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R L Travis

Publications and source records attributed to R L Travis.

32 records · Page 2Linked to original sources
PubMed1979

An electron microscope comparison of plasma membrane vesicles from meristematic and mature soybean root tissue.

Plasma membrane vesicles were isolated from homogenates of meristematic and mature soybean root tissue by differential sucrose gradient centrifugation. Vesicles were positively identified by the phosphotungstic acid-chromic acid procedure (PACP). The two preparations were comparable in size class distribution, mitochondrial contamination, and per cent plasma membrane vesicles present. Purity levels were estimated to be greater than 75%. The specificity of PACP was observed for a variety of cell types from both regions. Some variability in PACP staining was offset by careful modulation of the stain protocol and was found to be independent of developmental stage in subcellular fractions. Patchy or discontinuous staining, observed in both intact tissue and in subcellular fractions from both regions, was found to be a function of stain time.

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PubMed1977

Studies on the mechanism of action of dinitramine: effect on soybean root plasma membrane.

The effect of dinitramine, a selective herbicide, on the plasma membrane of the soybean (Glycine max L.) root was studied. Used as marker systems to observe the herbicide effect were two plasma-membrane-specific enzymes, pH 6.5 ATPase and glucan synthetase.The activity of pH 6.5 ATPase decreased significantly in membrane vesicles prepared from roots harvested 15 minutes after treatment with dinitramine. Maximum inhibition occurred in roots harvested 2 hours after treatment. Glucan synthetase activity decreased similarly within 2 hours of treatment.Membrane permeability to (86)Rb was rapidly increased by dinitramine.The activity of pH 6.5 ATPase returned to the control level within 8 hours of treatment with dinitramine.These results show dinitramine's initial site of action to be the plasma membrane, producing an over-all reduction in membrane function through inactivation of membrane-associated proteins.

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PubMed1976

Auxin-induced Changes in the Incorporation of H-Amino Acids into Soybean Ribosomal Proteins.

Auxin-induced activation of 80S ribosomes and polyribosome formation in mature soybean (Glycine max var. Hawkeye) hypocotyl (R. L. Travis, J. M. Anderson, and J. L. Key. 1973. Plant Physiol. 52: 608-612) in the presence of a mixture of radioactive amino acids correlates with an increased specific radioactivity of at least three ribosomal proteins; the labeling of one of these increased severalfold above the control level. Results of experiments with 5-fluorouracil and cycloheximide indicated that the proteins in question were synthesized in response to auxin and became associated with pre-existing ribosomes. Ribosome dissociation experiments indicated that these proteins were associated with the 60S ribosome subunit.

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PubMed1975

Studies on Pea Ribosomal Proteins: Conformational and Biological Activity Changes of Ribosomal Subunits Derived by NH(4)Cl Dissociation.

Ribosomal subunits prepared by NH(4)Cl dissociation (0.5 m) of the monomeric ribosomes were much less active in in vitro protein synthesis than those prepared by KCl dissociation. The decrease in activity correlated with a detachment of some proteins (L(2) and L(9) as shown by gel electrophoresis) within the 60S ribosomal subunits. Subunits prepared with 0.3 m NH(4)Cl retained L(2) and L(9), but the activity remained low. Incubation of these 60S subunits in TKM buffer (50 mm tris [pH 7.5], 20 mm KCl, and 5 mm MgCl(2)) for 20 min at 37 C restored the activity almost to the level of those obtained by KCl dissociation. Treatment of the 0.3 m NH(4)Cl-derived 60S subunits with a protein reagent, Procion brilliant blue, prior to extraction of the ribosomal proteins resulted in the loss of L(2) and L(9), showing that these proteins were made accessible for dye binding. These observations suggest that a considerable degree of unfolding of the 60S subunit occurs at 0.3 m NH(4)Cl (this apparently leads to a preferential detachment of L(2) and L(9) at 0.5 m NH(4)Cl) and that the activity of the purified subunits depends not only on the presence of L(2) and L(9) but also on the organization of these proteins within the 60S subunits.

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PubMed1974

Activation of 80S Maize Ribosomes by Red Light Treatment of Dark-grown Seedlings.

The in vitro protein synthetic activity of 80S ribosomes from leaves of dark-grown corn seedlings was enhanced (at low Mg(2+) levels) by a 5-minute red light treatment applied 2 hours prior to tissue harvest. The effect was completely reversed by an immediate brief far red treatment, suggesting that ribosome activation is controlled by the phytochrome system. Experiments in which the interval between light treatment and tissue harvest was shortened indicate that the response was quite rapid. The initial increase in activity was detected within 30 minutes, followed by a rapid increase during the next 1.5 hours. No further increase occurred after 2 to 3 hours.The change in ribosome activity relates, at least in part, to an increase in the level of peptidyl-tRNA associated with ribosomes. Removal of peptidyl-tRNA from light-treated ribosomes also completely reversed the red light effect. Activation of ribosomes by 2 to 3 hours continuous white light (as previously reported) differs from red light activation in that reversal of this response requires salt washing of the ribosomes in addition to removal of peptidyl-tRNA.

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PubMed1973

The interaction of respiration and photosynthesis in induction of nitrate reductase activity.

The respiration and photosynthesis requirement for induction and maintenance of nitrate reductase activity was determined on leaves of Hordeum vulgare L. In this induction, glucose substituted for light in both dark-grown and carbohydrate-depleted green leaves. Oxygen appeared to be required for induction in all cases studied. In light and under N(2), 3-(3,4-dichlorophenyl)-1,1-dimethylurea completely inhibited induction, presumably by inhibiting the production of O(2), Hence, under N(2) the leaves appeared to utilize both the O(2) produced by photosynthesis and the CO(2) produced by respiration. CO(2) fixation can then produce both photosynthate to drive the induction and terminal electron acceptors to allow photosynthetic electron flow. This possibility was further suggested by the observation that CO(2) was an absolute requirement for induction in carbohydrate-depleted barley leaves. Results obtained with respiratory inhibitors also indicated that respiration drove the induction of nitrate reductase.Exogenously supplied glucose also substantially slowed the loss of nitrate reductase that occurred when barley leaves were placed in darkness. It is presumed that glucose allowed the synthetic or activation phase of the induction to proceed more rapidly. Our results support the hypothesis that one of the main effects of light may be to supply photosynthate to support respiration, which then drives the induction process.

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PubMed1973

Influence of auxin and incubation on the relative level of polyribosomes in excised soybean hypocotyl.

The influence of incubation and auxin (2,4-D) on polyribosome level in soybean hypocotyl was studied.A marked drop in the relative level of polyribosomes in excised apical or meristematic tissue (0 to 5 millimeters below the cotyledons) occurred during incubation. The addition of auxin to the incubation medium did not affect polyribosome level. A similar decrease in polyribosome level occurred in excised elongating tissue (5 to 15 millimeters below cotyledons) during incubation. Auxin, however, caused a small but highly reproducible stabilization of polyribosomes in this tissue. There was a rapid, but small, auxin-independent increase in polyribosomes of basal or nongrowing hypocotyl (from 20 to 40 millimeters below cotyledons) during incubation, followed by a larger auxin-dependent increase in polyribosomes. While auxin is known to cause an increase in total ribosomes during incubation of the excised basal hypocotyl, the observed transformation from monoribosomes to polyribosomes was not dependent on new ribosome synthesis.Protein synthetic activity (poly U-directed phenylalanine incorporation) of the 80S monoribosomes at low Mg(2+) levels increased during incubation of the excised basal hypocotyl. The increase in ribosome activity was biphasic (an initial auxin-independent phase followed by an auxin-dependent increase in activity) correlating with the biphasic increase in polyribosomes. The enhanced activity of 80S monoribosomes was related, at least in part, to an increase in the level of peptidyl-tRNA associated with the ribosome population. Removal of peptidyl-tRNA from the ribosomes reversed the auxin effect.The hypothesis is advanced that the increase in polyribosomes in response to incubation and to auxin is preceded by and dependent upon the activation of 80S monoribosomes. This activation is in addition to a requirement for continued RNA synthesis, at least in part mRNA, for the transition from monoribosomes to polyribosomes.

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PubMed1971

Correlation between Polyribosome Level and the Ability to Induce Nitrate Reductase in Dark-grown Corn Seedlings.

Nitrate reductase can be induced in excised shoots of 3-day-old dark-grown Zea mays (var. WF9 x M14) seedlings in the absence of light. In contrast, leaves of 10-day-old dark-grown seedlings require a light treatment in order to induce enzymatic activity. Leaves of 10-day-old dark-grown seedlings contain a very low level of polyribosomes while 3-day-old shoots contain a very high level of polyribosomes. There is a gradual loss of polyribosomes from 3 to 10 days and a gradual loss of in vitro protein synthetic activity of the ribosome preparations. The loss of polyribosomes and decrease in their amino acid-incorporating activity correlate positively with the loss of ability to induce nitrate reducase activity as leaves of dark-grown corn seedlings age. These results corroborate and extend our previous results, in that light is not required for nitrate reductase induction per se in leaves of dark-grown seedlings but is required to reactivate the protein synthetic apparatus of older leaves.

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PubMed1970

Light-induced Development of Polyribosomes and the Induction of Nitrate Reductase in Corn Leaves.

Nitrate reductase activity was induced by nitrate in green corn (Zea mays) leaves in either light or darkness. The induction process required oxygen in darkness but not in light. A light treatment was required before the enzyme could be induced in etiolated leaves.The capacity for nitrate reductase induction by nitrate was positively correlated with the level of cytoplasmic polyribosomes under a variety of experimental conditions. (a) Light-grown leaves contained high levels of polyribosomes (84% of the total population, most of which were of the 80 S type); similarly high levels of nitrate reductase activity were induced. (b) The level of polyribosomes and the ability to form nitrate reductase activity rapidly decreased in light-grown leaves following transfer to an anaerobic environment in the dark; both parameters were maintained at a high level when light-grown leaves were kept in the light under anaerobic conditions. (c) The ability of light-grown leaves, previously placed in darkness under nitrogen to dissociate polyribosomes to monoribosomes, to form nitrate reductase activity again correlated with the level of reformed polyribosomes following transfer of the leaves back to light. (d) Etiolated leaves contained a low level of cytoplasmic polyribosomes (27%), and nitrate reductase activity was induced following exposure to light only after a lag of 2 to 4 hours. During this lag period there was a marked increase in the level of polyribosomes.The ability of leaves to form nitrate reductase activity and the level of polyribosomes also correlated with the level of in vitro incorporation of amino acids into protein by the isolated ribosome preparations. Thus, the apparent requirement of light for nitrate reductase induction in etiolated leaves seems not to be specific. Rather an influence of light upon the development of an active protein-synthesizing apparatus as evidenced by the state of polyribosomes is indicated.The results also show that energy from photosynthetic phosphorylation can be used to maintain cytoplasmic polyribosomes (and thus to drive cytoplasmic protein synthesis), at least under anaerobic conditions.

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PubMed1969

Evidence for an Inactivating System of Nitrate Reductase in Hordeum vulgare L. during Darkness That Requires Protein Synthesis.

The disappearance of nitrate reductase activity in leaves of Hordeum vulgare L. during darkness was inhibited by cycloheximide, actinomycin D, and low temperature. Thus, protein synthesis was probably required for the disappearance of nitrate reductase in the dark. Since chloramphenicol did not affect the rate of loss of activity, the degradation or inactivation apparently required protein synthesis by the cytoplasmic ribosomal system. Consistent with this observation, nitrate reductase is also reportedly located in the cytoplasm. Thus, the amount of nitrate reductase activity present in leaves of barley may be controlled by a balance between activating and inactivating systems.

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