bluuebunny/crossref_metadata_2025 huggingface dataset:
MAPK phosphorylation‐induced stabilization of ACS6 protein is mediated by the non‐catalytic C‐terminal domain, which also contains the cis‐determinant for rapid degradation by the 26S proteasome pathway
Authors: Joo Sunjoo , Liu Yidong , Lueth Abraham , Zhang Shuqun
Published: February 2008

Ethylene is an important hormone in plant growth, development and responses to environmental stimuli. The ethylene‐signaling pathway is initiated by the induction of ethylene biosynthesis, which is under tight regulation at both transcriptional and post‐transcriptional levels by exogenous and endogenous cues. 1‐Aminocyclopropane‐1‐carboxylic acid synthase (ACS) is the rate‐limiting enzyme that catalyzes the committing step of ethylene biosynthesis. Recently, we found that ACS2 and ACS6, two isoforms of the Arabidopsis ACS family, are substrates of a stress‐responsive mitogen‐activated protein kinase (MAPK) cascade. Phosphorylation of ACS2/ACS6 by MPK6 leads to the accumulation of ACS proteins and the induction of ethylene. In this report, we demonstrate that unphosphorylated ACS6 protein is rapidly degraded by the 26S proteasome pathway. The degradation machinery targets the C‐terminal non‐catalytic domain of ACS6, which is sufficient to confer instability to green fluorescent protein and luciferase reporters. Phosphorylation of ACS6 introduces negative charges to the C‐terminus of ACS6, which reduces the turnover of ACS6 by the degradation machinery. Consistent with this, other nearby conserved negatively charged amino acid residues are essential for ACS6 stability regulation. Protein degradation and phosphorylation are two important post‐translational modifications of proteins. This research reveals an intricate interplay between these two important processes in controlling the levels of cellular ACS activity, and thus ethylene biosynthesis. The post‐translational nature of both processes ensures a rapid response of ethylene induction, which is detectable within minutes after plants are exposed to stress.
Mutation of a mitochondrial outer membrane protein affects chloroplast lipid biosynthesis
Authors: Xu Changcheng , Moellering Eric R. , Fan Jilian , Benning Christoph
Published: February 2008

Lipid biosynthesis in plant cells is associated with various organelles, and maintenance of cell lipid homeostasis requires nimble regulation and coordination. In plants, environmental cues such as phosphate limitation require readjustment of the lipid biosynthetic machinery to substitute phospholipids by non‐phosphorous glycolipids. Biosynthesis of the galactoglycerolipids predominant in plants proceeds by a constitutive and an alternative pathway that is known to be induced in response to phosphate deprivation. Plant lipid galactosyltransferases involved in both pathways are associated with the plastid envelope membranes and are encoded by nuclear genes. To identify mechanisms governing the activity of the alternative galactoglycerolipid pathway, a genetic suppressor screen was conducted in the background of the digalactolipid‐deficient dgd1 mutant of Arabidopsis. A suppressor line that partially restored digalactoglycerolipid content in the dgd1 background carries a point mutation in a mitochondrial protein, which was tentatively designated DGD1 SUPPRESSOR 1 (DGS1). Presumed orthologs of this protein are present in plants, algae and fungi, but its molecular function is not yet known. In the dgd1 dgs1 double mutant, expression of nuclear genes encoding enzymes of the alternative galactoglycerolipid pathway is increased and hydrogen peroxide levels are elevated. This increase in hydrogen peroxide is proposed to be the reason for activation of the alternative pathway in the dgd1 dgs1 double mutant. Accordingly, hydrogen peroxide and treatments producing reactive oxygen also activate the alternative pathway in the wild‐type. These results likely implicate the production of reactive oxygen in the regulation of the alternative galactoglycerolipid pathway in plants.
Purification of an α‐L‐arabinofuranosidase from carrot cell cultures and its involvement in arabinose‐rich polymer degradation
Authors: Konno Haruyoshi , Yamasaki Yoshiki , Katoh Kenji
Published: February 2008

Konno, H., Yamasaki, Y. and Katoh, K. 1987. Purification of an α‐L‐arabinofurano‐sidase from carrot cell cultures and its involvement in arabinose‐rich polymer degradation.

An α‐L‐arabinofuranosidase (α‐L‐arabinofuranoside arabinofuranohydrolase, EC 3.2.1.55) was isolated from a homogenate of cell suspension cultures of carrot (Daucus carota L. cv. Kintoki). The buffer‐soluble enzyme was purified to homogeneity by a procedure involving ammonium sulfate fractionation, chromatography on DEAE‐Sephadex A‐50, Sephadex G‐150, Con A‐Sepharose 4B and CM‐Sephadex C‐50, and preparative polyacrylamide gel electrophoresis. The size of this enzyme as determined by polyacrylamide gel electrophoresis in the presence of sodium laurylsulfate and by Sephadex G‐200 gel filtration was 94 and 110 kDa, respectively. The isoelectric point was at pH 4.7. The Km and Vmax values for p‐nitrophenyl α‐L‐arabinofuranoside were 1.33 mM and 20.2 μimol (mg protein)‐1 h‐1, respectively. The optimal activity occurred at pH 4.2 with Mcllvaine buffer. The enzyme was stimulated by Ca2+ and Zn2+, whereas it was strongly inhibited by Cu2+, Ag2+, Hg2+, p‐chloromercuri‐benzoate and L‐arabono‐l,4‐lactone. The enzyme acted on beet arabinan in an exo‐fashion. Furthermore, the enzyme was partially involved in the hydrolysis of the ara‐binogalactan and pectic polymer purified from carrot cell walls.
Low temperature spectrophotometry of the phototransformation of Pfr to Pr in pelletable pea phytochrome
Authors: Manabe Katsushi
Published: February 2008

Manabe, K. 1987. Low temperature spectrophotometry of the phototransformation of Pfr to Pr, in pelletable pea phytochrome.

Low temperature spectrophotometry was used to study the phototransformation of Pfr to Pr in 1000–7000 g pelletable fractions extracted from dark grown pea (Pisum sativum L. cv. Alaska) epicotyls which had been irradiated with red and then far‐red light. At ‐170°C, far‐red irradiation of the pelletable phytochrome which had been pre‐irradiated with saturating fluence of red light before freezing caused formation of an intermediate (named I660), the difference spectrum of which showed a marked ab‐sorbance decrease at 740 nm and a concomitant small increase at about 660 nm. The inermediate I660 was converted to another intermediate (I660) when it was warmed above ‐80°C. The difference spectrum of this intermediate showed a positive peak at 670 nm. This intermediate was photoconverted to Pfr by red irradiation and also underwent dark reversion to Pfr at ‐60°C. I660 formed Pr if the temperature was above ‐10°C. The basic features of the phytochrome intermediates resemble those obtained in vivo and in degraded purified phytochrome.
Chilling injury and recovery in detached and attached leaves measured by chlorophyll fluorescence
Authors: Smillie Robert M. , Nott Robyn , Hetherington Suzan E. , Öquist Gunnar
Published: February 2008

Smillie, R. M., Nott, R., Hetherington, S. E. and Öyustt, G. 1987. Chilling injury and recovery in detached and attached leaves measured by chlorophyll fluorescence

Chilling injury was compared in detached and attached leaves chilled at 0 or 0.5°C by measuring the decrease in induced chlorophyll fluorescence in vivo. The fluorescence parameter measured was FR, the maximal rate of rise of induced chlorophyll fluorescence emission after irradiating dark‐adapted leaves. The plants used were bean, Phaseolus vulgaris L. cv. Pioneer, and maize, Zea mays L. cvs hybrid GH 390 and Northern Belle. Leaves were detached and placed on wet paper and covered with thin polyethylene film to prevent water loss during chilling. Leaves left attached on plants were treated similarly. When chilled in this way at 100% relative humidity, the chilling‐induced decrease in FR was the same in detached and attached leaves. For the attached leaves, the same result was obtained whether just a single leaf was chilled or the whole plant. Expression of chilling injury was greatest in fully turgid leaves and comparisons can be invalid unless the water status of the detached and attached leaves are the same. Problems arising from diurnal fluctuations in water potential of plants grown in a glasshouse were circumvented by placing leaves on the wet filter paper under polyethylene film prior to chilling, which allowed high water potentials to be regained, or mist sprays in the glasshouse were employed. Determinations of the time course for changes in FR of maize (cv. Northern Belle) during chilling at 0°C showed that FR decreased exponentially, at the same rate (time to 50% decrease in FR was 9.3 h) in detached and attached leaves. Chilling injury was largely reversible for the first 20 h of chilling stress as both detached and attached leaves recovered their pre‐chilling values of FR after a further 20 h at 20°C in darkness. Leaves chilled for 48 h showed partial recovery, while those chilled for 72 h did not recover. Recovery was impeded by light. Inability to recover from chilling as indicated by measurements of FR was paralleled by the incidence of visible symptoms of injury. It is concluded that detached and attached leaves behave similarly during chilling and short‐term recovery, provided a similarity in treatments is rigorously maintained.
Studies on [14C]‐glucose metabolism during shoot bud induction in cultured cotyledon explants of Pinus radiata
Authors: Bender Ludwig , Joy Richard W. , Thorpe Trevor A.
Published: February 2008

Bender, L., Joy IV, R. W. and Thorpe, T. A. 1987. Studies on [14C]‐glucose metabolism during shoot bud induction in cultured cotyledon explants of Pinus radiala.

Excised cotyledons of Pinus radiata D. Don, cultured under shoot‐forming (plus N6‐benzyladenine) and elongating (minus N6‐benzyladenine) conditions, were fed U‐[14C]‐glucose for 3 h in the light followed by a 3 h chase period immediately after excision (day 0) and after 3 days of culture (day 3). The incorporation of l4C into individual soluble metabolites as well as into protein was followed. No labelled citrate could be detected at day 0, however, a flow of 14C from glucose to glutamate/ glutamine occurred. During this stage the synthesis of glutamine strongly increased in the cotyledons supplied with N6‐benzyladenine, which suggests a positive influence of this cytokinin on nitrogen incorporation prior to differentiation. After 3 days of cultivation large amounts of labelled citrate were detected. An increased incorporation of label into protein due to the cytokinin treatment was not detected during the early culture period (days 0 and 3). Labelled amino acids were incorporated into protein to different degrees, but this was not influenced by the hormonal treatment.
Symbiotic properties ofLotus pedunculitisroot nodules induced byRhizobium lotiandBradyrhizobiumsp. (Lotus)
Authors: Vance Carroll P. , Reibach Paul H. , Pankhurst Clive E.
Published: February 2008

Vance, C. P., Reibach, P. H. and Pankhurst, C. E. 1987. Symbiotic properties ofLotus pedunculatusroot nodules induced byRhizobium lotiandBradyrhizobiumsp. (Lotus).

Symbiotic properties of root nodules were evaluated in glasshouse‐grownLotus pedunculatusCav. cv. Maku inoculated with either a fast‐growingRhizobium lotistrain NZP2037 or a slow‐growingBradyrhizobiumsp. (Lotus) strain CC814s. Although the nodule mass of plants inoculated with NZP2037 was twice that of plants inoculated with CC814s, the yield of NZP2037 shoots and roots was 50% that of CC814s shoots and roots. Nodules induced byBradyrhizobiumfixed substantially more N than nodules induced byR. loti.Glucose requirements [mol glucose (mol N2fixed)‐1] of nodules induced by CC814s and NZP2037 were 7.1 and 16.6, respectively. Nodule enzymes of carbon and nitrogen assimilation reflected the disparity of the two sym‐bioses. Xylem sap of the symbiosis with the higher yield contained a higher concentration of asparagine [9.86 μmol (ml xylem sap)‘] than did the lower yielding symbiosis [5.80 umol (ml xylem sap)“’]. Nodule CO2fixation was directly linked to nodule N assimilation in both symbioses. The results indicate that the difference between the two symbioses extend to nodule N and C assimilation and whole plant N transport. The data support a role for host plant modulation of bacterial efficiency and assimilation of fixed N.
Multiple‐site inhibition by colloidal elemental sulfur (S°) of respiration by mitochondria from young dormant α spores of Phomopsis viticola
Authors: Beffa TYello , Pezet Roger , Turian Gilbert
Published: February 2008

Beffa, T., Pezet, R. and Turian, G. 1987. Multiple‐site inhibition by colloidal elemental sulfur (S°) of respiration by mitochondria from young dormant α spores of Phomopsis viticola.

Mitochondria from young dormant α spores of Phomopsis viticola Sacc. (ATCC 44940) were isolated by grinding and differential centrifugation. They presented a good integrity of their inner and outer membranes as measured by biochemical assays. Electron microscopic analysis revealed an homogenous population. The highest respiratory activities were observed with NADH and ascorbate + tetra‐methyl‐p‐phenylenediamine (TMPD). Malate stimulated the oxidation of pyruvate, citrate or α‐ketoglutarate. The coupling of respiration to oxidative phosphorylation appeared at the time of spore germination. The respiratory activities of mitochondria isolated from young dormant α spores of P. viticola were strongly inhibited by S°. The sensitivity of mitochondrial oxidation of different substrates (NADH, pyruvate + malate, succinate and ascorbate + TMPD) to S° was heterogenous and indicated multiple‐site action. Thus preincubation of mitochondria with 30 μM S° before addition of substrates fully prevented NADH oxidation (>98%), and strongly inhibited oxidation of pyruvate + malate (85%), succinate (60%) and ascorbate + TMPD (74%). S° inhibited more rapidly the oxidation of succinate than that of other substrates. In the presence of dithiothreitol (DTT), S°‐inhibited oxidation of all substrates (except ascorbate + TMPD) could only be transiently and weakly reestablished. The inhibitory action of S° on the oxidation of NADH, pyruvate + malate and succinate was higher than that observed with sulfhydryl group reagents such as mersalyl, Hg‐acetate or p ‐ chloromercuribenzoate. In contrast to S° these SH‐group reagents could not inhibit oxidation of ascorbate + TMPD.

S°, by its dual capacity to oxidize the SH‐groups and to self‐reduce, probably at the level of cytochrome c oxidase, could produce a modification of the oxidation state of the respiratory complexes thereby disturbing the electron flux.
The effect of UV‐A light on cAMP level in the basidiomycete Schizophyllum commune
Authors: Yli‐Mattila Tapani
Published: February 2008

Yli‐Mattila, T. 1987. The effect of UV‐A light on cAMP level in the basidiomycete Schizophyllum commune.

The level of cyclic AMP was studied in two dikaryotic strains of Schizophyllum commune Fr. In the strain 3×4, requiring light for fruiting, the level of cAMP in 72‐h‐old colonies was 12.1 pmol (mg protein)‐1. The level of cAMP increased ca 50% within 2 h of the beginning of exposure to light (UV‐A, 1 h, 8.3 umol m‐2 s_1). During the following 8 h there was a slight decrease in the level of cAMP. In the dark controls the level of cAMP increased ca 13% within 5 h of the light treatment. This slight increase was continued during the next 19 h. In the strain 245 times 252, which forms more fruit bodies than strain 3×4, the increase was ca 110% within 10 h of the light treatment, while in the dark controls the level of cAMP in 82‐h‐old colonies was the same as in 72‐h‐old colonies [10.3 pmol (mg protein)‐1]. During the following 14 h the cAMP content increased sharply (ca 80%) in the dark controls, which might be connected with the ability of strain 245 × 252 to produce fruit bodies in darkness. In dark‐grown colonies of strain 3×4, the level of cAMP was higher in the marginal than in the central zones. The difference disappeared within 2 h of the beginning of exposure to light, since cAMP increased more in the central zone. This difference may be related to the ability of the marginal zone to form fruit bodies in light.
Effect of sugar level on phleinase induction in stem base of orchardgrass after defoliation
Authors: Yamamoto Shinro , Mino Ydsuke
Published: February 2008

Yamamoto, S. and Mino, Y. 1987. Effect of sugar level on phleinase induction in stem base of orchardgrass after defoliation.

The induction of phleinase (β‐D‐fructan fructohydrolase, EC 3.2.1.80) in stem base of orchardgrass (Dactylis glomerata L. clone N‐377) after defoliation was studied in relation to the concomitant changes in sugar and protein levels. Phleinase activity in the stubble increased accompanied by a decrease in sucrose and glucose levels. This activity also increased under shading conditions without cutting. The induction of phleinase in excised stem base was suppressed by exogenously supplied glucose, fructose or sucrose. The suppression increased with increasing concentrations of glucose and it was not overcome by cyclic adenosine 3′,5′‐monophosphate. Protein level in the stem base decreased after defoliation and the decrease was reversed by exogenous glucose. Some hypotheses concerning the induction mechanism of phleinase are discussed.
Hypocotyl growth of Pinus pinaster seedlings. Changes in α‐cellulose, and in pectic and hemicellulosic polysaccharides
Authors: Lorences Ester P. , Suarez Lisandro , Zarra Ignacio
Published: February 2008

Lorences, E. P., Suárez, L. and Zarra, I. 1987. Hypocotyl growth of Pinus pinaster seedlings. Changes in a‐cellulose, and in pectic and hemicellulosic polysaccharides.

The changes in pectic and hemicellulosic polysaccharides of hypocotyl cell walls during the growth of intact seedlings of Pinus pinaster Aiton were investigated, α‐Cellulose and the water‐soluble hemicellulose presented the most conspicuous changes during hypocotyl growth. The relative amount of the water‐soluble hemicellulose decreased from day 7 to day 13 when hypocotyls were in the rapid growth phase, and stabilized when hypocotyl growth ceased. In this fraction, the relative amount of non‐cellulosic glucose decreased dramatically during hypocotyl growth, while the relative amount of xylose increased. We suggest that these changes may be due to partial degradation of xyloglucan present in the water:soluble hemicellulose fraction, accompanied by the synthesis of a xylan.
Hypocotyl growth of Pinus pinaster seedlings. Changes in the molecular weight distribution of hemicellulosic polysaccharides
Authors: Lorences Ester P. , Suarez Lisandro , Zarra Ignacio
Published: February 2008

Lorences, E. P., Suárez, L. and Zarra, I. 1987. Hypocotyl growth of Pinus pinaster seedlings. Changes in the molecular weight distribution of hemicellulosic polysaccharides.

The changes in the molecular weight distribution of water‐soluble hemicelluloses and xyloglucan during hypocotyl growth of intact seedlings of Pinus pinaster Aiton were investigated. The mass‐average molecular weight of total polysaccharides of the hemicellulose fraction soluble in 4% KOH dramatically increased during hypocotyl growth while xyloglucan slightly decreased. These phenomena were due to an increase in the degree of polymerization of an arabinogalactan and a slight depolymer‐ization in the xyloglucan present in this fraction. In the hemicellulose fraction soluble in 24% KOH, xyloglucan increased its degree of polymerization from day 7 to 10 after which it decreased slightly. The xyloglucan of the hemicellulose fraction soluble in 4% KOH may thus be involved in cell wall loosening which makes cell wall expansion possible during hypocotyl growth.
Stomatal responses to rapidly imposed water stress and light/dark transition in norflurazon‐treated wheat leaves
Authors: Höglund Hans‐Olof , Klockare Rune
Published: February 2008

Hoglund, H. O. and Klockare, R. 1987. Stomatal responses to rapidly imposed water stress and light/dark transition in norflurazon‐treated wheat leaves.

Stomatal responses to rapidly imposed water stress and to light/dark transition were studied in leaves of wheat (Triticum aestivum L. cv. Starke II) treated with nor‐flurazon (NF) which is known to inhibit abscisic acid (ABA) accumulation. The stomatal response was studied in an open air flow system. It was shown that these plants have the ability to respond to externally added ABA. When the water potential in the nutrient solution was rapidly reduced, stomata in green plants responded with a transient opening followed by a strongly decreased aperture. NF‐treated plants responded with a similar rapid opening of stomata, but the following closure was strongly reduced. Transfer from light to darkness induced a rapid closure of stomata in green plants but the closing response was strongly delayed in NF‐treated plants. These results indicate that NF affects one or more regulators involved in the closure of stomata under rapidly imposed water stress and in the light/dark transition. The possibility that this regulator is ABA is discussed.
Subcellular distribution of pyruvate‐degrading enzymes in Chlamydomonas reinhardtii studied by an improved protoplast fractionation procedure
Authors: Kreuzberg Karlheinz , Klock Gerd , Grobheiser Dorte
Published: February 2008

The subcellular distribution of pyruvate‐degrading enzymes has been determined in Chlamydomonas reinhardtii (Dangeard) by protoplast induction with autolysine, dig‐itonin lysis and further fractionation by differential centrifugation using a Percoll cushion. Mitochondrial and plastidic fractions contained intact and physiologically competent organelles ‐ RC 1.7, ADP/O 2.7 and rate of malate oxidation 76 nmol O, (mg protein)‐1min‐1 for mitochondria, CO2; fixation 46.8 μmol (mg Chi)‐1 h‐1 for chloroplasts.

Results from protoplast fractionation were further confirmed by the determination of enzyme activities within trypsin‐treated organelles. Mitochondria (formate fermentation) and chloroplasts (chlorofermentation) were shown to possess the capacity for anaerobic pyruvate degradation. Pyruvate dehydrogenase (NAD+, EC 1.2.4.1), pyruvate formate‐lyase (EC 2.3.1.54) and lactate dehydrogenase (NADH, EC 1.1.1.27) showed equal distribution between mitochondria and chloroplasts, whereas activities of phosphotransacetylase (EC 2.3.1.8) and acetate kinase (EC 2.7.2.1) were only detectable in the mitochondrial fraction. NADH‐ and NADPH‐dependent activities of both alcohol dehydrogenase (EC 1.1.1.1) and aldehyde dehydrogenase (acylating, EC 1.2.1.10) were localized in the mitochondrial and cytoplasmic or the plastidic and cytoplasmic fractions, respectively, whereas pyruvate decarboxylase (EC 4.1.1.1) was only detected in the cytoplasmic fraction.
Internode length in Pisum. Action of gene lw
Authors: Jolly C. J. , Reid J. B. , Ross J. J.
Published: February 2008

Jolly, C. J., Reid, J. B. and Ross, J. J. 1987. Internode length in Pisum. Action of gene lw.

Mutant K29 of Pisum sativum L. is shown to possess a recessive gene at a new locus, lw, which results in reduced internode length, delayed flowering and increased symptoms of water congestion compared with the parental cv. Torsdag. The interaction of gene lw with the internode length genes na, le, la and cry5 is examined. Extracts from the shoots of Iw plants are shown to contain similar levels of gibberellin (GA)‐like substances to comparable Lw plants, but Iw plants do not elongate to the same extent as Lw plants when treated with GA19 GA19, or GA20. The effect of gene Iw is not graft‐transmissible. Unlike essentially isogenic dwarf lines possessing the GA‐synthesis genes le, Ih or Is, lw plants show a relative increase in elongation similar to Torsdag in response to photoperiod extensions from sources rich in far‐red light. These results suggest that gene lw probably does not reduce elongation by influencing GA‐synthesis and that the response to photoperiod extensions with far‐red light may depend on the level of GA.
γ‐Glutamylcyclotransferase in tobacco suspension cultures: Catalytic properties and subcellular localization
Authors: Steinkamp Reinhard , Schweihofen Barbara , Rennenberg Heinz
Published: February 2008

Steinkamp, R., Schweihofen, B. and Rennenberg, H. 1987. γ‐Glutamylcyclotransfer‐ase in tobacco suspension cultures: Catalytic properties and subcellular localization.

γ‐Glutamylcyclotransferase activity (EC 2.3.2.4) in ammonium sulfate precipitates (40–70% saturation) of extracts from cultured tobacco cells (Nicoliana tabacum L. cv. Samsun) was analyzed as liberation of 5‐oxo‐proline from L‐γ‐glutamyl dipeptides. The enzyme was highly specific for the sulfur containing γ‐glutamyl dipeptides γ‐glutamyl‐L‐methionine and γ‐glutamyl‐i.‐cysteine. Maximum activity was obtained at pH 8.7 and 35°C. As also observed with animal γ‐glutamylcyclotransferase, the tobacco enzyme exhibited a relatively low substrate affinity (γ‐glutamyl‐i.‐methionine: Km 2.2 ± 0.4 mM). In contrast to animal γ‐glutamylcyclotransferase, the tobacco enzyme was not inhibited by the D‐isomerof the substrate D‐γ‐glutamyl‐i.‐methionine; it also did not use the D isomer as a substrate. γ‐Glutamylcyclotransferase of tobacco cells was shown to be a soluble enzyme entirely localized in the cytoplasm.
Ethylene biosynthesis in tissues of young and mature avocado fruits
Authors: Sitrit Yaron , Blumenfeld Amos , Riov Joseph
Published: February 2008

Sitrit, Y., Blumenfeld, A. and Riov, J. 1987. Ethylene biosynthesis in tissues of young and mature avocado fruits.

Avocado (Persea americana Mill.) fruit tissues differ greatly in their capability to pro duce wound ethylene. In fruitlets, the endosperm lacks the ability to produce ethylene because no 1‐aminocyclopropane‐1‐carboxylic acid (ACC) is synthesized and no activity of the ethylene‐forming enzyme (EFE) is present. The cotyledons (embryo) do not produce significant amounts of ethylene at any of the developmental stages of the fruits, although in both young and mature fruits they contain a relatively high level of ACC synthase (EC 4.4.1.‐) activity. Because of the very low EFE activity present in the cotyledons, most of the ACC formed in this tissue is conjugated. Of the various fruitlet tissues, the seed coat has the highest potential to produce ethylene. This is due to a high ACC synthase activity and particularly a high EFE activity. Also, the seed coat is very sensitive to the autocatalytic effect of ethylene. Fruitletpericarp possesses a lower potential to produce ethylene than the seed coat. Towardruit maturiy, the endosperm disappears and the seed coat shrivels and dies so that the pericarp and the cotyledons remain as the only active tissues in the mature fruit. At this stage, the pericarp is the only tissue producing ethylene. Mature precli macteric pericarp has a lower potential to produce ethylene than fruitlet pericarpThe role of ethylene in regulating various physiological processes at different stages of fruit maturation is discussed.
Effects of growth regulators on light‐dependent anthocyanin production in Zea mays seedlings
Authors: Rengel Zdenko , Kordan Herbert A.
Published: February 2008

Rengel, Z. and Kordan, H. A. 1987. Effects of growth regulators on light‐dependent anthocyanin production in Zea mays seedlings.

The effects of ethylene, indolyl‐ and naphthylacetic acids, zeatin, benzyladenine, gib‐berellic acid and triiodobenzoic acid on anthocyanin production in seedlings of Zea mays L. cv. Golden Bantam were investigated. Endogenously produced and exogen‐ously supplied ethylene, as well as the other growth regulators tested markedly suppressed anthocyanin formation. Except for triiodobenzoic acid, the other growth regulators stimulated ethylene production, the amounts produced in the light being larger than those in the dark. Absorption of ethylene by permanganate as well as inhibition of ethylene production or action by Co2+ or Ag+ increased anthocyanin formation in maize seedlings above the level found in the control plants. The inhibiting effect of auxins and cytokinins on anthocyanin production was reversed by Co2+ or Ag+. In contrast, decreased anthocyanin formation caused by gibberellic acid or triiodobenzoic acid seemed unrelated to ethylene and could not be alleviated by Co2+ or Ag+.
Effect of an exogenous auxin on maize tissues. Alteration of protein synthesis and phosphorylation
Authors: Perez L. , Aguilar R. , Sánchez‐de‐Jiménez E.
Published: February 2008

Pérez, L., Aguilar, R. and Sánchez‐de‐Jiménez, E. 1987. Effect of an exogenous auxin on maize tissues. Alteration of protein synthesis and phosphorylation. ‐ Physiol. Plantarum 69: 517–522.

A synthetic auxin 2‐(2‐methyl‐4‐chloro)phenoxypropionic acid (MCPP), analogue of 2,4‐D, alters maize (Zea maysL. H‐30) germination while inducing callus formation. The effect of this auxin on protein synthesis and phosphorylation of the embryonic tissues was explored. Total cytoplasmic proteins were analysed for14C or32P incorporation into trichloroacetic acid precipitable material. MCPP significantly stimulated protein synthesis as well as protein phosphorylation. The protein synthesis pattern was highly altered in the presence of MCPP as analysed by two‐dimensional gel electrophoresis. Analyses by Sephadex G‐100 chromatography and by two‐dimensional gel electrophoresis of phosphorylated proteins indicate that the effect of MCPP on protein phosphorylation was only quantitative.
Free and conjugated gibberellins in dormancy and germination of apple seeds
Authors: Halińska Anna , Lewak St. , Domestica Malus
Published: February 2008

Halińska, A. and Lewak, St. 1987. Free and conjugated gibberellins in dormancy and germination of apple seeds.

The presence of gibberellin A4 (GA4) was confirmed in partly stratified seeds of apple (Malus domestica Borb., cv. Antonówka) by mass spectrometry of the methyl ester. Levels of free and conjugated gibberellins A4+7 and A9 changed during drying of mature seeds, during cold and warm stratification, as well as during germination of dormant and non‐dormant embryos. The temporary rise in GA4+7 during cold stratification and during the culture of dormant embryos as well as the lack of it under conditions of warm stratification, allowed us to postulate a role for GA4+7 in the removal of dormancy. In addition, GA9 was absent in dormant embryos and increased during cold stratification and during the culture of non‐dormant embryos. This suggests the involvement of GA9, in induction of normal development of the seedling. The equivalence between changes in free and conjugated GAs suggests that formation and hydrolysis of conjugates are involved in the control of the physiologically active levels of free GA4+7 and GA9.
Embryonal dormancy in apple seeds is controlled by free and conjugated gibberellin levels in the embryonic axis and cotyledons
Authors: Halinska Anna , Siriska Irena , Lewak St.
Published: February 2008

Halińska, A., Sińska, I. and Lewak, St. 1987. Embryonal dormancy in apple seeds is controlled by free and conjugated gibberellin levels in the embryonic axis and cotyledons.

Free and conjugated gibberellins (GAs) A4+7 and A9 were determined in embryonic axes and in cotyledons of seeds of apple (Malus domestica Borb., cv. Antonó wka) during breaking of dormancy under cold stratification. In both organs, the maximum level of free GA4+7 was found at day 30 of stratification, but the concentration was 700 times higher in axes than in cotyledons. Comparison of changes in free and conjugated GA4+7 levels during stratification allow us to suggest that the accumulation of free hormone in axes is, at the most, to 40% due to release from conjugates already present in the axis; that maximally 20% is derived from hydrolysis of cotyledonary conjugates translocated to axes; and that at least 40% originate from the novo biosynthesis of the hormone. Free and conjugated GA9 levels were similarly altered in axes and in cotyledons, markedly increasing at the end of afterripening. Both release of the free hormone from conjugates and biosynthesis of GA9, appeared to be involved in that increase; no translocation of free or bound GA9, between axes and cotyledons was demonstrated.
Isolation and characterization of an amyloplast envelope‐enriched fraction from immature maize endosperm
Authors: Gardner H. W. , Miernyk J. A. , Christianson D. D. , Khoo U.
Published: February 2008

Gardner, H. W., Miernyk, J. A., Christianson, D. D. and Khoo, U. 1987. Isolation and characterization of an amyloplast envelope‐enriched fraction from immature maize endosperm.

A 10000–100000 g pellet obtained by centrifugation of homogenates from immature (25 days after pollination) de‐embryonated maize (Zea mays L., cv. W64A‐normal and a typical hybrid) kernels was further fractionated by sedimentation on discontinuous sucrose density gradients. Particles with the highest carotenoid content (0.68% by weight carotenoids based upon total lipid) sedimented at densities of 1.083‐1.106 g ml‐1, coincident with the plastid envelope marker enzyme, galacto‐syltransferase (EC 2.4.1.46). Lipids extracted from the carotenoid‐rich fraction were mainly digalactosyldiacylglycerols, monogalactosyldiacylglycerols, phosphatidylcholines, phosphatidylinositols and phosphatidylglycerols, in order of molar abundance. With increasing particle density (>1.106 g ml1) the phospholipid and neutral lipid content increased, and the proportion of carotenoids and galactolipids decreased. Electron micrographs of the carotenoid‐rich fraction revealed vesicles ranging in size from < 0.1 to 0.5 um, as well as smaller granular membranes. The carotenoid‐rich membrane fraction was progressively more difficult to isolate as the endosperm matured, and freezing the immature endosperm prevented subsequent isolation. The lipid and enzyme composition and ultrastructural characteristics of the isolated fraction suggest that it is composed of amyloplast envelope vesicles.
Membrane phospholipid catabolism and Ca2+ activity in control of senescence
Authors: Leshem Ya'acov Y.
Published: February 2008

Leshem, Y. Y. 1987. Membrane phospholipid catabolism and Ca2+ activity in control of senescence.

A key role in the regulation of plant development and senescence appears to be a finely balanced equilibrium between membrane phospholipid catabolism on the one hand, and synthesis and remodelling on the other. In the catabolic “phosphatidyl‐linoleyl(‐enyl) cascade”, entering of Ca2+ into the cytosol triggers the catabolic process by binding to calmodulin and activating phospholipase A2, (EC 3.1.1.4). The latter proceeds to release linoleic or linolenic acid from the sn‐2 (stereospecific numbering) location of intact phospholipid, thus providing substrate for lipoxygenase (EC 1.13.11.12). The action of lipoxygenase then generates a series of oxy‐free radicals, ethylene, endogenous Ca2+ ionophores, malondialdehyde and jasmonic acid. These may recycle to the membrane, causing the entry of more Ca2+ and induction of a further, identical catabolic cycle. With increased cycling, membranes become progressively senescent and undergo biophysical changes altering microviscosity, fluidity, phase configurations of membrane phospholipids and transition temperatures. The cascade does not appear to be specific for the phospholipid substrate, and it is envisaged that besides phospholipase A2, both phospholipase B (EC 3.1.1.5) and lipolytic acylhydrolase could participate in the process.

A parallel process counteracting the above, is membrane remodelling and turnover, proceeding initially by the same Ca2+‐ and possibly calmodulin‐triggering, but leading via phospholipase C (EC 3.1.4.10) action and diacylglycerol formation to protein kinase activation and proton pump recharging. It is speculated that auxin and cytoki‐nin, albeit by different pathways, induce this route, for which membrane phospho‐inositides may be the preferred membrane‐associated phospholipid substrate.
The light‐harvesting and protective functions of carotenoids in photosynthetic membranes
Authors: Siefermann‐Harms Dorothea
Published: February 2008

Siefermann‐Harms, D. 1987. The light‐harvesting and protective functions of carotenoids in photosynthetic membranes.
Calcium messenger system: Role of protein phosphorylation and inositol bisphospholipids
Authors: Poovaiah B. W. , Reddy A. S. N. , McFadden J. J.
Published: February 2008

Poovaiah, B. W., Reddy, A. S. N. and McFadden, J. J. 1987. Calcium messenger system: Role of protein phosphorylation and inositol bisphospholipids.
Phosphatidylinositol kinases as regulators of GA‐stimulated α‐amylase secretion in barley (Hordeum vulgare)
Authors: Villasuso Ana Laura , Racagni Graciela E. , Machado Estela E.
Published: February 2008

Phosphorylated derivatives of phosphatidylinositol, in association with phosphatidylinositol 3‐kinase (PI3 kinase, EC 2.7.1.137) and phosphatidylinositol 4‐kinase (PI4 kinase, EC 2.7.1.67), play a key role in regulation of fundamental cell processes. We present evidence for a relationship between α‐amylase (EC 3.2.1.1) secretion regulated by GA and levels of phosphatidylinositol 3‐phosphate and phosphatidylinositol 4‐phosphate (PtdIns(4)P) in barley (Hordeum vulgare). Microsomal membranes were incubated in the presence of [γ‐32P]ATP, and radiolabeled membrane lipids were extracted and separated by TLC using a boric acid system. Treatment of aleurone layers with GA for short or long periods of time increased PI4 kinase activity. To evaluate the effect of PtdIns(4)P levels on GA signaling, we used phenylarsine oxide (PAO), an inhibitor of PI4 kinase activity. PAO reversibly reduced the α‐amylase secretion and protoplast cell vacuolation in a dose‐dependent manner. Wortmannin showed a similar inhibitory effect on α‐amylase secretion and PI4 kinase activity. GA evoked only a long‐term increase in PI3 kinase activity, which was also affected by PAO. The effect of PAO was suppressed by the reducing agent 2,3‐dimercapto‐1‐propanol (BAL), leading to restoration of secretion, vacuolation and PI4 kinase activity. In contrast, the effect of PAO on PI3 kinase activity was not abolished by BAL, suggesting that PI3 kinase is not involved in the secretion process. Likewise, the compound LY294002 inhibited PI3 kinase but had no effect on the secretion process. These findings indicate that PI4 kinase acts as a positive regulator of early GA signaling in aleurone.
Cellular distribution of ACT domain repeat protein 9, a nuclear localizing protein, in rice (Oryza sativa)
Authors: Kudo Toru , Kawai Akiko , Yamaya Tomoyuki , Hayakawa Toshihiko
Published: February 2008

Regulatory ACT domains serve as amino acid‐binding sites in certain amino acid metabolic enzymes and transcriptional regulators in bacteria. The ACT domain repeat protein (ACR) family in plants is primarily composed of four copies of the domain homologous to those of the bacteria Gln sensor GLND. In the current study, to evaluate the possible involvement of the protein OsACR9 in the Gln‐sensing system related to nitrogen (N) metabolism in rice (Oryza sativa L.), subcellular localization of OsACR9 and its accumulation and cellular distribution in various rice organs were examined by transient expression analysis and immunological methods using a monospecific antibody, respectively. Transient expression analysis of OsACR9 fused with a synthetic green fluorescent protein in cultured rice cells suggested nuclear localization of OsACR9. In rice roots, OsACR9 protein was distributed in epidermis, exodermis, sclerenchyma and vascular parenchyma cells, and its accumulation markedly increased after supply of NH+4. In rice leaf samples, OsACR9 protein was abundant in the vascular parenchyma and mestome‐sheath cells of young leaf blades at the early stage of development and in the vascular parenchyma and phloem‐companion cells of mature leaf sheaths. OsACR9 protein also showed a high level of accumulation in vascular parenchyma cells of dorsal vascular bundles and aleurone cells in young rice grains at the early stage of ripening. The possibility of the nuclear protein OsACR9 acting as a Gln sensor in rice is subsequently discussed through comparison of its spatiotemporal expression with that of Gln‐responsive N‐assimilatory genes.
Dependence of nitrate‐induced oxalate accumulation on nitrate reduction in rice leaves
Authors: Tian Hua , Jiang Linrong , Liu Ee , Zhang Jianjun , Liu Fang , Peng Xinxiang
Published: February 2008

Oxalate, a common constituent in many plants, is known to play important functional roles in plants. However, excess levels of oxalate in edible parts of plants adversely affect their quality as food. Understanding the regulatory mechanism in plants, particularly in food crops, is of both scientific and practical significance. While a number of studies have shown that nitrate can efficiently induce oxalate accumulation in plants, how it elicits such an effect is not well understood. This study aimed to gain a further insight into the mechanism underlying the nitrate‐induced oxalate accumulation. Nitrate‐N efficiently caused oxalate accumulation in rice leaves, depending on the nitrate concentrations and treatment time. In contrast, same nitrogen molar levels of the other N forms such as nitrite, ammonium, glutamate and urea either had no effect on the accumulation or even reduced the oxalate level. When glutamate, glutamine, asparate and asparagine were added into the nutrient solution that already contained saturating concentration of nitrate, both oxalate levels and NR activity were correspondingly decreased. In all of these modes of treatment, the change in NR activity was positively paralleled to that in oxalate levels. For a further confirmation, we generated the transgenic rice plants with a NR interference gene introduced. The result further demonstrated that in the transgenic plants, unlike in wild‐type plants, oxalate was no longer able to accumulate in response to the nitrate treatment even though the endogenous nitrate levels were substantially elevated. Taken together, our results suggest that the nitrate‐induced oxalate accumulation in rice leaves is dependent on the NR‐catalyzed nitrate reduction, rather than on nitrate itself or nitrite reduction or its downstream metabolites.
Increasing productivity accelerates host–parasite coevolution
Authors: D. C. LOPEZ‐PASCUA L. , BUCKLING A.
Published: February 2008

Host–parasite coevolution is believed to influence a range of evolutionary and ecological processes, including population dynamics, evolution of diversity, sexual reproduction and parasite virulence. The impact of coevolution on these processes will depend on its rate, which is likely to be affected by the energy flowing through an ecosystem, or productivity. We addressed how productivity affected rates of coevolution during a coevolutionary arms race between experimental populations of bacteria and their parasitic viruses (phages). As hypothesized, the rate of coevolution between bacterial resistance and phage infectivity increased with increased productivity. This relationship can in part be explained by reduced competitiveness of resistant bacteria in low compared with high productivity environments, leading to weaker selection for resistance in the former. The data further suggest that variation in productivity can generate variation in selection for resistance across landscapes, a result that is crucial to the geographic mosaic theory of coevolution.
Unequal allelic frequencies at the self‐incompatibility locus within local populations of Prunus avium L.: an effect of population structure?
Authors: STOECKEL S. , CASTRIC V. , MARIETTE S. , VEKEMANS X.
Published: February 2008

In this paper, we investigated the genetic structure and distribution of allelic frequencies at the gametophytic self‐incompatibility locus in three populations of Prunus avium L. In line with theoretical predictions under balancing selection, genetic structure at the self‐incompatibility locus was almost three times lower than at seven unlinked microsatellites. Furthermore, we found that S‐allele frequencies in wild cherry populations departed significantly from the expected isoplethic distribution towards which balancing selection is expected to drive allelic frequencies (i.e. identical frequency equal to the inverse of the number of alleles in the population). To assess whether this departure could be caused either by drift alone or by population structure, we used numerical simulations to compare our observations with allelic frequency distributions expected : (1) within a single deme from a subdivided population with various levels of differentiation; and (2) within a finite panmictic population with identical allelic diversity. We also investigated the effects of sample size and degree of population structure on tests of departure from isoplethic equilibrium. Overall, our results showed that the observed allele frequency distributions were consistent with a model of subdivided population with demes linked by moderate migration rate.
Testing Allsop and West’s size at sex change invariant within a fish species: a spurious ratio or a useful group descriptor?
Authors: LINDE M. , PALMER M.
Published: February 2008

Recently, it has been suggested that sequential hermaphrodites, from a variety of taxa and a wide range of sizes, change sex at the same relative size. It is said that there exists an invariant (a constant ratio) for such a life trait. However, recent criticisms point out that these results could be a statistical artefact. It has been argued that the wider the range ofx‐axis values (from 2 mm to 1.5 m in the case of sex change), the higher the probability of identifying an invariant by chance. Here, the invariance of the size at sex change ratio is analysed within a single fish species for which the size of sex change varies within a range of only 6.5 cm. Our results support the invariant rule that fishes change sex when reaching 79% of their maximum size.
Pathogenicity of Fusarium verticillioides and Fusarium oxysporum on Pinus nigra seedlings in northwest Spain
Authors: Martín‐Pinto P. , Pajares J. , Díez J.
Published: February 2008

Fusarium verticillioides may be responsible for causing significant damping‐off damage similar to that incited by F. oxysporum on forest seedlings, resulting in considerable losses in nurseries in northwest of Spain. Traditionally, F. oxysporum has been considered the most important agent of this disease in Spanish forest nurseries. However, recent studies have showed that F. verticillioides also has been frequently isolated from diseased plants. This has increased the necessity for a more comprehensive knowledge of the behaviour and pathogenicity of both Fusarium spp. isolated from these sites. The effect of Fusarium spp. on seed germination and on seedling mortality was analysed by inoculating the fungus at seeding. The in vitro growth of the two species was studied and is discussed in relation to in vivo virulence. Both species caused a reduction in seed germination and an increase in seedling mortality. Mortality caused by F. verticillioides treatments occurred sooner than that for F. oxysporum and the growth rate of F. verticillioides was also greater.