Temperature dependence of the membrane resistance in Characeae cells

Changes in the electrical resistance of internodal cells of Nitellopsis obtusa (Desv. in Lois) J. Gr. and Lychnothamnus barbatus (Meyen) Leonh., produced by short-lasting temperature changes (3-min intervals) in the range of 4⇌48°C were measured. In the whole temperature range examined the electrical resistance of the cell membranes underwent from 5 to 9 distinct changes; the overall changes were approximately hyperbolic, while in certain narrow temperature ranges they were non-monotonic, and in others linear. Arrhenius plots of these dependencies provide data which suggest a specific, stepwise character of changes in the permeability to ions, produced by temperature alterations and probably connected with corresponding modifications of cell membrane fluidity. This seems to support the view that the cell membranes of the examined plant species may exist in different, discrete, physiological states characteristic of certain temperature ranges.     

Analysis of distributions of mutants in clones of plant-cell aggregates

Summary The organization of plant cells (or any other genetic elements, such as organelles) into aggregates modifies the expected distribution of mutants in clones. The reason for the modification, and its effect on the use of the Luria-Delbrück fluctuation test, are discussed. The Luria-Delbriick test was used to show that the trait for chlorate resistance in cultured rose-cell aggregates appeared spontaneously and in the absence of chlorate ion.     

Calcium and pancreatic β-cell function 7. Evidence for cyclic AMP-induced translocation of intracellular calcium

The effect of cyclic AMP on calcium movements in the pancreatic β-cell was evaluated using an experimental approach based on in situ labelling of intracellular organelles of ob/ob-mouse islets with ⁴⁵Ca. Whereas the glucose-stimulated ⁴⁵Ca incorporation by mitochondria and secretory granules was increased under a condition known to reduce cyclic AMP (starvation), raised levels of this nucleotide (addition of 3-isobutyl-1-methylxanthine or N⁶,O^2′-dibutyryl adenosine 3′,5′-cyclic monophosphate) reduced the mitochondrial accumulation of ⁴⁵Ca. Conditions with increased cyclic AMP were associated with a stimulated efflux of ⁴⁵Ca from the secretory granules but not from the mitochondria. The microsomal fraction differed from both the mitochondrial and secretory granule fractions by accumulating more ⁴⁵Ca after the addition of 3-isobutyl-1-methylxanthine. The results suggest that cyclic AMP potentiates glucose-stimulated insulin release by increasing cytoplasmic Ca²⁺ at the expense of the calcium taken up by the organelles of the pancreatic β-cells.     

Gut Microbiome Fermentation Determines the Efficacy of Exercise for Diabetes Prevention

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Nuclear envelope‐associated dynein drives prophase centrosome separation and enables Eg5‐independent bipolar spindle formation

The microtubule motor protein kinesin‐5 (Eg5) provides an outward force on centrosomes, which drives bipolar spindle assembly. Acute inhibition of Eg5 blocks centrosome separation and causes mitotic arrest in human cells, making Eg5 an attractive target for anti‐cancer therapy. Using in vitro directed evolution, we show that human cells treated with Eg5 inhibitors can rapidly acquire the ability to divide in the complete absence of Eg5 activity. We have used these Eg5‐independent cells to study alternative mechanisms of centrosome separation. We uncovered a pathway involving nuclear envelope (NE)‐associated dynein that drives centrosome separation in prophase. This NE‐dynein pathway is essential for bipolar spindle assembly in the absence of Eg5, but also functions in the presence of full Eg5 activity, where it pulls individual centrosomes along the NE and acts in concert with Eg5‐dependent outward pushing forces to coordinate prophase centrosome separation. Together, these results reveal how the forces are produced to drive prophase centrosome separation and identify a novel mechanism of resistance to kinesin‐5 inhibitors.     

A physiological analogy of the niche for projecting the potential distribution of plants

Aim  To develop a physiologically based model of the plant niche for use in species distribution modelling. Location  Europe. Methods  We link the Thornley transport resistance (TTR) model with functions which describe how the TTR’s model parameters are influenced by abiotic environmental factors. The TTR model considers how carbon and nutrient uptake, and the allocation of these assimilates, influence growth. We use indirect statistical methods to estimate the model parameters from a high resolution data set on tree distribution for 22 European tree species. Results  We infer, from distribution data and abiotic forcing data, the physiological niche dimensions of 22 European tree species. We found that the model fits were reasonable (AUC: 0.79–0.964). The projected distributions were characterized by a false positive rate of 0.19 and a false negative rate 0.12. The fitted models are used to generate projections of the environmental factors that limit the range boundaries of the study species. Main conclusions  We show that physiological models can be used to derive physiological niche dimensions from species distribution data. Future work should focus on including prior information on physiological rates into the parameter estimation process. Application of the TTR model to species distribution modelling suggests new avenues for establishing explicit links between distribution and physiology, and for generating hypotheses about how ecophysiological processes influence the distribution of plants.     

PCR rescue and analysis of transgene sequences directly from crude extracts of transgenic embryos and plants

We report the application of a PCR-based method in conjunction with automated sequencing for the reliable detection and verification of transgenes in crude extracts of leaf and callus tissue from different plant species. Transformed tissue can be identified easily at any stage of the regeneration process, whether it is via embryogenesis or organogenesis. This allows researchers to focus their attention and resources on truly transformed tissues and avoid unwittingly culturing untransformed tissues. This protocol can also be used to rescue relatively large PCR products as well as duplexing the detection of transgenes. Direct sequencing of the PCR products allows confirmation of the integrity of the transgenein planta.     

SGT1b is required for HopZ3-mediated suppression of the epiphytic growth of Pseudomonas syringae on N. benthamiana

Type III secreted effectors shape the potential of bacterial pathogens to cause disease on plants. Some effectors affect pathogen growth only in specific niches. For example, HopZ3 causes reduced epiphytic growth of Pseudomonas syringae strain B728a on Nicotiana benthamiana. This raises the question of whether genes important for effector-triggered disease resistance are needed for responses to effectors whose major effect is in the epiphytic niche. We report that SGT1b, a protein known to be important for defense activation, is essential for HopZ3-mediated suppression of PsyB728a epiphytic growth. SGT1b is required for HopZ3- and AvrB3-induced cell death in N. benthamiana plants that express the Pto resistance gene from tomato. We suggest that HopZ3 activates R gene mediated responses in N. benthamiana.