Flow Chamber Assay to Image the Response of FRET-Based Nanosensors in Pollen Tubes to Changes in Medium Composition

Pollen tubes growing in the transmitting tract are presented with an extracellular matrix rich in a variety of substances. The expression of a multitude of genes for transport proteins in the pollen tube indicates that pollen tubes take up at least some of the components provided by the transmitting tract, for example nutrients, ions, or signaling molecules. FRET (Förster resonance energy transfer)-based nanosensors are perfectly suited to study the uptake of these molecules into pollen tubes. They are genetically encoded and can easily be expressed in Arabidopsis pollen tubes. Furthermore, the method is noninvasive and nanosensors for a wide range of substances are available. This chapter will describe the design of plasmids required to generate stable Arabidopsis lines with a pollen tube-specific expression of nanosensor constructs. We also present a method to germinate Arabidopsis pollen tubes in a flow chamber slide that allows the perfusion of the pollen tubes with liquid medium supplemented with the substrate of the nanosensor. Simultaneous evaluation of the FRET efficiency of the nanosensor by confocal microscopy reveals whether the substance is taken up by the pollen tubes. Together with the great number of available nanosensors this method can generate a detailed picture of the substances that are taken up during pollen tubes growth.