Microfluidic tools for developmental studies of small model organisms –nematodes,fruit flies,and zebrafish

Studying the genetics of development with small model organisms such as the zebrafish (Danio Rerio), the fruit fly (Drosophila melanogaster), and the soil-dwelling nematode (Caenorhabditis elegans), provide unique opportunities for understanding related processes and diseases in humans. These model organisms also have potential for use in drug discovery and toxicity-screening applications. There have been sweeping developments in microfabrication and microfluidic technologies for manipulating and imaging small objects, including small model organisms, which allow high-throughput quantitative biological studies. Here, we review recent progress in microfluidic tools able to manipulate small organisms and project future directions and applications of these techniques and technologies.     

Positive relationship between fruit removal by animals and seedling recruitment in a tropical forest

Fleshy-fruited plants rely on animal frugivores to disperse their seeds, and seed removal by frugivores may leave an imprint on seedling recruitment. However, to what extent plant–frugivore interactions are related to seedling recruitment has rarely been quantified at the community level, especially in species-rich tropical forests. In this study, we tested the effect of different plant traits on fruit removal by frugivores and tested the relative importance of fruit removal, plant traits and abiotic factors for seedling recruitment. We quantified plant–frugivore interactions of 22 fleshy-fruited plant species consumed by 56 diurnal frugivore species, and counted the number of seedlings that emerged along an elevational gradient in the Colombian Andes. We measured a set of plant traits (i.e., crop size; fruit size; seed load and mass; fruit nutritional contents), estimated the density of adult plants and recorded relevant abiotic factors (light, temperature and humidity). We found that fruit removal by frugivores was positively associated with crop size, but negatively associated with fruit length and unrelated to seed load and fruit nutritional content. Seedling densities were positively related to the density of adult plants, seed mass and fruit removal by animals. We found no relationship between abiotic factors and seedling recruitment. Our results indicate that fruit abundance and morphology are important determinants of fruit removal and that fruit removal is positively associated with seedling recruitment accounting for effects of species abundance and plant traits. We conclude that plant traits shape fruit removal and seedling recruitment at the community level, while these two crucial processes of forest regeneration are directly linked by seed dispersal of animals.     

Biological control of fruit-rot of jackfruit by rhizobacteria and food grade lactic acid bacteria

Fungal species causing fruit rot of jackfruit have been isolated from seven different locations of Birbhum and Burdwan districts of West Bengal, India. Each isolate showed more or less similar microscopic characteristics. A representative strain VBAM1, isolated from a severely infected jackfruit was identified as Rhizopus stolonifer by 28S rDNA sequence homology. Increased reducing sugar content in pectin broth indicates pectinase production by the pathogen. The pathogen was not inhibited by ⩾500 μg/ml of Mancozeb and Bavistin. Copper oxychloride, Blytone 50% a.i. showed antifungal activity at comparatively lower concentration (200 μg/ml). Two rhizospheric bacterial strains, Burkholderia cenocepacia VBC7 and Pseudomonas poae VBK1, and three different strains of Lactococcus lactis subsp. lactis can produce significant zones of inhibition against the pathogen in dual culture overlay plates. They induced mycelia breakage of pathogen as evidenced from scanning electron micrographs. When applied to whole plants, the strains reduced or prevented disease and when applied postharvest to Rhizopus inoculated fruit delayed and/reduced disease incidence. These agents were also re-isolated from the applied surfaces and survived for long time when mixed with suitable carrier base indicating stability in a formulation over time.     

Pectic substances,pectic enzymes and haze formation in fruit juices

The pectic substances, located primarily in the middle lamella between cells in higher plant tissues, are complex polysaccharides. They include the negatively charged rhamnogalacturonans, and the neutral arabinogalactans I and II and l-arabinans. These polysaccharides add viscosity to juices but may also form hazes and precipitates and retard maximum recovery of juices from the fruit. The rhamnogalacturonans are degraded by the enzymes pectin methylesterase and polygalacturonase normally present in plant tissues and by these enzymes and pectate lyase in microbially derived commercial pectic enzymes added during processing. The presence of a?abinofuranosidase, which degrades l-arabinans, in commercial pectic enzyme preparations, can cause haze formation in juices such as apple and pear.     

Interactions between terrestrial mammals and the fruits of two neotropical rainforest tree species

Mammalian frugivory is a distinctive biotic interaction of tropical forests; however, most efforts in the Neotropics have focused on cases of animals foraging in the forest canopy, in particular primates and bats. In contrast much less is known about this interaction when it involves fruits deposited on the forest floor and terrestrial mammals. We conducted a camera-trapping survey to analyze the characteristics of the mammalian ensembles visiting fruits of Licania platypus and Pouteria sapota deposited on the forest floor in a well preserved tropical rainforest of Mexico. Both tree species produce large fruits but contrast in their population densities and fruit chemical composition. In particular, we expected that more species of terrestrial mammals would consume P. sapota fruits due to its higher pulp:seed ratio, lower availability and greater carbohydrate content. We monitored fruits at the base of 13 trees (P. sapota, n = 4 and L. platypus, n = 9) using camera-traps. We recorded 13 mammal species from which we had evidence of 8 consuming or removing fruits. These eight species accounted for 70% of the species of mammalian frugivores active in the forest floor of our study area. The ensemble of frugivores associated with L. platypus (6 spp.) was a subset of that associated with P. sapota (8 spp). Large body-sized species such as Tapirus bairdii, Pecari tajacu and Cuniculus paca were the mammals more frequently interacting with fruits of the focal species. Our results further our understanding of the characteristics of the interaction between terrestrial mammalian frugivores and large-sized fruits, helping to gain a more balanced view of its importance across different tropical forests and providing a baseline to compare against defaunated forests.     

Ethylene production, shelf-life and evidence of RFLP polymorphisms linked to ethylene genes in melon (Cucumis melo L.)

Sixty three cultigens from eight market types of the melon (Cucumis melo L. subsp. melo) groups Cantaloupensis and Inodorus were evaluated for ethylene production rate, shelf-life (postharvest decay), and RFLP polymorphisms. The ethylene production rates of melon fruits at maturity and (after) postharvest decay were measured on individual genotypes. The ethylene production rates of individual genotypes ranged from undetectable to 103 nl/g per h. The mean ethylene production rates of the eight market types, ranked from highest to lowest, were Eastern U.S. type, Charentais, Western U.S. type, Long Shelf-Life cantaloupes (LSL), Galia, Ananas, Honeydew, and Casaba. Ethylene production and postharvest decay rating were positively significantly correlated (r ²=0.87, P=0.05). Orange-fleshed melon fruits produced significantly (P=0.05) more ethylene than did green- or white-fleshed types. Melon fruits with a netted rind had significantly (P=0.05 for orange-flesh fruits and 0.01 for green- or white-flesh fruits) higher ethylene production than did smooth-type fruits. Using probes made from cDNAs encoding ACC oxidase (MEL1) or ACC synthase (MEACS1) genes, RFLPs were detected melon cultigens of the eight marker types showing varying ethylene production rates and different flesh colors. Low ethylene production and green- and white-flesh color were associated (r ²=0.91; P=0.05) with the presence of a putative RFLP-MEL1 allele A ₀ (15-kb), whereas high ethylene production and orange-flesh color were associated with allele B ₀ (8.5-kb) in the homozygous condition, after probing MEL1 with EcoRV-digested genomic DNA. Also, after probing MEACS1 with NdeI-digested genomic DNA, RFLP polymorphism revealed five fragments denoted as A, B, C, D and E, with molecular sizes of 5.2-, 4.2-, 3.8-, 3.0- and 1.0-kb, respectively. A two-fragment pattern, AB, and a three-fragment pattern, ACE, the two predominant RFLP patterns, were also associated with low and high ethylene production, respectively. The ACE fragment pattern was also associated with orange-flesh melons. Scoring of both probes allowed for the unique classification of most melon market types consistent with ethylene production and the postharvest decay phenotypes. Therefore, these RFLPs might have utility in marker-assisted selection for the development of melons with enhanced postharvest keeping ability. Received: 26 March 1998 / Accepted: 12 January 2000