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Quantitative Structural Organization of Bulk Apical Membrane Traffic in Pollen Tubes
Gleb Grebnev1, Mislav Cvitkovic2,3, Carolin Fritz1
1Cell Biology, Department of Biology, Friedrich-Alexander-University Erlangen Nuremberg, 91058 Erlangen, Germany.
Plant Physiology
|June 3, 2020
Summary
Pollen tube growth balances secretion and endocytosis at the plasma membrane (PM). This study quantitatively shows secretion and lipid recycling occur apically, while endocytosis is subapical, supporting the classical tip growth model.
Area of Science:
- Plant cell biology
- Molecular and Cellular Biology
- Membrane trafficking
Background:
- Pollen tube tip growth requires precise regulation of plasma membrane (PM) composition through secretion and endocytosis.
- The classical model of apical secretion and subapical endocytosis has been debated due to the complex localization of regulatory proteins.
- Understanding the spatial dynamics of membrane traffic is crucial for elucidating pollen tube growth mechanisms.
Purpose of the Study:
- To quantitatively characterize the spatial organization of membrane traffic during pollen tube tip growth.
- To determine the specific sites of bulk secretion and endocytosis in relation to PM domains.
- To investigate the targeting mechanisms of transmembrane proteins and lipids during tip growth.
Main Methods:
- Quantitative analysis of FM4-64-labeled lipids and YFP-tagged transmembrane (TM) proteins in *Nicotiana tabacum* pollen tubes.
- Observation of pollen tubes under normal conditions and after treatment with Brefeldin A to inhibit secretion.
- Mathematical modeling of steady-state PM distributions and mapping of F-actin and trans-Golgi network positioning.
Main Results:
- Secretion delivers TM proteins and recycled membrane lipids to the same apical PM domain.
- FM4-64-labeled lipids, unlike analyzed TM proteins, undergo endocytic recycling in a distinct subapical region.
- Mathematical models supported experimental data and revealed differences in marker distributions.
- F-actin fringe and trans-Golgi network were mapped relative to secretion and endocytosis sites.
Conclusions:
- The study supports and refines the classical model of apical membrane traffic in elongating pollen tubes.
- Distinct apical and subapical domains are responsible for secretion/lipid recycling and endocytosis, respectively.
- This spatial segregation is key to regulating PM composition and facilitating tip growth.
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