Abstract
Pollen tube elongation is characterized by a highly-polarized tip growth process dependent on an efficient vesicular transport system and largely mobilized by actin cytoskeleton. Pollen tubes are an ideal model system to study exocytosis, endocytosis, membrane recycling, and signaling network coordinating cellular processes, structural organization and vesicular trafficking activities required for tip growth. Proteomic analysis was applied to identify Nicotiana tabacum Differentially Abundant Proteins (DAPs) after in vitro pollen tube treatment with membrane trafficking inhibitors Brefeldin A, Ikarugamycin and Wortmannin. Among roughly 360 proteins separated in two-dimensional gel electrophoresis, a total of 40 spots visibly changing between treated and control samples were identified by MALDI-TOF MS and LC–ESI–MS/MS analysis. The identified proteins were classified according to biological processes, and most proteins were related to pollen tube energy metabolism, including ammino acid synthesis and lipid metabolism, structural features of pollen tube growth as well modification and actin cytoskeleton organization, stress response, and protein degradation. In-depth analysis of proteins corresponding to energy-related pathways revealed the male gametophyte to be a reliable model of energy reservoir and dynamics.
Highlights
Pollen germination and pollen tube growth are essential processes in controlling sexual plant reproduction
To investigate the protein changes induced by membrane trafficking inhibitors, Nicotiana tabacum pollen was allowed to germinate for 60 min, and exo- and endocytosis inhibitors were added directly to the culture medium
Recent studies revealed that distinct clathrin-dependent and clathrin-independent endocytic pathways are involved in retrieving the excess of secreted plasma membrane that could be addressed to recycling or to degradation [44]
Summary
Pollen germination and pollen tube growth are essential processes in controlling sexual plant reproduction. Integrating many internal and external signals, these processes are highly sensitive to environmental fluctuations such as temperature, light, and drought [7]. Pollen functionality is a major focus in applied research aimed at improving plant productivity. Besides its importance for sexual reproduction, the pollen tube is a valid model for studying. The pollen tube is characterized by fast and energy-consuming polarized cell expansion called tip growth, depending on a highly efficient vesicular transport system largely mobilized by the actin cytoskeleton [35, 54]. The actin organization has been extensively studied in vivo, showing distinct arrays in the tip and in the subapical regions [10]. The rapid fringe dynamics is further regulated by a plethora of actin-binding proteins and it has been shown that BFA treatments affects membrane trafficking and destroys the actin fringe [32, 60]
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