Received March 15, 2006
Returned for revision April 11, 2006
Accepted June 8, 2006
Imaging of dynamic secretory vesicles in living pollen tubes of Picea meyeri using evanescent wave microscopy
Xiaohua Wang , Yan Teng , Qinli Wang , Xiaojuan Li , Xianyong Sheng , Maozhong Zheng , Jozef
amaj , Franti
ek Balu
ka , and Jinxing Lin *
Key Laboratory of Photosynthesis and Molecular Environment Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
Key Laboratory of Photosynthesis and Molecular Environment Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University Bonn, Department of Plant Cell Biology, Kirschallee 1, D-53115 Bonn, Germany; Institute of Botany, Slovak Academy of Sciences, Dubravska 14, SK-84223, Bratislava, Slovak Republic
Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University Bonn, Department of Plant Cell Biology, Kirschallee 1, D-53115 Bonn, Germany; Institute of Plant Genetics and Biotechnology, Slovak Academy of Sciences, Akademicka 2, SK-95007, Nitra, Slovak Republic
* Corresponding author; email: linjx{at}ibcas.ac.cn.
Evanescent wave excitation was used to visualize individual, FM4-64-labeled secretory vesicles in an optical slice proximal to the plasma membrane of Picea meyeri pollen tubes. A standard upright microscope was modified to accommodate the optics used to direct a laser beam at a variable angle. Under evanescent wave microscopy or total internal reflection fluorescence microscopy, fluorophores localized near the surface were excited with evanescent waves, which decay exponentially with distance from the interface. Evanescent waves with penetration depths of 60 to 400 nm were generated by varying the angle of incidence of the laser beam. Kinetic analysis of vesicle trafficking was made through a
300-nm optical section beneath the plasma membrane using time-lapse evanescent wave imaging of individual fluorescently labeled vesicles. Two-dimensional (2-D) trajectories of individual vesicles were obtained from the resulting time-resolved image stacks and were used to characterize the vesicles in terms of their average fluorescence and mobility, expressed here as the 2-D diffusion coefficient D (2). The velocity and direction of vesicle motions, frame-to-frame displacement, and vesicle trajectories were also calculated. Analysis of individual vesicles revealed for the first time that two types of motion are present, and that vesicles in living pollen tubes exhibit complicated behaviors and oscillations that differ from the simple Brownian motion reported in previous investigations. Furthermore, disruption of the actin cytoskeleton had a much more pronounced effect on vesicle mobility than did disruption of the microtubules, suggesting that actin cytoskeleton plays a primary role in vesicle mobility.