Comparison of Photosynthetic Activities in Triazine-Resistant and Susceptible Biotypes of Chenopodium album

V ictor B. Curwiel, G ert Schansker, O scar J . de Vos, and Jack J. S. van Rensen Department of Plant Physiology, Agricultural University Wageningen, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands Z. Naturforsch. 4 8 c , 2 7 8 -2 8 2 (1993); received November 26, 1992 Chloroplasts, Triazine-Resistance, Photosystem II, Photoinhibition, Fluorescence Triazine-resistant and susceptible Chenopodium album plants were grown at low and at high light irradiances. At the lower light irradiance the dry matter production of the resistant and the susceptible plants were almost similar. At the higher irradiance the resistant biotype had a significantly lower production. Fluorescence studies showed that the photochemical yield and the photosystem II electron transport rate were lower in the resistant biotype. It could be demonstrated in intact leaves that the lower productivity of the resistant biotype is caused by a higher sensitivity to photoinhibition. However, when studying effects of photoinhibition on electron flow and photophosphorylation in isolated thylakoids of the two biotypes, no signifi­ cant differences between resistant and susceptible plant materials were observed. It is suggest­ ed that the difference between resistant and susceptible biotypes connected with processes pro­ tective against photoinhibition in intact leaves, are lost during the isolation of thylakoids.