Three-dimensional visualization of tip-vesicles in growing pollen tubes by electron tomography

Area of Science:

• Plant Biology
• Cell Biology
• Structural Biology

Background:

• Pollen tube growth is crucial for fertilization in flowering plants.
• Tip-growing pollen tubes rely on dynamic vesicular trafficking for growth and development.
• Visualizing these vesicles has been difficult due to their small size and rapid movement.

Purpose of the Study:

• To illustrate the 3D ultrastructure of tip-vesicles in growing pollen tubes.
• To identify and characterize different types of vesicles involved in pollen tube tip growth.
• To investigate the role of the endoplasmic reticulum in vesicle formation at the pollen tube apex.

Main Methods:

• Room-temperature electron tomography (RT-ET) to visualize vesicle ultrastructure.
• Cryo-electron tomography (Cryo-ET) to study vesicle budding from the endoplasmic reticulum.
• Analysis of pollen tubes from lily, tobacco, and Arabidopsis.

Main Results:

• Distinguished five major types of tip-vesicles: secretory vesicles (SVs), electron-dense vesicles (DVs), clathrin-coated vesicles (CCVs), mini vesicles (MVs), and extracellular vesicles (EVs).
• Observed extensive tubular endoplasmic reticulum (ER) structures at the pollen tube apex.
• Identified vesicles budding from tip-localized ER, including coat protein complex II (COPII) vesicles.

Conclusions:

• Provides a structural basis for understanding vesicular trafficking in pollen tube tip growth.
• Highlights the role of ER in generating vesicles for polarized cell growth.
• Aids future research into vesicle-mediated membrane trafficking in plant reproduction.