Anna Rita Rivelli

Avenues for increasing salt tolerance of crops, and the role of physiologically based selection traits

Increased salt tolerance is needed for crops grown in areas at risk of salinisation. This requires new genetic sources of salt tolerance, and more efficient techniques for identifying salt-tolerant germplasm, so that new genes for tolerance can be introduced into crop cultivars. Screening a large number of genotypes for salt tolerance is not easy. Salt tolerance is achieved through the control of salt movement into and through the plant, and salt-specific effects on growth are seen only after long periods of time. Early effects on growth and metabolism are likely due to osmotic effects of the salt, that is to the salt in the soil solution. To avoid the necessity of growing plants for long periods of time to measure biomass or yield, practical selection techniques can be based on physiological traits. We illustrate this with current work on durum wheat, on selection for the trait of sodium exclusion. We have explored a wide range of genetic diversity, identified a new source of sodium exclusion, confirmed that the trait has a high heritability, checked for possible penalties associated with the trait, and are currently developing molecular markers. This illustrates the potential for marker-assisted selection based on sound physiological principles in producing salt-tolerant crop cultivars.

Factors affecting CO2 assimilation, leaf injury and growth in salt-stressed durum wheat

To examine the factors that affect tolerance to high internal salt concentrations, two tetraploid wheat genotypes that differ in the degree of salt-induced leaf injury (Wollaroi and Line 455) were grown in 150 mM NaCl for 4 weeks. Shoot biomass of both genotypes was substantially reduced by salinity, but genotypic differences appeared only after 3 weeks, when durum cultivar Wollaroi showed greater leaf injury and a greater reduction in biomass than Line 455. Ion accumulation, water relations, chlorophyll fluorescence and gas exchange were followed on one leaf (leaf 3) throughout its life. Salinity caused a large decrease in stomatal conductance (gs) of both genotypes. This was not due to poor water relations, as leaf turgor of both genotypes was higher in the salt treatment than in controls, so chemical signals were likely to have caused the decrease in gs. Reductions in assimilation rate were initially due to gs and, with time, were due to a combination of stomatal and non-stomatal limitations. The non-stomatal limitations were associated with a build up of Na+ above 250 mM. The efficiency of PSII photochemistry in Line 455 was unaffected throughout. However, in Wollaroi, the potential and actual quantum yield of PSII photochemistry began to decline as the leaf aged and the thermal energy dissipation of excess light energy (NPQ) increased. This coincided with high Na+ and Cl- concentrations in the leaf and with chlorophyll degradation, indicating that these later reductions in CO2 assimilation in Wollaroi were a consequence of a direct toxic ion effect. The earlier reduction in CO2 assimilation and greater leaf injury explain why growth of Wollaroi was less than Line 455. The most sensitive indicator of salinity stress was gs, followed by CO2 assimilation, with fluorescence parameters other than NPQ being no more sensitive than chlorophyll itself.

Culturable bacteria from Zn- and Cd-accumulating Salix caprea with differential effects on plant growth and heavy metal availability.

Aims:  To characterize bacteria associated with Zn/Cd‐accumulating Salix caprea regarding their potential to support heavy metal phytoextraction.

Effect of salinity on water relations and growth of wheat genotypes with contrasting sodium uptake

Four wheat genotypes with contrasting degrees of Na+ exclusion were selected to see if low Na+ uptake had an adverse effect on water relations or growth rates during exposure to saline conditions. Plants were grown in supported hydroponics with and without 150 mM NaCl, and sampled for measurements of water relations, biomass, stomatal conductance, and ion accumulation. After 4 weeks exposure to salt, biomass was reduced in all genotypes to a similar extent (about 50%), with the effect of salinity on relative growth rate confined largely to the first week. There was little difference between genotypes in the effect of salinity on water relations, as indicated by their relative water content and estimated turgor. Osmotic adjustment occurred in all genotypes, with one of the low-Na+ genotypes having the greatest adjustment. In the low-Na+ genotypes, osmotic adjustment depended on higher K+ and high organic solute accumulation. Stomatal conductance of all genotypes was reduced by saline conditions, but the reduction was greater in the low-Na+ genotypes. These genotypes also showed a larger fall in the value of carbon isotope discrimination measured in expanding leaves, indicating a greater transpiration efficiency when exposed to saline conditions. Chlorophyll fluorescence measurements failed to indicate damage to photochemical pathways in either high- or low-Na+ genotypes. These data indicate that selecting lines with low Na+ accumulation for the purpose of improving salt tolerance is unlikely to introduce limitations for osmotic adjustment.

Interactions between accumulation of trace elements and macronutrients in Salix caprea after inoculation with rhizosphere microorganisms.

Although the beneficial effects on growth and trace element accumulation in Salix spp. inoculated with microbes are well known, little information is available on the interactions among trace elements and macronutrients. The main purpose of this study was to assess the effect of phytoaugmentation with the rhizobacteria Agromyces sp., Streptomyces sp., and the combination of each of them with the fungus Cadophora finlandica on biomass production and the accumulation of selected trace elements (Zn, Cd, Fe) and macronutrients (Ca, K, P and Mg) in Salix caprea grown on a moderately polluted soil. Dry matter production was significantly enhanced only upon inoculation with Agromyces sp. Regarding the phytoextraction of Cd and Zn, shoot concentrations were mostly increased after inoculation with Streptomyces sp. and Agromyces sp. + C. finlandica. These two treatments also showed higher translocation factors from roots to the leaves for both Cd and Zn. The accumulation of Cd and Zn in shoots was related to increased concentrations of K. This suggests that microorganisms that contribute to enhanced phytoextraction of Cd and Zn affect also the solubility and thus phytoavailability of K. This study suggests that the phytoextraction of Zn and Cd can be improved by inoculation with selected microbial strains.

Effects of salinity on gas exchange, water relations and growth of sunflower (Helianthus annuus)

The aim of this study was to determine the response of sunflower (Helianthus annuus L. cv. Romsum HS90) to salinity in terms of gas exchange, ionic and water relations, and growth. Experiments were carried out in the glasshouse, where sunflower plants were exposed to increasing salinity levels using water with a wide range of electrical conductivity (0.39-20 dS m-1) to provide different degrees of salt stress. The CO2 assimilation rate (A), stomatal conductance and plant aboveground dry weight (DW) significantly decreased as electrical conductivity of the soil increased. The decline in photosynthesis measured in response to salt stress was proportionally greater than the decline in transpiration, resulting in a reduction of water use efficiency, at both the leaf and whole-plant levels. Among the factors inhibiting photosynthetic activity, those of a non-stomatal nature had a greater effect. In particular, an analysis of photosynthetic CO2 assimilation rate vs intercellular CO2 concentration (A vs Ci curves) indicated a reduction in activity of Rubisco (EC 4.1.1.39) as salinity levels increased. Under severe salt-stress conditions, chlorophyll fluorescence showed a slowing of electron transport at the PSII level. Salt accumulation in the rhizosphere caused a reduction in tissue water status that was partly associated with a decline in osmotic potential (Ψπ). Leaf ionic concentration was clearly correlated with values of leaf Ψπ. However, leaf ionic concentration showed discontinuous distribution between younger and older leaves, reflecting a strategy of plants to preserve younger and more metabolically-active leaves from accumulating salt to toxic levels.

Immunological evaluation of the alcohol‐soluble protein fraction from gluten‐free grains in relation to celiac disease

Celiac disease (CD) is a gluten-sensitive enteropathy with an immune basis. We established the immune reactivity of the alcohol-soluble fraction from two minor cereals (tef and millet) and two pseudocereals (amaranth and quinoa) which are believed to be nontoxic based on taxonomy. Grains were examined in intestinal T-cell lines (iTCLs), cultures of duodenal explants from HLA-DQ2(+) CD patients and HLA-DQ8 transgenic mice for signs of activation. Our data indicated that tef, millet, amaranth, and quinoa did not show any immune cross-reactivity toward wheat gliadin, and therefore confirming their safety in the diet of CD patients.

Accumulation of cadmium, zinc, and copper by Helianthus annuus L.: impact on plant growth and uptake of nutritional elements.

We investigated the effects on physiological response, trace elements and nutrients accumulation of sunflower plants grown in soil contaminated with: 5 mg kg−1 of Cd; 5 and 300 mg kg−1 of Cd and Zn, respectively; 5, 300, and 400 mg kg−1 of Cd, Zn, and Cu, respectively. Contaminants applied did not produce large effects on growth, except in Cd-Zn-Cu treatment in which leaf area and total dry matter were reduced, by 15%. The contamination with Cd alone did not affect neither growth nor physiological parameters, despite considerable amounts of Cd accumulated in roots and older leaves, with a high bioconcentration factor from soil to plant. By adding Zn and then Cu to Cd in soil, significant were the toxic effects on chlorophyll content and water relations due to greater accumulation of trace elements in tissues, with imbalances in nutrients uptake. Highly significant was the interaction between shoot elements concentration (Cd, Zn, Cu, Fe, Mg, K, Ca) and treatments. Heavy metals concentrations in roots always exceeded those in stem and leaves, with a lower translocation from roots to shoots, suggesting a strategy of sunflower to compartmentalise the potentially toxic elements in physiologically less active parts in order to preserve younger tissues.

Glucosinolate profile and distribution among plant tissues and phenological stages of field-grown horseradish

Profile and distribution of glucosinolates (GLS) were detected in plant tissues of horseradish at different developmental stages: beginning of vegetative re-growth, flowering and silique formation. The GLS profile varied widely in the different tissues: we identified 17 GLS in roots and sprouts, one of which was not previously characterized in horseradish, i.e. the 2(S)-hydroxy-2-phenylethyl-GLS (glucobarbarin) and/or 2(R)-hydroxy-2-phenylethyl-GLS (epiglucobarbarin), 11 already found in the roots, including the putative 2-methylsulfonyl-oxo-ethyl-GLS, and 5 previously recognized only in the sprouts. Fifteen of those GLS were also identified in young and cauline leaves, 12 in the mature leaves and 13 in the inflorescences. No difference in GLS profile was observed in plant among the phenological stages. Differences in concentrations of GLS, quantified as desulfated, were found in plant. At the beginning of vegetative re-growth, sprouts while showing the same profile of the roots were much richer in GLS having the highest total GLS concentrations (117.5 and 7.7μmolg(-1) dry weight in sprouts and roots, respectively). During flowering and silique forming stages, the roots still maintained lower amount of total GLS (7.4μmolg(-1) of dry weight, on average) with respect to the epigeous tissues, in which mature and young leaves showed the highest total concentrations (70.5 and 73.8μmolg(-1) of dry weight on average, respectively). Regardless of the phenological stages, the aliphatic GLS were always predominant in all tissues (95%) followed by indolic (2.6%) and benzenic (2.4%) GLS. Sinigrin contributed more than 90% of the total GLS concentration. Aliphatic GLS concentrations were much higher in the epigeous tissues, particularly in the mature and young leaves, while benzenic and indolic GLS concentrations were higher in the roots. Through the phenological stages, GLS concentration increased in young and mature leaves and decreased in cauline leaves and inflorescences, while it remained constant over time in roots.

Investigation of Glucosinolate Profile and Qualitative Aspects in Sprouts and Roots of Horseradish (Armoracia rusticana) Using LC-ESI–Hybrid Linear Ion Trap with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Infrared Multiphoton Dissociation

Within the family of Brassicaceae, an important source of glucosinolates (GLSs) is represented by horseradish ( Armoracia rusticana P. Gaertner, B. Meyer & Scherbius), cultivated for its roots, which are grated fresh or processed into a sauce and used as a condiment. The characteristic pungent flavor of the root depends on the abundance of the bioactive GLS molecules. In crude plant extracts (sprouts and roots) of an accession of horseradish largely diffused in the Basilicata region (southern Italy), which develops many sprouts and produces white, fiery, and sharp-flavored marketable roots, we characterized the GLS profile by LC-ESI-LTQ-FTICR-MS and IRMPD. In sprouts and roots we identified 16 and 11 GLSs, respectively. We confirmed the presence of sinigrin, 4-hydroxyglucobrassicin, glucobrassicin, gluconasturtin, and 4-methoxyglucobrassicin and identified glucoiberin, gluconapin, glucocochlearin, glucoconringianin, glucosativin, glucoibarin, 5-hydroxyglucobrassicin, glucocapparilinearisin or glucobrassicanapin, glucotropaeolin, and glucoarabishirsutain, not previously characterized in horseradish. Of particular note was the presence of the putative 2-methylsulfonyl-oxo-ethyl-GLS.