共查询到20条相似文献,搜索用时 15 毫秒
1.
The evolution of minor vein phloem and phloem loading 总被引:1,自引:0,他引:1
Phylogenetic analysis provides a rational basis for comparative studies of phloem structure and phloem loading. Although several types of minor vein companion cell have been identified, and progress has been made in correlating structural features of these cells with loading mechanisms, little is known about the phylogenetic relationships of the different types. To add to the available data on companion cells, we analyzed the ultrastructure of minor veins in Euonymus fortunei and Celastrus orbiculatis (Celastraceae) leaves and determined that in these species they are specialized as intermediary cells. This cell type has been implicated in symplastic phloem loading. The data were added to published data sets on minor vein phloem characteristics, which were then mapped to a well-supported molecular tree. The analysis indicates that extensive plasmodesmatal continuity between minor vein phloem and surrounding cells is ancestral in the angiosperms. Reduction in plasmodesmatal frequency at this interface is a general evolutionary trend, punctuated by instances of the reverse. This is especially true in the case of intermediary cells that have many plasmodesmata, but other distinguishing characteristics as well, and have arisen independently at least four, and probably six, times in derived lineages. The character of highly reduced plasmodesmatal frequency in minor vein phloem, common in crop plants, has several points of origin in the tree. Thus, caution should be exercised in generalizing results on apoplastic phloem loading obtained from model species. Transfer cells have many independent points of origin, not always from lineages with reduced plasmodesmatal frequency. 相似文献
2.
3.
Measurements of diurnal diameter variations of the xylem and phloem are a promising tool for studying plant hydraulics and xylem-phloem interactions in field conditions. However, both the theoretical framework and the experimental verification needed to interpret phloem diameter data are incomplete. In this study, we analytically evaluate the effects of changing the radial conductance between the xylem and the phloem on phloem diameter variations and test the theory using simple manipulation experiments. Our results show that phloem diameter variations are mainly caused by changes in the radial flow rate of water between the xylem and the phloem. Reducing the hydraulic conductance between these tissues decreases the amplitude of phloem diameter variation and increases the time lag between xylem and phloem diameter variation in a predictable manner. Variation in the amplitude and timing of diameter variations that cannot be explained by changes in the hydraulic conductance, could be related to changes in the osmotic concentration in the phloem. 相似文献
4.
5.
6.
7.
8.
Sherwin Carlquist 《Brittonia》2013,65(4):477-495
Interxylary phloem is here defined as strands or bands of phloem embedded within the secondary xylem of a stem or root of a plant that has a single vascular cambium. In this definition, interxylary phloem differs from intraxylary phloem, bicollateral bundles, pith bundles, and successive cambia. The inclusive but variously applied terms included phloem and internal phloem must be rejected. Histological aspects of interxylary phloem are reviewed and original data are presented. Topics covered include duration of interxylary phloem; relationship in abundance between sieve tubes in external phloem and interxylary phloem; distinctions between interxylary and intraxylary phloem; presence of parenchyma, fibers, and crystals in the interxylary phloem strands; development of cambia within interxylary phloem strands; three-dimensionalization and longevity of phloem, systematic distribution of interxylary phloem; physiological significance; and habital correlations. No single physiological phenomenon seems to explain all instances of interxylary phloem occurrence, but rapidity and volume of photosynthate transport seem implicated in most instances. 相似文献
9.
Diversity of the superfamily of phloem lectins (phloem protein 2) in angiosperms 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dinant S Clark AM Zhu Y Vilaine F Palauqui JC Kusiak C Thompson GA 《Plant physiology》2003,131(1):114-128
Phloem protein 2 (PP2) is one of the most abundant and enigmatic proteins in the phloem sap. Although thought to be associated with structural P-protein, PP2 is translocated in the assimilate stream where its lectin activity or RNA-binding properties can exert effects over long distances. Analyzing the diversity of these proteins in vascular plants led to the identification of PP2-like genes in species from 17 angiosperm and gymnosperm genera. This wide distribution of PP2 genes in the plant kingdom indicates that they are ancient and common in vascular plants. Their presence in cereals and gymnosperms, both of which lack structural P-protein, also supports a wider role for these proteins. Within this superfamily, PP2 proteins have considerable size polymorphism. This is attributable to variability in the length of the amino terminus that extends from a highly conserved domain. The conserved PP2 domain was identified in the proteins encoded by six genes from several cucurbits, celery (Apium graveolens), and Arabidopsis that are specifically expressed in the sieve element-companion cell complex. The acquisition of additional modular domains in the amino-terminal extensions of other PP2-like proteins could reflect divergence from its phloem function. 相似文献
10.
11.
12.
13.
14.
The phloem mobility of glucosinolates 总被引:6,自引:2,他引:4
The transport properties of glucosinolates within Brassica
napus are of interest as identification of the mechanism of
transport could lead to lower levels being obtained in specific tissues
such as the seeds. The phloem mobility of
35S-gluconapin (but-3-enylglucosinolate) and
35S-desulphogluconapin in oilseed rape plants has
been inferred from tissue distribution patterns, as well as from observed
coincident phloem mobility of 3H-gluconapin and
14C-sucrose. The measured relative phloem mobilities
for sinigrin (2-propenylglucosinolate),
3H-gluconapin,
35S-desulphogluconapin,
35S-desulphosinigrin,
14C-tryptophan, 3H-AIB
(-aminoisobutyric acid), and literature
values for a reduced 3H-oligogalacutonide elicitor
(degree of polymerization 6) and 14C-IAA
(indolylacetic acid), have been compared with the predicted values obtained
using the Kleier model for phloem mobility of xenobiotics. All the above
compounds show phloem systemicity, demonstrated using the
Ricinus assay, as predicted by the model. Log
Kow (octanol-water partition coefficient) values for
glucosinolates and desulphoglucosinolates measured at pH 4 and pH 7, and
the effect of pH on uptake by oilseed rape embryos are provided as evidence
against a weak acid trap mechanism acting in either the phloem mobility or
the accumulation of glucosinolates in oilseed rape embryos. The phloem
mobility of glucosinolates is explained by the intermediate permeability
hypothesis. In conclusion, it would appear that glucosinolates like other
groups of endogenous compounds have physicochemical properties allowing
phloem mobility as predicted by the Kleier model.Keywords:
Brassica napus, Ricinus communis, phloem
mobility, glucosinolates, Kleier model.
相似文献
15.
《Structure (London, England : 1993)》2023,31(4):464-479.e5
- Download : Download high-res image (243KB)
- Download : Download full-size image
16.
Transport of macromolecules through plasmodesmata and the phloem 总被引:2,自引:0,他引:2
Cell-to-cell communication is a pivotal process in the determination of cell fate during development and physiological adaptation in response to environmental stimuli. The intercellular trafficking of proteins and RNAs has emerged as a novel mechanism of cell-to-cell signaling in plants. As a strategy for efficient intercellular communication, plants have evolved plant-specific symplasmic communication networks via plasmodesmata (PD) and the phloem. PD are symplasmic channels connecting the cytoplasm of neighboring cells and are responsible for the local exchange of metabolites and signaling molecules. The phloem is the sieve-tube system that allows rapid, long-distance translocation of molecules. Together, PD and phloem conduits have been shown to allow the transport of proteins and RNAs in non-selective or/and selective modes. This review describes the current understanding of macromolecule trafficking through PD and the phloem. 相似文献
17.
S. Z. Ivanova A. G. Gorshkov A. V. Kuzmin I. I. Gordienko V. A. Babkin 《Russian Journal of Bioorganic Chemistry》2012,38(7):769-774
The paper presents results of the investigation of phenolic compounds of the bark of the Siberian larch (Larix sibirica Ledeb.) and the Dahurian larch (Larix gmelini (Rupr.) Rupr). The flavonoids, stilbenes, phenolic acids have been identified on the basis of chemical, chromatographic and spectral data. Quercetin-3-O-??-L-rhamnopyranoside has been found for the first time in the bark of the Larix genus. Phenolic compounds with pyrocatechol type of substitution of aromatic ring have been found to dominate in the phloem of the larch species considered. 相似文献
18.
A. Schulz 《Protoplasma》1986,130(1):12-26
Summary 48 hours after interrupting the root stele ofPisum, wound phloem initiated (proximally or distally to the wound) to reconnect the vascular stumps was found to contain some nucleate wound-sieve elements. At the elongating end of an incomplete wound-sieve tube these elements exhibit a sequence of ultrastructural changes as known from protophloem-sieve tubes. Elongation occurs by the addition of newly divided (wound-) sieve-element/companion-cell complexes. In order to dedifferentiate and assume a new specialization formerly quiescent stelar or cortical cells require at least one (mostly more) preliminary division. Companion cells are consequently obligatory sister cells to wound-sieve elements.By reconstruction using serial sections it could be shown that wound-sieve tubes elongate bidirectionally, starting in an early activated procambial cell of the stele. The elongation is directed by the existence of plasmodesmata, preferably when lying in primary pit fields, and by the plane of preceding divisions. Thus, the developing wound-sieve tube can deviate from the damaged bundle and radiate into the cortex as soon as the plane of the preceding divisions is favourable. In the opposite direction, elongating wound-sieve tubes run parallel to pre-existing phloem traces, thus broading their base at the bundle for the deviating part of the wound-sieve tube. Frequently an individual wound-sieve tube is supplemented at the bundle by a further wound-sieve tube which is partly running parallel to it. Both sieve tubes are interlinked with sieve plates by three-poled sieve elements.Ultrastructurally, the developmental changes of nucleate wound-sieve elements follow the known pattern. In spite of its contrasting origin and odd shape a mature wound-sieve element eventually has the same contents as regular sieve elements: sieve-element plastids, mitochondria, stacked ER and small amounts of P-protein within an electronlucent cytoplasm. 相似文献
19.
Metal speciation in xylem and phloem exudates 总被引:5,自引:0,他引:5
Summary Two computer programs based on simultaneous chemical equilibria were compared for calculation of chemical species in xylem
exudates. The first program, CHELATE, was developed to calculate the chemical species in xylem exudates while GEOCHEM was
developed to calculate the speciation of natural aquatic systems. The output of the two programs should be similar since they
are based on similar calculations. Data input to the programs consisted of concentration data for Ca, Cu, Fe, Mg, Mn, Zn,
NH4, PO4, pH and 28 organic ligands reported for xylem exudates from soybean (Glycine max (L.) Merr.) and tomato (Lycopersicon esculentum Mill.) plants grown in nutrient solution17. The organic ligands included amino acids and low molecular weight organic acids (e.g., citric and malic). With the exception of Fe, there were large differences between CHELATE and GEOCHEM in the calculated
speciation of nearly all metals in the xylem exudates. In general, there was better agreement between the programs for the
speciation of alkaline earth metals than for transition metals. Discrepancies between the two programs were attributed to
differences in 1) species considered and 2) stability constants. GEOCHEM considered a greater number of possible complexes.
In addition, stability constants for some complexes differed by as much as 10 fold between the two programs. When the data
base for GEOCHEM and CHELATE were the same, the output from CHELATE and GEOCHEM was almost identical. Thus, computations performed
by the two programs are equally valid, but it is essential that the data base used in chemical models be verified before interpreting
the output.
Average concentration data for Al, Au, Ca, Cu, Fe, K, La, Mg, Mn, Na, Rb, Zn, Cl, MoO4, PO4, SO4, HVO4, pH and 18 organic ligands in phloem exudates from Yucca (Yucca flaccida Haw.) were complied from available literature and analyzed by GEOCHEM. Amino acids were the predominant organic ligand analyzed.
Calculations revealed that alkali metals existed almost totally as the free ionic species (≥99%) whereas alkaline earth metals
were transported as complexes with organic acids (oxalic, malic, and asparagine). Aluminum and Fe were present as hydroxyl
species while <1% of micronutrients were transported as the free ion. Major micronutrient species were Cu-glutamine, Mn-asparagine
and Zn-alanine. Information on calculated species present in phloem exudates could be useful to guide studies for isolation
of metal-ligand complexes in phloem exudates. 相似文献
20.
The phloem of pumpkin and squash contains a dimeric chitin-binding lectin called PP2 (phloem protein 2). We have isolated three genomic clones from pumpkin (Cucurbita maxima Duch.) that encoded PP2. One clone, gPC13-1, contained two PP2 genes that were 99.8% identical over a region of 3055 nucleotides. This conserved region included 1922 bp of 5 non-coding sequence, 844 bp of protein coding sequence (including two introns), and 289 bp of 3 non-coding sequence. To examine the conservation of the phloem lectin within the genus Cucurbita, we analyzed nine different species for PP2, its mRNA, and the genes that encode PP2. DNA blot analysis indicated that each species contained genes that encoded PP2, however, there was considerable restriction fragment length polymorphism (RFLP) among the species. PP2 gene copy number reconstructions indicated that PP2 is encoded by a small gene family (two to eight genes). Although a high level of PP2 DNA polymorphism existed among species, a single mRNA (ca. 1 kb) was detected in each species. PP2, affinity-purified from the vascular exudate of each species, reacted with PP2-specific antibodies; five species contained a single PP2 polypeptide while four species contained two PP2 polypeptides. 相似文献