Glyphosate effects on gas exchange and chlorophyll fluorescence responses of two Lolium perenne L. biotypes with differential herbicide sensitivity

YANICARI MARCOS; TAMBUSSI E A; ISTILART C; CASTRO A M

PLANT PHYSIOLOGY AND BIOCHEMISTRY

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER

Lugar: Paris; Año: 2012 vol. 57 p. 210 - 217

0981-9428

Despite the extensive use of glyphosate great controversy remains about how it alters the physiology and metabolism of treated plants. Photosynthesis is not regarded to be a primary inhibitory target of glyphosate, but it has been reported to be affected by the herbicide. The aim of the current research was to determine herbicide effects on the light and dark reactions of photosynthesis comparing susceptible and glyphosate-resistant Lolium perenne biotypes. After glyphosate treatment, accumulation of reduced carbohydrates occurred previous to the decline of gas exchange. Stomatal conductance and CO2 assimilation are both affected earlier than chlorophyll fluorescence and amount of chlorophyll in susceptible plants. In the glyphosate-resistant biotype, stomatal conductance was the unique parameter slightly affected only after 5 days post-application. In susceptible plants, the initial glyphosate effects on gas exchange could be a response to a feedback regulation of photosynthesis. The herbicide affects actively growing tissues regardless of the inhibition on the photosynthesis, thereby the demand of assimilates decreased and consequently it induced an accumulation of carbohydrates in leaves. Stomatal conductance could be a very sensitive parameter to assess both the susceptibility/resistance to glyphosate in an early lapse before the visual phytotoxic symptoms become evident.