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Lateral ion transport in conjugated polymer films is studied using a special experimental geometry in which the top surface of the film is covered by a transparent ion barrier. Because of the barrier, when the oxidation level of the polymer is switched electrochemically, charge-compensating ions can only enter and leave the polymer from the edges. Since conjugated polymers are electrochromic, the color of the film changes during switching, and this can be monitored to provide information on the oxidation level of different parts of the film. Since the oxidation level cannot change until the cations arrive, the color also directly maps the positions of the cations. This geometry was employed to study cation transport in polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS). Upon reduction, the ions travel in a front from the edges to the center of the film. During the first-ever reduction, this cation front stays sharp, but in subsequent reduction scans the front moves 20-30 times faster and broadens as it moves. The higher the applied voltage, the faster the front moves, with a linear dependence. The velocity of the front also strongly depends on the initial oxidation level of the polymer. During oxidation, on the other hand, the entire film gradually darkens, with no front and no dependence of the switching speed on the applied potential.

The optical-mechanical-electrochemical coupling in polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), is studied during electrochemical switching. Cations enter this material during reduction, leading to an increase in volume. A special experimental geometry is used in which the top surface of the PPy film is covered by a transparent ion barrier, which constrains the charge-compensating cations to enter the film only at the edges. The cation concentration determines the volume of the polymer and is also directly related to the oxidation level of the polymer, which in turn determines its color. During electrochemical reduction, the edges of the film lighten, and this light color travels as a front to the center of the film. At the same time, the height of the film increases when and where the color lightens, and the increase in height is directly proportional to the change in color intensity. The height and the intensity attain their maximum values as the front passes and do not increase further thereafter, indicating that the ion concentration in the fully reduced state has a maximum value that is not exceeded. The color and volume changes are associated with only the first pair of peaks in the cyclic voltammogram, which represent only a fraction of the consumed charge in a typical electrochemical scan.

A finite element model for charge transport in conjugated polymers is developed based on transport equations for ionic and electronic charge coupled with the Poisson equation. The model behavior is fully explored, and its complexity is gradually increased to realize a full model that treats non-Fickian diffusion through nonconstant coefficients and that includes ion transport in the electrolyte. The simulation results are compared qualitatively with the experimental results for an ion-barrier-covered PPy(DBS) film during electrochemical reduction, and the model is found to successfully account for the dominant behaviors, including the emergence of a front. One of the key findings of the simulations is that migration must be taken into account to correctly describe ion ingress: none of the various simulations in which ion transport was only by diffusion predicted the experimental results. Another is that the front velocity is proportional to the applied voltage, as found experimentally, and that the cation front can move into the polymer with a velocity v ∼ √t even when the ions move by migration alone.

Lycopene content is an important factor for determining watermelon fruit quality. However, the low DNA polymorphism among cultivated watermelon (Citrullus lanatus) has hindered the ability to establish high quality genetic maps and study the quantitative trait loci (QTL) controlling the lycopene content trait. In this study, we successfully constructed a genetic map of watermelon to determine lycopene content and other horticultural fruit traits using a F 2 population developed from a cross between the two lines of watermelon LSW-177 and Cream of Saskatchewan. The genetic map contained 16 linkage groups covering a total length of 2,039.5 cM, which included 37 SSRs (Simple Sequence Repeat) and 107 CAPSs (Cleaved Amplified Polymorphic Sequences), with all of the CAPS markers developed from high-throughput re-sequencing of data from this study. Three CAPS markers (WII04E07-33,WII04E07-37,WII04E07-40) caused the F 2 population to perfectly co-segregate for each F 2 population plants. We also obtained 12 QTLs for all of the traits measured. Only one QTL (LCYB4.1) was detected with a high value of trait variation (83.50 %) that related to lycopene content and mapped on Chromosome 4 between CAPS markers WII04E07-33 and WII04E07-40, which could nearly account for all of the differences in lycopene content between the two parental strains. In this study, we highlighted 2,458 CAPS loci that were suitable for primer design with a polymorphism of 48.9 %, which is approximately a 12-fold increase from previous studies. The present map and QTLs will facilitate future studies on determining lycopene content related genes and cloning watermelon genes, while also providing for useful markers for breeding for lycopene content.

Generation of single-stranded DNA (ssDNA) is required for the template strand formation during DNA replication. Replication Protein A (RPA) is an ssDNA-binding protein essential for protecting ssDNA at replication forks in eukaryotic cells. While significant progress has been made in characterizing the role of the RPA-ssDNA complex, how RPA is loaded at replication forks remains poorly explored. Here, we show that the protein regulator of Ty1 transposition 105 (Rtt105) binds RPA and helps load it at replication forks. Cells lacking Rtt105 exhibit a dramatic reduction in RPA loading at replication forks, compromised DNA synthesis under replication stress, and increased genome instability. Mechanistically, we show that Rtt105 mediates the RPA-importin interaction and also promotes RPA binding to ssDNA directly, but is not present in the final RPA-ssDNA complex. Single-molecule studies reveal that Rtt105 affects the binding mode of RPA to ssDNA These results support a model in which Rtt105 functions as an RPA chaperone that escorts RPA to the nucleus and facilitates its loading onto ssDNA at replication forks.

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