NBS-LRR resistance gene homologues in rice

Research on Wear Mechanism of Surface Build-Up Welding Material of Brake Disc for Drilling Rig

In order to improve resisting performance of heat, wear and erosion as well as anti-thermal fatigue, surface build-up welding material of brake-disc for drilling rig with better performance is developed, and its wear mechanism is investigated based on friction and wear experiment at variable temperature. Morphology, constituents and phase structure of wear surface of brake disc are analyzed by employing SEM, EDAX and XRD when thermal equilibrium temperature is at 150°C and 300°C, and its tribological behaviour and wear mechanism of surface build-up welding materials are revealed. In initial stage of wear, friction temperature is lower and hard particles like AL2O3, SiO2, SiC, TiO in brake block plough the surface of brake-disc, oxide layer forms on friction surface with rise of friction temperature and its cracking and regenerating become a major way of wear, meanwhile hard grains in brake block slough off due to frequent ploughing and three-body abrasive wear occurs, and spalling of surface film is mainly caused by fatigue. In stage of high temperature wear, oxidization wear and plastic deformation of brake-disc increase greatly, brake-block starts to soften, severe adhesive wear occurs and spalling of surface film is mainly caused by adhesive tearing. Wear mechanism of brake-disc is comprehensive effects of abrasive, oxidizing and adhesive wear.

Microdissection and molecular manipulation of single chromosomes in woody fruit trees with small chromosomes using pomelo (Citrus grandis) as a model. II. Cloning of resistance gene analogs from single chromosomes

Amplification of resistance gene analogs (RGAs) is both a useful method for acquiring DNA markers closely linked to disease resistance (R) genes and a potential approach for the rapid cloning of R genes in plants. However, the screening of target sequences from among the numerous amplified RGAs can be very laborious. The amplification of RGAs from specific chromosomes could greatly reduce the number of RGAs to be screened and, consequently, speed up the identification of target RGAs. We have developed two methods for amplifying RGAs from single chromosomes. Method 1 uses products of Sau3A linker adaptor-mediated PCR (LAM-PCR) from a single chromosome as the templates for RGA amplification, while Method 2 directly uses a single chromosomal DNA molecule as the template. Using a pair of degenerate primers designed on the basis of the conserved nucleotide-binding-site motifs in many R genes, RGAs were successfully amplified from single chromosomes of pomelo using both these methods. Sequencing and cluster analysis of RGA clones obtained from single chromosomes revealed the number, type and organization of R-gene clusters on the chromosomes. We suggest that Method 1 is suitable for analyzing chromosomes that are unidentifiable under a microscope, while Method 2 is more appropriate when chromosomes can be clearly identified.