Juglone – a toxic chemical from Juglandaceae family

Juglone (C₁₀H₆O₃) (5-hydroxynaphthalene-1,4-dione) is a natural toxin that produced by many trees in Juglandaceae family, namely J. regia, J. nigra, J. cinerea, J. ailantifolia and J. mandshurica.  Juglone can be in many parts of the plants, such as leaves, net hull, bark, fruit, stem and roots, being highest in the roots and lowest for leaves and stem.  

Juglone is an herbicide, allows the plants to retard the growth of other competing plants nearby. It used in allelopathic mechanisms, going on under a walnut tree and affect the types of wild plants that grow there, is a strong toxin that may prevent plants from fully utilizing energy. 

However, greater quantities of juglone are generally present in the area immediately under the canopy of the tree, due to greater root density and it released in several ways: leaves falling and decaying, nut husks, and decay, and rain-wash off. Also Juglone can be produced by oxidation of other chemical in the plant such as hydroxyjuglone, which increase the potential effect of Juglone.  Juglone can affect the yield of maize, tomato, potato, eggplant and pepper, and ornamentals. 

Juglone is poorly soluble in water (52 mg/L) and is quickly sorbed by soil. Thus, it does not move very far in the soil and it can be degraded in soil (half-life 2 weeks for sandy soil). Sorption and degradation of juglone is highly affected by organic matter as other chemicals, the more organic matter in the soil the more juglone sorbed and degraded faster.

Degradation of juglone in water is pH dependent, it is strongly enhanced in alkaline conditions relative to lower pH in neutral or acid conditions. It degraded much faster at pH 9 (half-life 18 h) than pH 4.0 – 6.8  (half-life 60 days). Also, a low octanol:water partition coefficient for juglone (98.2 (log K_ow = 1.99)) indicated little capacity for these compounds to be adsorbed by suspended particulates and for bioaccumulation.

Thus, relatively rapid degradation of juglone, particularly in water, showed a low risk of residual toxicity associated with juglone and release.

Canonical SMILES: C1=CC2=C(C(=O)C=CC2=O)C(=C1)O
CAS: 481-39-0

References:

1. Wright, D.A., Mitchelmore, C.L., Dawson, R., Cutler, H.G., 2007. The influence of water quality on the toxicity and degradation of juglone (5-hydroxy 1,4-naphthoquinone). Environmental Technology 28:1091–1101.
2. Willis, R. J., 2000. Juglans spp., juglone and allelopathy.  Allelopathy Journal 7(1):51-55.
3. Paulsen, M.T., Ljungman, M., 2005. The natural toxin juglone causes degradation of p53 and induces rapid H2AX phosphorylation and cell death in human fibroblasts. Toxicol Appl Pharmacol. 209(1):1-9. doi:10.1016/j.taap.2005.03.005. PMID: 16271620.
4. Pascal, R., Françoise, S.M., Jean-Louis B.G., Serge, K., 1992. Toxicity of walnut husk washing waters. Water Research. 26(11):1503-1506. https://doi.org/10.1016/0043-1354(92)90070-K.

Pictures:

• https://www.forestag.com/products/black-walnut-juglans-nigra?variant=11891268868 (accessed September 21, 2018).
• https://www.weekendnotes.com/im/004/07/sassafras-nuts1.jpg (accessed September 28, 2018).
• https://www.fs.fed.us/ne/morgantown/4557/gypsymth/h602.html (accessed October 1, 2018).
• Structure: By Edgar181 - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2463538