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Hyperaccumulators are plants that can extract heavy metal ions from the soil and translocate those ions to the shoots, where they are sequestered and detoxified. Hyperaccumulation depends not only on the availability of mobilized metal ions in the soil, but also on the enhanced activity of metal transporters and metal chelators which may be provided by the plant or its associated microbes. The rhizobiome is captured by plant root exudates from the complex microbial community in the soil, and may colonize the root surface or infiltrate the root cortex. This community can increase the root surface area by inducing hairy root proliferation. It may also increase the solubility of metals in the rhizosphere and promote the uptake of soluble metals by the plant. The bacterial rhizobiome, a subset of specialized microorganisms that colonize the plant rhizosphere and endosphere, makes an important contribution to the hyperaccumulator phenotype. In this review, we discuss classic and more recent tools that are used to study the interactions between hyperaccumulators and the bacterial rhizobiome, and consider future perspectives based on the use of omics analysis and microscopy to study plant metabolism in the context of metal accumulation. Recent data suggest that metal-resistant bacteria isolated from the hyperaccumulator rhizosphere and endosphere could be useful in applications such as phytoextraction and phytoremediation, although more research is required to determine whether such properties can be transferred successfully to non-accumulator species.

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Germination is related with improvements of nutritional value of seeds, since it promotes accumulation of health-promoting phytochemicals. However, only few studies have investigated on phytochemicals accumulation during sprouting under sub-optimal conditions. Thus, we investigated the effect of salinity during germination of an einkorn (TMoM), an emmer (TDiZ) and a durum wheat (TDuC) genotype on the total polyphenols (TPC), free-and bound-phenolic acids [PAs; i.e. caffeic acid, syringic acid, Pcoumaric acid, trans-ferulic acid, and salicylic acid] contents and antiradical activity (Trolox equivalent antioxidant capacity; TEAC) of sprouts and wheatgrass. The following NaCl treatments were applied: 0 (control), 25, 50 and 100 mM NaCl concentration throughout the whole experiment, or 50 and 100 mM NaCl until sprout stage and then 0 mM until wheatgrass stage (recovery treatments). TMoM showed higher total bound-PAs both in sprouts and wheatgrass with respect to the other Triticum genotypes (+25% and 24%, respectively) as well as of total bound-PAs and bound-SA in the recovery treatments. Moderate salt stress significantly increased all the investigated variables in TDiZ. Salt stress induced higher TPC and TEAC as well as total free-PAs values till 50 mM NaCl in TDuC, whilst significantly lowered total boundPAs due to the negative variation of both P-CA (-84%) and trans-FA (-81%) acids. Results indicate that salinity during germination could be efficiently modulated to improve the nutritional quality of sprouts, wheatgrass and cereal-based products.

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Nitrogen (N) nutrition plays a key role for high yields and quality in durum wheat (Triticum turgidum L. subsp. durum (Desf.) Husn); in Mediterranean environments, data regarding N fertilisation management during the transition phase to conservation agriculture (CA) are limited. The aim of this work was to study the effects of N fertiliser forms and rates on yield and some quality traits of durum wheat, during the transition period to CA in Mediterranean areas; moreover, indication on the recommendable N form/rate combinations have been given. Field trials were carried out in south of Italy, during the first two years of transition to CA (from 2010 to 2012) in a durum wheat-based rotation. Following a split-plot design arranged on a randomised complete blocks with three replications, two N forms (main plots) -urea and calcium nitrate -and four N rates (sub-plots) -50, 100, 150 and 200 kg N ha -1 -plus an un-fertilised Control, were compared. The following parameters were analysed: grain yield, N-input efficiency, grains protein concentration (GPC), total gluten, gluten fractions and minerals concentration in kernels. Calcium nitrate gave the highest yield (4.48 t ha -1 ), as predicted by the quadratic model, at 146 kg N ha -1 , on average. This was particularly noticeable in 2012, when the distribution of rainfall and temperatures regimes as well as residues' status could have favoured such N-form. These results were confirmed by the observed higher values of all indices describing N-input efficiency. High GPC values (14.8%) were predicted at slightly higher N-rates (173 kg N ha -1 , averaging both N forms). In particular, gluten proteins and glutenin/gliadin ratio accrued as the N doses increased, reaching the highest values at 150 kg N ha -1 , also positively affecting the quality of durum wheat flour. Iron and zinc concentrations were noticeably increased (38% and 37% on average) by N supply, probably due to the enhanced water use efficiency under CA systems.Principal component analysis summarised properly the obtained results: analysing the N-rates at 150 kg N ha -1 , it was confirmed that yields and quality characteristics of durum wheat were optimised in the wettest year (2011) with calcium nitrate. Moreover, the scarce amount of residues characterising the transition phase to CA, requires N application rates not lower than 150 kg ha -1 in order to ensure stable yields and important quality traits. These N rates should be modulated as the accumulation of crop residues increases over time, thanks to long-term effects of CA on soil chemical, physical and biological properties. IntroductionSouthern Europe's environment is characterised by cool and wet winters and hot and dry summers with low and erratic rainfall distribution, and by soils with very low organic matter levels and nitrogen (N) content. Nitrogen is subjected to several losses with the main pathways being represented by ammonia volatilisation, denitrification and nitrate leaching (Plaza-Bonil et al., 2014). Moreover, in these environments ...

Conservation agriculture (CA) can be very strategic in degradation prone soils of Mediterranean environments to recover soil fertility and consequently improve crop productivity as well as the quality traits of the most widespread crop, durum wheat, with reference to protein accumulation and composition. The results shown by two years of data in a medium long-term experiment (7-year experiment; split-plot design) that combined two tillage practices (conventional tillage (CT) and zero tillage (ZT)) with two crop sequences (wheat monocropping (WW) and wheat-faba bean (WF)) are presented. The combination ZT + WF (CA approach) induced the highest grain yields (617 and 370 g m−2 in 2016 and 2017, respectively), principally due to an increased number of ears m−2; on the other hand, the lowest grain yield was recorded under CT + WW (550 and 280 g m−2 in 2016 and 2017, respectively). CA also demonstrated significant influences on grain quality because the inclusion of faba bean in the rotation favored higher N-remobilization to the grains (79.5% and 77.7% in 2017). Under ZT and WF, all gluten fractions (gliadins (Glia), high molecular-weight glutenins (GS), and low molecular-weight GS) as well as the GS/Glia ratio increased. In durum wheat-based farming systems in Mediterranean areas, the adoption of CA seems to be an optimal choice to combine high quality yields with improved soil fertility.

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