1-N-Naphthyl Phthalamic Acid (NPA)

Properties:

NPA is a potent inhibitor of polar auxin transport. Stock solution 10 mM in dimethyl sulfoxide. Store at -20°C. Effective concentrations to inhibit are in the range of 1-10 µM

Molecular Target:

Binding sites in the plasma membrane, Kd of binding around 7. NPA blocks auxin efflux.

Specificity

In contrast to TIBA, NPA does not cause bundling of actin in animal cells, but does so in plant cells. It is therefore thought to bind the efflux carrier. So far, no evidence for binding of NPA to PIN-proteins.

Physiological Effects:

• Inhibits gravitropism of maize roots at 1 µM, Inhibits gravitropism of maize coleoptiles at 10 µM  (Katekar et al. 1981).
• Inhibitis gravitropism of rice coleoptiles at (Gutjahr and Nick 2006)
• Inhibits auxin transport in rice coleoptiles at 5 µM (Godbolé et al. 2000)
• Inhibits pattern formation in tobacco cells at 5 µM (Campanoni et al. 2003, Maisch and Nick 2007)
• Inhibits division of tobacco cells at 50 µM (Campanoni et al. 2003)
• Causes bundling of actin (Dhonukshe et al. 2008)

Further reading

Katekar GF, Nave JF, Geissler AE (1981) Phytotropins. III. Naphthylphthalamic Acid Binding Sites On Maize Coleoptile Membranes As Possible Receptor Sites For Phytotropin Action. Plant Physiol 68, 1460-1464. Molecular properties, binding constants, structure-function relationship of different phytotropins.

Imhoff V, Muller P, Guern J, Delbarre A (2000) Inhibitors of the carrier-mediated influx of auxin in suspension-cultured tobacco cells. Planta (2000) 210: 580-588. Structure-function relationship for transport of 2,4-D and NAA in tobacco cells.