Journal Article

Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes

Aart J. E. van Bel, Peters, Winfried S., Knoblauch, Michael, Ehlers, Katrin

2001

Overview

Sieve tubes of legumes (Fabaceae) contain characteristic P-protein crystalloids with controversial function. We studied their behavior by conventional light, electron, and confocal laser scanning microscopy. In situ, crystalloids are able to undergo rapid (<1 sec) and reversible conversions from the condensed resting state into a dispersed state, in which they occlude the sieve tubes. Crystalloid dispersal is triggered by plasma membrane leakage induced by mechanical injury or permeabilizing substances. Similarly, abrupt turgor changes imposed by osmotic shock cause crystalloid dispersal. Because chelators generally prevent the response, divalent cations appear to be the decisive factor in crystalloid expansion. Cycling between dispersal and condensation can be induced in opened cells by repetitive exchange of bathing media containing either Ca2+ or chelators. Sr2+ and Ba2+, but not Mg2+, are equally active. In conclusion, the fabacean P-protein crystalloids represent a novel class of mechanically active proteinaceous structures, which provide an efficient mechanism with which to control sieve tube conductivity.

• Publisher: American Society of Plant Physiologists,American Society of Plant Biologists
• Subject: Biological Transport / Biological Transport - drug effects / Biomechanical Phenomena / calcium / Calcium - pharmacology / Cations / Cell Membrane Permeability / Cell membranes / Crystals / Dispersal / drug effects / Fabaceae / Fabaceae - physiology / Fabaceae - ultrastructure / Hydrostatic Pressure / inorganic ions / Lupinus polyphyllus / metabolism / Microscopy / organelles / pharmacology / Phaseolus vulgaris / Phloem / Physiological regulation / physiology / Plant cells / Plant Leaves / Plant Leaves - physiology / Plant Leaves - ultrastructure / plant proteins / Plant Proteins - metabolism / Plants / Plants, Medicinal / plasma membrane / Protein Conformation / Protein Conformation - drug effects / Sieve elements / Sieve tubes / Species Specificity / turgor / Turgor pressure / ultrastructure / Vicia faba