Photo-inhibition and the Effects of Protein Phosphorylation on Electron Transport in Wheat Thylakoids

The kinetics of changes in photosystem I (PSI), photosystemII (PSII), and whole chain (PSII and PSI) electron transport,chlorophyll fluorescence parameters, the capacity to bind atrazineand the polypeptide profiles of thylakoids isolated from wheatleaves on exposure to a photon flux density of 2000 µmolm^–2 s^–1 were determined. Severe and similar levelsof photo-inhibitory damage to both PSII and whole chain electrontransport occurred and were correlated with decreases in theratio of variable to maximal fluorescence, the proportionalcontribution of the rapid a phase of the fluorescence kineticsand the capacity to bind atrazine. Severe photo-inhibition ofelectron transport was not associated with a major loss of chlorophyllor total thylakoid protein. However, a small decrease in a 70kDa polypeptide together with increases in a number of low molecularmass polypeptides (8–24 kDa) occurred. Phosphorylation of thylakoid polypeptides alleviated photo-inhibitionof PSII electron transport but stimulated photoinhibitory damageto whole chain electron transport. The consequences of suchphosphorylation-induced effects on photoinhibition in vivo areconsidered. Key words: Chlorophyll fluorescence, electron transport, photo-inhibition, protein phosphorylation, thylakoid membranes, wheat (Triticum aestivum)     

Cloning of the nucleic acid-binding domain of the rat HnRNP C-type protein

A cDNA encoding the nucleic acid-binding domain of the hnRNP C-type protein has been cloned by DNA-affinity screening of pituitary-derived expression libraries. An analysis revealed sequence identity with the human C-type cDNA and demonstrated the presence of a peptide sequence contained within the single-stranded DNA-binding protein, UP2, which was absent from the human cDNA. Structural analysis of the protein encoded by the rat cDNA demonstrated a net charge of +15 with 14.56% and 6.33% lysines and arginines, respectively, and an amino acid sequence that is consistent with an extensive helix-loop-helix-turn-helix structure.     

Maize root responses to drought stress depend on root class and axial position

In this study we tested the hypotheses that root classes would exhibit distinctive anatomical and architectural responses to drought stress, and that those responses would vary along the root axes. The root systems of four maize (Zea mays L.) sweet corn genotypes designated SC1, SC2, SC3 and SC4 were phenotyped under well-watered and drought treatments in greenhouse mesocosms, permitting increasing stratification of moisture availability as the drought progressed. Anatomical and architectural responses to drought were evaluated for each root class. Lignin distribution was assessed by image processing of UV-illuminated root cross-sections acquired by laser ablation tomography. The two cultivars with less biomass reduction under drought, SC3 and SC4, substantially enhanced lateral root development along the apical segments of axial roots when plants were grown with drought stress. These segments grew into the deeper part of the mesocosm where more moisture was available. Apical segments of the axial and large lateral roots from drought-stressed plants were thicker and had greater theoretical axial water conductance than basal segments, especially in SC3 and SC4. Basal segments of crown roots of SC3 and SC4 showed increased lignification of the stele under drought. Root anatomical and architectural responses to drought are complex and vary among cultivars and root classes, and along root axes. Drought-induced proliferation of lateral roots on apical segments of axial roots would be expected to enhance deep water acquisition, while lignification of axial roots could help preserve axial water transport.

     

A method to study slug predation on seedlings in the field

Dandelion is a common Asteraceae species that populates disturbed sites and gaps within swards where it becomes an important competitor of grasses. The natural control against dandelion includes seedling predation, with slugs, particularly Arion lusitanicus, being the most important in the Czech Republic. However, the study of slug seedling consumption is difficult because naturally established seedlings are not always available. Therefore, we developed a method of exposing laboratory‐grown seedlings as bait for slug predation. Dandelion seeds were sown in plastic cups containing a bottom layer of moist substrate. The emerged seedlings were thinned to 20 and displayed in an open area. During 2008–2010, the seedling baits were placed at 15 sites at 1 month intervals throughout the dandelion vegetative season, in parallel with plasticine baits that monitored slug feeding activity. For each 1 month interval, seedling survival was observed for a period of 8 days, and the estimated time to death was calculated; the percentage of surviving seedlings was then recorded. This method of seedling presentation demonstrated that local and temporal variation in seedling survival is correlated with slug feeding activity. The advantage of this technique is that the seedlings in baits may be presented at any place and time, as required by the experimental design; however, we found that the estimated time to seedling death was shorter for the exposed baits than for the naturally established seedlings. The method is suitable for the study of plant species other than dandelion, and also for aims other than the study of spatiotemporal trends in seedling consumption by slugs.     

The octadecaneuropeptide ODN prevents 6‐hydroxydopamine‐induced apoptosis of cerebellar granule neurons through a PKC‐MAPK‐dependent pathway

Oxidative stress, induced by various neurodegenerative diseases, initiates a cascade of events leading to apoptosis, and thus plays a critical role in neuronal injury. In this study, we have investigated the potential neuroprotective effect of the octadecaneuropeptide (ODN) on 6‐hydroxydopamine (6‐OHDA)‐induced oxidative stress and apoptosis in cerebellar granule neurons (CGN). ODN, which is produced by astrocytes, is an endogenous ligand for both central‐type benzodiazepine receptors (CBR) and a metabotropic receptor. Incubation of neurons with subnanomolar concentrations of ODN (10^?18 to 10^?12 M) inhibited 6‐OHDA‐evoked cell death in a concentration‐dependent manner. The effect of ODN on neuronal survival was abrogated by the metabotropic receptor antagonist, cyclo_1–8[DLeu⁵]OP, but not by a CBR antagonist. ODN stimulated polyphosphoinositide turnover and ERK phosphorylation in CGN. The protective effect of ODN against 6‐OHDA toxicity involved the phospholipase C/ERK MAPK transduction cascade. 6‐OHDA treatment induced an accumulation of reactive oxygen species, an increase of the expression of the pro‐apoptotic gene Bax, a drop of the mitochondrial membrane potential and a stimulation of caspase‐3 activity. Exposure of 6‐OHDA‐treated cells to ODN blocked all the deleterious effects of the toxin. Taken together, these data demonstrate for the first time that ODN is a neuroprotective agent that prevents 6‐OHDA‐induced oxidative stress and apoptotic cell death.     

Effects of some alcohols on the conformation of mitochondrial H+-ATPase complex and F1-ATPase from pig heart

The conformations of the H+-ATPase complex and F1-ATPase in low concentrations of methanol, ethanol, n-propanol, iso-propanol and t-butanol were studied by circular dichroism. For F1-ATPase, all but methanol first increased and then decreased the circular dichroism magnitude of helical bands as the alcohol concentration was increased. With ethanol, n-propanol, iso-propanol and t-butanol, the alpha-helix content reached a maximum at about 5% alcohol and began to decrease at 10%. The content of beta-sheet showed the opposite effect, reaching a minimum at 5% and increasing slightly at higher concentrations. None of the alcohols studied had a significant effect on the conformation of the H+-ATPase complex. This difference implies that the alcohols had a greater effect on free F1-ATPase than on the membrane-bound F1-ATPase. The hydrophobic protein F0 and the membrane lipids in the H+-ATPase complex may stabilize and protect F1 from the effects of the alcohols.     

Temperature Dependence of Drug Interaction with the Platelet 5-Hydroxytryptamine Transporter: A Clue to the Imipramine Selectivity Paradox

Although [3H]imipramine is a selective radioligand for the 5-hydroxytryptamine (5-HT) transporter in human platelets, its affinity for binding to the 5-HT transporter complex at 0 degrees C (0.6 nM) is significantly higher than its potency for inhibition of [3H]5-HT uptake at the physiological temperature of 37 degrees C (Ki = 29 nM). As this apparent discrepancy could be related to the assay temperature, we studied the thermodynamics of drug interaction with the 5-HT transporter at assay temperatures between 0 degrees C and 37 degrees C, using as radioligands [3H]imipramine (0 degrees C and 20 degrees C) and [3H]paroxetine (20 degrees C and 37 degrees C), a newly available probe for the 5-HT transporter. At 20 degrees C, Ki values of 14 tricyclic and nontricyclic drugs for inhibition of [3H]imipramine and [3H]paroxetine binding to human platelet membranes were highly significantly correlated (r = 0.98, p less than 0.001), validating the use of these two radioligands to study the 5-HT transporter over a temperature range larger than was previously possible with [3H]imipramine alone. The affinity of imipramine for the 5-HT transporter is progressively enhanced with decreasing incubation temperature, thus favoring the selectivity of [3H]imipramine for the 5-HT transporter at 0 degrees C. At 37 degrees C, the Ki of imipramine for inhibition of [3H]paroxetine binding is 32 nM, and equals its Ki value for inhibition of 5-HT uptake into human platelets. With the exception of chlorimipramine, other tricyclic 5-HT uptake inhibitors showed a temperature sensitivity in their interaction with the 5-HT transporter similar to that of imipramine.(ABSTRACT TRUNCATED AT 250 WORDS)     

The uptake and intracellular distribution of [35S]trithiomolybdate in bovine liver in vivo

[35S] trithiomolybdate was administered intravenously to a group of four steer at two dose rates, 1 and 26 mg Mo per animal. Radioactivity appeared rapidly in the liver and was distributed in all the subcellular fractions examined. Examination by Sephadex G-100 gel-filtration of the cytosol fraction showed that distinct 35S-binding protein peaks were present. The protein-bound radioactivity was displaceable and was identified as [35S]thiomolybdates. No radioactivity eluted with metallothionein, but 35S was associated with the high molecular weight copper fraction, eluted in the void volume of the column, which increased transiently after the administration of the higher dose. It was suggested that the presence of protein-bound thiomolybdates in the liver gave rise to new ligands, which altered the equilibrium of copper between the different metal-binding proteins. This might be similar to the alteration in the copper-binding of albumin produced by the presence of thiomolybdates.