A Homoeotic Mutant of Arabidopsis thaliana with Leafy Cotyledons

Cotyledons are specialized leaves produced during plant embryogenesis. Cotyledons and leaves typically differ in morphology, ultrastructure, and patterns of gene expression. The leafy cotyledon (Iec) mutant of Arabidopsis thaliana fails to maintain this distinction between embryonic and vegetative patterns of plant development. Mutant embryos are phenotypically abnormal, occasionally viviparous, and intolerant of desiccation. Mutant cotyledons produce trichomes characteristic of leaves, lack embryo-specific protein bodies, and exhibit a vascular pattern intermediate between that of leaves and cotyledons. These results suggest that lec cotyledons are partially transformed into leaves and that the wild-type gene (LEC) functions to activate a wide range of embryo-specific pathways in higher plants.     

奶牛难产激发应激性急性肾上腺皮质功能不全——心衰、水电解质严重失调辩析

应激性急性肾上腺皮质功能不全症的病理机制十分复杂,目前人医的各类文献中大都以“垂体—肾上腺轴”功能不全、功能衰竭、或发生广泛性出血坏死性病演作解释。本病在奶牛分娩难产过程中并不少见,病牛的症状表现以心衰和失钠性低血症为主征。但在兽医临床上由于认识不足,曾有不少中外学者将奶牛产后卧地不起的各类疾病,含糊地统称为“母牛睡倒爬不起来综合征”;更由于救治不当,病牛常以淘汰或死亡告终。本文通过对一具体典型病例辨析,着重讨论了本病的基本病理反应和确立诊断依据,强调对本病救护施治时应遵循的基本原则,供同道们在分析和解决这一实际问题时参考。     

An optimal transition path for controlling greenhouse gases

Designing efficient policies to slow global warming requires an approach that combines economic tools with relations from the natural sciences. The dynamic integrated climate-economy (DICE) model presented here, an intertemporal general-equilibrium model of economic growth and climate change, can be used to investigate alternative approaches to slowing climate change. Evaluation of five policies suggests that a modest carbon tax would be an efficient approach to slow global warming, whereas rigid emissions- or climate-stabilization approaches would impose significant net economic costs.     

Comparison of German and Swiss Rainfall Simulators - Utility,Labour Demands and Costs

The utility, vehicle required, the time needed for assembly and relocation and the costs associated with six different rainfall simulators were studied. The results can be summarized as follows:

• 1 The simulator designed by Kainz & Eicher (1990) is the least expensive to operate. This simulator also has excellent experimental versatility. Its only restriction is a short slope length.
• 2 The rainfall simulator of Karl & Toldrian (1973) is also inexpensive to operate, but because of disadvantages such as low falling height, wind susceptibility, and the need for more workers than other simulators, it should be used mainly where other simulators are not practical (forests, steep slopes, or long slopes).
• 3 The rainfall simulator of Richter et al. (1988) has limited mobility in the field and is highly susceptible to wind drift. Moreover, its narrow plots do not cover a representative unit of a cultivated field.
• 4 The modified Swanson-type simulator (Auerswald, (1986) is suitable for large plots if a sufficient water supply is available.
• 5 The simulator of Kromer & Vöhringer (1988) has the highest fixed costs, but labour is used efficiently.
• 6 The simulator of Schmidt (1983) can only be considered for stationary use because of its long assembly time. Other disadvantages are narrow plot size and high wind susceptibility.

Depending on the selection of the simulator, total costs of between 400 DM and 2000 DM per plot should be expected even with high use rates.     

Managing Insect Resistance to Bacillus thuringiensis Toxins

Bacillus thuringiensis (B.t.) delta-endotoxins provide an alternative to chemical insecticides for controlling many species of pest insects. Recent biotechnological developments offer the promise of even greater use of B.t. toxins in genetically transformed pest-resistant crops. However, the discovery that insects can adapt to these toxins raises concerns about the long-term usefulness of B.t. toxins. Several methods for managing the development of resistance to B.t. toxins have been suggested, but none of these approaches offer clear advantages in all situations.     

NMR diffraction and spatial statistics of stationary systems

Nuclear magnetic resonance (NMR) spatial imaging data may be acquired, processed, and interpreted in ways that provide information directly analogous to diffraction experiments, with length scales determined by gradient strengths rather than radiation wavelengths. This approach, originally considered by Mansfield nearly two decades ago, provides access to autocorrelations of sample density that statistically characterize small-scale density variations. These NMR "Patterson functions" can be acquired orders of magnitude more rapidly than comparably resolved NMR images and are suitable for spatial characterization of small features in bulk samples, such as morphology in structural materials. Unlike hindered diffusion approaches, neither mobility, penetrants, nor transport time are required for examining granularity and porosity.