The naphthylphthalamic acid receptor (NPAR) is a plant cell plasma membrane protein that plays a pivotal role in the regulation of the movement of the plant hormone auxin. NPAR is being isolated from zucchini using a combination of immunoaffinity and chromatographic techniques. Flavenoids are shown to be NPAR ligands in vitro but the natural ligands are not known. Several specific flavenoids are being studied to determine the in vivo ligand. Auxin movement in plants is particularly important to their growth and development. The polar transport of auxin from its multiple sites of synthesis in the shoot apex and young leaves downward to the tissues in which it acts allows for a coordination of growth and development in disparate plant parts and helps maintain the developmental polarity of the plant body. The more local movement of auxin in and out of plant cells affects levels of free auxin in individual cellular compartments containing receptors for auxin's actions. The regulation of auxin movement is a major control point in plant development. Understanding how the NPA receptor works to control movement of auxin in plants would be a major contribution to our understanding of the way that auxin plays its pattern-generating and coordinating role in plant development and will advance our ability to manipulate plant growth for agricultural purposes.
