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T H Ho

Publications and source records attributed to T H Ho.

At least 73 records · Page 4Linked to original sources
PubMed1986

Mode of action of abscisic Acid in barley aleurone layers : induction of new proteins by abscisic Acid.

As part of a continuing effort to elucidate the mode of action of abscisic acid (ABA) in barley (Hordeum vulgare L. cv Himalaya) aleurone layers, we have investigated the induction of several polypeptides by ABA in this tissue. There were nine ABA-induced polypeptides as observed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and considerably more (at least 16 spots) on a two-dimensional gel. These proteins started to show enhanced synthesis 2 to 4 hours after ABA treatment, and their synthesis continued for at least 48 hours. In vitro translation using total RNA isolated from ABA-treated aleurone layers indicated that translatable mRNA levels of these proteins essentially paralleled the levels of in vivo synthesized proteins. The most abundant of the ABA-induced proteins was a 29 kilodalton polypeptide which was also synthesized in tissue incubated without ABA. In vivo synthesis of this protein declined as ABA concentration was decreased, with 1 nanomolar ABA approaching control level. Cell fractionation experiments located the 29 kilodalton major ABA-induced protein in 1,000g and 13,000g pellets; most other induced proteins were in the 80,000g supernatant. The 29 kilodalton protein appeared to be sensitive to degradation by sulfhydryl type proteases. As expected, the induction of these proteins by ABA was suppressed by gibberellic acid. Phaseic acid, the first stable metabolite of ABA, suppressed the gibberellic acid-enhanced alpha-amylase synthesis but was unable to induce the ABA-induced proteins. None of the ABA-induced proteins were secreted into the incubation medium. A 36 kilodalton ABA-induced protein showed cross-reactivity with antibody against a barley lectin specific for glucosamine, galactosamine, and mannosamine.

Journal Article↗
PubMed1986

Barley aleurone layers secrete a nuclease in response to gibberellic Acid : purification and partial characterization of the associated ribonuclease, deoxyribonuclease, and 3'-nucleotidase activities.

Incubation of barley (Hordeum vulgare L. cv Himalaya) half-seeds with gibberellic acid enhances the secretion of ribonuclease and deoxyribonuclease from aleurone tissue (MJ Chrispeels, JE Varner 1967 Plant Physiol 42: 398-406; L Taiz, JE Starks 1977 Plant Physiol 60: 182-189). These activities were over 50-fold greater in medium of half-seeds incubated with gibberellic acid than in control medium. Ribonuclease and deoxyribonuclease activities initially appeared in the medium 24 to 48 hours after hormone induction and increased for up to 96 hours. Both activities had a pH optimum of 6.0 and a temperature optimum of 55 degrees C. When the medium from gibberellic acid-treated half-seeds was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, the major ribonuclease and deoxyribonuclease activity bands comigrated. The two enzyme activities remained associated throughout a 2,700-fold purification employing ammonium sulfate fractionation, Heparin-Agarose affinity chromatography, and Reactive Blue 2-Agarose affinity chromatography. Also accompanying the ribonuclease and deoxyribonuclease activities throughout purification was the ability to hydrolyze the 3'-phosphoester linkage of 3'-AMP. The purified protein was composed of a single polypeptide with an apparent molecular weight of 36 kilodaltons as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It is concluded that in response to gibberellic acid, barley aleurone tissue secretes a nuclease having ribonuclease, deoxyribonuclease, and 3'-nucleotidase activities.

Journal Article↗
PubMed1986

Effect of heat shock on the metabolism of glutathione in maize roots.

High performance liquid chromatography analyses revealed that glutathione (GSH) and cysteine are two of the major low molecular weight thiol compounds in maize root extracts. Treatment of maize roots to heat shock temperatures of 40 degrees C resulted in a decrease of cysteine levels and an increase of GSH levels. Pulse labeling of maize roots with [(35)S]cysteine showed that the rate of incorporation of (35)S into GSH or glutathione disulfide (GSSG) in heat shocked tissues was twice that in nonheat shocked tissues. In addition, extracts from heat shocked maize, barley, and soybean tissues contained an unidentified low molecular weight compound that increased from 1.2- to 8-fold within 2 hours of heat shock treatment depending on the tissue and plant involved. Our results indicate that during heat shock there is an increase in the activity of the GSH synthetizing capacity in maize root cells. The elevated synthesis of GSH may be related to the cells capacity to cope with heat stress conditions.

Journal Article↗
PubMed1985

Metabolism of Abscisic Acid in Guard Cells of Vicia faba L. and Commelina communis L.

Metabolism of abscisic acid (ABA) was investigated in isolated guard cells and in mesophyll tissue of Vicia faba L. and Commelina communis L. After incubation in buffer containing [G-(3)H]+/-ABA, the tissue was extracted by grinding and the metabolites separated by thin layer chromatography. Guard cells of Commelina metabolized ABA to phaseic acid (PA), dihydrophaseic acid (DPA), and alkali labile conjugates. Guard cells of Vicia formed only the conjugates. Mesophyll cells of Commelina accumulated DPA while mesophyll cells of Vicia accumulated PA. Controls showed that the observed metabolism was not due to extracellular enzyme contaminants nor to bacterial action.Metabolism of ABA in guard cells suggests a mechanism for removal of ABA, which causes stomatal closure of both species, from the stomatal complex. Conversion to metabolites which are inactive in stomatal regulation, within the cells controlling stomatal opening, might precede detectable changes in levels of ABA in bulk leaf tissue. The differences observed between Commelina and Vicia in metabolism of ABA in guard cells, and in the accumulation product in the mesophyll, may be related to differences in stomatal sensitivity to PA which have been reported for these species.

Journal Article↗
PubMed1984

Azido auxins : photolysis in solution and covalent binding to soybean.

The potential of three auxin analogs, 4-, 5-, and 6-azidoindole-3-acetic (4-N(3)IAA, 5-N(3)IAA, and 6-N(3)IAA), as photoaffinity labeling agents for the detection and isolation of auxin receptors was assessed by irradiating these compounds at 365 nm on TLC plates, in solution, and in contact with soybean (Glycine max L. Merr. var. Wayne) hypocotyl. Photolysis on TLC plates produces immobile spots, indicating extremely polar or covalent binding of the photoproducts to the plates. On irradiation in buffer or in buffer containing sucrose, all three compounds decompose at rates that are first order in N(3)IAA to give fluorescent solutions. Photolysis through a Pyrex filter is slower than that through quartz, but the filter prevents tissue damage and allows a given dose of irradiation to photolyze all three N(3)IAAs to the same extent. The effects of photolysis of these compounds in vivo were evaluated with a straight growth assay using etiolated soybean hypocotyl segments. According to this assay, the photoproducts of the N(3)IAAs possess little auxin activity. Irradiation of soybean hypocotyl tissue after 1-hour exposure to 4-N(3)IAA in the dark causes the tissue to grow during 12 hours as much as tissue that is continuously exposed to 4-N(3)IAA in the dark for this period, suggesting that, on photolysis, this auxin analog binds irreversibly to an auxinsensitive site. Although the fluorescence intensity of the photolyzed N(3)IAAs is weak enough to require another method of detecting the bound analog under physiological conditions, the evidence for covalent binding of the N(3)IAAs on photolysis implies that these compounds will be satisfactory photoaffinity labeling agents.

Journal Article↗
PubMed1984

Azido auxins: quantitative binding data in maize.

The binding constants of three auxin analogs, 4-, 5-, and 6-azidoindole-3-acetic acid (4-, 5-, and 6-N(3)IAA), and of the photoproducts of 5-N(3)IAA to the naphthalene-1-acetic acid (NAA) binding sites of Zea mays L. WF9 x BR38 were determined to evaluate the potential of these analogs as photoaffinity labeling agents. We have found that 4- and 5-N(3)IAA bind to these sites with affinities similar to that of IAA, while 6-N(3)IAA and the photoproducts of 5-N(3)IAA bind less tightly. This binding is fully reversible in the dark. Binding of 5-N(3)IAA becomes covalent and irreversible upon UV irradiation, as evidenced by a 30% loss in NAA binding at sites pretreated with 5-N(3)IAA and UV irradiation, then washed extensively. IAA or NAA, included with this 5-N(3)IAA pretreatment, can protect the sites from blockage, whereas benzoic acid and tryptophan are unable to protect the site, indicating that 5-N(3)IAA specifically labels the auxin sites.

Journal Article↗
PubMed1984

Tissue specificity of the heat-shock response in maize.

The tissue specificity of the heat-shock response in maize was investigated. The ability to synthesize heat shock proteins (hsp) at 40 degrees C, as well as the intensity and duration of that synthesis, was analyzed in coleoptiles, scutella, green and etiolated leaves, suspension-cultured cells, germinating pollen grains, and primary root sections at different stages of development. One-dimensional sodium dodecyl sulfate gel electrophoresis of extracted proteins revealed that most of the tissues synthesized the typical set of 10 hsp, but that the exact characteristics of the response depended upon the tissue type. While elongating portions of the primary root exhibited a strong heat shock response, the more mature portions showed a reduced ability to synthesize hsp. Leaves, whether green or etiolated, excised or intact, constitutively synthesized a low level of hsp at 25 degrees C, and high levels could be induced at 40 degrees C. Suspension-cultures of Black Mexican sweet corn synthesized, besides the typical set of hsp, two additional polypeptides. In contrast to all the other tissues, germinating pollen grains could not be induced to synthesize the typical set of hsp but did synthesize two new polypeptides of 92 and 56 kD molecular weight.The heat shock response was transient for most of the tissues which synthesized the standard set of hsp. Hsp synthesis was detected up to 2 to 3 hours, but not at 10 hours of continuous 40 degrees C treatment. The exception was suspension cultured cells, in which hsp synthesis showed only a slight reduction after 10 hours at 40 degrees C. Tissue-specific differences in the heat-shock response suggest that there are differences in the way a given tissue is able to adapt to high temperature.We have confirmed the previous suggestion that maize hsp do not accumulate in substantial quantities. Using two-dimensional gel analysis, hsp could be detected by autoradiography but not by sensitive silver staining techniques.

Journal Article↗
PubMed1984

Azido auxins : photoaffinity labeling of auxin-binding proteins in maize coleoptile with tritiated 5-azidoindole-3-acetic Acid.

Tritiated 5-azidoindole-3-acetic acid (5-N(3)-[7-(3)H]IAA), a photoaffinity labeling agent, was used to photolabel proteins of a crude microsomal preparation from maize (Zea mays L., Bear Hybrid, WF9 x BR38) coleoptile. Approximately 50% of the bound radioactivity was solubilized in 5 molar urea containing Triton X-100, and the extract was fractionated using a variety of techniques. High performance liquid chromatography demonstrated that, although many membrane proteins incorporated tritiated label, only a few showed reduced incorporation in the presence of excess indole-3-acetic acid. By contrast, no detectable reduction in incorporation was observed in the presence of excess naphthalene-1-acetic acid. Results from isoelectric focusing gel electrophoresis indicate that the proteins that showed reduced incorporation of photolyzed 5-N(3)-[7-(3)H]IAA in the presence of IAA fell into two main groups: one which focuses between pH 5.2 and 5.7 (pI 4.8-5.3) and another around pH 6.2 (pI 5.8). In sodium dodecylsulfate polyacrylamide gel electrophoresis, the proteins migrated as four bands with apparent molecular weights of 60, 49, 45, and 37 kilodaltons. The auxin-transport inhibitor, 2,3,5-triiodobenzoic acid, competes for the labeling by 5-N(3)-[7-(3)H]IAA, suggesting that some of these proteins may be involved in auxin transport.

Journal Article↗
PubMed1984

Mode of action of abscisic Acid in barley aleurone layers : abscisic Acid induces its own conversion to phaseic Acid.

As a part of our effort to study the mode of action of abscisic acid (ABA) and its metabolites during seed germination, we have investigated the regulation of ABA metabolism in barley (Hordeum vulgare) aleurone layers and a few other plant tissues. The rate of conversion of [(3)H]ABA to [(3)H]phaseic acid (PA), the first stable metabolite of ABA, is enhanced by 2- to 5-fold in barley aleurone layers when the tissue is pretreated with ABA. However, the conversion of [(3)H]PA to [(3)H] dihydrophaseic acid (DPA), the next metabolite after PA, is not enhanced by pretreatment with either ABA or PA. The ABA enhancement of its own metabolism in barley aleurone layers is detectable with a pretreatment of ABA ranging from 10(-3) to 10(-4) molar. This apparent self-induction of ABA conversion to PA can be observed after the barley aleurone layers have been treated with 10(-5) molar ABA for as short as 2 hours, and is inhibited by the transcription inhibitor, cordycepin (3'-deoxyadenosine), or the translation inhibitor, cycloheximide. The self-induction of ABA conversion to PA also occurs in wheat aleurone layers, but not in other plant tissues that have been investigated, including corn root tips, barley embryos, barley, and soybean leaf discs. It is probably a phenomenon unique to the aleurone layers of some cereal grains. In view of the recent observations that ABA is able to induce new proteins in barley aleurone layers, we suggest that some of these ABA-induced proteins are involved in the conversion from ABA to PA in this tissue.

Journal Article↗
PubMed1983

Multiple molecular forms of the gibberellin-induced alpha-amylase from the aleurone layers of barley seeds.

A class of plant growth regulators, gibberellins, induce the synthesis of alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) in the aleurone layers of barley (Hordeum vulgare L. var. Himalaya) seeds. The purified alpha-amylase is composed of multiple isozymic forms with indistinguishable molecular weights, but different net charges. These alpha-amylase isozymes separate on isoelectric focusing gels into two groups, each containing multiple species. One group has an apparent isoelectric point (pI) of approximately 5.8 (the high pI group). The other group's pI values are around 4.5 (the low pI group). On some gels a small amount of protein focuses between the high and low pI isozymes. These proteins comigrate with the low pI isozymes upon reelectrophoresis. The synthesis of these two groups is temporally regulated. The high pI group is the dominant set of isozymes secreted from embryoless half seeds during the first two days of gibberellin administration. After four days, however, the major isozymes are those of the low pI group. This shift in isozyme pattern is due to a shift in their relative rates of synthesis. Peptide analysis of these two groups of isozymes with Staphylococcus aureus V8 protease and cyanogen bromide shows amino acid sequence differences. However, members within the same group have similar peptide patterns. Both groups of isozymes are synthesized in vitro in a wheat germ extract primed with poly(A)+ RNA isolated from gibberellin-treated aleurone layers. This indicates that the synthesis of the two groups of alpha-amylase isozymes is probably directed by two or more different populations of mature mRNA. A model that explains these observations and the available genetic information is that barley aleurone alpha-amylase isozymes are encoded by at least two sets of structural genes.

Amylases↗
PubMed1983

Heat shock proteins in maize.

The pattern of protein synthesis in roots of 3-day-old maize seedlings (Zea mays L.) is rapidly and dramatically altered when the incubation temperature is raised from 25 to 40 degrees C. One-dimensional sodium dodecyl sulfate gels reveal that although synthesis of the proteins observed at 25 degrees C continues at 40 degrees C, a new set of ;heat shock proteins' (hsp) is induced within 20 minutes of the temperature transition. The hsp have molecular weights of 87, 85, 79, 78, 77, 72, 70, 27, 22, and 18 kilodaltons. The 10 hsp are visible on autoradiograms but not on stained gels, suggesting that the proteins do not accumulate to any great extent.The induction of the hsp is transitory. With prolonged high temperature treatment, the synthesis of hsp continues for 4 hours in excised roots and for 8 hours in the roots of intact seedlings before declining sharply. Coincident to the decline in synthesis of the 10 hsp is the gradual increase in intensity of three new polypeptides having molecular weights of 62, 49.5, and 19 kilodaltons. These proteins begin to appear about the time that synthesis of the other 10 hsp becomes maximal.Shifting the temperature back to 25 degrees C also causes a decline in synthesis of hsp, but this decline occurs more rapidly than that seen during prolonged heat shock. A decrease in hsp synthesis becomes apparent 2 hours after the roots are returned to 25 degrees C.Shifting the temperature from 25 to 45 degrees C results in a pattern of protein synthesis different from that observed after a shift to 40 degrees C. Normal protein synthesis continues, except four proteins, which are produced in small amounts at lower temperatures, show greatly enhanced synthesis at 45 degrees C. These proteins have apparent molecular weights of 83, 81, 68, and 65 kilodaltons. Also, the 10 hsp listed above are not synthesized. It is suggested that at least two distinct high-temperature responses are present in maize, which may reflect the metabolic changes generated at different elevated temperatures.

Journal Article↗
PubMed1983

The acardiac foetus.

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Abnormalities, Severe Teratoid↗
PubMed1982

Effect of Ethylene on the Release of alpha-Amylase through Cell Walls of Barley Aleurone Layers.

A large portion of the gibberellic acid (GA(3))-induced alpha-amylase in isolated aleurone layers is transported into the incubation medium. In the presence of GA(3) and ethylene, an even larger portion of the enzyme is found in the medium. Employing an acid washing technique developed by Varner and Mense (Plant Physiol 1972 49:187-189), it was observed that ethylene significantly reduces the amount of alpha-amylase trapped by the thick cell walls of aleurone layers. However, the amount of enzyme remaining in the cell (within the boundary of plasma membrane) is not affected by ethylene. Ethylene has no observable effect on membrane formation as measured by the incorporation of [(32)P]orthophosphate into phospholipids. Because of these observations it is suggested that ethylene enhances the release of alpha-amylase, i.e. transport of alpha-amylase across cell walls, but not the secretion of alpha-amylase, i.e. transport of alpha-amylase past the barrier of plasma membrane. The possible mechanism of this ethylene effect is discussed.

Journal Article↗
PubMed1981

Characterization of a Gibberellin-Insensitive Dwarf Wheat, D6899 : EVIDENCE FOR A REGULATORY STEP COMMON TO MANY DIVERSE RESPONSES TO GIBBERELLINS.

The effects of gibberellin in two wheat varieties, Nainari 60 and D6899, have been studied. D6899 is a dwarf wheat having a single locus mutation, the Rht 3 gene ("Tom Thumb" gene), which is located on chromosome 4A. When compared with the standard height wheat variety, Nainari 60, D6899 does not have a slowdown in cellular metabolism such as respiration rate, protein content, rate of protein synthesis, and uptake of amino acids. The content of ATP is even higher in D6899. However, all of the gibberellin-mediated physiological processes that we have studied, including leaf elongation, synthesis and release of hydrolytic enzymes, and secretion of phosphate ions and reducing sugars in aleurone layers, are retarded in D6899. D6899 and Nainari 60 have essentially the same uptake and metabolism of gibberellin and their levels of endogenous inhibitors such as abscisic acid do not differ drastically. The dosage-response curve of the gibberellin-mediated alpha-amylase production indicates that a rate-limiting step, which is common to many of the diverse gibberellin responses, is partially blocked in D6899 wheat.

Journal Article↗
PubMed1980

Screening for barley mutants with altered hormone sensitivity in their aleurone layers.

A method, based on the diffusion assay of alpha-amylase on agar plates, was developed to screen for barley (Himalaya) mutants with altered sensitivity to gibberellic acid (GA(3)) or abscisic acid (ABA) in their aleurone layers. The seeds produced by sodium azide-mutagenized barley were screened for their ability to synthesize and secrete alpha-amylase when treated with different combinations of hormones. Various GA(3)-insensitive or supersensitive, ABA-insensitive, temperature-dependent GA(3)-insensitive, and constitutive mutants have been identified. Several stable mutants with altered GA(3) sensitivity were recovered. Two of the homozygous GA(3)-insensitive mutants have been preliminarily characterized. The GA(3)-enhanced production of alpha-amylase and release of phosphatase are hampered in these mutants. However, they have normal stem height, and the uptake of GA(3) by their aleurone layers appears to be the same as that of wild-type barley. They are most likely regulatory mutants affecting both alpha-amylase synthesis and phosphatase release.

Journal Article↗
PubMed1978

Intramuscular administration of 16 phenoxy omega 17,18,19,20 tetranor PGE2 methyl sulfonylamide for pre-operative cervical dilatation in first trimester nulliparae.

A single intramuscular dose of 500 microgram 16 phenoxy omega 17,18,19,20 tetranor PGE2 methyl sulfonylamide was used for cervical dilatation prior to vacuum aspiration in 80 first trimester nulliparae. Three hours after prostaglandin administration the cervix had dilated to 8 mm or more in 60 patients (75%). The uterus was evacuated in these patients without mechanical dilatation of the cervix. In the remaining 20 patients the cervix had dilated 4 to 7 mm. Further mechanical dilatation to 8 mm was carried out easily in most of these patients. Side effects included pain requiring analgesic (3 patients), vomiting (4 patients) and transient pyrexia (greater than 1 degrees C, 2 patients). There were no complications or damage to the uterus or the cervix during evacuation of the uterus.

Abortion, Induced↗
PubMedDate not supplied

The relevance of oncogenes as prognostic markers in cervical cancer.

To study the prevalence of the oncogenes c-myc, IFN-alpha; c-erbB2; H-ras codon 12, 13, and 61; c-fos; and E6/E7 oncogenes of human papillomavirus (HPV) 16 in patients with invasive carcinoma of the cervix and their prognostic significance, genomic DNA and RNA were isolated from tissues of 275 patients in Singapore with nonmetastatic cervical cancer and 32 patients with normal cervix. The levels of expression of the various oncogenes were quantified by PCR using the respective primers. When the PCR data on the DNA were analyzed by the log-rank test, IFN gamma (P = 0.02) and H-ras codon 12 and 13 (P = 0.02) were found to be prognostic. In the multivariate analysis, a statistically significant trend for increasing risk with higher quartiles was found for c-myc (P = 0.007) and c-erbB2 (P = 0.03). After adjusting for age and stage, a correlation appears between the amplification of the oncogenes c-myc, c-erbB2, and H-ras codon 12, 13, and 61 and the development of recurrent cervical cancer. Further adjustment to include the parameters of treatment and histology type did not change the outcome of the correlation observed.

Adult↗