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Summary• The effects of zinc (Zn) toxicity on photosynthesis and respiration were investigated in sugar beet (Beta vulgaris) plants grown hydroponically with 1.2, 100 and 300 lM Zn.• A photosynthesis limitation analysis was used to assess the stomatal, mesophyll, photochemical and biochemical contributions to the reduced photosynthesis observed under Zn toxicity.• The main limitation to photosynthesis was attributable to stomata, with stomatal conductances decreasing by 76% under Zn excess and stomata being unable to respond to physiological and chemical stimuli. The effects of excess Zn on photochemistry were minor. Scanning electron microscopy showed morphological changes in stomata and mesophyll tissue. Stomatal size and density were smaller, and stomatal slits were sealed in plants grown under high Zn. Moreover, the mesophyll conductance to CO 2 decreased by 48% under Zn excess, despite a marked increase in carbonic anhydrase activity. Respiration, including that through both cytochrome and alternative pathways, was doubled by high Zn.• It can be concluded that, in sugar beet plants grown in the presence of excess Zn, photosynthesis is impaired due to a depletion of CO 2 at the Rubisco carboxylation site, as a consequence of major decreases in stomatal and mesophyll conductances to CO 2 .Abbreviations: A N , net photosynthesis; AOX, alternative oxidase; APX, ascorbate peroxidase; BL, DL, MCL, NSL and SL, biochemical conductance, diffusional conductance, mesophyll conductance, and nonstomatal and stomatal limitations, respectively; C a , C C and C i, atmospheric, chloroplastic and substomatal CO 2 concentrations, respectively; CA, carbonic anhydrase; Chl, chlorophyll; ETR, electron transport rate; F PSII, actual photosystem II efficiency; FAAS, flame atomic absorption spectroscopy; F o , minimal Chl fluorescence in the dark; F v ⁄ F m , maximum potential photosystem II efficiency; g m and g s , CO 2 mesophyll and stomatal conductances, respectively; J max , in vivo maximum rate of electron transport driving regeneration of RuBP; Mn-SOD, manganese-superoxide dismutase; PPFD, photosynthetic photon flux density; PSII and PSI, photosystems II and I, respectively; V c,max , in vivo maximum rate of Rubisco carboxylation; WC, water content.

Cadmium and arsenic are two of the most important and toxic pollutants ubiquitous in the environment. The occurrence of numerous polluted areas as the affected by the accident of Aznalcóllar pyrite mine has promoted the employment of the phytoremediation as a feasible technology able to control and reduce the risk of this contamination at low cost. White lupin plant is proposed as a candidate for phytoremediation. This work aims to study if it is possible to use white lupin in phytoremediation of soils affected by acid pyrite sludge, with simultaneous As and Cd pollution. Pot and field experiments with sludge-affected soil were carried out. The pot trial showed that the NTA treatment increased Cd and As concentrations in lixiviates, exceeding the maximum permissible levels, so that its use in field experiments was avoided. In the field experiment, phytoextraction of Cd and As by lupin plants was very low, suggesting that it was not recommended for phytoextraction. However, lupin culture in the field produced several benefits as: increase of acid soil pH probably by citrate excretion, decrease in soluble As and Cd fractions in soil, high concentration of As and Cd in roots with accumulation of heavy metals in root nodules. All these results support the use of Lupinus albus for phytostabilization and revegetation of the spill polluted soils.

In response to Cd stress, higher plants utilise a number of defence systems, such as retention in cell walls, binding by organic molecules in the cytosol and sequestration in the vacuole. White lupin is a Cd-resistant legume that is of interest for phytoremediation of acidified and Cd-contaminated soils. The aim of this research was to evaluate the contributions of various mechanisms of Cd detoxification used by this species, focusing on cell-wall retention and binding by thiol-rich compounds. Retention of Cd by the cell wall of white lupin was well described by a Langmuir isotherm model. The percentage of total Cd adsorbed by the cell wall ranged from 29 to 47% in leaves, from 38 to 51% in stems and from 26 to 42% in roots depending on the Cd supply. Cadmium induced the synthesis of high levels of phytochelatins (PCs) in lupin plants, mainly in roots, with PC 3 being the major PC. The amount of Cd complexed by thiols accounted for approximately 20% of the total Cd in leaves, 40% in stems and 20% in roots. Therefore, cell-wall retention could account for more than twice the amount of Cd complexed by PCs in leaves and roots. In stems, both mechanisms contributed equally to Cd detoxification. These studies indicate that white lupin plants use cell-wall binding and, secondarily, the production of PCs, as effective mechanisms of Cd detoxification.

Crop Fe deficiency is a worldwide problem. The aim of this study was to assess the effects of foliar Fe applications in two species grown in different environments: peach (Prunus persica L. Batsch) trees grown in the field and sugar beet (Beta vulgaris L. cv. “Orbis”) grown in hydroponics. The distal half of Fe-deficient, chlorotic leaves was treated with Fe sulfate by dipping and using a brush in peach trees and sugar beet plants, respectively. The re-greening of the distal (Fe-treated) and basal (untreated) leaf areas was monitored, and the nutrient and photosynthetic pigment composition of the two areas were also determined. Leaves were also studied using chlorophyll fluorescence imaging, low temperature-scanning electron microscopy microanalysis, scanning transmission ion microscopy-particle induced X-ray emission and Perls Fe staining. The distal, Fe-treated leaf parts of both species showed a significant increase in Fe concentrations (across the whole leaf volume) and marked re-greening, with significant increases in the concentrations of all photosynthetic pigments, as well as decreases in de-epoxidation of xanthophyll cycle carotenoids and increases in photochemical efficiency. In the basal, untreated leaf parts, Fe concentrations increased slightly, but little re-greening occurred. No changes in the concentrations of other nutrients were found. Foliar Fe fertilization was effective in re-greening treated leaf areas both in peach trees and sugar beet plants. Results indicate that the effects of foliar Fe-sulfate fertilization in Fe-deficient, chlorotic leaves were minor outside the leaf surface treated, indicating that Fe mobility within the leaf is a major constraint for full fertilizer effectiveness in crops where Fe-deficiency is established and leaf chlorosis occurs.

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In the field, leaves may face very different light intensities within the tree canopy. Leaves usually respond with light-induced morphological and photosynthetic changes, in a phenomenon known as phenotypic plasticity. Canopy light distribution, leaf anatomy, gas exchange, chlorophyll fluorescence, and pigment composition were investigated in an olive (Olea europaea, cvs. Arbequina and Arbosana) orchard planted with a high-density system (1,250 trees ha(-1)). Sampling was made from three canopy zones: a lower canopy (<1 m), a central one (1-2 m), and an upper one (>2 m). Light interception decreased significantly in the lower canopy when compared to the central and top ones. Leaf angle increased and photosynthetic rates and non-photochemical quenching (NPQ) decreased significantly and progressively from the upper canopy to the central and the lower canopies. The largest leaf areas were found in the lower canopy, especially in the cultivar Arbequina. The palisade and spongy parenchyma were reduced in thickness in the lower canopy when compared to the upper one, in the former due to a decrease in the number of cell layers from three to two (clearly distinguishable in the light and fluorescence microscopy images). In both cultivars, the concentration of violaxanthin-cycle pigments and β-carotene was higher in the upper than in the lower canopy. Furthermore, the de-epoxidized forms zeaxanthin and antheraxanthin increased significantly in those leaves from the upper canopy, in parallel to the NPQ increases. In conclusion, olive leaves react with morphological and photosynthetic changes to within-crown light gradients. These results strengthen the idea of olive trees as "modular organisms" that adjust the modules morphology and physiology in response to light intensity.