International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 240-248 http://ecoevopublisher.com/index.php/ijmec 24 2 In walnut trees, juglanone exists in a non-toxic bound form. When plant tissues are damaged or metabolic products enter the soil, walnut ketone is transformed from a precursor (also known as hydrolyzed walnut ketone or walnut quinone glycoside) to a free state with strong inhibitory activity (Xu et al., 2023). Free juglandone is the main "weapon" of the chemical sensitivity of black walnut and has a significant inhibitory effect on seed germination and seedling growth of various plants (Nicolescu et al., 2020; Park et al., 2020). However, recent studies have indicated that the inhibitory effect of walnut leaf extract on certain plants is stronger than that of pure walnut ketone solution of the same concentration, suggesting that in addition to walnut ketone, there may be other chemosensitic substances with synergistic effects in walnut tissue. For instance, polyphenols such as tannins contained in walnut leaves and peels may exert effects different from those of juglanone on certain receptor plants, thereby jointly constituting the chemosensory "chemical pool" of walnut trees (Medic et al., 2021b; Zubay et al., 2021). Despite this, juglanone is undoubtedly the core component in the chemosensory strategy of black walnut, and its mechanism of action and environmental behavior have also become the focus of chemosensory ecology research. 3 The Mechanism of Action of 3-Juglanone and the Response of Target Plants 3.1 Effects on the physiology of adjacent plants Juglandone has significant inhibitory effects on seed germination, seedling growth and physiological functions of various plants (Ochekwu and Uzoma, 2020; Park et al., 2020). Plants affected by juglanone often show symptoms such as decreased germination rate, hindered root growth, and wilting and yellowing leaves. This is because when walnut ketone enters sensitive plants, it interferes with their basic physiological processes. For instance, sensitive crops (such as tomatoes and potatoes) grown under walnut trees often show slow growth, wilting and even death, which is attributed to the inhibition of the respiration and water and nutrient absorption functions of these crops by juglandone (Nicolescu et al., 2020). Greenhouse experiments have shown that the addition of juglanone significantly reduces the plant height, biomass and yield of sensitive plants (such as cucumbers and tomatoes) (Ochekwu and Uzoma, 2020; Medic et al., 2023). Research has found that when the concentration of juglanone in the soil reaches 1 mM, the yield of cucumber seedlings drops significantly. Moreover, juglanone can also inhibit secondary metabolism in cucumbers, reducing the plants' resistance to diseases and adverse conditions. Similarly, it was observed in the field that there were few herbaceous plants and a single dominant species under the black walnut grove, and the population vitality was significantly limited (Nicolescu et al., 2020). This indicates that the effects of walnut ketone on adjacent plants are multifaceted: including direct toxic effects that inhibit seed germination and seedling growth, as well as disrupting the metabolic balance within the recipient plants, thereby weakening their competitiveness and viability (Ochekwu and Uzoma, 2020; Medic et al., 2023). 3.2 Research progress on cellular and molecular mechanisms The chemosensory inhibitory effect of walnut ketone involves a series of disorder mechanisms at the receptor plant cell and molecular levels. Firstly, walnut ketone is an oxidized naphthoquinone that can generate excessive reactive oxygen species (ROS) in recipient plant cells, leading to lipid peroxidation and cell membrane damage. Walnut ketone has alkylation activity and can covalently bind to thiol groups on the cell membranes and enzyme proteins of receptor plants, interfering with the function of key enzymes (Han et al., 2021). In addition, juglanone can also interfere with the hormone balance and gene expression within plants. Research has found that the application of exogenous plant hormones (such as gibberellin and agonist) can partially alleviate the inhibition of juglandone on the germination and growth of water celery seedlings, suggesting that juglandone may inhibit growth by influencing the levels of endogenous hormones. From the perspective of gene expression, some studies conducted transcriptome analysis using the model plant rice and identified a series of genes induced or inhibited by walnut ketone, including antioxidant, defense-related genes and signal transduction components (Medic et al., 2021b). This indicates that the recipient plants will initiate defense responses under juglanone stress, but it is often difficult to counteract its toxic effects.
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