Actin3 promoter reveals undulating F-actin bundles at shanks and dynamic F-actin meshworks at tips of tip-growing pollen tubes

Pollen tubes show active cytoplasmic streaming. We isolated organelles from pollen tubes and tested their ability to slide along actin bundles in characean cell models. Here, we show that sliding of organelles was ATP-dependent and that motility was lost after N-ethylmaleimide or heat treatment of organelles. On the other hand, cytoplasmic streaming in pollen tube was inhibited by either N-ethylmaleimide or heat treatment. These results strongly indicate that cytoplasmic streaming in pollen tubes is supported by the "actomyosin"-ATP system. The velocity of organelle movement along characean actin bundles was much higher than that of the native streaming in pollen tubes. We suggested that pollen tube "myosin" has a capacity to move at a velocity of the same order of magnitude as that of characean myosin. Moreover, the motility was high at Ca2+ concentrations lower than 0.18 microM (pCa 6.8) but was inhibited at concentration higher than 4.5 microM (pCa 5.4). In conclusion, cytoplasmic streaming in pollen tubes is suggested to be regulated by Ca2+ through "myosin" inactivation.

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Circular F-actin bundles and a G-actin gradient in pollen and pollen tubes of Lilium davidii

Planta ◽

10.1007/s004250100543 ◽

2001 ◽

Vol 213 (5) ◽

pp. 722-730 ◽

Cited By ~ 27

Author(s):

Yan Li ◽

Sze-Yong Zee ◽

Yi-Min Liu ◽

Bing-Quan Huang ◽

Lung-Fei Yen

Keyword(s):

Pollen Tubes ◽

Actin Bundles ◽

Lilium Davidii

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Actin Bundles in The Pollen Tube

International Journal of Molecular Sciences ◽

10.3390/ijms19123710 ◽

2018 ◽

Vol 19 (12) ◽

pp. 3710 ◽

Cited By ~ 3

Author(s):

Shujuan Zhang ◽

Chunbo Wang ◽

Min Xie ◽

Jinyu Liu ◽

Zhe Kong ◽

...

Keyword(s):

Pollen Tube ◽

Tip Growth ◽

Imaging Techniques ◽

Embryo Sac ◽

Pollen Tubes ◽

Growth Strategy ◽

Regulation Mechanism ◽

Actin Bundles ◽

Angiosperm Pollen ◽

Plant Pollen

The angiosperm pollen tube delivers two sperm cells into the embryo sac through a unique growth strategy, named tip growth, to accomplish fertilization. A great deal of experiments have demonstrated that actin bundles play a pivotal role in pollen tube tip growth. There are two distinct actin bundle populations in pollen tubes: the long, rather thick actin bundles in the shank and the short, highly dynamic bundles near the apex. With the development of imaging techniques over the last decade, great breakthroughs have been made in understanding the function of actin bundles in pollen tubes, especially short subapical actin bundles. Here, we tried to draw an overall picture of the architecture, functions and underlying regulation mechanism of actin bundles in plant pollen tubes.

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Mechanism of Ca2+ inhibition of cytoplasmic streaming in lily pollen tubes

Journal of Cell Science ◽

10.1242/jcs.91.4.501 ◽

1988 ◽

Vol 91 (4) ◽

pp. 501-509 ◽

Cited By ~ 1

Author(s):

TADASHI KOHNO ◽

TERUO SHIMMEN

Keyword(s):

Actin Filaments ◽

Cytoplasmic Streaming ◽

Lilium Longiflorum ◽

Pollen Tubes ◽

Ionophore A23187 ◽

Filamentous Actin ◽

Actin Bundles ◽

Lily Pollen ◽

Subsequent Decrease

Using a Ca2+ ionophore, A23187, the free Ca2+ concentration ([Ca2+]) in the cytoplasm of pollen tubes of Lilium longiflorum was controlled from the cell exterior. At [Ca2+] higher than 1.0x10−5M (pCa5.0), cytoplasmic streaming was inhibited, and the inhibition was irreversible. The ATP content did not change, but actin filaments were fragmented and formed aggregates. A subsequent decrease in [Ca2+] almost stopped the progress of the actin filament fragmentation, but filamentous actin did not re-form from the fragmented actin. In a previous paper, we reported that pollen tube organelle movement along characean actin bundles was inhibited by Ca2+ at 10−5M levels and the inhibition was reversible. In the present study, the reversibility was also demonstrated using an in situ Ca2+ treatment. Organelles were isolated from pollen tubes that had been treated with high [Ca2+] and A23187. They moved along characean actin bundles in Ca2+-free medium. It is concluded that Ca2+ inhibition of cytoplasmic streaming can be attributed to both inactivation of myosin and fragmentation of actin. The irreversibility of Ca2+ inhibition in situ is attributed to the irreversible fragmentation of actin filaments.

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High resolution spot scan imaging of frozen, hydrated actin bundles with 400kV electrons

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122964 ◽

1992 ◽

Vol 50 (1) ◽

pp. 512-513

Author(s):

J. Jakana ◽

M.F. Schmid ◽

P. Matsudaira ◽

W. Chiu

Keyword(s):

High Resolution ◽

Binding Proteins ◽

Actin Binding ◽

Eukaryotic Cells ◽

Dimensional Structure ◽

Structural Basis ◽

Actin Bundle ◽

Actin Bundles ◽

3 Dimensional ◽

Macromolecular Assembly

Actin is a protein found in all eukaryotic cells. In its polymerized form, the cells use it for motility, cytokinesis and for cytoskeletal support. An example of this latter class is the actin bundle in the acrosomal process from the Limulus sperm. The different functions actin performs seem to arise from its interaction with the actin binding proteins. A 3-dimensional structure of this macromolecular assembly is essential to provide a structural basis for understanding this interaction in relationship to its development and functions.

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