Influence of high light and UV-B radiation on photosynthesis and D1 turnover in atrazine-tolerant and -sensitive cultivars of Brassica napus

An atrazine-tolerant mutant and an atrazine-sensitive cultivar of Brassica napus L. were grown under visible radiation (400 mu mol m(-2) s(-1), photos ynthetically active radiation, PAR) and then subjected to treatment conditi ons. These included short-term high PAR (1600 mu mol m(-2) s(-1)) which was given for 4 h either alone or in combination with an enhanced level of UV- B-BE radiation (4.6 kJ m(-2) h(-1) biologically effective UV-B, 280-320 nm) , Recovery from the radiation treatment was studied for 4 h under the light conditions for growth. Since it is known that the atrazine-tolerant mutant is susceptible to photoinhibition, one of the aims of the present study wa s to determine the effects of a supplemental, enhanced level of UV-B radiat ion with regard to the mutant, The results indicate an additive effect of U V-B radiation on F-v/F-m, photochemical yield and photosynthetic oxygen evo lution during both exposure and recovery, and also a higher susceptibility of the mutant to photoinhibitory PAR conditions alone and in combination wi th UV-B, which may have implications in a changing environment. Both cultiv ars also showed a higher D1 turnover during the radiation stress than durin g recovery, as shown by immunoblotting and S-35-methionine incorporation me asurements.