Acúmulo de ácido chiquímico em biótipos de espécies convolvuláceas e rubiáceas em resposta ao glyphosate

Abstract

The blockade on the route of the shikimic acid makes its to accumulate, which represents a direct inhibition of EPSPs. The investigation of the tolerant mechanisms allows an understanding about the evolution of the tolerance on the populations and assists on choosing the strategies for control of the tolerant species. The main objective of this work was to determine, by analysis of the accumulated shikimate on plants, if the modified action place (EPSPs enzyme) or limitation in the arrival of the glyphosate to the chloroplasts are involved on the tolerance of Convolvulaceae and Rubiaceae species to glyphosate. On this experiment with Convolvulaceae species, the treatments were arranged in a 3 x 2 x 4 + 1 factorial, whereby the first factor was the following species: I. grandifolia, I. indivisa and I. purpurea; the second factor was the sensitive and tolerant biotypes to glyphosate; and the last factor was four periods of evaluation after glyphosate application (2, 8, 24 and 72 hours), plus a witness plant without application. On the experiment with Rubiaceae species, the treatments were arranged in a 2 x 2 x 4 + 1 factorial, whereby the first factor was the following species: R. brasiliensis and B. latifolia; the second factor was the sensitive and tolerant biotypes to glyphosate; and the last factor was four periods of evaluation after glyphosate application (2, 8, 24 and 72 hours), plus a witness plant without application. The accumulation of shikimate was determined by biochemical analysis in laboratory. The I. indivisa showed a greater accumulation of glyphosate in the sensitive biotype to glyphosate, totalizing a 1,14 and 0,94 mg of shikimate build-up per green tissue gram (mg c. g-1 g.t.), on 72 HAA (hours after application) for the sensitive and tolerant biotypes respectively. The species R. brasiliensis and B. latifolia showed distinct behavior in relation to the shikimate accumulation, noting that the R. brasiliensis had no significative difference between biotypes, while B. latifolia showed higher accumulation of shikimate on the sensitive biotype (1,92 mg ac. g-1 g.t.), comparing to the tolerant biotype (1,64 mg ac. g-1 g.t.). It was possible to evidence that the tolerant biotype of the species I. indivisa and B. latifolia had accumulated less shikimic acid levels comparing to the sensitive biotype, indicating a limitation on the arrival of glyphosate to the chloroplasts.