Accumulation response of chloroplasts induced by mechanical stimulation in bryophyte cells
ABSTRACT 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.
- SourceAvailable from: Vitaly SineshchekovLight Sensing in Plants, Edited by M. Wada, K. Shimazaki, M. Iino, 01/2005: chapter 10: pages 91-98; Springer-Verlag, Tokyo.
Chapter: Chloroplast Photorelocation Movement[Show abstract] [Hide abstract]
ABSTRACT: Chloroplast photorelocation movement is one of the best-characterized plant organelle movements and is found in various plant species from alga to flowering plants. In general, low-intensity blue light induces a chloroplast accumulation response for efficient light capture and high-intensity blue light induces an avoidance response so that chloroplasts can avoid photodamage. Red light is also effective in some alga, moss, and fern species. It was shown that phototropin (phot) is a blue light receptor in land plants and neochrome (neo), which is a chimera photoreceptor between phytochrome and phototropin, is a red light receptor in ferns and possibly in alga. Although the signal transduction pathways and motility system of chloroplast movement is not clearly understood, several components involved in signaling or motility were identified through molecular genetic research using Arabidopsis thaliana and the involvement of actin filaments in the motility system is obvious in most plant species. This chapter summarizes the current progress in research on chloroplast photorelocation movement.12/2008: pages 235-266;
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ABSTRACT: Lead ions are particularly dangerous to the photosynthetic apparatus, but little is known about the effects of trace metals, including Pb, on regulation of chloroplast redistribution. In this study a new effect of lead on chloroplast distribution patterns and movements was demonstrated in mesophyll cells of a small-sized aquatic angiosperm Lemna trisulca L. (star duckweed). An analysis of confocal microscopy images of L. trisulca fronds treated with lead (15 μM Pb2+, 24 h) in darkness or in weak white light revealed an enhanced accumulation of chloroplasts in the profile position along the anticlinal cell walls, in comparison to untreated plants. The rearrangement of chloroplasts in their response to lead ions in darkness was similar to the avoidance response of chloroplasts in plants treated with strong white light. Transmission electron microscopy X-ray microanalysis showed that intracellular chloroplast arrangement was independent of the location of Pb deposits, suggesting that lead causes redistribution of chloroplasts, which looks like a light-induced avoidance response, but is not a real avoidance response to the metal. Furthermore, a similar redistribution of chloroplasts in L. trisulca cells in darkness was observed also under the influence of exogenously applied hydrogen peroxide (H2O2). In addition, we detected an enhanced accumulation of endogenous H2O2 after treatment of plants with lead. Interestingly, H2O2-specific scavenger catalase partly abolished the Pb-induced chloroplast response. These results suggest that H2O2 can be involved in the avoidance-like movement of chloroplasts induced by lead. Analysis of photometric measurements revealed also strong inhibition (but not complete) of blue-light-induced chloroplast movements by lead. This inhibition may result from disturbances in the actin cytoskeleton, as we observed fragmentation and disappearance of actin filaments around chloroplasts. Results of this study show that the mechanisms of the toxic effect of lead on chloroplasts can include disturbances in their movement and distribution pattern.PLoS ONE 02/2015; 10(2):e0116757. DOI:10.1371/journal.pone.0116757 · 3.53 Impact Factor