Gravity-induced absorbance changes in Phycomyces: a novel method for detecting primary responses of gravitropism

 The negative gravitropism of the sporangiophores of Phycomyces blakesleeanus Burgeff is elicited by different sensory inputs, which include flexure of the growing zone, buoyance of lipid globules and sedimentation of paracrystalline proteins, so-called octahedral crystals (C. Schimek et al., 1999a, Planta 210: 132–142). Gravity-induced absorbance changes (GIACs), which are associated with primary events of gravity sensing, were detected in the growing zones of sporangiophores. After placing sporangiophores horizontally, GIACs were detected after a latency of about 5 min, i.e. 15–25 min prior to gravitropic bending. The spectroscopic properties of the GIACs indicate that gravitropic stimulation could imply the reduction of cytochromes. The GIACs were spectrally distinct from light-induced absorbance changes (LIACs), showing that the primary responses of the light and gravity transduction chains are different. A dual stimulation with gravity and light generated GIAC-LIACs which were distinct from the absorbance changes occurring after the single stimuli and which indicate that light and gravity interact early in the respective transduction chains. Received: 2 September 1999 / Accepted: 9 November 1999     

Computer simulation of organogenesis: An approach to the analysis of shape changes in epithelial organs

Embryonic development of epithelial organ primordia often involves changes in several parameters, such as cell height, cell width, cell volume, amount of extracellular space, and cell number. Since these changes often occur simultaneously, it becomes difficult to “separate out” the role that each plays in the developmental process. A computer program has been written that allows the shape of epithelial organs to be reproduced based upon measurements of the primordium. A developmental sequence can be simulated by changing the dimensions of the primordium based upon either measurements of the developmental stages or theoretical projections of changes. The primordium is divided into blocks representing groups of cells, based upon characteristics of the different cell groups. The program allows differences in cell height and circular and spiral curvatures of the primordium to be simulated. Analysis of the optic primordium using this method has allowed recognition of several regional changes during optic cup formation. These are sequential constriction of cell apices at the margin of the optic cup, expansion of the apical surface toward the center of the retinal disc, and spreading of the future pigmented layer. Simulation of other organs permits regions of morphogenetic activity to be identified.     

Measurements and Modeling of Carbon and Nitrogen Cycling in Agroecosystems of Southern Wisconsin: Potential for SOC Sequestration during the Next 50 Years

Landmanagement practices such as no-tillage agriculture and tallgrass prairie restoration have been proposed as a possible means to sequester atmospheric carbon, helping to refurbish soil fertility and replenish organic matter lost as a result of previous agricultural management practices. However, the relationship between land-use changes and ecosystem structure and functioning is not yet understood. We studied soil and vegetation properties over a 4-year period (1995–98), and assembled measurements of microbial biomass, soil organic carbon (SOC) and nitrogen (N), N-mineralization, soil surface carbon dioxide (CO₂) flux, and leached C and N in managed (maize; Zea mays L.) and natural (prairie) ecosystems near the University of Wisconsin Agricultural Research Station at Arlington. Field data show that different management practices (tillage and fertilization) and ecosystem type (prairie vs maize) have a profound influence on biogeochemistry and water budgets between sites. These measurements were used in conjunction with a dynamic terrestrial ecosystem model, called IBIS (the Integrated Biosphere Simulator), to examine the long-term effects of land-use changes on biogeochemical cycling. Field data and modeling suggest that agricultural land management near Arlington between 1860 and 1950 caused SOC to be depleted by as much as 63% (native SOC approximately 25.1 kg C m⁻²). Reductions in N-mineralization and microbial biomass were also observed. Although IBIS simulations depict SOC recovery in no-tillage maize since the 1950s and also in the Arlington prairie since its restoration was initiated in 1976, field data suggest otherwise for the prairie. This restoration appears to have done little to increase SOC over the past 24 years. Measurements show that this prairie contained between 28% and 42% less SOC (in the top 1 m) than the no-tillage maize plots and 40%–47% less than simulated potential SOC for the site in 1999. Because IBIS simulates competition between C3 and C4 grass species, we hypothesized that current restored prairies, which include many forbs not characterized by the model, could be less capable of sequestering C than agricultural land planted entirely in monocultural grass in this region. Model output and field measurements show a potential 0.4 kg C m⁻² y⁻¹ difference in prairie net primary production (NPP). This study indicates that high-productivity C4 grasslands (NPP = 0.63 kg C m⁻² y⁻¹) and high-yield maize agroecosystems (10 Mg ha⁻¹) have the potential to sequester C at a rate of 74.5 g C m⁻² y⁻¹ and 86.3 g C m⁻² y⁻¹, respectively, during the next 50 years across southern Wisconsin. Received 28 December 1999; accepted 11 December 2000.     

Changing behavior of surface immunoglobulin on mouse B lymphocytes during immune development: I. LPS-induced changes in the lateral mobility of B lymphocyte surface immunoglobulins on two populations which express different surface immunoglobulin phenotypes

The redistribution of surface membrane immunoglobulin molecules (sIg) was studied in two functionally distinct populations of mouse splenic B lymphocytes, namely, those bearing membrane IgM(IgG^?) and those bearing IgG. Brief exposure to mitogenic doses of bacterial lipopolysaccharide (LPS) produced direct but differential effects on the subsequent ability of specific antibodies to induce this redistribution on each cell type. Studied as a function of temperature, antibody-induced redistribution of sIgM on cells previously exposed to LPS was observed to occur at temperatures lower than the temperatures required for similar sIgM redistribution on lymphocytes not exposed to LPS. In contrast, mitogen-treated sIgG⁺ cells demonstrated an opposite and long-lasting effect (at least 40 hr), requiring higher temperatures to allow sIgG movement comparable to that seen on untreated sIgG-bearing lymphocytes. Thus, we conclude that LPS interacts with both IgM⁺(IgG^?) and IgG⁺ lymphocytes, but that such interactions produced different membrane effects on each B-cell subset. This membrane change can therefore be useful as a quasi-functional differentiation marker. Furthermore, differences in sensitivity to cellular activation by LPS seen between sIgM-bearing (sIgG^?) and sIgG-bearing B cells may be a reflection of such direct, although different, membrane effects.