Does plasmolysis increase the drought tolerance of plant cells?

Summary Iljin's experiments withRhoeo discolor, cabbage and red beet which seemed to demonstrate increased drought resistance of plasmolysed tissue have been repeated, but his results could not be confirmed. The tissue plasmolysed in sucrose solutions, died either during stepwise plasmolysis and deplasmolysis or else later on, during exposure to unsaturated air within one or two days, even at the highest humidities. Iljin's error was apparently produced by a wrong interpretation of his tests of viability: the plasma of his dead cells did not disintegrate and retained anthocyanin by tonoplast plasmolysis.Plasmolysis proved harmful to all three objects investigated.In view of these results and earlier criticism of Iljin's analogous experiments on frost resistance by others, all experimental evidence produced in support of Iljin's mechanical theory of drought resistance should be reexamined.     

NAD hydrolysis: Chemical and enzymatic mechanisms

The pyridine nucleotide have important non-redox activities as cellular effectors and metabolic regulators [1–3]. The enzyme-catalyzed cleavage of the nicotinamide-ribosyl bond of NAD⁺ and the attendant delivery of the ADPRibosyl moiety to acceptors is central to these many diverse biological activities. Included are the medically important NAD-dependent toxins associated with cholera, diphtheria, pertussis, and related disease [4]; the reversible ADPRibosylation-mediated biological regulatory systems [5,6]; the synthesis of poly (ADPRibose) in response to DNA damage or cellular, division [7]; and the synthesis of cyclic ADPRibose as part of an independent, calcium-mediated regulatory system[8]. As will be presented in this chapter, all evidence points to both the chemical and enzyme-catalyzed cleavage of the nicotinamide-ribosyl bond being dissociative in character via an oxocarbenium intermediate.     

Diphtheria toxin. Site and configuration of ADP-ribosylation of diphthamide in elongation factor 2

Diphtheria toxin inactivates protein synthesis elongation factor 2 by catalyzing the ADP-ribosylation of a novel derivative of histidine, diphthamide, in the protein (Van Ness, B. G., Howard, J. B., and Bodley, J. W. (1980) J. Biol. Chem. 255, 10710-10716). In this report, we describe experiments involving nuclear Overhauser enhancement NMR spectroscopy which were undertaken to elucidate the site of ADP-ribosylation of diphthamide and the configuration of the glycosidic bond formed by the toxin. The essential result of these experiments is that, in ribosyl-diphthamide obtained by enzymatic digestion of ADP-ribosyl-elongation factor-2, the H-5 imidazole proton is near the R-4 proton of ribose. This result and others are consistent with the interpretation that diphtheria toxin covalently attaches ADP-ribose to the imidazole N-1 of diphthamide via an alpha-glycosidic linkage.     

Alteration of sea urchin embryo cell surface properties by mycostatin, a sterol binding antibiotic

Sea urchin embryos incubated in sea water containing mycostatin (MST), a polyene antibiotic, dissociate into single cells. Reaggregation of dissociated sea urchin embryo cells, and uptake of labeled precursors by these cells are also greatly inhibited although O₂ consumption is only slightly affected by this compound. It is known that mycostatin binds primarily to membrane sterols and affects only cells containing membrane sterols. Sea urchin cell membranes contain sterols. The effects of mycostatin on cell adhesion, reaggregation, and permeability seen in this study may be a result of an interaction with cell membrane sterols or sterol-associated molecules.     

Sepsis progression and outcome: a dynamical model

Background  

Sepsis (bloodstream infection) is the leading cause of death in non-surgical intensive care units. It is diagnosed in 750,000 US patients per annum, and has high mortality. Current understanding of sepsis is predominately observational and correlational, with only a partial and incomplete understanding of the physiological dynamics underlying the syndrome. There exists a need for dynamical models of sepsis progression, based upon basic physiologic principles, which could eventually guide hourly treatment decisions.     

Projected climate impacts to South African maize and wheat production in 2055: a comparison of empirical and mechanistic modeling approaches

Crop model‐specific biases are a key uncertainty affecting our understanding of climate change impacts to agriculture. There is increasing research focus on intermodel variation, but comparisons between mechanistic (MMs) and empirical models (EMs) are rare despite both being used widely in this field. We combined MMs and EMs to project future (2055) changes in the potential distribution (suitability) and productivity of maize and spring wheat in South Africa under 18 downscaled climate scenarios (9 models run under 2 emissions scenarios). EMs projected larger yield losses or smaller gains than MMs. The EMs’ median‐projected maize and wheat yield changes were ?3.6% and 6.2%, respectively, compared to 6.5% and 15.2% for the MM. The EM projected a 10% reduction in the potential maize growing area, where the MM projected a 9% gain. Both models showed increases in the potential spring wheat production region (EM = 48%, MM = 20%), but these results were more equivocal because both models (particularly the EM) substantially overestimated the extent of current suitability. The substantial water‐use efficiency gains simulated by the MMs under elevated CO₂ accounted for much of the EM?MM difference, but EMs may have more accurately represented crop temperature sensitivities. Our results align with earlier studies showing that EMs may show larger climate change losses than MMs. Crop forecasting efforts should expand to include EM?MM comparisons to provide a fuller picture of crop–climate response uncertainties.     

Conserved intron positions in ancient protein modules

Background  

The timing of the origin of introns is of crucial importance for an understanding of early genome architecture. The Exon theory of genes proposed a role for introns in the formation of multi-exon proteins by exon shuffling and predicts the presence of conserved splice sites in ancient genes. In this study, large-scale analysis of potential conserved splice sites was performed using an intron-exon database (ExInt) derived from GenBank.