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PubMed1996

Highly Branched Phenotype of the Petunia dad1-1 Mutant Is Reversed by Grafting.

The recessive dad1-1 allele conditions a highly branched growth habit resulting from a proliferation of first- and second-order branches. Unlike the wild-type parent, which has lateral branching delayed until the third or fourth leaf node distal to the cotyledons, dad1-1 initiates lateral branching from each cotyledon axil. In addition to initiating lateral branching sooner than the wild type, dad1-1 sustains branching through more nodes on the main shoot axis than the wild type. In keeping with a propensity for branching at basal nodes, dad1-1 produces second-order branches at the proximal-most nodes on first-order branches and small shoots from accessory buds at basal nodes on the main shoot axis. Additional traits associated with the mutation are late flowering, adventitious root formation, shortened internodes, and mild leaf chlorosis. Graft studies show that a dad1-1 scion, when grafted onto wild-type stock, is converted to a phenotype resembling the wild type. Furthermore, a small wild-type interstock fragment inserted between a mutant root stock and a mutant scion is sufficient to convert the dad1-1 scion from mutant to a near wild-type appearance. The recessive dad1-1 phenotype combines traits associated with cytokinin overexpression, auxin overexpression, and gibberellin limitation, which suggests a complex interaction of hormones in establishing the mutant phenotype.

Journal Article↗

PubMed1997

Anion-channel blockers interfere with auxin responses in dark-grown Arabidopsis hypocotyls.

Anion channels are thought to participate in signal transduction and turgor regulation in higher plant cells. The regulation of hypocotyl cell elongation is a situation in which these channels could play important roles because it involves ionic fluxes that are implicated in turgor control and orchestrated by various signals. We have used a pharmacological approach to reveal the contribution of anion channels in the regulation of the development of hypocotyls by auxins. Auxins induce an inhibition of elongation, a disintegration of the cortical cell layers, and the formation of adventitious roots on Arabidopsis thaliana hypocotyls grown in the dark. Anion-channel blockers such as anthracene-9-carboxylic acid, 4,4'-diisothiocyanatostilbene-2-2'-disulfonic acid, 4-acetamido-4'-isothiocyanato-stilbene-2-2'-disulfonic acid, and R(+)-methylindazone; indanyloxyacteic acid-94, which produce little or no stimulation of hypocotyl elongation by themselves, are able to counteract the inhibition and the disintegration induced by auxins with various efficiencies. This interference appears to be specific for auxins and does not occur when hypocotyl elongation is inhibited by other growth regulators such as ethylene or cytokinins. The putative involvement of anion channels in auxin signal transduction is discussed.

Anions↗

PubMed1999

Expansins are conserved in conifers and expressed in hypocotyls in response to exogenous auxin.

Differential display reverse transcription-polymerase chain reaction was used to detect the induction of gene expression during adventitious root formation in loblolly pine (Pinus taeda) after treatment with the exogenous auxin indole-3-butyric acid. A BLAST search of the GenBank database using one of the clones obtained revealed very strong similarity to the alpha-expansin gene family in angiosperms. A near-full-length loblolly pine alpha-expansin sequence was obtained using 5'- and 3'-rapid amplification of cDNA end cloning, and the deduced amino acid sequence was highly conserved relative to those of angiosperm expansins. Northern analysis indicates that alpha-expansin mRNA expression increases 50- to 100-fold in the base of hypocotyl stem cuttings from loblolly pine seedlings in response to indole-3-butyric acid, with peak expression occurring 24 to 48 h after induction.

Amino Acid Sequence↗

PubMed1967

Biosynthesis of phenolic compounds in first internodes of sorghum: lignin and related products.

Lignin biosynthesis in excised tissues of Sorghum vulgare variety Wheatland milo incubated in air with and without prior infiltration with H(2)O was presumably limited by H(2)O(2) production and was dependent upon an endogenous substrate, probably starch. In solution culture without shaking, this conversion of endogenous material was partially blocked at some step prior to p-hydroxycinnamic acid. The synthesis was light independent and continued protein synthesis was not required. The accumulation of lignin products was paralleled by an increase in dhurrin, alkaline sensitive esters of p-hydroxycinnamic, ferulic and sinapic acids, and flavin coenzymes, especially flavin-adenine dinucleotide. There was no detectable evidence of competition for substrates with other phenols such as anthocyanins or with the growth of adventitious roots. There was evidence, however, of mechanisms limiting lignification in the first internode in the intact seedling. Comparisons are made with lignin production in comparable tissues of Phleum.

Journal Article↗

PubMed1967

Partial purification of a legume nodulation factor present in coconut water.

The nodulation of adventitious roots growing from segments of bean hypocotyl tissue was used as a bioassay for the material present in coconut water which stimulated nodulation. The active material in coconut water is acidic, but it was not possible to extract it from an acid solution with organic solvents. A purification of approximately 70-fold (on a dry wt basis) was obtained using activated charcoal, but at least 10 different compounds were present in the active fractions. A purified fraction of coconut water, which is stimulatory to the growth of carrot root explants, was active in the nodulation assay at a concentration of 2 mug/ml. This represents a 4000-fold purification of the diffusible fraction of coconut water. The charcoal fractionation procedure can be applied to the active material present in extracts of bean leaves.

Journal Article↗

PubMed1987

An evaluation of 2,5-norbornadiene as a reversible inhibitor of ethylene action in deepwater rice.

Partial submergence of deepwater rice (Oryza sativa L. cv Habiganj Aman II) elicits three responses: enhancement of internodal elongation, inhibition of leaf growth, and promotion of adventitious root formation. All three responses can be induced in isolated stem sections by treatment with ethylene. Dose-response curves indicate that the responses are linearly related to the logarithm of the ethylene concentration over two orders of magnitude. Application of the cyclic olefin 2,5-norbornadiene (NBD) to ethylene-treated sections results in a parallel shift in dose-response curves to higher ethylene concentrations, indicating that NBD behaves as a competitive inhibitor of ethylene action. Internodal elongation of stem sections is promoted by gibberellic acid (GA(3)) in the absence of exogenous ethylene. Endogenous ethylene levels do not increase in GA(3)-treated sections, and application of NBD does not prevent GA(3)-promoted elongation. To the contrary, NBD treatment results in increased growth at intermediate GA(3) concentrations. These results support the idea that ethylene acts through endogenous GA in promoting growth in deepwater rice. NBD applied to GA(3)-treated stem sections results in increased ethylene production. This enhancement of ethylene formation is reversed by application of either ethylene or propylene, indicating that ethylene biosynthesis in rice internodes is under negative feedback control.

Journal Article↗

PubMed1992

Transgenic Tobacco Plants Coexpressing the Agrobacterium tumefaciens iaaM and iaaH Genes Display Altered Growth and Indoleacetic Acid Metabolism.

Transgenic tobacco (Nicotiana tabacum) SR1 plants expressing the Agrobacterium tumefaciens nopaline transferred DNA iaaH gene were transformed with a 35S-iaaM construct. The transformants displayed several morphological aberrations, such as adventitious root formation on stem and leaves, dwarfism, epinastic leaf growth, increased apical dominance, and an overall retardation in development. In addition, xylem lignification was higher than in wild type. Free and conjugated indoleacetic acid (IAA) levels were quantified by gas chromatography-multiple ion monitoring-mass spectrometry in leaves and internodes of wild-type plants and two transformed lines with different phenotypes. Both transformed lines contained elevated levels of free and conjugated IAA, which was associated with increased transcription of the iaaM gene. The line with the highest IAA level also had the most altered pattern of growth and development. These IAA-overproducing plants will provide a model system for studies on IAA metabolism, IAA interactions with other phytohormones, and IAA roles in regulating plant growth and development.

Journal Article↗

PubMed2003

The beta-subunit of the Arabidopsis G protein negatively regulates auxin-induced cell division and affects multiple developmental processes.

Plant cells respond to low concentrations of auxin by cell expansion, and at a slightly higher concentration, these cells divide. Previous work revealed that null mutants of the alpha-subunit of a putative heterotrimeric G protein (GPA1) have reduced cell division. Here, we show that this prototypical G protein complex acts mechanistically by controlling auxin sensitivity toward cell division. Loss-of-function G protein mutants have altered auxin-mediated cell division throughout development, especially during the auxin-induced formation of lateral and adventitious root primordia. Ectopic expression of the wild-type Galpha-subunit phenocopies the Gbeta mutants (auxin hypersensitivity), probably by sequestering the Gbetagamma-subunits, whereas overexpression of Gbeta reduces auxin sensitivity and a constitutively active (Q222L) mutant Galpha behaves like the wild type. These data are consistent with a model in which Gbetagamma acts as a negative regulator of auxin-induced cell division. Accordingly, basal repression of approximately one-third of the identified auxin-regulated genes (47 of 150 upregulated genes among 8300 quantitated) is lost in the Gbeta transcript-null mutant. Included among these are genes that encode proteins proposed to control cell division in root primordia formation as well as several novel genes. These results suggest that although auxin-regulated cell division is not coupled directly by a G protein, the Gbeta-subunit attenuates this auxin pathway upstream of the control of mRNA steady state levels.

Alleles↗

PubMed1998

Srchi13, a novel early nodulin from Sesbania rostrata, is related to acidic class III chitinases.

On the tropical legume Sesbania rostrata, stem-borne nodules develop after inoculation of adventitious root primordia with the microsymbiont Azorhizobium caulinodans. A cDNA clone, Srchi13, with homology to acidic class III chitinase genes, corresponds to an early nodulin gene with transiently induced expression during nodule ontogeny. Srchi13 transcripts accumulated strongly 2 days after inoculation, decreased from day 7 onward, and disappeared in mature nodules. Induction was dependent on Nod factor-producing bacteria. Srchi13 was expressed around infection pockets, in infection centra, around the developing nodule and its vascular bundles, and in uninfected cells of the central tissue. The specific and transient transcript accumulation together with the lipochitooligosaccharide degradation activity of the recombinant protein hint at a role of Srchi13 in normal nodule ontogeny by limiting the action of Nod factors.

Amino Acid Sequence↗

PubMed2004

Arabidopsis glucosyltransferase UGT74B1 functions in glucosinolate biosynthesis and auxin homeostasis.

Glucosinolates are a class of secondary metabolites with important roles in plant defense and human nutrition. Here, we characterize a putative UDP-glucose:thiohydroximate S-glucosyltransferase, UGT74B1, to determine its role in the Arabidopsis glucosinolate pathway. Biochemical analyses demonstrate that recombinant UGT74B1 specifically glucosylates the thiohydroximate functional group. Low Km values for phenylacetothiohydroximic acid (approximately 6 microm) and UDP-glucose (approximately 50 microm) strongly suggest that thiohydroximates are in vivo substrates of UGT74B1. Insertional loss-of-function ugt74b1 mutants exhibit significantly decreased, but not abolished, glucosinolate accumulation. In addition, ugt74b1 mutants display phenotypes reminiscent of auxin overproduction, such as epinastic cotyledons, elongated hypocotyls in light-grown plants, excess adventitious rooting and incomplete leaf vascularization. Indeed, during early plant development, mutant ugt74b1 seedlings accumulate nearly threefold more indole-3-acetic acid than the wild type. Other phenotypes, however, such as chlorosis along the leaf veins, are likely caused by thiohydroximate toxicity. Analysis of UGT74B1 promoter activity during plant development reveals expression patterns consistent with glucosinolate metabolism and induction by auxin treatment. The results are discussed in the context of known mutations in glucosinolate pathway genes and their effects on auxin homeostasis. Taken together, our work provides complementary in vitro and in vivo evidence for a primary role of UGT74B1 in glucosinolate biosynthesis.

Arabidopsis↗

PubMed2006

Variable tolerance of wetland tree species to combined salinity and waterlogging is related to regulation of ion uptake and production of organic solutes.

Melaleuca cuticularis and Casuarina obesa occur in wetlands, whereas Banksia attenuata occurs in adjacent well-drained sandy soils. Salt and waterlogging tolerances in these tree species were studied, as the levels of these stresses have increased in south-western Australia. Seedlings were exposed to 0.01, 200 or 400 mm NaCl, with or without waterlogging, in a sand culture with nutrient solution for 22 d in a glasshouse. Melaleuca cuticularis and C. obesa survived all treatments, and generally maintained high rates of net photosynthesis. Banksia attenuata tolerated neither waterlogging nor salinity. Salt tolerance of M. cuticularis and C. obesa was associated with the regulation of foliar sodium (Na+), chloride (Cl-) and potassium (K+) concentrations. Under saline-waterlogged conditions, this regulation was maintained in M. cuticularis, but was reduced in C. obesa. Foliage of these two species also contained appreciable levels of compatible organic solutes: methyl proline in M. cuticularis and proline in C. obesa; in both cases the concentrations increased at higher salinity. Melaleuca cuticularis formed a higher proportion of aerenchyma in adventitious roots than C. obesa, so enhanced internal root aeration in M. cuticularis might contribute to its higher tolerance of combined salinity and waterlogging.

Acclimatization↗

PubMed1980

Characterization of Tn904 insertions in octopine Ti plasmid mutants of Agrobacterium tumefaciens.

Seven Tn904 insertion mutants of pTi Ach5 affecting Agrobacterium tumefaciens virulence were studied. The mutant character was shown to be plasmid borne. Four of these mutants were avirulent and carried an insertion in restriction endonuclease HpaI fragment 12, a 3.3-megadalton fragment, which therefore appears to be a Ti plasmid region essential for virulence. Two mutants were attenuated in virulence. The inserts mapped close to HpaI fragment 12. One mutant giving rise to small tumors with excessive adventitious root formation on Kalanchoe daigremontiana carried an insertion in the right side of the common sequence in the deoxyribonucleic acid of the Ti plasmid detected in crown gall tumors. The insertion behavior of Tn904 was studied by analyzing 11 independently isolated and randomly chosen mutants. The Tn904 inserts did not affect oncogenicity, tumor morphology, bacterial transfer functions, octopine catabolism functions, or vital parts of the Ti plasmid, such as the origin of replication. Most of the Tn904 inserts were concentrated in a small part of the map. The size of additional deoxyribonucleic acid as a result of Tn904 inserts varied between 5 and 15 megadaltons. In two cases a Ti plasmid was found with two Tn904 insertions at different positions.

Arginine↗

PubMed1983

Initial stages in the morphogenesis of nitrogen-fixing stem nodules of Sesbania rostrata.

Morphogenesis of stem nodules in Sesbania rostrata was studied over a period of 6 days after inoculation with an appropriate species of Rhizobium. Nodulation sites were initially slightly raised, circular areas 0.3 to 0.6 mm in diameter and 4 to 5 mm apart in vertical rows along the length of the stem. Each site was underlaid by an adventitious root primordium. A site became susceptible to infection by a specific Rhizobium sp. when the root primordium broke through the epidermis, leaving a fissure. Rhizobia multiplied within this fissure and colonized the exposed intercellular spaces. The infection extended inward as narrow, branched intercellular threads moved into a cortical meristematic zone, where cell division was initiated, and invagination of infection thread branches into adjacent plant cells followed. Rhizobia were released into the plant cells and surrounded immediately by plant membrane. Intracellular rhizobia divided actively, leading to bacteroid-filled cells. Infected areas enlarged and coalesced as the nodule matured.

Cells, Cultured↗

PubMed1976

Mitotic activity in rice seedlings germinating under oxygen deficiency.

Rice seedlings germinating in oxygen-deficient environments do not manifest visual evidence of seminal or adventitious root growth or normal leaf growth, the coleoptile being the only seedling structure to emerge under these environmental conditions. Microscopic evidence, however, shows that mitotic activity occurs in the different tissues comprising the shoots of the seedlings germinating under oxygen deficiency. Thus evidence is presented here which shows that mitotic activity in rice seedlings germinating in oxygen-deficient environments is not confined solely to the emerging coleoptiles of the germinating seedlings.

Anaerobiosis↗

PubMed1995

Tissue cultures of Taxus baccata as a source of 10-deacetylbaccatin III, a precursor for the hemisynthesis of taxol.

Callus cultures of Taxus baccata L. cv. stricta were induced from hypocotyl and leaf explants on Woody Plant medium (hormone-free or additionated with phytohormones). Under continuous dark condition, adventitious roots were regenerated from hypocotyl- and leaf-derived callus cultures. Antibodies raised in rabbits against 10-succinyl-10-deacetylbaccatin III were used for the detection and the semi-quantitative determination of 10-deacetylbaccatin III in Taxus cultures. The presence of 10-deacetylbaccatin III in callus extracts was confirmed by TLC, HPLC using a photodiode array detector and mass spectrometry (CI-MS). The highest equivalent content of the taxoid derivatives (7.83 mg/100 g dry wt.) was detected in an extract from leaf-derived callus.

Chromatography, High Pressure Liquid↗

PubMed1992

Evolutionary biology and pathology of vitamin D.

There is mounting evidence that essentially all fungi, plants and animals living on earth produce provitamin D. It is likely that once exposed to sunlight, these provitamins are converted to previtamin D. It is unclear why fungi, phytoplankton, zooplankton and plants have the capacity to produce such large quantities of provitamin D. It is likely, however, that provitamin D and possibly vitamin D play an important biologic role in these organisms. Buchala and Schmid found, for example, that vitamin D3 promoted adventitious root development. It may be that provitamin D has a more fundamental function in lower life forms. Provitamin D and its photoproducts have UV absorption spectra that overlap with the ultraviolet absorption spectra from ultraviolet radiation-sensitive macromolecules including DNA, RNA and proteins. Thus, provitamin D and photoisomers could serve as a photon sink, and therefore, act as a natural sunscreen to protect lower life forms from the damaging effects of the high energy ultraviolet radiation that they are exposed to. It is more clear, however, that amphibians, reptiles, birds, mammals and humans all require vitamin D and that the vitamin D must be metabolized to 1,25(OH)2D3 before it can carry-out its physiologic functions on calcium and bone metabolism. The intense research activities during the past decade on the antiproliferative and differentiation activities of 1,25(OH)2D3 has opened a new chapter for this vitamin/hormone. 1,25(OH)2D3 and its analogs are being developed for the treatment of psoriasis, breast cancer, and leukemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1999

Seed germination patterns in green dragon (Arisaema dracontium, Araceae).

Arisaema dracontium (green dragon) is a perennial herb that is widely distributed in eastern North America. However, in Canada, at the northern edge of its distribution, the species is designated as "vulnerable" with respect to conservation status. In natural populations, seedlings are uncommon; the present study was undertaken in order to characterize seed and seedling properties in green dragon. Seeds were sampled from five sites, ranging from Ontario at the northern limit of the distribution range, to Louisiana in the south. Seed germinability ranged from 25 to 55%, depending upon source. Experiments indicated that neither the hard seed coat nor a water-soluble exudate from the seed was responsible for inducing or maintaining dormancy. Patterns of seed germination appear to reflect general climatic conditions at the sites where seeds had originated. Cold stratification at 3°C produced significantly greater relative germinability in all seed collections except the most southerly one, from Baton Rouge. These seeds also had a slower overall speed of germination. In contrast, germination of seeds from the most northerly site was promoted by cold stratification and occurred over a relatively brief period. Germination in alternating light and dark conditions decreased the speed of germination compared to germination in the dark, however exposure to light changed the phenology of germination by promoting development of adventitious roots and primary leaves in these seedlings.

Journal Article↗

PubMed2000

[A comparative study on chlorophyll content, chlorophyll fluorescence and diurnal course of leaf gas exchange of two ecotypes of banyan].

The morphological differences, chlorophyll contents, fluorescence and diurnal course of leaf gas exchange between terrestrial banyan and amphibious banyan were compared with pot culture. The amphibious banyan possesses well developed aerial and hydro-adventitious roots, and wider leaf with inclination of evolution toward mesophytic traits. The chlorophyll content of terrestrial banyan was higher than that of amphibious banyan. The diurnal course of leaf gas exchange indicated that net photosynthetic rate of terrestrial banyan was slightly higher than that of amphibious banyan grown in water, but much higher than that grown in soil. The amphibious banyan grown in water had the highest transpiration rate, the terrestrial banyan had a lower one, and the amphibious banyan grown in soil had the lowest. Linear regression analysis showed a positive correlation between net photosynthetic rate and stomatal conductance, implying that the stomatal conductance was dominant factor controlling the gas exchange. In this study, the term of intrinsic water use efficiency (net photosynthetic rate/stomatal conductance ratio, Intrinsic WUE) was applied to describe the photosynthesis and water properties, and the result showed that it was a more suitable measure compared to the usual WUE(net photosynthetic rate/transpiration rate). Among the three banyan plants examined, the amphibious banyan had the highest intrinsic WUE.

Adaptation, Physiological↗