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PubMed1975

Acceleration of dark reversion of phytochrome in vitro by calcium and magnesium.

Rates of dark reversion of the far red-absorbing form of phytochrome, Pfr, to the red-absorbing form, Pr, have been determined in the presence of several salts. Low concentrations of calcium chloride and magnesium chloride (up to 3 mm) accelerated the rate of dark reversion at all stages of purification of phytochrome from etiolated rye (Secale cereale L. cv. Balbo) seedlings. The complex kinetics of the dark reversion could be resolved into two first-order components. The effect of the added divalent cations was on the relative proportion of the fast and slow reacting components, rather than on the rate constants of the two populations. It was possible to reverse the effects of the cations by adding the chelating agents ethylene-bis-(oxyethylene-nitrilo) tetraacetic acid or ethylenediaminetetraacetate. The effect of the divalent cations is not a nonspecific ionic strength effect. The relative proportion of the two populations was also affected by the degree of purity of the phytochrome samples.

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PubMed1975

Phytochrome: A Re-examination of the Quaternary Structure.

Highly purified phytochrome samples from rye (Secale Cereale cv. Cougar) were fractionated by ultracentrifugation in isokinetic sucrose density gradients. Three protein species were separated with estimated sedimentation coefficients of 6.5S, 8.0S, and 11.5S. The 6.5S and 8.0S forms contained photoreversible phytochrome and produced a single subunit of 120,000 molecular weight upon reduction and electrophoresis in the presence of sodium dodecyl sulfate. The 11.5S species contained no detectable phytochrome. Reduction and electrophoresis of the 11.5S species in the presence of sodium dodecyl sulfate produced a major polypeptide of 32,000 molecular weight and a minor polypeptide of 48,000 molecular weight. The square tetrameric structures, observed by electron microscopy and previously thought to be phytochrome molecules, were found to be due to the presence of this 11.5S species in phytochrome preparations.

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PubMed1975

Effect of Temperature on Respiration of Mitochondria and Shoot Segments from Cold hardened and Nonhardened Wheat and Rye Seedlings.

The effect of temperature on respiration of mitochondria and tissue segments from three wheat (Triticum aestivum L.) and one rye (Secale cereale L.) cultivar grown at 2 and 24 C has been examined. Discontinuities in Arrhenius plots of respiratory activity against temperature were observed for mitochondria and tissue segments from seedlings grown at both temperatures. The rates of respiration decreased abruptly below the transition temperatures, resulting in increased energy of activation values for respiration. Transition temperatures were observed from 6 to 10 C during tissue segment respiration, and from 10 to 14 C during respiration by isolated mitochondria. Respiratory control and efficiency of phosphorylation were not affected markedly by either reaction temperature or growth temperature of the seedlings. No correlation was observed between the cold hardiness of the cultivars and the temperature at which structural transitions occurred in the mitochondria. Dry matter content of the seedlings increased markedly during growth at 2 C, but no appreciable changes in the levels of mitochondrial protein were observed. The results support the view that changes other than fatty acid unsaturation are involved in the abrupt change in mitochondrial membrane properties at low temperature.

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PubMed1976

Swelling and Contraction of Mitochondria from Cold-hardened and Nonhardened Wheat and Rye Seedlings.

A comparison of mitochondria isolated from 2 and 24 C grown winter wheat (Triticum aestivum L.) and winter rye (Secale cereale L.) seedlings revealed no correlation between changes in swelling and contraction characteristics and extent of cold hardiness. The swelling response changed markedly due to growth at low temperature, but the change was similar for the four cultivars examined. The swelling response was also observed to change rapidly during aging of isolated mitochondria, either at 2 or 24 C. Spontaneously swollen mitochondria, isolated from 24 C grown seedlings, contracted abruptly upon addition of certain oxidizable substrates, but this response was lost when seedlings were transferred from 24 to 2 C. Studies on the effect of various substrates and respiratory inhibitors on the swelling and contraction responses indicate that inhibitors which reduce or stop electron flow through the electron transport chain also inhibit substrate induced mitochondrial contraction.

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PubMed1976

Red Light-enhanced Phytochrome Pelletability: Re-examination and Further Characterization.

Red light-enhanced pelletability of phytochrome was observed in extracts of all 11 plants tested: Avena sativa L., Secale cereale L., Zea mays L., Cucurbita pepo L., Sinapis alba L., Pisum sativum L., Helianthus anuus L., Raphanus sativus L., Glycine max (L.) Merr., Phaseolus vulgaris L., and Lupinus albus L. This enhanced pelletability was observed in all 11 plants following in situ irradiation (in vivo binding) but only in Sinapis and Cucurbita after irradiation of crude extracts (in vitro binding). In vivo binding was not strongly dependent upon pH and, with few exceptions, was not markedly sensitive to high salt concentration, whereas in vitro binding was completely reversed by both high pH and high salt concentration. However, both binding phenomena were observed only with a divalent cation in the extract buffer. In vivo binding was further characterized using Avena which showed an increase in pelletability from less than 10% in dark control extracts to more than 60% in extracts of red light-irradiated shoots. The half-life for binding was 40 seconds at 0.5 C and was strongly temperature-dependent, binding being complete within 5 to 10 sec at 22 C. If pelletable phytochrome in the far red-absorbing form was photoconverted back to the red-absorbing form in situ, phytochrome was released from the pelletable condition with a half-life of 25 minutes at 25 C and 100 minutes at both 13 C and 3 C. No cooperativity in red light-enhanced pelletability with respect to phytochrome-far red-absorbing form was observed.

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PubMed1977

Mitochondrial Activity and Ethanol Accumulation in Ice-encased Winter Cereal Seedlings.

Cold-hardened dark-grown seedlings of winter wheat (Triticum aestivum L.) and winter rye (Secale cereale L.) are killed during total encasement in ice at -1 C at a rate related to the initial cold hardiness of the cultivars. Few plants remain alive after 7 days of encasement. Nonhardened seedlings are rapidly killed in ice. The respiratory properties of mitochondria isolated from plants after increasing periods of ice encasement decline slowly, and activity is little impaired when intact plants are about 50% killed. Electron microscopy indicates that mitochondrial structure is not disrupted until 3 weeks of ice encasement. Ethanol accumulates in hardened and nonhardened plants in ice, but at levels which are not toxic to the plants.

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PubMed1977

Relative insensitivity of mitochondria in hardened and nonhardened rye coleoptile cells to freezing in situ.

Mitochondria were isolated from excised coleoptiles of hardened and nonhardened winter rye (Secale cereale L. cv. Puma) seedlings which had been frozen extracellularly to different temperatures. No significant differences in the respiratory functions (ADP/O and respiratory control) were observed between mitochondria isolated from nonlethally and lethally frozen cells of both the hardened and nonhardened rye. These results suggest that mitochondria in situ can retain their normal function even after the cell was killed by the dehydrative stresses of extracellular freezing. Presumably, a different level of sensitivity to freezing stresses exists between mitochondrial and other membranous elements in the cell.

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PubMed1978

Comparative Investigation of the Action of Several Chlorosis-inducing Herbicides on the Biogenesis of Chloroplasts and Leaf Microbodies.

Seedlings of Triticum aestivum L. and Secale cereale L. were grown in the presence of six different (five having different chemical structures) chlorosis-inducing herbicides: aminotriazole and its derivative SDR 5175, haloxidine, Sandoz 6706, fluometuron, and EMD-IT 5914. Concentrations were applied which allowed the leaves to grow normally and to reach normal total amino nitrogen contents but evoked a complete chlorosis (less than 6% chlorophyll). The effects of the herbicides on the accumulation of several chloroplast constituents and on peroxisomal and mitochondrial marker enzyme activities were compared. Wheat and rye, in general, gave very similar results, wheat being more sensitive to unspecific inhibitory effects.In dark-grown plants, the herbicides had no or only minor effects on the rRNA pattern and on enzyme activities of the leaves. In the light, all herbicides applied prevented the accumulation of carotenoids and of chloroplastic rRNA. Consequently, ribulose-1,5-bisphosphate carboxylase activity was virtually absent. After all herbicide treatments in light, the leaves contained only rather low catalase activity. In the presence of aminotriazole and haloxidine, the chloroplast-specific NADP-glyceraldehyde-3-phosphate dehydrogenase and the peroxisomal enzymes glycolate oxidase and hydroxypyruvate reductase had high or even normal activities, as in untreated leaves. In leaves treated with Sandoz 6706, fluometuron, or EMDIT 5914, the activities of the latter three enzymes were, in parallel, only very low. Some herbicides interfered with enzyme activities in vitro, particularly with those of catalase and of glycolate oxidase. Among mitochondrial enzymes, cytochrome c oxidase activity was either unaffected or lower, while fumarase had considerably higher activities in the herbicide-treated, as compared to untreated leaves. The specific effects on peroxisomal enzymes cannot be explained by the hypothesis of herbicide-induced photodestructions in carotene-deficient plastids. Alternative explanations for the genesis of the chlorosis are discussed.

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PubMed1979

Phytochrome immunoaffinity purification.

We have developed a phytochrome immunoaffinity purification procedure that yields undegraded oat (Avena sativa L., cv. Garry) phytochrome of greater than 98% purity within 2 hours when starting with a brushite-purified preparation. Immunoaffinity-purified phytochrome, except for its greater purity, is indistinguishable from conventionally purified phytochrome by gel exclusion chromatography, isoelectric focusing, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We have also used the immunoaffinity technique to purify phytochrome from crude oat extracts, and from brushite-purified pea (Pisum sativum L., cv. Alaska) and rye (Secale cereale L., cv. Balbo) preparations.

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PubMed1981

Purification of Phytochrome by Affinity Chromatography on Agarose-Immobilized Cibacron Blue 3GA.

The binding of phytochrome to Cibacron Blue 3GA was utilized to develop a new affinity purification procedure for phytochrome. Brushite-purified phytochrome from rye (Secale cereale c.v. Cougar) was bound to agarose-immobilized blue dye in 0.1 molar potassium phosphate (pH 7.8), contaminating proteins washed out with 0.5 molar KCl, and homogeneous phytochrome eluted with 10 millimolar flavin mononucleate. Ninety-five per cent of the phytochrome applied bound, and 60 to 65% was eluted, giving a 25 to 30% yield for the complete one-day procedure. Affinity-purified rye phytochrome was identical to conventionally purified phytochrome in its behavior on sodium dodecyl sulfate gels, in gel exclusion chromatography, in sedimentation in sucrose density gradients and in its spectral properties.

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PubMed1982

Twenty-four-hour induction of freezing and drought tolerance in plumules of winter rye seedlings by desiccation stress at room temperature in the dark.

Exposure of seedlings of winter rye (Secale cereale L., cv. Puma) for 2 weeks or 24 hours to desiccation stress (40% relative humidity) at room temperature (21 degrees C) in the dark induced degrees of freezing and drought tolerance in the plumules comparable to those produced by cold conditioning for 2 weeks at 3 degrees C. The induction was associated with repression of growth and could not be produced in plumules excised from the seedlings indicating a requirement for translocation of nutrients from the endosperm. Rapid increase in osmotic pressure, soluble proteins, and phospholipids in plumules in association with the development of freezing and drought tolerance and the requirement of endosperm suggested diversion of nutrient from use in extension growth, to use in augmentation of protoplasm in plumule cells. Since cold acclimation slowed or arrested growth and is associated with augmentation of protoplasm, it is suggested that the common element in the induction of freezing tolerance by cold and drought is the necessity for producing a condition of augmented protoplasm and membranes in cells thus reinforcing a similar conclusion reached from seasonal studies on woody plants.

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PubMed1982

Correlation between Cold- and Drought-Induced Frost Hardiness in Winter Wheat and Rye Varieties.

Exposure of six wheat (Triticum aestivum L.) and one rye (Secale cereale L.) cultivar to 40% relative humidity for 24 hours induced the same degree of freezing tolerance in seedling epicotyls as did cold conditioning for 4 weeks at 2 degrees C.Frost hardiness varietal relationships were the same in desiccation-stressed and cold-hardened seedlings. Drought stress could, therefore, be used as a rapid and simple method for inducing frost hardiness in seedling shoots in replacement of cold conditioning.

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PubMed1982

Pyruvate orthophosphate dikinase from the immature grains of cereal grasses.

Pyruvate orthophosphate dikinase has been identified in the green grains of eight cereal grasses, most of which are classified as C(3) plants. The wheat (Triticum aestivum L. cv. Lerma Rojo) grain enzyme was further investigated: activity was low in very young grains, increased to a maximum at about 25 days after anthesis, then returned to a low level as the grain matured. It appeared to be located in the aleurone layer. A procedure was developed for obtaining partially purified preparations of pyruvate orthophosphate dikinase from the ears of wheat, oat (Avena sativa L.), barley (Hordeum distichum L.), and rye (Secale cereale L.). These preparations were suitable for measuring activities in both the forward and reverse reaction directions. The affinities of these enzymes for the six substrates (pyruvate, orthophosphate, and ATP in the forward reaction; phosphoenolpyruvate, pyrophosphate, and AMP in the reverse reaction) were determined and found to be similar to the reported affinities of the enzyme from the leaves of the C(4) plant Zea mays. A possible role for pyruvate orthophosphate dikinase in cereal grains is considered briefly.

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PubMed1982

Immunopurification and initial characterization of dicotyledonous phytochrome.

Antiserum was prepared against proteolytically undegraded phytochrome obtained from etiolated zucchini squash (Cucurbita pepo L., cv. Black Beauty). The antiserum was prepared by injecting into a rabbit immunoprecipitates between zucchini phytochrome and specific antiserum against undegraded oat (Avena sativa L., cv. Garry) phytochrome. Specific antiphytochrome immunoglobulins were purified from this crude serum by an affinity column consisting of conventionally purified undegraded pea phytochrome covalently linked to cyanogen bromide-activated agarose. These purified immunoglobulins were also linked to cyanogen bromide-activated agarose and were used to immunopurify zucchini, pea (Pisum sativum L., cv. Alaska), and lettuce (Lactuca sativa L., cv. Grand Rapids) phytochrome. All three dicotyledonous phytochromes exhibited a monomer size near 120,000 daltons by sodium dodecyl sulfate, polyacrylamide gel electrophoresis. Absorbance spectra of immunopurified zucchini phytochrome indicated that the ratio of visible to ultraviolet absorbance for purified zucchini phytochrome is lower than that observed for oat phytochrome. The isoelectric point of zucchini phytochrome, which was observed to be heterogeneous by this criterion, was found to be in the range of 6.5 to 7.0, higher than that observed for oat phytochrome. The electrophoretic mobility of zucchini phytochrome was found to be similar to that observed for oat and pea phytochrome under conditions that were nondenaturing and did not involve any molecular sieving effect. The amino acid analysis of zucchini phytochrome is similar to that reported previously for oat and rye (Secale cereale L., cv. Balbo) phytochrome.

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PubMed1982

Leucine transport in cells isolated from cold-hardened and nonhardened winter rye.

The properties of the leucine transport systems of cells isolated from dark-grown cold-hardened and nonhardened winter rye (Secale cereale L. cv. Puma) epicotyls were remarkably similar. After 1 hour of incubation, leucine was accumulated in the cells 80- to 100-fold above that of the external medium, but the transported leucine was not metabolized. Approximately one-third of the accumulated leucine was present in the vacuole after 40 minutes of incubation. At 25 degrees C, efflux of leucine from the vacuole was 6 to 10 times slower than it was from the cytoplasm, while at 5 degrees C efflux from the cells was inhibited.The apparent K(m) and V(max) for leucine uptake for both types of cells were of the order of 20 to 60 micromolar and 0.5 to 1.3 nanomoles per minute per 10(6) cells. The pH and temperature optima for both types of cells were 5 and 25 degrees C, respectively. The leucine transport system for these cells was relatively specific for amino acids lacking either bulky or charged groups on the amino acid side chains.Arrhenius plots for leucine uptake by hardened and nonhardened cells showed discontinuities at 13 degrees C, and the energies of activation were similar. The results suggests that biochemical changes which occur in rye cells upon cold hardening did not result in an observable perturbation of the properties of the leucine transport system.

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PubMed1982

Spin-Probe Studies during Freezing of Cells Isolated from Cold-Hardened and Nonhardened Winter Rye : MOLECULAR MECHANISM OF MEMBRANE FREEZING INJURY.

Mesophyll cells isolated from cold-hardened and nonhardened winter rye (Secale cereale L. cv. Puma) were spin-labeled with the fatty-acid spin probe N-oxyl-4,4-dimethyloxazolidine 5-ketostearic acid. The probe was intercalated within the cellular membranes and changes in probe motion were followed during extracellular freezing of the cells. A correlation was observed between the lethal freezing temperatures (LT(50)) of the cells and the maximum hyperfine splitting value achieved by the incorporated probe. Rigid limit spectra indicated that a more ordered average packing was attained by membranes of hardened cells which survived freezing to lower temperatures.Nonhardened cells fixed with osmic acid at lethal freezing temperatures, in the frozen state, showed both conversion of normal bilayered cellular membrane ultrastructure to an amorphous state and condensation of cellular membranes to form densely packed multibilayered vesicles. Taken together with the spin-labeling data, these results suggest that at least one molecular mechanism of extracellular freezing injury involves the irreversible conversion of planar membrane bilayers to structures having less ordered packing and increased surface curvatures.

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PubMed1982

Comparative Phytochrome Immunochemistry as Assayed by Antisera against Both Monocotyledonous and Dicotyledonous Phytochrome.

Preparation and characterization of antisera against lettuce (Lactuca sativa L., cv. Grand Rapids) and pea (Pisum sativum L., cv. Alaska) phytochrome is described. These antisera, together with previously obtained antisera against zucchini (Cucurbita pepo L., cv. Black Beauty) and oat (Avena sativa L., cv. Garry) phytochrome, were used to compare by Ouchterlony double immunodiffusion phytochrome isolated from etiolated lettuce, pea, bean (Phaseolus vulgaris L., cv. Taylor Horticultural Bush), zucchini, oat and rye (Secale cereale L., cv. Balbo) seedlings. Cross reactivity between monocotyledonous phytochrome and antidicotyledonous-phytochrome serum and between dicotyledonous phytochrome and antimonocotyledonous-phytochrome serum was always weak or not perceptible by this assay. Among the four dicotyledonous phytochromes examined, pea and bean were the most similar immunochemically as anticipated. Pea and lettuce phytochrome somewhat unexpectedly also exhibited similar immunochemical reactivity. Zucchini phytochrome by contrast was immunochemically distinct from pea, bean, and lettuce phytochrome, although it did react with all three antidicotyledonous-phytochrome sera. Initial attempts to identify immunoglobulins that would recognize phytochrome regardless of its source indicated that they may exist. Such immunoglobulins are of interest because they might react with one or more determinants that could be part of an active site of phytochrome. These immunoglobulins, once isolated, could thus serve as a potential probe for the active site of phytochrome.

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PubMed1982

Nature of photooxidative events in leaves treated with chlorosis-inducing herbicides.

Leaves of rye seedlings (Secale cereale L.) grown in the presence of four chlorosis-inducing herbicides under a low light intensity of 10 lux formed chlorophyll. When segments of such dim-light-grown leaves were exposed to 30,000 lux at either 0 degrees C or 30 degrees C, treatments with aminotriazole or haloxidine (group 1) showed no or only minor changes of their chlorophyll contents. In treatments with San 6706 or difunon (group 2), however, rapid photodestruction of chlorophyll occurred both at 0 degrees C and at 30 degrees C and was accompanied by an increase of malondialdehyde that was not seen in the presence of group 1 herbicides. Unlike the in vivo behavior, virtually equal rates of chlorophyll breakdown were observed for aminotriazole and San 6706 treatments in suspensions of isolated chloroplasts from 10 lux-grown leaves after exposure to strong light. The free radical scavengers p-benzoquinone and hydroquinone and the d-penicillamine copper complex exerting superoxide dismutating activity effectively prevented photooxidation of chlorophyll in 10 lux-grown herbicide-treated leaf segments or even restored an accumulation of chlorophyll at 30,000 lux. Ascorbate and several singlet oxygen or hydroxyl radical scavengers had no protective effects. Deuterium oxide and H(2)O(2) did not enhance the degradation of chlorophyll. Superoxide dismutase activity was decreased in leaves bleached in the presence of group 2 herbicides.

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