Spatio-temporal patterns of photosystem�II activity and plasma-membrane proton flows in Chara corallina cells exposed to overall and local illumination

Abstract

Pulse-amplitude modulated microfluorometry and an extracellular pH microprobe were used to examine light-induced spatial heterogeneity of photosynthetic and H(+)-transporting activities in cells of Chara corallina Klein ex Willd. Subcellular domains featuring different PSII photochemical activities were found to conform to alternate alkaline and acid zones produced near the cell surface, with peaks of PSII activity correlating with the position of acid zones. Buffers eliminated pH variations near the cell surface but did not destroy the variations in PSII photochemical yield (deltaF/Fm'). When a dark-adapted cell was exposed to actinic light, the PSII effective yield decreased within 5-15 min in the alkaline regions but rose after the initial decline in the acid regions. The light-induced decrease in deltaF/Fm' in the alkaline regions occurred prior to or synchronously with the steep rise in local pH. The kinetics of deltaF/Fm', Fm', and F observed in alkaline regions under overall illumination of Chara cells were replaced by those typical of acid regions, when the illumination area size was restricted to 1.5-2 mm. The data show that photoinduced patterns in photosynthetic activity are not predetermined by the particular structural organization of alkaline and acid cell regions but are subject to dynamic changes.

Plasma Membrane Domains Participate in pH Banding of Chara Internodal Cells

“…A close relationship between banding and photosynthesis has been confirmed by several studies showing enhanced photosynthesis at the acid regions in spite of a homogeneous distribution of chloroplasts (Lucas and Smith 1973, Plieth et al 1994, Bulychev et al 2001a, Bulychev and Vredenberg 2003). There is a broad consensus that the higher rates of photosynthesis at the acid regions are brought about by an enhanced availability of CO 2 after external conversion of HCO − 3 by a periplasmic carbonic anhydrase, but there also exist hypotheses about pH-dependent generation of bicarbonate or uptake of HCO − 3 (co-transport with protons) and internal conversion into CO 2 at either the acid or the alkaline regions of the cell (Ferrier 1980, Smith and Walker 1980, Walker et al 1980, Lucas 1983, Price et al 1985, Mimura et al 1993, Chau et al 1994, Ray et al 2003).…”

“…This is consistent with the finding that internodal cells of the main axis have a less important role in photosynthesis than the branchlets (Schulte et al 1994). Whether the development of charasomes and the pH banding is a prerequisite for local differences in the rate of photosynthesis or a secondary event remains to be investigated (Bulychev and Vredenberg 2003). …”

“…Together with an increased availability of carbon, acid bands feature enhanced photosynthesis, indicated through higher PSII activity and brighter Chl fluorescence, compared with alkaline regions (Plieth et al 1994, Bulychev et al 2001a, Bulychev and Vredenberg 2003). An intimate association of charasomes with subjacent chloroplasts has already been reported by Franceschi and Lucas (1980) and could also be observed in this study, indicating a close collaboration in energy metabolism.…”

Effect of cytoplasmic streaming on photosynthetic activity of chloroplasts in internodes of Chara corallina

“…The disparate influ ence of general and local illumination on fluorescence induction curves of in Chara cell chloroplasts (Fig. 2) was noted previously [12,14], but the causes of these distinctions remained unresolved up to now. Our results indicate clearly that the high quantum effi ciency of PSII and the low NPQ in chloroplasts of partly illuminated cells are due to continuous renewal of the medium around the illuminated chloroplasts.…”

“…Young cells without calcium depositions were placed in a transparent Plexiglas chamber, which was mounted on the stage of Axiovert 25 CFL inverted microscope (Zeiss, Germany). The fluorescence parameters of chloroplasts were mea sured on a microscopic cell region (~100 μm in diam eter) as described previously [12,13]. The coefficient of non photochemical quenching was calculated from the formula NPQ = (F m -/ where F m and designate the maximal yields of chlorophyll fluores cence induced by the saturating light pulse after dark adaptation and under actinic light, respectively.…”