Fluorescence transients in chloroplasts of Chara corallina cells during transmission of photoinduced signal with the streaming cytoplasm

Intracellular transport assisted by rotatory cytoplasmic movement in characean green algae exerts regulatory influence on plasmalemmal ion channels and photosynthetic activity of chloroplasts. In internodal cells of Chara corallina Klein ex Willd., the photoinduced signal transmitted with the flow of streaming cytoplasm for a distance of 1-3 mm from the site of its emergence was found to release or enhance non-photochemical quenching of chlorophyll fluorescence, depending on the intensity of background illumination in the analyzed area. Under dim background irradiance (10-30 mu mol quanta/(m(2)s)), the distant signal transferred from brightly illuminated 0.4-mm-wide area elicited a transient increase in maximal (F'(m)) and actual (F) fluorescence. However, at higher background irradiances, the arrival of the same signal resulted in strong quenching of F'(m) and in transitory changes of F. The transformation of low light response to F'(m) changes of opposite polarity occurred at some threshold irradiance. Hence, even slight variations in irradiance at the chloroplast layer, attributed to structural features of characean internodes, might promote formation of uneven photosynthetic profile under the influence of signals transmitted along the cell with the cytoplasmic flow. Analysis of chloroplast fluorescence in situ as a function of pH in experiments with intracellular perfusion indicated that the initial response to a distant light stimulus is caused by the transient increase in cytoplasmic pH in the area of fluorescence measurements.