ore complete understanding of this process. 14192894 A fully unified vascular cambium with clear radial files of initials and derivatives appears between the fifth and seventh internode beneath the apex. Here GUS expression is more sharply delineated on the side of the phloem, with apparent channeling of auxin down through the AIC316 site differentiating xylem elements as seen in primary xylem. This is in keeping with microscale measurements of IAA concentration through the cambial zone that show a more gradual decline on the side of the developing xylem. It will be interesting to see whether phloem-derived cytokinins are involved in maintaining the shape of this basipetal stream of auxin, as might be suggested by the sharper phloem-side boundary. One final observation provides tantalizing evidence that the phloem may play a role in shaping the transition from primary to secondary growth: the region of the stem where this transition takes place in Populus coincides with the age at which leaves transition from being sinks to sources of photosynthate. Conclusions In summary, the multiple routes of PAT in Populus stems described here together with an increasing appreciation of the role of phloem transport and the potential for local sites of IAA biosynthesis suggest that the dynamics of auxin transport in woody stems are more complex than once thought. Although text book models of the transition from primary to secondary growth usually depict an abrupt shift 19380617 from separate vascular bundles to continuous rings of xylem and phloem, the unification of these 
bundles is quite gradual. More importantly, these bundles anastomose throughout the stem and contain strands of parenchyma that function in PAT for as long as the leaves to which they are connected remain alive. Ray cells in turn provide a symplasmic route of exchange between these strands of primary xylem parenchyma and the developing vascular cambium. Given the longevity of ray parenchyma and their capacity for relatively rapid radial transport, future research should focus on the potential of these cells to synthesize, metabolize and transport auxin as well as other key plant growth regulators. Hepatitis C virus infection causes chronic hepatitis, which can lead to liver cirrhosis and hepatocellular carcinoma. Approximately 170 million people are infected with HCV worldwide, making HCV infection a serious global health problem. HCV is an enveloped virus with a positive single-stranded RNA genome, and belongs to the Flaviviridae family. The HCV genome encodes a large polyprotein precursor of approximately 3000 amino acids, which is cleaved into 10 proteins in the following order: Core, envelope 1, E2, p7, non-structural 2, NS3, NS4A, NS4B, NS5A, and NS5B. Until last year, the combination of pegylated-interferon with ribavirin was the standard therapy, resulting in a sustained virologic response in about half of the patients receiving this treatment. Two inhibitors of HCV NS3-4A protease, telaprevir and boceprevir, were recently approved as the first directly acting antiviral reagents for the treatment of HCV genotype 1, and have been used in combination with PEG-IFN and RBV. The SVR rate in the treatment of HCV genotype 1 using the new triple therapy is expected to be more than 70%. However, several severe side effects have appeared, such as skin rash by telaprevir, ageusia by boceprevir, and advanced anemia by telaprevir/boceprevir. Furthermore, the rapid emergence of resistant viruses by treatment with t
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