Calcium in gravitropism.  A re-examination.
For more than a decade it has been assumed that there is a strong relationship between Ca2+ and gravitropism. There is evidence to suggest that the movement of Ca2+ in the wall might regulate extension growth and that free intracellular Ca2+ might mediate signalling in statocytes. However, it is unlikely that changes in either wall Ca2+ or the concentration of free intracellular calcium, [Ca2+]i, act independently of each other. This results in ambiguity in both experimentation and interpretation of experimental information. It is also uncertain that the observed redistributions of wall Ca2+ are sufficient to induce bending and there is at present no direct evidence from measurement or imaging that changes in [Ca2+]i initiate or transduce gravitropic signals. The evidence relating Ca2+ to gravitropism is therefore substantial but still circumstantial. The involvement of free intracellular Ca2+ might best be tested using the new technologies of transgenic aequorin targeted to columella cells and thus resolve this important question. New information which relates control or orientation of tip-growing cells, such as pollen tubes, to cytosolic Ca2+ manipulation is presented. This information may be directly applicable to a gravitropic model system studied for many years, the Chara rhizoid.
Sinclair
W
W
Institute of Ecology and Resource Management, University of Edinburgh, UK.
Trewavas
A J
AJ
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism* / Q000502:physiology; D002473:Cell Wall / Q000187:drug effects / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D000460:Chlorophyta / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology*; D018466:Gravity Sensing / Q000187:drug effects / Q000502:physiology*; D018518:Plant Root Cap / Q000187:drug effects; D015290:Second Messenger Systems / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
D002147:Calmodulin; D002614:Chelating Agents; D000001:Calcimycin; D004533:Egtazic Acid; D004492:Edetic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium