Transport and metabolism of xylem cytokinins during lateral bud release in decapitated chickpea (Cicer arietinum) seedlings

Although cytokinins (CKs) are widely thought to have a role in promoting shoot branching, there is little data supporting a causative or even a correlative relationship between endogenous CKs and timing of bud outgrowth. We previously showed that lateral bud CK content increased rapidly following shoot decapitation. However, it is not known whether roots are the source of this CK. Here, we have used shoot decapitation to instantaneously induce lateral bud release in chickpea seedlings. This treatment rapidly alters rate and direction of solvent and solute (including CK) trafficking, which may be a passive signalling mechanism central to initiation of lateral bud release. To evaluate changes in xylem transport, intact and decapitated plants were infiltrated with [H-3]zeatin riboside ([H-3]ZR), a water-soluble blue dye or [H-3]H2O by injection into the hypocotyl. All three tracers were recovered in virtually all parts of the shoot within I h of injection. In intact plants, solute accumulation in the lateral bud at node 1 was significantly less than in the adjacent stipule and nodal tissue. In decapitated plants, accumulation of [H-3]ZR and of blue dye in the same bud position was increased 3- to 10-fold relative to intact plants, whereas content of [H-3]H2O was greatly reduced indicating an increased solvent throughput. The stipule and cut stem, predicted to have high evapotranspiration rates, also showed increased solute content accompanied by enhanced depletion of [H-3]H2O. To assess whether metabolism modifies quantities of active CK reaching the buds, we followed the metabolic fate of [H-3]ZR injected at physiological concentrations. Within 1 h, 80-95% of [H-3]ZR was converted to other active CKs (mainly zeatin riboside-5'phosphate (ZRMP) and zeatin (Z)), other significant, but unconfirmed metabolites some of which may be active (O-acetylZR, O-acetylZRMP and a compound correlated with sites of high CK-concentrations) and inactive catabolites (adenosine, adenine, 5'AMP and water). Despite rapid metabolic degradation, the total active label, which was indicative of CK concentration in buds, increased rapidly following decapitation. It can be inferred that xylem sap CKs represent one source of active CKs appearing in lateral buds after shoot decapitation.

Auditor conservatism and voluntary disclosure: Evidence from the Year 2000 systems issue

This study further examines the phenomenon of conservative auditor behaviour by considering the level of voluntary disclosure of Year 2000 remediation information in company annual reports. Previous studies have provided evidence of conservative auditor behaviour by examining the link between Big 6 auditor choice and accruals (Francis and Krishnan 1999; Becker et al., 1998; Defond and Subramanyam 1998). Protecting their reputation capital increases Big 6 auditor incentives to act conservatively to avoid litigation risk. We propose and find that Big 6 auditor clients disclose more Year 2000 remediation information than non–Big 6 auditor clients.

Phenomenological turbulence and innovation in knowledge systems

Most considerations of knowledge management focus on corporations and, until recently, considered knowledge to be objective, stable, and asocial. In this paper we wish to move the focus away from corporations, and examine knowledge and national innovation systems. We argue that the knowledge systems in which innovation takes place are phenomenologically turbulent, a state not made explicit in the change, innovation and socio-economic studies of knowledge literature, and that this omission poses a serious limitation to the successful analysis of innovation and knowledge systems. To address this lack we suggest that three evolutionary processes must be considered: self-referencing, self-transformation and self-organisation. These processes, acting simultaneously, enable system cohesion, radical innovation and adaptation. More specifically, we argue that in knowledge-based economies the high levels of phenomenological turbulence drives these processes. Finally, we spell out important policy principles that derive from these processes.

Caveolin interacts with the angiotensin II type 1 receptor during exocytic transport but not at the plasma membrane

The mechanisms involved in angiotensin II type 1 receptor (AT(1)-R) trafficking and membrane localization are largely unknown. In this study, we examined the role of caveolin in these processes. Electron microscopy of plasma membrane sheets shows that the AT(1)-R is not concentrated in caveolae but is clustered in cholesterol-independent microdomains; upon activation, it partially redistributes to lipid rafts. Despite the lack of AT(1)-R in caveolae, AT(1)-R. caveolin complexes are readily detectable in cells co-expressing both proteins. This interaction requires an intact caveolin scaffolding domain because mutant caveolins that lack a functional caveolin scaffolding domain do not interact with AT(1)-R. Expression of an N-terminally truncated caveolin-3, CavDGV, that localizes to lipid bodies, or a point mutant, Cav3-P104L, that accumulates in the Golgi mislocalizes AT(1)-R to lipid bodies and Golgi, respectively. Mislocalization results in aberrant maturation and surface expression of AT(1)-R, effects that are not reversed by supplementing cells with cholesterol. Similarly mutation of aromatic residues in the caveolin-binding site abrogates AT(1)-R cell surface expression. In cells lacking caveolin-1 or caveolin-3, AT(1)-R does not traffic to the cell surface unless caveolin is ectopically expressed. This observation is recapitulated in caveolin-1 null mice that have a 55% reduction in renal AT(1)-R levels compared with controls. Taken together our results indicate that a direct interaction with caveolin is required to traffic the AT(1)-R through the exocytic pathway, but this does not result in AT(1)-R sequestration in caveolae. Caveolin therefore acts as a molecular chaperone rather than a plasma membrane scaffold for AT(1)-R.

The spectrum of minimal defining sets of some Steiner systems

For a design D, define spec(D) = {\M\ \ M is a minimal defining set of D} to be the spectrum of minimal defining sets of D. In this note we give bounds on the size of an element in spec(D) when D is a Steiner system. We also show that the spectrum of minimal defining sets of the Steiner triple system given by the points and lines of PG(3,2) equals {16,17,18,19,20,21,22}, and point out some open questions concerning the Steiner triple systems associated with PG(n, 2) in general. (C) 2002 Elsevier Science B.V. All rights reserved.

Synaptic vesicle transport and synaptic membrane transporter sites in excitatory amino acid nerve terminals in Alzheimer disease

The apparent L-[H-3]glutamate uptake rate (v') was measured in synaptic vesicles isolated from cerebral cortex synaptosomes prepared from autopsied Alzheimer and non-Alzheimer dementia cases, and age-matched controls. The initial synaptosome preparations exhibited similar densities of D-[H-3]aspartate membrane binding sites (B-MAX values) in the three groups. In control brain the temporal cortex D-[H-3]aspartate B-MAX was 132% of that in motor cortex, parallel with the L- [H-3]glutamate v' values (temporal = 139% of motor; NS). Unlike D- [H-3]aspartate B-MAX values, L- [H-3]glutamate v' values were markedly and selectively lower in Alzheimer brain preparations than in controls, particularly in temporal cortex. The difference could not be attributed to differential effects of autopsy interval or age at death. Non-Alzheimer dementia cases resembled controls. The selective loss of vesicular glutamate transport is consistent with a dysfunction in the recycling of transmitter glutamate.

Skolem-type difference sets for cycle systems

Cyclic m-cycle systems of order v are constructed for all m greater than or equal to 3, and all v = 1(mod 2m). This result has been settled previously by several authors. In this paper, we provide a different solution, as a consequence of a more general result, which handles all cases using similar methods and which also allows us to prove necessary and sufficient conditions for the existence of a cyclic m-cycle system of K-v - F for all m greater than or equal to 3, and all v = 2(mod 2m).

Oxide ionic conductivity and microstructures of Sm- or La-doped CeO2-based systems

The concept of crystallographic index termed the effective index is suggested and applied to the design of ceria (CeO2)-based electrolytes to maximize oxide ionic conductivity. The suggested index considers the fluorite structure, and combines the expected oxygen vacancy level with the ionic radius mismatch between host and dopant cations. Using this approach, oxide ionic conductivity of Sm- or La-doped CeO2-based system has been optimized and tested under operating conditions of a solid oxide fuel cell. In the observation of microstructure in atomic scale, both Sm-doped CeO2 and La-doped CeO2 electrolytes had large micro-domains over 10 nm in the lattice. On the other hand, Sm or La and alkaline earth co-doped CeO2-based electrolytes with high effective index had small micro-domains around 1-3 nm in the microstructure. The large micro-domain would prevent oxide ion from passing through the lattice. Therefore, it is concluded that the improvement of ionic conductivity is reflected in changes of microstructure in atomic scale. (C) 2002 Elsevier Science B.V. All rights reserved.

Intracellular sorting and transport of proteins

The secretory and endocytic pathways of eukaryotic organelles consist of multiple compartments, each with a unique set of proteins and lipids. Specific transport mechanisms are required to direct molecules to defined locations and to ensure that the identity, and hence function, of individual compartments are maintained. The localisation of proteins to specific membranes is complex and involves multiple interactions. The recent dramatic advances in understanding the molecular mechanisms of membrane transport has been due to the application of a multi-disciplinary approach, intergrating membrane biology, genetics, imaging, protein and lipid biochemistry and structural biology. The aim of this review is to summarise the general principles of protein sorting in the secretory and endocytic pathways and to highlight the dynamic nature of these processes. The molecular mechanisms involved in this transport along the secretory and endocytic pathways are discussed along with the signals responsible for targeting proteins to different intracellular locations. (C) 2003 Elsevier Science Ltd. All rights reserved.

Low input tillage/cropping systems for limited resource areas

Agriculture in limited resource areas is characterized by small farms which an generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes: in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be beneficial. Agriculture in limited resource areas must produce the food and fiber needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and he acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system. (C) 2001 Elsevier Science B.V. All rights reserved.

Integrable impurity spin ladder systems

Two different types of integrable impurities in a spin ladder system are proposed. The impurities are introduced in such a way that the integrability of the models is not violated. The models are solved exactly with the Bethe ansatz equations as well as the energy eigenvalues obtained. We show for both models that a phase transition between gapped and gapless spin excitations occurs at a critical value of the rung coupling J. In addition, the dependence of the impurities on this phase transition is determined explicitly. In one of the models the spin gap decreases by increasing the impurity strength A. Moreover, for a fixed A, a reduction in the spin gap by increasing the impurity concentration is also observed.

Vps20p and Vta1p interact with Vps4p and function in multivesicular body sorting and endosomal transport in Saccharomyces cerevisiae

Vps4p (End13p) is an AAA-family ATPase that functions in membrane transport through endosomes, sorting of soluble vacuolar proteins to the vacuole, and multivesicular body (MVB) sorting of membrane proteins to the vacuole lumen. In a yeast two-hybrid screen with Vps4p as bait we isolated VPS20 (YMR077c) and the novel open reading frame YLA181c, for which the name VTA1 has recently been assigned (Saccharomyces Genome Database). Vps4p directly binds Vps20p and Vta1p in vitro and binding is not dependent on ATP-conversely, Vps4p binding to Vps20p is partially sensitive to ATP hydrolysis. Both ATP binding [Vps4p-(K179A)] and ATP hydrolysis [Vps4p-(E233Q)] mutant proteins exhibit enhanced binding to Vps20p and Vta1p in vitro. The Vps4p-Vps20p interaction involves the coiled-coil domain of each protein, whereas the Vps4p-Vta1p interaction involves the (non-coiled-coil) C-terminus of each protein. Deletion of either VPS20 (vps20Delta) or VTA1 (vta1Delta) leads to similar class E Vps(-) phenotypes resembling those of vps4Delta, including carboxypeptidase Y (CPY) secretion, a block in ubiquitin-dependent MVB sorting, and a delay in both post-internalisation endocytic transport and biosynthetic transport to the vacuole. The vacuole resident membrane protein Sna3p (whose MVB sorting is ubiquitin-independent) does not appear to exit the class E compartment or reach the vacuole in cells lacking Vps20p, Vta1p or Vps4p, in contrast to other proteins whose delivery to the vacuole is only delayed. We propose that Vps20p and Vta1p regulate Vps4p function in vivo.