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1.
2.
Molecular, functional and ultrastructural characterisation of plastids from six species of the parasitic flowering plant genus Cuscuta 总被引:3,自引:0,他引:3
Hydroponically cultivated barley plants were exposed to nitrogen (N)-deficiency followed by N-resupply. Metabolic and genetic
regulation of fructan accumulation in the leaves were investigated. Fructan accumulated in barley leaves under N-deficiency
was mobilized during N-resupply. The enhanced total activity of fructan-synthesizing enzymes, sucrose:sucrose 1-fructosyltransferase
(EC 2.4.1.99) and sucrose:fructan 6-fructosyltransferase (6-SFT; EC 2.4.1.10) caused by N-deficiency decreased with the mobilization
of fructan during N-resupply. The activity of the barley fructan-degrading enzyme, fructan exohydrolyase (EC 3.2.1.80) was
less affected by the N status. The low level of foliar soluble acid invertase activity under N-deficiency conditions was maintained
during the commencement of N-resupply but increased subsequently. Further analyses by sodium dodecyl sulfate-polyacrylamide
gel electrophoresis, western blot and northern blot demonstrated that the fructan accumulation and the total activity of fructan-synthesizing
enzymes correlated with the 6-SFT mRNA level. We suggest that the changes in fructan levels under N stress are intimately
connected with the regulation of fructan synthetic rate which is mostly controlled by 6-SFT.
Received: 25 October 1999 / Accepted: 15 February 2000 相似文献
3.
Recently, it has been shown that water fluxes across biological membranes occur not only through the lipid bilayer but also
through specialized water-conducting proteins, the so called aquaporins. In the present study, we investigated in young and
mature leaves of Brassica napus L. the expression and localization of a vacuolar aquaporin homologous to radish γ-tonoplast intrinsic protein/vacuolar-membrane
integral protein of 23 kDa (TIP/VM 23). In-situ hybridization showed that these tonoplast aquaporins are highly expressed
not only in developing but also in mature leaves, which export photosynthates. No substantial differences could be observed
between different tissues of young and mature leaves. However, independent of the developmental stage, an immunohistochemical
approach revealed that the vacuolar membrane of bundle-sheath cells contained more protein cross-reacting with antibodies
raised against radish γ-TIP/VM 23 than the mesophyll cells. The lowest labeling was detected in phloem cells. We compared
these results with the distribution of plasma-membrane aquaporins cross-reacting with antibodies detecting a domain conserved
among members of the plasma-membrane intrinsic protein 1 (PIP1) subfamily. We observed the same picture as for the vacuolar
aquaporins. Furthermore, a high density of gold particles labeling proteins of the PIP1 group could be observed in plasmalemmasomes
of the vascular parenchyma. Our results indicate that γ-TIP/VM 23 and PIP1 homologous proteins show a similar expression pattern.
Based on these results it is tempting to speculate that bundle-sheath cells play an important role in facilitating water fluxes
between the apoplastic and symplastic compartments in close proximity to the vascular tissue.
Received: 23 December 1999 / Accepted: 3 June 2000 相似文献
4.
Persello-Cartieaux F David P Sarrobert C Thibaud MC Achouak W Robaglia C Nussaume L 《Planta》2001,212(2):190-198
A model system based on the Arabidopsis thaliana (L.) Heynh. Ws ecotype and its naturally colonizing Pseudomonas thivervalensis rhizobacteria was defined. Pseudomonas strains colonizing A. thaliana were found to modify the root architecture either in vivo or in vitro. A gnotobiotic system using bacteria labelled with
green fluorescent protein revealed that P. thivervalensis exhibited a colonization profile similar to that of other rhizobacterial species. Mutants of A.thaliana affected in root hair development and possible hormone perception were used to analyze the plant genetic determinants of
bacterial colonization. A screen for mutants insensitive to P. thivervalensis colonization yielded two mutants found to be auxin resistant. This further supports a proposed role for bacterial auxin in
inducing morphological modifications of roots. This work paves the way for studying the interaction between plants and non-pathogenic
rhizobacteria in a gnotobiotic system, derived from a natural association, where interactions between both partners can be
genetically dissected.
Received: 6 January 2000 / Accepted: 20 May 2000 相似文献
5.
The assembly, organization and function of the photosynthetic apparatus was investigated in the wild type and a chlorophyll
(Chl) b-less mutant of the unicellular green alga Chlamydomonas reinhardtii, generated via DNA insertional mutagenesis. Comparative analyses were undertaken with cells grown photoheterotrophically
(acetate), photomixotrophically (acetate and HCO−
3) or photoautotrophically (HCO−
3). It is shown that lack of Chl b diminished the photosystem-II (PSII) functional Chl antenna size from 320 Chl (a and b) to about 95 Chl a molecules. However, the functional Chl antenna size of PSI remained fairly constant at about 290 Chl molecules, independent
of the presence of Chl b. Western blot and kinetic analyses suggested the presence of inner subunits of the Chl a-b light-harvesting complex of PSII (LHCII) and the entire complement of the Chl a-b light-harvesting complex of PSI (LHCI) in the mutant. It is concluded that Chl a can replace Chl b in the inner subunits of the LHCII and in the entire complement of the LHCI. Growth of cells on acetate as the sole carbon
source imposes limitations in the photon-use efficiency and capacity of photosynthesis. These are manifested as a lower quantum
yield and lower light-saturated rate of photosynthesis, and as lower variable to maximal (Fv/Fmax) chlorophyll fluorescence yield ratios. This adverse effect probably originates because acetate shifts the oxidation-reduction
state of the plastoquinone pool, and also because it causes a decrease in the amount and/or activity of Rubisco in the chloroplast.
Such limitations are fully alleviated upon inclusion of an inorganic carbon source (e.g. bicarbonate) in the cell growth medium.
Further, the work provides evidence to show that transformation of green algae can be used as a tool by which to generate
mutants exhibiting a permanently truncated Chl antenna size and a higher (per Chl) photosynthetic productivity of the cells.
Received: 10 November 1999 / Accepted: 22 December 1999 相似文献
6.
In malic enzyme-dependent crassulacean-acid-metabolism (ME-CAM) plants, malic acid is decarboxylated by NADP-ME and NAD-ME and generates pyruvate with CO2. Pyruvate is phosphorylated to phosphoenolpyruvate by pyruvate, Pi dikinase (PPDK) and is then conserved in gluconeogenesis. Although PPDK was considered to be located in chloroplasts (e.g., Mesembryanthemum crystallinum), it has recently been found to accumulate in both the chloroplasts and the cytosol in two Kalancho? species. In this study, the intracellular localization of PPDK was investigated in 22 ME-CAM species in 13 genera of 5 families by immunogold labeling and electron microscopy. This revealed that the pattern of intracellular localization of PPDK varies among the ME-CAM plants and is divided into three types: Chlt, in which PPDK accumulates only in the chloroplasts; Cyt-Chlt, in which PPDK accumulates in both chloroplasts and cytosol; and Cyt, in which PPDK accumulates predominantly in the cytosol. Members of a particular genus tend to have a common PPDK-localization type. In the Cactaceae, all species from seven genera were classified as Cyt. The photosynthetic tissues of all ME-CAM species, including the Cyt type, had substantial PPDK activity, suggesting that PPDK in the cytosol is active and probably plays a functional role. In the Chlt species, NADP-ME activity was relatively greater than NAD-ME activity. In the Cyt-Chlt and Cyt species, however, either the activity of NAD-ME was higher than that of NADP-ME or they were approximately the same. The species variation in the intracellular localization of PPDK is discussed in relation to CAM function and to molecular and phylogenetic aspects. 相似文献
7.
A cDNA encoding a novel inwardly rectifying potassium (K+
in) channel, LKT1, was cloned from a root-hair-specific cDNA library of tomato (Lycopersicon esculentum Mill.). The LKT1 mRNA was shown to be most strongly expressed in root hairs by Northern blot analysis. The LKT1 channel is a member of the
AKT family of K+
in channels previously identified in Arabidopsis thaliana (L.) Heynh. and potato (Solanum tuberosum L.). Moreover, LKT1 is closely related (97% identical amino acids) to potato SKT1. An electrophysiological comparison of
the two channels should therefore assist the identification of possible molecular bases for functional differences. For this
comparison, both channels were functionally expressed and electrophysiologically characterised within the same expression
system, i.e. Xenopus laevis oocytes. Voltage-clamp measurements identified LKT1 as a K+-selective inward rectifier which activates with slow kinetics upon hyperpolarising voltage pulses to potentials more negative
than −50 mV. The activation potential of LKT1 is shifted towards positive potentials with respect to SKT1 which might be due
to single amino acid exchanges in the rim of the channel's pore region or in the S4 domain. Like SKT1, LKT1 reversibly activated
upon shifting the external pH from 6.6 to 5.5, which indicates a physiological role for pH-dependent regulation of AKT-type
K+
in channels. The pharmacological inhibitor Cs+, applied externally, inhibited K+
in currents mediated by LKT1 and SKT1 half-maximally with a concentration (IC50) of 21 μM and 17 μM, respectively. In conclusion, LKT1 may serve as a low-affinity influx pathway for K+ into root hair cells. Comparison of homologous K+
in rectifiers from different plant species expressed in the same heterologous system allows conclusions to be drawn in respect
to structure-function relationships.
Received: 3 August 1999 / Accepted: 2 November 1999 相似文献
8.
Inactivation of DNA replication origins by the cell cycle regulator, trigonelline, in root meristems of Lactuca sativa 总被引:4,自引:0,他引:4
The effects of trigonelline (TRG) on the cell cycle in root meristems of Lactuca sativa L. were examined in the knowledge that TRG is a cell cycle regulator that causes cell arrest in G2, and prevents ligation
of replicons in S-phase. The hypothesis was tested that continuous exposure to TRG would perturb DNA replication which, in
turn, would lengthen the cell cycle and impair root elongation. Using DNA fibre autoradiography, mean replicon size was 31
and 13 μm in the TRG (3 mM) and control treatments, respectively. Trigonelline also resulted in a lengthening of both S-phase
and the cell cycle and a decrease in primary root elongation. Hence, replicon inactivation was responsible for the protracted
S-phase. Trigonelline treatment also resulted in a 1.6-fold increase in fork rate (13.8 μm h−1) compared with the control (8.4 m h−1). The faster fork rate in the larger replicons is in accord with the highly significant positive relationship already established
between fork rate and replicon size for various unrelated higher plants.
Received: 11 October 1999 / Accepted: 23 December 1999 相似文献
9.
Form of aluminium for uptake and translocation in buckwheat (Fagopyrum esculentum Moench) 总被引:5,自引:0,他引:5
The forms of Al for uptake by the roots and translocation from the root to the shoot were investigated in a buckwheat (Fagopyrum esculentum Moench, cv. Jianxi) that accumulates Al in its leaves. The Al concentration in the xylem sap was 15-fold higher in the plants
exposed to AlCl3 than in those exposed to an Al-oxalate (1:3) complex, suggesting that the roots take up Al in the ionic form. The Al concentration
in the xylem sap was 4-fold higher than that in the external solution after a 1-h exposure to AlCl3 solution and 10-fold higher after a 2-h exposure. The Al concentration in the xylem sap increased with increasing Al concentration
in the external solution. The Al uptake was not affected by a respiratory inhibitor, hydroxylamine, but significantly inhibited
by the addition of La. These results suggest that Al uptake by the root is a passive process, and La3+ competes for the binding sites for Al3+ on the plasma membrane. The form of Al in the xylem sap was identified by 27Al-nuclear magnetic resonance analysis. The chemical shift of 27Al in the xylem sap was around 10.9 ppm, which is consistent with that of the Al-citrate complex. Furthermore, the dominant
organic acid in the xylem sap was citric acid, indicating that Al was translocated in the form of Al-citrate complex. Because
Al is present as Al-oxalate (1:3) in the root, the present data show that ligand exchange from oxalate to citrate occurs before
Al is released to xylem.
Received: 10 December 1999 / Accepted: 3 February 2000 相似文献
10.
Microsatellite DNA in Actinidia chinensis: isolation, characterisation, and homology in related species 总被引:5,自引:0,他引:5
W.-G. Huang G. Cipriani M. Morgante R. Testolin 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(8):1269-1278
We have isolated and sequenced 263 microsatellite-containing clones from two small insert libraries of Actinidia chinensis enriched for (AC/GT) and (AG/CT) repeats, respectively. Primer pairs were designed for 203 microsatellite loci and successfully
amplified from both plasmid and A. chinensis genomic DNA. In this paper we report the sequences of 40 primer pairs for which we have demonstrated Mendelian segregation
in the progeny from controlled crosses. The polymorphism of ten microsatellites of each type was evaluated in four diploid
and six tetraploid genotypes of A. chinensis. All microsatellites proved to be polymorphic, the number of alleles per locus detected in polyacrylamide sequencing gels
ranging from 9 to 17. The high degree of polymorphism in Actinidia renders these markers useful either for mapping in A. chinensis or for fingerprinting cultivars of both domesticated kiwifruit species (A. chinensis and A. deliciosa). While most primer pairs produced single amplification products, about 20% generated banding patterns consistent with the
amplification of two different loci. This supports the hypothesis that diploid species of Actinidia (2n=2x=58) are polyploid in origin with a basic chromosome number x=14/15 and that chromosome duplication may have occurred during the evolution of the genus. Finally, we have assayed the cross-species
transportability of primer pairs designed from A. chinensis sequences and have found extensive cross-species amplification within the genus Actinidia; 75% of primer pairs gave successful amplification in the eight species assayed (A. arguta, A. rufa, A. polygama, A. chrysantha, A. callosa, A. hemsleyana, A. eriantha, and A. deliciosa), which are representative of the four sections into which the genus is currently split.
Received: 14 February 1998 / Accepted: 26 May 1998 相似文献
11.
When a brassinosteroid biosynthesis inhibitor, brassinazole (Brz), was applied at concentrations ranging from 0.1 to 2 μM,
Arabidopsis thaliana (L.) Heynh seedlings grown in the dark exhibited morphological features of light-grown plants, i.e. short hypocotyls, expanded
cotyledons, and true leaves, in a dose-dependent manner. Control (non Brz-treated) seedlings grown in the dark for 40 d did
not develop leaf primordia. However, treatment with the lowest concentration of Brz induced the development of leaf buds,
although it hardly induced any short hypocotyls, and treatment with the highest concentration of Brz induced both short hypocotyls
and leaves. Labeling experiments with the thymidine analogue 5-bromo-2′-deoxyuridine revealed that amplification of cell nuclei
and organellar nucleoids is activated in the shoot apical meristems of dark-grown Brz-treated seedlings. These results suggest
that Brz-treatment induces development of true leaves. Furthermore, condensation and scattering of plastid nucleoids, which
is known to occur during the differentiation of etioplasts into chloroplasts, was observed in the plastids of dark-grown Brz-treated
cotyledons. In addition, high levels of ribulose-1,5-bisphosphate carboxylase-oxygenase proteins accumulated in the plastids
of the cotyledons. Electron microscopy showed that the plastids were etioplasts with a prolamellar body and few thylakoid
membranes. These results suggest that Brz treatment in the dark induces the initial steps of plastid differentiation, which
occur prior to the development of thylakoid membranes. This is a novel presumed function of brassinosteroids. These cytological
changes seen in Brz-treated Arabidopsis were exactly the same as those seen in a brassinosteroid-biosynthesis-deficient mutant, det2, supporting the hypothesis that Brz has no side-effects except inhibiting brassinosteroid biosynthesis, and should prove
a useful tool in clarifying the role of brassinosteroids.
Received: 10 February 2000 / Accepted: 11 April 2000 相似文献
12.
Two-year-old rosemary (Rosmarinus officinalis L.) plants were subjected to severe stress by exposure to prolonged drought during a Mediterranean summer. Severely stressed
plants recovered completely after the autumn rainfalls although the relative water content remained below 35% for 3 months
and the chlorophyll content of leaves was reduced by up to 85% during the drought. In severe stress: (i) α-tocopherol increased
9-fold per g dry weight and 20-fold per unit of chlorophyll; (ii) lutein and β-carotene contents decreased on a dry-weight
basis, but an 80% increase in lutein and constant levels of β-carotene were observed on a chlorophyll basis; (iii) there were
transient and sustained increases in the de-epoxidation state of the xanthophyll cycle; and (iv) the highly oxidised abietane
diterpene isorosmanol increased 8-fold as a result of the oxidation of carnosic acid. With the autumn rainfalls, water status,
α-tocopherol and violaxanthin recovered first and the levels of photosynthetic pigments and abietane diterpenes increased
later. The photoprotection conferred by the xanthophyll cycle and the antioxidant function of tocopherols, lutein and diterpenes
may help to avoid irreversible damage in severe drought, making possible the recovery of functional membranes after the autumn
rainfalls. Besides, chlorophyll loss reduces the amount of photons absorbed by leaves, which enhances the photoprotective
and antioxidant capacity of leaves per amount of photons absorbed, since the ratios of xanthophylls, α-tocopherol and abietane
diterpenes to chlorophyll increase.
Received: 12 July 1999 / Accepted: 25 November 1999 相似文献
13.
Alfin1 transcription factor overexpression enhances plant root growth under normal and saline conditions and improves salt tolerance in alfalfa 总被引:11,自引:0,他引:11
Plant root development is an essential determinant of plant growth and crop yield that could be enhanced by induced changes in the expression of root-specific regulatory factors. We reported previously that Alfin1 binds DNA in a sequence-specific manner and that Alfin1 overexpression in transgenic alfalfa (Medicago sativa L.) enhances expression of the salt-inducible MsPRP2 gene in roots, suggesting that Alfin1 functions to regulate gene expression in roots. Here we show that Alfin1 is an essential gene for root growth and that its overexpression in transgenic plants confers a many-fold increase in root growth under normal and saline conditions. Alfin1-binding sites occur in promoters of genes expressed in roots of a wide variety of plant species and we propose that it is a general root growth regulator. Even though Alfin1 overexpression was under the control of the CaMV 35S promoter, plant shoot growth was not adversely affected. We show further that introduction of the Alfin1 transgene in plants confers a dominant characteristic that significantly increases plant growth and salt tolerance. 相似文献
14.
15.
Analytical electron microscopical investigations on the apoplastic pathways of lanthanum transport in barley roots 总被引:5,自引:0,他引:5
In transmission electron microscopy studies, lanthanum ions have been used as electron-opaque tracers to delineate the apoplastic
pathways for ion transport in barley (Hordeum vulgare L.) roots. To localize La3+ on the subcellular level, e.g. in cell walls and on the surface of membranes, electron-energy-loss spectroscopy and electron-spectroscopic
imaging were used. Seminal and nodal roots were exposed for 30 min to 1 mM LaCl3 and 10 mM LaCl3, respectively. In seminal roots, possessing no exodermis, La3+ diffusion through the apoplast was stopped by the Casparian bands of the endodermis. In nodal roots with an exodermis, however,
La3+ diffusion through the cortical apoplast had already stopped at the tight junctions of the exodermal cell walls resembling
the Casparian bands of the endodermis. Therefore, we conclude that in some specialized roots such as the nodal roots of barley,
the physiological role of the endodermis is largely performed by the exodermis.
Received: 28 July 1999 / Accepted: 24 February 2000 相似文献
16.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
17.
A cDNA fragment encoding a Lupinus albus. L. class-III chitinase, IF3, was isolated, using a cDNA probe from Cucumis sativus L., by in-situ plaque hybridization from a cDNA library constructed in the Uni-ZAP XR vector, with mRNAs isolated from mature
lupin leaves. The cDNA had a coding sequence of 293 amino acids including a 27-residue N-terminal signal peptide. A class-III
chitinase gene was detected by Southern analysis in the L. albus genome. Western blotting experiments showed that the IF3 protein was constitutively present during seed development and in
all the studied vegetative lupin organs (i.e., roots, hypocotyls and leaves) at two growth stages (7- and 20-d-old plants).
Accumulation of both the IF3 mRNA and IF3 protein was triggered by salicylic acid treatment as well as by abiotic (UV-C light
and wounding) and biotic stress conditions (Colletotrichum gloeosporioides infection). In necrotic leaves, IF3 chitinase mRNA was present at a higher level than that of another mRNA encoding a pathogenesis-related
(PR) protein from L. albus (a PR-10) and that of the rRNAs. We suggest that one role of the IF3 chitinase could be in the defense of the plant against
fungal infection, though our results do not exclude other functions for this protein.
Received: 15 March 1999 / Accepted: 12 July 1999 相似文献
18.
Phototolerance of lichens, mosses and higher plants in an alpine environment: analysis of photoreactions 总被引:8,自引:0,他引:8
Adaptation to excessive light is one of the requirements of survival in an alpine environment particularly for poikilohydric
organisms which in contrast to the leaves of higher plants tolerate full dehydration. Changes in modulated chlorophyll fluorescence
and 820-nm absorption were investigated in the lichens Xanthoria elegans (Link) Th. Fr. and Rhizocarpon geographicum (L.) DC, in the moss Grimmia alpestris Limpr. and the higher plants Geum montanum L., Gentiana lutea L. and Pisum sativum L., all collected at altitudes higher than 2000 m above sea level. In the dehydrated state, chlorophyll fluorescence was
very low in the lichens and the moss, but high in the higher plants. It increased on rehydration in the lichens and the moss,
but decreased in the higher plants. Light-induced charge separation in photosystem II was indicated by pulse-induced fluorescence
increases only in dried leaves, not in the dry moss and dry lichens. Strong illumination caused photodamage in the dried leaves,
but not in the dry moss and dry lichens. Light-dependent increases in 820-nm absorption revealed formation of potential quenchers
of chlorophyll fluorescence in all dehydrated plants, but energy transfer to quenchers decreased chlorophyll fluorescence
only in the moss and the lichens, not in the higher plants. In hydrated systems, coupled cyclic electron transport is suggested
to occur concurrently with linear electron transport under strong actinic illumination particularly in the lichens because
far more electrons became available after actinic illumination for the reduction of photo-oxidized P700 than were available
in the pool of electron carriers between photosystems II and I. In the moss Grimmia, but not in the lichens or in leaves, light-dependent quenching of chlorophyll fluorescence was extensive even under nitrogen,
indicating anaerobic thylakoid acidification by persistent cyclic electron transport. In the absence of actinic illumination,
acidification by ca. 8% CO2 in air quenched the initial chlorophyll fluorescence yield Fo only in the hydrated moss and the lichens, not in leaves of the higher plants. Under the same conditions, 8% CO2 reduced the maximal fluorescence yield Fm strongly in the poikilohydric organisms, but only weakly or not at all in leaves. The data indicate the existence of deactivation
pathways which enable poikilohydric organisms to avoid photodamage not only in the hydrated but also in the dehydrated state.
In the hydrated state, strong nonphotochemical quenching of chlorophyll fluorescence indicated highly sensitive responses
to excess light which facilitated the harmless dissipation of absorbed excitation energy into heat. Protonation-dependent
fluorescence quenching by cyclic electron transport, P700 oxidation and, possibly, excitation transfer between the photosystems
were effectively combined to produce phototolerance.
Received: 10 December 1999 / Accepted: 13 April 2000 相似文献
19.
A nonphotochemical-quenching-deficient mutant of Arabidopsis thaliana possessing normal pigment composition and xanthophyll-cycle activity 总被引:1,自引:0,他引:1
Higher-plant chloroplasts alter the distribution of absorbed radiant energy between photosynthesis and heat formation in
response to changing illumination level or environmental stress. Fluorescence imaging was used to screen 62 yellow-green T-DNA
insertion mutant lines of Arabidopsis thaliana (L.) Heynh. for reduced photoprotective nonphotochemical quenching (NPQ) capacity. Pulse-modulation fluorometry was employed
to characterize one line (denoted Lsr1−) that exhibited an approximately 50% reduction in NPQ compared to the wild type (WT). The loss in NPQ capacity was associated
with the ΔpH-dependent phase of quenching (qE). Under the growth conditions employed, pigment composition and levels of the
six photosystem-II light-harvesting chlorophyll a/b proteins were identical in mutant and WT. Changes in the in-vivo levels of the xanthophyll pigments violaxanthin, antheraxanthin,
and zeaxanthin in excess light were the same for mutant and WT. However, use of the violaxanthin de-epoxidase inhibitor dithiothreitol
indicated that a zeaxanthin-dependent component of NPQ was specifically reduced in the mutant. The mutant exhibited diminished
suppression of minimum fluorescence yield (F
o
) in intense light suggesting an altered threshold in the mechanism of response to light stress in the mutant. The NPQ-deficient
phenotype was meiotically transmissible as a semidominant trait and mapped near marker T27K12 on chromosome 1. The results
suggest that the mutant is defective in sensing the transthylakoid ΔpH that reports exposure to excessive illumination.
Received: 26 May 1999 / Accepted: 17 June 1999 相似文献
20.
Ermel FF Follet-Gueye ML Cibert C Vian B Morvan C Catesson AM Goldberg R 《Planta》2000,210(5):732-740
The development of pectin structural features during the differentiation of cambial derivatives was investigated in aspen
(Populus tremula L. × P. tremuloides Michx.) using biochemical and immunocytochemical methods. Comparisons were also made between active and resting tissues.
Active tissues, in particular cambial cells and phloem derivatives, were characterized by a high pectin content. Use of antibodies
raised against arabinan side chains of rhamnogalacturonan 1 (LM6), as well as biochemical analysis, revealed an obvious decrease
from the cortex to the differentiating xylem. Galactan side chains, detected with LM5 antibodies, were present mainly in the
cambial zone and enlarging xylem cells. In contrast, they were totally absent from sieve-tube cell walls. Image analysis of
LM5 immunogold labelling in the cambial zone showed a clustered distribution of galactan epitopes in the radial walls, a distribution
which might result from the association of two different periodic processes, namely the exocytosis of galactan and wall expansion.
Cessation of cambial activity was characterized by cell wall thickening accompanied by a sharp decrease in the relative amount
of pectin and a lowering of the degree of methylesterification. The data provide evidence that the walls of phloem and xylem
cells differ in their pectin composition even at a very early stage of commitment. These differences offer useful tools for
identifying the initial cells among their immediate neighbours.
Received: 12 June 1999 / Accepted: 20 October 1999 相似文献