Three-years-old trees of Satsuma mandarin (Citrus unshiu [Mak.] Marc.) cv. Okitsu were exposed to O3 fumigation during long term (one year) in open-top chambers. As a result of the treatment, chlorophyll a fluorescence and gas exchange parameters were modified with respect to trees growing in O3-free conditions. Net photosynthetic rate and stomatal conductance decreased and intercellular CO2 concentration increased according to a reduction of the non-cyclic electron flow and a lower capacity to reduce the quinone pool. O3 also reduced the development of non-photochemical quenching preventing the dissipation of excess excitation energy and, therefore, generated several alterations in photosynthetic apparatus. All these effects were obtained in long-term exposure and higher O3 concentration. In O3 ambient conditions, the effects were minor. and A. Calatayud ... [et al.].
Spinach (Spinacia oleracea L. cv. Clermont) leaves grown in open-top chambers and exposed to three different concentrations of ozone were measured for gas exchange, chlorophyll a fluorescence, antioxidant systems, and lipid peroxidation at the end of growing season. High O3 concentration reduced Fv/Fm, indicating that the efficiency in the energy conversion of photosystem 2 (PS2) was altered. The rate of non-cyclic electron transport rate and the capacity to reduce the quinone pool were also affected. The development of non-photochemical quenching was not high enough to decrease the photon excess in the PS2. The limitation of photosynthetic activity was probably correlated with stomata closure and with an increase in intercellular CO2 concentration. Under oxidative stress, superoxide dismutase (SOD) activity was stimulated in parallel with lipid peroxidation. We did not find any differences in the ascorbate (AsA) pool and ascorbate peroxidase (APX) or glutathione reductase (GR) activities between air qualities. Small, but similar responses were observed in spinach leaves exposed to ambient ozone concentration. and A. Calatayud ...[et al.].