Forisome dispersion inVicia fabais triggered by Ca²⁺hotspots created by concerted action of diverse Ca²⁺channels in sieve element

Abstract

Remote-controlled Ca(2+) influx, elicited by electropotential waves, triggers local signaling cascades in sieve elements and companion cells along the phloem of Vicia faba plants. The stimulus strength seems to be communicated by the rate and duration of Ca(2+) influx into sieve elements (SEs). The cooperative recruitment of Ca(2+) channels results in a graded response of forisome culminating in full sieve-tube occlusion. Several lines of evidence are integrated into a model that links the mode and strength of the electropotential waves (EPWs) with forisome dispersion, mediated by transiently enhanced levels of local Ca(2+) release dependent on both plasma membrane and ER Ca(2+) channels.

Involvement of the Sieve Element Cytoskeleton in Electrical Responses to Cold Shocks

“…therein). This Ca 2+ recruitment from internal stores, possibly by Ca 2+ -induced Ca 2+ release from smooth ER cisternae Hafke et al, 2009), may be required for the dispersion of forisomes, the ends of which seem to be in touch with the smooth ER Hafke and van Bel, 2013).…”

“…Furthermore, forisome dispersion within 5 to 50 s after cold shock (Fig. 4I) indicates Ca 2+ influx during the electrical response, since the forisome response requires large local near-plasma membrane Ca 2+ gradients Hafke et al, 2009). Forisome dispersion and DV 1 are strictly correlated, as Figure 5.…”

“…4D), suggesting that the two effectors act on the same Ca 2+ influx system located in the SE plasma membrane. Whether actin filaments also play a role in Ca 2+ release from the internal stores involved in forisome dispersion Hafke et al, 2009;Thorpe et al, 2010), as proposed for animal cells (Janmey, 1998, and refs. therein;Lange and Gartzke, 2006, and refs.…”

“…For instance, K + fluxes are regulated by actin dynamics (Hwang et al, 1997;Liu and Luan, 1998;Chérel, 2004), while Ca 2+ influx into the cytoplasm appears to be mediated by voltage-dependent Ca 2+ -permeable channels associated with microtubules (Mazars et al, 1997;Thion et al, 1998) or by mechanosensitive channels possibly associated with microfilaments (Wang et al, 2004;Zhang et al, 2007). Both types of Ca 2+ -permeable channels probably reside in the SE plasma membrane (Knoblauch et al, 2001;Hafke et al, 2007Hafke et al, , 2009Furch et al, 2009), where they are likely involved in Ca 2+ -dependent systemic signaling Hafke et al, 2009;van Bel et al, 2011;Hafke and van Bel, 2013). These channels are also putative initiators of Ca 2+ -induced signal transduction in SEs, leading to sieve-plate occlusion in response to local cold shocks (Thorpe et al, 2010).…”

Functional Evaluation of Proteins in Watery and Gel Saliva of Aphids

“…Consequently, stylet impalement into a sieve element may trigger the propagation of an electric potential wave resulting in a series of reactions in cells adjacent to the sieve tube (van Bel et al, 2014). All above types of Ca 2+ influx will collectively boost Ca 2+ concentration in sieve-element mictoplasm (Furch et al, 2009; Hafke et al, 2009), which will in turn evoke gating of Ca 2+ -activated Ca 2+ channels (CICR channels; Muir and Sanders, 1996) giving rise to massive Ca 2+ release from the sieve-element endoplasmic reticulum. In conclusion, diverse ways of Ca 2+ influx, brought about by physical events owing to stylet penetration, potentiate the elevation of Ca 2+ level in sieve elements leading to cascades of local and remote events.…”