Melatonin delays leaf senescence of postharvest Chinese flowering cabbage through ROS homeostasis.

Reactive oxygen species (ROS) trigger and accelerate leaf senescence. Melatonin, a low molecular compound with several biological functions in plants, is known to delay leaf senescence in different species, including Chinese flowering cabbage. However, the mechanism(s) underpinning melatonin-delayed leaf senescence remains unclear. Here, we found that melatonin lowered the expression of chlorophyll catabolic genes (BrPAO and BrSGR1) and senescence-associated genes (BrSAG12 and BrSEN4), decreased chlorophyll loss, minimized the alteration in Fv/Fm ratio and remarkably delayed senescence of Chinese flowering cabbage after harvest. Moreover, the over-accumulation of O2•-, hydrogen peroxide (H2O2) and malondialdehyde contents and the expression of respiratory burst oxidase homologues (RBOH) genes (BrRbohB, BrRbohC, BrRbohD, BrRbohD2 and BrRbohE) were significantly inhibited by melatonin treatment. Melatonin-treated cabbages also showed higher O2•-, OH• and DPPH radical scavenging capacity and enhanced activities of peroxidase (POD), superoxide dismutase (SOD) and their gene expressions. Up-regulation of key components of ascorbate-glutathione (AsA-GSH) cycle, the metabolic pathway that detoxify H2O2, was also observed in melatonin-treated cabbages. These findings suggest that melatonin-delayed postharvest leaf senescence of postharvest Chinese flowering cabbage may be mediated, at least in part, by maintaining ROS homeostasis through restraining RBOHs-catalyzed ROS production and enhancing the activity of ROS-scavenging system including major antioxidant enzymes and AsA-GSH cycle.

Influence of α-terpineol on the growth and morphogenesis of Penicillium digitatum.

BACKGROUND: Plant essential oils could act effectively against postharvest diseases, α-terpineol, a typical terpenoid of plant essential oils, exhibited strong antifungal activity in against Penicillium italicum, but the possible action mechanism remains undetermined. In present study, α-terpineol was evaluated for antibacterial activity against Penicillium digitatum along with the mode of their antibacterial action. RESULTS: The results showed that mycelial growth of P. digitatum was strongly inhibited by α-terpineol, with the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 2.00 and 8.00 µl/ml, respectively. Scanning electron microscopy observation revealed that α-terpineol obviously altered the morphology of P. digitatum hyphae by causing the loss of cytoplasm and distortion of mycelia. A rapid increase in the membrane permeability of P. digitatum was observed after treated with MIC or MFC of α-terpineol, evidenced by the release of cell constituents, the extracellular conductivity, and the extracellular pH. In addition, α-terpineol apparently induced a decrease in total lipid contents of P. digitatum cells, indicating the destruction of cell membrane structures after treatment. CONCLUSIONS: Based on our study, α-terpineol might affect the cell wall synthesis and lead to the disruption of cell wall. The cell wall disruption affected fungal morphogenesis, the integrity of membrane and leakage of intracellular components, these results suggested that α-terpineol treatment inhibited the growth of P. digitatum.

Comprehensive analysis of expressed sequence tags from the pulp of the red mutant 'Cara Cara' navel orange (Citrus sinensis Osbeck).

Expressed sequence tag (EST) analysis of the pulp of the red-fleshed mutant 'Cara Cara' navel orange provided a starting point for gene discovery and transcriptome survey during citrus fruit maturation. Interpretation of the EST datasets revealed that the mutant pulp transcriptome held a high section of stress responses related genes, such as the type III metallothionein-like gene (6.0%), heat shock protein (2.8%), Cu/Zn superoxide dismutase (0.8%), late embryogenesis abundant protein 5 (0.8%), etc. 133 transcripts were detected to be differentially expressed between the red mutant and its orange-color wild genotype 'Washington' via digital expression analysis. Among them, genes involved in metabolism, defense/stress and signal transduction were statistical overrepresented. Fifteen transcription factors, composed of NAM, ATAF, and CUC transcription factor (NAC); myeloblastosis (MYB); myelocytomatosis (MYC); basic helix-loop-helix (bHLH); basic leucine zipper (bZIP) domain members, were also included. The data reflected the distinct expression profile and the unique regulatory module associated with these two genotypes. Eight differently expressed genes analyzed in digital were validated by quantitative real-time polymerase chain reaction. For structural polymorphism, both simple sequence repeats and single nucleotide polymorphisms (SNP) loci were surveyed; dinucleotide presentation revealed a bias toward AG/GA/TC/CT repeats (52.5%), against GC/CG repeats (0%). SNPs analysis found that transitions (73%) outnumbered transversions (27%). Seventeen potential cultivar-specific and 387 heterozygous SNP loci were detected from 'Cara Cara' and 'Washington' EST pool.

[Growth inhibition and mechanism of cetyltrimethyl ammonium chloride on Chlorella vulgaris].

Growth inhibition of cetyltrimethyl ammonium chloride (CTAC), a cationic surfactants, on Chlorella vulgaris was investigated at batch culture in laboratory. Furthermore, the corresponding mechanisms were studied by the determination of absorption capacity, Zeta potential, activity of acid phosphatase and ultrastructure of algae. Results show that the growth inhibition by CATC is enhanced with its concentration increasing from 0.1 mg/L to 1 mg/L, and 96 h-EC50 of CTAC is 0.18 mg/L. In the presence of 0.3 mg/L CTAC in 8 d, the inhibition efficiency of biomass reaches 70.7%. Meanwhile, the absorption of nitrogen and iron is inhibited 83.9% and 86.2% respectively with Zeta potential of algae cell increasing from -12.5 mV to -6.7 mV. Furthermore, the relative activity of acid phosphatase declines to 23.1% at the same time. Plasmolysis, distortion of pyrenoid and swelling of lysosome is observed in the cell. Above phenomena indicates that CTAC increases the Zeta potential of algae cell and thus inhibites the absorption of nitrogen and iron. In addition, CTAC may affect the metabolism of phosphorus and change the ultrastructure of algae cell.

Fruit coloration difference between Fengwan, a late-maturing mutant and its original cultivar Fengjie72-1 of navel orange (Citrus sinensis Osbeck).

Fruit color is one of the most important external quality traits. Mutants with different color are useful for the study of regulating mechanism of coloration progress. A novel mutant, Fengwan, derived from Fengjie72-1 navel orange (Citrus sinensis L. Osbeck), has the distinctive characteristic of the coloration delay of 30 d or so, with the change in total soluble solid (TSS) and the ratio of TSS/acidity. In order to understand the mechanism underlying the difference of coloration between the mutant and the parental variety, the chlorophyll and carotenoid contents in the peel of two cultivars at different maturation stages were analyzed. The expression of genes responsible for some carotenoid biosynthetic enzymes (phytoene synthase, phytoene desaturase, zeta-carotene desaturase, beta-lycopene cyclase, beta-carotene hydroxylase) and chlorophyllase using the RT-PCR technique were also studied. The distinct decrease of chlorophyll in the peel of Fengwan navel orange occurred from early November to late November, about three weeks later than that of its original cultivar. Obvious accumulation of carotenoid in the peel of the mutant began on Dec.12, while that of the original cultivar began on Nov. 3. Analysis of independent-samples t-test showed that the chlorophyll content of the peel of Fengwan navel orange from October to November was significantly higher, and the carotenoid content from December to January was significantly lower than that in the peel of the parental line, Fengjie72-1 navel orange. The expression of chlorophyllase gene in the peel of Fengwan navel orange reached a maximum in January and kept at a slightly lower level from October to December than that of Fengjie 72-1 orange, while the time of gene expression about some carotenoid biosynthetic enzymes reaching a maximum in the peel of the mutant were one month later than that of the original cultivar.

Lycopene-epsilon-cyclase pre-mRNA is alternatively spliced in Cara Cara navel orange (Citrus sinensis Osbeck).

Lycopene-epsilon-cyclase is one of the key enzymes related to alpha-carotene metabolism in plants. A full-length cDNA of 1300 bp encoding lycopene-epsilon-cyclase (Lyce) was generated from Cara Cara navel orange, a unique navel orange containing both lycopene and beta-carotene in its pulp, with little or no alpha-carotene. The gene had a 14 bp nucleotides deletion and caused a terminal mutation. DNA sequence corresponding to the deletion region revealed that two repeats of 6 bp (AGGTGT) were flanking the region in both Cara Cara and its original variety, Washington navel oranges, but a 2 bp (AT) insertion was only found in Cara Cara which explain the alternative splicing character of the gene.