In this study we have exposed Selleck BMS202 wild-type and triazine-resistant plants of Canola to very high light intensities which caused photoinhibition. After one day the plants were transferred to a laboratory table with much less light. This cycle was repeated several days. The OJIP curve was each time measured after 1 day at high and after low light, respectively. The FIA analysis revealed that the photo-electrochemical component was suppressed Temozolomide after high light (and even completely abolished in the resistant biotype). There was a partial decrease of the photochemical component and a lower fluorescence parameter F o after high light. These effects were recovered after 1 day at the
low light of the laboratory. Materials and methods Plant material and growth conditions Canola (Brassica napus L.) seeds were planted on 18 September in a greenhouse at the University of Queensland, Brisbane, Australia. Sunrise was at about 5 am, sunset at about 6 pm. The roof of the greenhouse was cooled by water. Two plants of Vadimezan wild-type (S) and two of the resistant (R) biotype were used for the measurements. During day-time the temperature varied between 29 and 34°C; the photosynthetic photon flux density (PPFD) varied between 1,100 and 1,200 μmol photons m−2s−1 (HL). The fluorescence measurements were always performed at about 10 am and started on 23 October after the plants were exposed
to the high light. After 24 h in the greenhouse the plants were transferred to a table in the laboratory where the temperature varied between 21 and 23°C, and the PPFD was about 8 μmol photons m−2s−1 (LL). The plants were then transferred
several times from the laboratory to the greenhouse and back to the laboratory. Fluorescence measurements When following the effect of high light in the greenhouse and of low light in the laboratory, the same leaf of each individual plant under investigation was used. Measurements were performed at room temperature PJ34 HCl between 18 and 20°C. Induction curves of variable chlorophyll fluorescence were measured with a Plant Efficiency Analyzer (PEA, Hansatech Instruments Ltd, King’s Lynn, Norfolk, UK) using the standard clip for fixing the leaf in the proper position with respect to the optics of the instrument and kept in the dark for 20 min in the measuring unit. Fluorescence was excited with a 2 s pulse of red light (650 nm) obtained from light-emitting diodes at sub-maximal irradiance of about 280 W m−2 (approximately 1,500 μmol photons m−2s−1). Fluorescence data were recorded at a sampling rate of 10 μs in the lower time range between 0.01 and 0.2 ms, a sampling rate of 0.1 ms between 0.2 and 2 ms, a rate of 1 ms between 2 and 20 ms, and of 10 ms beyond 20 ms. Curves are plotted relative to F o which is the fluorescence level of the sample in the dark-adapted state.