Propagation of photoinduced signals with the cytoplasmic flow along Characean internodes: evidence from changes in chloroplast fluorescence and surface pH
Emerging evidence suggests that cytoplasmic streaming can regulate the plasma-membrane H+ transport and photosynthetic electron flow. Microfluorometric and surface pH measurements on Chara corallina internodes revealed the transmission of photoinduced signals by the cytoplasmic flow for a distance of few millimeters from the site of stimulus application. When a 30-s pulse of bright light was locally applied, the downstream cell regions responded with either release or enhancement of non-photochemical quenching of chlorophyll fluorescence, depending on the background irradiance of the analyzed cell area. Under dim background irradiance (<20 μmol m−2 s−1), the arrival of the distant signal from the brightly illuminated 400-μm-wide zone elevated the maximal fluorescence F m ′ in the analyzed downstream area, whereas at higher background irradiances it induced strong quenching of F m ′ . At intermediate irradiances the increase and decrease in F m ′ appeared as two successive waves. The transition between the F m ′ responses of opposite polarities occurred at a narrow threshold range of irradiances. This indicates that inevitable slight variations in irradiance at the bottom chloroplast layer combined with the cyclosis-transmitted signals may contribute to the formation of a photosynthetic activity pattern. The rapid cyclosis-mediated release of non-photochemical quenching, unlike the delayed response of opposite polarity, was associated with opening of H+ (OH−)-conducting plasma membrane channels, as evidenced by the concurrent alkaline pH shift on the cell surface. It is proposed that the initial increase in F m ′ after application of a distant photostimulus is determined, among other factors, by the wave of alkaline cytoplasmic pH.
KeywordsChlorophyll fluorescence Cyclosis Cytoplasmic pH Localized illumination Long-distance interactions Spatial patterns
Area of inspection
The maximum chlorophyll fluorescence induced by saturating light pulse under actinic light
Photon flux density
This work was supported by the Russian Foundation for Basic Research (Project No. 10-04-00968-a).
Conflict of interest
The authors declare that they have no conflict of interest.
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