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Calcium in gravitropism. A re-examination
1Institute of Ecology and Resource Management, University of Edinburgh, UK.
Planta
|September 7, 2001
Summary
Calcium (Ca2+) plays a role in plant gravitropism, but its exact function remains unclear. New research explores how intracellular calcium and wall-bound calcium interact to influence plant growth responses.
Area of Science:
- Plant Biology
- Biochemistry
Background:
- A strong link between calcium (Ca2+) and gravitropism has been assumed for over a decade.
- Evidence suggests Ca2+ movement in the cell wall regulates extension growth, and intracellular Ca2+ mediates signaling in statocytes.
Purpose of the Study:
- To clarify the ambiguous role of Ca2+ in plant gravitropism.
- To investigate the interplay between wall-bound Ca2+ and free intracellular Ca2+ ([Ca2+]i) in gravitropic responses.
- To present new findings on cytosolic Ca2+ manipulation in tip-growing cells applicable to gravitropism.
Main Methods:
- Reviewing existing evidence on Ca2+ and gravitropism.
- Discussing the limitations of current experimental approaches.
- Proposing the use of transgenic aequorin targeted to columella cells for future research.
- Presenting new data on cytosolic Ca2+ in tip-growing cells.
Main Results:
- The precise mechanisms by which Ca2+ influences gravitropism are still uncertain.
- Observed Ca2+ redistributions may not be sufficient to induce plant bending.
- Direct evidence linking changes in [Ca2+]i to the initiation or transduction of gravitropic signals is lacking.
- New information on cytosolic Ca2+ control in tip-growing cells is provided.
Conclusions:
- The relationship between Ca2+ and gravitropism is substantial but circumstantial.
- Further research, particularly using advanced imaging technologies like transgenic aequorin, is needed to resolve the role of intracellular Ca2+.
- Findings on tip-growing cells offer potential insights into gravitropic signaling models like the Chara rhizoid.