Leaf chemistry and food selection by common langurs (Presbytis entellus) in Rajaji National Park,Uttar Pradesh,India

Food selection in folivorous primates has been hypothesized to be correlated with leaf chemistry. To test this hypothesis, we conducted a 5-month study on Presbytis entellusin a moist deciduous forest in the Rajaji National Park,Uttar Pradesh, India. The study period covered two seasons, winter and spring. We used the percentage time spent feeding on each food item as an index of food selection, which we estimated from group scan data collected from one study group for 6 days each month. We estimated the selection ratio for each item as the ratio of time spent feeding to availability. We estimated food availability from vegetation sampling and phenological data in the home range of the study group. We estimated crude protein (CP), acid detergent fiber (ADF) and tannins in mature and young leaves of 12 major food species in the laboratory. Food selection is positively correlated with CP in winter and negatively correlated with ADF in both seasons. It also is correlated with CPJADF ratio, but to a lesser extent than the best predictor in winter and spring. Selection ratio is not correlated with CP and ADF in both seasons. It is probable that the inclusion of other factors, such as micronutrients,condensed tannins, and digestibility, might give a better prediction of food selection.     

Protein synthesis is not required for the inhibitory effect of selenite on cell colony formation and RNA synthesis

Selenite has been shown to undergo intracellular metabolism that results in its conversion to other low molecular weight Secontaining species and also to its incorporation into a selenocysteine residue in selenoprotein. In order to investigate whether the incorporation into protein is required for the cytotoxic effects of selenite, we have examined whether inhibition of protein synthesis prevents the inhibitory effect of selenite on the ability of cells to form colonies or to synthesize RNA. We have found that treatment of HeLa cells with cycloheximide inhibited protein synthesis by >90% but had no effect on the inhibitory effect of selenite on cell colony formation or RNA synthesis. Since protein synthesis is not necessary for these cytotoxic effects of selenite they are unlikely to result from an increase in the synthesis of selenoproteins.     

Grana stacking and protection of Photosystem II in thylakoid membranes of higher plant leaves under sustained high irradiance: An hypothesis

We propose yet another function for the unique appressed thylakoids of grana stacks of higher plants, namely that during prolonged high light, the non-functional, photoinhibited PS II centres accumulate as D1 protein degradation is prevented and may act as dissipative conduits to protect other functional PS II centres. The need for this photoprotective mechanism to prevent high D1 protein turnover under excess photons in higher plants, especially those grown in shade, is due to conflicting demands between efficient use of low irradiance and protection from periodic exposure to excessive irradiance.     

Domain conservation in several volvocalean cell wall proteins

Based on our previous work demonstrating that (SerPro)_x epitopes are common to extensin-like cell wall proteins in Chlamydomonas reinhardtii, we looked for similar proteins in the distantly related species C. eugametos. Using a polyclonal antiserum against a (SerPro)₁₀ oligopeptide, we found distinct sets of stage-specific polypeptides immunoprecipitated from in vitro translations of C. eugametos RNA. Screening of a C. eugametos cDNA expression library with the antiserum led to the isolation of a cDNA (WP6) encoding a (SerPro)_x-rich multidomain wall protein. Analysis of a similarly selected cDNA (VSP-3) from a C. reinhardtii cDNA expression library revealed that it also coded for a (SerPro)_x-rich multidomain wall protein. The C-terminal rod domains of VSP-3 and WP6 are highly homologous, while the N-terminal domains are dissimilar; however, the N-terminal domain of VSP-3 is homologous to the globular domain of a cell wall protein from Volvox carteri. Exon shuffling might be responsible for this example of domain conservation over 350 million years of volvocalean cell wall protein evolution.     

Reconstitution of iron-sulfur center B of Photosystem I damaged by mercuric chloride

Incubation of thylakoid membranes from spinach with low concentrations of mercuric chloride induces the loss of one of the iron-sulfur centers, F_B, in Photosystem I (PS I) and inhibits the electron transfer from PS I to the soluble electron carrier, ferredoxin. Reconstitution of this damaged iron-sulfur center has been carried out by incubating treated thylakoid membranes with exogenous FeCl₃ and Na₂S in the presence of-mercaptoethanol under anaerobic conditions. Low temperature EPR measurements indicate that center F_B is largely restored. Kinetic experiments show that the restored F_B can be photoreduced from P700. However, these reconstituted thylakoid membranes are still incompetent in the photoreduction of ferredoxin and NADP⁺, even though ferredoxin binding to the modified membranes was not impaired, indicating additional changes in the structure of the PS I complex must have occurred.     

Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU

Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Fscherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K⁺ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K⁺-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K⁺-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K⁺ ions with compounds that are less d eleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.     

Cultivation of Aspergillus niger in a pilot plant external-loop air-lift bioreactor

Abstract: Changes of the main hydrodynamic and oxygen transfer parameters during Aspergillus niger cultivation in an external-loop air-lift bioreactor of 200 dm³ operating capacity were investigated. The final average concentrations of biomass and citric acid obtained in batch fermentations were about 17 g 1^-1 and 90 g 1^-1, respectively. Significant influence of the increasing biomass concentration on the rheological properties of the broth and operating parameters was found. Volumetric oxygen transfer coefficient. k ^L a , was found to be dependent on the apparent viscosity of the broth with an exponent of -0.984.     

Selective disruption of energy flow from phycobilisomes to Photosystem I

Efficient production of ATP and NADPH by the light reactions of oxygen-evolving photosynthesis demands continuous adjustment of transfer of absorbed light energy from antenna complexes to Photosystem I (PS I) and II (PS II) reaction center complexes in response to changes in light quality. Treatment of intact cyanobacterial cells with N-ethylmaleimide appears to disrupt energy transfer from phycobilisomes to Photosystem I (PS I). Energy transfer from phycobilisomes to Photosystem II (PS II) is unperturbed. Spectroscopic analysis indicates that the individual complexes (phycobilisomes, PS II, PS I) remain functionally intact under these conditions. The results are consistent with the presence of connections between phycobiliproteins and both PS II and PS I, but they do not support the existence of direct contacts between the two photosystems.Abbreviations Chl chlorophyll - EPR electron paramagnetic resonance - NEM N-ethylmaleimide - PBS phycobilisome - PS photosystem