Showing papers in "Plant and Cell Physiology in 1998"
Journal Article•
1,024 citations
TL;DR: Results indicated that JA works as an inducer of basic PR genes, and also as an inhib itor for acidicPR genes, while SA does the opposite.
Abstract: Salicylic acid (SA) and jasmonic acid (JA) are essential compounds in the pathogen- and wound-signaling path ways accompanying induced expression of acidic and basic pathogenesis-related (PR) protein genes, respectively. How ever, on the effect of exogenously supplied SA and JA in in duction of PR gene expression, conflicting results have been obtained using various plant materials at different de velopmental stages. There is no clear evidence on these effects in the presence of both signals at the same time. We analyzed the effect of SA on wound- and JA-induced basic PR gene expression and that of JA on SA-induced acidic PR gene expression in mature tobacco leaves. Wound-in duced accumulation of transcripts for all 4 basic PR genes tested was enhanced in the presence of MeJA, and in hibited in the presence of SA. On the other hand, expres sion of all 3 acidic PR genes tested was induced by SA and was inhibited by MeJA. Using antibodies raised against acidic PR-l and PR-2 proteins, these effects were confirm ed at the protein level. These results indicated that JA works as an inducer of basic PR genes, and also as an inhib itor for acidic PR genes, while SA does the opposite.
439 citations
TL;DR: Very consistent trends across plant species were observed for changes in carotenoid composition (pools of carotenes, VAZ, and other xanthophylls) in response to light environment, as long as it is assumed that in some species /^- carotene can be replaced by a-carotene and in a few plant species lutein can be replacement by lactucaxanthin.
Abstract: A survey was conducted of the magnitude of energy dissipation in photosystem II (expressed as nonphotochemical quenching of chlorophyll fluorescence, NPQ) as well as leaf carotenoid composition of a wide range of different plant species growing in deep shade and/or full sun. Consistently higher levels of the reversible component of NPQ as well as higher degrees of rapidly attainable de-epoxidation of the xanthophyll cycle (VAZ) pool were observed in sun leaves compared to deep shade leaves. It is concluded that these altered features of the xanthophyll cycle allowed sun leaves to dissipate excess energy more effectively over the short term. In addition to the rapid increase in reversible NPQ, shade leaves exhibited a slow further, and sustained, increase in NPQ. In contrast to these deep shade leaves experimentally exposed to high PFDs, understory leaves experiencing highly variable PFD in their natural environment appeared to be able to dissipate excess excitation energy adequately via xanthophyll cycle-dependent thermal dissipation. Furthermore, very consistent trends across plant species were observed for changes in carotenoid composition (pools of carotenes, VAZ, and other xanthophylls) in response to light environment, as long as it is assumed that in some species /^-carotene can be replaced by a-carotene and in a few plant species lutein can be replaced by lactucaxanthin. Sun leaves consistently exhibited much greater levels of VAZ than shade leaves but very similar levels of lutein and neoxanthin (all on a Chi basis) as well as an only slightly higher ratio of total carotenes to the pool of all xanthophylls.
255 citations
TL;DR: It is shown that green light drives 14 C02-fixation deep within spinach leaves compared to red and blue light, and the importance of green light in photosynthesis is discussed.
Abstract: l4 CO2-fixation in spinach occurs in the middle of the palisade mesophyll [Nishio et al. (1993) Plant Cell 5: 953], however, ninety percent of the blue and red light is attenuated in the upper twenty percent of a spinach leaf [Cui et al. (1991) Plant Cell Environ. 14: 493]. In this report, we showed that green light drives 14 C02-fixation deep within spinach leaves compared to red and blue light. Blue light caused fixation mainly in the palisade mesophyll of the leaf, whereas red light drove fixation slightly deeper into the leaf than did blue light. I4 C02-fixation measured under green light resulted in less fixation in the upper epidermal layer (guard cells) and upper most palisade mesophyll compared to red and blue light, but led to more fixation deeper in the leaf than that caused by either red or blue light. Saturating white, red, or green light resulted in similar maximal 14 CO2-fixation rates, whereas under the highest irradiance of blue light given, carbon fixation was not saturated, but it asymptotically approached the maximal 14 CO2-fixation rates attained under the other types of light. The importance of green light in photosynthesis is discussed.
230 citations
221 citations
TL;DR: Flavonoid metabolic engineering has and will give new perspectives in plant molecular biologyBesides its industrial application, it has become feasible to modify the pathway and flower color through genetic engineering.
Abstract: Thanks to the rapid progress in molecular biology of flavonoid biosynthesis and plant transformation, it has become feasible to modify the pathway and flower color through genetic engineering. One of the advantages of molecular breeding is that flower color can be specifically modified without changing the other characteristics of the targeted variety. Novel flower color varieties such as brickred petunias and violet carnations have been successfully made by expression of heterologous flavonoid genes. Flavonoid metabolic engineering has and will give new perspectives in plant molecular biology besides its industrial application.
213 citations
TL;DR: Positional cloning showed that AGR encodes a root-specific member of a novel membrane-protein family with limited homology to bacterial transporters.
Abstract: Mutations in the Agr locus of Arabidopsis thaliana impair the root gravitropic response. Root growth of agr mutants is moderately resistant to ethylene and to an auxin transport inhibitor. Vertically placed agr roots grow into agar medium containing IAA or naphthalene-1-acetic acid, but not into medium containing 2,4-D. Positional cloning showed that AGR encodes a root-specific member of a novel membrane-protein family with limited homology to bacterial transporters.
201 citations
TL;DR: ABA plays a decisive role in the regulation of seed germination at supraoptimal temperatures and is responsible for high-temperature inhibition of germination of lettuce seeds.
Abstract: Fluridone, an inhibitor of ABA biosynthesis, restored the seed germination of lettuce (Lactuca sativa L. cv. Grand Rapids) and many other plant species at supraoptimal temperatures. ABA content in lettuce seeds after imbibition quickly decreased at 23°C, but not at 33°C (a supraoptimal temperature). Fluridone caused a decrease in ABA content at 33°C, which suggests that the maintenance of high ABA content could be responsible for high-temperature inhibition of germination of lettuce seeds. This probably results from an increase in the rate of ABA biosynthesis at the higher temperature. The present study indicates that ABA plays a decisive role in the regulation of seed germination at supraoptimal temperatures.
163 citations
TL;DR: In this paper, the agravitropic nature of root growth of an auxin-resistant mutant of Arabidopsis, aux1, was restored when the synthetic auxin 1-naphthaleneacetic acid (NAA) was added to the growth medium; aux1 roots were not resistant to NAA.
Abstract: The agravitropic nature of root growth of an auxin-resistant mutant of Arabidopsis, aux1, was restored when the synthetic auxin 1-naphthaleneacetic acid (NAA) was added to the growth medium; aux1 roots were not resistant to NAA. Neither indole-3-acetic acid nor, 2,4-dichlorophenoxyacetic acid had the same effects as NAA. These differential effects of the three auxins on aux1 defects suggest that AUX1 may encode the auxin influx carrier according to the model proposed by Delbarre et al.
155 citations
TL;DR: In vivo and in vitro evidence that each AHP can function as a phospho-transmitting HPt domain with an active histidine site was obtained, and it was demonstrated that AHP1 exhibits in vivo ability to complement a mutational lesion of the yeast YPD1 gene, encoding a typical HPtdomain involved in an osmosensing signal transduction.
Abstract: His to Asp phosphorelay signal transduction mechanisms involve three types of widespread signaling components: a sensor His-kinase, a response regulator, and a histidine-containing phosphotransfer (HPt) domain. In Arabidopsis, several sensor His-kinases have recently been discovered (e.g., ETR1 and CKI1) through extensive genetic studies. Furthermore, a recent search for response regulators in this higher plant revealed that it possesses a group of response regulators (ARR-series), each of which exhibits the phospho-accepting receiver function. However, no signal transducer containing the HPt domain has been reported. Here we identify three distinct Arabidopsis genes (AHP1 to AHP3), each encoding a signal transducer containing a HPt domain. Both in vivo and in vitro evidence that each AHP can function as a phospho-transmitting HPt domain with an active histidine site was obtained by employing both the Escherichia coli and yeast His-Asp phosphorelay systems. It was demonstrated that AHP1 exhibits in vivo ability to complement a mutational lesion of the yeast YPD1 gene, encoding a typical HPt domain involved in an osmosensing signal transduction. It was also demonstrated that AHPs can interact in vitro with ARRs through the His-Asp phosphotransfer reaction. It was thus suggested that the uncovered sensors-AHPs-ARRs lineups may play important roles in propagating environmental stimuli through the multistep His-Asp phosphorelay in Arabidopsis.
154 citations
TL;DR: Results suggest that dehydration-induced accumulation of free leucine and isoleucine is achieved independent of ABA, as compared to the wild-type plants where this mutation was isolated.
Abstract: In an attempt to elucidate the physiological role of ABA in seed dormancy and the adaptive response to dehydration, we isolated an ABA-deficient mutant of Arabidopsis thaliana (L.) Heynh. which germinated in the presence of a gibberellin biosynthetic inhibitor. Genetic analysis showed this mutation is a new allele of a recently reported locus aba2, and therefore has been designated aba2-2. The levels of endogenous ABA in fresh and dehydrated tissues of the aba2-2 mutant were highly reduced compared to those of wild-type plants. As a consequence, aba2-2 plants wilt and produce seeds with reduced dormancy. Dark germinated seedlings of the aba2-2 mutant showed true leaves, which were not observed in those of the wild type, indicating that aba2-2 embryos grew precociously during seed maturation. In the dehydrated tissues of the wild-type plants, the levels of free proline, isoleucine and leucine were elevated to a content approximately 100-fold higher than those in fresh tissues. In contrast to the wild-type plants, dehydration-induced accumulation of proline was highly suppressed in the aba2-2 mutant plants while that of leucine and isoleucine accumulated. Furthermore, exogenous application of ABA to wild-type plants promoted accumulation of free proline, but not leucine nor isoleucine. These results suggest that dehydration-induced accumulation of free leucine and isoleucine is achieved independent of ABA.
TL;DR: Betaine treatment resulted in the induction of a subset of low temperature responsive genes, such as the wcor410, and wcor413, that are also induced by salinity or drought stresses and was able to improve the tolerance to photoinhibition of PSII and the steady-state yield of electron transport over PSII in a manner that mimicked cold-acclimated plants.
Abstract: The accumulation of the osmolyte betaine was found to be correlated with the development of freezing tolerance (FT) of two wheat cultivars where it increases by about three fold during the cold' acclimation period. Exogenous betaine application resulted in a large increase in total osmolality mostly due to betaine accumulation. Plants that accumulated betaine are more tolerant to freezing stress since a four day exposure to 250 mM betaine resulted in a LT50 of -8° C (in spring wheat Glenlea) and -9° C (in winter wheat Fredrick) compared to — 3°C (Glenlea) and — 4°C (Fredrick) for control non-exposed plants. Betaine treatment (250 mM) during cold acclimation increased FT in an additive manner since the LT50 reached — 14°C (Glenlea) and -22° C (Fredrick) compared to -8° C (Glenlea) and — 16°C (Fredrick) for plants that are cold acclimated in the absence of betaine. These results show that betaine treatment can improve FT by more than 5°C in both non-acclimated and cold-acclimated plants. The betaine treatment resulted in the induction of a subset of low temperature responsive genes, such as the wcor410, and wcor413, that are also induced by salinity or drought stresses. In addition to these genetic responses, betaine treatment was also able to improve the tolerance to photoinhibition of PSII and the steady-state yield of electron transport over PSII in a manner that mimicked cold-acclimated plants. These data also suggest that betaine improves FT by eliciting some of the genetic and physiological responses associated with cold acclimation.
TL;DR: The cloning of the fifth cDNA of an AsAP isozyme which localizes in spinach glyoxysomes is reported, and the H2O2-scavenging system maintained by AsAP and the regeneration system of AsA in spinach Glyoxysome is discussed.
Abstract: cDNAs encoding two cytosolic and two chloroplastic ascorbate peroxidase (AsAP) isozymes from spinach have been cloned recently [Ishikawa et al. (1995) FEBS Lett. 367: 28, (1996) FEBS Lett. 384: 289]. We herein report the cloning of the fifth cDNA of an AsAP isozyme which localizes in spinach glyoxysomes (gAsAP). The open reading frame of the 858-base pair cDNA encoded 286 amino acid residues with a calculated molecular mass of 31,507 Da. By determination of the latency of AsAP activity in intact glyoxysomes, the enzyme, as well as monodehydroascorbate (MDAsA) reductase, was found to be located on the external side of the organelles. The cDNA was overexpressed in Escherichia coli (E. coli). The enzymatic properties of the partially purified recombinant gAsAP were consistent with those of the native enzyme from intact glyoxysomes. The recombinant enzyme utilized ascorbate (AsA) as its most effective natural electron donor; glutathione (GSH) and NAD(P)H could not substitute for AsA. The substrate-velocity curves with the recombinant enzyme showed Michaelis-Menten type kinetics with AsA and hydrogen peroxide (H2O2); the apparent Km values for AsA and H2O2 were 1.89 +/- 0.05 mM and 74 +/- 4.0 microM, respectively. When the recombinant enzyme was diluted with AsA-depleted medium, the activity was stable over 180 min. We discuss the H2O2-scavenging system maintained by AsAP and the regeneration system of AsA in spinach glyoxysome.
TL;DR: In this article, the authors reported the detection of programmed cell death (PCD) in senescent leaf tissue and DNA ladders, resulting from the cleavage of nuclear DNA into oligonucleosomal fragments in apoptotic cells, were detected by gel electrophoresis and southern hybridization.
Abstract: Cell death caused by senescence of leaves has been thought to be a type of programmed cell death (PCD or apoptosis) for many years, however, no studies at the nuclear level associated with PCD have been reported. In this study, leaf tissue from five different plant species, Philodendron hastatum, Epipremnum aureum, Bauhinia purpurea, Delonix regia, and Butea monosperma was used to detect the evidence of the PCD. Here, we report the detection of PCD in senescent leaf tissue. DNA ladders, resulting from the cleavage of nuclear DNA into oligonucleosomal fragments in apoptotic cells, were detected by gel electrophoresis and southern hybridization only in senescent (but not in non-senescent) leaves in all five plant species. DNA fragmentation and nuclear DNA condensation were further confirmed by using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end in situ labeling (TUNEL) method. Fluorescence was clearly detected in the nuclei of mesophyll cells in senescent leaves. By contrast, there was no TUNEL staining in green healthy leaves. Our results provide direct evidence to support the notion that natural senescence of the leaves is indeed an apoptotic process during plant development.
TL;DR: Four cDNAs for spermidine synthase, which converts the diamine putrescine to the higher polyamine sperMidine using decarboxylated S-adenosylmethionine as the co-factor, were isolated from Nicotiana sylvestris, Hyoscyamus niger, and Arabidopsis thaliana.
Abstract: Four cDNAs for spermidine synthase (SPDS), which converts the diamine putrescine to the higher polyamine spermidine using decarboxylated S-adenosylmethionine as the co-factor, were isolated from Nicotiana sylvestris, Hyoscyamus niger, and Arabidopsis thaliana. When the N.sylvestris SPDS cDNA was expressed in a SPDS-deficient E. coli mutant, the recombinant protein showed high SPDS activity, but did not have any spermine synthase activity. The plant SPDSs have molecular masses of about 34 kDa, possess the co-factor binding motifs which have been proposed for S-adenosylmethionine, and are more homologous in amino acid sequence to tobacco putrescine N-methyltransferase (PMT) than to SPDSs from mammals and E. coli. The SPDS gene is expressed in root, stem, and leaf in N.sylvestris, whereas the PMT gene is expressed only in root. The potential evolution of plant SPDS and PMT, and their evolutionary relationships with animal SPDS are discussed.
TL;DR: Evidence is reported for the presence of the mRNAs of thioredoxin h, oryzacystatin-I, and actin in the rice phloem sap collected by the insect laser method, suggesting that these macromolecules are probably transported from the companion cells.
Abstract: Evidence is reported for the presence of the mRNAs of thioredoxin h, oryzacystatin-I, and actin in the rice phloem sap collected by the insect laser method. As the sieve element, the core component of the phloem, is enucleated, these macromolecules are probably transported from the companion cells.
TL;DR: A new hypothesis is proposed to explain the metabolic regulation of intracellular pH in plants and replace the classic biochemical pH-stat, which is assumed to have evolved as a security mechanism for the "proton system" so that it could cope with the potential acidification of the cytoplasm under environmental stress.
Abstract: A new hypothesis is proposed to explain the metabolic regulation of intracellular pH (especially of the cytoplasm) in plants and replace the classic biochemical pH-stat [Davies (1973) Symp. Soc. Exp. Biol. 27: 513]. Alternative route glycolysis [Plaxton (1996) Annu. Rev. Plant Physiol. Plant Mol. Biol. 47: 185], alternative pathway respiration [Day et al. (1996) Plant Physiol. 110: 1], and malate-derived lactic and alcoholic fermentation (alternative pathway fermentation), all unique to plants, are organized into a novel mechanism that functions in toto as biochemical pH-stat. Its uniqueness to plants is examined from the evolutionary viewpoint that plants adopted the proton as the ion with which to create the electrochemical potential difference across the plasma membrane to energize uphill transports ("proton system"). The biochemical pH-stat is assumed to have evolved as a security mechanism for the "proton system" so that it could cope with the potential acidification of the cytoplasm under environmental stress.
TL;DR: Data indicate that there is an AO multigene family in Arabidopsis, and atAO-1 protein was shown to be highly similar to one of the maize AOs in respect to a region thought to be involved in determination of substrate specificity, suggesting that they might encode a similar type of AO.
Abstract: Using degenerate primers designed by deduced amino acid sequences of known aldehyde oxidases (AO) from maize and bovine, two independent cDNA fragments were amplified by reverse transcription-polymerase chain reaction (PCR). The two corresponding full-length cDNAs (atAO-1 and atAO-2; 4,484 and 4,228 bp long, respectively) were cloned by screening the Arabidopsis cDNA library followed by rapid amplification of cDNA end-PCR. These cDNAs are highly homologous at both the nucleotide and amino acid sequence levels, and the deduced amino acid sequences showed high similarity with those of maize and tomato AOs. They contain consensus sequences for two iron-sulfur centers and a molybdenum cofactor (MoCo)-binding domain. In addition, another cDNA having a sequence similar to that of the cDNAs was screened (atAO-3; 3,049 bp), and a putative AO gene (AC002376) was reported on chromosome 1, which (atAO-4) was distinct from, but very similar to, the above three AOs. atAO-1, 2, 3, and 4 were physically mapped on chromosomes 5, 3, 2 and 1, respectively. These data indicate that there is an AO multigene family in Arabidopsis. atAO-1 protein was shown to be highly similar to one of the maize AOs in respect to a region thought to be involved in determination of substrate specificity, suggesting that they might encode a similar type of AO, which could efficiently oxidize indole-3-acetaldehyde to indole-3-acetic acid (IAA). atAO-1 and atAO-2 genes were expressed at higher levels in lower hypocotyls and roots of the wild-type seedlings, while atAO-3 was slightly higher in cotyledons and upper hypocotyls. The expression of atAO-1 was more abundant in the seedlings of an IAA overproducing mutant (superroot1; sur1) than in those of wild type. atAO-2 and atAO-3 transcripts were rather evenly distributed in these seedlings. A possible involvement of atAO genes in phytohormone biosynthesis in Arabidopsis is discussed.
TL;DR: It is concluded that GLDHase, L-gulono-y-lactone oxidase and L-galactono- y- lact one oxidase are homologous in spite of the difference in substrates and electron acceptors.
Abstract: L-Galactono-y-lactone dehydrogenase (EC 1.3.2.3, GLDHase) was partially purified from mitochondria of sweet potato tuberous roots over 600-fold on a specific activity basis, followed by purification of the enzyme protein of 56 kDa by a preparative SDS-PAGE. The absorption spectrum of the hydroxylapatite column-purified GLDHase showed peaks at 448 and 373 nm, suggesting the presence of flavin as a prosthetic group. The activity of GLDHase was inhibited by lycorine, an alkaloid which inhibits ascorbic acid biosynthesis in vivo. N-terminal partial sequences of four internal polypeptides generated by partial digestion of GLDHase with V8 protease were determined. The deduced nucleotide sequences were used to amplify a cDNA fragment of the GLDHase gene. The clone encoded a polypeptide of 581 amino acid residues with a molecular mass of 66 kDa. The deduced amino acid sequence showed 77% identity with that of cauliflower GLDHase, and significant homology to those of L-gulono-y-lactone oxidase (22% identity) from rat and L-galactono-y-lactone oxidase from yeast (17% identity), which are enzymes involved in L-ascorbic acid biosynthesis in these organisms. The absorption spectrum and cDNA sequence suggested that the flavin group bound noncovalently. We conclude that GLDHase, L-gulono-y-lactone oxidase and L-galactono-y-lactone oxidase are homologous in spite of the difference in substrates and electron acceptors. Genomic Southern analysis suggested that GLDHase gene exists as a single copy in the genome of sweet potato.
TL;DR: Data suggest that in response to auxin depletion, endogenous mJA could be produced and act by linking physiological events thus leading to alkaloid biosynthesis activation.
Abstract: The effect of methyl jasmonate (mJA), jasmonic acid and traumatic acid, derivatives of the octadecanoic pathway, on the production of alkaloids by cell suspension cultures of Catharanthus roseus L. (G) Don was investigated. Cells cultured in the presence of auxin (m-cells) did not accumulate alkaloids. The addition of exogenous mJA to mcells restored the ability to produce alkaloids. In cells cultured in a 2,4-D-starved medium (p-cells), exogenous mJA greatly increased alkaloid production. Similar data were obtained for jasmonic acid. In contrast, traumatic acid had no effect on alkaloid production. The sensitivity of cell suspension cultures to exogenous mJA was restricted to the first four days of subculture corresponding to the active growth phase, whereas the alkaloid accumulation occurred only during the stationary phase of the subculture (days 6 to 10). When p-cells were treated with octadecanoic pathway inhibitors, the ability to produce alkaloids was strongly reduced. The addition of exogenous mJA always restored the ability to produce alkaloids. These data suggest that in response to auxin depletion, endogenous mJA could be produced and act by linking physiological events thus leading to alkaloid biosynthesis activation.
TL;DR: The ORF sll1468 of Synechocystis sp.
Abstract: The ORF sll1468 of Synechocystis sp. PCC6803 was identified as a gene for beta-carotene hydroxylase by functional complementation in a beta-carotene-producing Escherichia coli. The gene product of ORF sll1468 added hydroxyl groups to the beta-ionone rings of beta-carotene (beta, beta-carotene) to form zeaxanthin (beta, beta-carotene-3,3'-diol). This newly identified beta-carotene hydroxylase does not show overall amino acid sequence similarity to the known beta-carotene hydroxylases. However, it showed significant sequence similarity to beta-carotene ketolases of marine bacteria and a green alga.
TL;DR: Cyclic electron transport around PSI through the NAD(P)H dehydrogenase complex (NDH) in tobacco leaf disks, measured as an increase in the dark level of Chi fluorescence after the onset of darkness, was inhibited by antimycin A, an inhibitor of ferredoxin quinone reductase (FQR), suggesting that antimYcin A inhibits not only the FQR-mediated cyclic flow but also the NOH-dependent flow.
Abstract: Cyclic electron transport around PSI through the NAD(P)H dehydrogenase complex (NDH) in tobacco leaf disks, measured as an increase in the dark level of Chi fluorescence after the onset of darkness, was inhibited by antimycin A, an inhibitor of ferredoxin quinone reductase (FQR), suggesting that antimycin A inhibits not only the FQR-mediated cyclic flow but also the NOH-dependent flow. This electron flow was inhibited also by amytal, an inhibitor of mitochondrial NDH and by nigericin. The reduction of plastoquinone was detected when NADPH and ferredoxin were added to the suspension of the osmotically ruptured chloroplasts of the wild type and NDH-defective mutant. Because the addition of NADPH alone did not induce the reduction, membrane-bound ferredoxin NADP + reductase (FNR) was supposed to reduce ferredoxin, which may be a more direct electron donor for the plastoquinone reduction. The presence of two types of reducing enzymes was suggested from the bi-phasic inhibition of plastoquinone reduction by antimycin A in the wild type. It is proposed that the reducing activity inhibited by antimycin A at a low concentration is attributed to FQR and the less sensitive activity to NDH.
TL;DR: It is suggested that the expression of the rice cytosolic GR gene is regulated via ABA-mediated signal transduction pathway under environmental stresses through the use of a putative cytosol isoform.
Abstract: We have isolated a cDNA (RGRC2) encoding glutathione reductase (GR) from rice (Oryza sativa L.). The comparison of deduced amino acid sequences from RGRC2 and other plant GR cDNAs indicated that RGRC2 encodes a putative cytosolic isoform. The recombinant RGRC2 protein had enzymatic properties comparable to those of GR from rice embryo. Subcellular fractionation showed that the RGRC2 protein is localized primarily in cytosol. mRNA and protein of RGRC2 were observed mainly in roots and calli but little in leaf tissues. Southern blot analysis showed that the RGRC2 gene exists as a single copy gene. Here, we have also isolated a genomic clone completely corresponding to RGRC2. The RGRC2 gene is split into 16 exons spread about 7.4 kb of chromosomal DNA, with coding sequence beginning in the 2nd exon and ending in the 16th exon. From the presence of two ABA-responsive elements in the 5'-flanking region of RGRC2, we examined the expression in rice seedlings treated with ABA and the ABA-related environmental stresses, chilling, drought and salinity. The expression of RGRC2 was strongly induced by all these treatments. We suggest that the expression of the rice cytosolic GR gene is regulated via ABA-mediated signal transduction pathway under environmental stresses.
TL;DR: This paper aims to provide a history of Japanese biotechnology and its applications in the field of dentistry and medicine, as well as some suggestions for future research.
Abstract: Chuan-Yin Wu, Takahiro Adachi, Tetsuya Hatano, Haruhiko Washida-, Akihiro Suzuki and Fumio Takaiwa 1 Department of Biotechnology, National Institute of Agrobiological Resources, Tsukuba, Ibaraki, 305-0856 Japan 2 Department of Immunology, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo, 113-0034 Japan 3 Faculty of Science, Shimane University, Matsue, Shimane, 690-0823 Japan 4 Faculty of Horticulture, Chiba University, Matsudo, Chiba, 271-0092 Japan
TL;DR: An expression sequence tag database of higher plants was screened by in silico profile analysis for response regulators of the two-component regulatory system and two closely related clones corresponding to one of the extracted candidates were isolated from Arabidopsis thaliana.
Abstract: An expression sequence lag database of higher plants was screened by in silico profile analysis for response regulators of the two-component regulatory system. Two closely related clones (ARR1 and ARR2), corresponding to one of the extracted candidates, were isolated from Arabidopsis thaliana. The two genes were comparably expressed in all tissues, and at higher levels in the roots. The amino-terminal half of their translation products was highly conserved. This is where a phosphate receiver domain with the landmark aspartate residue and a putative DNA-binding domain were located. Their carboxyl-terminal halves, although less similar to each other, included glutamine-rich and proline-rich regions characteristic of the transcriptional activation domain of eukaryotes. This architecture resembles that of typical bacterial response regulators serving as transcription factors.
TL;DR: In this article, the root NH4+ influx was measured in 3-week-old hydroponically grown rice seedlings (Oryza sativa L., cv. IR72) under conditions of N deprivation and NH4/+ resupply, using 13NH4+ as a tracer.
Abstract: Ammonium influx into roots and N translocation to the shoots were measured in 3-week-old hydroponically grown rice seedlings (Oryza sativa L., cv. IR72) under conditions of N deprivation and NH4/+ resupply, using 13NH4/+ as a tracer. Root NH4/+ influx was repressed in plants continuously supplied with NH4/+ (at 0.1 mM), but a high proportion of absorbed N (20 to 30%) was translocated to the shoot in the form of N assimilates during the 13-min loading and desorption periods. Interruption of exogenous NH4/+ supply for periods of 1 to 3 d caused NH4/+ influx to be de-repressed. This same treatment caused N translocation to the shoot to decline rapidly, until, by 24 h, less than 5% of the absorbed 13N was translocated to the shoot, illustrating a clear priority of root over shoot N demand under conditions of N deprivation. Upon resupplying 1 mM NH4/+ root NH4/+ influx responded in a distinct four-phase pattern, exhibiting periods in which NH4/+ influx was first enhanced and subsequently reduced. Notably, a 25 to 40% increase in root influx, peaking at ~2 h following re-exposure was correlated with a 4- to 5-fold enhancement in shoot translocation and a repression of root GS activity. The transient increase of NH4/+ influx was also observed in seedlings continuously supplied with NO3/- and subsequently transferred to NH4/+. Extended exposure to NH4/+ caused root NH4+ influx to decrease progressively, while shoot translocation was restored to ~30% of incoming NH4/+. The nature of the feedback control of NH4/+ influx as well as the question of its inducibility are discussed.
TL;DR: Findings suggest that the expression of VM23 is tightly related to cell elongation, particularly in cotyledons and roots of radish tap root.
Abstract: A major membrane intrinsic protein (VM23) in vacuoles of radish (Raphanus) tap root was investigated. The cDNAs for two isoforms of VM23, gamma- and delta-VM23, encode polypeptides of 253 and 248 amino acids, respectively. gamma- and delta-VM23 correspond to the gamma- and delta-TIP (tonoplast intrinsic protein) of Arabidopsis. The deduced amino acid sequences of the two VM23 isoforms were 60% identical. The amino-terminal sequence of gamma-VM23 showed agreement with the direct sequence of the purified VM23, suggesting that gamma-VM23 is the most abundant molecule among the VM23 isoforms. When mRNAs of gamma- and delta-VM23 were injected into Xenopus oocytes, the osmotic water permeability of oocytes increased 6-fold (60 to 200 microns s-1) of the control oocytes. The transcripts of both isoforms were detected in a high level in growing hypocotyls and young leaves, but delta-VM23 was not detected in seedling roots. Light illumination enhanced the transcription of two genes of VM23 in cotyledons and roots but suppressed their expression in hypocotyls the growth of which was inhibited by light. These findings suggest that the expression of VM23 is tightly related to cell elongation.