Recently, there has been a trend towards healthy food. Consumers are looking for products that have health-promoting properties in addition to their taste. Actinidia fruit, apart from being tasty, contains valuable nutrients. They are high in vitamin C, polyphenols, and pectins and low in calories. These pro-health properties allow kiwiberry fruit to qualify in the group of so-called superfoods. All tested cultivars belong to two species of Actinidia, well tolerating conditions of moderate climate with negative temperatures in winter. The cultivars differed significantly in mineral content, color, firmness, weight and content of antioxidant substances. Summer pruning (lightening) increased the content of N, P, K, extract, and NO3 and resulted in darker fruit color. However, it slightly decreased the content of polyphenols. 'Sientiabrskaja' can be recommended for consumption as the cultivar richest in polyphenols and with the highest health-promoting values.

Kiwifruit vines are generally sensitive to waterlogging stress. So far, molecular responses of different kiwifruit genotypes for waterlogging stress are less well-explored. In this study, using RNA-sequencing, we examined transcriptional regulation in the roots of a waterlogging-tolerant genotype KR5 (Actinidia valvata), and a sensitive genotype ‘Hayward’ (Actinidia deliciosa) subjected to 0, 12, 24, and 72 h of waterlogging. Compared with 0 h, transcriptional adjustments of these two genotypes occurred as early as 12 h and became notably pronounced 72 h after waterlogging. Waterlogging stress for 72 h promoted the expression of genes involved in ethylene biosynthesis, sucrose and hexose transport, anaerobic fermentation, nitrate reduction, alanine accumulation, and reactive oxygen scavenging in both genotypes. The differential regulation of genes encoding 9-cis-epoxycarotenoid dioxygenase, phosphoglucomutase, alanine-glyoxylate transaminase, and other enzymes pointed to their diverse strategies upon waterlogging in these two genotypes. In addition, more sucrose and trehalose contents, as well as a higher activity of alcohol dehydrogenase and manganese superoxide dismutases were stimulated in KR5 roots after 72h of waterlogging than that in ‘Hayward’. Overall, our results provided more insights into the molecular basis of the waterlogging response in kiwifruit.

Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. is abundant of vitamin C and bioactive compounds with high antioxidant activities. In this study, eight wild A. arguta accessions from different areas in Northeast China were collected. Some bioactive compounds were examined on the different tissues of different germplasms including four kinds of leaves, petioles and fruits. The method of UPLC-MS was used to detect the flavonoid compounds. The results showed that some bioactive compounds including vitamin C, soluble sugar, free amino acid, total phenolics and flavonoids content showed significant differences between six tissues of A. arguta accessions and showed significant variability with maturity. In eight accessions, the highest vitamin C content was found in young apical leaves of ‘CBS-6’ (7.47 mg/g fresh weight), and the highest soluble sugar content was in fruits of ‘CJ-1’ (196.52 mg/g fresh weight) and the highest total phenolic content and total flavonoids content were in young apical leaves of ‘CBS-11’ (3.48 mg/g fresh weight) and of ‘CBS-3’ (2.00 mg/g fresh weight), respectively. Ten flavonoid compounds including kaempferol, isorhamnetin and quercetin were detected in leaves, petioles and fruits. The total content of flavonoids were highest in young apical leaves (10219.84 µg·g-1) and the lowest in fruits (78.75 µg·g-1). Based on the comparison of the contents of several bioactive compounds, the two accessions ‘CJ-1’ and ‘CBS-8’ had relatively outstanding performance, and in the comprehensive evaluation of the antioxidant activity among different tissues, the young leaves had the strongest antioxidant activity. These results highlighted the antioxidant potentialities of A. arguta leaves as a major source of phenolics and vitamin C as well as flavonoids. It provided a theoretical basis for the utilization of leaves of A. arguta.

Diacylglycerol kinase (DGK) is a lipid kinase that phosphorylates diacylglycerol (DAG) to generate phosphatidic acid (PA). Based on converting one important signaling molecule (DAG) to another (PA), DGK plays an important role in plant responses to abiotic stress including waterlogging stress. However, no studies have been reported on the characterization of the DGK gene family in the waterlogging-tolerant kiwifruit germplasm, Actinidia valvata Dunn. Here, we identified 18 AvDGK genes in the A. valvata genome. The phylogenetic analysis showed that AvDGKs can be classified into three clusters, and members within the same cluster have similar domain distribution, exon-intron structures and conserved motif compositions. Chromosome localization analysis revealed that all the AvDGK genes are located across 18 different chromosomes. There were 29 duplicated gene pairs in kiwifruit and all had undergone purifying selection during evolution. Promoter cis-element analysis revealed that the cis-elements within AvDGK genes are associated with multiple functions, including phytohormone signal transduction, stress response, and plant growth and development. The expression pattern analyses indicated that AvDGK play an important role in the fruit development and plant response to waterlogging stress. AvDGKs gene family in the tetraploid A. valvata genome might promote PA synthesis and subsequent signal transduction both under short-term and long-term waterlogging stress. These results provide information regarding the structural characteristics and potential function of DGK genes within kiwifruit and lay a fundamental basis for further research into breeding for enhancing the kiwifruit’s tolerance to waterlogging stress.

An understanding of the mechanism underlying fruit ripening is critical for fruit quality improvement. Although post-harvest ethylene application is known to enhance the onset of fruit ripening, exact mechanisms remain unclear. To characterize the fruit ripening process and mechanism, we investigated the effects of exposing kiwifruit cultivars ‘Hayward’ and ‘Gamrok’ to exogenous ethylene treatment post-harvest using comprehensive proteomic analyses. Comparative two-dimensional gel electrophoresis showed that most of the proteins aggregated in ethylene-treated samples compared to the control (non-treated). We observed that among all ethylene treatments, 95 proteins from ‘Hayward’ and 106 from ‘Gamrok’ were differentially expressed. Interestingly, among the elicited protein successfully identified by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry, 50% from “Hayward’ and 60% from ‘Gamrok’ are associated with fruit ripening. Furthermore, 18% and 10% of proteins, respectively, are associated with defense response, whereas other major proteins are related to protein biosynthesis and photosynthesis/Calvin cycle. Interactions between identified proteins were demonstrated by bioinformatic analysis, providing insights into biological pathways and molecular functions in post-harvest kiwifruit ripening elicited by ethylene application. The present proteomic study in accordance with physiological analysis provides a quantitative evaluation of fruit ripening in response to exogenous ethylene in post-harvest kiwifruit.