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1.
Callose accumulates in the walls of cells undergoing megasporogenesis during embryo sac formation in angiosperm ovules. Deficiencies
in callose deposition have been observed in apomictic plants and causal linkages between altered callose deposition and apomictic
initiation proposed. In apomictic Hieracium, embryo sacs initiate by sexual and apomictic processes within an ovule, but sexual development terminates in successful
apomicts. Callose deposition and the events that lead to sexual termination were examined in different Hieracium apomicts that form initials pre- and post-meiosis. In apomictic plants, callose was not detected in initial cell walls and
deficiencies in callose deposition were not observed in cells undergoing megasporogenesis. Multiple initial formation pre-meiosis
resulted in physical distortion of cells undergoing megasporogenesis, persistence of callose and termination of the sexual
pathway. In apomictic plants, callose persistence did not correlate with altered spatial or temporal expression of a β-1,3-glucanase
gene (HpGluc) encoding a putative callose-degrading enzyme. Expression analysis indicated HpGluc might function during ovule growth and embryo sac expansion in addition to callose dissolution in sexual and apomictic plants.
Initial formation pre-meiosis might therefore limit the access of HpGluc protein to callose substrate while the expansion of aposporous embryo sacs is promoted. Callose deposition and dissolution
during megasporogenesis were unaffected when initials formed post-meiosis, indicating other events cause sexual termination.
Apomixis in Hieracium is not caused by changes in callose distribution but by events that lead to initial cell formation. The timing of initial
formation can in turn influence callose dissolution.
Received: 18 April 2000 / Accepted: 10 July 2000 相似文献
2.
Apomixis is facultative in characterized members of the genus Hieracium. The three components that comprise the apomictic mechanism include apospory followed by autonomous embryo and endosperm
formation. The time of aposporous embryo sac initiation and mode of embryo sac formation are different in Hieracium piloselloides (D3) and Hieracium aurantiacum (A3.4). Genetic studies have shown that a single dominant locus encodes all three components of apomixis in both species
(Bicknell et al. 2000). We histologically examined a range of related, genetically characterized apomictic Hieracium plants derived from D3 and A3.4 to assess conservation of the apomictic mechanism in different genetic backgrounds. The plants
varied in ploidy, and also in the amount of DNA introduced from sexual Hieracium pilosella (P4). An apomictic hybrid from a cross between the two apomicts was also examined. The developmental processes observed in
the parental apomicts were not conserved in the examined plants and alterations occurred in the components of apomixis. One
plant also exhibited adventitious embryony. The results show that other genetic factors can modify apomixis with respect to
time of initiation, spatial location, and mode of developmental progression. Both the apomictic locus and the modifiers are
essential for efficient penetrance of the trait in Hieracium. Some of the findings in Hieracium correspond with observations in Ranunculus and this is discussed in terms of models for apomictic development and the control of apomixis in crops.
Received: 21 June 1999 / Revision accepted: 17 November 1999 相似文献
3.
The negative gravitropism of the sporangiophores of Phycomyces blakesleeanus Burgeff is elicited by different sensory inputs, which include flexure of the growing zone, buoyance of lipid globules and
sedimentation of paracrystalline proteins, so-called octahedral crystals (C. Schimek et al., 1999a, Planta 210: 132–142).
Gravity-induced absorbance changes (GIACs), which are associated with primary events of gravity sensing, were detected in
the growing zones of sporangiophores. After placing sporangiophores horizontally, GIACs were detected after a latency of about
5 min, i.e. 15–25 min prior to gravitropic bending. The spectroscopic properties of the GIACs indicate that gravitropic stimulation
could imply the reduction of cytochromes. The GIACs were spectrally distinct from light-induced absorbance changes (LIACs),
showing that the primary responses of the light and gravity transduction chains are different. A dual stimulation with gravity
and light generated GIAC-LIACs which were distinct from the absorbance changes occurring after the single stimuli and which
indicate that light and gravity interact early in the respective transduction chains.
Received: 2 September 1999 / Accepted: 9 November 1999 相似文献
4.
Sexual and apomictic development in Hieracium 总被引:2,自引:2,他引:0
Most members of the genus Hieracium are apomictic and set seed without fertilization, but sexual forms also exist. A cytological study was conducted on an apomictic
accession of H. aurantiacum (A3.4) and also H. piloselloides (D3) to precisely define the cellular basis for apomixis. The apomictic events were compared with the sexual events in a
self-incompatible isolate of H. pilosella (P4). All plants were maintained as vegetatively propagated lines each derived from a single plant. Sexual P4 exhibited characteristic
events of polygonum-type embryo sac formation, showed no latent apomitic tendencies, and depended upon fertilization to set
seed. In contrast, D3 and A3.4 were autonomous aposporous apomicts, forming both embryo and endosperm spontaneously inside
an unreduced embryo sac. The two apomicts exhibited distinct mechanisms, but variation was also observed within each apomictic
line. Seeds from apomicts often contained more than one embryo. A degree of developmental instability was also observed amongst
germinated seedlings and included variation in meristem and cotyledon number, altered phyllotaxis, callus formation, and seedling
fusion. In most cases abnormal seedlings developed into normal plants. Such phenomena were not observed following germination
of hybrid seeds derived from crosses between sexual P4 and the apomictic plants. The three plants can now be used in inheritance
studies and also to investigate the molecular mechanisms controlling apomixis.
Received: 11 February 1998 / Revision accepted: 23 July 1998 相似文献
5.
Mastoparan induces Ca2+-dependent deflagellation of the unicellular green alga Chlamydomonas moewusii Gerloff, as well as the activation of phospholipase C and the production of inositol 1,4,5-trisphosphate (InsP3; T. Munnik et al., 1998, Planta 207: 133–145). Even in the absence of extracellular Ca2+, mastoparan still induces deflagellation (L.M. Quarmby and H.C. Hartzell, 1994, J Cell Biol 124: 807–815; J.A.J. van Himbergen
et al., 1999, J Exp Bot, in press) suggesting that InsP3 mediates Ca2+ release from intracellular stores. To test this hypothesis, cells were pre-loaded with 45Ca2+ and their plasma membranes permeabilized by digitonin. Subsequent treatment of the cells with mastoparan (3.5 μM) induced
release of intracellular 45Ca2+. Mastoparan also activated phospholipase C in permeabilized cells, as demonstrated by the breakdown of 32P-phosphatidylinositol 4,5-bisphosphate and the production of diacylglycerol. The mastoparan analogues mas7 and mas17 were
also effective and their efficacy was correlated with their biological activity. X-ray microanalysis showed that electron-dense
bodies (EDBs) are a major Ca2+ store in C. moewusii. Analysis of digitonin-permeabilized cells showed that EDBs lost calcium at digitonin concentrations that released radioactivity
from 45Ca2+-labelled cells, suggesting that 45Ca2+ monitored the content of EDBs. X-ray microanaysis of living cells treated with mastoparan also revealed that calcium was
released from EDBs.
Received: 30 December 1998 / Accepted: 25 June 1999 相似文献
6.
Sucrose synthase (SS), a key enzyme in plant carbohydrate metabolism, has recently been isolated from Anabaena sp. strain PCC 7119, and biochemically characterized; two forms (SS-I and SS-II) were detected (Porchia et al. 1999, Planta
210: 34–40). The present study describes the first isolation and characterization of a prokaryotic SS gene, susA, encoding SS-II from that strain of Anabaena. A 7 kbp DNA fragment containing an open reading frame (EMBL accession number AJ010639) with about 30–40% amino acid identity
with plant SSs was isolated from an Anabaena subgenomic library. The putative SS gene was demonstrated to encode an SS protein by expression in Escherichia coli. The biochemical properties of the recombinant enzyme were identical to those of the enzyme purified from the cyanobacterial
cells. The deduced amino acid sequence of the Anabaena SS diverged from every plant SS reported. The occurrence of SS in cyanobacteria of different taxonomic groups was investigated.
The enzyme occurs in several filamentous nitrogen-fixing cyanobacteria but not in two species of unicellular, non-diazotrophic
cyanobacteria.
Received: 5 January 2000 / Accepted: 7 March 2000 相似文献
7.
Mature ovules of Dianthus (Caryophyllaceae) were histologically observed by clearing and serial sectioning to characterize the cells of the embryo
sac. The results show that the mature embryo sac was located deep inside the hemitropous ovule due to thick nucellar tissue
at the micropylar region. For the isolation of the embryo sacs, ovules were collected from ovaries of flowers 1 day after
anthesis, and treated with an enzyme solution for digesting cell walls on a gyratory shaker. After 12 h of enzyme treatment,
these ovules were dissected using a glass needle under an inverted microscope to release the embryo sacs. The embryo sacs,
characterized by their specific size, were successfully released by these successive treatments. The viability of the embryo
sacs was more than 80% as assessed with fluorescein diacetate staining. Fluorescent staining with 4,6-diamidino-2-phenylindole
revealed the nuclei of the egg apparatus in the isolated embryo sacs. The procedure for isolating embryo sacs established
in this study will offer a new approach to further in vitro studies on fertilization in Dianthus.
Received: 20 January 1999 / Revision received: 12 July 1999 / Accepted: 17 August 1999 相似文献
8.
Olga Rotreklová 《Biologia》2008,63(1):61-66
Two pollen stainability tests (Alexander’s stain and acetocarmine) were used to detect differences in pollen viability of
the sexual, apomictic and sterile plants of Hieracium subgen. Pilosella. In sexual taxa (Hieracium bauhini and H. densiflorum), the average stainability was 93.7–98.4%. Similarly high stainability (92.2–97.2%) was found in the apomictic Hieracium pilosellinum and in the majority of the apomictic populations (or plants) of the pentaploid and hexaploid H. bauhini. In some apomictic plants of Hieracium bauhini the average pollen stainability was 49.0–75.4%. The lowest pollen stainability was found in the sterile plants, i.e. the
triploid H. pistoriense (33.6%) and the pentaploid H. brachiatum (29.6%). 相似文献
9.
In many plant species with multiovulate ovaries, a considerable reduction in the number of ovules takes place. However, the
underlying physiological causes are not clear. In Prunus spp., although flowers present two ovules, usually only one seed is produced. We have followed the development and degeneration
of the two ovules in apricot (Prunus armeniaca L.) and examined the extent to which carbohydrates within the ovule might be involved in determining the fate of the ovule.
While the primary ovule grows in the days following anthesis, growth of the secondary ovule is arrested. Starch distribution
along the different ovular tissues exhibits several changes that are different in the two ovules. Primary ovule growth is
inversely related to starch content and this growth takes place independently of pollination since it occurs in the same way
in pollinated and unpollinated flowers. In the secondary ovule, starch disappears simultaneously from all ovular structures
and callose is layered at the chalazal end of the nucellus. The size of the secondary ovule does not change significantly
from anthesis to degeneration, and callose starts to accumulate 5 days after anthesis. Likewise, this process occurs independently
of pollination. These results are discussed in terms of the implications of the starch content of ovules in fertilization
success and ovule fate.
Received: 26 August 1997 / Revision accepted: 17 December 1997 相似文献
10.
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
11.
Various membrane-impermeable, water-soluble fluorescent tracers with different molecular weights were microinjected into
the central cell of the embryo sac of Torenia fournieri Lind. before and during fertilization. Before anthesis, there was high symplastic permeability between the central cell and
the egg apparatus cells. In this stage, fluorescent tracers up to 10 kDa could pass from the central cell into the egg apparatus
cells, whereas those with larger molecular weight remained in the central cell. As the embryo sac matured, symplastic permeability
decreased such that 2 d after anthesis only tracers less than 3 kDa could spread from the central cell into the egg cell.
There appeared to be no symplastic permeability between the primary endosperm and zygote after fertilization, since tracers
as small as 521 Da could not pass into the zygote in about half of the microinjected embryo sacs. This is the first report
of a change in cell-to-cell communication among the cells of the female germ unit before and after fertilization.
Received: 16 December 1999 / Accepted: 4 February 2000 相似文献
12.
Two isoforms of chalcone synthase (CHS) were isolated from cDNA libraries derived from UV-A-irradiated anthocyanin-accumulating
(DCb) and non-accumulating (DCs) cell cultures of carrot (Daucus carota L.). The clones designated as DcCHS1, which were present only in the DCb library, had a deduced primary sequence of 389 amino
acids and an expected molecular mass of 42.7 kDa, and seem to be alleles of those cloned by Ozeki et al. (1993). The second
isoform (DcCHS2) was present in both libraries. It had the highest degree of similarity (97.7%) to parsley CHS over all 397
amino acids. The expected molecular mass of the corresponding protein was 43.6 kDa. Results obtained from Southern blot analysis
indicated the existence of at least two CHS genes in carrot. A transient enhancement of the DcCHS1 mRNA level after continuous
irradiation with UV-A light could only be observed in anthocyanin-accumulating cultures, whereas an increase in DcCHS2 mRNA
was seen in both cell lines. The maximum accumulation of CHS mRNA occurred 48 h after the onset of UV-A irradiation. In the
European wild carrot the accumulation of DcCHS1 mRNA was restricted to the red central flowers, whereas the DcCHS2 mRNA was
detectable in all red and white petals, as well as leaves, but was absent in stems and roots. The expression of DcCHS1 was
restricted to anthocyanin-accumulating cells or organs. The heterologous expression of both cDNAs in Escherichia coli resulted in immunostainable bands of different sizes on the Western blot and high levels of catalytic CHS activity.
Received: 2 September 1999 / Accepted: 30 November 1999 相似文献
13.
High-efficiency induction of soybean hairy roots and propagation of the soybean cyst nematode 总被引:8,自引:0,他引:8
Cotyledon explants of 10 soybean [Glycine max (L.) Merr.] cultivars were inoculated with Agrobacterium rhizogenes strain K599 with and without binary vectors pBI121 or pBINm-gfp5-ER possessing both neomycin phosphotransferase II (nptII) and β-glucuronidase (gus) or nptII and green fluorescent protein (gfp) genes, respectively. Hairy roots were produced from the wounded surface of 54–95% of the cotyledon explants on MXB selective
medium containing 200 μg ml−1 kanamycin and 500 μg ml−1 carbenicillin. Putative individual transformed hairy roots were identified by cucumopine analysis and were screened for transgene
incorporation using polymerase chain reaction. All of the roots tested were found to be co-transformed with T-DNA from the
Ri-plasmid and the transgene from the binary vectors. Southern blot analysis confirmed the presence of the 35S-gfp5 gene in the plant genomes. Transgene expression was also confirmed by histochemical GUS assay and Western blot analysis for
the GFP. Attempts to induce shoot formation from the hairy roots failed. Infection of hairy roots of the soybean cyst nematode
(Heterodera glycines Ichinohe)-susceptible cultivar, Williams 82, with eggs of H. glycines race 1, resulted in the development of mature cysts about 4–5 weeks after inoculation. Thus the soybean cyst nematode could
complete its entire life cycle in transformed soybean hairy-root cultures expressing GFP. This system should be ideal for
testing genes that might impart resistance to soybean cyst nematode.
Received: 13 July 1999 / Accepted: 8 August 1999 相似文献
14.
R. N. Morgan J. Alvernaz L. Arthur W. W. Hanna P. Ozias-Akins 《Sexual plant reproduction》1997,10(3):127-135
Apomixis has never been reported in natural populations of pearl millet [Pennisetum glaucum (L.) R.Br.], although many wild relatives of pearl millet are obligate or facultative aposporous apomicts. Four-nucleate aposporous
embryo sacs are formed from somatic cells of the nucellus that do not undergo meiosis. Two mutants of pearl millet, female sterile (fs) and stubby head, have two developmental characteristics in common: a significant reduction in head length compared with
the wild-type and the formation of aposporous embryo sacs. Reproductive development in fs and stubby head mutants was examined in depth because of the potential for illuminating basic cellular or developmental factors
that may function to alter embryo sac development. Genetic analysis of stubby head showed that this phenotype is conferred
by genes at two loci linked in coupling within 29 cM. Crosses between fs and stubby head mutants showed that, despite the similarities in phenotypes, the mutations are at different loci. The mutants
differ from wild-type in their inflorescence structure from the time of initiation of spikelet primordia through terminal
differentiation of the ovule. Both mutations could be categorized as meristic, since a change in inflorescence branch or organ
number was common and gynoecium development varied. We speculate that heterochronic development of the floral meristem and
organ initiation/specification programs may be the underlying mechanism for phenotypic changes in these mutants throughout
the floral phase.
Received: 25 October 1996 / Accepted: 13 March 1997 相似文献
15.
Monoclonal antibodies that recognize pectins were used for the localization of esterified (JIM7) and acidic, unesterified
(JIM5) forms of pectin in pollen tube walls of Ornithogalum virens L. (x = n = 3). The results indicated that the distribution of the two forms of pectin in the pollen tube wall depended on
the medium (liquid or solid) used for pollen germination. In pollen tubes grown in the liquid medium, the localization of
JIM7 was limited to the very tip of the pollen tube, whereas the localization of JIM5 indicated a uniform distribution of
unesterified pectins in the very tip of the tube and along the subapical parts of the tube wall. In tubes germinated on the
medium stabilized with agar (1–2%) the localization of JIM7 and JIM5 indicated the presence of both forms of pectin in the
tube tip and along the whole length of the pollen tube wall in a ring-like pattern. Thus, the localization of esterified pectins
in the sub-apical part of the pollen tube wall, below the apex of the tube, is described for the first time. Measurements
of the growth rates of pollen tubes growing on the two types of medium indicated that oscillations in tube growth rate occur
but these do not coincide with the pattern of pectin distribution in the tube wall. Our results complement the previous data
obtained for the localization of JIM5 and JIM7 in pollen tube walls of other plant species. (Y.-Q. Li et al. 1994, Sex Plant
Reprod 7: 145–150) and provide new insight into an understanding of the construction of the pollen tube wall and the physiology
of pollen grain germination.
Received: 25 January 1999 / Accepted: 23 June 1999 相似文献
16.
Microtubule organization plays an important role in plant morphogenesis; however, little is known about how microtubule arrays
transit from one organized state to another. The use of a genetically incorporated fluorescent marker would allow long-term
observation of microtubule behavior in living cells. Here, we have characterized a Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) cell line that had been stably transformed with a gfp-mbd construct previously demonstrated to label microtubules (J. Marc et al., 1998, Plant Cell 10: 1927–1939). Fluorescence levels
were low, but interphase and mitotic microtubule arrays, as well as the transitions between these arrays, could be observed
in individual gfp-mbd-transformed cells. By comparing several attributes of transformed and untransformed cells it was concluded that the transgenic
cells are not adversely affected by low-level expression of the transgene and that these cells will serve as a useful and
accurate model system for observing microtubule reorganization in vivo. Indeed, some initial observations were made that are
consistent with the involvement of motor proteins in the transition between the spindle and phragmoplast arrays. Our observations
also support the role of the perinuclear region in nucleating microtubules at the end of cell division with a progressive
shift of these microtubules and/or nucleating activity to the cortex to form the interphase cortical array.
Received: 2 June 1999 / Accepted: 13 August 1999 相似文献
17.
Takashi Okada Andrew S. Catanach Susan D. Johnson Ross A. Bicknell Anna M. Koltunow 《Sexual plant reproduction》2007,20(4):199-211
Asexual seed formation (apomixis) in Hieracium aurantiacum occurs by mitotic embryo sac formation without prior meiosis in ovules (apomeiosis), followed by fertilization-independent
embryo and endosperm development. Sexual reproduction begins first in Hieracium ovules with megaspore mother cell (MMC) formation. Apomixis initiates with the enlargement of somatic cells, termed aposporous
initial (AI) cells, near sexual cells. AI cells grow towards sexually programmed cells undergoing meiosis, which degrade as
the dividing nuclei of AIs obscure and displace them. Following Agrobacterium-mediated transformation of an aneuploid Hieracium aurantiacum apomict, a somaclonal mutant designated “loss of apomeiosis 1” (loa1) was recovered, which had significantly lost the ability to form apomictic seed. Maternal apomictic progeny were rare and
low levels of germinable seedlings were primarily derived from meiotically derived eggs. Cytological analysis revealed defects
in AI formation and function in loa1. Somatic cells enlarged some distance away from sexual cells and unlike AI cells, these expanded away from sexual cells without
nuclear division. Surprisingly, many accumulated callose in the walls, a marker associated with meiotically specified cells.
These defective AI (DAI) cells only had partial sexual identity as they failed to express a marker reflecting entry to meiosis
that was easily detected in MMCs and they ultimately degraded. DAI cell formation did not lead to a compensatory increase
in functional sexual embryo sacs, as collapse of meiotic embryo sacs was prevalent in the aneuploid somaclonal mutant. Positional
cues that are important for AI cell differentiation, growth and fate may have been disrupted in the loa1 mutant and this is discussed.
The authors Takashi Okada, Andrew S. Catanach and Susan D. Johnson made equal contributions to the data. 相似文献
18.
Intracellular chloroplast photorelocation in the moss Physcomitrella patens is mediated by phytochrome as well as by a blue-light receptor 总被引:3,自引:0,他引:3
The light-induced intracellular relocation of chloroplasts was examined in red-light-grown protonemal cells of the moss Physcomitrella patens. When irradiated with polarized red or blue light, chloroplast distribution in the cell depended upon the direction of the
electrical vector (E-vector) in both light qualities. When the E-vector was parallel to the cross-wall (i.e. perpendicular
to the protonemal axis), chloroplasts accumulated along the cross-wall; however, no accumulation along the cross-wall was
observed when the E-vector was perpendicular to it (i.e. parallel to the protonemal axis). When a part of the cell was irradiated
with a microbeam of red or blue light, chloroplasts accumulated at or avoided the illumination point depending on the fluence
rate used. Red light of 0.1–18 W m−2 and blue light of 0.01–85.5 W m−2 induced an accumulation response (low-fluence-rate response; LFR), while an avoidance response (high-fluence-rate response;
HFR) was induced by red light of 60 W m−2 or higher and by blue light of 285 W m−2. The red-light-induced LFR and HFR were nullified by a simultaneous background irradiation of far-red light, whereas the
blue-light-induced LFR and HFR were not affected at all by this treatment. These results show, for the first time, that dichroic
phytochrome, as well as the dichroic blue-light receptor, is involved in the chloroplast relocation movement in these bryophyte
cells. Further, the phytochrome-mediated responses but not the blue-light responses were revealed to be lost when red-light-grown
cells were cultured under white light for 2 d.
Received: 7 September 1999 / Accepted: 15 October 1999 相似文献
19.
Light-induced expression of the Gsa gene encoding the heme and chlorophyll biosynthetic enzyme glutamate 1-semialdehyde aminotransferase in Chlamydomonas reinhardtii was previously shown to involve Ca2+ and calmodulin (CaM) (C. lm et al. 1996, Plant Cell 8: 2245–2253). To further analyze the signal transduction pathway for
light-induced Gsa expression, the effects of several pharmacological agents were examined. Treatment of light-dark synchronized cells with
the heterotrimeric G-protein agonist Mas-7 caused partial induction of Gsa in the dark. The phospholipase C inhibitor U73122 inhibited light induction of Gsa. Exposure of cells to light caused a sustained 3-fold increase in cellular d-inositol 1,4,5-trisphosphate (InsP3) concentration. KN-93, a specific inhibitor of Ca2+/CaM-dependent protein kinase II, inhibited light induction of Gsa. In contrast, cyclosporin A, a specific inhibitor of the Ca2+/CaM-dependent phosphoprotein phosphatase calcineurin, did not affect light induction of Gsa. These results, together with the earlier results, suggest the involvement of a canonical signal transduction pathway for
light-regulated Gsa expression that involves a heterotrimeric G-protein activation, phospholipase C-catalyzed InsP3 formation, InsP3-dependent Ca2+ release, and activation of a downstream signaling pathway through a Ca2+/CaM-dependent protein kinase.
Received: 21 October 1999 / Accepted: 3 December 1999 相似文献
20.
Iron limitation led to a large increase in extracellular ferricyanide (Fe[III]) reductase activity in cells of the green
alga Chlamydomonas reinhardtii Dangeard. Mass-spectrometric measurement of gas exchange indicated that ferricyanide reduction in the dark resulted in a
stimulation of respiratory CO2 production without affecting the rate of respiratory O2 consumption, consistent with the previously postulated activation of the oxidative pentose phosphate pathway in support of
Fe(III) reduction by iron-limited Chlamydomonas cells (X. Xue et al., 1998, J. Phycol. 34: 939–944). At saturating irradiance, the rate of ferricyanide reduction was stimulated
almost 3-fold, and this stimulation was inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. Ferricyanide reduction during
photosynthesis resulted in approximately a 50% inhibition of photosynthetic CO2 fixation at saturating irradiance, and almost 100% inhibition of CO2 fixation at sub-saturating irradiance. Photosynthesis by iron-sufficient cells was not affected by ferricyanide addition.
Addition of 250 μM ferricyanide to iron-limited cells in which photosynthesis was inhibited (either by the presence of glycolaldehyde,
or by maintaining the cells at the CO2 compensation point) resulted in a stimulation in the rate of gross photosynthetic O2 evolution. Chlorophyll a fluorescence measurements indicated a large increase in non-photochemical quenching during ferricyanide reduction in the
light; the increase in nonphotochemical quenching was abolished by the addition of nigericin. These results suggest that reduction
of extracellular ferricyanide (mediated at the plasma membrane) interacts with both photosynthesis and respiration, and that
both of these processes contribute NADPH in the light.
Received: 15 September 1999 / Accepted: 14 October 1999 相似文献