Safening Mechanism of Dymron and Dimepiperate on Azimsulfuron-Treated Rice.

2001

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.

Section: Metabolism Of Rice Herbicides In Plantsmentioning

confidence: 99%

Metabolism and selectivity of rice herbicides in plants

2001

“…may be dependent on cytochrome P-450 reactions (Shim et al 1990b). Dymron may display safening effects partially by enhancing the metabolism of not only a sulfonylurea herbicide, but also a chloroacetamide herbicide via enhancing cytochrome P-450 activity, as well as dimepiperate (Nishizaka et al 1991;Shirakura et al 1988Shirakura et al , 1996Yun et al 1999). Dymron is also known to reduce the uptake of bensulfuron-methyl by rice seedlings .…”

Section: Concentrationmentioning

confidence: 99%

“…Pretilachlor is a chloroacetamide herbicide commonly used to control some broadleaf weeds and annual grasses in transplanted ricefields (Murakami 1990). Dymron [1‐(α,α‐dimethybenzyl)‐3‐( p ‐tolyl)urea], an urea herbicide (sedge killer), however, is known to protect rice from injury caused by chloroacetamide herbicides, pretilachlor and thenylchlor (Ogasawara et al 1991), as well as sulfonylurea herbicides, bensulfuron methyl and azimsulfuron (Nishizaka et al 1991; Shirakura et al 1996), and dymron may enhance oxidative or cytochrome P‐450 activity in rice. However, Omokawa et al (1996 ) reported that dymron reduced the uptake of bensulfuron‐methyl by rice seedlings, and quantitative changes in the metabolism of bensulfuron‐methyl by safened rice seedlings were observed, but these did not appear to support the involvement of enhanced herbicide metabolism in the safening action of dymron.…”

Section: Introductionmentioning

confidence: 99%

Relationship between safening activity of dymron and fenclorim to pretilachlor and glutathione S‐transferase activity in rice

Deng

Yamada

2001

Dymron [1‐(α,α‐dimethybenzyl)‐3‐(p‐tolyl)urea] and fenclorim (4,6‐dichloro‐2‐phenylpyrimidine) were found to exhibit a safening activity on the growth of rice (Oryza sativa L.) seedlings against pretilachlor [2‐chloro‐2′,6′diethyl‐N‐(2‐propoxyethyl)acetanilide] injury. By pretilachlor treatment at 10–6 and 10–5 mol L–1, the elongation of the third leaves of rice seedlings was reduced by approximately 20 and 40%, and that of the fourth leaves was reduced by approximately 40 and 80%, respectively. Upon the treatment of dymron at 3 × 10–6 and 10–5 mol L–1 in combination with pretilachlor, the growth inhibition was half alleviated in the third leaves, and the length of the fourth leaves was almost recovered from 10–6 mol L‐1 pretilachlor injury, and was 20–25% recovered from 10–5 mol L–1 pretilachlor injury. Upon the treatment of fenclorim at 3 × 10–6 and 10–5 mol L–1 in combination with pretilachlor, the growth inhibition of rice seedlings was almost alleviated in both the third and the fourth leaves. This result indicated that dymron and fenclorim showed almost the same safening effect on the fourth leaf growth against 10–6 mol L‐1 pretilachlor injury, although fenclorim showed higher effects at higher concentrations of pretilachlor. Glutathione S‐transferase (GST) activities in rice seedlings were investigated after being treated with a herbicide and safener. By pretilachlor treatment at 10–6 and 10–5 mol L–1, the GST activity was approximately 32 and 72% increased in roots, respectively, and a little increased (7–13%) in shoots of two‐leaf‐stage rice seedlings. By dymron treatment at 3 × 10–6−10–5 mol L–1, the GST activity was 2–30% increased in roots, but was not increased in shoots. By their combination treatment, the GST activity was almost the same or less than that by treatment with pretilachlor alone. In contrast, by fenclorim treatment alone, the GST activity was 43–52 and 33–45% increased in roots and shoots of rice seedlings, respectively. By the combination treatment of pretilachlor and fenclorim, the GST activity was increased 73–126% in shoots and 101–139% in roots, and was much more increased in both shoots and roots compared with treatment of pretilachlor or fenclorim alone. It was found that dymron showed less effect in increasing the GST activity than fenclorim. It is also suggested that dymron did not increase the GST activity in shoots but did increase it slightly in roots, and showed almost no effect on GST increase by pretilachlor in shoots, or rather reduced the increase in roots. From the above results, fenclorim and dymron may have different mechanisms of safening effects on the protection of rice seedlings against pretilachlor injury.

“…However, the GST activity might not play a major role in the safening action of dymron on pretilachlor injury (Deng et al 2001). In contrast, the safening action of dymron against sulfonylurea herbicides such as azimsulfuron [1‐(4,6‐dimethoxypyrimidin‐2‐yl)‐3‐[2‐methyl‐4‐(2‐methyl‐2 H ‐tetrazol‐5‐yl)‐2 H ‐pyrazole‐3‐sulfonyl]urea] and bensulfuron‐methyl [methyl‐2‐[[[[[(4,6‐dimethoxypyrimidin‐2‐yl)‐amino]‐carbonyl]‐amino]‐sulfonyl]‐methyl]‐benzoate] on rice seedlings was induced by the enhancement of O ‐demethylation of both herbicides (Shirakura et al 1996) and the reducing absorption of bensulfuron‐methyl into the seedlings (Omokawa et al. 1996).…”

Section: Introductionmentioning

confidence: 99%

Differential safening activity of dymron and fenclorim on pretilachlor injury in rice seedlings in soil

Miyauchi¹,

Kobayashi

2002

The safening activity of dymron [1‐(α,α‐dimethylbenzyl)‐3‐(p‐tolyl)urea] and fenclorim [4,6‐dichloro‐2‐phenylpyrimidine] on the phytotoxic activity of pretilachlor [2‐chloro‐2′,6′‐diethyl‐N‐(2‐propoxyethyl)acetanilide] on rice seedlings was examined in both water and soil culture. The safening activity of fenclorim in water culture was greater than that of dymron, whereas the activity of fenclorim in soil was lower than that of dymron. The fenclorim concentration in soil water was lower than that of dymron at all times when determined after the application at the same concentrations. The phytotoxic activity of pretilachlor and the safening activities of dymron and fenclorim were well correlated with the concentration of each in soil water but not with the amount in total soil. The adsorption of fenclorim on soil solids was greater than those of dymron and pretilachlor. It was suggested that both the phytotoxic activity of pretilachlor and the safening activities of dymron and fenclorim were dependent on their concentrations in soil water, which were primarily dominated by the adsorption on soil.