The intensity of the mutualistic relationship between aphids and ants depends mainly on the composition and amount of honeydew. We used the model system Tanacetum vulgare-Metopeurum fuscoviride to study age-related differences in honeydew production and composition and its effect on the mutualism between M. fuscoviride and the ant Lasius niger. First and second instar larvae of M. fuscoviride produced only half of the amount of honeydew as older larvae or adults. There were, however, no differences between age classes in the total honeydew sugar concentration, which averaged approx. 80 μg sugar/μl honeydew. Honeydew sugar composition also did not differ between age classes, and melezitose was the dominant sugar (59% in all classes). The amino acid concentration, by contrast, increased significantly with aphid age, reaching 22.6 nmol per μl honeydew in adult M. fuscoviride. This increase was mainly caused by asparagine and glutamine, while there were no differences in the concentrations of the five other regularly detected amino acids and cystine, respectively. The intensity of ant-attendance was significantly lower in colonies of first and second instar larvae than in colonies of older age classes. Ant-attendance correlated with the amount of honeydew produced, and not with the total amino acid concentration. 相似文献
Summary. An important sequence motif identified by sequence analysis is shared by the ACT domain family, which has been found in a number of diverse proteins. Most of the proteins containing the ACT domain seem to be involved in amino acid and purine synthesis and are in many cases allosteric enzymes with complex regulation enforced by the binding of ligands. Here we explore the current understanding of the ACT domain function including its role as an allosteric module in a selected group of enzymes. We will further describe in more detail three of the proteins where some understanding is available on function and structure: i) the archetypical ACT domain protein E. coli 3PGDH, which catalyzes the first step in the biosynthesis of L-Ser, ii) the bifunctional chorismate mutase/prephenate dehydratase (P-protein) from E. coli, which catalyzes the first two steps in the biosynthesis of L-Phe, and iii) the mammalian aromatic amino acid hydroxylases, with special emphasis on phenylalanine hydroxylase, which catalyzes the first step in the catabolic degradation of L-phenylalanine (L-Phe). The ACT domain is commonly involved in the binding of a small regulatory molecule, such as the amino acids L-Ser and L-Phe in the case of 3PGDH and P-protein, respectively. On the other hand, for PAH, and probably for other enzymes, this domain appears to have been incorporated as a handy, flexible small module with the potential to provide allosteric regulation via transmission of finely tuned conformational changes, not necessarily initiated by regulatory ligand binding at the domain itself.Current address: Protein Biophysics & Delivery, Novo Nordisk A/S, Novo Allé, 2880 Bagsværd, Denmark. 相似文献
The amino acid and humic acid requirements of Saccharothrix algeriensis NRRL B-24137 for growth and production of the dithiolopyrrolone antibiotics were studied in a semi-synthetic medium (SSM). Nature and concentration of amino acids and humic acid strongly influenced the growth and dithiolopyrrolone specific production.
The highest value of thiolutin (acetyl-pyrrothine) specific production was obtained in the presence of 1 g/l humic acid (336 mg/g DCW), and in the presence of 5 mM l-cystine (309 mg/g DCW) as compared to 19 mg/g DCW obtained with the control. Furthermore, thiolutin production was increased about six-fold, four-fold and three-fold in the presence of l-proline, l-glutamic acid and dl-histidine, respectively. In contrast, the production of thiolutin was reduced by addition of other amino acids such as l-glutamine, dl-ethionine, l-methionine and l-arginine. The highest value of isobutyryl-pyrrothine production was obtained in the presence of 2,6-diaminopimelic acid and l-lysine (7.8 and 1.0 mg/g DCW, respectively). However, the highest value of butanoyl-pyrrothine production was obtained in the presence of humic acid (6.6 mg/g DCW), followed by l-cysteine and l-proline (3.6 and 3.2 mg/g DCW, respectively). In addition, the maximum specific production of senecioyl-pyrrothine (29 mg/g DCW) and tigloyl-pyrrothine (21 mg/g DCW) was obtained in the presence of humic acid. We found that, except for isobutyryl-pyrrothine, production of all dithiolopyrrolones was favoured by addition of l-proline. The maximum specific production was obtained with l-proline at concentrations of 2.50 mM for thiolutin (133 mg/g DCW), 1.25 mM for senecioyl-pyrrothine, tigloyl-pyrrothine and butanoyl-pyrrothine production (29, 23 and 3.9 mg/g DCW, respectively). Production of all dithiolopyrrolones strongly decreased as the l-methionine or dl-ethionine concentration was increased in the culture medium. 相似文献
1 Insecticidal proteins can be excreted in the honeydew when sap-sucking insects feed on insect-resistant transgenic plants. Honeydew can be an important source of carbohydrates, thus potentially exposing a broad range of honeydew-feeding insects to transgene products. 2 Snowdrop lectin ( Galanthus nivalis agglutinin; GNA) dissolved in a 2 m sucrose solution had no antifeedant effect on female aphid parasitoids ( Aphidius ervi ) but had a direct negative effect on their longevity. 3 When feeding on honeydew from Rhopalosiphum padi feeding on a GNA-containing artificial diet, Aphidius ervi suffered a longevity reduction that was more pronounced than was to be expected based on the detected GNA concentration in the honeydew. 4 Analysis of carbohydrate and amino acid composition revealed that a change in honeydew composition caused by a GNA-effect on the aphids could be a possible explanation for the additional reduction in parasitoid longevity. 5 When comparing the effect of honeydew from Sitobion avenae and R. padi feeding on GNA-expressing or nontransformed wheat plants on A. ervi longevity, aphid species was found to have a significant effect, whereas the wheat variety had no effect. The latter result was probably due to low GNA expression levels in the plants. Differences in nutritional suitability between honeydew from R. padi and S. avenae could be explained by differences in carbohydrate and amino acid composition. 6 This is the first study to demonstrate that GNA ingested by aphids and transported into the honeydew can negatively affect the parasitoids consuming this honeydew. 7 We recommend that honeydew should be considered as a route of exposure to transgene products in future risk assessment studies. 相似文献
The effects of doubled ambient [CO2] and different temperature levels on young Pinus sylvestris growing in phytotron chambers were studied. Five chambers were supplied with ~380 (‘ambient air’) and five with ~700 μmol mol−1 CO2 (‘elevated [CO2]’). Temperature levels in the chambers ranged in increment steps of 2°C from −4°C to +4°C relative to the long-term monthly
(day and night) average air temperature levels in Berlin–Dahlem. Substrate was medium fertile; soil moisture and air humidity
were kept constant. After three vegetation periods twigs and stems were harvested, weighed, homogenized, and analyzed chemically.
There was no significant temperature effect on wood mass accumulation, clearest positive [CO2] effect occurred in the youngest twigs. In total, wood mass increased by 28.5% at doubled ambient [CO2]. N-contents (percentage) decreased at elevated [CO2] in the uppermost stem sections and not in twig wood causing wider C/N ratios in total. In response to elevated temperature,
N-contents decreased slightly in twigs (~0.3%). Traces of free glucose, fructose and sucrose, which decreased from the top
to the bottom, were found in stem wood, in contrast to traces of starch that increased from the top to the bottom. In response
to elevated [CO2] only a little more (0.05%) was accumulated in the top shoot and in tendency; glucose, fructose, and sucrose contents were
lower at the bottom of stems as compared to the control. There was no obvious response of these non-structural carbohydrates
to elevated temperature except for starch that decreased to half of the content from the lowest to the highest temperature
level. Among the hemicellulose compounds, rhamnose and arabinose declined from the top shoot to the bottom of stem, whereas
4-O-methyl-d-glucuronic-acid, mannose, and xylose increased. Contents (percentage) of galactose remained approximately stable along the
stem. The clearest positive effect of elevated [CO2] along the whole stem was found for mannose with differences of 0.6–0.3%. In contrast to rhamnose and arabinose that showed
a negative response to elevated [CO2], mannose was reduced towards the uppermost stem sections. The 4-O-methyl-d-glucuronic-acid was slightly lowered at the bottom, and galactose and xylose showed no [CO2] response. The only hemicellulose compound which reacted to temperature elevation was galactose. It increased slightly (~0.1%
per 1°C). Cellulose and lignin (Klason) behaved oppositely: cellulose increased and lignin decreased from the top to the bottom.
These structural components behaved reversely also in response to elevated [CO2]. In stem parts above the bottom section, cellulose content was slightly higher at elevated [CO2], and lignin content was slightly lower at the bottom. Lignin reacted to temperature elevation by a very slight increase
on the average (~0.1% per one 1°C). Cellulose, however, decreased by ~0.2% per 1°C temperature elevation. The importance of
persistent sinks of carbon in woody plant parts is discussed in respect to the greenhouse effect. 相似文献
The available amino acid sequences of the α-amylase family (glycosyl hydrolase family 13) were searched to identify their
domain B, a distinct domain that protrudes from the regular catalytic (β/α)8-barrel between the strand β3 and the helix α3. The isolated domain B sequences were inspected visually and also analyzed
by Hydrophobic Cluster Analysis (HCA) to find common features. Sequence analyses and inspection of the few available three-dimensional
structures suggest that the secondary structure of domain B varies with the enzyme specificity. Domain B in these different
forms, however, may still have evolved from a common ancestor. The largest number of different specificities was found in
the group with structural similarity to domain B from Bacillus cereus oligo-1,6-glucosidase that contains an α-helix succeeded by a three-stranded antiparallel β-sheet. These enzymes are α-glucosidase,
cyclomaltodextrinase, dextran glucosidase, trehalose-6-phosphate hydrolase, neopullulanase, and a few α-amylases. Domain B
of this type was observed also in some mammalian proteins involved in the transport of amino acids. These proteins show remarkable
similarity with (β/α)8-barrel elements throughout the entire sequence of enzymes from the oligo-1,6-glucosidase group. The transport proteins, in
turn, resemble the animal 4F2 heavy-chain cell surface antigens, for which the sequences either lack domain B or contain only
parts thereof. The similarities are compiled to indicate a possible route of domain evolution in the α-amylase family.
Received: 4 December 1996 / Accepted: 13 March 1997 相似文献
Aboveground disturbances are common in dynamic riparian environments, and Salix nigra is well adapted with a vigorous resprouting response. Soil moisture stresses are also common, and S. nigra is flood tolerant and drought sensitive. The objective of this study was to quantify nonstructural carbohydrate (NSC) reserves
in S. nigra following shoot removal and soil moisture treatments. NSC reserves provide energy for regeneration of shoot tissue until
new functional leaves are developed. Three soil moisture treatments: well-watered (W), periodic flooding (F) and drought (D);
and three shoot removal treatments: no shoots removed (R0), partial shoot removal (R1), and complete shoot removal (R2) were
applied. Plants were harvested when new shoot development was observed (day 13). Statistical significance in the 3 × 3-factorial
design was determined in two-factor ANOVA at P < 0.05. Both roots and cuttings were important reservoirs for NSC during resprouting response, with decreases in root (31%)
and cutting (14%) biomass in R2 compared to R0. Rapid recovery of photosynthetic surface area (from 15 to 37% of R0) was found
in R1. A clear pattern of starch mobilization was found in roots in R0, R1 and R2, with lowest root starch concentration in
W, F higher than W, and D higher than F. Shoot starch concentration was lower in F and D compared to W in R0, however, in
R1 shoot starch was reduced in W compared to F and D, possibly indicating reduced rates of translocation during soil moisture
stress. Evidence of osmotic adjustment was found in roots and shoots with higher total ethanol-soluble carbohydrates (TESC)
during soil moisture stress in F and D treatments. Total plant NSC pool was greater in F and D treatments compared to W, and
progressively reduced from R0 to R1 to R2. Results indicated negative effects of drought, and to a lesser extent periodic
flooding on resprouting response in S. nigra, with implications for reduced survival when exposed to combined stresses of aboveground disturbance and soil moisture. 相似文献
The possibility was considered that osmotic adjustment, the ability to accumulate solutes in response to water stress, may contribute to growth rate differences among closely-related genotypes of trees. Progeny variation in osmotic adjustment and turgor regulation was investigated by comparing changes in osmotic and pressure potentials, soluble carbohydrates, and amino acids in osmotically stressed seedlings in 4 full-sib progenies of black spruce [ Picea mariana (Mill.) B. S. P.] that differed in growth rate under drought. Osmotic stress was induced by a stepwise increase in the concentration of polyethylene glycol (PEG)-3350 from 10 (w/v) to 18 and 25%, which provided osmotic potentials in solution culture of -0.4, -1.0 and -2.0 MPa each for 3 days. All 4 progenies maintained a positive cell turgor even at 25% PEG, due to a significant decline in osmotic potential. Although total amino acids, principally proline, increased, ca 60% of the decrease in osmotic potential was attributable to soluble carbohydrates and glucose was the major osmoregulating solute. There was little progeny variation in any of measured parameters in unstressed seedlings. Compared to two slower-growing progenies, the two progenies capable of more vigorous growth under drought in the field accumulated more soluble carbohydrates (mainly glucose and fructose), developed lower osmotic potential and maintained higher turgor pressure when osmotically-stressed in solution culture. The ability to adjust osmotically and maintain turgor under drought stress could thus be a useful criterion for the early selection of faster-growing, drought-tolerant genotypes. 相似文献