Junfeng Guan

Effects of Nitric Oxide on the Quality and Pectin Metabolism of Yali Pears During Cold Storage

Abstract The effect of fumigation with 10, 20, and 30 μL L −1 nitric oxide (NO) was investigated to study the effects of NO on the quality of Yali pears during cold storage. The ethylene production, composition of cell walls, and cell-wall-modifying enzyme activities were measured on fruits which were fumigated with NO (20 μL L −1 ). The results showed that NO not only reduced the peak value of ethylene production rate, the soluble sugar, soluble solid content, maintained higher firmness, starch, and NO content, but also retarded the degradation of covalent soluble pectin, accumulation of ionic soluble pectin and water soluble pectin. Moreover, NO fumigation decreased the activities of polygalacturonase (PG) and β-galactosidase (β-Gal) and delayed the peak of PG activity of fruits. Therefore, it indicated that NO fumigation could delay the softening and ripening of Yali pears.

Effects of 1-MCP on reactive oxygen species, polyphenol oxidase activity, and cellular ultra-structure of core tissue in ‘Yali’ pear (Pyrus bretschneideri Rehd.) during Storage

Abstract1-methylcyclopropene (1-MCP) has been shown to delay fruit ripening and senescence during storage. In this study, we investigated the effects of 1.0 μL·L−1 1-MCP on the biochemical changes and cellular ultra-structure of the core tissue in ‘Yali’ pear (Pyrus bretschneideri Rehd.) fruits stored at 25 ± 2°C. Our results showed that 1-MCP treatment significantly decreased the rates of respiration and ethylene production before their climacteric peaks, inhibited the development of core browning, lowered the chlorogenic acid content and polyphenol oxidase activity before the onset of core browning, and preserved high levels of superoxide dismutase activity, ascorbic acid, and glutathione contents. Furthermore, it suppressed the accumulation of hydrogen peroxide, superoxide anion, and malondialdehyde in the core tissue, maintained the integral structure of the cell membrane and organelle, and delayed the accumulation of electron-opaque matters in the vacuoles of core cells. These results suggested that 1-MCP treatment could reduce the injury caused by reactive oxygen, inhibit the oxidation of phenolics, and keep the cell membrane intact in core cells, thus, delaying the core browning in ‘Yali’ pear during storage.

Effects of 1-Methylcyclopropene on NO Content, NOS Activity, and H2O2 Content in Postharvest Suli Pears

Studies were conducted over the effects of 1-methylcycolpropene (1-MCP) treatment on postharvest life of Suli pears (Pyrus bretschneideri Rehd.) stored at room and cold temperatures on nitric oxide (NO), nitric oxide synthase (NOS) activity, and hydrogen dioxide (H2O2). Results showed that the 1-MCP treatment had little effect on total soluble solids (TSS) at both room and cold temperatures. 1-MCP delayed softening of Suli pear fruits, decreased respiratory rate and H2O2 accumulation, and increased NO and NOS activity at room temperature storage, while the effect of cold temperature storage was relatively inferior. There was a significant positive correlation between NOS activity and NO content. It is concluded that 1-MCP had effects on endogenous NO content and accumulation of H2O2. Similarly, H2O2 acting as a signaling molecule via regulating NO level affects the ripening and senescence of Suli pears.

Molecular Characterization of Ethylene-Regulated Anthocyanin Biosynthesis in Plums During Fruit Ripening

Anthocyanin accumulation is an important physiological process that occurs during plum fruit ripening. Currently, little is known about the molecular mechanisms of ethylene-regulated anthocyanin accumulation in plum fruit. To better understand this process, ethylene production, anthocyanin content, and the expression of genes involved in anthocyanin biosynthesis and ethylene signaling were studied in the postharvest ‘Oishi-wase’ plum (Prunus salicina Lindl. cv. ‘Oishi-wase’) fruit. Ethylene treatment significantly enhanced the anthocyanin accumulation in plum fruit peel, while 1-methylcyclopropene (1-MCP) treatment resulted in considerable reduction in anthocyanin content. Furthermore, ethylene treatment significantly enhanced the expression levels of the seven structural genes, i.e., PsPAL, PsCHS, PsCHI, PsF3H, PsDFR, PsLDOX, and PsUFGT, that were involved in the anthocyanin biosynthetic pathway, while 1-MCP treatment showed an opposite effect. Similar to the structural genes, the master transcription factor PsMYB10 messenger RNA (mRNA) was also induced by ethylene and suppressed by 1-MCP, and this was positively correlated with ethylene production, anthocyanin accumulation, and the expression profile of the structural genes. The expression patterns of the ethylene signal pathway-associated genes, including two ethylene receptors (PsERS1 and PsETR1) and seven ethylene-responsive factors (PsERFs), were also positively correlated with that of PsMYB10 and most of the structural genes involved in the anthocyanin biosynthetic pathway. Further analysis indicated that PsERS1, PsETR1, PsERF1a, PsERF1b, PsERF2a, PsERF3a, and PsERF3b might be involved in the anthocyanin biosynthetic pathway of plum fruit. These results suggest that the ethylene signaling pathway plays an important role in regulating anthocyanin biosynthesis of postharvest plum fruit.

Calcium content and its correlated distribution with skin browning spot in bagged Huangguan pear.

Skin browning spot (SBS) is an important physiology disorder that often occurs in bagged fruit at the mature stage in the Huangguan (Pyrus bretschneideri × Pyrus pyrifolia) pear. Using atomic absorption spectrometry, X-ray microanalysis, and the potassium-pyroantimonate precipitation method, the water-soluble and total Ca2+, Mg2+, and K+ contents, their microdistribution, and the Ca2+ localization were investigated in bagged Huangguan pear fruit in the presence and absence of SBS. Our results show that the water-soluble and total Ca2+ contents in both the skin and flesh tissue and the total Ca2+ content only in the skin tissue of the fruits with SBS were significantly lower compared to those of the fruits without SBS. However, a higher K+ content in the skin tissue was found in the fruits with SBS. There were no significant differences in the water-soluble and total Mg2+ contents in the skin and flesh tissue between the fruits with and without SBS. In addition, the results of the X-ray microanalysis were consistent with changes in the total Ca2+, Mg2+, and K+ contents in the skin and flesh tissue of the pear fruit that were affected by SBS. Compared to the skin tissue of pear fruit without SBS and the healthy part near the lesion zone of SBS, the lesion zone of SBS exhibited a high accumulation of Ca2+ grains in the cell membrane of the epidermis cells, while fewer Ca2+ grains were found in the vacuoles and cell walls. Altogether, these results indicate that Ca2+ deficiency and the cellular Ca2+ distribution in skin tissue contributed to the occurrence of SBS in bagged Huangguan pear fruit.

Effects of 1-MCP on softening, yellowing and H2O2 content in post-harvest ‘Jingbaili’ pear fruit during and after cold storage

Abstract‘Jingbaili’ pear (Pyrus ussuriensis Maxim.) fruit shows rapid softening, yellowing and short shelf-life at ambient temperature storage. In this study, ‘Jingbaili’ pear fruits were treated with 1.0 μL·L−1 1-methylcyclopropene (1-MCP) for 24 hours at 25 ± 2°C and then stored at 0°C. After 60 and 120 days of cold storage at 0°C, pear fruits were removed and stored at 20 ± 2°C to assess their shelf-life. The results indicated that the 1-MCP treatment delayed the decrease in firmness and chlorophyll (a, b, and a+b) content of peel, reduced the rates of respiration and ethylene production, and inhibited the accumulation of hydrogen peroxide (H2O2), which was observed in the untreated fruits during and after cold storage. Less difference was found in soluble solids content (SSC) between the control and 1-MCP-treated fruits during storage. The correlation analysis showed that flesh H2O2 content was negatively related to firmness and also peel H2O2 content to peel chlorophyll a+b content. These results suggested that the 1-MCP treatment could delay the fruit softening and chlorophyll degradation by suppressing the accumulation of H2O2 content during and after cold storage in ‘Jingbaili’ pear.

Changes of chlorogenic acid content and its synthesis-associated genes expression in Xuehua pear fruit during development

Abstract According to synthetic pathway of plant chlorogenic acid (CGA), the expression patterns of genes encoding enzymes that are associated with CGA synthesis were studied in normally developed Xuehua pear fruit. The study demonstrated that CGA content in peel and flesh of Xuehua pear decreased as fruit development progressed, with a higher level in peel. The expression levels of PbPAL1, PbPAL2, PbC3H, PbC4H, Pb4CL1, Pb4CL2, Pb4CL6, PbHCT1 and PbHCT3 genes decreased in fruit, which was consistent with the pattern of variation in CGA content. That indicated that these genes might be key genes for influencing fruit CGA synthesis in Xuehua pear. However, Pb4CL7 gene expression profile is not consistent with variation of CGA content, hence, it may not be a key gene involved in CGA synthesis.