Abstract
Characean internodal cells develop alternating patterns of acid and alkaline zones along their surface in order to facilitate uptake of carbon required for photosynthesis. In this study, we used a pH-indicating membrane dye, 4-heptadecylumbiliferone, to study the kinetics of alkaline band formation and decomposition. The differences in growth/decay kinetics suggested that growth occurred as an active, autocatalytic process, whereas decomposition was due to diffusion. We further investigated mutual interactions between internodal cells and found that their alignment parallel to each other induced matching of the pH banding patterns, which was mirrored by chloroplast activity. In non-aligned cells, the lowered photosynthetic activity was noted upon a rise of the external pH, suggesting that the matching of pH bands was due to a local elevation of membrane conductance by the high pH of the alkaline zones of neighboured cells. Finally, we show that the altered pH banding pattern caused the reorganization of the cortical cytoplasm. Complex plasma membrane elaborations (charasomes) were degraded via endocytosis, and mitochondria were moved away from the cortex when a previously acid region became alkaline and vice versa. Our data show that characean internodal cells react flexibly to environmental cues, including those originating from neighboured cells.
Highlights
The multicellular characean green algae are a long established group of the plant kingdom and closely related to higher plants
Since the pH at the alkaline regions rises up to 10, meaningful quantitative measurements are only possible with the aid of ion specific microelectrodes (e.g. Fisahn et al 1989; Bulychev et al 2001a). Both microelectrode and fluorescent dye measurements have shown that alkaline spots grow and coalesce to form the alkaline bands (Bulychev et al 2003; Absolonova et al 2018a)
We investigated the effect of pH band interaction on the organization of the cortical cytoplasm with focus on the distribution of charasomes and cortical mitochondria
Summary
The multicellular characean green algae are a long established group of the plant kingdom and closely related to higher plants Fisahn et al 1989; Bulychev et al 2001a) Both microelectrode and fluorescent dye measurements have shown that alkaline spots grow and coalesce to form the alkaline bands (Bulychev et al 2003; Absolonova et al 2018a). The disadvantage of these two methods is that the changes in the pH can only be measured in the medium outside the cells. We used a fluorescent dye, 4-heptadecylumbiliferone, which monitors the pH at the plasma membrane
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