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1.
Inhibition of protein synthesis by cycloheximide during vetch seed germination, did not prevent globulin breakdown as indicated
by a decrease in vicilin- and legumin-specific immunosignals on Western blots. Protein bodies isolated from embryo axes and
cotyledons of dry vetch (Vicia sativa L.) seeds using a non-aqueous method were found to be free of cytoplasmic and organellar contaminations. Lysates of these
purified protein bodies were capable of degrading globulins; this process was blocked by the cysteine proteinase (CPR) inhibitor
iodoacetic acid. Protein bodies contained the papain-like CPR2 and CPR4, and the legumain-like CPR VsPB2. In vitro assays showed that albumin extracts from protein bodies degraded oligopeptide substrates in the PepTag-Assay and degraded
the legumain substrate N-benzoyl-asparaginyl-p-nitroanilide. We conclude that, during germination, globulin mobilization is initiated by stored CPRs in protein bodies of
embryonic axes as well as cotyledons, and that de-novo-formed proteolytic enzymes mainly mediate bulk degradation of stored globulin in cotyledons after germination.
Received: 14 February 2000 / Accepted: 16 August 2000 相似文献
2.
The temporal and spatial distribution of cysteine proteinases (CPRs) was analyzed immunologically and by in situ hybridization to identify the CPRs involved in the initiation of storage-globulin degradation in embryonic axes and cotyledons
of germinating vetch (Vicia sativa L.). At the start of germination several CPRs were found in protein bodies in which they might have been stored in the mature
seeds. Cysteine proteinase 1 was predominantly found in organs like the radicle, which first start to grow during germination.
Cysteine proteinase 2 was also present at the start of germination but displayed a less-specific histological pattern. Proteinase
B was involved in the globulin degradation of vetch cotyledons as well. The histological pattern of CPRs followed the distribution
of their corresponding mRNAs. The latter were usually detected earlier than the CPRs but the in situ hybridization signals were histologically not as restricted as the immunosignals. Proteolytic activity started in the radicle
of the embryonic axis early during germination. Within 24 h after imbibition it had also spread throughout the whole shoot.
At the end of germination, newly synthesized CPRs might have supplemented the early detectable CPRs in the axis. In the cotyledons,
only the abaxial epidermis and the procambial strands showed proteinase localization during germination. Both CPR1 and CPR2,
as well as the less common proteinase B, might have been present as stored proteinases. Three days after imbibition, proteolytic
activity had proceeded from the cotyledonary epidermis towards the vascular strands deeper inside the cotyledons. The histochemical
detection of the CPRs was in accordance with the previously described histological pattern of globulin mobilization in germinating
vetch [Tiedemann J, et al. (2000)]. A similar link between the distribution of CPRs and globulin degradation was found in
germinating seeds of Phaseolus vulgaris L. The coincidence of the histological patterns of globulin breakdown with that of the CPRs indicates that at least CPR1,
CPR2 and proteinase B are responsible for bulk globulin mobilization in the seeds of the two legumes.
Received: 14 February 2000 / Accepted: 16 August 2000 相似文献
3.
Schlereth A Becker C Horstmann C Tiedemann J Müntz K 《Journal of experimental botany》2000,51(349):1423-1433
Vicilin and legumin, the storage globulins of mature dry vetch (Vicia sativa L.) seeds, are found in protein bodies which are present not only in the cotyledons, but also in the radicle, axis and shoot (together, for reasons of simplicity, here called axis). When at 24 h after the start of imbibition (hai) the radicle breaks through the seed coat a major part of the globulins in the axis has already been degraded, whereas in the cotyledons globulin breakdown cannot yet be detected. Globulin mobilization starts with the degradation of vicilin. At 48 hai when globulin mobilization in the cotyledons just begins, the axis is already nearly depleted of globulins. Mobilization of storage globulin is probably brought about by a complex of different cysteine proteinases (CPRs). The papain-like CPR2 and CPR4, and the legumain-like VsPB2, together with their mRNAs, are already present in axes and cotyledons of dry seeds. This means that they must have been formed during seed maturation. Additional papain-like CPRs are formed later during germination and seedling growth. CPR4 and VsPB2 together with their corresponding mRNAs become undetectable as germination and seedling growth proceed. VsPB2 and VsPB2-mRNA are substituted by the homologous legumain-like proteinase B and its mRNA. The composition of stored and newly formed CPRs undergoes developmental changes which differ between axes and cotyledons. It is concluded that storage globulin mobilization in germinating vetch seeds is started by stored CPRs, whereas the mobilization of the bulk of globulin is predominantly mediated by CPRs which are formed de novo. 相似文献
4.
Heteroblasty in Arabidopsis thaliana was analyzed in a variety of plants with mutations in leaf morphology using a tissue-specific β-glucuronidase gene marker.
Some mutants exhibited their mutant phenotypes specifically in foliage leaves. The phenotypes associated with the foliage-leaf-specific
mutations were also found to be induced ectopically in cotyledons in the presence of the lec1 mutation. Moreover, the features of an emf1lec1 double mutant showed that cotyledons can be partially converted into carpelloids. When heteroblastic traits were examined
in foliage leaves in the presence of certain mutations or natural deviations by histochemical analysis of the expression of
the tissue-specific marker gene, it was found that ectopic expression of the developmental program for the first foliage leaves
in lec1 cotyledons seemed to affect the heteroblastic features of the first set of foliage leaves, while foliage leaves beyond the
third position appeared normal. Similarly, in wild-type plants, discrepancies in heteroblastic features, relative to standard
features, of foliage leaves at early positions seemed to be eliminated in foliage leaves at later positions. These results
suggest that heteroblasty in foliage leaves might be affected in part by the heteroblastic stage of the preceding foliage
leaves but is finally controlled autonomously at each leaf position.
Received: 9 July 1999 / Accepted: 17 August 1999 相似文献
5.
Narbonin is a 2S protein from the globulin fraction of narbon bean (Vicia narbonensis L.) cotyledons. Its amino acid composition and the pattern of its regulated accumulation in developing seeds led to the suggestion
that narbonin could be a storage protein. Therefore, it was expected to be present in protein bodies of the storage tissue
cells. Comparison of the cDNA-derived amino acid sequence with a directly determined partial N-terminal sequence revealed
that the primary translation product of narbonin mRNA lacks a transient N-terminal signal peptide (V.H. Nong et al., 1995,
Plant Mol Biol 28: 61–72). Narbonin polypeptides that had been synthesized in a cell-free translation system supplemented
with dog pancreas microsomes were not protected against degradation by posttranslationally added proteases (protease protection
assay). In accordance with the lack of a signal peptide this indicates that the polypeptide was not cotranslationally sequestered
into the microsomes. The protein-body fraction that had been isolated from mature narbon bean cotyledons by a non-aqueous
gradient centrifugation procedure was free of narbonin; this was found in the soluble cell fraction. In electron micrographs,
narbonin could be localized in the cytoplasm using the immuno gold-labelling technique. Previously, it had already been shown
that narbonin is too slowly degraded during narbon bean germination to act as a storage protein. From all these results it
has to be concluded that narbonin is a cytoplasmic protein which does not belong to the storage proteins in the restricted
sense. Other possible functions are discussed.
Received: 18 November 1996 / Accepted: 28 February 1997 相似文献
6.
Seeds of Cichorium intybus L. var. foliosum cv. Flash were sown in acid-washed vermiculite and grown in a controlled-environment growth chamber. After 1 month of growth,
plantlets did not contain sucrose:sucrose 1-fructosyltransferase (1-SST), the key enzyme in fructan biosynthesis. No fructan
could be observed. Some of the plants were submitted to drought for 2 weeks. Glucose, fructose and sucrose concentrations
increased in roots and leaves of stressed plants and the fructan concentration in roots and leaves was ten times higher than
in control plants. The onset of fructan synthesis coincided with the increase in 1-SST activity in roots. Expression of the
1-SST gene could be observed in roots and leaves of stressed plants.
Received: 12 July 1999 / Accepted: 16 October 1999 相似文献
7.
During sunflower (Helianthus annuus L.) seed formation there was an active period of lipid biosynthesis between 12 and 28 days after flowering (DAF). The maximum
in-vitro acyl-acyl carrier protein (ACP) thioesterase activities (EC 3.1.2.14) were found at 15 DAF, preceding the largest
accumulation of lipid in the seed. Data from the apparent kinetic parameters, V
max and K
m, from seeds of 15 and 30 DAF, showed that changes in acyl-ACP thioesterase activity are not only quantitative, but also qualitative,
since, although the preferred substrate was always oleoyl-ACP, the affinity for palmitoyl-ACP decreased, whereas that for
stearoyl-ACP increased with seed maturation. Bisubstrate assays carried out at 30 DAF seemed to indicate that the total activity
found in mature seeds is due to a single enzyme with 100/75/15 affinity for oleoyl-ACP/stearoyl-ACP/palmitoyl-ACP. In contrast,
at 15 DAF, enzymatic data together with partial sequences from cDNAs indicated the presence of at least two enzymes with different
properties, a FatA-like thioesterase, with a high affinity for oleoyl-ACP, plus a FatB-like enzyme, with preference for long-chain
saturated fatty acids, both being expressed during the active lipid biosynthesis period. Competition assays carried out with
CAS-5, a mutant with a higher content of palmitic acid in the seed oil, indicated that a modified FatA-type thioesterase is
involved in the mutant phenotype.
Received: 17 December 1999 / Accepted: 25 February 2000 相似文献
8.
Role of extensin peroxidase in tomato (Lycopersicon esculentum Mill.) seedling growth 总被引:3,自引:0,他引:3
It is proposed that inhibition of extensin peroxidase activity leads to a less rigid cell wall and thus promotes cell expansion
and plant growth. A low-molecular-weight inhibitor derived from the cell walls of suspension-cultured tomato cells was found
to completely inhibit extensin peroxidase-mediated extensin cross-linking in vitro at a concentration of 260 μg/ml. The inhibitor
had no effect upon guaiacol oxidation catalyzed by extensin peroxidase or horseradish peroxidase. We have demonstrated that
the light-irradiated inhibition of plant growth may be partially offset by inhibition of endogenous extensin peroxidase activity.
Overall plant growth was enhanced by up to 15% in the presence of inhibitor relative to control plants. Inhibitor-treated
and illuminated tomato hypocotyls grew up to 15% taller than untreated controls. The inhibitor had no effect upon etiolated
plants over a 15-d period, suggesting that only low levels of peroxidase-mediated cross-linking can be found in the cell walls
of etiolated plants. SDS-PAGE/Western blots of ionically bound protein from both etiolated and illuminated hypocotyls identified
a doublet at 57/58.5 kDa which is immuno-reactive with antibodies raised to tomato extensin peroxidase. Levels of the 58.5-kDa
protein, determined by SDS-PAGE, were at least threefold higher in illuminated tomato hypocotyls than in etiolated hypocotyls.
Three fold higher levels of extensin peroxidase, elevated in-vitro extensin cross-linking activity and 15% higher levels of
cross-linked, non-extractable extensin were observed in illuminated tomato hypocotyls compared with etiolated tomato hypocotyls.
This suggests that white-light inhibition of tomato hypocotyl growth appears to be mediated, at least partially, by deposition
of cell wall extensin, a process regulated by Mr-58,500 extensin peroxidase. Our results indicate that the contribution of peroxidase-mediated extensin deposition to plant
cell wall architecture may have an important role in plant growth.
Received: 22 July 1999 / Accepted: 11 October 1999 相似文献
9.
Summary. The presence of abundant oil bodies in the mature olive pollen grain has led us to focus on the behavior of these lipid bodies
during pollen development and in vitro pollen germination. The appearance, increase, and accumulation of lipid bodies have
been determined by following the sequential development of the pollen grain. Semithin slices of anthers and pollen grains
were stained with Sudan Black B in order to identify neutral lipids. Ultrastructural studies were also carried out. Our results
show a notable increase in lipid bodies between the young-pollen-grain stage and the mature-pollen-grain stage. Substantial
polarization of lipid bodies was observed after 1 or 2 h of pollen incubation in germination medium. During pollen tube growth,
the lipid bodies are located near the germinative aperture after 3 h of incubation, as well as inside the pollen tube, thus
suggesting that the lipid bodies move from the pollen grain to the pollen tube. After 7 h of germination the presence of lipid
bodies inside the pollen tube is no longer substantial. Our results support the idea that lipid bodies are involved in pollen
germination, stigma penetration, and pollen tube growth. These results are discussed in connection with their implications
for the pollen germination process.
Received June 4, 2002; accepted October 29, 2002; published online April 8, 2003
RID="*"
ID="*" Correspondence and reprints: Departamento de Bioquímica, Biología Celular y Molecular de Plantas, Estación Experimental
del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008 Granada, Spain. 相似文献
10.
Ion antagonism in phytochrome-mediated calcium-dependent germination of turions of Spirodela polyrhiza (L.) Schleiden 总被引:1,自引:0,他引:1
The light-dependent germination response of turions (resting fronds) is mediated by phytochrome and requires the presence
of Ca2+ in the medium (K.-J. Appenroth and H. Augsten, 1990, Photochem. Photobiol. 52: 61–65). The Ca2+ requirement of germination is apparent only in the presence of exogenous Mg2+. A competitive ion antagonism was demonstrated between Ca2+ and Mg2+ in this physiological response; Mg2+ could also be replaced by Ba2+ or Sr2+. Without exog-enous Mg2+, a Ca2+ concentration as low as 0.9 μM fulfilled the Ca2+ requirement. This type of ion antagonism resembled the competitive Ca/Mg interaction reported previously for calcium-binding
proteins. The physiological response was blocked by inhibitors of Ca2+ uptake (verapamil, La3+). It was concluded that uptake of Ca2+ from the external medium is an essential step in the phytochrome-mediated germination of turions. The results are in agreement
with the assumption that the uptake of Ca2+ is blocked at the side of entry by other alkaline earth ions. Treatment of turions with Mg2+ (1 mM) for 24 h at varying times after the red light pulse in otherwise virtually Ca2+-free KNO3 solution resulted in a response similar to a Ca2+ step-down treatment. This is in agreement with the assumption that the Ca2+- and the Mg2+-sensitive periods coincide. The ion interaction described here represents the first photophysiological example in plants
of an antagonistic effect between Ca2+ and Mg2+ similar to that which occurs in vitro with calmodulin.
Received: 12 June 1998 / Accepted: 28 December 1998 相似文献
11.
12.
Somatic embryogenesis induced by the simple application of abscisic acid to carrot (Daucus carota L.) seedlings in culture 总被引:3,自引:0,他引:3
Seedlings of carrot (Daucus carota L. cv. Red Cored Chantenay) formed somatic embryos when cultured on medium containing abscisic acid (ABA) as the sole source
of growth regulator. The number of embryos per number of seedlings changed depending on the concentration of ABA added to
the medium, with a maximum embryo number at 1 × 10−4 M ABA. Seedling age was critical for response to exogenous ABA; no seedling with a hypocotyl longer than 3.0 cm was able to
form an embryo. Removal of shoot apices from seedlings completely inhibited the embryogenesis induced by application of exogenous
ABA, suggesting that the action of ABA requires some substance(s) that is translocated basipetally from shoot apices through
hypocotyls. Histologically, somatic embryos shared common epidermal cells and differentiated not through the formation of
embryogenic cell clumps, but directly from epidermal cells. These morphological traits are distinct from those of embryogenesis
via formation of embryogenic cell clumps, which has been found in embryogenic carrot cultures established using 2,4-dichlorophenoxyacetic
acid or other auxins. These results suggest that ABA acts as a signal substance in stress-induced carrot seedling somatic
embryogenesis.
Received: 22 April 2000 / Accepted: 8 June 2000 相似文献
13.
Egg cells were analysed cytologically during the female receptivity period in maize (Zea mays L., line A 188). Three classes of egg cell were distinguished: type A – small, non-vacuolated cells with a central nucleus;
type B – larger cells with small vacuoles surrounding the perinuclear cytoplasm located in the middle of the cell; type C
– big cells with a large apical vacuole and the mid-basal perinuclear cytoplasm. The less-dense cytoplasm of the vacuolated
egg cells usually contained numerous cup- or bell-shaped mitochondria. The three egg types appear to correspond to three late
stages of egg cell differentiation. The frequencies of each of the three egg types were monitored in developing maize ears
before and after pollination. In young ears, with the silks just extending out of the husks, small A-type cells were found
in about 86% of ovules. Their frequency decreased to about 58% at the optimum silk length, remained unchanged in non-pollinated
ears, and fell to 16% at the end of the female receptivity period. However, after pollination and before fertilisation the
frequency of these cells decreased to about 33%, and the larger vacuolated egg cells (types B and C) prevailed. At various
stages of the receptivity period, pollination accelerated changes in the egg population, increasing the number of ovules bearing
larger, vacuolated egg cells. Experiments with silk removal demonstrated that putative pollination signals act immediately
after pollen deposition and are not species-specific.
Received: 5 February 1999 / Accepted: 28 August 1999 相似文献
14.
The metabolic responses occurring in cucumber (Cucumis sativus L.) roots (a strategy-I plant) grown under iron-deficiency conditions were studied in-vivo using 31P-nuclear magnetic resonance spectroscopy. Iron starvation induced activation of metabolism leading to the consumption of
stored carbohydrates to produce the NAD(P)H, ATP and phosphoenolpyruvate necessary to sustain the increased activity of the
NAD(P)H:Fe3+-reductase, the H+-ATPase (EC 3.6.1.35) and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Activation of catabolic pathways was supported by
the enhancement of glycolytic enzymes and concentrations of the metabolites glucose-6-phosphate and fructose-6-phosphate,
and by enhancement of the respiration rate. Moreover, Fe-deficiency induced a slight increase in the cytoplasmic (pHc) and vacuolar (pHv) pHs as well as a dramatic decrease in the vacuolar phosphate (Pi) concentration. A comparison was done using fusicoccin
(FC), a fungal toxin which stimulates proton extrusion. Changes in pHc and pHv were measured after addition of FC. Under these conditions, a dramatic alkalinization of the pHv of −Fe roots was observed, as well as a concomitant Pi movement from the vacuole to the cytoplasm. These results showed that
Fe starvation was indeed accompanied by the activation of metabolic processes useful for sustaining the typical responses
occurring at the plasma-membrane level (i.e. increases in the NAD(P)H:Fe3+-reductase and H+-ATPase activities) as well as those involved in the homeostasis of pHc. The decrease in vacuolar Pi levels induced by Fe-deficiency and FC and movement of Pi from the vacuole to the cytoplasm
suggest a possible involvement of this compound in the cellular pH-stat system.
Received: 30 July 1999 / Accepted: 11 November 1999 相似文献
15.
16.
Increased ethylene evolution accompanies seed germination of many species including Pisum sativum L., but only a little is known about the regulation of the ethylene biosynthetic pathway in different seed tissues. Biosynthesis
of the direct ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), the expression of ACC oxidase (ACO), and ethylene
production were investigated in the cotyledons and embryonic axis of germinating pea seeds. An early onset and sequential
induction of ACC biosynthesis, accumulation of Ps-ACO1 mRNA and of ACO activity, and ethylene production were localized almost exclusively in the embryonic axis. Maximal levels
of ACC, Ps-ACO1 mRNA, ACO enzyme activity and ethylene evolution were found when radicle emergence was just complete. Treatment of germinating
seeds with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornadiene showed that endogenous
ethylene regulates its own biosynthesis through a positive feedback loop that enhances ACO expression. Accumulation of Ps-ACO1 mRNA and of ACO enzyme activity in the embryonic axis during the late phase of germination required ethylene, whereas Ps-ACS1 mRNA levels and overall ACC contents were not induced by ethylene treatment. Ethylene did not induce ACO in the embryonic
axis during the early phase of germination. Ethylene-independent signalling pathways regulate the spatial and temporal pattern
of ethylene biosynthesis, whereas the ethylene signalling pathway regulates high-level ACO expression in the embryonic axis,
and thereby enhances ethylene evolution during seed germination.
Received: 28 September 1999 / Accepted: 27 December 1999 相似文献
17.
The aim of this work was to examine the role of fructose 2,6-bisphosphate (Fru-2,6-P2) in photosynthetic carbon partitioning. The amount of Fru-2,6-P2 in leaves of tobacco (Nicotiana tabacum L. cv. Samsun) was reduced by introduction of a modified mammalian gene encoding a functional fructose-2,6-bisphosphatase
(EC 3.1.3.46). Expression of this gene in transgenic plants reduced the Fru-2,6-P2 content of darkened leaves to between 54% and 80% of that in untransformed plants. During the first 30 min of photosynthesis
sucrose accumulated more rapidly in the transgenic lines than in the untransformed plants, whereas starch production was slower
in the transgenic plants. On illumination, the proportion of 14CO2 converted to sucrose was greater in leaf disks of transgenic lines possessing reduced amounts of Fru-2,6-P2 than in those of the control plants, and there was a corresponding decrease in the proportion of carbon assimilated to starch
in the transgenic lines. Furthermore, plants with smaller amounts of Fru-2,6-P2 had lower rates of net CO2 assimilation. In illuminated leaves, decreasing the amount of Fru-2,6-P2 resulted in greater amounts of hexose phosphates, but smaller amounts of 3-phosphoglycerate and dihydroxyacetone phosphate.
These differences are interpreted in terms of decreased inhibition of cytosolic fructose-1,6-bisphosphatase resulting from
the lowered Fru-2,6-P2 content. The data provide direct evidence for the importance of Fru-2,6-P2 in co-ordinating chloroplastic and cytosolic carbohydrate metabolism in leaves in the light.
Received: 8 February 2000 / Accepted: 25 April 2000 相似文献
18.
The ABA INSENSITIVE1 (ABI1) and ABI2 genes encode homologous type-2C protein phosphatases with redundant yet distinct functions in abscisic acid (ABA) responses.
Results from Northern blot analysis showed that ABA- and mannitol-inducible expression of the COR47 and COR78/LTI78/RD29A (COR78) genes was more impaired in the abi2 mutant of Arabidopsis thaliana (L.) Heynh than in the abi1 mutant. Furthermore, ABA-plus-mannitol treatments were additive towards COR47 gene expression; however, the ABA-deficient aba1 mutant showed reduced COR expression relative to the wild type in response to mannitol and ABA-plus-mannitol treatments.
These results support the notion that drought- and ABA-signalling pathways are separate yet overlapping. To facilitate quantitative
analysis of the genetic control of tissue-specific ABA- and desiccation-response pathways, we analyzed ABA- and mannitol-inducible
expression of a carrot (Daucus carota L.) Dc3 promoter:uidA (β-glucuronidase; GUS) chimaeric reporter (Dc3-GUS) in transgenic wild-type, ABA-deficient aba1, and ABA-insensitive abi1 and abi2 mutants. The Dc3 promoter directed ABA- and mannitol-inducible GUS expression in Arabidopsis guard cells and the two treatments were additive. The aba1, abi1, and abi2 mutant genotypes had reduced GUS expression in guard cells of cotyledons in response to mannitol, whereas abi1 and abi2 mutants were reduced in ABA-inducible GUS expression, consistent with overlapping ABA- and drought-response pathways. Quantitative
fluorometric GUS assays of leaf extracts showed that abi2 mutants responded less to exogenous ABA than did abi1 mutants, and abi2 mutants responded more to mannitol than did abi1 mutants. We conclude that Dc3-GUSArabidopsis is a tractable system in which to study tissue-specific ABA and drought signalling and suggest that ABI2 functions predominantly over ABI1 in COR78 and COR47 gene expression and guard-cell Dc3-GUS expression.
Received: 23 May 1999 / Accepted: 3 December 1999 相似文献
19.
Chemical composition of apoplastic transport barriers in relation to radial hydraulic conductivity of corn roots (Zea mays L.) 总被引:5,自引:0,他引:5
The hydraulic conductivity of roots (Lpr) of 6- to 8-d-old maize seedlings has been related to the chemical composition of apoplastic transport barriers in the endodermis
and hypodermis (exodermis), and to the hydraulic conductivity of root cortical cells. Roots were cultivated in two different
ways. When grown in aeroponic culture, they developed an exodermis (Casparian band in the hypodermal layer), which was missing
in roots from hydroponics. The development of Casparian bands and suberin lamellae was observed by staining with berberin-aniline-blue
and Sudan-III. The compositions of suberin and lignin were analyzed quantitatively and qualitatively after depolymerization
(BF3/methanol-transesterification, thioacidolysis) using gas chromatography/mass spectrometry. Root Lpr was measured using the root pressure probe, and the hydraulic conductivity of cortical cells (Lp) using the cell pressure
probe. Roots from the two cultivation methods differed significantly in (i) the Lpr evaluated from hydrostatic relaxations (factor of 1.5), and (ii) the amounts of lignin and aliphatic suberin in the hypodermal
layer of the apical root zone. Aliphatic suberin is thought to be the major reason for the hydrophobic properties of apoplastic
barriers and for their relatively low permeability to water. No differences were found in the amounts of suberin in the hypodermal
layers of basal root zones and in the endodermal layer. In order to verify that changes in root Lpr were not caused by changes in hydraulic conductivity at the membrane level, cell Lp was measured as well. No differences
were found in the Lp values of cells from roots cultivated by the two different methods. It was concluded that changes in
the hydraulic conductivity of the apoplastic rather than of the cell-to-cell path were causing the observed changes in root
Lpr.
Received: 17 March 1999 / Accepted: 22 June 1999 相似文献
20.
Zhang W Peumans WJ Barre A Astoul CH Rovira P Rougé P Proost P Truffa-Bachi P Jalali AA Van Damme EJ 《Planta》2000,210(6):970-978
A novel plant lectin was isolated from salt-stressed rice (Oryzasativa L.) plants and partially characterized. The lectin occurs as a natural mixture of two closely related isoforms consisting
of two identical non-covalently linked subunits of 15 kDa. Both isoforms are best inhibited by mannose and exhibit potent
mitogenic activity towards T-lymphocytes. Biochemical analyses and sequence comparisons further revealed that the rice lectins
belong to the subgroup of mannose-binding jacalin-related lectins. In addition, it could be demonstrated that the lectins
described here correspond to the protein products of previously described salt-stress-induced genes. Our results not only
identify the rice lectin as a stress protein but also highlight the possible importance of protein-carbohydrate interactions
in stress responses in plants.
Received: 27 July 1999 / Accepted: 11 November 1999 相似文献