A fíeld experiment was conducted to evaluate the effects of Cu and Pb on photosynthesis and growth characteristics of oats. The plants grown on the site with elevated levels of Cu-Pb were reduced in height and biomass, compared to control plants, and appeared chlorotic while the accumulations of both Cu and Pb in the above-ground parts were in the range considered to be phytotoxic. Cu and Pb led to a pronounced reduction (47 %) of chlorophyll (Chl) (a + b) content, accompanied by proportional changes in ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity. Hence Cu and Pb effects did not result in the destruction of the photosynthetic apparatus but in its coordinated reduction. Growth at the heavy metal contaminated site resulted in a decreased (7 %) quantum yield of photochemistry in photosystem 2 (PS2), as given by the ratio Fy/Fn, measured in dark adapted leaves in the field. The half-rise time (ti/2) from the initial (Fq) to maximal (F^) Chl fluorescence was increased, suggesting that the amount of active pigments associated with the photochemical apparatus decreased and that the functional Chl antennae size of the photosynthetic apparatus was smaller compared to the control plants. Although Cu and Pb affected the photosynthetic apparatus in multiple ways, the prevailing effect was that on RuBPCO activity, which in tum must háve limited the overall photosynthetic activity.
A sand-culture experiment was conducted in open-top chambers which were constructed in a greenhouse to investigate the responses of salt-stressed wheat (Triticum aestivum L.) to O3. Plant seeding of JN17 (a popular winter wheat cultivar) was grown in saltless (-S) and saline (+S, 100 mM NaCl) conditions combined with charcoal-filtered air (CF, < 5 ppb O3) and elevated O3 (+O3,
80 ± 5 ppb, 8 h day-1) for 30 d. O3 significantly reduced net photosynthetic rate (PN), stomatal conductance, chlorophyll contents and plant biomass in -S treatment, but no considerable differences were noted in those parameters between +O3+S and CF+S treatments. O3-induced loss in cellular membrane integrity was significant in -S plants, but not in +S plants evidenced by significant elevations being measured in electrolyte leakage (EL) and malondialdehyde (MDA) content in -S plants, but not in +S plants. Both O3 and salinity increased proline content and stimulated antioxidant enzymes activities. Soluble protein increased by salinity but decreased by O3. Abscisic acid (ABA) was significantly elevated by O3 in -S plants but not in +S plants. The results of this study suggested that the specificity of different agricultural environments should be considered in order to develop reliable prediction models on O3 damage to wheat plants. and Y. H. Zheng ... [et al.].