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PubMed1983

Mechanical properties of the plasma membrane of isolated plant protoplasts : mechanism of hyperosmotic and extracellular freezing injury.

The volume of isolated protoplasts of rye (Secale cereale L. cv Puma) in a suspending solution at constant concentration is shown to be negligibly changed by tensions in the plasma membrane which approach that tension necessary to lyse them. This allows a detailed investigation of the plasma membrane stress-strain relation by micropipette aspiration.Over periods less than a second, the membrane behaves as an elastic two-dimensional fluid with an area modulus of elasticity of 230 millinewtons per meter. Over longer periods, the stress-strain relation approaches a surface energy law-the resting tension is independent of area and has a value of the order 100 micronewtons per meter. Over longer periods the untensioned area, which is defined as the area that would be occupied by the molecules in the membrane at any given time if the tension were zero, increases with time under large imposed tensions and decreases under sufficiently small tension. It is proposed that these long term responses are the result of exchange of material between the plane of the membrane and a reservoir of membrane material. The irreversibility of large contractions in area is demonstrated directly, and the behavior of protoplasts during osmotically induced cycles of contraction and expansion is explained in terms of the membrane stress-strain relation.

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PubMed1983

Changes in the Electrophoretic Patterns of the Soluble Proteins of Winter Wheat and Rye following Cold Acclimation and Desiccation Stress.

The degrees of freezing tolerance acquired by winter wheat (Triticum aestivium L.) and rye (Secale cereale L. cv Puma) were similar following a 4-week cold conditioning and a 24-hour desiccation stress. Soluble proteins were extracted from shoots of cold-conditioned or desiccation-stressed seedlings and electrophoresed on sodium dodecyl sulfate-polyacrylamide gels. Quantitative changes in the electrophoretic patterns of the soluble proteins of the different cultivars grown in different environments were detected, but the changes were not equivalent following cold conditioning and desiccation stress. The abundance of two polypeptide bands showed a significant increase correlated to the degree of freezing tolerance and, hence, the polypeptides in these bands may play a role in the development of freezing tolerance.

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PubMed1983

Light-Induced Breakdown of NADPH-Protochlorophyllide Oxidoreductase In Vitro.

Light-induced loss of the enzyme protochlorophyllide reductase (EC 1.6.99.1.), already described as a characteristic of whole plants, has now been demonstrated in vitro using etioplast membrane preparations of Avena Sativa L. var Peniarth and Secale cereale L. var Rheidol. Some evidence is presented, based upon temperature, pH, and inhibitor sensitivity of the process, that loss of enzyme may be the result of proteolysis. The light-induced process can, in vitro, be largely prevented by addition of the substrates of the reductase, protochlorophyllide and NADPH. It is concluded that light causes the breakdown of the reductase in vivo and in vitro by producing ligand-free enzyme as a consequence of the photoconversion reaction.

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PubMed1983

Provisions of reductant for the hydroxypyruvate to glycerate conversion in leaf peroxisomes : a critical evaluation of the proposed malate/aspartate shuttle.

A series of experiments, with Secale cereale and Triticum aestivum var Argee, to evaluate critically the ability of a malate/aspartate shuttle to provide reducing equivalents to drive hydroxypyruvate reduction to glycerate led to the conclusion that the shuttle, as previously envisioned, does not supply NADH to the peroxisomal matrix. First, analysis of coupled malate dehydrogenase and glutamate-oxaloacetate transaminase activities in the directions required for intraperoxisomal NADH generation indicated that the peroxisomal enzyme activities were insufficient to account for necessary rates of photorespiratory carbon flux. Second, although the peroxisomal isozyme of malate dehydrogenase comprised a substantial portion (40%) of total cellular activity, less than 7% of the cellular glutamate-oxaloacetate transmaminase activity was associated with the peroxisomes. Third, a peroxisomal extract was able to reduce added NAD only slowly upon addition of malate and glutamate. The rate of NAD reduction was greatly enhanced in the presence of exogenously added glutamateoxaloacetate transaminase. Finally, intact peroxisomes were unable to reduce hydroxypyruvate to glycerate when supplied with malate and glutamate in the absence of exogenously added pyridine nucleotides, although they readily reduced hydroxypyruvate when exogenous pyridine nucleotides were supplied. Three alternative mechanisms, which are in agreement with observed data and which could serve to supply the reducing power to the peroxisomal matrix, are discussed.

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PubMed1983

Effect of cold acclimation on intracellular ice formation in isolated protoplasts.

When cooled at rapid rates to temperatures between -10 and -30 degrees C, the incidence of intracellular ice formation was less in protoplasts enzymically isolated from cold acclimated leaves of rye (Secale cereale L. cv Puma) than that observed in protoplasts isolated from nonacclimated leaves. The extent of supercooling of the intracellular solution at any given temperature increased in both nonacclimated and acclimated protoplasts as the rate of cooling increased. There was no unique relationship between the extent of supercooling and the incidence of intracellular ice formation in either nonacclimated or acclimated protoplasts. In both nonacclimated and acclimated protoplasts, the extent of intracellular supercooling was similar under conditions that resulted in the greatest difference in the incidence of intracellular ice formation-cooling to -15 or -20 degrees C at rates of 10 or 16 degrees C/minute. Further, the hydraulic conductivity determined during freeze-induced dehydration at -5 degrees C was similar for both nonacclimated and acclimated protoplasts. A major distinction between nonacclimated and acclimated protoplasts was the temperature at which nucleation occurred. In nonacclimated protoplasts, nucleation occurred over a relatively narrow temperature range with a median nucleation temperature of -15 degrees C, whereas in acclimated protoplasts, nucleation occurred over a broader temperature range with a median nucleation temperature of -42 degrees C. We conclude that the decreased incidence of intracellular ice formation in acclimated protoplasts is attributable to an increase in the stability of the plasma membrane which precludes nucleation of the supercooled intracellular solution and is not attributable to an increase in hydraulic conductivity of the plasma membrane which purportedly precludes supercooling of the intracellular solution.

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PubMed1983

Abscisic Acid-induced freezing resistance in cultured plant cells.

The effect of abscisic acid (ABA) on the cold hardiness of cell suspension was investigated. Cell suspension cultures of winter wheat (Triticum aestivum L. cv Norstar), winter rye (Secale cereale L. cv Cougar), and bromegrass Bromo inermis Leyss treated with 7.5 x 10(-5) molar ABA for 4 days at 20 degrees C could tolerate -30 degrees C, whereas the control cultures tolerated only -7 to -8 degrees C. The optimum concentration for increasing the cold hardiness of the cultures was 7.5 x 10(-5) molar. The degree of cold hardiness and the rate of hardening obtained by ABA treatment was significantly higher than that induced by low temperature alone. Of ten species tested, ABA was only effective on those cultures which were capable of cold hardening upon exposure to low temperatures. The results suggest that ABA bypasses the cold requirement for hardening and also suggests that ABA triggers the genetic system(s) responsible for inducing the hardening process.

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PubMed1983

Freezing injury and root development in winter cereals.

Upon exposure to 2 degrees C, the leaves and crowns of rye (Secale cereale L. cv ;Puma') and wheat (Triticum aestivum L. cv ;Norstar' and ;Cappelle') increased in cold hardiness, whereas little change in root cold hardiness was observed. Both root and shoot growth were severely reduced in cold-hardened Norstar wheat plants frozen to -11 degrees C or lower and transplanted to soil. In contrast, shoot growth of plants grown in a nutrient agar medium and subjected to the same hardening and freezing conditions was not affected by freezing temperatures of -20 degrees C while root growth was reduced at -15 degrees C. Thus, it was apparent that lack of root development limited the ability of plants to survive freezing under natural conditions.Generally, the temperatures at which 50% of the plants were killed as determined by the conductivity method were lower than those obtained by regrowth. A simple explanation for this difference is that the majority of cells in the crown are still alive while a small portion of the cells which are critical for regrowth are injured or killed.Suspension cultures of Norstar wheat grown in B-5 liquid medium supplemented with 3 milligrams per liter of 2,4-dichlorophenoxyacetic acid could be cold hardened to the same levels as soil growth plants. These cultures produce roots when transferred to the same growth medium supplemented with a low rate of 2,4-dichlorophenoxyacetic acid (<1 milligram per liter). When frozen to -15 degrees C regrowth of cultures was 50% of the control, whereas the percentage of calli with root development was reduced 50% in cultures frozen to -11 degrees C. These results suggest that freezing affects root morphogenesis rather than just killing the cells responsible for root regeneration.

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PubMed1983

A pathway for photosynthetic carbon flow to mannitol in celery leaves : activity and localization of key enzymes.

In the polyol producing plant, celery (Apium graveolens L.), mannitol is a major photosynthetic product and a form in which carbohydrate is translocated. Measurements of whole leaf extracts of celery indicated substantial activity of the following enzymes: mannose-6-P reductase, mannose-6-P isomerase, mannitol-1-P phosphatase, and nonreversible glyceraldehyde-3-P dehydrogenase. The activities of these enzymes were either undetectable or very low in the nonpolyol producing plants, Secale cereale L. (rye) and Vigna mungo (L.) Hepper (black gram).Mesophyll protoplasts were enzymically isolated from celery leaves, broken with a Yeda press and the intracellular localization of the above enzymes for mannitol synthesis studied following differential and/or sucrose density gradient centrifugation of the protoplast extract. These data suggested the enzymes involved in mannitol synthesis are exclusively localized in the cytoplasm. Ninety-five to 100% of the activity of these enzymes, along with the cytoplasmic marker enzyme phosphoenolpyruvate carboxylase, was found in the cytosolic fraction.We propose the pathway of photosynthetic carbon flow from triose-P to mannitol in celery occurs via fructose-6-P, mannose-6-P, and mannitol-1-P; these final reactions being catalyzed by the cytoplasmic enzymes, mannose-6-P isomerase, NADPH-dependent mannose-6-P reductase, and mannitol-1-P phosphatase, respectively. The requirement for NADPH may be met via the cytoplasmically located NADP-linked nonreversible glyceraldehyde-3-P dehydrogenase.

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PubMed1984

Characterization by enzyme-linked immunosorbent assay of monoclonal antibodies to pisum and Avena phytochrome.

Nine monoclonal antibodies to pea (Pisum sativum L.) and 16 to oat (Avena sativa L.) phytochrome are characterized by enzyme-linked immunosorbent assay against phytochrome from six different sources: pea, zucchini (Cucurbita pepo L.), lettuce (Lactuca sativa L.), oat, rye (Secale cereale L.), and barley (Hordeum vulgare L.). All antibodies were raised against phytochrome with a monomer size near 120,000 daltons. Nevertheless, none of them discriminated qualitatively between 118/114-kilodalton oat phytochrome and a photoreversible, 60-kilodalton proteolytic degradation product derived from it. In addition, none of the 23 antibodies tested discriminated substantially between phytochrome-red-absorbing form and phytochrome-far red-absorbing form. Two antibodies to pea and six to oat phytochrome also bound strongly to phytochrome from the other species, even though these two plants are evolutionarily widely divergent. Of these eight antibodies, two bound significantly to all of the six phytochrome preparations tested, indicating that these two may recognize highly conserved regions of the chromoprotein. Since the molecular function of phytochrome is unknown, these two antibodies may serve as unique probes for regions of this pigment that are important to its mode of action.

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PubMed1984

Accumulation of Plastoquinone A during Low Temperature Growth of Winter Rye.

Chloroplasts isolated from rye (Secale cereale L. cv Puma) grown at 5 degrees C (RH) accumulated 260% more plastoquinone A (PQA) per plastid than chloroplasts isolated from rye grown at 20 degrees C (RNH). The number of plastoglobuli increased by 270% in RH chloroplasts compared with RNH plastids. When RH plastids were lysed and washed, the number of plastoglobuli associated with thylakoid membranes decreased significantly, yet the PQA levels remained high. Room temperature fluorescence induction indicated that (a) there is no change in the size of the PQA pool immediately available for photochemistry in RNH and RH thylakoids and (b) there is a pool of oxidized PQA present in RNH and RH thylakoids which is not available for photochemistry. The accumulated PQA in RH thylakoids may reflect an increased nonphotochemical function such as regulation of thylakoid protein phosphorylation or protection against photoinhibition.

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PubMed1984

Photoregulation of Anthocyanin Synthesis : VIII. Effect of Light Pretreatments.

A comparative study of the spectral sensitivity of anthocyanin production in dark-grown and light-pretreated systems was carried out in Brassica oleracea L., Lycopersicon esculentum Mill., Secale cereale L. and Spirodela polyrrhiza L. Light pretreatments bring about an enhancement of the inductive, red-far red reversible response in all systems, a decrease of the continuous irradiation response in cabbage, rye, and tomato seedlings, and an enhancement of the continuous irradiation response in cabbage leaf disks. Light pretreatments also bring about a marked change in the spectral sensitivity of the continuous irradiation response. The different effect of light pretreatments on the photosensitivity of the response to short and long wavelength irradiations suggests that two photoreceptors, phytochrome and cryptochrome, may be involved in the photoregulation of anthocyanin production.

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PubMed1984

Behavior of the Plasma Membrane of Isolated Protoplasts during a Freeze-Thaw Cycle.

Cryomicroscopy of protoplasts isolated from nonacclimated (NA) rye leaves (Secale cereale L. cv Puma) revealed that the predominant form of injury following cooling to the minimum temperature for 50% survival (LT(50)) (-5 degrees C) was expansion-induced lysis of the plasma membrane during warming and thawing of the suspending medium when the decreasing osmolality resulted in osmotic expansion of the protoplasts. When cooled to temperatures below the LT(50), the predominant form of injury was loss of osmotic responsiveness following cooling so that the protoplasts were osmotically inactive during warming. Only a low incidence (<10%) of expansion-induced lysis was observed in protoplasts isolated from acclimated (ACC) leaves, and the predominant form of injury following cooling to the LT(50) (-25 degrees C) was loss of osmotic responsiveness. The tolerable surface area increment (TSAI) which resulted in lysis of 50% of a population (TSAI(50)) of NA protoplasts osmotically expanded from isotonic solutions was 1122 +/- 172 square micrometers. Similar values were obtained when the protoplasts were osmotically expanded from hypertonic solutions. The TSAI determined from cryomicroscopic measurements of individual NA protoplasts was similar to the TSAI(50) values obtained from osmotic manipulation. The TSAI(50) of ACC protoplasts expanded from isotonic solutions (2145 +/- 235 square micrometers) was approximately double that of NA protoplasts and increased following osmotic contraction. Osmotic contractions were readily reversible upon return to isotonic solutions. During freeze-induced dehydration, endocytotic vesicles formed in NA protoplasts whereas exocytotic extrusions formed on the surface of ACC protoplasts. During osmotic expansion following thawing of the suspending medium, the endocytotic vesicles remained in the cytoplasm of NA protoplasts and the protoplasts lysed before their original volume and surface area were regained. In contrast, the exocytotic extrusions were drawn back into the surface of ACC protoplasts as the protoplasts regained their original volume and surface area.

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PubMed1984

Red-far red reversibility of anthocyanin synthesis in dark-grown and light-pretreated seedlings.

The rate of escape from red-far red reversibility for anthocyanin synthesis is lower in dark-grown than in light-pretreated seedlings of Brassica oleracea L. Red Acre, Secale cereale L. Cougar, and Lycopersicon esculentum Mill. Beefsteak. This observation is consistent with the suggestion that there might be two pools of phytochrome, a labile one, characterized by fast disappearance of phytochrome-far-red absorbing form, and a stable one, characterized by slow disappearance of phytochrome-far-red absorbing form, and that the proportion between the two pools might be different in dark-grown and light-pretreated seedlings.

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PubMed1984

Fluorescence Properties Indicate that Photosystem II Reaction Centers and Light-Harvesting Complex Are Modified by Low Temperature Growth in Winter Rye.

Thylakoids isolated from winter rye (Secale cereale L. cv Puma) grown at 20 degrees C (nonhardened rye, RNH) or 5 degrees C (cold-hardened rye, RH) were characterized using chlorophyll (Chl) fluorescence. Low temperature fluorescence emission spectra of RH thylakoids contained emission bands at 680 and 695 nanometers not present in RNH thylakoids which were interpreted as changes in the association of light-harvesting Chl a/b proteins and photosystem II (PSII) reaction centers. RH thylakoids also exhibited a decrease in the emission ratio of 742/685 nanometers relative to RNH thylakoids.Room temperature fluorescence induction revealed that a larger proportion of Chl in RH thylakoids was inactive in transferring energy to PSII reaction centers when compared with RNH thylakoids. Fluorescence induction kinetics at 20 degrees C indicated that RNH and RH thylakoids contained the same proportions of fast (alpha) and slow (beta) components of the biphasic induction curve. In RH thylakoids, however, the rate constant for alpha components increased and the rate constant for beta components decreased relative to RNH thylakoids. Thus, energy was transferred more quickly within a PSII reaction center complex in RH thylakoids. In addition, PSII reaction centers in RH thylakoids were less connected, thus reducing energy transfers between reaction center complexes. We concluded that both PSII reaction centers and light-harvesting Chl a/b proteins had been modified during development of rye chloroplasts at 5 degrees C.

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PubMed1985

Permeability of the suberized mestome sheath in winter rye.

Mestome sheath cells of winter rye (Secale cereale L. cv Puma) deposit suberized lamellae in their secondary cell walls. Histochemical tests including acid digestion and staining with Sudan IV and Chelidonium majus root extract were used to detect the presence of suberin in the primary cell wall. There was no evidence of a Casparian band between adjacent mestome sheath cells. Fluorescent dye techniques were used to trace solute movement through the rye leaf apoplast. Calcofluor white M2R, a fluorescent dye which binds to cell walls as it moves apoplastically, proved to be too limited in its mobility in leaves to test mestome sheath permeability. Trisodium 3-hydroxy-5,8,10 pyrene trisulfonate, a fluorescent dye which is mobile in the apoplast, moved easily up the vascular bundles in the transpiration stream, and diffused outward from the veins to the epidermal cell walls within minutes of reaching a particular level in the leaf. We conclude that the suberized mestome sheath of rye leaves is freely permeable to solutes moving apoplastically through radial primary cell walls.

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PubMed1985

Chloroplast Biogenesis 49 : Differences among Angiosperms in the Biosynthesis and Accumulation of Monovinyl and Divinyl Protochlorophyllide during Photoperiodic Greening.

Various angiosperms differed in their monovinyl and divinyl protochlorophyllide biosynthetic capabilities during the dark and light phases of photoperiodic growth. Some plant species such as Cucumis sativus L., Brassica juncea (L.) Coss., Brassica kaber (DC.) Wheeler, and Portulaca oleracea L. accumulated mainly divinyl protochlorophyllide at night. Monocotyledonous species such as Avena sativa L., Hordeum vulgare L., Triticum secale L., Zea mays L., and some dicotyledonous species such as Phaseolus vulgaris L., Glycine max (L.) Merr., Chenopodium album L., and Lycopersicon esculentum L. accumulated mainly monovinyl protochlorophyllide at night.Under low light intensities meant to simulate the first 60 to 80 minutes following daybreak divinyl protochlorophyllide appeared to contribute much more to chlorophyll formation than monovinyl protochlorophyllide in species such as Cucumis sativus L. Under the same light conditions, species which accumulated mainly monovinyl protochlorophyllide at night appeared to form chlorophyll preferably via monovinyl protochlorophyllide.THESE RESULTS WERE INTERPRETED IN TERMS OF: (a) a differential contribution of monovinyl and divinyl protochlorophyllide to chlorophyll formation at daybreak in various plant species; and (b) a differential regulation of the monovinyl and divinyl protochlorophyllide biosynthetic routes by light and darkness.

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PubMed1985

Control of plastidic glycolipid synthesis and its relation to chlorophyll formation.

Mechanisms restricting the accumulation of chloroplast glycolipids in achlorophyllous etiolated or heat-treated 70S ribosome-deficient rye leaves (Secale cereale L. cv "Halo") and thereby coupling glycolipid formation to the availability of chlorophyll, were investigated by comparing [(14)C]acetate incorporation by leaf segments of different age and subsequent chase experiments. In green leaves [(14)C]acetate incorporation into all major glycerolipids increased with age. In etiolated leaves glycerolipid synthesis developed much more slowly. In light-grown, heat-bleached leaves [(14)C]acetate incorporation into glycolipids was high at the youngest stage but declined with age. In green leaves [(14)C]acetate incorporation into unesterified fatty acids and all major glycerolipids was immediately and strongly diminished after application of an inhibitor of chlorophyll synthesis, 4,6-dioxoheptanoic acid. The turnover of glyco- or phospholipids did not differ markedly in green, etiolated, or heat-bleached leaves. The total capacity of isolated ribosome-deficient plastids for fatty acid synthesis was not much lower than that of isolated chloroplasts. However, the main products synthesized from [(14)C]acetate by chloroplasts were unesterified fatty acids, phosphatidic acid, and diacylglycerol, while those produced by ribosome-deficient plastids were unesterified fatty acids, phosphatidic acid, and phosphatidylglycerol. Isolated heat-bleached plastids exhibited a strikingly lower galactosyltransferase activity than chloroplasts, suggesting that this reaction was rate-limiting, and lacked phosphatidate phosphatase activity.

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PubMed1986

Low temperature development of winter rye leaves alters the detergent solubilization of thylakoid membranes.

Thylakoids isolated from leaves of winter rye (Secale cereale L. cv Puma) grown at either 20 or 5 degrees C were extracted with the nonionic detergents Triton X-100 and octyl glucoside. Less total chlorophyll was extracted from 5 degrees C thylakoids by these detergents under all conditions, including pretreatment with cations. Thylakoids from either 20 or 5 degrees C leaves were solubilized in 0.7% Triton X-100 and centrifuged on sucrose gradients to purify the light harvesting complex (LHCII). Greater yields of LHCII were obtained by cation precipitation of particles derived from 20 degrees C thylakoids than from 5 degrees C thylakoids. When 20 and 5 degrees C thylakoids were phosphorylated and completely solubilized in sodium dodecyl sulfate, no differences were observed in the (32)Pi-labeling characteristics of the membrane polypeptides. However, when phosphorylated thylakoids were extracted with octyl glucoside, extraction of LHCII associated with the 5 degrees C thylakoids was markedly reduced in comparison with the extraction of LHCII from 20 degrees C membranes. Since 20 and 5 degrees C thylakoids exhibited significant differences in the Chl content and Chl a/b ratios of membrane fractions produced after solubilization with either Triton X-100 or octyl glucoside, and since few differences between the proteins of the two membranes could be observed following complete denaturation in sodium dodecyl sulfate, we conclude that the integral structure of the thylakoid membrane is affected during rye leaf development at low temperature.

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