Effects of Ozone on Photosynthetic Components and Radical Scavenging System in Leaves of Rice (Oryza sativa L.)

Abstract

The chronic effects of ambient levels of O3 on photosynthetic components and radical scavenging system of leaves at different positions on the main stem of Japanese rice (Oryza sativa L.) were investigated. Two cultivars of Japanese rice (Koshihikari and Kinuhikari) were planted in plastic boxes filled with flooded Andisol in 9 chambers on 15 May, and exposed daily to charcoal-filtered air or O3 at 60 or 100 nl l -1 (ppb) (10:00-17:00) from 30 May to 20 September 2007. The activity and concentration of ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco) in the leaves of both cultivars were not significantly affected by exposure to O3. However, the concentrations of chlorophyll in the lower leaves on the main stem of both cultivars were significantly reduced by the exposure to 100 ppb O3, while the exposure to O3 significantly increased the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR) and glutathione reductase (GR); regardless of the leaf position in the two cultivars. Although no significant combined effect of O3 and cultivar on the concentration of chlorophyll, the activity and concentration of Rubisco, or the concentration of antioxidants and activity of radical scavenging enzymes was observed, there was a highly positive correlation between the AOT40 (accumulated exposure over a threshold of 40 ppb) of O3 and the relative activity of APX, MDAR or GR in leaves exposed to O3 to that in leaves exposed to charcoal-filtered air of both cultivars. These results suggest that APX, MDAR and GR played important roles in the antioxidative response of Japanese rice to O3. However, the detoxification capacity of reactive oxygen species by APX, MDAR and GR was insufficient to prevent the adverse effects of ambient levels of O3 on the concentration of chlorophyll in the two cultivars of Japanese rice.

Effect of ambient levels of ozone on photosynthetic components and radical scavenging system in leaves of African cowpea varieties

“…Rubisco activity in the leaves was determined using the procedure of Tissue et al (1993) and has been described in detail by Inada et al (2008). The concentration of chlorophyll was determined by the method of Barnes et al (1992) and has been described in detail by Inada et al (2008).…”

“…The activities of superoxide dismutase (SOD), catalase (CAT), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were measured by the methods of Inada et al (2008). For the measurement of activities of SOD, CAT, GR, MDAR and DHAR, 100 mg leaf samples stored at -80 °C were homogenised to fine powders with a mortar and pestle containing some amount of quartz sand and PVPP in liquid nitrogen.…”

“…The concentrations of ascorbate and glutathione were measured according to the procedure of Inada et al (2008). For total ascorbate, 30 mg of leaf sample stored at -80°C was homogenised in a mortar and pestle containing some amount of quartz sand, without PVPP with liquid nitrogen.…”

Evaluation of O₃ effect on net photosynthetic rate in flag leaves of rice (<i>Oryza sativa</i> L.) by stomatal O₃ flux and radical scavenging enzyme activities

“…The supernatant of the sample was used for determination of Rubisco concentration. Details of the measurement of Rubisco and chlorophyll concentrations are described in our previous report (Inada et al, 2008).…”

“…The APX activity was measured according to the method of Nakano and Asada (1981), and was defined as the oxidation rate of ascorbic acid by H 2 O 2 . Details of the measurement of APX activity are described in our previous report (Inada et al, 2008).…”