bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of Picea rubens seedlings to intermittent mist varying in acidity, and in concentrations of sulfur‐, and nitrogen‐containing pollutants
Authors: Jacobson Jay S. , Bethard Twylene , Heller Laurence I. , Lassoie James P.
Published: May 2006

Two‐year‐old red spruce seedlings (Picea rubens Sarg.) growing in. field chambers were repeatedly exposed to acidic mist with a factorial combination of 3 fluctuating levels of acidity: median pH values of 3.0 (range of 2.5 to 3.5), 3.5 (range of 3.0 to 4.0), and 4.0 (range of 3.5 to 4.5). and 3 ion compositions: sulfate. nitrate and ammonium, and a combination of all 3 ions. The experiment was performed during the growing season over a period of 3.5 months. Mist exposures were intermittent with 5 wet‐dry cycles for each 16‐h overnight exposure period, Foliar necrosis occurred on seedlings treated with the most acidic mist and was most severe when the mist contained sulfate. At a median pH of 3.5, a value close to that of cloud water occurring in the eastern United States, injury developed with sulfuric acid mist, but not. when the mist contained nitric acid. The combination of high acidity and sulfate significantly decreased volume of aboveground tissues, while high acidity and nitrate increased volume. Root and needle dry weights were not affected. However, high acidity of mist was associated with increased leader shoot length. These results indicate, that there is a risk of foliar injury and changes in growth of red spruce with cloud water at a median acidity of pH 3.5 or below, especially when there are high concentrations of sulfate and low concentrations of nitrate.
Hypersensitive lignification response as the mechanism of non‐host resistance of wheat against oat crown rust
Authors: Moerschbacher Bruno M. , Noll Ulrike , Ocampo Carlos A. , Flott Berenike E. , Gotthardt Uwe , Wüslefeld Andreas , Reisener Hans‐Joachim
Published: May 2006

Seven‐day‐old seedlings of the near‐isogenic wheat (Triticum aestivum L.) lines Prelude and Prelude‐Sr5, susceptible and resistant to wheat stem rust, respectively, were inoculated with uredospores of the oat crown rust fungus Puccinia coronata Cda. f. sp. avenae Fraser & Led. Fluorescence microscopy revealed that the majority of colonies developed intercellular infection structures including haustorial mother cells and haustoria after penetration of wheat mesophyll cells. All penetrated cells became necrotic, and exhibited bright yellow autofluorescence. This autofluorescence was not extractable with alkali, and fluorescent cells stained positively with phloroglucinol/HCI, suggesting that hypersensitive cell death was correlated with cellular lignification. Accordingly, the lignin biosynthetic enzymes phenylalanine ammonia‐lyase (EC4.3.1.5). 4‐coumarate:CoA ligase (EC6.2.1.12), cinnamyl‐alcohol dehydrogenase (EC1.1.1.149), and peroxidases (EC1.11.1.7) increased in activity during the expression of resistance. The induced pattern of peroxidase iso/ymes closely resembled that observed for highly incompatible wheat/wheat stem rust interactions. Furthermore, an elieitor was extracted from oat crown rust germlings. which induces lignification when injected into the intercellular space of wheat leaves. This elieitor appears to be functionally similar to that isolated from wheat stem rust germlings. The results suggest that the non‐host resistance of wheat to the xenopara‐site oat crown rust closely resembles the race/cullivar‐speeific resistant mechanism of highly resistant wheat varieties to wheat stem rust.
Diel patterns of CO2 exchange for epiphytic cacti differing in succulence
Authors: Nobel Park S. , Hartsock Terry L.
Published: May 2006

Net CO: uptake over 24‐h periods was examined for 6 species of epiphytic cacti. which as a group number about 120 species that vary considerably in stem succulence. Nocturnal CO, uptake as a percentage of the total daily CO, uptake increased from 0% for Rhipsalis houlletiana to 14% for Epipliyl/urn pittieri to 21% for E. oxypetnluin to 51% for R. rhornbea to 87% for Schlumbergera truncata to 98% for Cryplocercus anthonyamis. For R. houlletiana and S. truncata, maximum net CO, uptake occurred at a photosynthetically active radiation of only 200 μmol m−2 s−1, as is typical for shade plants. Short‐term drought of R. rhombea caused a shift favoring nocturnal CO, uptake. For the 6 species examined, increased reliance on nocturnal CO, uptake characteristic of Crassulacean acid metabolism (CAM) was closely correlated with increases in stem thickness, fresh weight per unit area, water mass per unit area, and to a somewhat lesser extent with another measure of succulence, water mass per unit mass of chlorophyll.
Temperature dependent reduction of protochlorophyllide in darkness followed by the assembly of active photosystems in pigment mutant C‐2A’ of Scenedesmus obliquus
Authors: Kotzabasis Kiriakos , Römer Susanne , Senger Horst
Published: May 2006

In the wild type of Scenedesmus obliquus strain D3 grown heterotrophically, the chlorophyll biosynthesis and thus the reduction of protochlorophyllide to chlorophyllide takes place in darkness. However, in pigment mutant C‐2A’ of Scenedesmus obliquus only traces of protochlorophyllide are reduced under optimal growth conditions in darkness. By lowering the growth temperature from 33° to 15–25°C, protochlorophyllide can be reduced in darkness. At 20°C this process is about 10 times more active than at 33°C, but reaches only about 13% of the light‐dependent chlorophyll biosynthesis. The chlorophylls synthesized at the lower temperatures are inserted into the pigment‐protein complexes and photosystem I as well as photosys‐tem II capacities are developed. The rate of light‐independent protochlorophyllide reduction at lower temperatures is not limited by the enzyme PChlide‐oxidoreductase itself, but rather by its substrate, being in turn limited by the amount of 5‐amino levulinic acid (ALA) available.
Plant growth retardants as tools in physiological research
Authors: Grossmann Klaus
Published: May 2006

Besides being applied in agriculture and horticulture, the new types of plant growth retardants from norbornanodiazetine, triazole, pyrimidine, 4‐pyridine and imidazole structure are increasingly used in physiological research. As inhibitors of special cytochrome P‐450 dependent monooxygenases they allow valuable insights in the regulation of terpenoid metabolism concerning phytohormones and sterols, thus showing relations to cell division, cell elongation and senescence.
Seasonal changes in stomatal responses of sweet cherry and plum to water status in detached leaves
Authors: Yoon Tae Myung , Richter Hanno
Published: May 2006

Seasonal changes in the relationship between stomatal responses and water potential components in detached leaves of sweet cherry (Prunus avium L. cv. Bigarreau Morreau) and plum (Prunus domestica L. cv. Queen Victoria) were examined by the simultaneous measurement of stomatal conductance and water relation parameters derived from pressure‐volume curves. The water potential threshold for stomatal closure in sweet cherry leaves throughout the season and in plum leaves until mid‐July varied nearly in parallel with changes in the osmotic potential at the turgor loss point. From August onward, closing reactions of plum stomata had no relationship to the turgor loss point. Stomata of sweet cherry leaves opened more widely and showed slower reactions to dehydration early in the season than later. Seasonal changes of stomatal conductance and stomatal responses to dehydration in both species seem thus to be influenced by fruit development and ripening.
A rooting inhibitor present in Norway spruce seedlings grown at high irradiance ‐ a putative cytokinin
Authors: Bollmark Marie , Eliasson Lennart
Published: May 2006

Cuttings from seedlings of Picea abies L. (Karst.) grown under high light (HL). rooted slowly and incompletely, whereas rooting in cuttings from seedlings grown under low light (LL) was rapid and almost complete. Immunoaffinity chromatograpriy (IAC) with antibodies against isopentenyl adenosine ([9‐RIiP) and trans‐zeatin riboside (I9R]Z) was used to isolate cytokinin‐like compounds from extracts of the cuttings. These compounds were separated by HPLC and quantified with a UV‐detector. [9R]iP‐type and [9R]Z‐type compounds were also quantified using an enzyme immunoassay (ELISA). Levels of both [9R]iP‐type and [9R]Z‐type cytokinins were considerably higher in seedlings grown under HL than in those grown under LL. An unidentified compound (X), occurring in high amounts in the hypocotyls of HL seedlings and isolated by IAC and HPLC, inhibited rooting in cuttings from LL seedlings. Compound X was metabolised during the rooting period. Although X was retained on the imnimmoaffinity column, it did not bind to the antibodies to the degree necessary to allow quantification by ELISA. Treatment with acid phosphatase (EC 3.1.3.2) and β‐glucosidase (EC 3.2.1.21) converted X into other unknown compounds. Some of these cross‐ieacted with [9R)iP antibodies in ELISA.
Ethylene accelerates the breakdown of cytokinins and thereby stimulates rooting in Norway spruce hypocotyl cuttings
Authors: Bollmark Marie , Eliasson Lennart
Published: May 2006

Cuttings were taken from 4‐week‐old seedlings of Norway spruce (Picea abies L. Karst.) raised at two different irradiation levels. Rooting experiments showed that root formation was increased by the ethylene formed by adding 1‐aminocyclopropane‐1‐carboxylic acid ACC or Ethrel, especially in the slowly rooting cuttings grown under high light (HL). Cobaltousion. an ethylene synthesis inhibitor, delayed rooting, especially in the easily rooted cuttings grown under low light (LL).

Compounds isolated from the cuttings using immunoaffinity chromatography, on a column with antibodies against cytokinins, and separated by HPLC decreased in amount during the first week of the rooting period. An increase in ethylene production accelerated this process, especially in cuttings grown under HL, whereas cobaltous ion delayed it. We suggest that ethylene stimulates rooting by enhancing the degradation of cytokinins.
Identification of indole‐3‐acetaldehyde and indole‐3‐acetaldehyde reductase in Chinese cabbage
Authors: Ludwig‐Müller Jutta , Hilgenberg Willy
Published: May 2006

Indole‐3‐acetaldehyde (IAAId) was identified as a natural compound in Chinese cabbage (Brassica campestris L. ssp. pekinensis cv. Granat) seedlings by chemical conversion to indole‐3‐acetaldoxime (1AOX) followed by mass spectroscopy. The lAAId reductase (EC 1.2. 3.1), an enzyme with a molecular mass of 32 kDa, was extracted, purified 5‐fold and characterized. The enzymatic IAAld reduction showed a pH optimum at 6–7 and a marked preference for NADPH as cofactor The Km value for IAAld was 125 μM, for NADPH 36 μM. The enzyme reaction was inhibited at high NADPH concentrations (>200 μM) and modulated by IAA and indole‐3‐ethanol (IEt). Sulfhydryl reagents inhibited IEt formation, suggesting the participation of SH‐groups in the reaction. Phenylacetaldehyde and benzaldehyde were competitive substrates, while acetaldehyde acted partly as an inhibitor, and partly as an activator on the IAAld reduction. IAAld reductase activity was also detected in other Brassica species. The importance of this enzyme is discussed with respect to the possibilities of IAA biosynthesis in the Brassicaceae.
Role of growth regulators in the senescence of Arabidopsis thaliana leaves
Authors: Zacarias Lorenzo , Reid Michael S.
Published: May 2006

A homozygous, dominant, C2H4‐resistant line of Arabidopsis thaliana (L.) Heynh (cv. Columbia; er) was selected from ethylmethylsulfonate‐mutagenized seed, and used to test the role of C2H4 and other growth regulators in senescence of mature leaves. Chlorophyll (Chl) loss from disks excised from leaves of er was much slower than that from wild‐type (WT) disks, whether they were held in the light or in the dark. C2H4 accelerated Che loss from WT disks but had no effect on the yellowing of mutant disks. C2H4 biosynthesis was higher in disks from the mutant plants, particularly in the light. In the dark, treatment with the cytokinin, 6‐benzyladenine (BA), reduced Chl loss from wild‐type disks, but had no effect on mutant disks. In the light, BA treatment stimulated chlorophyll breakdown in both wild type and mutant disks. Treatment with abscisic acid (ABA) stimulated chlorophyll loss in wild‐type and mutant disks, whether they were held in the light or the dark. C2H4 production was stimulated in ABA‐treated disks, but they still yellowed even when C2H4 production was inhibited by application of aminooxyacetic acid (AOA). These data indicate that C2H4 is only one of the factors involved in leaf senescence, and that the promotion of senescence by ABA is not mediated through its stimulation of C2H4 production.
Changes in chloroplast peroxidase activities in relation to chlorophyll loss in barley leaf segments
Authors: Kuroda Molonaka , Oaiawa Tetsuo , Imagawa Hiroshi
Published: May 2006

Total peroxidase activity increased during senescence of excised barley (Hordeum vulgare L. cv. Kashimamugi) leaves. Kinetin treatment furter increased total peroxidase activity but repressed chlorophyll degradation in excised barley leaves. When isoperoxidases were extracted from barley leaf segments. 4 cationic and 4 anionic isozymes were found in polyacrylamide gel electrophorests during leaf senescence. The chloroplasts contained only two cationic isoperoxidase activities. One (designated C4) was repressed by kinetin. and the other (C3) was increased by kinetin. Glucosamine, which also repressed the degradation of chlorophyll, completely repressed C4 activity but did not affect C3 activity. The induction with senescence, and the repression with kinetin and glucosamine, suggest chat chloroplast isoperoxidase C4 may function as a chlorophyll‐degrading enzyme during barley leaf senescence.
Thigmotropism and the modulation of tropistic curvature by mechanical perturbation in cucumber hypocotyls
Authors: Takahashi Hideyuki , Jaffe Mordecai J.
Published: May 2006

Mechanical perturbation (MP) applied unilaterally to cucumber (Cucumis sativus L.) hypocotyls induced thigmotropic curvature toward the stimulus. Gravitropic or phototropic curvature of the hypocotyl was inhibited by symmetrical application of MP to both sides of the hypocotyl. When both MP and IAA were unilaterally applied simultaneously to the same side, the hypocotyls always bent toward the MP stimulus, as in thigmotropism alone. Thus, the exogenous IAA did not control the direction of curvature. Aminoethoxyvinyl glycine (AVG) blocked thigmotropism as well as gravitropism and phototropism, but promoted IAA‐induced curvature. MP‐stimulated ethylene evolution peaked about 4 h after MP, followed by a peak of thigmotropic curvature. For all tropisms more ethylene evolved from the stimulated side than from the other side of the hypocotyls. MP‐induced ethylene acting as a growth inhibitor, auxin‐transport inhibitor, and/or modulator of tissue sensitivity to auxin, may be involved in thigmotropism and MP‐induced inhibition of various tropisms. Ethylene produced as a result of MP was not affected by the removal of cotyledons. This MP‐induced ethylene was additive to that of phototropically or gravitropically stimulated ethylene.
Composition of the cell walls of different asparagus (Asparagus officinalis) tissues
Authors: Waldron Keith W. , Selvendran Robert R.
Published: May 2006

Portions of stems from the base of asparagus spears (Asparagus officinalis L. cv. Connovor Collossus) were dissected to give the following tissues: (1) pith, which was free of vascular bundles, (2) two surrounding layers, parenchyma and fibre I and II (PFI and PFII), containing parenchyma and vascular bundles, (3) sclerenchyma sheath, (4) epidermis and sub‐epidermal layers and (5) asparagus vascular fibre (AVF). The alcohol‐insoluble residues (AIRs) from these tissues were shown to be free of starch. They were analysed for moisture and protein, and the component sugars were released by two hydrolytic procedures, which helped to distinguish the sugars from non‐cellulosic polysaccharides and cellulose. The AIRs from pith and epidermal tissues were relatively low in xylose, but were rich in cellulosic glucose, and sugars associated with pectic polysaccharides such as galacturonic acid, galactose and arabinose. Their major component polysaccharides (in decreasing amounts) were inferred to be pectic polysaccharides, cellulose, and hemicelluloses. AIR from sclerenchyma was rich in glucose and xylose, suggesting the presence of much cellulose and (acidic) xylans. The AIRs of PFI, PFII and AVF contained significant amounts of xylose in addition tn other sugars, and the major polysaccharides inferred to be present were pectic polysaccharides, cellulose and hemicelluloses, a significant proportion of which may be acidic xylans. Methylation analysis of the AIRs confirmed the above inferences. The bulk of the glucosyl residues were (1–4)‐linked, and there were small but significant amounts of (1–4, 6)‐linked glucosyl residues (the linkage characteristic of xyloglucans) in all the preparations. The presence of (1–4)‐linked galactosyl, (1–5)‐linked arabinosyl, terminal galactosyl, terminal arabinosyl, (1–2)‐ and (1–2, 4)‐linked rhamnosyl residues in all the AIRs except that from sclerenchyma, confirmed the presence of significant levels of pectic polysaccharides in all the parenchyma tissues. All the preparations containing vascular tissues contained significant amounts of (1–4)‐linked xylosyl residues, probably derived from acidic xylans. Even in the AIR of pith, a significant amount of (1–4)‐linked xylosyl residues were detected. This may be due to the ability of these cells and the parenchyma cells associated with the vascular bundles, to undergo lignification in mature asparagus plants.
Effect of maturation and storage on asparagus (Asparagus officinalis) cell wall composition
Authors: Waldron Keith W. , Selvendran Robert R.
Published: May 2006

Changes in the cell wall composition of stems of asparagus (Asparagus officinalis L. cv. Connovor Collossus) during maturation and during storage in modified atmospheres were investigated. Alcohol‐insoluble residues from portions of stems were analysed for changes in alkali‐soluble phenolics and in the constituent sugars and their glycosidic linkages. Maturation‐related changes down the stem involved increased levels of (l–4)‐linked xylosyl residues from xylans, cellulose and phenolics, which arise from the lignified vascular and sclerenchyma tissues, and a decrease in the levels of (l–5)‐linked arabinosyl residues from pectic arabinans from the parenchy‐matous tissues. Storage under aerobic conditions permitted stem elongation in the apical sections and secondary thickening in the basal sections. This was due to continued tissue maturation. Storage under anaerobic conditions inhibited such changes. In accordance with these effects of storage on stem physiology, maturation‐related changes in cell wall components were enhanced by storage only under aerobic conditions. However, levels of (1–4)‐linked galactosyl residues which remained relatively constant during maturation, decreased substantially (ca 50%) in all stem sections during both aerobic and anaerobic storage.
Indole‐3‐acetic acid uptake in isolated protoplasts of the moss Funaria hygrometrica
Authors: Geier Ulrike , Werner Olaf , Bopp Martin
Published: May 2006

Protoplasts of the moss Funaria hygrometrica Hedw were used to study the mechanism of Indole‐3‐acetic acid (IAA) accumulation. Three main components appeared to be involved.

1. The pH gradient between plasma and outer medium is the basis for an anion trap. The protonophores carbonylcyanide m‐chlorophenylhydrazone (CCCP) and carbonylcyanide p–trifluoromethoxyphenylhydrazone (FCCP) reduce IAA accumulation by destruction of the pH gradient.

2 An intact efflux carrier could be demonstrated by an increase of IAA accumulation with the efflux inhibitors 2,3,5–trüodo‐benzoic acid (TIBA) and 1‐naphthy‐phthalamic acid (NPA). In efflux experiments, reduction of IAA efflux by the two inhibitors was directly demonstrated.

3. The existence of an influx carrier was concluded from the strong stimulation of IAA accumulation by calcium in calcium‐deprived protoplasts. It is postulated that this carrier system transports IAA anions, protons and Ca2+. A computer simulation of the accumulation process with the three components, including internal IAA concentration determined by enzyme‐linked immunosorbent assay (ELISA), gave a highly accurate description of the data measured in the different experiments.
Diurnal changes in phosphoenolpyruvate carboxylase and pyruvate, orthophosphate dikinase properties in the natural environment: interplay of light and temperature in a C4 thermophile
Authors: Gramnaatikopoulos George , Manetas Yiannis
Published: May 2006

Activities of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured in leaf extracts of field grown Amaranthus paniculatus L. (C4) during a natural diurnal irradiance and temperature pattern. Enzyme assays were run at both fixed (30°C) and the corresponding leaf temperature at the time of harvest. Light activation of PEP carboxylase (PEPCase) at fixed assay temperatures was expressed as a decrease in S0–5 (PEP) after a threshold (> 330 μmol m–2 s–1) photon fluence rate was surpassed at noon. Earlier in the morning, increase in apparent enzyme affinity for PEP was observed when the assay was run at leaf temperature, indicating a physiologically meaningfull effect of temperature on S0.5 (PEP). The 3.3‐fold increase in PEPCase activity at low PEP and fixed assay temperature between the minimal and maximal irradiance and temperature hours of the day, became 12.8‐, 11.5‐ and 7.4‐fold when assays were run at the corresponding leaf temperature during three diurnal cycles with respective temperature differences (max minus min) of 9.0, 8.3 and 7.4°C. The extent of malate inhibition was the same for both day and night forms of PEPCase assayed at 35°C, but increased considerably with night enzyme at 25°C. The results indicate that light increases the apparent affinity of PEPCase for PEP and that at lower temperatures malate becomes more inhibitory. Pyruvate orthophosphate dikinase activity started to increase immediately after sunrise and the 10‐fold increase at fixed temperature became 14.8‐, 14.2‐ and 13.1‐fold when assays were run at the above leaf temperatures. This indicates that the light effect predominates with pyruvate, orthophosphate dikinase, while with phosphoenolpyravate carboxylase, light and temperature co‐operate to increase the day enzyme activities.
Biochemical changes induced by accelerated aging in sunflower seeds. II. RNA populations and protein synthesis
Authors: Gidrol Xavier , Noubhani Abdelmajid , Pradet Alain
Published: May 2006

Sunflower seeds (Helianthus annuus L. cv Rodeo) slowly lose their viability when subjected to accelerated aging (42°C and 100% relative humidity). After 12 h imbibition, in vivo protein labelling profiles show dramatic changes as a function of accelerated aging. Total and poly(A+)‐RNA content of embryonic axes were similar regardless of the time spent in hot and wet conditions. However, the ability of mRNA to be translated in cell‐free system was largely reduced in acceleratedly aged seeds. In vitro protein synthesis revealed the observed changes to be largely quantitative rather than qualitative, and to result mainly from post‐transcriptional regulation. However, the induction of two proteins (15 and 43 kDa) subsequent to accelerated aging resulted from an increase in their corresponding mRNA, The accelerated aging treatment of sunflower seeds primarily induces quantitative changes in the translation of pre‐existing mRNA, rather than the production of new mRNA species.
Intact mesophyll protoplasts from Zea mays as a source of phosphoenolpyruvate carboxylase unaffected by extraction: Advantages and limitations
Authors: Petropoulou Y. , Manetas Y. , Gavalas N. A.
Published: May 2006

Isolated intact mesophyll protoplasts from Zea mays L. were used as an enzyme source for studying properties of phosphoenolpyruvate (PEP) carboxylase (EC 4.1 1 31) just after release from cells into the reaction medium. After the injection of protoplasts into the assay mixture, an initial lag of activity was observed, mainly due to the time necessary for complete disruption of protoplasts by the osmotic shock. The final specific activity obtained was ca 18 μmol mg‐1 of liberated protein min‐1, a value comparable to that usually achieved after arduous purification. Under the assay conditions employed, the chloroplasts were not disrupted and the retention of their proteins, together with the use of purified mesophyll protoplasts, were obviously the reasons for the high specific activity obtained. The activity and properties of phosphoenolpyruvate carboxylase stored in isolated protoplasts were stable for at least 24 h at 5°C. The main difference between the protoplast‐derived and the routinely extracted enzyme was the sensitivity to malate inhibition, which was partially lost in the extracted phosphoenolpyruvate carboxylase; no difference was found in the Km(PEP). The stress imposed by the protoplast isolation procedure diminished the sensitivity of the enzyme to malate inhibition, so that it can be inferred that the real malate sensitivity of pbosphocnolpyruvale carboxylase is even greater and that it is grossly underestimated with routinely extracted enzyme.
Altered protein synthesis during in situ oat leaf senescence
Authors: Lalonde Louise , Dhindsa Rajinder S.
Published: May 2006

Quantitative and qualitative changes in protein synthesis during in situ senescence of oat (Avena saliva L. cv. Victory) leaf have been examined. The rate of protein synthesis shows a transitory increase during early stages of senescence. This increase is not accompanied by a corresponding increase in amino acid uptake and is smaller when expressed on a dry weight rather than a protein basis. Total protein, total RNA and poly(A)+‐RNA decline rapidly during senescence. Analysis of protein populations with 2‐D SDS‐PAGE shows that while some proteins decline sharply during leaf senescence, the synthesis of several others is induced or enhanced. Synthesis of new proteins shown in this study may explain the reported requriement for protein synthesis in leaf senescence.
Effect of light quality (blue, red) and fluence rate on the synthesis of pigments and pigment‐proteins in maize and black pine mesophyll chloroplasts
Authors: Milivojević Dragica , Eskins Kenneth
Published: May 2006

Maize (Zea mays L. hybrid ZP‐704) and black pine (Pinus nigra Arn.) were grown for five days at low fluence rate (0.4–4.0, μmol m–2 s−1) in blue or red light. Compared to red light of the same fluence rate, blue light effects in maize were repressive for the accumulation of Chita, b, carotenoids and light‐harvesting complex‐2 (LHC‐2) proteins. The maximal reduction of proteins bound to the light‐harvesting complex of photosystem 2 and pigments was attained at different fluence rate levels. In black pine, blue light compared to the red of the same fluence rate level either activated or reduced accumulation of pigments and LHC proteins, the effect being dependent on its fluence rate level. At fluence less than 3.0 μmol m−2 s−1 blue light was more efficient for the synthesis of Chi a, b and carotenoids, hut for LHC‐2 complexes, fluence rates between 0.4 and 1.5 [μmol m−2 s−1 were more effective. In pine the effects of the two lights on the accumulation of pigments and LHC proteins were demonstrated separately and were dependent on fluence rate level. This suggests irradianoe‐controlled activation/deactivation of the photoreceptor at the level of the cell.
Characterization of a cell wall β‐galactosidase of Cicer arietinum epicotyls involved in cell wall autolysis
Authors: Dopico Berta , Nicolás Gregorio , Labrador Emilia
Published: May 2006

β‐Galactosidase (EC 3.2.1.23) has been established as the main enzyme involved in the autolytic process. The enzyme extracted from cell walls of epicotyls of Cicer arietinum L. cv. Castellana with 3 M LiCl is a 45 kDa protein composed of a single subunit, having an optimum pH of 4; an optimum temperature of 45°C and Km and Vmax of 1.72 mM and 18.5 nkat (mg protein)–1 respectively, as evaluated against p‐nitrophenyl‐β‐d‐galactopyranoside. The enzyme is inhibited by Hg2+, d‐galactono‐1,4‐lactone and galactose, substances that also inhibit the autolytic process. Ca2+ and EDTA, which do not affect the activity of the β‐gaiactosidase, do however modify the hydrolysis of the cell wall mediated by the enzyme, and they also inhibit the autolytic process. Ca2+ decreased both processes, whereas EDTA increased them; and when both substances were added together, their individual effects were neutralized. The effects of both agents is probably due to modifications in the cell wall that prevent access of the enzyme to its substrate.
Cell wall localization of the natural substrate of a β‐galactosidase, the main enzyme responsible for the autolytic process of Cicer arietinum epicotyl cell walls
Authors: Dopico Berta , Nicolos Gregário , Labrador Emilia
Published: May 2006

The Hw pectic fraction, extracted with hot water, is the major component of 4 days old epicotyl cell walls of Cicer arietinum L. cv. Castellana and is formed of arabinose and galactose, with smaller amounts of rhamnose, xylose, glucose and mannose. The cell wall 2βIII enzymatic fraction, with β‐galactosidase activity (EC 3.2.1.23) and the main enzyme responsible for the autolytic process, essentially acts on the Hw fraction, and is able to hydrolyze 560 μg of this fraction per g of epicotyls, releasing mainly galactose as monosaccharide.

The 2βIII fraction acts very weakly on the other polysaccharide fractions of the cell wall, both pectic and hemicellulosic, releasing 80, 60 and 14 μg per g of epicotyls from the fractions extracted with oxalate (Ox), KOH 10% (KI) and KOH 24% (KII), respectively. It can be concluded that the natural substrate of this enzyme is the Hw pectic fraction, probably an arabinogalactan that is found in the cell wall in isolated form or as side chains of the rhamnogalacturonan I.
Submergence tolerance of rice – A new glasshouse method for the experimental submergence of plants
Authors: Adkins S. W. , Shiraishi T. , McComb J. A.
Published: May 2006

A new method is described for evaluation of submergence tolerance of rice (Oryza sativa L.) plants. Responses of a range of cultivars corresponded with known differences in field performance. The method 1) allows fast and effective determination of submergence tolerance, 2) allows screening of many plants in a small glasshouse area, 3) provides for recovery of superior plants for seed collection, 4) allows manipulation of many environmental variables to mimic the natural submergence environment, and 5) uses simple, inexpensive, readily available equipment. Physiological studies performed with this method gave results similar to those obtained from field studies and showed that submergence tolerance increased in older plants; it decreased with increasing depth, increasing temperature and with high or low light levels. The system is ideal for the rapid evaluation of rice germplasm under controlled conditions and physiological studies on the mechanism of rice submergence tolerance.
Somaclonal variation in rice – Submergence tolerance and other agronomic characters
Authors: Adkins S. W. , Shiraishi T. , McComb J. A. , Ratanopol S. , Kupkanchanakul T. , Armstrong L. J. , Schultz A. L.
Published: May 2006

The ability to withstand complete submergence was studied in R2 seedlings raised by self‐pollination from 158 R1 plants regenerated from callus of mature rice seeds (cultivars FR13A and Calrose). Compared to parental controls, significant improvement in submergence tolerance as assessed by percentage survival, number of new leaves and chlorophyll content of the third leaf, was found in 5 of the 115 cv. FR13A somaclones and 3 of the 43 cv. Calrose somaclones tested using an aquarium system in a controlled‐temperature glasshouse. With some exceptions these improvements were also observed in the R3 generation when tested under field conditions in Thailand. Variation in other agronomically important characters was observed in the R2 plants grown in a temperature glasshouse under 2 contrasting environments.
Effects of sulphur dioxide on leaf photosynthesis: the role of temperature and humidity
Authors: Kropff M. J. , Smeets W. L. M. , Meijer E. M. J. , van der Zalm A. J. A. , Bakx E. J.
Published: May 2006

The effect of temperature and humidity on SO2–induced photosynthetic depression was determined in gas exchange experiments with leaves of Vicia faba, L. Stomatal behaviour was sensitive to humidity resulting in higher uptake rates of SO2 and stronger reductions of photosynthesis at low VPD (vapour pressure deficit). After a fumigation period of 2 h, when the photosynthetic rate had stabilized, photosynthesis of leaves exposed to SO2 at 8°C was reduced much more than at 18°C at the same rate of SO2 uptake. Data analysis with a mechanistic model revealed that this effect was due to the slower rate of S(IV) oxidation at lower temperatures, resulting in higher accumulation of S(IV) and thus stronger reduction of photosynthesis. These results were confirmed by experimental analyses of the S(IV) concentration in leaves following fumigation, which showed that more S(IV) accumulated in leaves exposed at a lower temperature. This may explain the high sensitivity of plants exposed to SO2 under winter conditions, when both VPD and temperature are low.
Engineered resistance against plant virus diseases
Authors: Nejidat Ali , Clark W. Gregg , Beachy Roger N.
Published: May 2006

The development of genetic engineering techniques has enabled the production of transgenic plants that are resistant to viral diseases. Expressing the coat protein (CP) gene of a virus in Iransgenic plants confers resistance against the virus from which the gene was isolated, and to other closely related strains and viruses. This approach has been demonstrated to be effective in conferring protection against viruses from different virus groups including alfalfa mosaic virus, cucumovirus. ilarvirus, potex‐virus, potyvirus, tobamovirus and tobravirus. The data available indicate that several factors may affect the efficiency of the protection obtained including the level of the CP in the transgenic plants, the plant in which the CP gene is expressed and enviromental conditions. These and other aspects of coat protein mediated resistance are discussed.
Recent progress on sperm characterization in flowering plants
Authors: Russell S. D. , Cresti M. , Dumas C.
Published: May 2006

The organization, isolation and physiology of the angiosperm male gamete has recently emerged as an area of special interest. Detailed in vivo studies have revealed: (1) that the functional unit of male reproduction is a‘male germ unit,’composed of two sperm cells and a physically associated vegetative nucleus; (2) that the two sperm cells are often cytoplasmically dimorphic, and (3) that some sperm cells appear to undergo preferential fertilization, preferentially fusing with either the egg or the proendospermaric central cell. Male gamete isolation has provided enrichments of up to 107 cells ml–1, with sperm integrity and viability demonstrated by the flunrochromatic reaction and ATP levels. Although results from biochemical and hybridoma antibody characterization are still preliminary, they indicate that sperm cells possess polypeptide expression patterns that are different from those of surrounding cells. These findings suggest the existence of an independent developmental program in the angiosperm male gamete.
Isolectins in Narcissus: complexity, inter‐ and intraspecies differences and developmental control
Authors: Van Damme Els J. M. , Peumans Willy J.
Published: May 2006

Using high resolution ion‐exchange chromatography and isoelectric focusing the heterogeneity of the daffodil (Narcissus sp.) lectin in terms of isolectin composition was analyzed. A survey of about 30 cultivars and species of Narcissus demonstrates (i) that they all contain over 50 different lectin polypeptides and (ii) that there are pronounced inter‐ and intraspecies differences in the isolectin patterns. Analyses of lectin preparations isolated from different tissues at different developmental stages further indicate that the isolectin composition is tissue specific and developmentally regulated. Finally, affinity chromatography experiments suggest differences in affinity for a mannose‐Sepharose 4B column of different isolectins.
Seasonal changes in nitrogen fractions of Pachysandra terminalis, a forest evergreen chamaephyte
Authors: Yoshie Fumio , Arai Hirohito , Nakashima Hideaki , Kawano Shoichi
Published: May 2006

Seasonal changes in several forms of nitrogen were investigated in the evergreen chamaephyte Pachysandra terminalis Sieb. et Zucc. growing in temperate evergreen coniferous forest. After plants sprouted new shoots, nitrogen accumulated largely as proteins in the leaves from summer to late autumn and, additionally, during a short spring period in the following year. Proteins accumulated in the overwintered leaves decreased markedly in summer, indicating that they were used for new shoot growth. A similar change was found in Fraction 1 protein. This is consistent with the seasonal changes in photosynthetic capacity and carboxylation efficiency observed in previous studies. The allocation of nitrogen to Fraction 1 protein increased in the spring, presumably to utilize better the relatively high light intensity at the forest floor before leaf expansion of the understory deciduous plants. In contrast to protein nitrogen, soluble nitrogen was present largely in stems and rhizomes. Aspargine was the major component of the amino acid pool in all organs throughout the year, especially in stems in summer. Since asparagine has the highest N:C ratio (2N:4C), an amino acid pool dominated by asparagine is economic in the use of carbon and advantageous for the carbon‐limited environment of the forest understory.
Analysis by high‐performance liquid chromatography of free amino acids extracted from needles of drought‐stressed and shaded Pinus ponderosa seedlings
Authors: Vance Nan C. , Zaerr Joe B.
Published: May 2006

Free amino acid concentrations in needles of drought‐stressed and shaded seedlings of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) were analyzed to determine the influence of low irradiance on a biochemical response to drought stress. A convenient method was developed for separating and quantitating amino acids in needle extracts using derivatization with dansyl chloride and reversed‐phase high‐performance liquid chromatography (HPLC). Twenty‐one amino acids were separated on an Ultrasphere ODS CIS column and detected with a fluorescence spectrophotometer. As little as 10 pmol of each were detected with good peak separation and reproducible retention times. The results of HPLC analysis showed that drought and shading induced an increase in total amino acid concentrations in needles; shading had the greater effect. Arginine and proline concentrations increased most in needles of drought‐stressed seedlings and remained high in unshaded seedlings recovering from drought 48 h after rewatering. Arginine and glutamine increased most in the shaded seedlings, which did not survive severe drought. The large increase in arginine in both drought‐stressed and severely shaded seedlings suggests that sequestering and storage of ammonia are important when stress reduces carbon fixation.
Axillary bud growth in relation to adventitious root formation in cuttings
Authors: Hansen Jürgen , Kristensen Kristian
Published: May 2006

Single‐node leaf‐bud cuttings of Schefflera arboricola Hayata and Stephanotis floribunda Brongn. were set and root formation, onset of axillary bud growth and plant height were measured. An increase in the number of roots in Schefflera, which was achieved with increasing cutting position on the stock plant (measured from top to base) or with increasing stem length below the node, accelerated the onset of axillary bud growth and resulted in an increase in plant height. Increasing the number of roots per cutting in Stephanotis through an increase in basal temperature also accelerated bud and shoot growth. Positional effects on root formation in Stephanotis showed no relationship with axillary bud growth and plant height. A positive relationship between number of roots per cutting and axillary bud growth was found among clones of Stephanotis. In general the results suggest that, with some exceptions, the onset of axillary bud growth is accelerated in cuttings as a result of accelerated root formation and a higher number of roots per cutting.
Biosynthèse des acides gras polyinsaturés des glycérolipides de la feuille d'olivier
Authors: Zarrouk M. , Marzouk B. , Chérif A.
Published: May 2006

The patterns of incorporation of [l‐14C]‐acetate into the glycerolipid fatty acids of leaves of olive plants (Olea europea L. cv. Chétoui) suggested a specific pathway for a‐linolenic acid biosynthesis. The results confirmed the involvement of phosphati‐dylcholine in galactolipid metabolism, and seemed to exclude the role of that mole‐cule as a substrate for desaturation of oleate to linoleate. The two oleate desaturation steps seemed to occur rapidly on the diacylgalactosylglycerol molecule for biosynthesis of galactolipid linolenate. In addition, the results indicated a slow sequen‐tial desaturation of oleate to linolenate via linoleate in the phospholipid molecules (phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol).
Primary and secondary induction requirements for flowering of Festuca rubra
Authors: Heide O. M.
Published: May 2006

In three high‐latitude populations of red fescue 15 to 21 weeks of primary induction at 6°C/8 h short day (SD) conditions were required for optimum flowering in subsequent long days (LD) at 15 to 18°C. The optimum temperature for SD induction was 9°C, the critical temperature being 15°C. In two of the populations only marginal induction took place in LD at 6 and 9°C, in a third population from 69°30′N latitude induction was equally effective in SD and LD at these temperatures. After primary induction in SD a transition to LD was required for initiation of inflorescence primordia, 12 to 16 LD cycles (24 h) being required for full secondary induction at 18°C. Marginal LD secondary induction caused a high proportion of viviparous proliferation even in fully seminiferous populations. The populations varied also in morphological characters, highlighting the genetic and taxonomic variability within the F. rubra complex.
Arginine utilization by Chlorella autotrophica and Chlorella saccharophila
Authors: Laliberté Gilles , Hellebust Johan A.
Published: May 2006

Chlorella saccharophila can utilize the amino acids arginine, glutamate. ornithine and proline as sole sources of nitrogen for growth. By comparison C. autotrophica utilized only arginine and ornithine. Following osmotic shock of Chlorella autotrophica from 50 to 150% artificial seawater rapid synthesis of proline (the main osmoregulatory solute in this alga) occurred in cells grown on arginine or citrulline. However, little proline synthesis occurred in ornithine‐grown cells. Distribution of radiolabelled carbon from [14C]‐arginine assimilation following osmotic shock of C. autotrophica agrees with the following pathway of arginine utilization: arginine→citrulline→ornithine→glutamate semialdehyde→pyrroline‐5‐carboxylate→proline. These 4 steps are catalysed by arginine deiminase (EC 3.5.3.6), citrullinase (EC 3.5.1.20), ornithine transaminase (EC 2.6.1.13) and pyrroline‐5‐carboxylate reductase (EC 1.5.1.2), respectively. Of these 4 enzymes, only arginine deiminase and pyrroline‐5‐carboxylate reductase were detected in the crude extract of the 2 Chlorella species. Arginine deiminase did not require specific cations for optimal activity. The deimi‐nase showed maximal activity at pH 8.0 and followed Michaelis‐Menten kinetics with an apparent Km for L‐arginine of 0.085 mM for the C. autotrophica enzyme and 0.097 mM for that of C. saccharophila. The activity of arginine deiminase was not influen‐ced by growing C. saccharophila on arginine. Ornithine competitively inhibited arginine deiminase with an apparent K, of 2.4 mM for the C. autotrophica enzyme, and 3.8 mM for that of C. saccharophila. Arginine utilization by Chlorella is discussed in relation to that of other organisms.
Effect of nitrate and ammonium concentration on nitrate reductase activity in five species of mycorrhizal fungi
Authors: Sarjala Tytti
Published: May 2006

The nitrate reducing capacity of pure cultures of Cenococcum geophilum (Sow.) Ferd. & Winge, Paxillus involutes (Batsch: Fr.) Fr. (strains 1 and 2), Piloderma croceum Erikss. & Hjortst., Suillus variegatus (Fr.) O. Kuntze (strains 1 and 2) and an ectendomycorrhizal (E‐strain) fungus was measured using an in vivo nitrate reductase (EC 1.6.6.3) assay. Differences between species and strains were established. The nitrate concentration of the culture medium influenced the nitrate reductase activities of the E‐strain fungus and one strain of S. variegatus. The nitrate reductase activity of certain species and strains was a function of nitrate concentration. Addition of ammonium to the growth medium did not have any significant effect on the in vivo or in vitro nitrate reductase activity. The in vivo nitrate reductase activity in the mycelia of C. geophilum and the E‐strain fungus decreased during 28 day growth in modified Melin‐Norkrans medium. For mycelia of Paxillus involutus, Piloderma croceum and S. variegatus grown on agar the in vitro assays showed higher nitrate reductase activity than the in vivo assays.
Effects of preconditioning on electrolyte leakasge and lipid composition in black spruce (Picea mariand) stressed with polyethylene giycol
Authors: Zwiazek Janusz J. , Blake Terence J.
Published: May 2006

Black spruce (Picea mariana Mill. B. S. P.) rooted cuttings were grown in solution culture and preconditioned by osmotically stressing plants with polyethylene glycol. After relief from preconditioning stress, water relations, membrane leakiness, and the composition of lipids and fatty acids were compared in preconditioned and control, unconditioned plants. Both groups of plants were subsequently subjected to a severe osmotic stress with polyethylene glycol and examined again. Osmotic stress decreased shoot water potentials and increased the leakage of electrolytes from shoots of stressed, compared with unstressed, plants. However, both unstressed and stressed preconditioned plants leaked less electrolytes compared with unconditioned plants. Changes in sterol, phospholipid and glycolipid composition were observed in preconditioned unstressed and stressed plants. Sterol and phospholipid levels de clined as a result of stress, and preconditioning resulted in a decline in sterol: phospholipid ratios in plants.