Pollen tubes extend rapidly in an oscillatory manner from the extreme
Pollen tubes extend rapidly in an oscillatory manner from the extreme type of polarized growth tip growth and offer a thrilling system for learning the spatiotemporal control of polarized cell growth. will become discussed. tradition cultured pollen keeps its polarity and developmental identification. pollen tubes develop synchronously and uniformly and exhibit highly polarized cytoplasmic organization with the apical region packed with exocytic vesicles (Physique. 1B). Although each pollen tube contains two sperm cells embedded in the vegetative cytoplasm the sperm genome does not seem to contribute to the genetic control of pollen tube growth. Instead it is controlled by the haploid genome carried by the vegetative nucleus and thus lethal mutations affecting tube growth can be maintained in heterozygous plants which facilitates genetic analysis of essential genes involved in polarity and growth control. These advantages combined with the ease with which live imaging is performed with pollen tubes make it one of the most exciting systems for the studies of polarity and tip growth. Physique 1 The pollen tube system: Directional and polarized cell growth To efficiently reach their target in the ovary pollen tubes elongate LY315920 at an astonishing rate (up to 1 1 cm/hr) to an extraordinary length (e.g. the length of corn silk) by polarized tip growth which is strictly dependent on polar exocytosis that delivers cell membrane and wall materials to the growing tip as in other tip growing systems [4-8]. An intriguing question is usually how pollen tubes design their structural and molecular machineries to achieve such rapid polar growth. At the sub-cellular level pollen tube growth requires a highly polarized cytoplasmic organization [5 6 As the pollen tube grows periodic cross-wall callose deposition isolates the pollen protoplast which contains the biosynthetic machinery and the male germ unit in the LY315920 tip region of the elongating tube. This process is usually analogous to septum formation in fungal hyphae. The tip region displays four distinct zonings: an apical zone essentially packed with exocytic vesicles accumulated as a typical V shape to facilitate massive tip-targeted exocytosis a subapical organelle-rich zone a nuclear zone and a vacuolated zone that may extend toward the grain . Cytoplasmic streaming drives organelles moving rapidly back and forth along the main axis of the pollen tube in a reverse fountain pattern which maintains the distribution of membranous structures and releases exocytic vesicles to LY315920 the apical zone . A LY315920 complete picture of the Rabbit Polyclonal to PPGB (Cleaved-Arg326). cytoskeletal elements and dynamics that regulate the polar organization of the tube cytoplasm and targeted exocytosis is usually emerging [7 9 Due to a higher global turgor pressure the exocytosis-based membrane and wall structure extension must be in conjunction with the spatiotemporal legislation of cell wall structure technicians. Both experimental and computational techniques have recently supplied important insights in to the cell wall structure technicians during pollen suggestion development. On the molecular level latest studies have got uncovered a Rho GTPase-based self-organizing signaling network that handles tip development in pollen pipes its inter-connection using the cytoskeletal components as well as the polarized exocytosis [13 16 Many excellent latest reviews provide essential insights in to the molecular systems under pollen pipe tip development [6-8 21 Our current review will concentrate on the latest advancements in the structural basis of the process and its own interface using the Rho GTPase-based signaling network. Emphasis will get towards the evaluation and contrast from the systems for tip development of pollen pipes with those of other systems. 2 The structural system: Functions in structure and regulation 2.1 The cytoskeleton Pollen tubes contain two major cytoskeletal elements microtubules (MTs) and actin microfilaments (F-actin) which are highly organized and dynamic through their interaction with various actin-binding proteins and microtubule-associated proteins [22 25 MTs are involved in the organization of spitzenk?per (the exocytosis organizing center) and organelle movement and regulate the efficiency of tip growth but not essential for this growth [28-30]. In contrast F-actin structures are quintessential for tip.