bluuebunny/crossref_metadata_2025 huggingface dataset:
Remote sensing and petroleum seepage: a review and case study
Authors: Van Der Meer Freek , Van Dijk Paul , Van Der Werff Harald , Yang Hong
Published: March 2003

When reservoirs leak, varying quantities of oil and gas migrate to the surface as macroseeps, which are visible, and microseeps, which are invisible. This review article describes the mechanisms of seepage and the resulting surface manifestations in relation to optical high‐resolution remote sensing data. Oil pools and tar deposits (macroseeps) often can be detected directly by remote sensing. Microseeps are more difficult to study using remote sensing, but they give rise to vegetation stress, and cause geochemical alterations in soil and rocks, which can be studied indirectly using hyperspectral sensors. An integrated methodology is presented to combine various geoscience and remote sensing datasets for seepage detection. A combination of red‐edge modelling algorithms and spectral matching tools is identified that provides a validated technique for onshore microseepage detection. These remote sensing tools are not only important for petroleum exploration, but also have environmental implications because seeps emit greenhouse gases. A statistical data integration approach was developed based on Bayesian assumptions, which can be used to integrate hyperspectral remote sensing data, other satellite remote sensing data, and ancillary field geological and geochemical datasets, for modelling microseepage. In a case study from the Ventura basin (Santa Barbara) in Southern California, Probe‐1 data from the 1998 Geosat Group Shoot are integrated with field and subsurface geological and geochemical data to predict possible sites of hydrocarbon microseepage.
Intracontinental subduction and Palaeozoic inheritance of the lithosphere suggested by a teleseismic experiment across the Chinese Tien Shan
Authors: Poupinet G. , Avouac J.‐Ph. , Jiang M. , Wei S. , Kissling E. , Herquel G. , Guilbert J. , Paul A. , Wittlinger G. , Su H. , Thomas J.‐C.
Published: March 2003

Teleseismic tomography across the Chinese Tien Shan shows that seismic wave speeds in the lithosphere beneath central Tien Shan are high and therefore the lithosphere is not weaker than that beneath the adjacent undeformed Tarim and Junggar basins. There is evidence for significant velocity contrasts within the lithosphere that are presumably inherited from the Palaeozoic collision history. The high‐velocity, thick Yili block observed underneath the northern Tien Shan is a clue for shortening by a intracontinental subduction. The observed geometry is consistent with a simple model of intracontinental subduction and suggests that, during orogeny, the lithosphere has remained heterogeneous and has deformed along existing planes of weakness rather than by homogeneous thickening of a particularly weak lithosphere.
A new proposal for the late Cenozoic geodynamic evolution of the western Mediterranean
Authors: Gelabert Bernadí , Sàbat Francesc , Rodríguez‐Perea Antonio
Published: March 2003

A simple mechanism of arcuate fold belt and back‐arc basin formation is presented based on the opening of mega‐continental tension gashes along pre‐existing, deep, parallel and steep faults that separate lithospheric units with different properties. If plate convergence is parallel to these faults, the fault‐bounded units open at right angles to the convergence vector, adopting an arcuate shape with thrusting in front of the bowed‐out units and extensional basin opening between the separated units. This model is applied to the Cenozoic geodynamic evolution of the western Mediterranean. After the Iberian collision 35–30 Ma, several ellipsoidal basins (Valencia, Alboran, North Algerian and Liguro–Provençal) developed by 10 Ma along the eastern margin of the Iberian plate. The formation of these basins is attributed to an increase in NE–SW horizontal tectonic palaeostress during early–middle Miocene times resulting from the post‐subduction collision of the Tethyan oceanic lithosphere.
Latest marine horizon north of Qomolangma (Mt Everest): implications for closure of Tethys seaway and collision tectonics
Authors: Wang Chengshan , Li Xianghui , Hu Xiumian , Jansa L. F.
Published: March 2003

The newly discovered marine horizon at Zhepure Syncline, north of Qomolangma, revises timing of the closure of the eastern Neo‐Tethys seaway in the central Himalayas. The marine Pengqu Formation conformably overlies a Lutetian shallow‐water carbonate platform and comprises shales interbedded with sandstones deposited in a neritic shelf environment. The strata are dated by nannofossils and foraminifera as late early Lutetian to late Priabonian age (NP15–NP20, deposited ≈ 47–34 Ma), indicating that the final closure of the Tethys seaway in this region occurred at ∼ 34 Ma. The newly discovered strata provide evidence about emplacement of a major thrust sheet south of southern Tibet prior to ∼ 37 Ma, which affected the regional climate.
Response of precipitation over Greenland and the adjacent ocean to North Pacific warm spells during Dansgaard–Oeschger stadials
Authors: Kiefer Thorsten , Lorenz Stephan , Schulz Michael , Lohmann Gerrit , Sarnthein Michael , Elderfield Henry
Published: March 2003

ABSTRACTPalaeoceanographic reconstructions from the North Atlantic indicate massive ice breakouts from East Greenland near the onset of cold Dansgaard–Oeschger (D–O) stadials. In contrast to these coolings in the North Atlantic area, a new sea‐surface temperature record reveals concomitant warm spells in the northern North Pacific. A sensitivity experiment with an atmospheric general circulation model is used to test the potential impact of sea‐surface warmings by 3.5 °C in the North Pacific, on top of otherwise cold stadial climate conditions, on the precipitation regime over the Northern Hemisphere ice sheets. The model predicts a maximum response over East Greenland and the Greenland Sea, where a 40% increase in net annual snow accumulation occurs. This remote effect of North Pacific warm spells on the East Greenland snow‐accumulation rate may play an important role in generating D–O cycles by rebuilding the ice lost during ice breakouts. In addition, the increased precipitation over the Greenland Sea may help to sustain the D–O stadial climate state.
Monochromatic infra‐sound waves recorded offshore Ecuador: possible evidence of methane release
Authors: Pontoise B. , Hello Y.
Published: March 2003

ABSTRACT Methane is known to be a greenhouse gas but it is difficult to estimate its significance. We have identified a new approach for monitoring fluxes of methane from large areas of sea floor. During spring 1998, we conducted an offshore passive seismic experiment using 13 three‐component digital Ocean Bottom Seismometers. During this 3‐week experiment, we recorded unusual sustained and intense monochromatic infrasound waves (6–7 Hz). The origin of the noise is tentatively interpreted as pressure‐waves resulting from oscillating clouds of bubbles. Such clouds must have a characteristic size of ∼ 10 m, at depths of 5–15 m, and must contain more than 1010 bubbles of 1 mm radius to produce the observed frequency. The presence of a Bottom Simulating Reflector in the study area suggests that gas seepage may occur at the seafloor, near 500 m depth. Then, bubbles of gas, namely methane, could form in the water column. Although highly speculative, Ocean Bottom Seismometer records could potentially be useful for monitoring gas seeps and/or related unusual behaviour of the seabed.
Active hydrate destabilization in Lake Baikal, Siberia?
Authors: De Batist Marc , Klerkx Jan , Van Rensbergen Pieter , Vanneste Maarten , Poort Jeffrey , Golmshtok Alexander Y. , Kremlev Andrei A. , Khlystov Oleg M. , Krinitsky Petr
Published: March 2003

ABSTRACT In this paper, we present new seismic and heat‐flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper‐than‐normal and regions of shallower‐than‐normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift‐basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre‐existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present‐day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature.
RNA binding characteristics of a 16 kDa glycine‐rich protein from maize
Authors: Ludevid M. Dolors , Freire Miguel Angel , Gómez Jordi , Burd Christopher G. , Albericio Fernando , Giralt Ernest , Dreyfuss Gideon , Pagès Montserrat
Published: March 2003

We have previously described a developmentally regulated mRNA in maize that accumulates in mature embryos and is involved in a variety of stress responses in the plant. The sequence of the encoded 16 kDa protein (MA 16) predicts that it is an RNA‐binding protein, since it possesses a ribonucleoprotein consensus sequence‐type RNA‐binding domain (CS‐RBD). To assess the predicted RNA binding property of the protein and as a starting point to characterize its function we have used ribohomopolymer‐binding assays. Here we show that the MA16‐encoded protein binds preferentially to uridine‐ and guanosine‐rich RNAs. In light of these results a likely role for this protein in RNA metabolism during late embryogenesis and in the stress response is discussed.
Members of the acetohydroxyacid synthase multigene family of Brassica napus have divergent patterns of expression
Authors: Ouellet Thérèse , Rutledge Robert G. , Miki Brian L.
Published: March 2003

Brassica species possess the most complex acetohydroxyacid synthase (AHAS) multigene family reported for plants. The AHAS genes code for an essential enzyme in branched‐chain amino acid biosynthesis. In the allotetraploid species, B. napus, four (AHAS1–4) of the five AHAS genes have been cloned and sequenced. The transcripts were examined by RNase protection assays using gene‐specific, antisense RNA probes. Only AHAS1, AHAS2 and AHAS3 were shown to be expressed in B. napus and one of the diploid progenitor species B. campestris or B. oleracea. AHAS1 and AHAS3 are highly conserved genes that presumably code for the essential AHAS housekeeping functions. They were expressed as low abundance mRNA in all somatic and reproductive tissues examined. AHAS2, which is structurally distinct from all other plant AHAS genes, was only expressed in mature ovules and extra‐embryonic tissues of immature seeds. This study provides direct evidence for multiple AHAS isoforms in plants and for an AHAS gene which is developmentally regulated in a tissue‐specific manner. The discovery raises questions concerning the functional significance of AHAS in seed development.
Differential response of maize catalases and superoxide dismutases to the photoactivated fungal toxin cercosporin
Authors: Williamson John D. , Scandalios John G.
Published: March 2003

Many fungi of the genus Cercospora produce a light‐induced, photoactivated polyketide toxin called cercosporin. In the presence of light an excited form (triplet state) of the toxin molecule is produced which, depending on the reducing potential of the environment, reacts with molecular oxygen to produce singlet oxygen and/or superoxide radicals. In this paper a system is presented for analysis of antioxidant defense gene response using purified cercosporin under conditions demonstrated to favor superoxide formation. Under the assay conditions employed, changes in total catalase activity, as well as individual isozyme protein levels generally mirrored the changes observed in corresponding steady‐state RNA levels in response to applied cercosporin. In contrast, while transcript accumulation for most maize superoxide dismutases increased dramatically, both total superoxide dismutase activity and individual isozyme protein levels remained constant in all toxin treatments. In one case, the analyses indicated that there are two distinct transcripts that hybridize with a gene‐specific probe for Sod3. These two transcripts responded differentially to applied toxin (levels of the larger transcript increased while the smaller decreased), whereas corresponding steady‐state levels for the SOD‐3 isozyme proteins remained constant. This suggests that protein turnover might play a role in the response of these SODs to activated oxygen species.
Vicilin with carboxy‐terminal KDEL is retained in the endoplasmic reticulum and accumulates to high levels in the leaves of transgenic plants
Authors: Wandelt Christine I. , Khan M. Rafiqul I. , Craig Stuart , Schroeder Harmut E. , Spencer Donald , Higgins Thomas J.V.
Published: March 2003

Gene constructs were designed to test the effect of the endoplasmic reticulum (ER)‐targeting signal, KDEL, on the level of accumulation of a foreign protein in transgenic plants. The gene for the pea seed protein vicilin was modified by the addition of a sequence coding for this tetrapeptide at its carboxyl terminus. The altered gene was placed under the control of a CaMV 35S promoter and its expression in the leaves of both tobacco and lucerne (alfalfa) was compared with that of an equivalent vicilin construct lacking the KDEL‐coding sequence. The presence of the ER‐targeting signal led to a greatly enhanced accumulation of the heterologous protein. In lucerne and tobacco leaves, the level of vicilin‐KDEL protein was 20 and 100 times greater than that of the unmodified vicilin, respectively. These differences in expression level could not be explained by corresponding differences in the steady‐state levels or the translatability of the mRNAs. However, when the stability of vicilin and vicilin‐KDEL proteins was compared in their respective transgenic hosts, unmodified vicilin was found to be degraded with a half‐life of 4.5 h while vicilin‐KDEL was much more stable with a half‐life of more than 48 h.

Immunogold labelling of leaf tissues from transgenic lucerne and tobacco showed the presence of vicilin associated with large aggregates within the ER lumen of vicilin‐KDEL plants. No such aggregates were detected in transgenic plants expressing wild‐type vicilin.

It is concluded that the carboxy‐terminal KDEL caused the retention of the modified vicilin in the ER, and that this retention led to the increased stability and higher level of accumulation of vicilin‐KDEL in leaves of transgenic plants.
Characterization of cDNAs encoding two isoforms of granule‐bound starch synthase which show differential expression in developing storage organs of pea and potato
Authors: Dry Ian , Smith Alison , Edwards Anne , Bhattacharyya Madan , Dunn Paul , Martin Cathie
Published: March 2003

We have isolated cDNA clones to two isoforms of granule‐bound starch synthase (GBSS) from pea embryos and potato tubers. The sequences of both isoforms are related to that of glycogen synthase from E. coli and one, GBSSI, is very similar to the waxy protein of maize and other species. In pea, GBSSII carries a novel 203‐amino‐acid domain at its N‐terminus. Genes encoding both proteins are expressed during pea embryo development, but GBSSII is most highly expressed earlier in development than GBSSI. Similarly, GBSSI and GBSSII are differentially expressed in developing potato tubers. Expression of both isoforms is much lower in other organs of pea than in embryos. GBSSII is expressed in every organ tested while GBSSI is not expressed in roots, stipules or flowers. The possible consequences of this differential use of GBSS isoforms are discussed.
Photoresponses of transgenic Arabidopsis seedlings expressing introduced phytochrome B‐encoding cDNAs: evidence that phytochrome A and phytochrome B have distinct photoregulatory functions
Authors: McCormac Alex C. , Wagner Doris , Boylan Margaret T. , Quail Peter H. , Smith Harry , Whitelam Garry C.
Published: March 2003

The photocontrol of hypocotyl elongation has been studied in two transgenic lines of Arabidopsis thaliana which contain elevated levels of phytochrome B encoded by either an introduced rice‐ or Arabidopsis‐derived cDNA driven by the 35S CaMV promoter. Inhibition of hypocotyl growth in etiolated seedlings of the phyB‐transformed lines was saturated at photon fluence rates of continuous red light (R) which were markedly lower than those required for inhibition of growth in seedlings of the isogenic wild‐type (WT). Inhibition of hypocotyl growth in etiolated seedlings of the phyB‐transgenic lines under continuous far‐red irradiation (FR), however, showed the same relationship with fluence rate as WT. Light‐grown seedlings of the phyB‐transgenic lines responded to end‐of‐day FR by an acceleration of growth, in a manner comparable with WT. This response was unaltered when the end‐of‐day FR was extended from a 15 min pulse to 14 h of continuous irradiation. The response of light‐grown, phyB‐transformed seedlings to decreasing R:FR ratio was also qualitatively similar to WT, i.e. increased elongation growth of the hypocotyl and petioles occurred under low R:FR quantum ratio. However, absolute elongation growth was markedly less in the transgenic seedlings at all R:FR ratios tested than in WT. Together, these data indicate that seedlings over‐expressing phytochrome B are more responsive to R than are WT, but are unaltered in their responsiveness to FR. By contrast, seedlings overexpressing phytochrome A are more responsive than WT to both R and FR; whereas the phytochrome B‐deficient mutant hy3 is unresponsive to R while retaining WT‐like responsiveness to FR. These data indicate that in WT etiolated seedlings phytochrome A mediates the effects of continuous FR, and phytochrome B the effects of continuous R. The evidence thus supports the conclusion that these two molecular species of the photoreceptor have differential regulatory roles in the plant.
The self‐incompatibility response in Papaver rhoeas is mediated by cytosolic free calcium
Authors: Franklin‐Tong Vernonica E. , Ride Jon P. , Read Nick D. , Trewavas Anthony J. , Franklin F. Christopher H.
Published: March 2003

The role of Ca2+ signalling during the self‐incompatibility (SI) response in Papaver rhoeas L. has been investigated using Ca2+‐sensitive dyes. Pollen tubes were micro‐injected with Calcium Green‐1 and cytosolic free calcium ([Ca2+]i) imaged using laser scanning confocal microscopy (LSCM). Addition of incompatible stigmatic S‐glycoproteins induced a transient increase in the level of [Ca2+]i in pollen tubes. In contrast, no rise in [Ca2+]i was detectable after addition of either compatible or heat‐denatured incompatible stigmatic S‐glycoproteins. The elevation of [Ca2+]i was followed by the specific inhibition of pollen tube growth in incompatible reactions. It has been shown previously that gene expression in pollen tubes is switched on during an incompatible reaction. Since the [Ca2+]i transient appeared to originate from the region where the nuclei are located, Ca2+ may be involved in locally regulating the expression of these genes. The photoactivation of caged Ca2+ to artificially elevate [Ca2+]i resulted in the inhibition of pollen tube growth and thus mimicked the SI response. Taken together, the results provide an important link between a transient rise in [Ca2+]i and the biological phenomenon of inhibition of pollen tube growth and demonstrate, for the first time, direct evidence that the SI response in P. rhoeas is mediated by [Ca2+]i.
amp1 ‐ a mutant with high cytokinin levels and altered embryonic pattern, faster vegetative growth, constitutive photomorphogenesis and precocious flowering
Authors: Chaudhury Abdul M. , Letham Stuart , Craig Stuart , Dennis Elizabeth S.
Published: March 2003

amp1, a mutant of Arabidopsis thaliana has a phenotype altered in three different aspects of plant development; spatial pattern, photomorphogenetic growth, and initiation of flowering. While fewer than 0.1% of the seedlings of wild‐type plants are non‐dicot as many as 20% of the seedlings of the amp1 mutant are tricot or tetracot. The rate of leaf initiation is faster and vegetative phyllotaxy is altered in amp1. When grown in the dark amp1 seedlings show morphogenetic properties similar to light‐grown wild‐type plants: they do not form an apical hook, have hypocotyls shorter than wild‐type plants and form etiolated true leaves. amp1 mutant flowers significantly earlier than congenic Amp1 plants. The mutant has six times more cytokinin than wild‐type suggesting that endogenous cytokinin levels might play an important role in mediating these different developmental processes. AMP1 might code for a negative regulator of cytokinin biosynthesis, or may be required for the degradation of cytokinin.
The developmental and tissue‐specific expression of tobacco phytochrome‐A genes
Authors: Adam Eva , Szell Marta , Szekeres Miklos , Schaefer Eberhard , Nagy Ferenc
Published: March 2003

Plant photomorphogenesis is regulated by at least three different types of photoreceptors, among them the best characterized is phytochrome. Throughout their development plants express several types of phytochrome apoproteins that are encoded by members of a small multigene family. Two genes have been isolated from Nicotiana tabacum, designated Nt‐PHY‐A1 and A2, encoding type‐A phytochrome apoproteins. Chimeric genes, containing the promoter regions of the PHY‐A1 and A2 genes fused to the GUS or to the CAT reporter genes, were then constructed and transferred into tobacco. The expression characteristics of the endogenous PHY‐A1, PHY‐A2 genes, as well as those of the PHY‐A1‐GUS/CAT, PHY‐A2‐GUS/CAT transgenes were determined by RNase protection assays and by GUS histochemical staining. It is reported here that (i) the expression levels of the tobacco PHY‐A genes and those of the transgenes are downregulated by light, (ii) this light‐sensitive expression is mediated, at least partially, by phytochrome and further modified by (iii) a developmental programme and (iv) a welldefined organ and tissue‐specific pattern. Furthermore, it is shown that the expression of the PHY‐A genes is not affected by the circadian clock. It is concluded that the expression of these tobacco genes is controlled by, at least, three different regulatory mechanisms at the level of transcription.
The promoters of two carboxylases in a C4 plant (maize) direct cell‐specific, light‐regulated expression in a C3 plant (rice)
Authors: Matsuoka Makoto , Kyozuka Junko , Shimamoto Ko , Kano‐Murakami Yuriko
Published: March 2003

C4 plants have two carboxylases which function in photosynthesis. One, phosphoenolpyruvate carboxylase (PEPC) is localized in mesophyll cells, and the other, ribulose bisphosphate carboxylase (RuBPC) is found in bundle sheath cells. In contrast, C3 plants have only one photosynthetic carboxylase, RuBPC, which is localized in mesophyll cells. The expression of PEPC in C3 mesophyll cells is quite low relative to PEPC expression in C4 mesophyll cells. Two chimeric genes have been constructed consisting of the structural gene encoding β‐glucuronidase (GUS) controlled by two promoters from C4 (maize) photosynthetic genes: (i) the PEPC gene (pepc) and (ii) the small subunit of RuBPC (rbcS). These constructs were introduced into a C3 cereal, rice. Both chimeric genes were expressed almost exclusively in mesophyll cells in the leaf blades and leaf sheaths at high levels, and no or very little activity was observed in other cells. The expression of both genes was also regulated by light. These observations indicate that the regulation systems which direct cell‐specific and light‐inducible expression of pepc and rbcS in C4 plants are also present in C3 plants. Nevertheless, expression of endogenous pepc in C3 plants is very low in C3 mesophyll cells, and the cell specificity of rbcS expression in C3 plants differs from that in C4 plants. Rice nuclear extracts were assayed for DNA‐binding protein(s) which interact with a cis‐regulatory element in the pepc promoter. Gel‐retardation assays indicate that a nuclear protein with similar DNA‐binding specificity to a maize nuclear protein is present in rice. The possibility that differences in pepc expression in a C3 plant (rice) and C4 plant (maize) may be the result of changes in cis‐acting elements between pepc in rice and maize is discussed. It also appears that differences in the cellular localization of rbcS expression are probably due to changes in a trans‐acting factor(s) required for rbcS expression.
Inhibition of plant plasma membrane phosphoinositide phospholipase C by the actin‐binding protein, profilin
Authors: Drøbak Bjørn K. , Watkins Peter A.C. , Valenta Rudolf , Dove Stephen K. , Lloyd Clive W. , Staiger Christopher J.
Published: March 2003

A key event in signal transduction in many eukaryotes is activation of polyphosphoinositide‐specific phospholipase C (PIC). This enzyme hydrolyses the plasma membrane‐associated lipid, phosphatidylinositol(4,5)bisphosphate (Ptdlns(4,5)P2) which leads to the production of the two second messenger molecules: inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) and 1,2‐diacylglycerol (DG). In plants, an enzyme which functionally resembles mammalian PIC is known to exist in the plasma membrane, but little is understood about how its activity is regulated. The recent discovery of several plant proteins with 30–40% homology to the mammalian actin‐ and phosphoinositide‐binding protein, profilin, has prompted an investigation as to whether these proteins (plant profilins) are able to interact with polyphosphoinositides and, if so, whether such interactions have physiological relevance for signal transduction via the plant phosphoinositide system.

In this study it is demonstrated that a direct and highly specific interaction does exist between plant profilin and polyphosphoinositides and that these interactions dramatically affect the ability of plant plasma membrane phosphoinositide phospholipase C to utilize phosphoinositides for second messenger production. These data are the first to demonstrate a functional role of plant profilin in controlling polyphosphoinositide turnover and also provide the first evidence for a direct effect of an actin‐binding protein on a membrane‐associated signalling enzyme. These findings indicate a novel mechanism for control of plant phosphoinositide turnover, and suggest a possible link between plant cell activation, second messenger production and modulation of cytoskeletal dynamics.
Potato lectin: a modular protein sharing sequence similarities with the extensin family, the hevein lectin family, and snake venom disintegrins (platelet aggregation inhibitors)
Authors: Kieliszewski Marcia J. , Showalter Allan M. , Leykam Joseph F.
Published: March 2003

Potato (Solanum tuberosum) lectin, is a chimeric chitin‐binding protein comprised of a lectin domain fused to a hydroxyproline‐rich glycoprotein domain. Here peptide sequence information from both domains is presented. A partial sequence of a major tryptic peptide T2: Leu‐Pro‐Ser‐Hyp‐Hyp‐Hyp‐Hyp‐Hyp‐Hyp‐(His)‐Hyp‐Ser‐Hyp‐Hyp‐Hyp‐Hyp‐Ser‐Hyp‐Hyp‐Ser‐Hyp‐Hyp‐Hyp‐Hyp‐Ser‐Hyp‐Hyp‐ was similar to the ‘P3’ type extensin major repetitive sequence: Ser‐Hyp‐Hyp‐Hyp‐Hyp‐Ser‐Hyp‐Ser‐Hyp‐Hyp‐Hyp‐Hyp‐suggesting common evolutionary origins for the extensins and the hydroxyproline‐rich glycoprotein (HRGP) domain of potato lectin. Furthermore, alignment of three chymotryptic peptides from potato lectin, C1: Cys‐Gly‐Thr‐Thr‐Ser‐Asp‐Tyr, C2: Cys‐Ser‐Pro‐Gly‐Tyr, and C8: Thr‐Gly‐Glu‐Cys‐Cys‐Ser‐Ile with similar sequences from the hevein lectin family indicates that they have homologous chitin‐binding domains, and hence have common evolutionary origins. Finally, all plant chitin‐binding domains examined bore a remarkable sequence similarity, particularly in the spacing of Cys residues, to the disintegrins (platelet aggregation inhibitors) which occur in crotalid and viperid snake venoms. As such, sequence similarities not only identify potato lectin as a member of both the hevein and extensin families of plant proteins, but also suggest that an archetypal polypeptide module gave rise to both the plant chitin‐binding domain and the reptile disintegrins.
Xanthophyll biosynthesis in chromoplasts: isolation and molecular cloning of an enzyme catalyzing the conversion of 5,6‐epoxycarotenoid into ketocarotenoid
Authors: Bouvier Florence , Hugueney Philippe , D'Harlingue Alain , Kuntz Marcel , Camara Bilal
Published: March 2003

The late steps of carotenoid biosynthesis in plants involve the formation of xanthophylls. Little is known about the enzymology of these steps. This paper reports the purification to homogeneity of a xanthophyll biosynthetic enzyme from Capsicum annuum chromoplasts, which catalyzes the conversion of the ubiquitous 5,6‐epoxycarotenoids, antheraxanthin and violaxanthin, into capsanthin and capsorubin, respectively. Owing to its bifunctionality, the name capsanthin‐capsorubin synthase is proposed for this new enzyme. The purified enzyme is a monomer with a molecular mass of 50 kDa. Antibodies raised against this enzyme allowed the isolation of a full‐length cDNA clone encoding a capsanthin capsorubin synthase high molecular weight precursor. The primary deduced structure reveals the presence of a consensus nucleotide binding site. The capsanthin‐capsorubin synthase gene is specifically expressed during chromoplast development in fruits accumulating ketocarotenoids, but not in mutants impaired in this biosynthetic step.
Nuclear—organelle interactions: the immutans variegation mutant of Arabidopsis is plastid autonomous and impaired in carotenoid biosynthesis
Authors: Wetzel Carolyn M. , Jiang Cai‐Zhong , Meehan LeAnn J. , Voytas Daniel F. , Rodermel Steven R.
Published: March 2003

The immutans (im) variegation mutant of Arabidopsis thaliana contains green‐ and white‐sectored leaves due to the action of a nuclear recessive gene. The mutation is somatically unstable, and the degree of sectoring is influenced by light and temperature. Whereas the cells in the green sectors contain normal chloroplasts, the cells in the white sectors are heteroplastidic and contain non‐pigmented plastids that lack organized lamellar structures, as well as small pigmented plastids and/or rare normal chloroplasts. This indicates that the plastids in im white cells are not affected equally by the nuclear mutation and that the expression of immutans is ‘plastid autonomous’. In contrast to other variegation mutants with heteroplastidic cells, the defect in im is not maternally inherited. immutans thus represents a novel type of nuclear gene‐induced variegation mutant. It has also been found that the white tissues of immutans accumulate phytoene, a non‐colored C40 carotenoid intermediate. This suggests that immutans controls, either directly or indirectly, the activity of phytoene desaturase (PDS), the enzyme that converts phytoene to zeta‐carotene in higher plants. However, im is not the structural gene for PDS. A secondary effect of carotenoid deficiency, both in immutans and in wild‐type plants treated with a herbicide that blocks carotenoid synthesis, is an increase in acid ribonuclease activity in white tissue. It is concluded that the novel variegation generated by the immutans mutation should offer great insight into the complex circuitry that regulates nuclear—organelle interactions.
Efficient transformation of rice (Oryza sativa L.) mediated by Agrobacterium and sequence analysis of the boundaries of the T‐DNA
Authors: Hiei Yukoh , Ohta Shozo , Komari Toshihiko , Kumashiro Takashi
Published: March 2003

A large number of morphologically normal, fertile, transgenic rice plants were obtained by co‐cultivation of rice tissues with Agrobacterium tumefaciens. The efficiency of transformation was similar to that obtained by the methods used routinely for transformation of dicotyledons with the bacterium. Stable integration, expression and inheritance of transgenes were demonstrated by molecular and genetic analysis of transformants in the R0, R1 and R2 generations. Sequence analysis revealed that the boundaries of the T‐DNA in transgenic rice plants were essentially identical to those in transgenic dicotyledons. Calli induced from scutella were very good starting materials. A strain of A. tumefaciens that carried a so‐called ‘super‐binary’ vector gave especially high frequencies of transformation of various cultivars of japonica rice that included Koshihikari, which normally shows poor responses in tissue culture.
Reduction of the chloroplastic fructose‐1,6‐bisphosphatase in transgenic potato plants impairs photosynthesis and plant growth
Authors: Koßmann Jens , Sonnewald Uwe , Willmitzer Lothar
Published: March 2003

Transgenic potato plants expressing reduced levels of the chloroplastic isoform of fructose‐1,6‐bisphosphatase (cp‐FBPase) were created via the antisense RNA technique. Transformants with different levels of FBPase activity were selected and analysed with respect to photosynthesis, carbon metabolism, and growth. FBPase activity of less than 15% of wild‐type levels led to reduced growth rates, probably due to the reduction of photosynthetic activity. A significant decrease in tuber yield is observed in plants with a FBPase activity below 15% of wild‐type levels, whereas plants with 36% of wild‐type enzyme activity still give normal tuber yields, even though they demonstrate a lowered photosynthetic capacity. Decreased photosynthesis also results in a reduction of total carbohydrate contents in leaves. Interestingly, increased carbohydrate partitioning towards soluble sugars is observed in plants displaying less than 15% of the wild‐type FBPase activity. When excised leaf discs are placed on sucrose‐containing media in darkness, discs derived from plants with a reduced FBPase activity accumulate higher amounts of starch. Possible implications are discussed.
Osmotic stress enhances the competence of Beta vulgaris vacuoles to respond to inositol 1,4,5‐trisphosphate
Authors: Allen Gethyn J. , Sanders Dale
Published: March 2003

Isolated vacuoles from Beta vulgaris storage roots respond to the intracellular signalling molecule inositol 1,4,5‐trisphosphate (InsP3). Whole vacuole patch clamp enables measurement of an inward current (cytosol‐directed) induced by cytosolic InsP3 which is fully reversible upon removal of InsP3. The reversal potentials of the InsP3‐induced whole vacuolar currents indicate a permeability ratio (P,Ca:P,K) of 200:1. Competence of vacuoles to respond to InsP3 is dependent upon the root tissue undergoing hyperosmotic stress before vacuole isolation. The magnitude of the hyperosmotic stress and the density of InsP3‐induced current per unit membrane area are exponentially related. A standing osmotic gradient across the vacuolar membrane further enhances the InsP3‐induced current, the current being larger when there is net water flux from the cytosol to the vacuolar lumen. InsP3‐induced currents are not affected by the cytosolic free Ca2+ concentration. The conductance of InsP3‐induced single channel currents varied greatly between individual outside‐out patches, but all showed a non‐linear increase in single channel current at physiological potentials. The reversal potentials of these currents indicated a PCa:PK of between 100:1 and 800:1.

The significance of these findings is discussed in relation to technical aspects of monitoring InsP3‐induced currents in plant vacuoles and in the context of the physiological roles of InsP3 and its receptor in cell water relations.
The phenotype of some late‐flowering mutants is enhanced by a locus on chromosome 5 that is not effective in the Landsberg erecta wild‐type
Authors: Koornneef Maarten , Blankestijn‐de Vries Hetty , Hanhart Corrie , Soppe Wim , Peeters Ton
Published: March 2003

Late‐flowering mutants that have been described in ecotypes other than Landsberg erecta (Ler) have been found to be dominant alleles of the FRI locus located on chromosome 4, which determines lateness in many very late ecotypes. The extreme lateness of dominant FRI alleles depends on dominant alleles at the FLC locus that maps on the top of chromosome 5. FLC alleles with this effect have been found in all ecotypes tested (Col, Ws, S96, Est and Li) except Ler. Most likely the same locus confers lateness to the luminidependens (ld) mutant. Genotypes with a dominant FRI allele and the monogenic recessive ld mutant are only slightly later with recessive Ler alleles at the FLC locus. Genotypes where the dominant FLC alleles are combined with FRI or with the ld mutant, are strongly responsive to vernalization, which is much less effective in the FLC‐Ler background.
The gene for the major cuticular wax‐associated protein and three homologous genes from broccoli (Brassica oleracea) and their expression patterns
Authors: Pyee Jaeho , Kolattukudy P.E.
Published: March 2003

The gene for the major protein (WAX9) found in surface wax of broccoli, designated wax9D, and three homologous genes (wax9A, B and C) were isolated from a genomic library using the previously isolated cDNA encoding the WAX9 protein as the probe; all four genes were sequenced. Genomic Southern blot analysis using the WAX9 cDNA as a probe showed the presence of at least four homologous genes in broccoli genome. The sequence of the originally isolated WAX9 cDNA matched with that of gene D. All four genes have an intron two codons before the stop codon. The putative promoter regions of the four genes, beyond the first 200 bp immediately 5′ to the translation start sites, are quite different. Essential elements such as TATA and CAAT boxes and several regions homologous to the promoter regions of other plant ltp genes were identified. The expression patterns of the genes were determined by RT‐PCR with gene‐specific primers and sequencing of the PCR products. All the genes were expressed in leaves and flower buds. While genes A, B and D also were expressed in stems and open flowers, expression of gene C was not detected in these organs. None of them were expressed in roots. The 972 bp 5′‐flanking region of wax9D when fused to β‐glucuronidase (GUS) gene, directed tissue‐specific GUS expression in transgenic tobacco plants; GUS expression was found in the epidermis of leaves, stems and flower petals, sepals, trichomes, and ovules but not in roots.
A polymorphic bipartite motif signals nuclear targeting of early auxin‐inducible proteins related to PS‐IAA4 from pea (Pisum sativum)
Authors: Abel Steffen , Theologis Athanasios
Published: March 2003

The plant hormone, indoleacetic acid (IAA), transcriptionally activates two early genes in pea, PS‐IAA4/5 and PS‐IAA6, that encode short‐lived nuclear proteins. The identification of the nuclear localization signals (NLS) in PS‐IAA4 and PS‐IAA6 using progressive deletion analysis and site‐directed mutagenesis is reported. A C‐terminal SV40‐type NLS is sufficient to direct the β‐glucuronidase reporter to the nucleus of transiently transformed tobacco protoplasts, but is dispensible for nuclear localization of both proteins. The dominant and essential NLS in PS‐IAA4 and PS‐IAA6 overlap with a bipartite basic motif which is polymorphic and conserved in related proteins from other plant species, having the consensus sequence (KKNEK)KR‐X(24–71)‐(RSXRK)/(RK/RK). Both basic elements of this motif in PS‐IAA4, (KR‐X41‐RSYRK), function interdependently as a bipartite NLS. However, in PS‐IAA6 (KKNEKKR‐X36‐RKK) the upstream element of the corresponding motif contains additional basic residues which allow its autonomous function as an SV40‐type monopartite NLS. The spacer‐length polymorphism, X(24–70), in respective bipartite NLS peptides of several PS‐IAA4‐like proteins from Arabidopsis thaliana does not affect nuclear targeting function. The structural and functional variation of the bipartite basic motif in PS‐IAA4‐like proteins supports the proposed integrated consensus of NLS.
Alternative splicing results in two different transcripts for H‐protein of the glycine cleavage system in the C4 species Flaveria trinervia
Authors: Kopriva Stanislav , Cossu Roberto , Bauwe Hermann
Published: March 2003

Alternative splicing is a well‐known post‐transcriptional regulatory mechanism in eukaryotic organisms but there are only very few reports on alternative splicing in plants. The analysis of cDNAs encoding H‐protein of the glycine decarboxylase multi‐enzyme complex from the C4 species Flaveria trinervia revealed the presence of two transcript populations that differ in the length of their coding regions by six nucleotides. Otherwise, including their 3′ non‐translated region, they are identical. From a genomic Southern analysis and from the sequencing of several independent cDNA clones it is evident that both types of transcript are derived from a single‐copy gene. This gene, FTgdcsH, has been cloned and sequenced. It comprises four short exons. The two alternative splice sites are located at the end of intron 1. The shorter transcript closely corresponds to published H‐protein mRNA sequences from other organisms. The longer transcript encodes two additional alanine residues very close to the N‐terminus of the mature H‐protein. A quantification of the relative amounts of both transcripts in different organs revealed that, with 80–90% of the total H‐protein mRNA, the alternative mRNA dominates in leaves whereas roots contain more of the ‘correctly’ spliced transcript. It is concluded that, in F. trinervia and with a distinct organ preference, alternative splicing leads to the synthesis of two different H‐proteins of the glycine cleavage system.
Identification of genes required for pollen‐stigma recognition in Arabidopsis thaliana
Authors: Hülskamp Martin , Kopczak Steven D. , Horejsi Thomas F. , Kihl Brenda K. , Pruitt Robert E.
Published: March 2003

In higher plants, cell‐cell recognition reactions taking place following pollination allow the selective restriction of self‐pollination and/or interspecific pollination. Many of these systems function by regulating the process of water transfer from the cells found at the stigmatic surface to the individual pollen grain. Interspecific pollination studies on the cruciferous weed Arabidopsis thaliana revealed only a broad specificity of pollen recognition such that pollen from all tested members of the crucifer family were recognized, whereas pollen from almost all other species failed to hydrate. Genetic analysis of A. thaliana has identified three genes that are essential for this recognition process. Recessive mutations in any of these genes result in male sterility due to the production of pollen grains that fail to hydrate when placed on the stigma, but that are capable of hydrating and growing a pollen tube in vitro. Results from mixed pollination experiments suggest that the mutant pollen grains specifically lack a functional pollen‐stigma recognition system. All three mutations described also result in a defect in the wax layer normally found on stems and leaves, similar to previously described eceriferum (cer) mutations. Genetic complementation and mapping experiments demonstrated that the newly identified mutants are allelic to the previously identified genes cer1, cer3 and cer6. TEM analysis of the ultrastructure of the pollen coating revealed that all of the mutant pollen grains bear coatings of normal thickness and that tryphine lipid droplets are missing in cer1‐147, are reduced in size in cer6‐2654 and appear normal in cer3‐2186. Temperature shift experiments revealed that the block in the recognition step of the mutant pollen grains can be suppressed by pollination at lower temperatures but not by reduced temperatures during pollen development. These results suggest that the lipids which are altered in the cer mutations may be important in regulating some biophysical property of the pollen coating.
Arrangement of cell layers in the shoot apical meristems of periclinal chimeras influences cell fate
Authors: Marcotrigiano Michael , Bernatzky Robert
Published: March 2003

Utilizing a complete set of six periclinal graft chimeras composed of Nicotiana tabacum and Nicotiana glauca (TGG, GTT, TTG, GGT, TGT, and GTG), the fate of the three apical cell layers in both vegetative and reproductive organs has been traced. An analysis of leaf phenotype indicated that only rarely did deviations from expected cell lineage occur and in only TTG did such deviations originate in the shoot apical meristem rather than during leaf development. In most plants that possess a stratified shoot apical meristem, gametes are derived from the second apical layer (L2). A phenotypic and/or DNA analysis of seed progeny following reciprocal crosses between all chimeras and their component species indicated that pollen and eggs were sometimes derived from non‐L2 lineage in all but one periclinal chimera. There was no evidence for non‐L2‐derived gametes in 95 crosses where GTT was a parent whereas 40 of 104 crosses with TTG as a parent yielded some offspring that resulted from non‐L2‐derived gametes. Of these 40 cases, non‐L2‐derived pollen grains were responsible 39 times while non‐L2‐derived eggs were responsible just once. Therefore, the occurrence of non‐L2‐derived gametes was not random. The disruption of ‘normal’ lineage patterns was dependent on the specific arrangement of genetically dissimilar tissue layers in the shoot apices of the chimeras and was different for different organs.
Distinct CG and CNG DNA methyltransferases in Pisum sativum
Authors: Pradhan Sriharsa , Adams Roger L.P.
Published: March 2003

DNA methyltransferase activity, present in low salt extracts of nuclei from young pea shoot apices, has been fractionated into two different species by assaying with model substrates. The CG methyltransferase (an unstable enzyme believed to be of 140 kDa) methylates cytosine only in oligonucleotides with CG and CI dinucleotide targets while an enzyme of 110 kDa (the CNG methyltransferase) methylates the cytosines in 5′‐CAG‐3′ and 5′‐CTG‐3′ target sequences, especially when hemimethylated, but not in 5′‐CCG‐3′ nor in 5′‐CGG‐3′ target sequences present in oligonucleotides.
Comparative mapping in Arabidopsis and Brassica, fine scale genome collinearity and congruence of genes controlling flowering time
Authors: Lagercrantz Ulf , Putterill Joanna , Coupland George , Lydiate Derek
Published: March 2003

The model dicotyledonous plant, Arabidopsis thaliana, is closely related to Brassica crop species. It is intended that information concerning the genetic control of basic biological processes in Arabidopsis will be transferable to other species. Genome collinearity and its potential to facilitate the identification of candidate genes in Arabidopsis homologous to genes controlling important agronomic traits in Brassica was investigated. Genetic mapping in B. nigra identified two loci influencing flowering time (FT), with loci on linkage groups 2 and 8 explaining 53% and 12% of the total variation in FT, respectively. The CO gene exerts an important control over FT in A. thaliana, and B. nigra homologues of CO probably also play an important role in regulating FT. B. nigra homologues of CO were identified on linkage groups 2 and 8, the homologue on group 2 was coincident with the major locus controlling FT while the homologue on group 8 was within the 90% confidence interval of the weaker FT gene. The CO homologue on group 2 exhibits abundant allelic variation suggesting that it naturally controls a wide range of flowering times. Fine‐scale A. thaliana/B. nigra comparative mapping demonstrated short‐range collinearity between the genomes of Arabidopsis and Brassica. Eleven DNA fragments spaced over a 1.5 Mb contig in A. thaliana were used as RFLP probes in B. nigra. Three collinear representations of the A. thaliana contig were identified in B. nigra, with one interrupted by a large chromosomal inversion. Collinearity over this range will allow the resources generated by the Arabidopsis genome project to facilitate map‐based cloning in Brassica crops.