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ρ-Cymene was one of the major components of volatiles released by croftonweed. The allelopthy of r-cymene on the growth of upland rice seedlings was performed. Hydrogen peroxide generation, malondialdehyde (MDA) content, proline content, total ascorbate (ascorbate/dehydroascorbate), reduced/oxidized glutathione, and the levels of induction of antioxidant enzyme were studied in the seedlings of upland rice. ρ-Cymene inhibited the growth of upland rice seedlings. Exposure of upland rice seedlings to ρ-cymene increased levels of H^sub 2^O^sub 2^, MDA, and proline, indicating lipid peroxidation and induction of oxidative stress. Activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase were significantly elevated during the treatment period (7-15 d) compared with enzymes in the upland rice seedlings unexposed to r-cymene, thereby indicating the enhanced generation of reactive oxygen species (ROS) upon ρ-cymene exposure. These results suggest that activation of the antioxidant system by ρ-cymene led to the formation of ROS that resulted in cellular damage and decreased growth of upland rice seedlings.
Nomenclature: Croftonweed, Ageratina adenophora (Sprenge) King & H.E. Robins. (synonym: Eupatorium adenophora Sprenge); rice, Oryza sativa L.
Key words: ρ-Cymene, reactive oxygen species, antioxidant enzymes.
Allelopathy has been shown to facilitate the invasion of some exotic species into previously diverse systems (Hierro and Callaway 2003; Knight et al. 2007). Allelopathic plants exert detrimental effects via the release of plant compounds (allelochemicals) through leaching, root exudation, volatilization, and decomposition of plant materials (Weir et al. 2006) and can interfere with the metabolism of other plants. If the effect of such compounds is harmful to plant growth and development, it becomes a biotic or allelochemical stress (Romero-Romero et al. 2005).
In general, various types of environmental stresses mediate their impact through oxidative stress caused by generation of reactive oxygen species (ROS) (Blokhina et al. 2003). ROS such as singlet oxygen (1O2), superoxide radicals (O2 2), hydroxyl radicals (OH2), and hydrogen peroxide (H2O2) are highly reactive and toxic molecules that can cause oxidative damage to membranes, DNA, proteins, photosynthetic pigments, and lipids (Apel and Hirt 2004). Recently, ROS generation and related oxidative stress has been proposed as one of the modes of action of plant growth inhibition by allelochemicals (Weir et al. 2004). However, very little is known about the action of allelochemicals/phytotoxins...