Sieve Element Capo Channels as Relay Stations between Remote Stimuli and Sieve Tube Occlusion in Vicia faba.

摘要

Damage induces remote occlusion of sieve tubes in Vicia faba by forisome dispersion, triggered during the passage of an electropotential wave (EPW). This study addresses the role of Capo channels and cytosolic Capo elevation as a link between EPWs and forisome dispersion. Capo channel antagonists affect the initial phase of the EPW as well as the prolonged plateau phase. Resting levels of sieve tube Capo of ~50 nM were independently estimated using Capo-selective electrodes and a Capo-sensitive dye. Transient changes in cytosolic Capo were observed in phloem tissue in response to remote stimuli and showed profiles similar to those of EPWs. The measured elevation of Capo in sieve tubes was below the threshold necessary for forisome dispersion. Therefore, forisomes need to be associated with Capo release sites. We found an association between forisomes and endoplasmic reticulum (ER) at sieve plates and pore-plasmodesma units where high-affinity binding of a fluorescent Capo channel blocker mapped an increased density of Capo channels. In conclusion, propagation of EPWs in response to remote stimuli is linked to forisome dispersion through transiently high levels of parietal Capo, release of which depends on both plasma membrane and ER Capo channels.