This work analyses the effects of alternation of light/dark periods pretreatment (AL) in tobacco plantlets (Nicotiana tabacum L. cv.Virginie vk51) growing in solution with low concentration of the clomazone herbicide. The experimentation has been carried out by exposing the plantlets to successive and regulated periods of light (16min light/8min dark cycles, PAR 50μmolm(-2)s(-1)) for three days. The photosynthesis efficiency was determined by mean of the chlorophyll fluorescence and JIP-test. The AL pretreatment improved the clomazone tolerance; this has been observed by the increase in the leaf area of the plant, the maximal photochemical quantum efficiency of PSII (Fv/Fm), the actual PSII efficiency (ФPSII), the performance index (PIabs), the electron flux beyond Quinone A (1-VJ), and also by the diminution of the energy dissipating into heat (DI0/RC). Furthermore, AL pretreatment led to low accumulation of hydrogen peroxide (H2O2) which proves that the scavenging enzymatic system have been activated before clomazone treatment. In the plantlets pretreated with AL, with regard to the ascorbate content, some of antioxidant enzyme whose function is associated with it have continued to scavenge reactive oxygen species (ROS) induced by clomazone, such as ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). So, the observed photooxidative damages induced by clomazone herbicide were noticeably reduced.
Keywords: Chlorophyll fluorescence; JIP-test; Light; Nicotiana tabacum; Photosynthesis; Photosystem II; Tolerance.
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