Influence of Root Oxygen Deficiency on Photosynthesis and Antioxidant Status in Barley Plants1

Roots of barley plants (Hordeum vulgare L., cv. Alfa) were subjected to hypoxia for 120 h. By 72 to 120 h of soil flooding, a noticeable decrease in the rate of CO₂ assimilation and transpiration was observed. A drop in the activities of Rubisco and photorespiratory enzymes was found. We examined the changes in the activities of enzymes involved in the antioxidative system and stress markers related to membrane integrity, namely, lipid peroxidation and electrolyte leakage. Catalase and peroxidase activities were increased during the experiment, whereas superoxide dismutase activity drastically decreased.     

Water stress injuries and tolerance as related to potassium efflux from winter rape hypocotyls

Desiccation- or immersion-induced injuries in isolated winter rape ( Brassica napus L. var. oleifera cv. Górczański) hypocotyls were highly correlated with potassium efflux and were reversible if the tissue damage was not severe (i.e. when less than 20% of electrolytes leaked from stressed tissue). The time-course of leakage of potassium and other electrolytes showed that increased membrane permeability might result from stress-induced disturbances in membrane integrity. Increased stress tolerance in hypocotyls predehydrated to a water saturation deficit of about 60% seemed to be due to stabilization of membrane structure rather than to promotion of a repair mechanism. The hardening effect of predehydration was more effective for potassium efflux than for efflux of other electrolytes.     

ENHANCEMENT OF INTRACELLULAR PROLINE LEVEL IN CELLS OF ANACYSTIS NIDULANS (CYANOBACTERIA) EXPOSED TO DELETERIOUS CONCENTRATIONS OF COPPER1

The intracellular proline level in Anacystis nidulans cells was enhanced when the cells were exposed to sublethal concentrations of Cu²⁺; the degree of enhancement was positively related to the concentration of Cu²⁺. Analysis by high-performance liquid chromatography confirmed that the enhancement of proline levels was the most pronounced change in the composition of the free amino acid pool during copper treatment. A direct supply of exogenous proline to the cultures lowered the inhibitory influence of Cu²⁺on the growth of cells. Further experiments showed that the supply of exogenous proline lowered the leakage of potassium ions from cells exposed to deleterious concentrations of Cu²⁺. The inhibition of potassium leakage was particularly pronounced when proline was supplied prior to Cu²⁺treatment. The present study suggests that enhanced proline protects cell membranes from being affected by deleterious concentrations of Cu²⁺.     

Interaction of Pseudomonas aeruginosa Exotoxin A with the human Sec61 complex suppresses passive calcium efflux from the endoplasmic reticulum

According to live-cell calcium-imaging experiments, the Sec61 complex is a passive calcium-leak channel in the human endoplasmic reticulum (ER) membrane that is regulated by ER luminal immunoglobulin heavy chain binding protein (BiP) and cytosolic Ca²⁺-calmodulin. In single channel measurements, the open Sec61 complex is Ca²⁺ permeable. It can be closed not only by interaction with BiP or Ca²⁺-calmodulin, but also with Pseudomonas aeruginosa Exotoxin A which can enter human cells by retrograde transport. Exotoxin A has been shown to interact with the Sec61 complex and, thereby, inhibit ER export of immunogenic peptides into the cytosol. Here, we show that Exotoxin A also inhibits passive Ca²⁺ leakage from the ER in human cells, and we characterized the N-terminus of the Sec61 α-subunit as the relevant binding site for Exotoxin A.     

Leakage of adenylates during cold methanol/glycerol quenching of Escherichia coli

Effective and rapid inactivation of cellular metabolism is a prerequisite for accurate metabolome analysis. Cold methanol quenching is commonly applied to stop any metabolic activity and, at the same time remaining the cells’ integrity. However, it is reported that especially prokaryotic cells like Escherichia coli and Corynebacterium glutamicum tend to leak intracellular metabolites during cold methanol quenching. In this work leakage of adenylates is quantified for different quenching fluids. Further, a methanol/glycerol based quenching fluid is proposed, which reduces leakage drastically compared to the commonly applied methanol/water solution (16% ATP leakage compared to more than 70%).     

Hypobaric hypoxia down-regulated junctional protein complex: Implications to vascular leakage

Acute mountain sickness (AMS) can cause capillary hyper-permeability and vasogenic edema. However, its underlying mechanisms remained unclear and there is no previous in vitro study on AMS. We therefore conducted an in vitro study and examined whether continuous hypobaric hypoxia (CHH) could alter expression of junctional protein complex of vascular endothelial cells, causing hyper-permeabilization. EA.hy926 human endothelial cells were exposed to either CHH or normoxia for up to 24 h. Flow cytometry using annexin V/propidium iodide co-staining demonstrated that cell death had no significant difference at 12-h, but was increased by CHH at 24-h. Transendothelial resistance (TER) of endothelial cell monolayer was progressively decreased by CHH from 1-h to 24-h. Western blot analysis and immunofluorescence study demonstrated decreased expression levels of VE-cadherin, PECAM-1 and ZO-1 junctional proteins at both 12-h and 24-h exposure time-points. Interestingly, while the main form of ZO-1 (220 kDa) was decreased, its degraded form (100 kDa) was increased by 24-h CHH that might be linked to the increased cell death. Our data have demonstrated that CHH caused vascular endothelial hyper-permeability and defective junctional protein complex by reducing expression levels of VE-cadherin, PECAM-1, and ZO-1. Taken together, these data may explain pathophysiology underlying vascular hyper-permeability in AMS.