Identification of putative viroplasms within banana cells infected by banana streak MY virus.

The badnavirus replication cycle is poorly understood and most knowledge is based on extrapolations from model viruses such as Cauliflower mosaic virus (CaMV). However, in contrast to CaMV, badnaviruses are thought not to produce viroplasms and therefore it has been a mystery as to where virion assembly occurs. In this study, ultrathin sections of a banana leaf infected with a badnavirus, banana streak MY virus (BSMYV), were examined by transmission electron microscopy. Electron-dense inclusion bodies (EDIBs) were sporadically distributed in parenchymatous tissues of the leaf, most commonly in the palisade and spongy mesophyll cells. These EDIBs had a characteristic structure, comprising an electron-dense core, a single, encircling lacuna and an outer ring of electron-dense material. However, much less frequently, EDIBs with two or three lacunae were observed. In the outer ring, densely packed virions were visible with a shape and size consistent with that expected for badnaviruses. Immunogold labelling was done with primary antibodies that detected the N-terminus of the capsid protein and strong labelling of the outer ring but not the central core or lacuna was observed. It is concluded that the EDIBs that were observed are equivalent in function to the viroplasms of CaMV, although obviously different in composition as there is not a paralogue of the transactivation/viroplasm protein in the badnavirus genome. It is postulated that production of a viroplasm could be a conserved characteristic of all members of the Caulimoviridae.

Cell wall proteome analysis of banana fruit softening using iTRAQ technology.

Softening is important for quality formation in some climacteric fruits. The molecular mechanism underlying fruit softening is, however, not well understood. In this study, we performed a comparative cell wall proteomics analysis on pre-climacteric (P1) and post-climacteric (P2) banana fruit, corresponding to fruit at the mature green stage and softening ripening stage, respectively, using isobaric tags for relative and absolute quantitation (iTRAQ) technology. A total of 5230 proteins were identified in both sample groups, of which 928 were predicted to be secreted proteins. Of the secreted proteins, 162 were differentially expressed in P2 versus P1. The majority of these proteins had catalytic activity, binding activity, electron carrier activity and antioxidant activity. Compared with P1, P2 had 105 and 57 up- and down-regulated proteins, respectively. GO and KEGG-pathway analysis of these differentially expressed secreted proteins revealed that most were implicated in cell wall metabolism, stress and defense response, signaling, and protein metabolism and modification. Quantitative RT-PCR further validated some key differentially expressed secreted proteins associated with cell wall metabolism, stress and defense response, signaling and protein destination. Our results represent the first cell wall proteome of banana fruit and comprehensive proteomic study of banana fruit softening. SIGNIFICANCE: Softening, which is the consequence of cell wall and turgor modification, is one of the most important factors determining banana fruit quality. The molecular mechanism regulating fruit softening in harvested banana is not currently well understood. In this study, we performed a comparative cell wall proteome analysis for pre-climacteric (P1) and post-climacteric (P2) banana fruit, corresponding to the mature green stage and softening ripening stage, respectively, using iTRAQ technology. We found 162 differentially expressed secreted proteins that were mainly implicated in cell wall metabolism, stress response and defense, signaling, and protein metabolism and modification. We have presented the first cell wall proteome of banana fruit and conducted a comprehensive proteomic study of banana fruit softening that will help to develop strategies to improve the sensorial quality and reduce post-harvest fruit losses.

Endophytic interaction of Bacillus sp. in micropropagated banana plantlets.

The banana tree is associated with different species of endophytic bacteria that can stimulate plant growth. However, further studies are needed to better understand the relationships between this group of bacteria and the host plant. The objective of this study was to investigate the localization of the EB-40 (Bacillus sp.) through anatomical and ultrastructural analyses in micropropagated banana plantlets. The results demonstrated the effective colonization of the EB-40 isolate in the intercellular and intracellular spaces, as well as in the rhizosphere region. The wall of endophytic bacteria contains calcium and nitrogen. The EB-40 isolate was also observed to associate with the plasma membrane and cell wall. These results further our understanding of the mechanisms involved in the colonization of plant cells by endophytic bacteria in micropropagated banana plantlets.

A stress associated NAC transcription factor MpSNAC67 from banana (Musa x paradisiaca) is involved in regulation of chlorophyll catabolic pathway.

Process of senescence includes multiple steps involving break-down of chlorophyll to degrade photosynthetic machinery. In this study, we showed that a stress-associated NAC transcription factor MpSNAC67 regulates senescence by promoting chlorophyll-catabolic genes. MpSNAC67 encodes a transcriptional activator and its promoter activity is restricted to vascular tissue of banana. Expression of MpSNAC67 showed positive responses to multiple abiotic stress conditions suggesting that MpSNAC67 is a stress associated NAC transcription factor. Transgenic banana lines overexpressing MpSNAC67 showed highly senesced phenotype including yellowing and de-greening of leaves similar to etiolated leaves. Transgenic leaves possessed low chlorophyll content and failed to retain normal chloroplast morphology including loss of granum thylakoid, non-uniform chloroplast membrane and increased number as well as size of plastoglobulins. In a gel shift assay MpSNAC67 could retard the mobility of chlorophyll catabolic genes such as PAO-like (Pheophorbide-a-oxygenase), HCAR-like (hydroxymethyl chlorophyll-a-reductase), NYC/NOL-like (Chlorophyll-b-reductase) as well as ORS1-like (a SenNAC). Expression of these genes were highly elevated in transgenic lines which indicate that MpSNAC67 is a positive regulator of senescence in banana and exercise its effect by regulating the expression of chlorophyll catabolic genes and ORS1.

Utilization of two agrowastes for adsorption and removal of methylene blue: kinetics and isotherm studies.

Fresh water streams contaminated with synthetic dye-containing effluents pose a threat to aquatic and human life either by preventing aquatic photosynthesis or by entering into the food chain. Adsorptive removal of such dyes with potent biosorbents is an important technique to reduce bioaccumulation and biomagnifications of the dyes in human life. We report use of betel nut (BN) husk and banana peel (BP), two most abundant ligno-cellulosic wastes, as efficient adsorbents for the removal of the basic dye methylene blue (MB). The adsorption by BN and BP was consistently high over wide ranges of pH and temperature, suggesting their dye removal potential in diverse conditions. Physico-chemical studies, e.g. scanning electron microscopy and Fourier transform-infrared spectroscopy studies, revealed changes in surface topology and functional moieties of BN and BP post adsorption, implying dye interaction with the biomass surface. The dye adsorption in both cases followed pseudo-second-order kinetics. While adsorption of MB by BN was better fitted with the Temkin isotherm model, adsorption with BP followed both Langmuir and Freundlich isotherm models. Our studies concluded that both adsorbents efficiently remove MB from its aqueous solution with BP proved to be marginally superior to BN.

Tissue cell assisted fabrication of tubular catalytic platinum microengines.

We report a facile platform for mass production of robust self-propelled tubular microengines. Tissue cells extracted from fruits of banana and apple, Musa acuminata and Malus domestica, are used as the support on which a thin platinum film is deposited by means of physical vapor deposition. Upon sonication of the cells/Pt-coated substrate in water, microscrolls of highly uniform sizes are spontaneously formed. Tubular microengines fabricated with the fruit cell assisted method exhibit a fast motion of ∼100 bodylengths per s (∼1 mm s(-1)). An extremely simple and affordable platform for mass production of the micromotors is crucial for the envisioned swarms of thousands and millions of autonomous micromotors performing biomedical and environmental remediation tasks.

External mouthpart morphology in the Tenuipalpidae (Tetranychoidea): Raoiella a case study.

The use of low-temperature scanning electron microscopy (LTSEM) to study external mouthpart morphology in the Tenuipalpidae, in particular the genus Raoiella, has brought some aspects of the mechanics of feeding in this group into question. In addition, an LTSEM study on the specialized feeding behaviour of Raoiella indica Hirst (Tetranychoidea: Tenuipalpidae) revealed host plant use in this species could be affected by stomatal complex morphology.

Ultrastructural changes and the distribution of arabinogalactan proteins during somatic embryogenesis of banana (Musa spp. AAA cv. 'Yueyoukang 1').

A better understanding of somatic embryogenesis in banana (Musa spp.) may provide a practical way to improve regeneration of banana plants. In this study, we applied scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to visualize the ultrastructural changes during somatic embryogenesis of banana (Musa AAA cv. 'Yueyoukang 1'). We also used histological and immunohistochemical techniques with 16 monoclonal antibodies to study the spatial distribution and cellular/subcellular localization of different arabinogalactan protein (AGP) components of the cell wall during somatic embryogenesis. Histological study with periodic acid-Schiff staining documented diverse embryogenic stages from embryogenic cells (ECs) to the late embryos. SEM revealed a mesh-like structure on the surface of proembryos which represented an early structural marker of somatic embryogenesis. TEM showed that ECs were rich in juvenile mitochondria, endoplasmic reticulum and Golgi stacks. Cells in proembryos and early globular embryos resembled ECs, but they were more vacuolated, showed more regular nuclei and slightly more developed organelles. Immunocytochemical study revealed that the signal of most AGP epitopes was stronger in starch-rich cells when compared with typical ECs. The main AGP component in the extracellular matrix surface network of banana proembryos was the MAC204 epitope. Later, AGP immunolabelling patterns varied with the developmental stages of the embryos. These results about developmental regulation of AGP epitopes along with developmental changes in the ultrastructure of cells are providing new insights into the somatic embryogenesis of banana.

Structure, morphology and thermal characteristics of banana nano fibers obtained by steam explosion.

In this work, cellulose nanofibers were extracted from banana fibers via a steam explosion technique. The chemical composition, morphology and thermal properties of the nanofibers were characterized to investigate their suitability for use in bio-based composite material applications. Chemical characterization of the banana fibers confirmed that the cellulose content was increased from 64% to 95% due to the application of alkali and acid treatments. Assessment of fiber chemical composition before and after chemical treatment showed evidence for the removal of non-cellulosic constituents such as hemicelluloses and lignin that occurred during steam explosion, bleaching and acid treatments. Surface morphological studies using SEM and AFM revealed that there was a reduction in fiber diameter during steam explosion followed by acid treatments. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. TGA and DSC results showed that the developed nanofibers exhibit enhanced thermal properties over the untreated fibers.

Protection of ultrastructure in chilling-stressed banana leaves by salicylic acid.

OBJECTIVE: Chilling tolerance of salicylic acid (SA) in banana seedlings (Musa acuminata cv., Williams 8818) was investigated by changes in ultrastructure in this study. METHODS: Light and electron microscope observation. RESULTS: Pretreatment with 0.5 mmol/L SA under normal growth conditions (30/22 degrees C) by foliar spray and root irrigation resulted in many changes in ultrastructure of banana cells, such as cells separation from palisade parenchymas, the appearance of crevices in cell walls, the swelling of grana and stromal thylakoids, and a reduction in the number of starch granules. These results implied that SA treatment at 30/22 degrees C could be a type of stress. During 3 d of exposure to 7 degrees C chilling stress under low light, however, cell ultrastructure of SA-pretreated banana seedlings showed less deterioration than those of control seedlings (distilled water-pretreated). CONCLUSION: SA could provide some protection for cell structure of chilling-stressed banana seedling.

Microstructural changes of osmotically dehydrated tissues of apple, banana, and potato.

Scanning electron microscopy examination was conducted on osmotically dehydrated tissues of apple, banana, and potato. High-quality stereo images and surface parameters were recorded from two sets of samples: fresh samples and osmotically dehydrated samples for each material studied. Scanning electron microscopy micrographs revealed that osmotic treatment had a significant effect on the structural properties (cell wall, middle lamella) for the different plant materials. The intercellular spaces were larger for materials treated at higher temperature (55 degrees C) and higher concentration of sucrose solution (70%). The cell wall and middle lamella observed in Golden Delicious apple appeared larger than those in Cox apple, banana, and potato, and probably contributed to the observed descending order of water loss and solid gain as: Golden Delicious > Cox > potato > banana.

[Ultrastructural observation of banana shoot-tip cell during cryopreservation by vitrification].

Excised shoot-tips produced from banana plants belonging to cv. Guangdong No.1 (ABB group) were cryopreserved successfully by vitrification using the PVS2 solution. Ultrastructural of banana shoot-tips cells was also observed by using electron micryoscopy (TEM). The results showed that the plasmolysis became more and more severe during the course of dehydration. Cells were mainly damaged during the freezing and thawing process. Most cell protoplasts condensed, and cell organelles, cell membranes and nucleus envelopes were lethally injured after cryopreservation. But only a few cells located in the meristematic dome arose reversible process although their structures were varied. They could survive and regenerate plantlets after freezing conservation.

Ultrastructural changes associated with cryopreservation of banana ( Musa spp.) highly proliferating meristems.

Cryopreservation has been shown to improve the frequency of virus elimination - specifically cucumber mosaic virus and banana streak virus - from banana ( Musa spp.) plants. To understand the mode of action of cryopreservation for the eradication of viral particles, we examined the ultrastructure of meristem tips at each step of the cryopreservation process. Excised meristematic clumps produced from infected banana plants belonging to cv. Williams (AAA, Cavendish subgroup) were cryopreserved through vitrification using the PVS-2 solution. We demonstrated that the cryopreservation method used only allowed survival of small areas of cells in the meristematic dome and at the base of the primordia. Cellular and subcellular changes occurring during the cryopreservation process are discussed.