To evaluate the phytoremediation capability of some poplar and willow clones a hydroponic screening for cadmium tolerance, accumulation and translocation was performed. Rooted cuttings were exposed for 3 weeks to 50 μM cadmium sulphate in a growth chamber and morpho-physiological parameters and cadmium content distribution in various parts of the plant were evaluated. Total leaf area and root characteristics in clones and species were affected by cadmium treatment in different ways. Poplar clones showed a remarkable variability whereas willow clones were observed to be more homogeneous in cadmium accumulation and distribution. This behaviour was further confirmed by the calculation of the bio-concentration factor (BCF) and the translocation factor (Tf). Mean values of all the clones of the two Salicaceae species showed that willows had a far greater ability to tolerate cadmium than poplars, as indicated by the tolerance index (Ti), calculated on the dry weight of roots and shoots of plants. As far as the mean values of Tf was concerned, the capacity of willows to translocate was double that of poplars. On the contrary, the mean values of total BCF in poplar clones was far higher with respect to those in willows. The implications of these results in the selection of Salicaceae clones for phytoremediation purposes were discussed.

Spinach (Spinacia oleracea L.) leaves stressed by irrigation with water containing 1% (w/v) NaCl for 20 days had low conductance to CO2 diffusion both at the stomata and in the mesophyll. Mesophyll anatomy changed in salt-stressed leaves, which could have accounted for the decreased mesophyll conductance. Ribulose- 1,5-bisphosphate carboxylase/oxygenase in vitro activity and content were not affected by up to 20 days exposure to salinity but decreased when leaves were exposed to salt stress for longer than 20 days. Salt accumulation also caused a drop of Ca and Mg which might have decreased membrane stability and chlorophyll content, respectively. Measurements of chlorophyll fluorescence indicated that the 20-day-long salt stress did not directly affect photochemistry. We conclude that salinity reduces photosynthesis primarily by reducing the diffusion of CO2 to the chloroplast, both by stomatal closure and by changes in mesophyll structure which decreases the conductance to CO2 diffusion within the leaf. The capacity for carbon metabolism is eventually reduced but that occurs after substantial decreases in the conductance to CO2 diffusion.

BACKGROUND: The Mediterranean region suffers water deficit that affects fruit yield and quality. Grafting improves crop tolerance to disease and drought, but the taste and quality of fruit may be negatively affected. The aim of the present work was to determine the quality parameters of mini-watermelon, ungrafted or grafted onto a squash hybrid rootstock, and grown under different irrigation regimes: 1.0, 0.75, and 0.5 of evapotranspiration (ET) rates.

Worldwide, there are many large areas moderately contaminated with heavy metals and/or organics that have not been remediated due to the high cost and technical drawbacks of currently available technologies. Methods with a good potential for coping with these limitations are emerging from phytoremediation techniques, using, for example, specific amendments and/or plants selected from various candidates proven in several investigations to be reasonably efficient in extracting heavy metals from soil or water, or in co-metabolizing organics with bacteria flourishing or inoculated in their rhizospheres. Populus and Salix spp., two genera belonging to the Salicaceae family, include genotypes that can be considered among the candidates for this phytoremediation approach. This review shows the recent improvements in analytical tools based on the identification of useful genetic diversity associated with classical growth, physiological and biochemical traits, and the importance of plant genotype selection for enhancing phytoremediation efficiency. Particularly interesting are studies on the application of the phytoremediation of heavy metals and of chlorinated organics, in which microorganisms selected for their degradation capabilities were bioaugmented in the rhizosphere of Salicaceae planted at a high density for biomass and bioenergy production.

Variability of cadmium tolerance and distribution in plant organs was investigated in ten selected poplar clones from different species, hybrids and genotypes. To this end, plants were exposed for three weeks to 50 microM CdSO4 in hydroponics. Cadmium accumulation in roots, stem and leaves as well as biomass production and photosynthesis maintenance varied greatly among clones. The metal mostly accumulated in roots, up to 80% in some clones, and interestingly, only 50% in some others. In general, metal tolerance reflected the degree of photosynthesis inhibition, which was higher in clones with high cadmium accumulation in leaves. Biomass production, net photosynthesis, transpiration, and pigment content were differently reduced in cadmium-treated clones with respect to control. The variability of cadmium distribution among leaves, stem, and roots provides candidate poplars for specific phytoremediation processes of contaminated waters and soils.

The interaction of cadmium (Cd) with photosynthesis was investigated in poplar (Populus x canadensis Mönch., clone A4A, Populus nigra L., clone Poli) and willow (Salix alba L., clone SS5) clones that had different leaf metal concentrations in preliminary experiments. Plants grown in the presence of 50 microm CdSO(4) for 3 weeks under hydroponic conditions were used to examine leaf gas exchange, chlorophyll fluorescence parameters and images, and for Cd detection using energy dispersive X-ray fluorescence (ED-XRF). Leaves were finally analysed for Cd and phytochelatin concentrations. Results showed that SS5 had the highest leaf Cd concentration and high gas exchange activity similar to that of Poli, which had the lowest Cd concentration. Leaf fluorescence images evidenced in large undamaged areas of SS5 corresponded to high values of F(v)/F(m), F(o), PhiPSII, qP and NPQ, while patches of dark colour (visible necrosis) close to the main vein corresponded to low values of these parameters. In A4A, these necrotic patches were more diffuse on the leaf blade and associated with a range of fluorescence parameter values. ED-XRF analysis indicated that Cd was only detectable in necroses of SS5 leaves, while in A4A it was relatively more diffuse. Phytochelatins (PCs) were not detected in SS5, while their concentration was high in both Poli and A4A. The absence of these molecules in SS5 is thought to favour confinement of high accumulations of Cd to necrotic areas and gives SS5 the ability to maintain high photosynthesis and transpiration in remaining parts of the leaf.

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Among metals, Ni has been indicated as one of the most dangerous for the environment, and plants exposed to this metal are frequently reported to undergo a severe stress condition. In this work, the tolerance responses to different Ni concentrations at physiological and biochemical levels were evaluated in Amaranthus paniculatus L., a plant species previously characterised for their ability to phytoremove Ni from metal-spiked water. Results indicated a good metal tolerance of this plant species at environmentally relevant Ni concentrations, while clear symptoms of oxidative damages were detected at higher Ni concentrations, both in roots and leaves, by measuring lipid peroxide content. At the photosynthetic level, pigment content determination, chlorophyll fluorescence image analysis and gas-exchange parameter measurements revealed a progressive impairment of the photosynthetic machinery at increasing Ni concentrations in the solution. Regarding biochemical mechanisms involved in antioxidative defence and metal binding, antioxidative enzyme (ascorbate peroxidase, APX; catalase, CAT; guaiacol peroxidase, GPX; superoxide dismutase, SOD) activity, polyamine (PA) content, polyamine oxidase (PAO) activity and organic acid (OA) content were differently affected by Ni concentration in the growth solution. A role for GPX, SOD, PAs, and oxalic and citric acid in Ni detoxification is suggested. These results can contribute to elucidate the tolerance mechanisms carried out by plants when facing environmentally relevant Ni concentrations and to identify some traits characterising the physiological and biochemical responses of Amaranthus plants to the presence and bioaccumulation of Ni.