Metabolism and selectivity of rice herbicides in plants

Abstract

Chemical weed control with effective and highly active herbicides has been very useful and convenient means. It has contributed to stable crop production and is labor saving. Recent herbicides have had characteristics such as high effectiveness without causing environmental pollution or harmful effects, and appropriate herbicides having high activity, low toxicity, high selectivity and being non‐persistent have been developed. The metabolism of rice herbicides used mainly in Japan, such as sulfonylurea, chloroacetamide, acylamide, urea, thiocarbamate, pyrazole, triazine, diphenyl ether, phthalimide, phenoxy, aryloxyphenoxypropionate, etc., is reviewed, and its involvement in selectivity is also discussed. The metabolism of herbicides is closely related to their activity and selectivity. Differential herbicide metabolism in plants is a contributing factor of selectivity between crops and weeds. Chemicals that are more detoxified in crops and/or more activated or less detoxified in weeds are considered as being effective and selective herbicides. The metabolism of various types of rice herbicides includes: oxidative reaction (ring and chain hydroxylation, O‐ and N‐dealkylation), hydrolysis and subsequent glucose conjugation, and glutathione conjugation in rice. These detoxicative activities are much higher in rice than weeds in paddies, and this leads to the selectivity of herbicides. Enzymes, oxidase, P‐450 mono‐oxygenase, esterase, acylamidase, glucosyl transferase, glutathione transferase, etc., play important roles in herbicide metabolism and selectivity.

Sensibilidade de plantas de arroz ao herbicida bispyribac-sodium em função de doses e locais de aplicação

“…Essa característica tem feito com que alguns produtores cometam alguns abusos na dose do produto. Para os cultivares mais sensíveis, doses acima das recomendadas causam intoxicação e prejuízos ao desenvolvimento das plantas da cultura (Usui, 2001;Santos et al, 2006). No entanto, o bispyribac-sodium é altamente catiônico; as cargas presentes nas moléculas do herbicida fazem com que ele fique fortemente ade rid o às par tíc ula s de argil a e mat éri a orgânica do solo, perdendo a ação (Leite et al, 1998;Kobayashi, 2004).…”

Effects of 2,4-D on the germination of megaspores and initial development of Regnellidium diphyllum Lindman (Monilophyta, Marsileaceae)

“…At low concentrations, it stimulates growth of plant cells and on interacting with endogenous hormones like ethylene, giberellic acid, abscisic acid and even auxins, 2,4-D can break seed dormancy, stimulating the germination process (Brady and McCourt, 2003). On the other hand, high concentrations or successive applications of this herbicide retarded or even inhibited the germination of dicotyledonous and monocotyledonous seeds (Usui, 2001).…”

“…Of all the commonly used herbicides from the phenoxy class, 2,4-dichlorophenoxyacetic acid (2,4-D) most effectively controls broad-leaved plants when applied post-emergence. The herbicide presents auxinic activity and stimulates the production of ethylene and hydrogen cyanide, causing phytotoxicity (Usui, 2001).…”

“…Herbicides can widely vary in the mode of action and effects across various phylogenetic groups of plants (Fairchild et al, 1997), indicating the potential use of aquatic plants as bioindicators. Plants differ in their capacity to transform and degrade herbicides, since different types and activities of enzymes work on this metabolism (Usui, 2001).…”

“…Wetlands receive inputs of herbicides commonly used to control weeds through direct deposit from aircraft spraying, lateral drift and runoff from fields. Required characteristics of modern herbicides include high effectiveness without causing environmental pollution or harmful effects, high activity, low toxicity, high selectivity and being non-persistent (Usui, 2001).…”