The cell layers of the Arabidopsis primary root are arranged in a simple radial pattern. The outermost layer is the lateral root cap and lies outside the epidermis that surrounds the ground tissue. The files of epidermal and lateral root cap cells converge on a ring of initials (lateral root cap/epidermis initial) from which the epidermal and lateral root cap tissues of the seedling are derived, once root growth is initiated after germination. Each initial gives rise to a clone of epidermal cells and a clone of lateral root cap cells. These initial divisions in the epidermal/lateral root cap initial are defective in tornado1 (trn1) and trn2 plants indicating a requirement for TRN1 and TRN2 for initial cell function. Furthermore, lateral root cap cells develop in the epidermal position in trn1 and trn2 roots indicating that TRN1 and TRN2 are required for the maintenance of the radial pattern of cell specification in the root. The death of these ectopic lateral root cap cells in the elongation zone (where lateral root cap cells normally die) results in the development of gaps in the epidermis. These observations indicate that TRN1 and TRN2 are required to maintain the distinction between the lateral root cap and epidermis and suggest that lateral root cap fate is the default state. It also suggests that TRN1 and TRN2 repress lateral root cap fate in cells in the epidermal location. Furthermore, the position-dependent pattern of root hair and non-root hair cell differentiation in the epidermis is defective in trn1 and trn2 mutants. Together these results indicate that TRN1 and TRN2 are required for the maintenance of both the radial pattern of tissue differentiation in the root and for the subsequent circumferential pattern within the epidermis.
Low cycle fatigue (LCF) and creep fatigue interaction (CFI) behaviour of P92 steel welded joint were investigated experimentally and numerically. Strain‐controlled LCF tests at different strain amplitudes and CFI tests at different peak strain holding time were conducted. Evolutions of cyclic stress response, mean stress, and creep strain during cycling were described, in which the influence of strain amplitude and holding time were investigated. A specific heat treatment process was proposed to get the homogenous simulated material of fine grain region and coarse grain region in the heat affected zone. Material parameters of parent material, fine grain heat affected zone, coarse grain heat affected zone, and weld metal in the unified viscoplasticity model were then determined and validated. To predict the LCF and CFI behaviour of welded joint, 3‐dimensional unified viscoplasticity model with a modified isotropic variable was compiled into ABAQUS UMAT. The comparison between the predicted and experimental result under LCF and CFI loadings showed that the simulation results were reasonable and agreed with the experimental data well.
The map positions of a set of eight T-DNA insertions in the Arabidopsis genome have been determined by using closely linked visible markers. The insertions are dispersed over four of the five chromosomes. Each T-DNA insert contains one or more of the chimeric marker genes neomycin phosphotransferase (neo), hygromycin phosphotransferase (hpt), phosphinothricin acetyltransferase (bar), beta-glucuronidase (gusA) and indole-3-acetamide hydrolase (iaaH). The neo, hpt and bar marker genes are dominant in a selective germination assay or when used as DNA markers in a polymerase chain reaction. These dominant markers will allow recombinants to be discerned in a germinating F2 population, one generation earlier than with a conventional recessive marker. The transgenic marker lines will speed up and simplify the isolation of recombinants in small genetic intervals, a rate-limiting step in positional cloning strategies. The transgenic lines containing the hpt marker will also be of interest for the isolation of deletion mutants at the T-DNA integration sites.
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