Fluorescent Labeling and Confocal Microcopy of Plastids and Stromules

While chlorophyll has served as an excellent label for plastids in green tissue, the development of fluorescent proteins has allowed their ready visualization in all tissues of the plants, revealing new features of their morphology and motility, including the presence of plastid extensions known as stromules. Gene regulatory sequences in nuclear transgenes that target proteins to plastids, as well as in transgenes introduced into plastid genomes, can be assessed or optimized through the use of fluorescent protein reporters. Fluorescent labeling of plastids simultaneously with other subcellular locations reveals dynamic interactions and mutant phenotypes. Transient expression of fluorescent protein fusions is particularly valuable to determine whether or not a protein of unknown function is targeted to the plastid. Fluorescent biosensors can assay molecules such as ATP, calcium, or reactive oxygen species. Particle bombardment and agroinfiltration methods described here are convenient for imaging fluorescent proteins in plant organelles. With proper selection of fluorophores for labeling the components of the plant cell, confocal microscopy and multiphoton microscopy can produce extremely informative images at high resolution at depths not feasible by standard epifluorescence microscopy.