Dark‐induced chloroplast relocation depends on actin filaments in the liverwort Apopellia endiviifolia along with the light‐ and cold‐induced relocations

Abstract

Chloroplasts move to the periclinal walls of cells under weak light to harness light energy for photosynthesis and to anticlinal walls to avoid strong light. These responses involve the cytoskeleton components microtubules and/or actin filaments. In the dark, chloroplasts move to the anticlinal cell walls bordering neighbouring cells (dark‐positioning response), but this response in various plants normally requires a prolonged dark incubation period, which has hampered analysis. However, we recently demonstrated the dark‐positioning response that can be induced after a short period of dark incubation in the liverwort Apopellia endiviifolia. Here, we investigated whether the cytoskeleton components function in the dark‐positioning response of A. endiviifolia cells. Microtubules and actin filaments were fluorescently visualised in A. endiviifolia cells and were disrupted following treatment with the microtubule and actin filament polymerisation inhibitors. The dark‐positioning response was unaffected in the cells with disrupted microtubules. By contrast, the dark‐positioning response was inhibited by the disruption of actin filaments. The disruption of actin filaments also restricted chloroplast mobility during light‐ and cold‐dependent chloroplast movements in A. endiviifolia. Therefore, the dark‐positioning response of A. endiviifolia depends solely on an actin filament‐associated motility mechanism, as do the light‐ and cold‐dependent chloroplast responses.

Functional comparison of phototropin from the liverworts Apopellia endiviifolia and Marchantia polymorpha

“…Comparison of the photo-thermochemical data for Aephot and Mpphot revealed that Aephot was less sensitive to variations in light and temperature and showed weaker photoproduct formation for the LOV domain than Mpphot (Figure 1). However, previous studies have reported no notable differences in chloroplast movement responsiveness to light and temperature between A. endiviifolia and M. polymorpha, 18,19,30,31 which raises the following question: How does A. endiviifolia regulate its chloroplast movements under fluctuating light and temperature conditions in nature? We speculate that A. endiviifolia performs a higher activity in Aephot-mediated signaling (e.g., higher Aephot accumulation and kinase activity, and downstream factor functions) for chloroplast movements or it only survives in its kind of habitat only (e.g., shady area with little light fluctuation).…”