Cell Shape and Movement in Plant Cells (BIO 127) PDF

BIO 127 Ch2. Cell Shape and Movement A. Cytoskeleton B. Cell Shape and Movement in Plant Cells C. Cell Shape and Movement in Animal Cells 1 Chapter II. Cell Shape and Movement A. Cytoskeleton B. Cell Shape and Move...

BIO 127 Ch2. Cell Shape and Movement A. Cytoskeleton B. Cell Shape and Movement in Plant Cells C. Cell Shape and Movement in Animal Cells 1 Chapter II. Cell Shape and Movement A. Cytoskeleton B. Cell Shape and Movement in Plant Cells C. Cell Shape and Movement in Animal Cells Copyright © 2022. This course material is intended solely for the personal use of the student enrolled in BIO 127. No part of this course material can be reproduced, reposted, or replicated without permission from the Genetics and Molecular Biology Division, Institute of Biological Sciences, CAS, UPLB. Plant cells with rigid cell walls cannot easily change shape different cell shapes Plant cells actin filaments microtubules cellulose microfibrils oriented parallel to the MTs because cellulose synthase creates cellulose microfibrils as it moves along microtubule “tracks” Plant Cytoskeleton non-growing cell elongating cell The final shape of a plant organ depends on… …the direction in which all its constituent cells expand The direction of cell expansion in plants depends on: 1. orientation of the cellulose microfibrils - same as the cytoplasmic MT the primary cell wall of an elongating carrot cell The direction of cell expansion in plants depends on: 2. controlled cell expansion based on the combination of a. turgor pressure b. cell wall plasticity Turgor pressure >> local tensile strength of CW  cell expansion The direction of cell expansion in plants depends on … Mechanisms to enhance cell wall plasticity 1. Local secretion of H+ into the wall by H+ pumping ATPase Low pH can reduce number of weak bonds 2. Activation of enzymes that can hydrolyze glycosidic and other covalent bonds in the cell wall 3. Plant growth-regulators influence microtubule orientation microtubules – determine final cell shape Mechanisms to enhance cell wall plasticity 3. Plant growth-regulators Auxin o Cell growth o Cell division & expansions  Axial elongation – shoots  Lateral expansion – root swelling  Isodiametric expansion - fruits Acid growth hypothesis Auxin activates proton pumps in the cell wall to make its pH acidic. Low pH activates wedge-shaped expansins which separate cellulose microfibrils from cross-linking polysaccharides. Cross-linking polysaccharides become more susceptible to cleavage by cell wall- loosening enzymes. Cellulose fibers loosen and increase cell wall extensibility. Turgor pressure pushes against the cell wall allowing the cell to expand Campbell and Reece, 2008  Plant Intracellular Movement: Cytoplasmic Streaming Nitella a giant multinucleated green algae by diffusion, a protein will take 2 weeks to move from one end of the cell to the other with cytoplasmic streaming: 75 μm/ sec a continuous ribbon of cytoplasm streams along a gentle helical path down one side of the cell and back across the other end Mechanism for cytoplasmic streaming Crude actin-rich gels from cells myosin removed No more streaming and contraction Mechanism for cytoplasmic streaming Chloroplasts are attached to underlying bundles of AF of the cell cortex AF aligned with the same polarity Myosin molecules move along the AF https://phys.org/news/2020-08-success-growth-biodiesel.html Size enhancement of Arabidopsis thaliana by high-speed myosin XI. High-speed myosin XI was developed by replacing the motor domain of Arabidopsis myosin XI, which determines the rate of cytoplasmic flow, with the motor domain of Chara corallina. Expression of high-speed of myosin XI increases the size of plants (Arabidopsis thaliana) concomitantly with elevation of cytoplasmic streaming velocity. Credit: Motoki Tominaga https://phys.org/news/2020-08-success-growth-biodiesel.html https://www.youtube.com/watch?v=BB5rvjZzgFU  Copyright © 2023. JCADeriquito, RMAlcabedos, NOVilla All rights reserved. No part of these slides may be published without the authors’ consent.