Responses of photosynthetic and defence systems to high temperature stress in Quercus suber L. seedlings grown under elevated CO inferior 2

摘要

Growth in elevated CO inferior 2 led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO inferior 2-grown plants. No down-regulation of photosynthesis was found after six months of growth under elevated CO inferior 2. Photosynthetic rates at 15 degree C or 35 degree C were also higher in elevated than in ambient CO inferior 2-grown plants, when measured at their respective CO inferior 2 growth condition. Stomata of elevated CO inferior 2-grown plants were less responsive to temperature as compared to ambient CO inferior 2 plants. The after effect of a heat-shock treatment (4 h at 45 degree C in a chamber with 80% of relative humidity and 800-1000 mu mol m superior - superior 2 s superior - superior 1 photon flux density) on A(max) was less in elevated than in ambient CO inferior 2-grown plants. At the photochemical level, the negative effect of the heat-shock treatment was slightly more pronounced in ambient than in elevated CO inferior 2-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO inferior 2-grown plants, in comparison to ambient CO inferior 2 plants, is suggested by the increase in superoxide dismutase activity, after I h at 45 degree C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO inferior 2-grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO inferior 2-grown plants immediately after 1 h at 45 degree C. The observed increase in catalase after 1 h at 45 degree C in both ambient and elevated CO inferior 2-grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature.