The HKT1 Na+ transporter protects plant fertility by decreasing Na+ content in stamen filaments.

Salinity stress can greatly reduce seed production because plants are especially sensitive to salt during their reproductive stage. Here, we show that the sodium ion transporter AtHKT1;1 is specifically expressed around the phloem and xylem of the stamen in Arabidopsis thaliana to prevent a marked decrease in seed production caused by salt stress. The stamens of AtHKT1;1 mutant under salt stress overaccumulate Na+, limiting their elongation and resulting in male sterility. Specifically restricting AtHKT1;1 expression to the phloem leads to a 1.5-fold increase in the seed yield upon sodium ion stress. Expanding phloem expression of AtHKT1;1 throughout the entire plant is a promising strategy for increasing plant productivity under salinity stress.

Outer layer scintillating fiber for low-energy ß-ray detection.

Standard plastic scintillating fiber cannot detect low-energy ß-rays as the cladding prevents them from reaching the fiber core. We developed an outer-layer scintillating (OLS) fiber with a plastic scintillator on the outermost layer for low-energy ß-ray detection. The concept of fiber construction is presented. The fundamental optical properties of the OLS fiber, such as the emission spectrum, attenuation length, and scintillation decay time, were evaluated. Here, Ni-63 with a maximum energy of 67.0 keV was used as a low-energy ß-emitting nuclide. Simulation studies on the interaction between low-energy electrons emitted from Ni-63 and a single fiber were performed prior to actual measurements. The data showed that Ni-63 can be measured using silicon photomultiplier photosensors in a coincidence mode. The OLS fiber was effective for low-energy ß-ray detection.

Length-force characteristics of in vivo human muscle reflected by supersonic shear imaging.

Recently, an ultrasound-based elastography technique has been used to measure stiffness (shear modulus) of an active human muscle along the axis of contraction. Using this technique, we explored 1) whether muscle shear modulus, like muscle force, is length dependent; and 2) whether the length dependence of muscle shear modulus is consistent between electrically elicited and voluntary contractions. From nine healthy participants, ankle joint torque and shear modulus of the tibialis anterior muscle were measured at five different ankle joint angles during tetanic contractions and during maximal voluntary contractions. Fascicle length, pennation angle, and tendon moment arm length of the tetanized tibialis anterior calculated from ultrasound images were used to reveal the length-dependent changes in muscle force and shear modulus. Over the range of joint angles examined, both force and shear modulus of the tetanized muscle increased with increasing fascicle length. Regression analysis of normalized data revealed a significant linear relationship between force and shear modulus (R(2) = 0.52, n = 45, P < 0.001). Although the length dependence of shear modulus was consistent, irrespective of contraction mode, the slope of length-shear modulus relationship was steeper during maximal voluntary contractions than during tetanic contractions. These results provide novel evidence that length-force relationship, one of the most fundamental characteristics of muscle, can be inferred from in vivo imaging of shear modulus in the tibialis anterior muscle. Furthermore, the estimation of length-force relationship may be applicable to voluntary contractions in which neural and mechanical interactions of multiple muscles are involved.