Distribution of Charasomes in Chara: Banding Pattern and Effect of Photosynthetic Inhibitors

Abstract

Charasomes are structured elaborations of plasmalemma of some Charophytes which may be involved in enhanced transport of ions or inorganic carbon across the plasmalemma. They show a highly non-uniform distribution. We report here a novel method of quantifying charasome population density, using scanning electron microscopy of cell fragments removed from the cell wall. Consistent differences in density can occur in neighbouring regions of the membrane. The distribution of densities is not normal, but is skewed toward lower densities, with large areas of membrane showing no charasomes. Contrary to previous published reports, we found no correlation with acid and alkaline banding patterns. Inhibition of photosynthesis by either dark or DCMU (dichlorophenyl dimethyl urea, an inhibitor of photosystem II) results in a complete loss of charasomes in 1-3 weeks.

Photosynthesis-dependent formation of convoluted plasma membrane domains in Chara internodal cells is independent of chloroplast position

“…5 ). Charasomes were never detected in pale cells lacking well-developed chloroplasts consistent with the observation that photosynthesis is required for charasome development (Bisson et al 1991 ; Chau et al 1994 ; Schmoelzer et al 2011 ). Apart from this prerequisite, every cell of the vegetative part of the thallus of Chara australis seems to have the capacity for charasome formation, although to different extent.…”

“…The possibility to stain charasomes in living cells, with the aid of fluorescent plasma membrane and endocytic markers (Klima and Foissner 2008 ; Schmoelzer et al 2011 ), confirmed the earlier electron microscopical studies about the presence of charasomes in the internodal cells of the main axis, the branches, and the branchlets (Fig. 1a ; Bisson et al 1991 ; Chau et al 1994 ; Franceschi and Lucas 1980 and references therein). Under steady state conditions, charasome size and abundance correlated with the pH banding pattern as revealed by the pH indicating dye phenol red (Fig.…”

“…This is consistent with our observations that charasomes were often found in windows which were produced at the previously charasome-free alkaline regions and, on the other hand, charasomes were often found to be absent from windows produced at the previously charasome-rich acidic zones. More rapidly changing pH banding patterns (within few hours) have been described elsewhere, and it is unlikely that they correspond to the distribution of charasomes because of their slow growth (e.g., Bisson et al 1991 ).…”

“…We also investigated the internodal cells which had been incubated in darkness for 2 weeks in order to degrade the charasomes. These cells likewise produced acid and alkaline bands, although they contained no or only very few, small charasomes which were evenly distributed along the longitudinal cell walls (Bisson et al 1991 ; Schmoelzer et al 2011 ). The results obtained with the internodal cells of the branchlets were similar to those obtained with the internodal cells of the main axis and independent of the size of windows which had a diameter between 60 and 400 μm.…”

Microtubule organization differs between acid and alkaline bands in internodal cells of Chara but bands can develop in the absence of microtubules

“…A feature of the acid bands is enhanced chloroplast development, probably due to increased availability of CO2. In consequence, the acid bands are often darker green in appearance (Price et al 1985;Bisson et al 1991) and this can provide a convenient indicator for the existence of pH bands. In certain environments, Ca 2 § of cellular origin (McConnaughey and Falk 1991) accumulates as CaCO 3 in the walls of alkaline bands resulting in prominent encrustations, also reliable markers of pH banding.…”