Correlation between chloroplast motility and elastic properties of tobacco mesophyll protoplasts |
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Authors: | Joanna Augustynowicz Ma?gorzata Lekka Kveta Burda Halina Gabry? |
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Institution: | (1) Department of Plant Physiology and Biochemistry, The Jan Zurzycki Institute of Molecular Biology, Jagiellonian University, al. Mickiewicza 3, 31-120 Kraków, Poland;(2) Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Kraków, Poland |
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Abstract: | Translocations of chloroplasts induced by blue light were investigated in both leaves and protoplasts isolated from leaf mesophyll
of Nicotiana tabacum. In the leaf tissue, the responses of chloroplasts were similar to those observed in other, higher and lower plant species.
Weak and strong light induced movements of chloroplasts towards cell walls perpendicular and parallel to the light direction,
respectively. Treatment with cytochalasin D, an actin-disturbing agent, blocked the movements. This shows that actin is involved
in the motile system of chloroplast translocation in tobacco. By monitoring the response of chloroplasts to light in isolated
protoplasts, we addressed the question whether the presence of the cell wall is necessary for the translocations of chloroplasts
to occur. In control protoplasts (isolated at room temperature from unstressed leaves), no clear light intensity-dependent
changes were observed in chloroplast distribution pattern. In contrast, in protoplasts obtained from plants treated with 4
°C for 8 h the chloroplasts maintained their responsiveness to light. Atomic Force Microscopy was used to measure elastic
properties of the protoplasts. Young’s modulus, which reflects rigidity of the material, was 10 times higher for protoplasts
of the coldstressed plants as compared to those isolated from the control plants. The rigidity of protoplasts isolated from
the plants treated with low temperature was reduced four-fold by exposure to cytochalasin D. It appears that the status of
protoplast actin is a factor responsible for elasticity of protoplasts. We speculate that unknown, cold stress-induced factors,
maintain the orientational movements due to anchorage of the actin cytoskeleton in the plasma membrane despite the cell wall
removal. |
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Keywords: | actin blue light chloroplast movement cold stress cytochalasin cytoskeleton Nicotiana tabacum protoplast Atomic Force Microscopy |
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