Foliar-applied manganese and phosphorus in deficient barley: Linking absorption pathways and leaf nutrient status.

Foliar fertilization delivers essential nutrients directly to plant tissues, reducing excessive soil fertilizer applications that can lead to eutrophication following nutrient leaching. Foliar nutrient absorption is a dynamic process affected by leaf surface structure and composition, plant nutrient status, and ion physicochemical properties. We applied multiple methods to study the foliar absorption behaviors of manganese (Mn) and phosphorus (P) in nutrient-deficient spring barley (Hordeum vulgare) at two growth stages. Nutrient-specific chlorophyll a fluorescence assays were used to visualize leaf nutrient status, while laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to visualize foliar absorption pathways for P and Mn ions. Rapid Mn absorption was facilitated by a relatively thin cuticle with a low abundance of waxes and a higher stomatal density in Mn-deficient plants. Following absorption, Mn accumulated in epidermal cells and in the photosynthetically active mesophyll, enabling a fast (6 h) restoration of Mn-dependent photosynthetic processes. Conversely, P-deficient plants developed thicker cuticles and epidermal cell walls, which reduced the penetration of P across the leaf surface. Foliar-applied P accumulated in trichomes and fiber cells above leaf veins without reaching the mesophyll and, as a consequence, no restoration of P-dependent photosynthetic processes was observed. This study reveals new links between leaf surface morphology, foliar-applied ion absorption pathways, and the restoration of affected physiological processes in nutrient-deficient leaves. Understanding that ions may have different absorption pathways across the leaf surface is critical for the future development of efficient fertilization strategies for crops in nutrient-limited soils.

Comparative Metabolomics and Molecular Phylogenetics of Melon (Cucumis melo, Cucurbitaceae) Biodiversity.

The broad variability of Cucumis melo (melon, Cucurbitaceae) presents a challenge to conventional classification and organization within the species. To shed further light on the infraspecific relationships within C. melo, we compared genotypic and metabolomic similarities among 44 accessions representative of most of the cultivar-groups. Genotyping-by-sequencing (GBS) provided over 20,000 single-nucleotide polymorphisms (SNPs). Metabolomics data of the mature fruit flesh and rind provided over 80,000 metabolomic and elemental features via an orchestra of six complementary metabolomic platforms. These technologies probed polar, semi-polar, and non-polar metabolite fractions as well as a set of mineral elements and included both flavor- and taste-relevant volatile and non-volatile metabolites. Together these results enabled an estimate of "metabolomic/elemental distance" and its correlation with the genetic GBS distance of melon accessions. This study indicates that extensive and non-targeted metabolomics/elemental characterization produced classifications that strongly, but not completely, reflect the current and extensive genetic classification. Certain melon Groups, such as Inodorous, clustered in parallel with the genetic classifications while other genome to metabolome/element associations proved less clear. We suggest that the combined genomic, metabolic, and element data reflect the extensive sexual compatibility among melon accessions and the breeding history that has, for example, targeted metabolic quality traits, such as taste and flavor.

Sensitive Detection of Phosphorus Deficiency in Plants Using Chlorophyll a Fluorescence.

Phosphorus (P) is a finite natural resource and an essential plant macronutrient with major impact on crop productivity and global food security. Here, we demonstrate that time-resolved chlorophyll a fluorescence is a unique tool to monitor bioactive P in plants and can be used to detect latent P deficiency. When plants suffer from P deficiency, the shape of the time-dependent fluorescence transients is altered distinctively, as the so-called I step gradually straightens and eventually disappears. This effect is shown to be fully reversible, as P resupply leads to a rapid restoration of the I step. The fading I step suggests that the electron transport at photosystem I (PSI) is affected in P-deficient plants. This is corroborated by the observation that differences at the I step in chlorophyll a fluorescence transients from healthy and P-deficient plants can be completely eliminated through prior reduction of PSI by far-red illumination. Moreover, it is observed that the barley (Hordeum vulgare) mutant Viridis-zb(63), which is devoid of PSI activity, similarly does not display the I step. Among the essential plant nutrients, the effect of P deficiency is shown to be specific and sufficiently sensitive to enable rapid in situ determination of latent P deficiency across different plant species, thereby providing a unique tool for timely remediation of P deficiency in agriculture.

Multielemental fingerprinting as a tool for authentication of organic wheat, barley, faba bean, and potato.

The multielemental composition of organic and conventional winter wheat, spring barley, faba bean, and potato was analyzed with inductively coupled plasma-optical emission spectrometry (ICP-OES) and -mass spectrometry (ICP-MS). The crops were cultivated in two years at three geographically different field locations, each accommodating one conventional and two organic cropping systems. The conventional system produced the highest harvest yields for all crops except the nitrogen-fixing faba bean, whereas the dry matter content of each crop was similar across systems. No systematic differences between organic and conventional crops were found in the content of essential plant nutrients when statistically analyzed individually. However, chemometric analysis of multielemental fingerprints comprising up to 14 elements allowed discrimination. The discrimination power was further enhanced by analysis of up to 25 elements derived from semiquantitative ICP-MS. It is concluded that multielemental fingerprinting with semiquantitative ICP-MS and chemometrics has the potential to enable authentication of organic crops.

Extensive metabolic cross-talk in melon fruit revealed by spatial and developmental combinatorial metabolomics.

• Variations in tissue development and spatial composition have a major impact on the nutritional and organoleptic qualities of ripe fleshy fruit, including melon (Cucumis melo). To gain a deeper insight into the mechanisms involved in these changes, we identified key metabolites for rational food quality design. • The metabolome, volatiles and mineral elements were profiled employing an unprecedented range of complementary analytical technologies. Fruits were followed at a number of time points during the final ripening process and tissues were collected across the fruit flesh from rind to seed cavity. Approximately 2000 metabolite signatures and 15 mineral elements were determined in an assessment of temporal and spatial melon fruit development. • This study design enabled the identification of: coregulated hubs (including aspartic acid, 2-isopropylmalic acid, ß-carotene, phytoene and dihydropseudoionone) in metabolic association networks; global patterns of coordinated compositional changes; and links of primary and secondary metabolism to key mineral and volatile fruit complements. • The results reveal the extent of metabolic interactions relevant to ripe fruit quality and thus have enabled the identification of essential candidate metabolites for the high-throughput screening of melon breeding populations for targeted breeding programmes aimed at nutrition and flavour improvement.

The Arabidopsis ATP-binding cassette protein AtMRP5/AtABCC5 is a high affinity inositol hexakisphosphate transporter involved in guard cell signaling and phytate storage.

Arabidopsis possesses a superfamily of ATP-binding cassette (ABC) transporters. Among these, the multidrug resistance-associated protein AtMRP5/AtABCC5 regulates stomatal aperture and controls plasma membrane anion channels of guard cells. Remarkably, despite the prominent role of AtMRP5 in conferring partial drought insensitivity upon Arabidopsis, we know little of the biochemical function of AtMRP5. Our phylogenetic analysis showed that AtMRP5 is closely related to maize MRP4, mutation of which confers a low inositol hexakisphosphate kernel phenotype. We now show that insertion mutants of AtMRP5 display a low inositol hexakisphosphate phenotype in seed tissue and that this phenotype is associated with alterations of mineral cation and phosphate status. By heterologous expression in yeast, we demonstrate that AtMRP5 encodes a specific and high affinity ATP-dependent inositol hexakisphosphate transporter that is sensitive to inhibitors of ABC transporters. Moreover, complementation of the mrp5-1 insertion mutants of Arabidopsis with the AtMRP5 cDNA driven from a guard cell-specific promoter restores the sensitivity of the mutant to abscisic acid-mediated inhibition of stomatal opening. Additionally, we show that mutation of residues of the Walker B motif prevents restoring the multiple phenotypes associated with mrp5-1. Our findings highlight a novel function of plant ABC transporters that may be relevant to other kingdoms. They also extend the signaling repertoire of this ubiquitous inositol polyphosphate signaling molecule.

Simultaneous iron, zinc, sulfur and phosphorus speciation analysis of barley grain tissues using SEC-ICP-MS and IP-ICP-MS.

The increasing prevalence of iron (Fe) and zinc (Zn) deficiencies in human populations worldwide has stressed the need for more information about the distribution and chemical speciation of these elements in cereal products. In order to investigate these aspects, barley grains were fractionated into awns, embryo, bran and endosperm and analysed for Fe and Zn. Simultaneously, phosphorus (P) and sulfur (S) were determined since these elements are major constituents of phytic acid and proteins, respectively, compounds which are potentially involved in Fe and Zn binding. A novel analytical method was developed in which oxygen was added to the octopole reaction cell of the ICP-MS. This approach greatly improved the sensitivity of sulfur, measured as (48)SO(+). Simultaneously, Fe was measured as (72)FeO(+), P as (47)PO(+), and Zn as (66)Zn(+), enabling sensitive and simultaneous analysis of these four elements. The highest concentrations of Zn, Fe, S and P were found in the bran and embryo fractions. Further analysis of the embryo using SEC-ICP-MS revealed that the speciation of Fe and Zn differed. The majority of Fe co-eluted with P as a species with the apparent mass of 12.3 kDa, whereas the majority of Zn co-eluted with S as a 3 kDa species, devoid of any co-eluting P. Subsequent ion pairing chromatography of the Fe/P peak showed that phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate: IP(6)) was the main Fe binding ligand, with the stoichiometry Fe(4)(IP(6))(18). When incubating the embryo tissue with phytase, the enzyme responsible for degradation of phytic acid, the extraction efficiency of both Fe and P was doubled, whereas that of Zn and S was unaffected. Protein degradation on the other hand, using protease XIV, boosted the extraction of Zn and S, but not that of Fe and P. It is concluded that Fe and Zn have a different speciation in cereal grain tissues; Zn appears to be mainly bound to peptides, while Fe is mainly associated with phytic acid.

Antisense reduction of serine hydroxymethyltransferase results in diurnal displacement of NH4+ assimilation in leaves of Solanum tuberosum.

Serine hydroxymethyltransferase (SHMT) is part of the mitochondrial enzyme complex catalysing the photorespiratory production of serine, ammonium and CO(2) from glycine. Potato plants (Solanum tuberosum cv. Solara) with antisensed SHMT were generated to investigate whether photorespiratory intermediates accumulated during light lead to nocturnal activation of the nitrogen-assimilating enzymes glutamine synthetase (GS) and glutamate synthase (GOGAT). The transformant lines contained 70-90% less SHMT protein, and exhibited a corresponding decrease in mitochondrial SHMT activity. SHMT antisense plants displayed lower photosynthetic capacity and accumulated glycine in light. Glycine was converted to serine in the second half of the light period, while serine, ammonium and glutamine showed an inverse diurnal rhythm and reached highest values in darkness. GS/GOGAT protein levels and activities in the transgenics also reached maximum levels in darkness. The diurnal displacement of NH(4)(+) assimilation was accompanied by a change in the subunit composition of GS(2), but not GS(1). It is concluded that internal accumulation of post-photorespiratory ammonium is leading to nocturnal activation of GS/GOGAT, and that the time shift in ammonia assimilation can constitute part of a strategy to survive photorespiratory impairment.