The rice disease resistance gene,Xa21, encodes a receptor kinase-like protein consisting of leucine-rich repeats in the putative extracellular domain and a serine/threonine kinase in the putative intracellular domain. The putative XA21 kinase domain was expressed as maltose-binding and glutathione S-transferase fusion proteins inEscherichia coli. The fusion proteins are capable of autophosphorylation. Phosphoamino acid analysis of the glutathioneS-transferase fusion protein indicates that only serine and threonine residues are phosphorylated. The relative phosphorylation rate of the XA21 kinase against increasing enzyme concentrations follows a first-order rather than second-order kinetics, indicating an intramolecular phosphorylation mechanism. Moreover, the active XA21 kinase cannot phosphorylate a kinase-deficient mutant of XA21 kinase. The enzymatic activity of the XA21 kinase in a buffer containing Mn²⁺ is at least 15 times higher than that with Mg²⁺. The K _m andV _max of XA21 kinase for ATP are 0.3 μm and 8.4 nmol/mg/min, respectively. Tryptic phosphopeptide mapping reveals that multiple sites on the XA21 kinase are phosphorylated. Finally, our data suggest that the region of XA21 kinase corresponding to the RD kinase activation domain is not phosphorylated, revealing a distinct mode of action compared with the tomato Pto serine/threonine kinase conferring disease resistance.

The electron gas in LaAlO ₃ /SrTiO ₃ heterostructures typically exhibits positive photoconductivity (PPC). Here, we report negative photoconductivity (NPC) induced by visible light in LaAlO ₃ /SrTiO ₃ heterostructures grown in low oxygen pressure (~10 ⁻⁶ Torr). In contrast to the persistent PPC effect in LaAlO ₃ /SrTiO ₃ heterostructures, the NPC effect is transient and wavelength independent. The origin of the NPC effect can be mainly attributed to enhanced electron scattering from oxygen-vacancy-related electron traps, confirmed by wavelength-dependent photoconductance and light-assisted Hall measurements. Our results provide a deeper insight into the complex interaction between light and oxygen vacancy in oxide electron gas.

Gas sensing performance characterization systems are essential for the research and development of gas sensing materials and devices. Although existing systems are almost completely automatically operated, the accuracies of gas concentration control and of pressure control and the ability to simultaneously detect different sensor signals still require improvement. In this study, a high-precision gas sensing material characterization system is developed based on vacuum technology, with the objective of enabling the precise and simultaneous measurement of electrical responses. Because of the implementation of vacuum technology, the gas concentration control accuracy is improved more than 1600 times, whereas the pressure of the test ambient condition can be precisely adjusted between vacuum and 1.2 bar. The vacuum-assisted gas-exchanging mechanism also enables the sensor response time to be determined more accurately. The system is capable of performing sensitivity, selectivity, and stability tests and can control the ambient relative humidity in a precise manner. More importantly, the levels of performance of three different optical signal measurement set-ups were investigated and compared in terms of detection range, linearity, noise, and response time, based on which of their scopes of application were proposed. Finally, single-period and cyclical tests were performed to examine the ability of the system to detect optical and electrical responses simultaneously, both at a single wavelength and in a spectral region.