Spread the news: systemic dissemination and local impact of Ca²⁺ signals along the phloem pathway.
We explored the idea of whether electropotential waves (EPWs) primarily act as vehicles for systemic spread of Ca(2+) signals. EPW-associated Ca(2+) influx may trigger generation and amplification of countless long-distance signals along the phloem pathway given the fact that gating of Ca(2+)-permeable channels is a universal response to biotic and abiotic challenges. Despite fundamental differences, both action and variation potentials are associated with a sudden Ca(2+) influx. Both EPWs probably disperse in the lateral direction, which could be of essential functional significance. A vast set of Ca(2+)-permeable channels, some of which have been localized, is required for Ca(2+)-modulated events in sieve elements. There, Ca(2+)-permeable channels are clustered and create so-called Ca(2+) hotspots, which play a pivotal role in sieve element occlusion. Occlusion mechanisms play a central part in the interaction between plants and phytopathogens (e.g. aphids or phytoplasmas) and in transient re-organization of the vascular symplasm. It is argued that Ca(2+)-triggered systemic signalling occurs in partly overlapping waves. The forefront of EPWs may be accompanied by a burst of free Ca(2+) ions and Ca(2+)-binding proteins in the sieve tube sap, with a far-reaching impact on target cells. Lateral dispersion of EPWs may induce diverse Ca(2+) influx and handling patterns (Ca(2+) signatures) in various cell types lining the sieve tubes. As a result, a variety of cascades may trigger the fabrication of signals such as phytohormones, proteins, or RNA species released into the sap stream after product-related lag times. Moreover, transient reorganization of the vascular symplasm could modify cascades in disjunct vascular cells.
Institute of General Botany, Justus-Liebig University, Senckenbergstrasse 17, D-35390 Giessen, Germany.
Aart J E
AJ
van Bel
Alexandra C U
AC
Furch
Torsten
T
Will
Stefanie V
SV
Buxa
Rita
R
Musetti
Jens B
JB
Hafke
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D055724:Electrophysiological Phenomena; D052585:Phloem / Q000378:metabolism*; D059828:Plant Cells / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism; D015398:Signal Transduction
D015220:Calcium Channels; D010940:Plant Proteins; D002118:Calcium
Calcium hotspots; calcium signatures; eletropotential waves; long-distance signalling; phloem pathway; sieve element cytoskeleton; sieve elements; sieve tube occlusion.