No abstract

Seeds from the myxospermous species Plantago ovata release a polysaccharide-rich mucilage upon contact with water. This seed coat derived mucilage is composed predominantly of heteroxylan (HX) and is utilized as a gluten-free dietary fiber supplement to promote human colorectal health. In this study, a gamma-irradiated P. ovata population was generated and screened using histological stains and Fourier Transform Mid Infrared (FTMIR) spectroscopy to identify putative mutants showing defects in seed coat mucilage HX composition and/or structure. FTMIR analysis of dry seed revealed variation in regions of the IR spectra previously linked to xylan structure in Secale cereale (rye). Subsequent absorbance ratio and PCA multivariate analysis identified 22 putative mutant families with differences in the HX IR fingerprint region. Many of these showed distinct changes in the amount and subtle changes in structure of HX after mucilage extrusion, while 20% of the putative HX mutants identified by FTMIR showed no difference in staining patterns of extruded mucilage compared to wild-type. Transcriptional screening analysis of two putative reduced xylan in mucilage (rxm) mutants, rxm1 and rxm3, revealed that changes in HX levels in rxm1 correlate with reduced transcription of known and novel genes associated with xylan synthesis, possibly indicative of specific co-regulatory units within the xylan biosynthetic pathway. These results confirm that FTMIR is a suitable method for identifying putative mutants with altered mucilage HX composition in P. ovata, and therefore forms a resource to identify novel genes involved in xylan biosynthesis.

No abstract

In this study, to investigate the physiological and molecular mechanisms of melatonin inhibiting the postharvest rot of blueberry fruits, blueberry fruits were dipped in 0.3 mmol L−1 melatonin solution for 3 min and stored at 0°C for 80 days. The results indicated that melatonin did not significantly (p > 0.05) inhibit the mycelial growth or spore germination of Alternaria alternata, Botrytis cinerea, and Colletotrichum gloeosporioides. In addition, an in vivo study revealed that melatonin treatment increased the enzymatic activities of phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), polyphenol oxidase (PPO), and peroxidase (POD) in fruits. Furthermore, genes related to jasmonic acid synthesis were upregulated (VaLOX, VaAOS, and VaAOC), as were those related to pathogenesis-related proteins (VaGLU and VaCHT) and phenylpropane metabolism (VaPAL, VaC4H, Va4CL, VaCAD, VaPPO, and VaPOD), which promoted the accumulation of total phenols, flavonoids, anthocyanins, and lignin in the fruits. These results suggest that melatonin enhances the postharvest disease resistance of blueberry fruits by mediating the jasmonic acid signaling pathway and the phenylpropane pathway.

Pitaya fruits have high senescence rates throughout their postharvest storage period. Additionally, studies have confirmed that melatonin plays a regulatory role in plant senescence. However, the involvement of melatonin in the postharvest senescence of fruits remains unclear. In this study, two cultivars of pitaya fruit, 'Zihonglong' and 'Jinghonglong' , were treated with melatonin and then evaluated for characteristics of senescence while in storage for 10 days. The results showed that melatonin treatment delayed fruit senescence in both pitaya cultivars, as indicated by the inhibition of weight loss, decay incidence, relative membrane permeability, and malondialdehyde (MDA) content, as well as the maintenance of the total soluble solids and ascorbic acid contents and the reduced respiration intensity. In addition, melatonin treatment reduced the O 2 •production rates, H 2 O 2 contents, and lipoxygenase activities but enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both pitaya cultivars. These results indicate that melatonin may contribute to delaying senescence in pitaya fruits. This study shows the potential of the use of melatonin in the postharvest storage of pitaya fruits, as well as other horticultural fruits.

We investigated the effects of melatonin (MT) treatment on the physiological quality and cell wall metabolism of kiwifruit during a 12-day shelf life period (20 ± 1 °C, 90 ± 5% RH), after 90 days of cold storage (0 ± 0.5 °C, 90 ± 5% RH). Our results showed that MT treatment delayed kiwifruit softening, as evidence by the enhanced endurance of a healthy appearance, quality, color difference L* value, and firmness of the fruit flesh. MT treatment reduced fruit decay rate, respiration rate, and malondialdehyde content; furthermore, MT-treated kiwifruit maintained high levels of total soluble solids, titratable acid, and ascorbic acid. Additionally, MT inhibited the decrease in fruit pectin, cellulose, and hemicellulose contents; it delayed the increase in watersoluble pectin content and kept pectin methyl esterase, polygalacturonase, cellulase, and β-galactosidase activities low. These results indicated that melatonin may have reduced the speed of softening of kiwifruit and preserved fruit quality by inhibiting enzymatic degradation of the cell wall, and by delaying pro-pectin, cellulose, and hemicellulose degradation, as well as the increase of water-soluble pectin content. These findings indicate that MT treatment may be an effective measure to delay kiwifruit postharvest cell-wall metabolism and preserve fruit quality.

The present work investigated the effects of different concentrations of melatonin (0, 50, 100, and 200 μmol L-1) on the quality and antioxidant activity of fresh-cut pitaya (Hylocereus undatus) fruits. Results revealed that melatonin treatments significantly increased the firmness, total soluble solids, and titratable acidity of post-harvest fruits, and inhibited the rate of weight loss. When compared with the control treatment, the application of melatonin maintained higher contents of vitamin C and total phenolics in fresh-cut pitaya fruits during storage. Melatonin also decreased cell membrane electrolyte leakage and polyphenol oxidase activity, with 100 μmol L-1 melatonin treatment showing the best effects. In addition, 100 μmol L-1 melatonin significantly increased the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (APX), thus decreasing the accumulation of H2O2 and O2- during storage. Collectively, these findings indicate that melatonin treatment could contribute to delaying the ripening and senescence of fresh-cut pitaya fruits, and has potential application in the preservation of fresh-cut pitaya fruits during storage.

Fresh bamboo shoots (Chimonobambusa quadrangularis) are subjected to senescence (e.g., lignification and browning) during postharvest storage. This study investigated the effects of 1-MCP and SO2 treatment on bamboo shoot senescence and its regulation mechanism in order to extend bamboo shoot storage time. 1-MCP and SO2 treatments significantly inhibited the browning and lignification of fresh bamboo shoots during storage, according to the results. Its lower browning index and lignin content are directly related to its lower lignin content compared to the CK control group. The browning index and lignin content of the 1-MCP + SO2 treatment during the late storage period were 90.55% and 81.50% of the CK treatment, respectively. The result of the in-depth analysis suggested that 1-MCP and SO2 treatments reduced nutrient loss and maintained the nutritional value of bamboo shoots by inhibiting respiration and physiological metabolism. The PPO activity was inhibited to inhibit the browning process. Moreover, the scavenging ability of ROS was enhanced, the accumulation of MDA was inhibited, and the senescence of bamboo shoots was delayed after higher contents of total flavonoids and ascorbic acid were maintained and the activities of ascorbic acid peroxidase and superoxide dismutase were stimulated. Furthermore, lignin biosynthesis was hindered, and the lignification of bamboo shoots was delayed after the activities of POD and PAL were inhibited. In brief, 1-MCP + SO2 treatment is capable of inhibiting the physiological metabolism, browning, and lignification of bamboo shoots, maintaining good quality during storage, and delaying the senescence of bamboo shoots. Clarifying the senescence mechanism of bamboo shoots is of great significance for expanding the bamboo shoot industry and slowing down rocky desertification in karst mountainous areas.