Experimental Study on Shear Behavior of Reinforced-Concrete Members Fully Wrapped with Large Rupture-Strain FRP Composites

This paper presents an experimental study on the shear behavior of RC members fully wrapped with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites, which are a new type of FRP material characterized by a much larger rupture strain (LRS) compared with conventional FRPs (i.e., made of carbon, glass, and aramid fibers). A total of 10 PET fully-wrapped RC beams, which were designed to fail in shear and with different shear-span to effective-depth ratios, transverse reinforcement ratios and shear strengthening ratios, were tested under 4-point bending loads. The overall load-deflection responses and the shear deformation of the beams as well as the strain development of the transverse steel reinforcement and the FRP jackets were carefully observed. Based upon the extensive strain measurements, the shear contributions by concrete, FRPs, and transverse reinforcement are differentiated. It was found that the use of PET FRP composites as the jacket material of RC members could shift the mode of shear failure from a brittle one to an ideal ductile one whereas the ultimate state of the members is no longer caused by FRP fracture. In order to efficiently predict the shear strength of RC members wrapped by LRS FRPs, the effective strain in LRS FRPs and the degradation of concrete at the peak member shear strength should be appropriately considered

Patterning of Virus-Infected Glycine max Seed Coat Is Associated with Suppression of Endogenous Silencing of Chalcone Synthase Genes

Most commercial Glycine max (soybean) varieties have yellow seeds because of loss of pigmentation in the seed coat. It has been suggested that inhibition of seed coat pigmentation in yellow G. max may be controlled by homology-dependent silencing of chalcone synthase (CHS) genes. Our analysis of CHS mRNA and short-interfering RNAs provide clear evidence that the inhibition of seed coat pigmentation in yellow G. max results from posttranscriptional rather than transcriptional silencing of the CHS genes. Furthermore, we show that mottling symptoms present on the seed coat of G. max plants infected with some viruses can be caused by suppression of CHS posttranscriptional gene silencing (PTGS) by a viral silencing suppressor protein. These results demonstrate that naturally occurring PTGS plays a key role in expression of a distinctive phenotype in plants and present a simple clear example of the elucidation of the molecular mechanism for viral symptom induction

Suppression of RNA-dependent RNA polymerase 6 in tomatoes allows potato spindle tuber viroid to invade basal part but not apical part including pluripotent stem cells of shoot apical meristem

RNA-dependent RNA polymerase 6 (RDR6) is one of the key factors in plant defense responses and suppresses virus or viroid invasion into shoot apical meristem (SAM) inNicotiana benthamiana. To evaluate the role ofSolanum lycopersicum(Sl) RDR6 upon viroid infection, SlRDR6-suppressed (SlRDR6i) 'Moneymaker' tomatoes were generated by RNA interference and inoculated with intermediate or lethal strain of potato spindle tuber viroid (PSTVd). Suppression of SlRDR6 did not change disease symptoms of both PSTVd strains in 'Moneymaker' tomatoes. Analysis of PSTVd distribution in shoot apices byin situhybridization revealed that both PSTVd strains similarly invade the basal part but not apical part including pluripotent stem cells of SAM in SlRDR6i plants at a low rate unlike a previous report inN.benthamiana. In addition, unexpectedly, amount of PSTVd accumulation was apparently lower in SlRDR6i plants than in control tomatoes transformed with empty cassette in early infection especially in the lethal strain. Meanwhile, SlRDR6 suppression did not affect the seed transmission rates of PSTVd. These results indicate that RDR6 generally suppresses PSTVd invasion into SAM in plants, while suppression of RDR6 does not necessarily elevate amount of PSTVd accumulation. Additionally, our results suggest that host factors such as RDR1 other than RDR6 may also be involved in the protection of SAM including pluripotent stem cells from PSTVd invasion and effective RNA silencing causing the decrease of PSTVd accumulation during early infection in tomato plants