Chloroplast movement has been studied in many plants but mainly as a model system for light signaling. However, we recently showed that the avoidance response of chloroplasts is also induced by mechanical stimulation in fern protonemal cells. Here we report the discovery of a mechanically induced accumulation response of chloroplasts in bryophytes. When mechanical stimulation was directly applied with a capillary to a part of a cell, chloroplasts moved towards and accumulated at the pressed site within 30 min after the onset of stimulation in all species tested. The accumulation movement of chloroplasts was inhibited by Cremart but not by cytochalasin B in red-light-grown protonemata of Physcomitrella patens (Hedw.) B., S. & G. To determine the contribution of external Ca(2+) to the response, we examined the effects on the accumulation movement of gadolinium (Ga(3+)), an inhibitor of stretch-activated ion channels, and lanthanum (La(3+)), a potent inhibitor of calcium channels. Mechano-relocation of chloroplasts was abolished by these drugs, but no effects were observed on photo-relocation of chloroplasts, irrespective of light colors and intensity. These results suggest that influx of external Ca(2+) through the plasma membrane is essential for the early steps in signaling of mechano-relocation of chloroplasts whose motility system is dependent on microtubules.
"The challenge now is to determine if these observed activities are responsible for the perception of mechanical stimuli. Treatment with gadolinium (Gd 3þ ) ions and spider venom, known to inhibit MS ion channels (Yang and Sachs, 1989; Chen et al., 1996), can also prevent many of the mechanosensory responses described above, including pollen tube growth, root and hypocotyl gravitropism , cold acclimation, and chloroplast migration (Ding and Pickard, 1993a; Tahtiharju et al., 1997; Sato et al., 2003; Dutta and Robinson, 2004; Soga et al., 2004). However, the Ca 2þ increase observed in response to wind is insensitive to treatment with Gd 3þ (Knight et al., 1992), and the specificity of gadolinium inhibition in plant cells has been questioned (White, 1998). "
"Unexpectedly, opposite directional movement was observed in the moss Physcomitrella patens , Ceratodon purpureus , and the liverwort Marchantia polymorpha . Chloroplasts moved towards the stimulation site in these bryophytes (Sato et al. 2002). Representative images of mechano-accumulation and avoidance response are shown in Fig. 2. The time required to reach the maximum level in the mechano-accumulation response in P. patens (0.5 h) is apparently shorter than that of the avoidance response in the fern A. capillus-veneris (1–2 h). "
[Show abstract][Hide abstract] ABSTRACT: The study of chloroplast photorelocation movement is progressing rapidly now that mutants for chloroplast movement have become available in Arabidopsis thaliana. However, mechanistic approaches in cell biology still stand to elucidate the mechanisms and regulations of such movement. The fern Adiantum capillus-veneris and the moss Physcomitrella patens are particularly suitable materials for analyzing the kinetics of intracellular chloroplast movement. In these plants, chloroplast movement is induced by red light as well as blue light, mediated by phytochrome and blue light receptor, respectively. In this paper, we review the unique force-generating system for chloroplast motility in P. patens. In addition to light-induced chloroplast movement, we also summarize mechanically induced chloroplast movement in these plants and the motility systems involved. Finally, the different dependency of mechano- and photo-relocation movement on external Ca(2+) is discussed.
Journal of Plant Research 03/2003; 116(1):1-5. DOI:10.1007/s10265-002-0073-3 · 1.82 Impact Factor
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