Juglone

Juglone is an organic compound classified as a hydroxy-naphthoquinone, specifically 5-hydroxy-1,4-naphthoquinone. Its chemical formula is C10H6O3. Juglone occurs naturally in Juglans species, most notably black walnut (Juglans nigra), and is found in various tree tissues such as roots, husks, leaves, and wood. It is the main allelopathic agent produced by many walnut trees and can be released into the surrounding environment through root exudation and the decomposition of plant material.

Ecologically, juglone can inhibit germination and growth of a wide range of other plants in a zone around a walnut tree, sometimes called the juglone or allelopathic zone. Sensitivity is species-dependent and influenced by environmental factors such as soil type, moisture, and microbial activity. Some species show tolerance or even benefit, while many common garden species are adversely affected.

Chemically, juglone is relatively hydrophobic and has limited water solubility but dissolves in organic solvents. It is light-sensitive and can degrade when exposed to sunlight. In plant cells, juglone can interfere with mitochondrial respiration and photosynthesis, and it can react with thiol groups in proteins, contributing to its phytotoxic effects and the generation of reactive oxygen species in some contexts.

Uses and safety: Juglone has been studied for antimicrobial and antifungal properties and has been explored in natural dye applications and horticultural research. Because of general toxicity to plants, animals, and humans at higher exposures, it is not used as a medicine and handling should avoid ingestion or prolonged skin contact. In ecological settings, its presence influences plant community composition around walnut trees and can complicate cultivation of nearby crops.