Beitrag zur Kenntnis der Resistenzphänomene einzelner Pflanzen gegenüber dem phytotoxischen Wirkstoff Simazin

Abstract. The metabolism of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) in the resistant species, corn (Zea inays L.) and scrghum (Sorghum vulgare Pers.) was not the same. In corn, atrazine was metabolized via both the 2-hydroxylation and N-dealkylation pathways while sorghum metabolized atrazine zvia the N.dealkylation pathway. Atrazine metabolism in corn yielded the metabolites, 2-hydroxy-4-ethylamino-6-isopropylamino-s-triazine (hydroxyatrazine), 2-hydroxy-4-amino-6-isopropylamino-s-triazine (hydroxycompound I), and 2-hydroxy-4-amino-6-ethylamino-s-triazine (hydroxycompound II). None of these hydroxylated derivatives appeared as metabolites of atrazine in sorghum.Hydroxycompounds I and II were formed in 2 ways in corn: (1) by benzoxazinone-catalyzed hydrolysis oif 2-chloro-4-amino-6-isopropylamino-s-triazine (compound I) and 2-chloro.4-aminc-6-ethylamino-s-triazine (compound II) that were formed by N.deadkylation of atrazine and (2) by N-dealkylation of hydroxyatrazine, the major atrazine metabolite in corn. The interaction of the 2-hydroxylation and N-detilkylation pathways in corn results in the formation of the 3 hydroxylated non-phytotoxic derivatives of atrazine.Metabolism of 2-chloro-4-ethl-laiinio-6-isopropylamiiino-s-triazine (atrazine) in hligher plants was shown to be an important factor in herbilcidal selectivity. Detoxication of atrazine was reported to occur via the 2-hydroxylation and N-dealkylation pathways in higher plants (12). Corn is resistant to atrazine and 2-chloro-4,6-bis (ethylamino) -s-triazine (simazine) largely because of its ability to convert the 2 herbicides rapidly to non-phytotoxic, 2-hydroxv -4 -ethylamino-6-isopropyl-amino-s-triazine (hydroxyatrazine), and 2-hydroxy-4,6-bis (ethylamino)-s-triazine (hydroxysimazine) (1,2,5,10,12). The conversion of the 2-chlorotriazines to their 2-hydroxy derivatives is catalyzed non-enzymatically by a cyclic hydroxamate, 2,4-dihydroxy-3-keto-7-methoxy-1,4-benzoxazine (benzoxazinone) present in corn plants ( 1, 5, 9). The hydroxylation reaction appears to be correlated with the presence of benzoxazinone in different species (4,12). N-Dealkylation of atrazine occurred in higher plants to form 2-chloro-4-amino-6-isopropylamino-striazine (compound I) and 2-chloro-4-amino-6-ethylamino-s-triazine (compound II) (12,13,14). In resistant sorghum, only the N-dealkylation pathway was reported to be active, but in, corn both hydroxylation and N-dealkylation pathways were active.Autoradiographic evidence indicated that after a 48-hr atrazine treatment period, corn and sorghum yielded at least 1 common water-soluble metabolite of atrazine, but corn produced 2 other metabolites, neither of which was hydroxyatrazine (12).Hydroxylation of compounds I and II to fornm hydroxycompounds I and II (fig 1) is pos-sible in benzoxazinone-containing corn, but not in sorghum. N-Dealkylation of hydroxvatrazine (fig 1) could also occuir in corn to give hydroxyconu ounds I ande II. Such a reaction would not occur in sorghumi since atrazin.e is not conve...

Section: Methodsmentioning

confidence: 63%

mentioning

confidence: 99%

Atrazine Metabolism in Resistant Corn and Sorghum

Shimabukuro

1968

“…Although the physiological role of DIMBOA is unknown, various workers have postulated its involvement in: (a) detoxification of s-triazine herbicides (21,26); (b) iron transport (25); (c) resistance to fungal infection in corn and wheat (2,7,8,20); and (d) as a factor in insect resistance (17,19). Because of the instability of DIMBOA, Whitney and Mortimore (30) have postulated that its degradation product, MBOA, may be involved in the resistance of corn to bacteria.…”

mentioning

confidence: 99%

Decomposition of 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one in Aqueous Solutions

Woodward¹,

Corcuera²,

Helgeson³

et al. 1978

140

Cyclic hydroxanc acids present in some species of Gramineae have been reported to be Important In resbtace of these plnts to fngi aNd insects. Since The amount of DIMBOA5 (Fig. 1) and its glucoside may total more than 1% of the dry wt of corn plants (14,16). In aqueous solutions near neutral pH, free DIMBOA has been reported to decompose quantitatively to MBOA and formic acid (28,29). This facile decomposition of DIMBOA to MBOA has been used for the measurement of DIMBOA content ofcorn by isotopic dilution (15), spectrofluorometry (3), and IR analysis (22). By each method, MBOA is the compound actually measured, and 100% conversion of DIMBOA to MBOA is assumed.

“…The nonenzymatic hydroxylation reaction was catalyzed by a cyclic hydroxamate isolated from corn and identified as benzoxazinone (10,11,19,28).…”

Section: Miaterials and Methodsmentioning

confidence: 99%

Glutathione Conjugation

Shimabukuro¹,

Frear²,

Swanson³

et al. 1971

168

The primary factor for atrazine selectivity in corn (Zea mays) is the activity of a soluble enzyme, glutathione Stransferase, which detoxifies atrazine by catalyzing the formation of an atrazine-glutathione conjugate (GSatrazine). The nonenzymatic, benzoxazinone-catalyzed hydrolysis of atrazine to hydroxyatrazine contributed to the total resistance of corn to atrazine, but the nonenzymatic detoxication pathway does not seem to be essential for resistance. All corn lines investigated, except for susceptible GT112, rapidly detoxified atrazine by glutathione conjugation. Only GT112 had low glutathione S-transferase activity. Hydroxyatrazine was found in significant quantities only when atrazine was introduced initially into the roots. The amount of hydroxyatrazine formed was nearly equal for susceptible GT112 and most of the resistant corn lines investigated. This investigation indicates that some plants protect themselves against toxic organic hialide compounds witlh a mechanism similar to that known to exist in animals. and the closely related metabolite 'y-glutamyl-S-(4-ethylamino-6-isopropylamino-2-s-triazino)cysteine from resistant sorghum indicated the presence of a third metabolic pathway for atrazine degradation (15). N-Dealkylation was previously identified as another atrazine degradation pathway in plants (23,24). The recovery of atrazine-inhibited photosynthesis in both sorghum and corn leaf discs was accompanied by a rapid conversion of atrazine to GS-atrazine rather than to hydroxyatrazine (24, 25). The two peptide-conjugated metabolites will be referred to collectively in this paper as GS-atrazine since both compounds chromatograph as a single spot (metabolite B) (24) upon separation by thin layer chromatography (15).The isolation and characterization of the enzyme, glutathione S-transferase, from corn, sorghum, and other resistant species, indicated an enzymatic reaction for the formation of GS-atrazine (6). The presence of this highly active enzymatic pathway in corn leaf tissue suggests that the formation of GS-atrazine is the key factor in the resistance of corn to atrazine (25). This investigation was undertaken to show that the principal factor for atrazine selectivity in corn was the enzymatic formation of GS-atrazine rather than the nonenzymatic hydrolysis of atrazine to hydroxyatrazine as reported (3,7,11,18). MIATERIALS AND METHODSThe substituted s-chlorotriazines, atrazinel and simazine, are two of the most widely used herbicides for the control of annual weeds in fields of corn and sorghum. Both of these herbicides are believed to be metabolized similarly in plants, and their mode of action is the same. These compounds are effective inhibitors of the Hill reaction in photosynthesis (5, 16) and are known to reduce the rate of CO2 fixation in plants (1,27,29).Resistance of corn to the 2-chloro-s-triazines has been attributed to the nonenzymatic detoxication of the herbicides to hydroxyatrazine and hydroxysimazine (3,7,11,18). The nonenzymatic hydroxylation reaction was catalyzed by a...