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At least 433 records · Page 24Linked to original sources
PubMed1996

Photosystem II Excitation Pressure and Development of Resistance to Photoinhibition (II. Adjustment of Photosynthetic Capacity in Winter Wheat and Winter Rye).

Winter wheat (Triticum aestivum L. cv Monopol), spring wheat (Triticum aestivum L. cv Katepwa), and winter rye (Secale cereale L. cv Musketeer) grown at 5[deg]C and moderate irradiance (250 [mu]mol m-2 s-1) (5/250) exhibit an increased tolerance to photoinhibition at low temperature in comparison to plants grown at 20[deg]C and 250 [mu]mol m-2 s-1 (20/250). However, 5/250 plants exhibited a higher photosystem II (PSII) excitation pressure (0.32-0.63) than 20/250 plants (0.18-0.21), measured as 1 - qP, the coefficient of photochemical quenching. Plants grown at 20[deg]C and a high irradiance (800 [mu]mol m-2 s-1) (20/800) also exhibited a high PSII excitation pressure (0.32-0.48). Similarly, plants grown at 20/800 exhibited a comparable tolerance to photoinhibition relative to plants grown at 5/250. In contrast to a recent report for Chlorella vulgaris (D.P. Maxwell, S. Falk, N.P.A. Huner [1995] Plant Physiol 107: 687-694), this tolerance to photoinhibition occurs in winter rye with minimal adjustment to polypeptides of the PSII light-harvesting complex, chlorophyll a/b ratios, or xanthophyll cycle carotenoids. However, Monopol winter wheat exhibited a 2.5-fold stimulation of sucrosephosphate synthase activity upon growth at 5/250, in comparison to Katepwa spring wheat. We demonstrate that low-temperature-induced tolerance to photoinhibition is not a low-temperature-growth effect per se but, instead, reflects increased photosynthetic capacity in response to elevated PSII excitation pressure, which may be modulated by either temperature or irradiance.

Journal Article↗
PubMed1996

Peroxygenase-Catalyzed Fatty Acid Epoxidation in Cereal Seeds (Sequential Oxidation of Linoleic Acid into 9(S),12(S),13(S)-Trihydroxy-10(E)-Octadecenoic Acid).

Peroxygenase-catalyzed epoxidation of oleic acid in preparations of cereal seeds was investigated. The 105,000g particle fraction of oat (Avena sativa) seed homogenate showed high peroxygenase activity, i.e. 3034 [plus or minus] 288 and 2441 [plus or minus] 168 nmol (10 min)-1 mg-1 protein in two cultivars, whereas the corresponding fraction obtained from barley (Hordeum vulgare and Hordeum distichum), rye (Secale cereale), and wheat (Triticum aestivum) showed only weak activity, i.e. 13 to 138 nmol (10 min)-1 mg-1 protein. In subcellular fractions of oat seed homogenate, peroxygenase specific activity was highest in the 105,000g particle fraction, whereas lipoxygenase activity was more evenly distributed and highest in the 105,000g supernatant fraction. Incubation of [1-14C]linoleic acid with the 105,000g supernatant of oat seed homogenate led to the formation of several metabolites, i.e. in order of decreasing abundance, 9(S)-hydroxy-10(E),12(Z)-octadecadienoic acid, 9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid, cis-9,10-epoxy-12(Z)-octadecenoic acid [mainly the 9(R),10(S) enantiomer], cis-12,13-epoxy-9(Z)-octadecenoic acid [mainly the 12(R),13(S) enantiomer], threo-12,13-dihydroxy-9(Z)-octadecenoic acid, and 12(R),13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoic acid. Incubation of linoleic acid with the 105,000g particle fraction gave a similar, but not identical, pattern of metabolites. Conversion of linoleic acid into 9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid, a naturally occurring oxylipin with antifungal properties, took place by a pathway involving sequential catalysis by lipoxygenase, peroxygenase, and epoxide hydrolase.

Journal Article↗
PubMed1996

Immunolocalization of Antifreeze Proteins in Winter Rye Leaves, Crowns, and Roots by Tissue Printing.

During cold acclimation, antifreeze proteins (AFPs) that are similar to pathogenesis-related proteins accumulate in the apoplast of winter rye (Secale cereale L. cv Musketeer) leaves. AFPs have the ability to modify the growth of ice. To elucidate the role of AFPs in the freezing process, they were assayed and immunolocalized in winter rye leaves, crowns, and roots. Each of the total soluble protein extracts from cold-acclimated rye leaves, crowns, and roots exhibited antifreeze activity, whereas no antifreeze activity was observed in extracts from nonacclimated rye plants. Antibodies raised against three apoplastic rye AFPs, corresponding to a glucanase-like protein (GLP, 32 kD), a chitinase-like protein (CLP, 35 kD), and a thaumatin-like protein (TLP, 25 kD), were used in tissue printing to show that the AFPs are localized in the epidermis and in cells surrounding intercellular spaces in cold-acclimated plants. Although GLPs, CLPs, and TLPs were present in nonacclimated plants, they were found in different locations and did not exhibit antifreeze activity, which suggests that different isoforms of pathogenesis-related proteins are produced at low temperature. The location of rye AFPs may prevent secondary nucleation of cells by epiphytic ice or by ice propagating through the xylem. The distributions of pathogenesis-induced and cold-accumulated GLPs, CLPs, and TLPs are similar and may reflect the common pathways by which both pathogens and ice enter and propagate through plant tissues.

Journal Article↗
PubMed1996

Effect of Cold Hardening on the Components of Respiratory Decarboxylation in the Light and in the Dark in Leaves of Winter Rye.

In the dark, all decarboxylation reactions are associated with the oxidase reactions of mitochondrial electron transport. In the light, photorespiration is also active in photosynthetic cells. In winter rye (Secale cereale L.), cold hardening resulted in a 2-fold increase in the rate of dark respiratory CO2 release from leaves compared with nonhardened (NH) controls. However, in the light, NH and cold-hardened (CH) leaves had comparable rates of oxidase decarboxylation and total intracellular decarboxylation. Furthermore, whereas CH leaves showed similar rates of total oxidase decarboxylation in the dark and light, NH leaves showed a 2-fold increase in total oxidase activity in the light compared with the dark. Light suppressed oxidase decarboxylation of end products of photosynthesis 2-fold in NH leaves and 3-fold in CH leaves in air. However, in high-CO2, light did not suppress the oxidase decarboxylation of end products. Thus, the decrease in oxidase decarboxylation of end products observed in the light and in air reflected glycolate-cycle-related inhibition of tricarboxylic acid cycle activity. We also showed that the glycolate cycle was involved in the decarboxylation of the end products of photosynthesis in both NH and CH leaves, suggesting a flow of fixed carbon out of the starch pool in the light.

Journal Article↗
PubMed1997

Characterization of a maize beta-amylase cDNA clone and its expression during seed germination.

A maize (Zea mays L.) cDNA clone (pZMB2) encoding beta-amylase was isolated from a cDNA library prepared from the aleurone RNA of germinating kernels. The cDNA encodes a predicted product of 488 amino acids with significant similarity to known beta-amylases from barley (Hordeum vulgare), rye (Secale cereale), and rice (Oryza sativa). Glycine-rich repeats found in the carboxyl terminus of the endosperm-specific beta-amylase of barley and rye are absent from the maize gene product. The N-terminal sequence of the first 20 amino acids of a beta-amylase peptide derived from purified protein is identical to the 5th through 24th amino acids of the predicted cDNA product, indicating the absence of a conventional signal peptide in the maize protein. Recombinant inbred mapping data indicate that the cDNA clone is single-copy gene that maps to chromosome 7L at position 83 centimorgans. Northern blot analysis and in vitro translation-immunoprecipitation data indicate that the maize beta-amylase is synthesized de novo in the aleurone cells but not in the scutellum during seed germination.

Amino Acid Sequence↗
PubMed1997

Cold Acclimation and Freezing Tolerance (A Complex Interaction of Light and Temperature).

By comparing growth under five different temperature and irradiance regimes (20[deg]C and 800, 250, and 50[mu]mol m-2 s-1 and 5[deg]C and 250 and 50 [mu]mul m-2 s-1), we have examined the effects of light, temperature, and the relative reduction state of photosystem II on plant morphology, freezing tolerance (lethal temperature at which freezing injury occurs [LT50]), transcript levels of Lhcb and two cold-stimulated genes (Wcs19 and Wcs120), and photosynthetic adjustment in winter rye (Secale cereale L. cv Musketeer). We show, for the first time to our knowledge, that in addition to adjustments in photosynthetic capacity, nonphotochemical quenching capacity and tolerance to photoinhibition, the accumulation of the cold-induced transcript Wcs19, and the compact plant morphology usually associated with cold-hardening are correlated with the relative reduction state of photosystem II rather than with growth temperature or growth irradiance per se. In contrast, the acquisition of maximal LT50, as well as Lhcb and Wcs120 mRNA accumulation, appears to be dependent on both growth temperature and growth irradiance but in an independent, additive manner. The results are discussed with respect to the possible role of the modulation of chloroplastic redox poise in photosynthetic acclimation to cold-hardening temperatures and the attainment of maximal LT50.

Journal Article↗
PubMed1997

Effect of Cold Acclimation on the Lipid Composition of the Inner and Outer Membrane of the Chloroplast Envelope Isolated from Rye Leaves.

The lipid composition of the inner and outer membranes of the chloroplast envelope isolated from winter rye (Secale cereale L. cv Puma) leaves was characterized before and after cold acclimation. In nonacclimated leaves the inner membrane contained high proportions of monogalactosyldiacylglycerols (MGDG, 47.9 mol% of the total lipids) and digalactosyldiacylglycerols (DGDG, 31.1 mol%) and a low proportion of phosphatidylcholine (PC, 8.1 mol%). The outer membrane contained a similar proportion of DGDG (30.0 mol%); however, the proportion of MGDG was much lower (20.1 mol%) and the proportion of PC was much higher (31.5 mol%). After 4 weeks of cold acclimation, the proportions of these lipid classes were significantly altered in both of the inner and outer membranes. In the inner membrane the proportion of MGDG decreased (from 47.9 to 38.4 mol%) and the proportion of DGDG increased (from 31.1 to 39.3 mol%), with only a slight change in the proportion of PC (from 8.1 to 8.8 mol%). In the outer membrane MGDG decreased from 20.1 to 14.8 mol%, DGDG increased from 30.0 to 39.9 mol%, and PC decreased from 31.5 to 25.4 mol%. Thus, both before and after cold acclimation, the proportion of MGDG was much higher in the inner membrane than in the outer membrane. In contrast, the proportion of PC was higher in the outer membrane than in the inner membrane. The relationship between the lipid composition of the inner and outer membranes of the chloroplast envelope and freeze-induced membrane lesions is discussed.

Journal Article↗
PubMed1999

Antifreeze proteins in winter rye leaves form oligomeric complexes

Antifreeze proteins (AFPs) similar to three pathogenesis-related proteins, a glucanase-like protein (GLP), a chitinase-like protein (CLP), and a thaumatin-like protein (TLP), accumulate during cold acclimation in winter rye (Secale cereale) leaves, where they are thought to modify the growth of intercellular ice during freezing. The objective of this study was to characterize the rye AFPs in their native forms, and our results show that these proteins form oligomeric complexes in vivo. Nine proteins were separated by native-polyacrylamide gel electrophoresis from apoplastic extracts of cold-acclimated winter rye leaves. Seven of these proteins exhibited multiple polypeptides when denatured and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After isolation of the individual proteins, six were shown by immunoblotting to contain various combinations of GLP, CLP, and TLP in addition to other unidentified proteins. Antisera produced against individual cold-induced winter rye GLP, CLP, and TLP all dramatically inhibited glucanase activity in apoplastic extracts from cold-acclimated winter rye leaves, and each antiserum precipitated all three proteins. These results indicate that each of the polypeptides may be exposed on the surface of the protein complexes. By forming oligomeric complexes, AFPs may form larger surfaces to interact with ice, or they may simply increase the mass of the protein bound to ice. In either case, the complexes of AFPs may inhibit ice growth and recrystallization more effectively than the individual polypeptides.

Journal Article↗
PubMed1999

Snow-mold-induced apoplastic proteins in winter rye leaves lack antifreeze activity

During cold acclimation, winter rye (Secale cereale L.) plants secrete antifreeze proteins that are similar to pathogenesis-related (PR) proteins. In this experiment, the secretion of PR proteins was induced at warm temperatures by infection with pink snow mold (Microdochium nivale), a pathogen of overwintering cereals. A comparison of cold-induced and pathogen-induced proteins showed that PR proteins accumulated in the leaf apoplast to a greater level in response to cold. The PR proteins induced by cold and by snow mold were similar when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and examined by immunoblotting. Both groups of PR proteins contained glucanase-like, chitinase-like, and thaumatin-like proteins, and both groups exhibited similar levels of glucanase and chitinase activities. However, only the PR proteins induced by cold exhibited antifreeze activity. Our findings suggest that the cold-induced PR proteins may be isoforms that function as antifreeze proteins to modify the growth of ice during freezing while also providing resistance to the growth of low-temperature pathogens in advance of infection. Both functions of the cold-induced PR proteins may improve the survival of overwintering cereals.

Journal Article↗
PubMed2000

Starch-branching enzymes preferentially associated with A-type starch granules in wheat endosperm.

Two starch granule-bound proteins (SGP), SGP-140 and SGP-145, were preferentially associated with A-type starch granules (>10 microm) in developing and mature wheat (Triticum aestivum) kernels. Immunoblotting and N-terminal sequencing suggested that the two proteins were different variants of SBEIc, a 152-kD isoform of wheat starch-branching enzyme. Both SGP-140 and SGP-145 were localized to the endosperm starch granules but were not found in the endosperm soluble fraction or pericarp starch granules younger than 15 d post anthesis (DPA). Small-size starch granules (<10 microm) initiated before 15 DPA incorporated SGP-140 and SGP-145 throughout endosperm development and grew into full-size A-type starch granules (>10 microm). In contrast, small-size starch granules harvested after 15 DPA contained only low amounts of SGP-140 and SGP-145 and developed mainly into B-type starch granules (<10 microm). Polypeptides of similar mass and immunologically related to SGP-140 and/or SGP-145 were also preferentially incorporated into A-type starch granules of barley (Hordeum vulgare), rye (Secale cereale), and triticale (x Triticosecale Wittmack) endosperm, which like wheat endosperm have a bimodal starch granule size distribution.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1970

The effects of simazine and temperature on photosynthesis in rye.

Temperature during growth had a strong influence on light-saturated rates of photosynthesis and respiration in rye (Secale cereale). Carbon dioxide uptake was depressed at the low temperatures and reached maximal values higher than 30 milligrams of carbon dioxide per square decimeter per hour at the intermediate temperatures. Respiration rates increased substantially while growth temperature decreased. Simazine treatment (0.00, 0.03, 0.08, 0.12 milligrams per liter) resulted in no significant stimulatory or inhibitory effects at low temperatures, but progressively inhibited growth and photosynthesis at the higher temperatures. Respiration rates were not significantly influenced. Thus, the effect of simazine is strongly temperature-dependent and is more pronounced on photosynthesis than respiration.

Journal Article↗
PubMed1971

"Disaggregation" of phytochrome in vitro-a consequence of proteolysis.

The relationship between a large molecular weight (9S) and a small molecular weight (4.5S, 60,000 molecular weight) species of phytochrome was examined to determine if the larger species was an aggregate of the smaller. Alterations of pH, salt concentration, or phytochrome concentration did not cause any observable formation of the large form from the small form. However, in partially purified phytochrome extracts from Secale cereale L. and Avena sativa L., the large form was converted to the small form over time at 4 C in the dark. This breakdown was inhibitable by the protease inhibitor phenylmethanesulfonyl fluoride. When highly purified large molecular weight rye phytochrome was incubated with a neutral protease isolated from etiolated oat shoots, the large phytochrome was converted to the small form without qualitative visible absorbancy changes. The effect of the oat protease could be mimicked by a wide variety of commercial endopeptidases, including trypsin. Examination of the trypsin-induced breakdown on sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that as the size of the photoreversible unit changes from large to small, the size of its constituent polypeptide chains is reduced from 120,000 to 62,000 molecular weight. These experiments provide evidence that the endogenous breakdown observed in extracts is a result of contaminant protease and, consequently, that the small molecular weight species of phytochrome is an artifact due to proteolysis.

Journal Article↗
PubMed1972

The dark reactions of rye phytochrome in vivo and in vitro.

The dark reactions of Secale cereale L. cv. Balbo phytochrome have been investigated in coleoptile tips and in extensively purified extracts of large molecular weight phytochrome. Destruction, but not reversion, was detected in vivo. The effects of various inhibitors of an in vitro phytochrome-degrading protease did not support a view of proteolytic attack as the basis of in vivo destruction. In vitro, rye phytochrome (about 240,000 molecular weight) reverted extremely rapidly, even at 5 C. The reversion curves were resolved into two first order components. The previously studied 60,000 molecular weight species, obtained by controlled proteolysis of large rye phytochrome, showed a similar two-component pattern, but a much slower over-all reversion rate. This reduction in rate was caused mainly by the reversion of a greater percentage of the small phytochrome as the slow component. Sodium dithionite markedly accelerated the reversion rate of both large and small forms, but oxidants, at concentrations low enough to avoid chromophore destruction, had no effect. Both large and small crude Avena sativa L. phytochrome showed two-component reversion kinetics.

Journal Article↗
PubMed1973

Comparative immunochemistry of phytochrome.

Partially purified high molecular weight preparations of phytochrome, estimated to be close to 440,000 molecular weight based upon chromatography through a calibrated Bio-Gel P-300 column, were obtained from Garry and Newton oats (Avena Sativa L., cv. Garry and cv. Newton), rye (Secale cereale L., cv. Balbo), barley (Horedum vulgare L., cv. Harrison), and pea (Pisum sativum L., cv. Alaska) by a sequence of three chromatographic steps: brushite, diethylaminoethyl cellulose, and Bio-Gel P-300. No significant differences were observed between these preparations during purification or subsequent handling. In addition, a low molecular weight form of phytochrome was purified from Garry oats. Two specific antisera against a low molecular weight form of phytochrome (60,000 molecular weight) obtained from etiolated Garry oat seedlings are characterized and used to compare the phytochrome preparations. Double diffusion assays indicated antigenic identity between all preparations except that pea phytochrome yielded a spur when compared to oat phytochrome. Micro complement fixation assays yielded complete identity between Garry and Newton oat phytochrome, reduced activity with rye and barley phytochrome, and a complete lack of activity with pea phytochrome at the serum dilutions assayed. Immunoelectrophoretic assays indicated that all high molecular weight phytochrome preparations were homogeneous by this criterion and that there were only slight differences between the preparations in electrophoretic mobility. Large and small forms of phytochrome isolated from Garry oats were found to be very similar antigens when tested with the anti-small phytochrome sera, although the small form was observed to electrophorese at a much slower rate than the large.

Journal Article↗
PubMed1973

Purification of oat and rye phytochrome.

A purification procedure employing normal chromatographic techniques is outlined for isolating phytochrome from etiolated oat (Avena sativa L.) seedlings. Yields in excess of 20% (25 milligrams or more) of phytochrome in crude extract were obtained from 10- to 15-kilograms lots. The purified oat phytochrome had an absorbance ratio (A(280) nm/A(665) nm) of 0.78 to 0.85, comparable to reported values, and gave a single major band with an estimated molecular weight of 62,000 on electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. A modification of the oat isolation procedure was used to isolate phytochrome from etiolated rye Secale cereale cv. Balbo) seedlings. During isolation rye phytochrome exhibited chromatographic profiles differing from oat phytochrome on diethylaminoethyl cellulose and on molecular sieve gels. It eluted at a higher salt concentration on diethylaminoethyl cellulose and nearer the void volume on molecular sieve gels. Yields of 5 to 10% (7.5-10 milligrams) of phytochrome in crude extract were obtained from 10- to 12-kilogram seedling lots. The purified rye phytochrome had an absorbance ratio of 1.25 to 1.37, significantly lower than values in the literature and gave a single major band with an estimated molecular weight of 120,000 on electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. It is suggested that the absorbance ratio and electrophoretic behavior of rye phytochrome are indices of purified native phytochrome, and that oat phytochrome as it has been described is an artifact which arises as a result of endogenous proteolysis during isolation. A rationale is provided for further modifications of the purification procedure to alleviate presumed protease contaminants.

Journal Article↗
PubMed1973

Lipids in rye seedlings in relation to vernalization.

Increasing the chilling time from 1 to 8 weeks decreased the time to heading of winter rye (Secale cereale var. Sangaste) to approximate that of the spring variety (Prolific). On a dry weight basis, the total phospholipid content of the embryos was higher in Sangaste but declined in both varieties during chilling. The proportions of the individual phospholipid components were similar for both varieties and showed similar responses during the 8-week chilling period. Phosphatidylcholine declined and phosphatidic acid increased in both varieties during the treatment.During the initial 3 weeks, an increased accumulation of linolenic acid and a corresponding decline in linoleic acid occurred for all the lipid components and then remained relatively stable. The glycolipids were more unsaturated than the phospholipids; however, the amount of linolenate was approximately doubled in both during the treatment. In general, the fatty acid content of the respective lipid classes were similar for both varieties.

Journal Article↗
PubMed1974

The effect of growth in 99.8 deuterium oxide on the ultrastructure of winter rye.

A preliminary report dealing with the ultrastructural effects of culture in a 99.8% D(2)O (deuterium oxide) environment on winter rye (Secale cereale L. cv. Winter) is presented. In general, the cells of D(2)O-cultured seedlings appeared similar to the cells of H(2)O-cultured seedlings. However, differences were found in chloroplast and dictyosome morphology, and ribosome number.

Journal Article↗
PubMed1975

Phytochrome Characterization by Rabbit Antiserum against High Molecular Weight Phytochrome.

Both small and large sizes of phytochrome purified from Garry oat (Avena sativa L. ev. Garry) as well as large phytochrome purified from Newton oat (A. sativa L. cv. Newton), rye (Secale cereale L. cv. Balbo), barley (Hordeum vulgare L. cv. Harrison), and pea (Pisum sativum L. cv. Alaska) seedlings are characterized by a specific antiserum against large Garry oat phytochrome. A spur is observed by double diffusion assay against large and small Garry oat phytochrome indicating only partial identity. In micro-complement fixation assays, large Garry oat phytochrome yields greater activity than small Garry oat phytochrome. In addition, the peak of activity is shifted to a higher antigen concentration with small phytochrome. Phytochrome, red-absorbing form, and phytochrome, far redabsorbing form, are indistinguishable by both double diffusion and micro-complement fixation assay. The different grass phytochromes are antigenically identical by double diffusion assay. Immunoelectrophoretic analyses of oat and rye large phytochrome, after proteolysis, suggest that there are one or a few regions of the molecule especially susceptible to hydrolysis by a wide variety of endopeptidases.

Journal Article↗