protonemata had an enrichment in microtubules near the upper flank, whereas 14% of vertical protonemata were enriched near one of the side walls. Oryzalin and amiprophos-methyl (APM) disrupted microtubules, gravitropism, and normal tip growth and zonation, but did not prevent plastid sedimentation. We hypothesize that a microtubule redistribution plays a role in gravitropism in this protonema. This appears to be the first report of an effect of gravity on microtubule distribution in plants.
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Abbreviations
- APM:
-
amiprophos-methyl
- DIC:
-
differential interference contrast
- DMSO:
-
dimethyl sulfoxide
- EGTA:
-
ethylene glycolbis-(β-amino-ethylether) N,N,N',N'-tetraacetic acid
- FITC:
-
fluorescein isothiocyanate
- GS:
-
gravitropic stimulus
- MT:
-
microtubule
- PIPES:
-
piperazine-N,N'-bis-2-ethanesulfonic acid
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Schwuchow, J., Sack, F.D. & Hartmann, E. Microtubule distribution in gravitropic protonemata of the mossCeratodon . Protoplasma 159, 60–69 (1990). https://doi.org/10.1007/BF01326635
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DOI: https://doi.org/10.1007/BF01326635