Onset of sheath extension and duration of lamina extension are major determinants of the response of maize lamina length to plant density

Background and Aims Plants regulate their architecture strongly in response to density, and there is evidence that this involves changes in the duration of leaf extension. This questions the approximation, central in crop models, that development follows a fixed thermal time schedule. The aim of this research is to investigate, using maize as a model, how the kinetics of extension of grass leaves change with density, and to propose directions for inclusion of this regulation in plant models. • Methods Periodic dissection of plants allowed the establishment of the kinetics of lamina and sheath extension for two contrasting sowing densities. The temperature of the growing zone was measured with thermocouples. Two-phase (exponential plus linear) models were fitted to the data, allowing analysis of the timing of the phase changes of extension, and the extension rate of sheaths and blades during both phases. • Key Results The duration of lamina extension dictated the variation in lamina length between treatments. The lower phytomers were longer at high density, with delayed onset of sheath extension allowing more time for the lamina to extend. In the upper phytomers—which were shorter at high density—the laminae had a lower relative extension rate (RER) in the exponential phase and delayed onset of linear extension, and less time available for extension since early sheath extension was not delayed. • Conclusions The relative timing of the onset of fast extension of the lamina with that of sheath development is the main determinant of the response of lamina length to density. Evidence is presented that the contrasting behaviour of lower and upper phytomers is related to differing regulation of sheath ontogeny before and after panicle initiation. A conceptual model is proposed to explain how the observed asynchrony between lamina and sheath development is regulated.

Solution structure and novel insights into the determinants of the receptor specificity of human relaxin-3

Relaxin- 3 is the most recently discovered member of the relaxin family of peptide hormones. In contrast to relaxin- 1 and - 2, whose main functions are associated with pregnancy, relaxin- 3 is involved in neuropeptide signaling in the brain. Here, we report the solution structure of human relaxin- 3, the first structure of a relaxin family member to be solved by NMR methods. Overall, relaxin- 3 adopts an insulin- like fold, but the structure differs crucially from the crystal structure of human relaxin- 2 near the B- chain terminus. In particular, the B- chain C terminus folds back, allowing Trp(B27) to interact with the hydrophobic-core. This interaction partly blocks the conserved RXXXRXXI motif identified as a determinant for the interaction with the relaxin receptor LGR7 and may account for the lower affinity of relaxin- 3 relative to relaxin for this receptor. This structural feature is likely important for the activation of its endogenous receptor, GPCR135.

Spatial topography of the neurofibrillary tangles in cortical and subcortical regions in progressive supranuclear palsy

Objective: To study the topography of neurofibrillary tangles (NFT) in cortical and subcortical areas in progressive supranuclear palsy (PSP). Methods: Pattern analysis was carried out on tau-positive NFT in eight PSP cases. Results: Of the areas studied, NFT were randomly distributed in 68%, regularly distributed in 3%, and clustered in 29%. A regular distribution of clusters was more frequent in cortical than subcortical areas. Conclusion: NFT topography in subcortical areas was similar to inclusions in the synucleinopathy multiple system atrophy (MSA) but in cortical areas was comparable to other tauopathies. © 2006 Elsevier Ltd. All rights reserved.

The effects of vigabatrin of the visual system

This thesis considers the visual electrophysiological effects of vigabatrin (an anti-epileptic drug, which acts by increasing the levels of the inhibitory neurotransmitter GABA on the retina of the eye compared to the concentric visual field defects which have been found associated with the drug. Flash and pattern ERG's, EOG's multifocal ERG's (VERIS), flash and pattern VEP's and visual fields were tested. Although VEP's have been shown not to be affected by vigabatrin, these were recorded to complete the testing. Initially, of the eight vigabatrin patients with known visual field defects, 7 showed abnormally delayed 30Hz flicker a-wave latencies, 5 abnormally delayed 30Hz b-wave latencies and 6 abnormally low 30Hz amplitudes. Also 7 showed an abnormally prolonged latency of oscillatory potential 1 (OP1). The two patients taking vigabatrin at the time of testing showed low EOG Arden index values. The VERIS results correlated well with the severity of the visual field defects. Following this finding, eleven healthy subjects received vigabatrin over a 10-day period. No changes were seen in the visual fields, however, the photopic ERG b-wave latency significantly increased (although not to abnormal values). A matched pairs study with eleven vigabatrin, patients and eleven epileptic patients, who had never taken vigabatrin supported the findings of abnormal 30Hz flicker b-wave and OP latencies associated with vigabatrin, again with the VERIS results correlating to the severity of the visual field defect. The abnormal 30Hz flicker and VERIS responses indicate involvement of the cone photoreceptors and the OP's show an effect on the amacrine cells. The ERG increase in the photopic b-wave latency also suggests involvement of the bipolar cells, however, this effect and the reversible effect on the Arden index after cessation of the drug may be unrelated to the visual field defect. To conclude this thesis, a field specific VEP stimulus was developed to assess the retinal function in the peripheral field of paediatric patients. It comprises of a dartboard stimulus with a central 0-5 degree black and white chequered stimulus, a blank 5-30 degree annulus and a 30-60 degree peripheral chequered stimulus. When optimised on four vigabatrin patients it was found that no peripheral response can be evoked with a field loss exceeding 30-35 degrees. Co-operation was found to be successful in children as young as four years old.