Two independent biochemical pathways for isopentenyl diphosphate and isoprenoid biosynthesis in higher plants

In the early times of isoprenoid research, a single pathway was found for the formation of the C₅ monomer, isopentenyl diphosphate (IPP), and this acetate/mevalonate pathway was supposed to occur ubiquitously in all living organisms. Now, 40 years later, a totally different IPP biosynthesis route has been detected in eubacteria, green algae and higher plants. In this new pathway glyceraldehyde 3-phosphate (GAP) and pyruvate are precursors of isopentenyl diphosphate, but not acetyl-CoA and mevalonic acid. In green tissues of three higher plants it was shown that all chloroplastbound isoprenoids (β-carotene, phytyl chains of chlorophylls and nona-prenyl chain of plastoquinone-9) are formed via the GAP/pyruvate pathway, whereas the cytoplasmic sterols are formed via the acetate/mevalonate pathway. Also, isoprene, emitted by various plants at high light conditions by action of the plastid-bound isoprene synthase, is formed via the new GAP/pyruvate pathway. Thus, in higher plants, there exist two separate and biochemically different IPP biosynthesis pathways: (1) the novel alternative GAP/pyruvate pathway apparently bound to the plastidic compartment and (2) the classical cytoplasmic acetate/mevalonate pathway. This new GAP/pyruvate pathway for IPP formation allows a reasonable interpretation of previous odd results concerning the biosynthesis of chloroplast isoprenoids, which, so far, had mainly been interpreted assuming compartmentation differences. The novel GAP/pyruvate pathway for IPP formation in plastids appears as a heritage of their prokaryotic, endosymbiotic ancestors.     

Experimental manipulation of immune-mediated disease and its fitness costs for rodent malaria parasites

Background  

Explaining parasite virulence (harm to the host) represents a major challenge for evolutionary and biomedical scientists alike. Most theoretical models of virulence evolution assume that virulence arises as a direct consequence of host exploitation, the process whereby parasites convert host resources into transmission opportunities. However, infection-induced disease can be immune-mediated (immunopathology). Little is known about how immunopathology affects parasite fitness, or how it will affect the evolution of parasite virulence. Here we studied the effects of immunopathology on infection-induced host mortality rate and lifetime transmission potential – key components of parasite fitness – using the rodent malaria model, Plasmodium chabaudi chabaudi.     

Multispectral fluorescence and reflectance imaging at the leaf level and its possible applications

Images taken at different spectral bands are increasingly used for characterizing plants and their health status. In contrast to conventional point measurements, imaging detects the distribution and quantity of signals and thus improves the interpretation of fluorescence and reflectance signatures. In multispectral fluorescence and reflectance set-ups, images are separately acquired for the fluorescence in the blue, green, red, and far red, as well as for the reflectance in the green and in the near infrared regions. In addition, 'reference' colour images are taken with an RGB (red, green, blue) camera. Examples of imaging for the detection of photosynthetic activity, UV screening caused by UV-absorbing substances, fruit quality, leaf tissue structure, and disease symptoms are introduced. Subsequently, the different instrumentations used for multispectral fluorescence and reflectance imaging of leaves and fruits are discussed. Various types of irradiation and excitation light sources, detectors, and components for image acquisition and image processing are outlined. The acquired images (or image sequences) can be analysed either directly for each spectral range (wherein they were captured) or after calculating ratios of the different spectral bands. This analysis can be carried out for different regions of interest selected manually or (semi)-automatically. Fluorescence and reflectance imaging in different spectral bands represents a promising tool for non-destructive plant monitoring and a 'road' to a broad range of identification tasks.     

Inhibitory activity of Indian spice plant Cinnamomum zeylanicum extracts against Alternaria solani and Curvularia lunata, the pathogenic dematiaceous moulds

Background

Enteric fever is an endemic problem in Nepal and Widal agglutination test is widely used for its diagnosis but a normal baseline titer in healthy population and cutoff values have not been established.

Methods

We measured average baseline antibody titers against "O" and "H" antigens of Salmonella enterica serotype Typhi and "H" antigens of serotypes Paratyphi A and Paratyphi B among apparently healthy blood donors in Nepal. The antibody titers were measured using Standard Widal Confirmatory Quantitative Tube test.

Results

Among the 100 blood samples collected from healthy volunteers, 62 individuals had significant antibody titers (≥ 1:20) against one of the four antigens against S. enterica. Among 54 samples with an anti-O titer against serotype Typhi, 15 and 36 samples had titers of ≥ 1:60 and ≥ 1:40, respectively. A significant proportion (12% of all) had anti-O titer of ≥ 1:80. Similarly, among the 59 samples demonstrating anti-H titers of ≥ 1:20 to S. enterica serotype Typhi, 29 had a titer of ≥ 1:80 and 12 had 1:160. For S. enterica serotypes Paratyphi A and B, anti-H titers of ≥ 1:20 were found only in 12% and 3%, respectively, of all samples tested.

Conclusion

When a single Widal agglutination titer is used for the diagnosis of enteric fever, it will be more appropriate to change the currently used cutoff levels against S. enterica serotype Typhi to > 1:80 for anti-O and > 1:160 for anti-H titers for Nepal.     

Blue,Green and Red Fluorescence Signatures and Images of Tobacco Leaves*

Laser-induced fluorescence images of the leaf of an aurea mutant of Nicotiana tabacum were recorded for the blue and green fluorescence at 440 and 520 nm and the red chlorophyll fluorescence at 690 and 735 nm. The results obtained were compared with direct measurements of the fluorescence emission spectra of leaves using a conventional spectrofluorometer. The highest emission of blue (F440) and green fluorescence (F520) within the leaf was found in the leaf veins, particularly the main leaf vein. In contrast, the intercostal fields of leaves, which exhibited the highest chlorophyll content, showed only a very low blue and green fluorescence emission, which was much lower than the red and far-red chlorophyll fluorescence emission bands (F690 and F735). Correspondingly, the ratio of blue to red leaf fluorescence F440/F690 of upper and lower leaf side was much higher in the leaf veins (values 1.2 to 1.5) than in intercostal fields (values of 0.6 to 0.7). The results also demonstrated that in the intercostal fields the major part of the blue-green fluorescence was reabsorbed by chlorophylls and carotenoids. A partial reabsorption of the red fluorescence band near 690 nm by leaf chlorophyll took place, but did not affect the far-red fluorescence band near F735. As a consequence the chlorophyll fluorescence ratio F690/F735 exhibited significantly higher values in the chlorophyll-poor leaf vein regions (1.7 to 1.8) than in the chlorophyll-rich intercostal fields (0.8 to 1.3). Imaging spectroscopy of leaves was shown to be much more precise than the screening of fluorescence signatures by conventional fluorometers. It clearly demonstrated that the blue-green fluorescence and the red chlorophyll fluorescence of leaves exhibit an inverse contrast to each other. The advantage of the fluorescence imaging spectroscopy, which allows the simultaneous screening of the whole leaf surface and distinct parts of it, and its possible application in the detection of stress effects or local damage by insects and pathogens, is discussed.     

Alzheimer's Disease

Peptide aldehyde inhibitors of the chymotrypsin-like activity of the proteasome (CLIP) such as N-acetyl-Leu-Leu-Nle-H (or ALLN) have been shown previously to inhibit the secretion of beta-amyloid peptide (A beta) from cells. To evaluate more fully the role of the proteasome in this process, we have tested the effects on A beta formation of a much wider range of peptide-based inhibitors of CLIP than published previously. The inhibitors tested included several peptide boronates, some of which proved to be the most potent peptide-based inhibitors of beta-amyloid production reported so far. We found that the ability of the peptide aldehyde and boronate inhibitors to suppress A beta formation from cells correlated extremely well with their potency as CLIP inhibitors. Thus, we conclude that the proteasome may be involved either directly or indirectly in A beta formation.     

gamma-Secretase cleavage site specificity differs for intracellular and secretory amyloid beta

The final step in A beta generation is the cleavage of the C-terminal 99 amino acid residues of the amyloid precursor protein by gamma-secretase. gamma-Secretase activity is closely linked to the multi-transmembrane-spanning proteins presenilin 1 and presenilin 2. To elucidate whether the cleavage site specificities of gamma-secretase leading to the formation of secreted and intracellular A beta are identical, we made use of point mutations close to the gamma-cleavage site, known to have a dramatic effect on the 42/40 ratio of secreted A beta. We found that the selected point mutations only marginally influenced the 42/40 ratio of intracellular A beta, suggesting differences in the gamma-secretase cleavage site specificity for the generation of secreted and intracellular A beta. The analysis of the subcellular compartments involved in the generation of intracellular A beta revealed that A beta is not generated in the early secretory pathway in the human SH-SY5Y neuroblastoma cell line. In this study we identified late Golgi compartments to be involved in the generation of intracellular A beta. Moreover, we demonstrate that the presence of processed PS1 is not sufficient to obtain gamma-secretase processing of the truncated amyloid precursor protein construct C99, proposing the existence of an additional factor downstream of the endoplasmic reticulum and early Golgi required for the formation of an active gamma-secretase complex.     

Differences in photosynthetic activity, chlorophyll and carotenoid levels, and in chlorophyll fluorescence parameters in green sun and shade leaves of Ginkgo and Fagus

The differences in pigment levels and photosynthetic activity of green sun and shade leaves of ginkgo (Ginkgo biloba L.) and beech (Fagus sylvatica L.) are described. Sun leaves of both tree species possessed higher levels in chlorophylls (Chl) and carotenoids on a leaf area basis, higher values for the ratio Chl a/b and lower values for the ratio Chl/carotenoids (a+b)/(x+c) in comparison to shade leaves. The higher photosynthetic rates P(N) of sun leaves (ginkgo 5.4+/-0.9 and beech 8.5+/-2.1 micromol m(-2)s(-1)) were also reflected by higher values for the Chl fluorescence decrease ratios R(F)(d) 690 and R(F)(d) 735. In contrast, the shade leaves had lower P(N) rates (ginkgo 2.4+/-0.3 and beech 1.8+/-1.2 micromol m(-2)s(-1)). In both tree species the stomatal conductance G(s) was significantly higher in sun (range: 70-19 1 mmol m(-2)s(-1)) as compared to shade leaves (range: 5-55 mmol m(-2)s(-1)). In fact, at saturating light conditions there existed a close correlation between G(s) values and P(N) rates. Differences between sun and shade leaves also existed in several other Chl fluorescence ratios (F(v)/F(m), F(v)/F(o), and the stress adaptation index Ap). The results clearly demonstrate that the fan-shaped gymnosperm ginkgo leaves show the same high and low irradiance adaptation response as the angiosperm beech leaves.