Three cDNA clones (GmHSP23.9, GmHSP22.3, and GmHSP22.5) representing three different members of the low-molecular-weight (LMW) heat shock protein (HSP) gene superfamily were isolated and characterized. A fourth cDNA clone, pFS2033, was partially characterized previously as a full-length genomic clone GmHSP22.0. The deduced amino acid sequences of all four cDNA clones have the conserved carboxyl-terminal LMW HSP domain. Sequence and hydropathy analyses of GmHSP22, GmHSP22.3, and GmHSP22.5, representing HSPs in the 20 to 24 kDa range, indicate they contain amino-terminal signal peptides. The mRNAs from GmHSP22, GmHSP22.3, and GmHSP22.5 were preferentially associated in vivo with endoplasmic reticulum (ER)-bound polysomes. GmHSP22 and GmHSP22.5 encode strikingly similar proteins; they are 78% identical and 90% conserved at the amino acid sequence level, and both possess the C-terminal tetrapeptide KQEL which is similar to the consensus ER retention motif KDEL; the encoded polypeptides can be clearly resolved from each other by two-dimensional gel analysis of their hybrid-arrest translation products. GmHSP22.3 is less closely related to GmHSP22 (48% identical and 70% conserved) and GmHSP22.5 (47% identical and 65% conserved). The fourth cDNA clone, GmHSP23.9, encodes a HSP of ca. 24kDa with an amino terminus that has characteristics of some mitochondrial transit sequences, and in contrast to GmHSP22, GmHSP22.3, and GmHSP22.5, the corresponding mRNA is preferentially associated in vivo with free polysomes. It is proposed that the LMW HSP gene superfamily be expanded to at least six classes to include a mitochondrial class and an additional endomembrane class of LMW HSPs. 相似文献
Two proteins encoded by bacteriophage T7, the gene 2.5 single-stranded DNA binding protein and the gene 4 helicase, mediate homologous DNA strand exchange. Gene 2.5 protein stimulates homologous base pairing of two DNA molecules containing complementary single-stranded regions. The formation of a joint molecule consisting of circular, single-stranded M13 DNA, annealed to homologous linear, duplex DNA having 3'- or 5'-single-stranded termini of approximately 100 nucleotides requires stoichiometric amounts of gene 2.5 protein. In the presence of gene 4 helicase, strand transfer proceeds at a rate of > 120 nucleotides/s in a polar 5' to 3' direction with respect to the invading strand, resulting in the production of circular duplex M13 DNA. Strand transfer is coupled to the hydrolysis of a nucleoside 5'-triphosphate. The reaction is dependent on specific interactions between gene 2.5 protein and gene 4 protein. 相似文献
Interactive effects of seven years of compaction due to wheel traffic and tillage on root density, formation of arbuscular mycorrhizae, above-ground biomass, nutrient uptake and yield of corn (Zea mays L.) were measured on a coastal plain soil in eastern Alabama, USA. Tillage and soil compaction treatments initiated in 1987 were: 1) soil compaction from tractor traffic with conventional tillage (C,CT), 2) no soil compaction from tractor traffic with conventional tillage (NC,CT), 3) soil compaction from tractor traffic with no-tillage (C,NT), and, 4) no soil compaction from tractor traffic with no-tillage (NC,NT). The study was arranged as a split plot design with compaction from wheel traffic as main plots and tillage as subplots. The experiment had four replications. In May (49 days after planting) and June, (79 days after planting), root biomass and root biomass infected with arbuscular mycorrhizae was higher in treatments that received the NC,NT treatment than the other three treatments. In June and July (109 days after planting), corn plants that received C,CT treatment had less above-ground biomass, root biomass and root biomass infected with mycorrhizae than the other three treatments. Within compacted treatments, plants that received no-tillage had greater root biomass and root biomass infected with mycorrhizae in May and June than plants that received conventional tillage. Corn plants in no-tillage treatments had higher root biomass and root biomass infected with mycorrhizae than those in conventional tillage. After 7 years of treatment on a sandy Southeastern soil, the interactive effects of tillage and compaction from wheel traffic reduced root biomass and root biomass infected with mycorrhizae but did not affect plant nutrient concentration and yield. ei]J H Graham 相似文献
A thick (ca. 40 m) sequence of coastal eolian sediments occurs on a narrow peninsula on the eastern end of the island of Madeira, located in the Eastern Atlantic at 33°N latitude. The sediments consist of black volcanic sands (with or without bioclasts) as well as clay units up to 2 m thick. A series of inceptisols (Eutrochrepts) and one alfisol (a Hapludalf) are developed in these sediments. Land snail shells and secondary carbonates, in the form of well-developed rhizoliths, calcretes, fissure-fills, and soil nodules, are present in abundance. The chronology of the sequence was determined by 14C and U---Th analyses of land snail shells and secondary carbonates and amino acid epimerization analysis of land snail shells. All sediments, including the clay units, are originally of eolian origin, derived from the beach to the south of the deposit, but some have been redeposited by colluviation. Temporal variation in the lithology of the sediments relates to variations in sea-level, with black sands being deposited during lower sea level stands and clays at the lowest. It is suggested that fine marine sediments, exposed during low sea-level stands, may also be the dominant source of silty or clayey units in other coastal eolian deposits in the subtropical Atlantic and Mediterranean.
The sequence spans from 200,000–300,000 years ago up to the 20th century. Sedimentation was discontinuous and often rapid; erosional hiatuses are present. During the Holocene, eolian sands started accumulating at 8200 yr B.P. during a transgressive phase and stopped at 4500 yr B.P. as sea level approached its present height. Colluviation increased dramatically following the first human settlement of the island in the 15th century and continued up to the 20th century, as dated by amino acid epimerization analysis of land snails. Earlier periods of colluviation were identified from the age distribution of land snail shells redeposited in younger colluvium.
Paleoenvironmental reconstruction was based mainly on soil and sediment features (including rhizolith morphology) and land snail faunas but also on stable isotope variations (13C, 18O) in land snails and secondary carbonates, pollen (generally not well preserved), and phytoliths. Most of the portion of the Middle Pleistocene represented in the sequence was characterized by moderately dry conditions, in comparison to the late Pleistocene and Holocene. During the last interglacial, relatively wet conditions occurred, wetter than during the Holocene interglacial. Moderately moist conditions were present during the accumulation of the thick unit dating to ca. 80,000 yr B.P. As sea level fell subsequent to this period, conditions appear to have become drier. Starting ca. 50,000–55,000 yr B.P., conditions were especially wet, but prior to the last glacial maximum, markedly arid conditions ensued. Toward the end of the last glacial, wet conditions returned and produced the best-developed soil preserved in the sequence. Moderately moist conditions occurred during the early to middle Holocene but apparently become slightly drier after 4500 yr B.P. The impact of human settlement can be seen in the loss of woody vegetation and enhanced gullying and colluviation during the last ca. 500 years. 相似文献
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
Ligand binding to a linear lattice composed of N sites, under general conditions of cooperativity and number of sites covered upon binding, m, is approached in terms of the theory of contracted partition functions. The partition function of the system obeys a recursion relation leading to a generating function that provides an exact analytical solution for any case of interest. Site-specific properties of the lattice are derived from simple transformations of the analytical expressions. The McGhee-von Hippel model is obtained as a special case in the limit N --> infinity. The derivation is straightforward and involves no combinatorial arguments. Partition functions and site-specific properties are also derived for the case of non-cooperative binding to a two-dimensional torus of length N, containing s sites in its section for a total of sN sites. The torus provides a relevant model for ligand binding to double-stranded DNA (s = 2) or protein helices (s = 3,4). It is proved that non-cooperative binding to the two-dimensional torus can mimic cooperative binding to a one-dimensional linear lattice when m = s. The dimensional embedding of the lattice and the geometry of interaction of its sites play a crucial role in defining the binding properties of the system accessible to experimental measurements. Hence, caution must be exercised in the interpretation of Scatchard plots in terms of the one-dimensional McGhee-von Hippel model, especially when m < or = 4 and the geometry of the system is clearly two-dimensional. 相似文献