The amino acid distribution in rachis xylem sap and phloem exudate of Vitis vinifera 'Cabernet Sauvignon' bunches

Integrated metabolomic and transcriptomic analyses reveal the molecular mechanism of amino acid transport between source and sink during tea shoot development

KEY MESSAGE

The weighted gene co-expression network analysis and antisense oligonucleotide-mediated transient gene silencing revealed that CsAAP6 plays an important role in amino acid transport during tea shoot development. Nitrogen transport from source to sink is crucial for tea shoot growth and quality formation. Amino acid represents the major transport form of reduced nitrogen in the phloem between source and sink, but the molecular mechanism of amino acid transport from source leaves to new shoots is not yet clear. Therefore, the composition of metabolites in phloem exudates collected by the EDTA-facilitated method was analyzed through widely targeted metabolomics. A total of 326 metabolites were identified in the phloem exudates with the richest variety of amino acids and their derivatives (93), accounting for approximately 39.13% of the total metabolites. Moreover, through targeted metabolomics, it was found that the content of glutamine, glutamic acid, and theanine was the most abundant, and gradually increased with the development of new shoots. Meanwhile, transcriptome analysis suggested that the expression of amino acid transport genes changed significantly. The WGCNA analysis identified that the expression levels of CsAVT1, CsLHTL8, and CsAAP6 genes located in the MEterquoise module were positively correlated with the content of amino acids such as glutamine, glutamic acid, and theanine in phloem exudates. Reducing the CsAAP6 in mature leaves resulted in a significant decrease in the content of glutamic acid, aspartic acid, alanine, leucine, asparagine, glutamine, and arginine in the phloem exudates, indicating that CsAAP6 played an important role in the source to sink transport of amino acids in the phloem. The research results will provide the theoretical basis and genetic resources for the improvement of nitrogen use efficiency and tea quality.

Insights into the Uptake, Distribution, and Metabolism of 3-Isobutyl-2-hydroxypyrazine in Grapevine Using a Stable Isotope Tracer

Methoxypyrazines (MPs) are potent aroma compounds that have been predominately studied in grape berries but can also be detected in other vine tissues. The synthesis of MPs in berries from hydroxypyrazines by VvOMT3 is well established, but the origin of MPs in vine tissues that have negligible VvOMT3 gene expression is unknown. This research gap was addressed through the application of stable isotope tracer 3-isobutyl-2-hydroxy-[²H₂]-pyrazine (d₂-IBHP) to the roots of Pinot Meunier L1 microvines and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) quantification of HPs from grapevine tissues following a novel solid-phase extraction method. Four weeks post-application, d₂-IBHP and its O-methylated product 3-isobutyl-2-methoxy-[²H₂]-pyrazine (d₂-IBMP) were present in excised cane, berry, leaf, root, and rachis material. Translocation of d₂-IBHP and d₂-IBMP was investigated, but results were inconclusive. Nonetheless, knowledge that d₂-IBHP, and potentially d₂-IBMP, are translocated from roots to other vine organs, including the berries, could provide opportunities for controlling MP accumulation in grapevine tissues pertinent to winemaking.

Survivorship and Development of the Invasive Lycorma delicatula (Hemiptera: Fulgoridae) on Wild and Cultivated Temperate Host Plants

The invasive spotted lanternfly, Lycorma delicatula, (White Hemiptera: Fulgoridae) continues to spread throughout the Eastern United States. This species exhibits a broad host range, with tree of heaven, Ailanthus altissima (Mill.) Swingle, commonly referred to as the preferred host. Here, we evaluated 2-wk survivorship of early nymphal instars, late nymphal instars, and adult L. delicatula on single diets of ten wild and cultivated hosts: tree of heaven; apple, Malus domestica; peach, Prunus persica; black cherry, P. serotina Ehrh; black locust, Robinia pseudoacacia L.; black walnut, Juglans nigra L.; common hackberry Celtis occidentalis L.; mulberry Morus alba L.; sugar maple Acer saccharum Marshall; white oak, Quercus alba L.. Among them, early and late instars had significantly greater survivorship on tree of heaven and black walnut and adults had greatest survivorship on tree of heaven. Additionally, we evaluated development and survivorship of L. delicatula from newly hatched nymphs to adulthood on single diets of tree of heaven, black walnut, grapevine, apple, and peach, and mixed diets of tree of heaven plus one other host. Single host diets that supported L. delicatula development to adulthood were tree of heaven and black walnut. Interestingly, mixed diets also supported development, and reduced development time to adults by up to 12% compared with the single tree of heaven diet. Our results suggest that within agroecosystems and across landscapes, L. delicatula can develop on single hosts such as tree of heaven, but also on multiple host plants, yielding adults earlier in the growing season.

Complexation of Amino Acids with Cadmium and Their Application for Cadmium-Contaminated Soil Remediation

The interaction of amino acids with toxic heavy metals influences their immobilization and bioavailability in soils. However, the complexation ability of amino acids with Cd has not been well studied. The complexes of amino acids and cadmium were investigated by density functional theory (DFT) calculations and Fourier transform infrared spectrometry (FTIR) analyses. The complex structures were found to be [COc, COc] for fatty amino-cadmium and PheCd2+, [COc, COc, COs] for GluCd2+ and ThrCd2+, respectively. The complex energy of these conformers followed the order PheCd2+> AlaCd2+ > LeuCd2+ > GluCd2+ > GlyCd2+ > ThrCd2+. Importantly, all of the complex energy values were less than zero, indicating that these complexes could be easily dissolved in water. The Cd2+ concentration decreased with increasing amino acid concentration in aqueous solution. The complex stability constants (logβ) followed the order PheCd2+> AlaCd2+ > LeuCd2+ > GluCd2+ > GlyCd2+ > ThrCd2+, consistent with the order of the calculated complex energy values. The Cd removal efficiencies by Thr, Glu, Gly, Ala, Leu, and Phe were 38.88%, 37.47%, 35.5%, 34.72%, 34.04%, and 31.99%, respectively. In soil batch tests, the total Cd concentration in soil decreased in the presence of amino acids, while the Cd concentration in water increased from 231.97 μg/L to 652.94~793.51 μg/L. The results of sequential extraction showed that the acid-extractable fraction and the reducible fraction of Cd sharply decreased. Consequently, the significant features of amino acids along with their biocompatibility make them potentially applicable chelators in Cd-contaminated soil remediation processes.

Xylem sap phosphorus sampling using microdialysis-a non-destructive high sampling frequency method tested under laboratory and field conditions

For a better understanding of plant nutrition processes, it is important to study the flux of nutrients within plants. However, existing xylem sap sampling methods are typically destructive and do not allow for repeated, highly frequent measurements of nutrient concentration. In this paper, we present a novel use of microdialysis (MD) for characterizing xylem sap phosphate (PO43-) concentration as a possible alternative to destructive sampling. First, MD probes were tested under laboratory conditions in vitro, in a stirred solution test, and in vivo, using beech tree stem segments. Exponential decline in the relative recovery (RR) with an increasing MD pumping rate allows for determining an optimal sampling interval (i.e., the maximum amount of sample volume with the minimum required concentration). The RR changed only minimally, with a change in the simulated sap flow velocity during the in vivo stem segment test. This suggests that MD can be applied over a range of naturally occurring sap flow velocities. Differences in the ionic strength between the xylem sap and the perfusate pumped through the MD did not influence the RR. Then, MD was successfully applied in a 24 h field campaign in two beech trees of different ages and allowed for in situ assessments of the diurnal variation of PO43- concentration and (together with xylem flow measurements) flux variability in living trees. Both beech trees exhibited the same diurnal pattern in PO43- concentrations with higher concentrations in the younger tree. The xylem PO43- concentration measured with MD was in the same order of magnitude as that received through destructive sampling in the younger tree. The MD probes did not show a decline in RR after the field application. We showed that MD can be applied to capture the PO43- concentration dynamics in the xylem sap with bihourly resolution under field conditions.

Trunk Girdling Increased Stomatal Conductance in Cabernet Sauvignon Grapevines, Reduced Glutamine, and Increased Malvidin-3-Glucoside and Quercetin-3-Glucoside Concentrations in Skins and Pulp at Harvest

Girdling is a traditional horticultural practice applied at fruit set or other phenological stages, and is used mostly as a vine management. In grapevines, it is used primarily for table grapes to improve berry weight, sugar content, color, and to promote early harvest. The objective of this study was to evaluate the effect of trunk girdling applied at veraison, in 'Cabernet Sauvignon' wine grapes (Vitis vinifera L.), on agronomical and physiological parameters during vine development from the onset of ripening (veraison) to harvest, and additionally to quantify the effect of girdling on primary and secondary metabolism. Girdling was applied 146 days after pruning (dap) at veraison, when berry sampling for metabolomics and agronomical evaluations commenced, with a further three sampling dates until harvest, at 156 dap (30% maturation, 10 days after girdling-dag), 181 dap (70% maturation, 35 dag), and 223 dap (commercial harvest, 77 dag). Skin/pulp and seed tissues were extracted separately and metabolomics was performed using one-dimensional proton nuclear magnetic resonance (1D 1H NMR) spectroscopy and high performance liquid chromatography (HPLC-DAD). At harvest, girdling significantly increased stomatal conductance (gs) in vines, decreased glutamine concentrations, and increased anthocyanin and flavonol concentrations in the skin/pulp tissues of grape berries. Berry weight was reduced by 27% from 181 dap to harvest, and was significantly higher in grapes from girdled vines at 181 dap. Sugars, organic acids, and other amino acids in skin/pulp or seeds were not significantly different, possibly due to extra-fascicular phloem vessels transporting metabolites from leaves to the roots. Using a metabolomics approach, differences between skin/pulp and seeds tissues were meaningful, and a greater number of secondary metabolites in skin/pulp was affected by girdling than in seeds. Girdling is a simple technique that could easily be applied commercially on vine management to improve berry color and other phenolics in 'Cabernet Sauvignon' grapes.

Foliar application of urea to Tempranillo vines increased the amino acid concentration of the must

The aim of this study was to investigate the impact of fertilisation with foliar urea of Vitis vinifera var. Tempranillo on the concentration of amino acids in must and on their evolution during the final stage of grape ripening. Foliar urea fertilisation increased the concentration of amino nitrogen, ammonium nitrogen and yeast assimilable nitrogen (YAN) in Tempranillo must. In addition, fertilisation with foliar urea produced an increase in the concentration of many amino acids in the must. This increase was especially noticeable in the case of the most important amino acids for yeast metabolism throughout the alcoholic fermentation (arginine, glutamic acid, aspartic acid, histidine, serine and lysine). After comparing the results of this study with other ones, we may state that: in order to increase the amino acid concentration in must, it is important to apply the urea several times instead of making just one single application. Moreover, it is important to use a preparation of urea without biuret, which is a phytotoxic carbamyl urea formed as a condensation product arising from urea thermal decomposition.

Fruit Salad in the Lab: Comparing Botanical Species to Help Deciphering Fruit Primary Metabolism

Although fleshy fruit species are economically important worldwide and crucial for human nutrition, the regulation of their fruit metabolism remains to be described finely. Fruit species differ in the origin of the tissue constituting the flesh, duration of fruit development, coordination of ripening changes (climacteric vs. non-climacteric type) and biochemical composition at ripeness is linked to sweetness and acidity. The main constituents of mature fruit result from different strategies of carbon transport and metabolism. Thus, the timing and nature of phloem loading and unloading can largely differ from one species to another. Furthermore, accumulations and transformations of major soluble sugars, organic acids, amino acids, starch and cell walls are very variable among fruit species. Comparing fruit species therefore appears as a valuable way to get a better understanding of metabolism. On the one hand, the comparison of results of studies about species of different botanical families allows pointing the drivers of sugar or organic acid accumulation but this kind of comparison is often hampered by heterogeneous analysis approaches applied in each study and incomplete dataset. On the other hand, cross-species studies remain rare but have brought new insights into key aspects of primary metabolism regulation. In addition, new tools for multi-species comparisons are currently emerging, including meta-analyses or re-use of shared metabolic or genomic data, and comparative metabolic flux or process-based modeling. All these approaches contribute to the identification of the metabolic factors that influence fruit growth and quality, in order to adjust their levels with breeding or cultural practices, with respect to improving fruit traits.

Studying Phloem Loading with EDTA-Facilitated Phloem Exudate Collection and Analysis

Sugars that are produced by photosynthesis in the leaves are transported in the phloem to heterotrophic sink tissues like roots, fruit, or flowers. Since sugars inside the highly specialized cells of the phloem move by bulk flow, it is the loading and unloading of sugars that determines the rates of allocation between organs. Here, a method is described for the relative quantification of sugars that are loaded into the phloem in leaves. It is based on EDTA-facilitated phloem exudate collection and, therefore, requires control experiments to exclude measurement artifacts. It can be applied to a wide range of plant species, including dicots, monocots, and trees.

Putting primary metabolism into perspective to obtain better fruits

Background

One of the key goals of fruit biology is to understand the factors that influence fruit growth and quality, ultimately with a view to manipulating them for improvement of fruit traits.

Scope

Primary metabolism, which is not only essential for growth but is also a major component of fruit quality, is an obvious target for improvement. However, metabolism is a moving target that undergoes marked changes throughout fruit growth and ripening.

Conclusions

Agricultural practice and breeding have successfully improved fruit metabolic traits, but both face the complexity of the interplay between development, metabolism and the environment. Thus, more fundamental knowledge is needed to identify further strategies for the manipulation of fruit metabolism. Nearly two decades of post-genomics approaches involving transcriptomics, proteomics and/or metabolomics have generated a lot of information about the behaviour of fruit metabolic networks. Today, the emergence of modelling tools is providing the opportunity to turn this information into a mechanistic understanding of fruits, and ultimately to design better fruits. Since high-quality data are a key requirement in modelling, a range of must-have parameters and variables is proposed.