An improved fluorimetric HPLC method for quantifying tocopherols in Brassica rapa L. subsp. sylvestris after harvest

Ascophyllum nodosum Based Extracts Counteract Salinity Stress in Tomato by Remodeling Leaf Nitrogen Metabolism

Biostimulants have rapidly and widely been adopted as growth enhancers and stress protectants in agriculture, however, due to the complex nature of these products, their mechanism of action is not clearly understood. By using two algal based commercial biostimulants in combination with the Solanum lycopersicum cv. MicroTom model system, we assessed how the modulation of nitrogen metabolites and potassium levels could contribute to mediate physiological mechanisms that are known to occur in response to salt/and or osmotic stress. Here we provide evidence that the reshaping of amino acid metabolism can work as a functional effector, coordinating ion homeostasis, osmotic adjustment and scavenging of reactive oxygen species under increased osmotic stress in MicroTom plant cells. The Superfifty biostimulant is responsible for a minor amino acid rich-phenotype and could represent an interesting instrument to untangle nitrogen metabolism dynamics in response to salinity and/or osmotic stress.

Physiological and Nutraceutical Quality of Green and Red Pigmented Lettuce in Response to NaCl Concentration in Two Successive Harvests

Nutritional eustress such as salinity or nutrient stress applied in soilless systems, is a convenient pre-harvest factor efficient in modulating the phytochemical components of horticultural crops, by triggering defensive mechanisms and accumulating plant secondary metabolites in plants tissues. Nevertheless, genetic material (cultivars with different pigmentation) dictates lettuce metabolites and physiological response to extrinsic eustress, with red leaf cultivars being highly nutrient packed notwithstanding the stress. Product quality can be meliorated equally by applying several cuts, a practice proven to increase bioactive compounds accumulation. In this study, we analyzed the effects of four salinity levels (1, 10, 20 and 30 mM NaCl) on green and red pigmented Salad Bowl lettuce (Lactuca sativa L. var. acephala) in two successive harvests cultivated in a floating raft system. The morphological parameters, mineral composition, leaf gas exchanges, bioactive compounds, and antioxidant activity of both cultivars were assessed. The green cultivar exhibited superior crop productivity but was more prone to salinity effect than the red cultivar. Irrespective of cultivar and cut order, the net photosynthesis decreased with increasing salinity in the nutrient solution. The second cut incurred higher dry biomass, greater accumulation of most minerals and higher photosynthetic activity. In red lettuce, 20 mM NaCl proved adequate eustress to increase phytonutrients and beneficial minerals (K, Ca, and Mg) with minimal loss of yield. Mild salinity and sequential harvest have proven effective pre-harvest tools in positively modulating the quality of lettuce. Eustress interaction with genotype was demonstrated as a promising field for future breeding programs targeting select genotypes for agronomic application of eustress to improve the nutraceutical value of vegetable crops.

Morphological and Physiological Responses Induced by Protein Hydrolysate-Based Biostimulant and Nitrogen Rates in Greenhouse Spinach

Plant-derived protein hydrolysates (PHs) are gaining prominence as biostimulants due to their potential to improve yield and nutritional quality even under suboptimal nutrient regimens. In this study, we investigated the effects of foliar application of a legume-derived PH (0 or 4 mL L−1) on greenhouse baby spinach (Spinacia oleracea L.) under four nitrogen (N) fertilization levels (0, 15, 30, or 45 kg ha−1) by evaluating morphological and colorimetric parameters, mineral composition, carbohydrates, proteins, and amino acids. The fresh yield in untreated and biostimulant-treated spinach plants increased in response to an increase in N fertilization from 1 up to 30 kg ha−1, reaching a plateau thereafter indicating the luxury consumption of N at 45 kg ha−1. Increasing N fertilization rate, independently of PH, lead to a significant increase of all amino acids with the exception of alanine, GABA, leucine, lysine, methionine, and ornithine but decreased the polyphenols content. Interestingly, the fresh yield at 0 and 15 kg ha−1 was clearly greater in PH-treated plants compared to untreated plants by 33.3% and 24.9%, respectively. This was associated with the presence in of amino acids and small peptides PH ‘Trainer®’, which act as signaling molecules eliciting auxin- and/or gibberellin-like activities on both leaves and roots and thus inducing a “nutrient acquisition response” that enhances nutrients acquisition and assimilation (high P, Ca, and Mg accumulation) as well as an increase in the photochemical efficiency and activity of photosystem II (higher SPAD index). Foliar applications of the commercial PH decreased the polyphenols content, but on the other hand strongly increased total amino acid content (+45%, +82%, and +59% at 0, 15, and 30 kg ha−1, respectively) but not at a 45-kg ha−1-rate. Overall, the use of PH could represent a sustainable tool for boosting yield and nitrogen use efficiency and coping with soil fertility problems under low input regimens.

Hordeum vulgare and Hordeum maritimum respond to extended salinity stress displaying different temporal accumulation pattern of metabolites

Hordeum maritimum With. (= H. marinum Huds. subsp. marinum, 2n=14) is a wild cereal present in the saline depressions of the Soliman and Kelbia Sebkhas, which contributes significantly to annual biomass production in Tunisia. This species is able to tolerate high NaCl concentrations at the seedling stage without showing symptoms of toxicity; however, the tolerance strategy mechanisms of this plant have not yet been unravelled. Our metabolite analysis, performed on leaves of H. maritimum during extended stress in comparison with Hordeum vulgare L. cv. Lamsi, has revealed an adaptive response of the wild species based on a different temporal accumulation pattern of ions and compatible metabolites. Further, wild and cultivated genotypes with contrasting salt-tolerant behaviour display different pattern of metabolites when salt stress is prolonged over 2 weeks. In particular, when exposed to up to 3 weeks of 200mM NaCl salt stress, H. maritimum is able to maintain lower leaf concentrations of sodium and chloride, and higher concentrations of potassium compared with H. vulgare. This likely restricts sodium entry into plants at the root level, and uses the toxic ions, glycine betaine and low levels of proline for osmotic adjustment. Under prolonged stress, the accumulation of proline increases, reaching the highest levels in concomitance with the decrease of potassium to sodium ratio, the increase of hydrogen peroxide and decrease of chlorophylls. The modulation of proline accumulation over time can be interpreted as an adaptive response to long-term salinity. Moreover, once synthetised glycine betaine is transported but not metabolised, it can contribute together with proline to osmotically balance H. maritimum leaves and protect them from oxidative stress. The 2-3 week delay of H. maritimum in showing the symptoms of stress and damages compared with H. vulgare could be important in the survival of plants when soil salinity is not a permanent condition, but just a transient state of stress.

Dataset on antioxidant metabolites and enzymes activities of freshly harvested sweet cherries (Prunus avium L.) of Campania accessions

In this article, we reported the original data obtained by the study of metabolites and enzymes involved in sweet cherry antioxidant system. We measured hydrogen peroxide (H2O2) and malondialdehyde (MDA), which are indicator of oxidative stress. Moreover, we measured the concentration of reduced and oxidized ascorbate and glutathione that are involved in ROS detoxification together with phenolics, anthocyanins and tocopherols. Among antioxidant enzymes, we analyzed the activities of ascorbate peroxidase (APX; EC 1.11.1.11), and the soluble and bound forms of polyphenol oxidase (PPO; EC 1.10.3.1) and guaiacol peroxidase (POD; EC 1.11.1.7). The data reported in this paper are related to the research article "Metabolic characterization and antioxidant activity in sweet cherry (Prunus avium L.) Campania accessions", authored by Mirto et al. (2018) [1].

Durum wheat seedling responses to simultaneous high light and salinity involve a fine reconfiguration of amino acids and carbohydrate metabolism

Durum wheat plants are extremely sensitive to drought and salinity during seedling and early development stages. Their responses to stresses have been extensively studied to provide new metabolic targets and improving the tolerance to adverse environments. Most of these studies have been performed in growth chambers under low light [300-350 µmol m^-2 s^-1 photosynthetically active radiation (PAR), LL]. However, in nature plants have to face frequent fluctuations of light intensities that often exceed their photosynthetic capacity (900-2000 µmol m^-2 s^-1 ). In this study we investigated the physiological and metabolic changes potentially involved in osmotic adjustment and antioxidant defense in durum wheat seedlings under high light (HL) and salinity. The combined application of the two stresses decreased the water potential and stomatal conductance without reducing the photosynthetic efficiency of the plants. Glycine betaine (GB) synthesis was inhibited, proline and glutamate content decreased, while γ-aminobutyric acid (GABA), amides and minor amino acids increased. The expression level and enzymatic activities of Δ1-pyrroline-5-carboxylate synthetase, asparagine synthetase and glutamate decarboxylase, as well as other enzymatic activities of nitrogen and carbon metabolism, were analyzed. Antioxidant enzymes and metabolites were also considered. The results showed that the complex interplay seen in durum wheat plants under salinity at LL was simplified: GB and antioxidants did not play a main role. On the contrary, the fine tuning of few specific primary metabolites (GABA, amides, minor amino acids and hexoses) remodeled metabolism and defense processes, playing a key role in the response to simultaneous stresses.

Durum Wheat Roots Adapt to Salinity Remodeling the Cellular Content of Nitrogen Metabolites and Sucrose

Plants are currently experiencing increasing salinity problems due to irrigation with brackish water. Moreover, in fields, roots can grow in soils which show spatial variation in water content and salt concentration, also because of the type of irrigation. Salinity impairs crop growth and productivity by inhibiting many physiological and metabolic processes, in particular nitrate uptake, translocation, and assimilation. Salinity determines an increase of sap osmolality from about 305 mOsmol kg-1 in control roots to about 530 mOsmol kg-1 in roots under salinity. Root cells adapt to salinity by sequestering sodium in the vacuole, as a cheap osmoticum, and showing a rearrangement of few nitrogen-containing metabolites and sucrose in the cytosol, both for osmotic adjustment and oxidative stress protection, thus providing plant viability even at low nitrate levels. Mainly glycine betaine and sucrose at low nitrate concentration, and glycine betaine, asparagine and proline at high nitrate levels can be assumed responsible for the osmotic adjustment of the cytosol, the assimilation of the excess of ammonium and the scavenging of ROS under salinity. High nitrate plants with half of the root system under salinity accumulate proline and glutamine in both control and salt stressed split roots, revealing that osmotic adjustment is not a regional effect in plants. The expression level and enzymatic activities of asparagine synthetase and Δ1-pyrroline-5-carboxylate synthetase, as well as other enzymatic activities of nitrogen and carbon metabolism, are analyzed.