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Published online by Cambridge University Press: 12 June 2017
Studies were conducted to determine the effect on photosynthesis, the absorption, and the metabolism of simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] in two biotypes of common groundsel (Senecio vulgaris L.). Simazine inhibited photosynthesis in the susceptible (S) plants, but resistant (R) plants were unaffected. When the herbicide was removed from the S biotype after 24 hr, photosynthesis resumed. Both biotypes absorbed the herbicide equally well and were unable to metabolize simazine during 96 hr. The greatest concentration of 14C activity (80 to 90%) was located in the chloroform-soluble fraction of the foliage of each biotype and was identified as simazine. Small amounts of radioactivity (10 to 15%) occurred in the water-soluble fraction, but there was no differential increase in water-soluble simazine metabolites. A different mechanism of resistance than previously reported for triazine-resistant plants may be operative in one groundsel biotype.