The Effect of 5OH-1,4-Naphthoquinone on Norway Spruce Seeds during Germination

Abstract

The effect of 5-OH-1,4-naphthoquinone (50H-NQ), a known inhibitor of germination and growth and an inducer of oxidative stress, on seeds from Norway spruce (Picea abies) during germination was studied. 50H-NQ was activated by homogenate from seeds to reactive species that reduce oxygen to superoxide radicals in vitro. Increasing concentrations of 50H-NQ increased lipid peroxidation during this activation. Small effects of 50H-NQ on germination of seeds were observed at concentrations up to 200 Mm. However, higher concentrations, e.g. 500 and 1000 AM, exerted more pronounced effects on seeds. These results suggest that the effect of 50H-NQ was a delay rather than an inhibition of germination. However, the effect of 50H-NQ on postgerminative growth was more potent than that on germination, and higher concentrations inhibited growth >97%. These results suggest that the seeds have a very effective defense system against quinone and reactive oxygen species, since the small effects of 50H-NQ on germination and postgermination at concentrations up to 200 AM can be explained by the formation of a metabolite of 50H-NQ that is not as reactive with oxygen as the original quinone. The 50H-NQ metabolite collected during germination experiments showed differences in its absorption spectrum in comparison with 50H-NQ, which suggest changes in structure. This metabolite was reduced by quinone reductase, but reduction of oxygen to superoxide radicals was not detected during its activation with homogenate from seeds. This metabolite may arise via a conjugation reaction, since the addition of 500 Mm uridine 5'-diphosphoglucuronic acid or 3'-phosphoadenosine-5'-phosphosulfate to the incubation mixture during activation of this metabolite by homogenate from seeds in vitro inhibited reduction of oxygen to superoxide radicals by 50 and 64%, respectively. The constitutive levels of superoxide dismutase and catalase were sufficient to prevent oxygen toxicity during activation of 50H-NQ, since these enzymes were not induced when the seeds were treated with 200 AM 50H-NQ.

Occurrence and Fate of the Phytotoxin Juglone in Alley Soils under Black Walnut Trees

“…Juglone (5‐hydroxy‐1,4‐naphthoquinone) (Table 1) is believed to be released by walnut trees ( Juglans spp) into the soil and accumulate to toxic levels sufficient to limit the growth of competing plants near the trees. Evidence of juglone toxicity comes from: (1) field observation of walnut toxicity toward certain plants causing symptoms collectively referred to as walnut wilt (Dana and Lerner, 1994; Tentinger, 2003); (2) hydroponics‐based solution culture toxicity testing, which demonstrated that juglone is potentially toxic to certain plant species (Funk et al, 1979; Rietveld, 1983; Segura‐Aguilar et al, 1992; Jose and Gillespie, 1998b; Kocacaliskan and Terzi, 2001; Hejl and Koster, 2004); and (3) field evidence of juglone accumulation in soils (Ponder and Tadros, 1985; De Scisciolo et al, 1990; Jose and Gillespie, 1998a). Whether juglone toxicity occurs at the target plant or not depends on its mode of toxic action and whether sufficient juglone concentrations in soil are available to invoke a toxic response.…”

“…In solution culture, Hejl and Koster (2004) reported that juglone interference with maize plants occurred at the roots of target plants by disrupting plasma membrane K + –ATPase activity and associated plant water and nutrient uptake. Some plants appear to have a protective capacity against oxidative stress from juglone by emitting enzymes that metabolize the compound to less toxic hydroquinones (Segura‐Aguilar et al, 1992; Matvienko et al, 2001). Juglone that has been released by source plants into the soil, if not irreversibly sorbed or degraded, will accumulate on soil particles in dynamic equilibrium with the solution phase and serve as an additional pool of juglone for the target plant/organism.…”

“…(2) hydroponics-based solution culture toxicity testing, which demonstrated that juglone is potentially toxic to certain plant species (Funk et al, 1979;Rietveld, 1983;Segura-Aguilar et al, 1992;Jose and Gillespie, 1998b;Kocacaliskan and Terzi, 2001;Hejl and Koster, 2004); and (3) field evidence of juglone accumulation in soils (Ponder and Tadros, 1985;De Scisciolo et al, 1990;Jose and Gillespie, 1998a). Whether juglone toxicity occurs at the target plant or not depends on its mode of toxic action and whether sufficient juglone concentrations in soil are available to invoke a toxic response.…”

Soil hypha‐mediated movement of allelochemicals: arbuscular mycorrhizae extend the bioactive zone of juglone

“…The chemical responsible for its allelopathy is juglone (5-hydroxy-1, 4 naphthoquinone) (Rice 1974), which has also been isolated from many other plants in the walnut family (Juglandaceae), including Juglans regia (Daglish 1950;Prataviera, Kuniyuki & Ryugo 1983;Ponder & Tadros 1985). This aromatic phytotoxic compound occurs naturally in all parts of the plant, but particularly in leaves and roots (Segura-Aguilar, Hakman & Rydstrom 1992). The plant contains large amounts of nontoxic and colourless hydrojuglone, which is transformed, for example, in the soil after cleavage of the glycosidic bond and oxidation of the aglycone to the toxic and orange juglone (Bertin, Yang & Weston 2003).…”

A review of suitable companion crops for black walnut

“…Roots, leaves, and hulls contain large quantities of harmless hydrojuglone, which may be oxidized to juglone (Segura-Aguilar et al 1992), then transferred to neighboring plants primarily as a root exudate in the rhizosphere of the black walnut trees (Bertin et al 2003). In susceptible plants, juglone interferes with respiration and photosynthesis (Hejl et al 1993).…”