This experiment aimed to correlate the oxidative burst with the Mn accumulation and metabolism within the chloroplast lamellae of UV-B irradiated rice. Oryza sativa L. cv. Safari plants were grown (Lidon and Ramalho, 2011) over a 28-days period, in nutrient solutions containing N, P, K, Ca, Mg, Al, Fe, Mo, B, Cu, Zn, (in mg L-1 – respectively, 40, 10, 40, 40, 40, 40, 20, 2, 0.05, 0.2, 0.01 and 0.01; iron was added as hexahydrated FeCl3) and increasing Mn concentrations (0.5, 2 and 8 mg·L-1). The solutions were adjusted daily to pH 4.5, the volume kept constant at the original level, and were renewed every 5 days. Under these growth conditions, the impact of UV-B radiation on photosynthetic related parameters was studied after an UV-B irradiation performed 1 h per day for 7 days (between 8 and 14 days after germination), with a ten narrow-band (k 311 nm), that resulted in a total biological effective UV-B (UVBBE) of 2.975 kJ m-2day-1 and a total of 20.825 kJ m-2 (Lidon et al., 2012). In the 15th 21st and 28th days after germination, in non UV-B treated rice, the shoot amount of Mn in the 0.5, 2 and 8 mg L-1 showed a 1.7, 2.6 and 2.9 fold increase, being the trends in the related UV-B irradiated treatments similar but about 20-15% lower. The thylakoid membranes further showed similar overall Mn increases but different accumulation kinetics for these range of treatments and experimental periods. Additionally, the shoots electrolytic conductance did not varied significantly among the non UV-B treated rice but decreased significantly after UV-B irradiation during all the experimental period. It was found that with and without UV-B irradiation the 2 and 8 mg L-1 treatments were associated to the synthesis of a thylakoid protein with an average molecular mass of 36.5 kDa and a Mn:protein ratio of about 1. This protein exhibits superoxide dismutase activity, as well as a high content of Gln, Asp, Glu, Leu and Gly. Its EPR spectrum is characteristic of high-spin Mn(II), in a S=5/2 ground state. A comparative study of SDS polyacrylamide gel profiles of thylakoid polypeptides from the various treatments, with and without UV-B irradiation, also disclosed quantitative changes, as well as that 37/36-kDa polypeptide. In non UV-B and UV-B irradiated rice, the photosynthetic electron transport rates coupled to PSII and PSI, during the experimental period considered, showed significant increases until the 8-mg·L–1 Mn treatment. In this context, the related superoxide production of thylakoids (monitored by EPR spectroscopy) also showed minimum values from the 0.5-mg·L–1 Mn treatment onwards, which, as shown by the thiobarbituric acid reaction was coupled to a non-significant variation of the acyl lipid peroxidation. It was concluded that in Oryza sativa L. cv. Safari high levels of Mn induces the synthesis of a thylakoid manganese protein, that mimics superoxide dismutase functioning and that can shield the oxidative burst under UV-B irradiation.
|Title of host publication||Abstracts - 2nd Annual Meeting of UV4Growth COST-Action FA0906|
|Publication status||Published - 1 Jan 2013|
|Event||2nd Annual Meeting of UV4Growth COST-Action FA0906 Mikulov, Czech Republic - |
Duration: 1 Jan 2013 → …
|Conference||2nd Annual Meeting of UV4Growth COST-Action FA0906 Mikulov, Czech Republic|
|Period||1/01/13 → …|