Issue
Agronomie
Volume 23, Number 2, March 2003
Page(s) 147 - 151
DOI http://dx.doi.org/10.1051/agro:2002072
Agronomie 23 (2003) 147-151
DOI: 10.1051/agro:2002072

Persistence and detoxification of Pretilachlor and Fenclorim in rice (Oryza sativa)

Luciano Scarponia, Daniele Del Buonoa and Costantino Vischettib

a  Dipartimento di Scienze Agroambientali e della Produzione Vegetale - Università degli studi di Perugia, Borgo XX Giugno 72, 06121, Italy
b  Centro di Studio sulla Chimica e Biochimica dei Fitofarmaci - CNR, Borgo XX Giugno 72, 06121 Perugia, Italy

(Received 28 March 2002; accepted 30 May 2002)

Abstract
The contents and persistence of pretilachlor (P) and of the safener fenclorim (F) in rice treated with P, F and their mixture were investigated in relation to the expression of glutathione-S-transferase (GST) activity in response to treatments. F failed to reduce the accumulation of P, however it was able to reduce its persistence in rice shoots. On the other hand, while P did not reduced F persistence, it determined a greater than two-fold F accumulation in plants. Therefore, a detoxification mechanism common to the two compounds but favourable to P was hypothesised. This mechanism consists in an activation of GST activity toward P as substrate [GST(P)] in response to all treatments. The activation levels were found to be proportional to the amount of persistent P and F, and to be additive following the P-F mixture treatment. The kinetic parameters V $_{{\rm max}}$ and K $_{\rm m}$ of GST(P) were increased and decreased, respectively, in rice shoots treated with P, F and particularly with P-F mixture. Therefore, a defence mechanism toward P, consisting in an increased expression of GST(P) in rice plant, both as the global amount of the enzyme in the protein "pull" and the induction of the enzyme isoforms more sensitive to P, in response to all treatments, especially the P-F mixture treatment, is confirmed. This finding is consistent with the observed effect of F on P persistence and detoxification in the rice shoots.

Résumé
Persistance et détoxication du pretilachlore et du fenclorim dans le riz (Oryza sativa). On a étudié la teneur et la persistence du pretilachlore (P) et du fenclorim (F), un antidote, dans le riz traité avec P, F et un mélange des deux par référence à l'activité de la glutathion-S-transférase (GST) en réponse aux traitements en question. F n'a pas réussi à réduire l'accumulation de P, mais a pu réduire sa persistance dans les pousses de riz. D'autre part, P n'a pas réduit la persistance de F, mais a déterminé une accumulation plus que double de F dans les plantes. Donc a-t-on soulevé l'hypothèse d'un mécanisme de détoxication commun aux deux composés, mais favorable à P. Ce mécanisme consiste en une activation de l'activité GST à l'égard de P comme substrat [GST(P)] en réponse à tous les traitements. On a relevé que les niveaux d'activation étaient proportionnels à la quantité de P et F persistants, et additifs dans le cas du traitement avec le mélange P-F. Les paramètres cinétiques V $_{{\rm max}}$ et K $_{\rm m}$ de [GST(P)] ont été respectivement augmentés et diminués dans les pousses de riz traitées avec P, F et particulièrement avec le mélange P-F. On a eu donc confirmation d'un mécanisme de défense à l'égard de P, consistant en une expression accrue de [GST(P)] dans la plante de riz, en ce qui concerne tant la quantité globale de l'enzyme dans le " pull " protéique que l'induction des isoformes enzymatiques plus sensibles à P, en réponse à tous les traitements et surtout au traitement à base de mélange P-F. Ce résultat concorde avec ce qui a été observé quant à l'effet de F sur la persistance et la détoxication de P dans les pousses de riz.


Key words: Oryza sativa / pretilachlor / fenclorim / persistence / glutathione-S-transferase

Mots clés : Oryza sativa / pretilachlore / fenclorim / persistence / glutathion-S-transférase

Correspondence and reprints: Luciano Scarponi
    e-mail: scarponi@unipg.it

© INRA, EDP Sciences 2003

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