Wenping Xu

Aroma characterization based on aromatic series analysis in table grapes

Aroma is an important part of quality in table grape, but the key aroma compounds and the aroma series of table grapes remains unknown. In this paper, we identified 67 aroma compounds in 20 table grape cultivars; 20 in pulp and 23 in skin were active compounds. C6 compounds were the basic background volatiles, but the aroma contents of pulp juice and skin depended mainly on the levels of esters and terpenes, respectively. Most obviously, ‘Kyoho’ grapevine series showed high contents of esters in pulp, while Muscat/floral cultivars showed abundant monoterpenes in skin. For the aroma series, table grapes were characterized mainly by herbaceous, floral, balsamic, sweet and fruity series. The simple and visualizable aroma profiles were established using aroma fingerprints based on the aromatic series. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) showed that the aroma profiles of pulp juice, skin and whole berries could be classified into 5, 3, and 5 groups, respectively. Combined with sensory evaluation, we could conclude that fatty and balsamic series were the preferred aromatic series, and the contents of their contributors (β-ionone and octanal) may be useful as indicators for the improvement of breeding and cultivation measures for table grapes.

Selection of reference genes for miRNA qRT-PCR under abiotic stress in grapevine

Grapevine is among the fruit crops with high economic value, and because of the economic losses caused by abiotic stresses, the stress resistance of Vitis vinifera has become an increasingly important research area. Among the mechanisms responding to environmental stresses, the role of miRNA has received much attention recently. qRT-PCR is a powerful method for miRNA quantitation, but the accuracy of the method strongly depends on the appropriate reference genes. To determine the most suitable reference genes for grapevine miRNA qRT-PCR, 15 genes were chosen as candidate reference genes. After eliminating 6 candidate reference genes with unsatisfactory amplification efficiency, the expression stability of the remaining candidate reference genes under salinity, cold and drought was analysed using four algorithms, geNorm, NormFinder, deltaCt and Bestkeeper. The results indicated that U6 snRNA was the most suitable reference gene under salinity and cold stresses; whereas miR168 was the best for drought stress. The best reference gene sets for salinity, cold and drought stresses were miR160e + miR164a, miR160e + miR168 and ACT + UBQ + GAPDH, respectively. The selected reference genes or gene sets were verified using miR319 or miR408 as the target gene.

Proteomic analysis of pear (Pyrus pyrifolia) ripening process provides new evidence for the sugar/acid metabolism difference between core and mesocarp

Pears are one of the most popular nutrient‐rich fruits in the world. The pear core and mesocarp have significantly different metabolism, although they display similar profiles. Most strikingly, the core is more acidic in taste. Our results showed that there is more titrated acid but lower total soluble solids in the core compared to the mesocarp, and the content of citric acid was more than 17‐fold higher in the core compared to the mesocarp at the ripening stage. Proteomics was used to investigate the difference between core and mesocarp tissues during “Cuiguan” pear ripening. Fifty‐four different protein expression patterns were identified in the core and mesocarp. In general, common variably expressed proteins between the core and mesocarp were associated with important physiological processes, such as glycolysis, pyruvate metabolic processes, and oxidative stress. Further, protein level associated qRT‐PCR verification revealed a higher abundance of fructose‐bisphosphate aldolase and NADP‐dependent malic enzymes, which may play a role in the low acid content in the mesocarp, whereas a higher abundance of disulfide isomerase‐like 2‐2 and calcium‐dependent lipid‐binding in the core may explain why it is less prone to accumulate sugar. The different levels of a few typical ROS scavenger enzymes suggested that oxidative stress is higher in the core than in the mesocarp. This study provides the first characterization of the pear core proteome and a description of its variation compared to the mesocarp during ripening.

Effects of root restriction on the ultrastructure of phloem in grape leaves

In this study, the ultrastructure of phloem and its surrounding parenchyma cells in grape leaves from plants subjected to root restriction or without (control) was systematically investigated for the first time through transmission electron microscopy. The results show that the sieve element (SE) and companion cells (CC) in the main veins of leaves subjected to root restriction were smaller in size than those in the control leaves. The number of plasmodesmata between CC and SE in leaves subjected to root restriction was greater than in the control leaves, but the number of plasmodesmata between phloem parenchyma cells (PP) in leaves subjected to root restriction was less than in the control leaves. Also, the average diameters of SE and CC in the branch veins were smaller in leaves subjected to root restriction than in the control leaves, but their cell walls were thicker and the number of plasmodesmata between PP was less. In the minor veins, the SE and CC were smaller in leaves subjected to root restriction than in the control leaves, and the number of plasmodesmata between CC and SE, SE and PP, and CC and PP were greater. Moreover, less intercellular space among PP cells was observed in minor veins of leaves subjected to root restriction, which was in contrast to the main veins where more intercellular space among PP cells was observed in the leaves subjected to root restriction compared to control leaves. These results therefore demonstrated that changes in the ultrastructure of the phloem of grape leaves are a result of adaptation to the stress of root restriction. Key words : Root restriction, leaf, phloem, ultrastructure.

In-Depth Aroma and Sensory Profiling of Unfamiliar Table-Grape Cultivars

We present an in-depth analysis of aroma profiles and sensory attributes, employing solid-phase microextraction gas chromatography/mass spectrometry (SPME-GC-MS) to identify the key compounds driving consumer preference in 19 unfamiliar cultivars. In combination with popular cultivars, we identified a total of 100 compounds in all table grapes, of which 26 key volatiles were correlated with consumer liking. Based on this relationship, five aroma combinations (AC) were formulated, wherein 33 compounds contributed to aroma intensity, and thus, were viewed as active volatiles. The fruity, floral, and sweet aromas were further divided into secondary aromatic series, of which the apple, citrus, orange, rose, geranium, violet, and honey aromas constituted the predominant series in unfamiliar cultivars. Xiangyue and Heikuixiang emerged as the preferred table grapes according to our analysis. By comparison, the popular cultivars showed relatively fewer volatiles, but their contents were much greater than the large number of volatiles identified in the unfamiliar cultivars.

Characterization of the ABA Receptor VlPYL1 That Regulates Anthocyanin Accumulation in Grape Berry Skin

ABA plays a crucial role in controlling several ripening-associated processes in grape berries. The soluble proteins named as PYR (pyrabactin resistant)/PYL (PYR-like)/RCAR (regulatory component of ABA receptor) family have been characterized as ABA receptors. Here, the function of a grape PYL1 encoding gene involved in the response to ABA was verified through heterologous expression. The expression level of VlPYL1 was highest in grape leaf and fruit tissues of the cultivar Kyoho, and the expression of VlPYL1 was increased during fruit development and showed a reduction in ripe berries. Over-expression of VlPYL1 enhances ABA sensitivity in Arabidopsis. Using the transient overexpression technique, the VlPYL1 gene was over-expressed in grape berries. Up-regulation of the VlPYL1 gene not only promoted anthocyanin accumulation but also induced a set of ABA-responsive gene transcripts, including ABF2 and BG3. Although tobacco rattle virus (TRV)-induced gene silencing (VIGS) was not successfully applied in the “Kyoho” grape, the application of the transient overexpression technique in grape fruit could be used as a novel tool for studying grape fruit development.

Hydrogen cyanamide improves endodormancy release and blooming associated with endogenous hormones in ‘Summit’ sweet cherry trees

ABSTRACT A trial was conducted to verify the effect of hydrogen cyanamide (HC) application on endodormancy release and blooming of ‘Summit’ sweet cherry trees, as well as on endogenous gibberellic acids (GAs) and abscisic acid (ABA) levels which were identified and quantified by gas chromatography/mass spectrometry in branches with spurs. Results showed that HC efficiently hastened endodormancy release and budbreak, shortened blooming duration and improved fruit set. Furthermore, bioactive GAs play different roles in the process of endodormancy release and blooming. GA3 was recognised as the highest isomer of bioactive GA and was closely related with endodormancy release improved by HC treatment as well as GA4. GA7 displayed a rapid increase when buds went into the burst stage and associated with promoted budburst and blooming by HC treatment. GA1 showed irregular changes during this process. A higher GAs:ABA ratio was observed in HC-treated ‘Summit’ branches from endodormancy release until full bloom. However, a reciprocal pattern occurred thereafter due to senescence of the flowers.