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Reversible calcium-regulated stopcocks in legume sieve tubes.
M Knoblauch1, W S Peters, K Ehlers
1Institut für Allgemeine Botanik und Pflanzenphysiologie, Justus-Liebig-Universität, Senckenbergstrasse 17-21, D-35390 Giessen, Germany. michael.knoblauch@bot1.bio.uni-giessen.de
The Plant Cell
|May 8, 2001
Summary
Legume P-protein crystalloids rapidly disperse to block sieve tubes upon injury or osmotic shock. Divalent cations like calcium trigger this reversible response, controlling plant vascular conductivity.
Area of Science:
- Plant Biology
- Plant Physiology
- Biochemistry
Background:
- Legumes (Fabaceae) possess unique P-protein crystalloids within sieve tubes.
- The precise function of these crystalloids has been a subject of debate.
Purpose of the Study:
- To investigate the dynamic behavior and function of P-protein crystalloids in legume sieve tubes.
- To elucidate the triggers and mechanisms controlling crystalloid dispersal and condensation.
Main Methods:
- Conventional light microscopy
- Electron microscopy
- Confocal laser scanning microscopy
- In situ cell manipulation and observation
Main Results:
- P-protein crystalloids exhibit rapid (<1 sec), reversible transitions between condensed and dispersed states.
- Dispersal, occluding sieve tubes, is triggered by plasma membrane leakage (mechanical injury, permeabilizers) and osmotic shock.
- Divalent cations (Ca2+, Sr2+, Ba2+) are crucial for crystalloid expansion, with chelators preventing the response.
- Reversible cycling between states is achievable in opened cells via cation/chelator exchange.
Conclusions:
- Fabacean P-protein crystalloids are mechanically active protein structures.
- They provide an efficient, cation-dependent mechanism for controlling sieve tube conductivity in response to environmental or mechanical stress.