Post-ingestive feedbacks and associative learning regulate the intake of unsuitable sterols in a generalist grasshopper.
(1/794)
Behavioural studies of the grasshopper Schistocerca americana were undertaken to identify the mechanisms that regulate the intake of dietary sterols. In the first experiment, grasshoppers were allowed to feed on spinach, a plant containing only unsuitable sterols; immediately after this first meal, a suitable or unsuitable sterol was injected into the haemolymph. Grasshoppers injected with unsuitable sterols had second meals on spinach that were significantly shorter than those of grasshoppers injected with suitable sterols, indicating that unsuitable dietary sterols are detected post-ingestively. In the second experiment, grasshoppers were fed food containing only unsuitable sterols and were then presented with glass-fibre discs containing different concentrations of a suitable sterol or sucrose only (the control). The results suggest that grasshoppers do not use a direct feedback operating on mouthpart chemoreceptors to regulate their intake of suitable sterols. In the third experiment, grasshoppers were presented with artificial diets containing different sterols and flavours, and feeding was observed over a sequence of meals. The results from both the first and last experiments suggest a role for associative learning in regulating the intake of unsuitable sterols. (+info)
The food matrix of spinach is a limiting factor in determining the bioavailability of beta-carotene and to a lesser extent of lutein in humans.
(2/794)
Carotenoid bioavailability depends, amongst other factors, on the food matrix and on the type and extent of processing. To examine the effect of variously processed spinach products and of dietary fiber on serum carotenoid concentrations, subjects received, over a 3-wk period, a control diet (n = 10) or a control diet supplemented with carotenoids or one of four spinach products (n = 12 per group): whole leaf spinach with an almost intact food matrix, minced spinach with the matrix partially disrupted, enzymatically liquefied spinach in which the matrix was further disrupted and the liquefied spinach to which dietary fiber (10 g/kg wet weight) was added. Consumption of spinach significantly increased serum concentrations of all-trans-beta-carotene, cis-beta-carotene, (and consequently total beta-carotene), lutein, alpha-carotene and retinol and decreased the serum concentration of lycopene. Serum total beta-carotene responses (changes in serum concentrations from the start to the end of the intervention period) differed significantly between the whole leaf and liquefied spinach groups and between the minced and liquefied spinach groups. The lutein response did not differ among spinach groups. Addition of dietary fiber to the liquefied spinach had no effect on serum carotenoid responses. The relative bioavailability as compared to bioavailability of the carotenoid supplement for whole leaf, minced, liquefied and liquefied spinach plus added dietary fiber for beta-carotene was 5.1, 6.4, 9.5 and 9.3%, respectively, and for lutein 45, 52, 55 and 54%, respectively. We conclude that the bioavailability of lutein from spinach was higher than that of beta-carotene and that enzymatic disruption of the matrix (cell wall structure) enhanced the bioavailability of beta-carotene from whole leaf and minced spinach, but had no effect on lutein bioavailability. (+info)
Expression of alfalfa mosaic virus coat protein in tobacco mosaic virus (TMV) deficient in the production of its native coat protein supports long-distance movement of a chimeric TMV.
(3/794)
Alfalfa mosaic virus (AlMV) coat protein is involved in systemic infection of host plants, and a specific mutation in this gene prevents the virus from moving into the upper uninoculated leaves. The coat protein also is required for different viral functions during early and late infection. To study the role of the coat protein in long-distance movement of AlMV independent of other vital functions during virus infection, we cloned the gene encoding the coat protein of AlMV into a tobacco mosaic virus (TMV)-based vector Av. This vector is deficient in long-distance movement and is limited to locally inoculated leaves because of the lack of native TMV coat protein. Expression of AlMV coat protein, directed by the subgenomic promoter of TMV coat protein in Av, supported systemic infection with the chimeric virus in Nicotiana benthamiana, Nicotiana tabacum MD609, and Spinacia oleracea. The host range of TMV was extended to include spinach as a permissive host. Here we report the alteration of a host range by incorporating genetic determinants from another virus. (+info)
Rapid purification of membrane extrinsic F1-domain of chloroplast ATP synthase in monodisperse form suitable for 3D-crystallization.
(4/794)
A new chromatographic procedure for purification of the membrane extrinsic F1-domain of chloroplast ATP synthase is presented. The purification is achieved by a single anion exchange chromatography step. Determination of the enzyme-bound nucleotides reveals only 1 mole of ADP per complex. The purified enzyme shows a latent Ca(2+)-dependent ATPase activity of 1.0 mumol.mg-1 min-1 and a Mg(2+)-dependent activity of 4.4 mumol.mg-1 .min-1. Both activities are increased up to 8-10-fold after dithiothreitol activation. Analysis of the purified F1-complex by SDS/PAGE, silver staining and immunoblotting revealed that the preparation is uncontaminated by fragmented subunits or ribulose-1,5-bisphosphate carboxylase/oxygenase. Gel filtration experiments indicate that the preparation is homogenous and monodisperse. In order to determine the solubility minimum of the purified F1-complex the isoelectric point of the preparation was calculated from pH mapping on ion exchange columns. In agreement with calculations based on the amino acid sequence, a slightly acidic pI of 5.7 was found. Using ammonium sulphate as a precipitant the purified CF1-complex could be crystallized by MicroBatch. (+info)
Quenching of chlorophyll fluorescence by triplets in solubilized light-harvesting complex II (LHCII).
(5/794)
The quenching of chlorophyll fluorescence by triplets in solubilized trimeric light harvesting complexes was analyzed by comparative pump-probe experiments that monitor with weak 2-ns probe pulses the fluorescence yield and changes of optical density, DeltaOD, induced by 2-ns pump pulses. By using a special array for the measurement of the probe fluorescence (Schodel R., F. Hillman, T. Schrotter, K.-D. Irrgang, J. Voight, and G. Biophys. J. 71:3370-3380) the emission caused by the pump pulses could be drastically reduced so that even at highest pump pulse intensities, IP, no significant interference with the signal due to the probe pulse was observed. The data obtained reveal: a) at a fixed time delay of 50 ns between pump and probe pulse the fluorescence yield of the latter drastically decreased with increasing IP, b) the recovery of the fluorescence yield in the microseconds time domain exhibits kinetics which are dependent on IP, c) DeltaOD at 507 nm induced by the pump pulse and monitored by the probe pulse with a delay of 50 ns (reflecting carotenoid triplets) increases with IP without reaching a saturation level at highest IP values, d) an analogous feature is observed for the bleaching at 675 nm but it becomes significant only at very high IP values, e) the relaxation of DeltaOD at 507 nm occurs via a monophasic kinetics at all IP values whereas DeltaOD at 675 nm measured under the same conditions is characterized by a biphasic kinetics with tau values of about 1 microseconds and 7-9 microseconds. The latter corresponds with the monoexponential decay kinetics of DeltaOD at 507 nm. Based on a Stern-Volmer plot, the time-dependent fluorescence quenching is compared with the relaxation kinetics of triplets. It is shown that the fluorescence data can be consistently described by a quenching due to triplets. (+info)
Isolation of a highly active PSII-LHCII supercomplex from thylakoid membranes by a direct method.
(6/794)
We have developed a simple and novel method to isolate a highly pure and active photosystem (PS) II complex, directly from thylakoid membranes. This complex is a discrete particle and contains all the proteins of the oxygen evolving complex and a set of chlorophyll alb binding proteins. The intactness of both the donor side and the acceptor side has resulted in a very high oxygen evolution activity and therefore offers a superior experimental system to that of PSII enriched membrane fragments in which there is heterogeneity in activities and biochemical composition. (+info)
Availability of food folate in humans.
(7/794)
The aim of our study was to determine whether the area-under-the-plasma-response-curve method with the positive area (AUC+) as primary analysis variable is suitable to evaluate the availability of food folate in humans. Healthy volunteers (n = 20) received four test meals in a randomized, four-period cross-over design as follows: meal A, 600 g spinach; meal B, 300 g spinach; meal C, 0.4 mg folic acid in water; meal D, folate-free control meal. Blood samples were drawn before administration of the test meals and up to 10 h postprandially. Plasma folate was significantly increased for up to 6 h after uptake of spinach and folic acid (P < 0.007), whereas the response curve after the control meal decreased slightly but significantly (P < 0.007). To calculate the net increase of plasma folate, the values were corrected by the individual predose concentrations. The AUC+ was calculated with these corrected values. The mean AUC+ was highest after consumption of meal A (71.2 +/- 24.0 h x nmol/L) followed by meal C (61.8 +/- 23. 8 h x nmol/L) and meal B (41.4 +/- 19.4 h x nmol/L). The AUC+ after meal B was significantly lower than after the other two meals (P < 0. 05). The results suggest that the AUC method with multiple blood sampling is useful for assessing the availability of food folate in humans. (+info)
Chloroplast class I and class II aldolases are bifunctional for fructose-1,6-biphosphate and sedoheptulose-1,7-biphosphate cleavage in the Calvin cycle.
(8/794)
Class I and class II aldolases are products of two evolutionary non-related gene families. The cytosol and chloroplast enzymes of higher plants are of the class I type, the latter being bifunctional for fructose-1,6- and sedoheptulose-1,7-P2 in the Calvin cycle. Recently, class II aldolases were detected for the cytosol and chloroplasts of the lower alga Cyanophora paradoxa. The respective chloroplast enzyme has been shown here to be also bifunctional for fructose-1,6- and sedoheptulose-1,7-P2. Kinetics, also including fructose-1-P, were determined for all these enzymes. Apparently, aldolases are multifunctional enzymes, irrespective of their class I or class II type. (+info)