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101.
A pyrenoid-based carbon-concentrating mechanism is present in terrestrial bryophytes of the class Anthocerotae 总被引:2,自引:0,他引:2
It has been widely accepted that carbon assimilation in bryophytes is exclusively based on the conventional C3 photosynthetic pathway. The occurrence of biochemical CO2-concentrating mechanisms (C4 or Crassulacean acid metabolism), which have developed in plants in the last 20–100 million years, has been discounted for bryophytes from studies of the carbon isotope composition (13C) of organic material. In contrast cyanobacteria and many algae show active accumulation of dissolved inorganic carbon via biophysical CO2-concentrating mechanisms which are also found in the photobiont partners in certain lichens. The presence of a pyrenoid, a granular particle within the chloroplast, has been linked with CO2-concentrating mechanism activity in green algae and lichens and we now show that such a mechanism is categorically associated with the occurrence of a pyrenoid in bryophytes belonging to the class of Anthocerotae. These observations have significant evolutionary implications for the development of terrestrial photosynthesis during the colonisation of the land, raising the intriguing question of why the pyrenoid-based CO2-concentrating mechanism did not persist in the terrestrial environment.Abbreviations and Symbols CCM
carbon-concentrating mechanism
- DIG
dissolved inorganic carbon (CO2+HCO
3
-
+CO
2
-
)
- DW
dry weight
- K0.5
external concentration of CO2 at which half-maximal rates of CO2 assimilation are reached
- Rubisco
ribulose-l,5-bisphosphate carboxylase-oxygenase
-
carbon isotope discrimination (%)
- 13C
carbon isotope ratio (%)
This work was supported by the Natural Environment Research Council (GR3/8813) and the Leverhulme Trust. We thank Prof. A. Roy Perry (National Museum of Wales, Cardiff), Dr. B. Coppins and Mr. D. Long (Royal Botanic Garden Edinburgh) for access to herbarium specimens and Mr. M. Fletcher for providing living bryophytes. 相似文献
102.
The rad16 gene of Schizosaccharomyces pombe: a homolog of the RAD1 gene of Saccharomyces cerevisiae. 总被引:6,自引:2,他引:4
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A M Carr H Schmidt S Kirchhoff W J Muriel K S Sheldrick D J Griffiths C N Basmacioglu S Subramani M Clegg A Nasim et al. 《Molecular and cellular biology》1994,14(3):2029-2040
The rad10, rad16, rad20, and swi9 mutants of the fission yeast Schizosaccharomyces pombe, isolated by their radiation sensitivity or abnormal mating-type switching, have been shown previously to be allelic. We have cloned DNA correcting the UV sensitivity or mating-type switching phenotype of these mutants and shown that the correcting DNA is encompassed in a single open reading frame. The gene, which we will refer to as rad16, is approximately 3 kb in length, contains seven introns, and encodes a protein of 892 amino acids. It is not essential for viability of S. pombe. The predicted protein is the homolog of the Saccharomyces cerevisiae RAD1 protein, which is involved in an early step in excision-repair of UV damage from DNA. The approximately 30% sequence identity between the predicted proteins from the two yeasts is distributed throughout the protein. Two-hybrid experiments indicate a strong protein-protein interaction between the products of the rad16 and swi10 genes of S. pombe, which mirrors that reported for RAD1 and RAD10 in S. cerevisiae. We have identified the mutations in the four alleles of rad16. They mapped to the N-terminal (rad10), central (rad20), and C-terminal (rad16 and swi9) regions. The rad10 and rad20 mutations are in the splice donor sequences of introns 2 and 4, respectively. The plasmid correcting the UV sensitivity of the rad20 mutation was missing the sequence corresponding to the 335 N-terminal amino acids of the predicted protein. Neither smaller nor larger truncations were, however, able to correct its UV sensitivity. 相似文献
103.
Three methods of increasing the productivity of somatic embryogenesis in Medicago sativa L. were investigated. In the basic procedure, somatic embryos were initiated from young petioles and carried through several phases: callus formation, suspension culture, selection of the embryogenic fraction by sieving, development, maturation, desiccation and storage. The suspensions were normally separated into three fractions by sieving. Fraction I (<200 m) containing nonembryogenic cells or cell clusters was discarded. Fraction II (200–500 m) consisting of embryogenic cell clusters was collected for embryo development and maturation. Fraction III (over 500 M) containing the mixture of petiole residues with large pieces of calli and globular somatic embryos was usually discarded. Several methods to scale-up the suspension phase were unsuccessful. Direct subculture of the entire suspension by the addition of fresh liquid medium resulted in the loss of embryogenic capacity by the third subculture. Subculture of fraction II decreased embryogenic cell mass, and hence reduced total productivity. The recycling of fraction III back to fresh B5g liquid medium resulted in high productivity in the first culture but further subculture of this fraction resulted in a rapid decline in the embryogenic capacity.As an alternative, somatic embryos from the first tissue culture cycle were also used as explants for the initiation of secondary embryogenic callus. The embryogenic capacity of these somatic embryo explants declined rapidly as they matured. More than 100 secondary somatic embryos could be induced from embryo explants removed from development medium at 10 days after sieving the suspension, but only 40 somatic embryos were produced from each mature somatic embryo explant, and 13 from desiccated embryos. The secondary somatic embryos were comparable to the primary embryos in quality according to germination tests. The implications of the results to the efficiency of somatic embryo production of Medicago are discussed.Abbreviations ABA
abscisic acid
- 2,4-d
2,4-dichlorophenoxyacetic acid
- DAS
days after sieving
- PPF
photosynthetic photon flux density
- SE
somatic embryo 相似文献
104.
Assembly of vaccinia virus: effects of rifampin on the intracellular distribution of viral protein p65. 总被引:21,自引:19,他引:2
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The cytoplasmic assembly of vaccinia virus is reversibly blocked by the antibiotic rifampin, leading to the accumulation of partially membrane-delineated rifampin bodies in infected cells. Rifampin-resistant vaccinia virus mutants have point mutations in the D13L gene, which is controlled by a late promoter and expresses a 65-kDa protein, designated p65. To further characterize the mechanism of rifampin inhibition and the function of p65 in virus assembly, we raised antibodies to this protein. Immunoreactive p65 was expressed at late times of infection, and neither its expression nor its turnover was affected by rifampin. Virus-associated p65 could be extracted only with denaturing detergents from purified virions, suggesting that it is an integral viral component. Immunofluorescence studies showed that p65 is localized to the sites of virus assembly. Also, immunoelectron microscopy showed p65 to be associated with viral crescents as well as spherical, immature virions, in both cases predominantly on the inner or concave surface. In the presence of rifampin, p65 was found in large, cytoplasmic inclusion bodies that were distinct from rifampin bodies. The rifampin bodies themselves were labeled with p65 antibodies only after reversal of the rifampin block, predominantly on the viral crescents which rapidly formed following removal of the drug. We propose that p65 functions as an internal scaffold in the formation of viral crescents and immature virions, analogously to the matrix proteins of other viruses. 相似文献
105.
Stephanie W. Watts Marlene L. Cohen† Patrick Q. Mooney† Bryan G. Johnson† Darryle D. Schoepp† Melvyn Baez† 《Journal of neurochemistry》1994,62(3):934-943
Abstract: Heterogeneity of the 5-hydroxytryptamine2 (5-HT2) receptor across species has been implicated in several pharmacological and physiological studies. Although 5-HT2 receptors in the rat have been linked to increases in Phosphoinositide (PI) hydrolysis, little evidence exists to support the association of guinea pig 5-HT2 receptors with Pl hydrolysis, the second messenger generally linked with 5-HT2receptors. In the present study, we have taken a molecular and biochemical approach to determining whether species differences in brain 5-HT2 receptors exist between rat and guinea pig. First, we isolated partial cortical 5-HTa receptor cDNA clones that encompassed the third intracellular loop, a receptor area putatively important in receptor-effector coupling. The amino acid sequences deduced from the cDNA clones for rat and guinea pig brain 5-HT2 receptor were 97% homologous. However, the guinea pig 5-HT2 receptor had two tandem substitutions that disrupted a potential alpha helix in the region of the third cytoplasmic loop, which theoretically could alter the intracellular coupling of the guinea pig cortical 5-HT2 receptor. Because of these molecular differences, we examined further the pharmacological activation of the brain 5-HT2 receptor from guinea pig. 5-HT and the 5-HT2 receptor agonist α-methyl-5-HT increased PI hydrolysis in guinea pig cortical slices whereas the 5-HT1c receptor agonist 5-methyltryptamine was significantly less potent. In addition, the 5-HT2 receptor antagonists LY53857, ketanserin, and spiperone blocked 5-HT-stimulated Pl hydrolysis. These pharmacological data suggested that activation of the 5-HT2 receptor in guinea pig cortical slices was associated with PI hydrolysis. Thus, although areas of the guinea pig brain 5-HT2 receptor that influence receptor-effector coupling were different from the rat, such differences were not critical to receptor-effector coupling because, as in the rat, guinea pig brain 5-HT2 receptors were also coupled to PI hydrolysis. 相似文献
106.
The decline and disappearance of Littorella uniflora from oligotrophic waters which have become eutrophic has been associated with shading or reduced CO2 supply. However NO
inf3
sup–
concentrations can reach very high levels (100–2000 mmol m–3 compared with <1–3 in oligotrophic habitats). To investigate the impact of NO
inf3
sup–
loading alone, plants were grown under three NO
inf3
sup–
regimes (very low, near-natural and high). The interactive effects of NO
inf3
sup–
and photon flux density (low and high regimes) on N assimilation and accumulation, CO2 concentrating mechanisms, C3 photosynthesis and growth were also examined. The results were unexpected. Increased NO
inf3
sup–
supply had very little effect on photosynthetic capacity, crassulacean acid metabolism (CAM) or lacunal CO2 concentrations ([CO2]i), although there was considerable plasticity with respect to light regime. In contrast, increased NO
inf3
sup–
supply resulted in a marked accumulation of NO
inf3
sup–
, free amino acids and soluble protein in shoots and roots (up to 25 mol m–3, 30 mol m–3 and 9 mg g–1 fresh weight respectively in roots), while fresh weight and relative growth rate were reduced. Total N content even under the very low NO
inf3
sup–
regime (1.6–2.3%) was mid-range for aquatic and terrestrial species (and 3.1–4.3% under the high NO
inf3
sup–
regime). These findings, together with field data, suggest that L. uniflora is not growth limited by low NO
inf3
sup–
supply in natural oligotophic habitats, due not to an efficient photosynthetic nitrogen use but to a slow growth rate, a low N requirement and to the use of storage to avoid N stress. However the increased NO
inf3
sup–
concentrations in eutrophic environments seem likely have detrimental effects on the long-term survival of L. uniflora, possibly as a consequence of N accumulation. 相似文献
107.
B. S. Griffiths 《Plant and Soil》1994,164(1):25-33
Food web studies from a range of ecosystems have demonstrated that the fauna contributes about 30% of total net nitrogen mineralization.
This results mainly from the activities of microbial-feeding microfauna (nematodes and protozoa). Microbial and microfaunal
activity is concentrated at spatially discrete and heterogeneously distributed organic substrates, including the rhizosphere.
The dynamics of microfauna and their effect on nutrient cycling and microbial processes at these sites is reviewed. The potential
manipulation of microfauna, either as an experimental tool to further understand soil microbial ecology or as a practical
means of managing nutrient flows in agroecosystems, is discussed. 相似文献
108.
Artificial destratification of a small tropical reservoir: effects upon the phytoplankton 总被引:3,自引:3,他引:0
Seasonal changes in the phytoplankton community of a small tropical reservoir were monitored over a four year period comprising
of an initial two seasonal cycles during which the water column stratified strongly for extended periods each year, and two
further seasonal cycles after installation of a mechanical aeration system to induce artificial destratification.
In the unmanaged reservoir, the concentration of chlorophyll a at 0.5 m reached maximum values (on one occasion > 90 mg m−3) when the water column was stratified and the epilimnion was very shallow (ca 2 m depth). The hypolimnion at this time was anoxic (less than 2% oxygen saturation) and had a high concentration of bacteriochlorophyll
(100–200 mg m−3).
The phytoplankton community of the unmanaged reservoir was generally dominated by cyanobacteria (Cylindrospermopsis raciborskii, Anabaena tenericaulis) during the warmer months of the year (November–March) (but replaced by chlorophyta, dinophyceae and euglenophyceae after
periods of intense rain) and by bacillariophyceae (Synedra ulna var. chaseana, S. tenera) during the cooler, dry months.
In the artificially destratified reservoir (8 h aeration day−1), the phytoplankton community was largely dominated by diatoms except after depletion of the silica content of the water
column which caused diatoms to be replaced by cyanobacteria (dominated by A. tenericaulis) and a range of chlorophytes.
The changing pattern of stratification and circulation of the water column in the unmanaged reservoir caused repeated disruption
of the established phytoplankton assemblage with peaks of high biomass associated with transient cyanobacterial blooms. Continuous
aeration and the consequent increase in the ratio mixed: euphotic depth provided conditions suitable for dominance of the
phytoplankton by diatoms, as long as silica was available, and resulted in average chlorophyll levels higher than in the unmanaged
reservoir (120 ± 10 v. 64 ± 9 mg m−2).
Hierarchical fusion analysis based on the biomass of species differentiated the phytoplankton samples into cluster groups
that could be related primarily to stratification or mixing of the water column. 相似文献
109.
110.
Enzymological and mutational analysis of a complex primary hyperoxaluria type 1 phenotype involving alanine:Glyoxylate aminotransferase peroxisome-to-mitochondrion mistargeting and intraperoxisomal aggregation 总被引:6,自引:1,他引:5
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C. J. Danpure P. E. Purdue P. Fryer S. Griffiths J. Allsop M. J. Lumb K. M. Guttridge P. R. Jennings J. I. Scheinman S. M. Mauer N. O. Davidson 《American journal of human genetics》1993,53(2):417-432
Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease caused by a deficiency of the liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT). Three unrelated PH1 patients, who possess a novel complex phenotype, are described. At the enzymological level, this phenotype is characterized by a complete, or nearly complete, absence of AGT catalytic activity and reduced AGT immunoreactivity. Unlike normal individuals in whom the AGT is confined to the peroxisomal matrix, the immunoreactive AGT in these three patients was distributed approximately equally between the peroxisomes and mitochondria. The peroxisomal AGT appeared to be aggregated into amorphous core-like structures in which no other peroxisomal enzymes could be identified. Mutational analysis of the AGT gene showed that two of the three patients were compound heterozygotes for two previously unrecognized point mutations which caused Gly41→Arg and Phe152→Iso amino acid substitutions. The third patient was shown to be a compound heterozygote for the Gly41→Arg mutation and a previously recognized Gly170→Arg mutation. All three patients were homozygous for the Pro11→Leu polymorphism that had been found previously with a high allelic frequency in normal populations. It is suggested that the Phe152→Iso and Gly170→Arg substitutions, which are only eighteen residues apart and located in the same highly conserved internal region of 58 amino acids, might be involved in the inhibition of peroxisomal targeting and/or import of AGT and, in combination with the Pro11→Leu polymorphism, be responsible for its aberrant mitochondrial compartmentalization. On the other hand, the Gly41→Arg substitution, either in combination with the Pro11→Leu polymorphism or by itself, is predicted to be responsible for the intraperoxisomal aggregation of the AGT protein. 相似文献