Pollen tube growth: signal perception and temporary growth arrest

Abstract

Pollen tubes are among the fastest growing polarized plant cells and must traverse the stigma, style and ovary to deliver male gametes. The style constitutes the longest and most complex phase of this journey yet the molecular and biomechanical logic of pollen tube behavior within this tissue remains poorly integrated. Here we synthesize recent genetic, live-imaging and biochemical studies to assemble a coherent sequence from ionic gradients, actin dynamics and vesicle trafficking to cell wall remodeling, and propose an integrative signal-mechanics feedback framework for long-distance guidance, arrest and reactivation. Within this framework, arrest at the stylar base is interpreted as an actively regulated checkpoint rather than passive waiting. We further place this view in a broader evolutionary context by comparing prolonged progamic phase in gymnosperms with delayed fertilization in Fagaceae, where ovule immaturity is coupled to intermittent pollen tube arrest and reactivation within the pistil. From this synthesis we derive three testable predictions: localized remodeling of the stylar base extracellular matrix may modulate pollen tube reactivation by altering mechanical resistance and engaging FER/LRX-related mechanosensory Ca2+ signaling; AGPs may support the ionic environment required for exocytosis through local Ca2+ supply; and female tissues actively maintain or restart tube quiescence in delayed-fertilization systems. Finally, we highlight several unresolved questions and methodological bottlenecks that point toward future directions. This conceptual synthesis bridges insights from model and non-model species, provides a predictive perspective on long-distance tip growth and its evolutionary diversification, and outlines a forward-looking agenda for plant reproductive biology.