Walnut juglone

Juglans spp. J. nigra L. . 1. regia L. Juglandaceae Walnut Juglone Thompson (1935) ... 

Juglone [481-39-0] (Cl Natural Brown 7 Cl 75500) was isolated from the husks of walnuts in 1856 (50). Juglone belongs to the Juglandaceae family of which there are a number of species Jug/ans cinerea (butter nuts), J. regia (Persian walnuts), and J. nigra (black walnuts). Persian walnuts were known to the ancient Romans who brought them over from Asia Minor to Europe. As early as 1664, the American colonists knew how to extract the brown dye from the nuts of the black walnut and butternut trees, both native to eastern North America (51). 

In 1885, from a detailed study of juglone (52) it was proposed that its stmcture was 5-hydroxy-l,4-naphthoquinone (9). This stmcture was confirmed by oxidizing 1,5-dihydroxynaphthalene with potassium dichromate in sulfuric acid (53). Juglone occurs in walnuts as a glycoside of its reduced form, 1,4,5-trihydroxynaphthalene (54). Later it was deterrnined that the sugar is in the 4-position (10) (55). 

The toxic influence exerted by Juglans nigra (black walnut) on other plants has been attributed to 5-hydroxy-1,4-naphthoquinone (juglone) (11,31). Hydrojuglone is present in the root bark, leaves, and fruit husks. This compound is not considered toxic, but it is oxidized to the toxic juglone upon exposure to air (51). Rainfall... 

Davis (19) in 1940 extracted and purified the toxic substance frcm the hulls and roots of walnut (JugIans) and found it to be identical to juglone (5-hydroxy-l,4-naphthoquinone). This compound proved to be a powerful toxin when injected into the stems of tomato, potato and alfalfa plants. The allelopathic action in the case of juglone (walnut tree and its vicinity) is well established. 

Significantly more Nitrobacter inhabited the soil in plots of walnut mixed with European alder than in plots of walnut mixed with autumn-olive or walnut alone. Apparently juglone concentrations were not sufficient to inhibit populations of these nitrifying microorganisms. 

To gain more understanding of the European alder decline and because of our concern about the future growth of black walnut planted with nitrogen-fixing species, a study was initiated to measure soil juglone concentration and to estimate the number of Nitrobacter and Nltrosomonas bacteria in a black walnut plantation containing plots of black walnut alone and in mixture with European alder and autumn-olive. 

Soil samples were collected in mid-November at a distance of 0.9 m from each walnut tree at depths of 0-8, 8-16, and 16-30 cm for juglone estimates. Special effort was taken to avoid locating sample plots near dead or declining European alder trees. Another set of samples was collected at 0.9 m from walnut trees in the same plots at depths of 0-4, 4-8, 8-16, and 16-24 cm for Nitrobacter and Nitrosomonas counts. 

The mean juglone concentration in soil beneath plots of autumn-olive/ black walnut was significantly lower than in soil beneath European alder/black walnut and black walnut-alone plots (Table I). Juglone concentrations also differed with sampled depth (Table I). Significantly higher concentrations were present at the 0-8 cm depth than at lower depths. 

The higher juglone concentrations in the surface soil and within a few centimeters of the soil surface beneath the walnut was due to the presence of leaves, fruit, and roots. Juglone concentrations in this bottomland plantation followed a pattern similar to treatment differences reported for a companion upland mixed planting (26). However, results from the present Investigation showed juglone... 

Table I. Juglone Concentration in Soil According to Depth and Treatment in a Mixed Planting of Black Walnut and Nitrogen-fixing Species...

Quinone Colors depend on mordant and pH 1. benzoquinone 2. naphthaquinone 3. anthraquinone Carthamine Juglone Alizarin Purpurin Walnut or butternut (Juglans sp.) Rubiaceae family Sorrel (Rumex sp.) Poligonaceae family Forms lake with mordant For 3. pH >7 -> violet-blue pH < 7-> yellow-red AL rose-red Ca bluish-red Zn red-violet Fe black-violet Cr=red brown... 

Naphthaquinones are rare. Among the naphthaquinones juglone (1.64) is relatively common. It is found in walnuts. Anthraquinone is the most widely distributed of the quinones in higher plants and fungi. There are numerous compounds. The anthtraquinone emodin (1.65) occurs as a rhamnoside in rhubarb roots. 

This enzyme exhibits no hydroxylase activity and is involved in the final synthesis of many naturally occurring /t-quinoncs. e.g. the naphthaquinone juglone in walnut (1.58) and the benzoquinone arbutin (hydroquinone-(3-D-glucopyranoside 2.46). Arbutin is a plant cryo-protectant that stabilizes membranes (Hincha et al., 1999). This compound has medicinal properties and has, for example, been used to treat urinary tract infections in humans. It is also used to lighten skin color, because it inhibits tyrosinase and hence the formation of melanin. The derivative deoxyarbutin (2.47 note the difference in the sugar molecule) was recently reported to be considerably more effective as a skin-lightening compound (Boissy et al., 2005). 

Figure 2. Chromatograms A, walnut extracted from the fiber B, juglone untreated C, juglone after acidification and D, C after neutralization. AU samples were eluted in System 1.

Juglone (5-hydroxy-1,4-naphthoquinone) is a water-soluble yellow pigment that is exuded from leaves, fruits, bark, and roots of black walnut Juglans nigra), English walnut (J. regia), and hickory (Carya ovata) trees, among others. 

It is well known that vegetables such as tomatoes or lettuce do not thrive near walnut trees. Juglone and a few related compounds are responsible for this effect. At a concentration of 0.002%, juglone completely prevents germination of lettuce seeds. It is thought that rain wash from walnut leaves and exudation from roots transport juglone to the soil (Soderquist 1979 Terzi et al. 2003 Terzi 2008). 

Terzi 1 (2008) AUelopathic effects of juglone and decomposed walnut leaf juice on musk melon and cucumber seed germination and seedUng growth. Afr J Biotechnol 7 1870-1874... 

The fresh fruit-shell of Juglans regia (English walnut) contains the naphthoquinone constituent juglone, which is mutagenic and possibly carcinogenic. The juglone content of dried shells has not yet been studied adequately. 

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