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Although control of xylem ion loading is essential to confer salinity stress tolerance, specific details behind this process remain elusive. In this work, we compared the kinetics of xylem Na+ and K+ loading between two halophytes (Atriplex lentiformis and quinoa) and two glycophyte (pea and beans) species, to understand the mechanistic basis of the above process. Halophyte plants had high initial amounts of Na+ in the leaf, even when grown in the absence of the salt stress. This was matched by 7-fold higher xylem sap Na+ concentration compared with glycophyte plants. Upon salinity exposure, the xylem sap Na+ concentration increased rapidly but transiently in halophytes, while in glycophytes this increase was much delayed. Electrophysiological experiments using the microelectrode ion flux measuring technique showed that glycophyte plants tend to re-absorb Na+ back into the stele, thus reducing xylem Na+ load at the early stages of salinity exposure. The halophyte plants, however, were capable to release Na+ even in the presence of high Na+ concentrations in the xylem. The presence of hydrogen peroxide (H2O2) [mimicking NaCl stress-induced reactive oxygen species (ROS) accumulation in the root] caused a massive Na+ and Ca2+ uptake into the root stele, while triggering a substantial K+ efflux from the cytosol into apoplast in glycophyte but not halophytes species. The peak in H2O2 production was achieved faster in halophytes (30 min vs 4 h) and was attributed to the increased transcript levels of RbohE. Pharmacological data suggested that non-selective cation channels are unlikely to play a major role in ROS-mediated xylem Na+ loading.

The aim of this study was to compare the effects of foliar fertilization with a nitrogen (N) fertilizer containing nanoparticles (nN) with those of foliar fertilization with urea on the characteristics of pomegranate fruits cv. Ardestani. The experiment was carried out using a completely randomized block design with five treatments and four replications (trees) per treatment during two consecutive years, 2014 and 2015. Two foliar applications of nN (0.25 and 0.50 g N/L, equivalent to ≈1.3 and 2.7 g N/tree or 0.9 and 1.8 kg N/ha; nN1 and nN2, respectively) and urea (4.6 and 9.2 g N/L, equivalent to ≈24.4 and 48.8 g N/tree or 16.3 and 32.5 kg N/ha; U1 and U2, respectively) were applied at full bloom and 1 month later, and trees not treated with any N fertilizer were used as a control. Results show that foliar N fertilization increased fruit yield (by 17% to 44%) and number of fruits per tree (by 15% to 38%). The highest fruit yields (17.8 and 21.9 kg/tree) and number of fruits per tree (62.8 and 70.1/tree) were obtained with the treatment nN2 (1.8 kg N/ha), whereas the lowest fruit yields (12.4 and 16.2 kg/tree) and number of fruits per tree (45.5 and 55.3/tree) were recorded in the control trees. The treatments U1 and nN2 increased fruit length (the latter only in the second season), whereas the treatment U1 increased average fruit weight (10% to 11%). The treatment nN2 increased aril juice and total soluble solids (TSS) in both seasons and titratable acidity (TA) only in the first one, whereas the treatment U1 increased TSS in both seasons and aril juice and TA in the second season. Treatments nN2 and U1 also increased total sugars and decreased total anthocyanins. On the other hand, fruit diameter, fruit cracking, peel thickness, aril content, weight of 100 arils, juice pH, maturity index, antioxidant activity, and total phenolic compounds were unaffected by N fertilization. Nitrogen fertilization increased the leaf concentration of N, whereas the leaf concentrations of P, K, Mn, and Zn were unaffected. Results indicate that pomegranate fruit yield was improved similarly with two applications (at full bloom and one month later) of nN fertilizer at a rate of 1.8 kg N/ha and with two applications of urea at a rate of 16.3 kg N/ha. Furthermore, fruit quality was improved more with the nN fertilizer at a rate of 1.8 kg N/ha than with two applications of urea at a rate of 16.3 kg N/ha.

Early season foliar fertilization with different nutrients is a promising tool in pomegranate grown in poor, high pH soils. The effects of foliar fertilization with FeSO4 and the synthetic chelate Fe(III)-EDDHA (Fe(III)-ethylendiaminedi(o-hydroxyphenylacetate)) on fruit yield and physicochemical characteristics were assessed in a two-season field trial. Fertilizers were sprayed at full bloom and one month later, using Fe concentrations of 1.3 and 2.6 mM for FeSO4 and 1.1 and 2.1 mM for the Fe-chelate. Both doses of FeSO4 and the higher chelate dose increased leaf Fe concentrations and fruit yield, with the best results being observed with 2.6 mM FeSO4 (20–31% increases in yield). On the other hand, leaf N, P, K, Ca, and Mn concentrations were not affected by foliar Fe fertilization. The only treatment that increased the number of fruits per tree, aril juice content and juice total soluble solids and decreased juice total acidity in both seasons was 2.6 mM FeSO4. Both FeSO4 doses caused consistent increases in the maturity index and total sugars in juice, along with minor decreases in juice total phenolic compounds. The antioxidant activity in juice was slightly decreased by 2.6 mM FeSO4. In conclusion, early season foliar Fe fertilization had positive effects on pomegranate yield and quality, with FeSO4 being better than Fe(III)-EDDHA.