bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physiological effects of long term exposure to low concentrations of SO2 and NH3 on poplar leaves
Authors: van Hove L. W. A. , van Kooten O. , van Wijk K. J. , Vredenberg W. J. , Adema E. H. , Pieters G. A. 
Published: May 2006

Shoots of poplar (Populus euramericana L. cv. Flevo) were exposed to filtered air, SO2, NH3 or a mixture of SO2 and NH3 for 7 weeks in fumigation chambers. After this exposure gas exchange measurements were carried out using a leaf chamber. As compared to leaves exposed to filtered air, leaves pretreated with 112 μg m−3 SO2 showed a small reduction in maximum CO2 assimilation rate (Pmax) and stomatal conductance (gs). They also showed a slightly higher quantum yield and dark respiration. In addition, the fluorescence measurements indicated that the Calvin cycle of the leaves pretreated with 112 μg m−3 SO2 was more rapidly activated after transition from dark to light. An exposure to 64 μg m−3 NH3 had a positive effect on Pmax, stomatal conductance and NH3 uptake of the leaves. This positive effect was counteracted by an SO2 concentration of 45 μg m−3. The exposure treatments appeared to have no effect on the relationship between net CO2‐assimilation and gs. Also, no injury of the leaf cuticle or of epidermal cells was observed.Resistance analysis showed that NH3 transfer into the leaf can be estimated from data on the boundary layer and stomatal resistance for H2O transfer and NH3 concentration at the leaf surface, irrespective of whether the leaves are exposed for a short or long time to NH3 or to a mixture of NH3 and SO2. In contrast SO2 uptake into the leaves was only partly correlated to the stomatal resistance. The results suggest a large additional uptake of this gas by the leaves. The possibility of a difference in path length between SO2 and H2O molecules is proposed.
Metabolism of C19‐ and C20‐gibberellins by cell‐free preparations from immature Phaseolus coccineus seed
Authors: Malcolm Joan M. , Crozier Alan , Turnbull Colin G. N. , Jensen Einar 
Published: May 2006

Gibberellin biosynthesis pathways were investigated using isotopically‐labelled C19‐ and C20‐gibberellins and cell‐free preparations from immature seed of Phaseous coccineus cv. Prizewinner. The initial steps in an early 13‐hydroxylation pathway involved the conversion gibberellin A12‐aldehyde (GA12‐aldehyde) to GA12 which was 13‐hydroxylated to yield GA53, Metabolism of GA53 yielded GA44. In contrast to other cell‐free systems, GA44 was not further converted, either as a δ‐lactone or an open‐lactone structure, to the C‐20 aldehyde GA19. GA19 was, however, metabolised to GA20, GA5 and GA1. GA20 represented a branch point in the pathway as it was converted both to GA1, which was an end product, and GA5 which was further converted to GA6. Like GA1, GA6 was also an end‐product of the early 13‐hydroxylation pathway.A non‐13‐hydroxylation pathway involving GA4, GA15, GA24 GA37 and GA36 also originated from GA12. The terminal product of this pathway was the 3β‐hydroxy C19‐gibberellin, GA4.
Effects of agar concentration on water status and growth of rose plants cultured in vitro
Authors: Ghashghaie J. , Brenckmann F. , Saugier B. 
Published: May 2006

Rose (Rose hybrida cv. Madame G. Delbard) was micropropagated in vitro on agar at varying concentrations: 0, 4, 5.5, 6, 7.5, 8, 9 and 15 g l−1. Water status of the culture medium, leaf water potential, plant growth and propagation rate were investigated.Water potential of the medium was lincar function of agar concentration, and gel strength increased linearly from zero as agar concentration increased from 5 to 15 g l−1.Except for liquid medium, where shoot proliferation (total shoot number) was imparied by vitrification, fresh and dry weights and unmber of tatal shoots decreased linearly with increasing agar concentration. At low agar concentration, where water potential of the gelled medium was high, only few among numerous shoots that had attained a length of >0.3 cm were usable. Number of usable (elongated) shoots was significanly higher at a moderate level of agar, namely 7.5 g l−1. This can be explained in terms of the antagonistic actions of cytokinin and water on shoot elongation.At low agar concentration, leaf water potential and absolute water content were high. At high agar concentration, under gel water deficit, leaf water potential and absolute water content were low but an osmotic adjustment maintained turgor pressure. At moderate agar concentration, when the number of usable shoots was high, lower leaf turgor was found.
The occurrence of haemoglobin and hydrogenase in nodules of twelve Casuarina‐Frankia symbiotic associations
Authors: Sellstedt A. , Reddell P. , Rosbrook P. 
Published: May 2006

Seedlings of Casuarina cunninghamiana Miq., C. equisetifolia L. and C. glauca Sieber growing in N‐deficient potting mix were inoculated with Frankia sp. from each of 4 different sources. After ca 4 months, plants were harvested and nodules from the 12 Casuarina‐Frankia combinations evaluated for (1) concentrations of haemoglobin (measured as CO‐reactive haem) and (2) occurrence of hydrogenase. The aim was to determine if these factors were related to nitrogen accumulation and biomass production.There were marked host‐Frankia source interactions with up to 10‐fold differences in plant dry weight and 50‐fold differences in the efficiency of nitrogen fixation (as estimated by N2 accumulated mg−1 nodule dry weight). Differences in plant growth and nitrogen accumulation were apparently related to nodule specific activity, because the 12 associations had similar nodulation characteristics, e.g. time for nodulation to occur.The concentration of haemoglobin in Casuarina nodules ranged from 0 to 27 nmol haem (g FW)−1. There was a strong linear correlation between concentrations of haemoglobin and dry weights of the whole plants (r=0.77, 0.92 and 0.97, P≤0.05) for C. cunninghamiana, C. equisetifolia and C. glauca symbiotic associations, respectively. However, the linear correlation between concentration of haemoglobin and nitrogen content of whole plant was lower (r=0.60, 0.64 and 0.71, P≤0.05) for the three Casuarina symbioses, respectively, and there was only a poor correlation between haemoglobin concentration in nodules and the rate of nitrogen accumulation on nodule weight basis. This indicates that haemoglobin concentration is not the sole physiological determinant of nitrogen fixation in Casuarina.All the Casuarina‐Frankia symbiotic associations studied also showed the presence of a hydrogen uptake enzyme. The activity of the enzyme ranged from 5.1 to 34.1 μmol H2 (g FW)−1 h−1, and hydrogen uptake was not correlated with plant dry weight, nitrogen content or the rate of nitrogen fixation. Hydrogen evolution could not be detected in any of the associations.
Prior temperature exposure affects subsequent chilling sensitivity
Authors: Saltveit Mikal E. 
Published: May 2006

The chilling sensitivity of small discs or segments of tissue excised from chillingsensitive species was significantly altered by prior temperature exposure subsequent to holding the tissue at chilling temperatures as measured by a number of physiological processes sensitive to chilling. This temperature conditioning was reversible by an additional temperature exposure before chilling, and mature‐green and red‐ripe tomato tissue exhibit similar chilling sensitivities.Exposing pericarp discs excised from tomato fruit (Lycopersicon esculentum Mill. cv. Castelmart), a chilling‐sensitive species, to temperatures from 0 to 37°C for 6 h before chilling the discs at 2.5°C for 4 days significantly altered the rate of ion leakage from the discs, but had no effect on the rate of ion leakage before chilling and only a minimal effect on discs held at a non‐chilling temperature of 12°C. Exposing chillingsensitive tissue to temperatures below that required to induce heat‐shock proteins but above 20°C significantly increased chilling sensitivity as compared to tissue exposed to temperatures between 10 and 20°C. Rates of ion leakage after 4 days of chilling at 2.5°C were higher from fruit and vegetative tissue of chilling‐sensitive species (Cucumis sativus L. cv. Poinsett 76, and Cucurbita pepo L. cv. Young Beauty) that were previously exposed for 6 h to 32°C than from similar tissue exposed to 12°C. Exposure to 32 and 12°C had no effect on the rate of ion leakage from fruit tissue of chilling tolerant species (Malus domestica Borkh. cv. Golden Delicious, Pyrus communis L. cv. Bartlett). Ethylene and CO2 production were higher and lycopene synthesis was lower in chilled tomato pericarp discs that were previously exposed for 6 h to 32°C than the values from tissue exposed to 12°C for 6 h before chilling. Increased chilling sensitivity induced by a 6 h exposure to 32°C could be reversed by subsequent exposure to 12°C for 6 h.
Changes in protein synthesis and translatable messenger RNA populations associated with ABA‐induced cold hardiness in potato (Solatium commersonii)
Authors: Tseng M. J. , Li P. H. 
Published: May 2006

Plantlets of Solanum commersonii Dun, PI 458317 stem‐culture were treated with abscisic acid (ABA) (3.78 to 113.5 μM) at a 20°/15°C day/night temperature regime for 14 days. Cold hardiness increased from—3.3°C to—8.4°C (killing temperature) after 7 days of ABA treatment and remained at this level thereafter. During the course of treatment (14 days), the synthesis of polypeptides was investigated and poly(A+)‐RNA was isolated. Translation products of poly(A+)‐RNA in a rabbit reticulocyte lysate system were then analyzed by 2‐D polyacrylamide gel electropho‐resis. During the 14 days of ABA treatment, 30 ABA‐induced polypeptides were identified. The synthesis of one group of polypeptides was stable and prominent throughout the treatment period. The other group was transient. The most prominent and stable polypeptides had molecular weights of 21 (pi 6.0, 6.3), 22 (pI 6.0, 6.3), 31 (pi 4.5) and 83 (pi 5.4, 5.5, 5.6) ItDa. About one‐third of the new polypeptides appeared after cold hardiness reached a maximum (after 7 days of ABA treatments.ABA treatment alters translatable mRNA populations during the development of cold hardiness. Several mRNAs, encoding in vitro translation products at 26 (pi 6.0, 6.3, 6.4), and 27 (pi 6.0, 6.3, 6.4), 40 (pi 6.4) and 50 (pi 4.5) kDa were identified during course of the ABA treatment. These proteins may play important roles for the development of cold hardiness in tuber‐bearing S. commersonii.
Physiological effects of a long term exposure to low concentrations of NH3, NO2 and SO2 on Douglas fir (Pseudotsuga menziesii)
Authors: van Hove L. W. A. , Bossen M. E. , Mensink M. G. J. , van Kooten O. 
Published: May 2006

The above‐ground parts of two years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed to filtered air, NH3, NO2+, SO2 (66, 96 and 95 μg m−3, respectively), to a mixture of NO2+NH3 (55 + 82 μg m−3) or SO2+NO2 (128 + 129 μg m−3), for 8 months in fumigation chambers. Both chlorophyll fluorescence and gas exchange measurements were carried out on shoots which had sprouted at the beginning of the exposure period. The chlorophyll fluorescence measurements were performed after 3 and 5 months of exposure (average shoot age 70 and 140 days, respectively). Light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. In addition, light response curves of net CO2 assimilation were determined after 5 months of exposure. After 3 months of exposure (average shoot age 70 days) all exposure treatments showed a lower maximum electron transport rate (Jmax) as compared to the control shoots (filtered air). A large reduction (45%) was observed for shoots exposed to SO2+NO2. During the exposure period between 3 and 5 months (average shoot age 70 and 140 days, respectively) a decrease of Jmax was observed for all treatments. Jmax had further declined some time after termination of the exposure, when average shoot age was 310 days.Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum net CO2 assimilation (Pmax) as compared to the control shoots. However, shoots exposed to NO2 showed no reduction and even a higher Pmax was observed for shoots exposed to NH3 or NO2+NH3. Needles of these treatments also showed a higher chlorophyll content which might explain the contradictory results obtained for these treatments: the increased amount of photosynthetic units counteracts the reduction in Jmax and consequently no reduction in Pmax is measured. Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum stomatal conductance (gs). However, the stomatal opening was larger than could be expected on basis of their (maximum) CO2 assimilation rate. Consequently, water use efficiency of these shoots was lower than that of the control shoots. Also shoots exposed to NO2 had a lower water use efficiency due to a significantly higher maximum gs. Shoots exposed to NH3 showed a high transpiration rate in the dark, indicating imperfect stomatal closure.
Aluminium effects on Scenedesmus obtusiusculus with different phosphorus status. II. Growth, photosynthesis and pH
Authors: Greger Maria , Tillberg Jan‐Eric , Johansson Monica 
Published: May 2006

Synchronously dividing cultures of the unicellular green alga Scenedesmus obtusiusculus were cultivated for 24 or 70 h in medium high (1000 μM) or low (60 μM) in phosphorus. Aliquots of AlCl3 (0, 37, 74, 111, 148, 185, or 222 μmol) were added daily to 1 l cell suspension at the end of the cell division phase. Algae were also grown in media with different pH, adjusted with HCl, in the absence of AlCl3.Effects of Al on cell metabolism vary with the intracellular Al concentration and with the concentration of Al available per cell. When the concentration of phosphorus is low, internal concentrations of Al are high and the chlorophyll content and the net dry matter production per cell increase, whereas the photosynthesis and the cell division are increased. Presence of Al in a low P medium decreases the pH of the medium down to 4.5. There are only small effects of Al in the presence of P, due to precipitation of most of the Al with P in the medium.Despite the Al‐induced decrease of the pH of the culture medium, effects caused by Al cannot be explained as a pH effect. Instead, the Al effect may, at least to some extent, be related to a decrease in availability of P in the metabolism, due to formation of aluminium phosphate inside the cell.
Evidence for the expression of morphological and biochemical characteristics of C3‐photosynthesis in chlorohyllous callus cultures of Zea mays
Authors: Lavergne D. , Nato A. , Dupuis J.‐M. , Péan M. , Chagvardieff P. 
Published: May 2006

A Zea mays callus culture containing chlorophyll was established and grown photomixotrophically. Cell chloroplast structure, and pigment and soluble protein contents were examined. Expression of some key enzymes of C4 carbon metabolism was compared with that of etiolated (heterotrophic) and green photoautotrophic leaves. Chlorophyll content of the callus was 15–20% that of green leaves. Soluble protein content of callus was half that of leaf cells. Electron microscopic observations showed that green callus cells contained only typical granal chloroplasts. Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.38) activities in green callus were ca 30% those of green leaves but 2–3 times higher than in etiolated leaves. Quantitative enzyme protein determination, using antibodies specific to maize leaf Rubisco showed that the chloroplastic carboxylase represented about 7% of total soluble protein in green callus, in parallel to its low chlorophyll content. The specific activity of Rubisco in callus and leaves was unchanged.Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activity in green callus was about 20% that of green leaves and similar to that measured in etiolated leaves. Apparent Km (PEP) values (0.08 mM) for PEPC isolated from green callus and etiolated leaves were very different from values (0.5 mM) obtained with PEPC from green leaves. These kinetic characteristics together with the absence of inhibition by malate and activation by glucose‐6‐phosphate suggest that the properties of PEPC isolated from green callus and etiolated maize leaves are very similar to those of PEPPC from C3 plants. Using PEPC antibodies specific to green maize leaf enzyme, immunotitration of PEPC preparations containing identical enzyme units allowed complete precipitation of the green leaf enzyme with increasing antibody volumes. In contrast, 60–70% of the activity of PEPC from etiolated and green callus was inhibited, suggesting low affinity for the maize green leaf PEPC antiserum (typical C4 form). Ouchterlony double diffusion tests revealed only partial recognition of PEPC in green callus and etiolated leaves.NAD‐malate dehydrogenase (NAD‐MDH, EC 1.1.1.37) activity in callus was 2 and 3 times higher, respectively, than in etiolated and green leaves. NADP‐malic enzyme (NADP‐ME, EC 1.1.1.40) activity in callus cultures was much lower than in green leaves. All our data support the hypothesis that cultures of fully dedifferentiated chlorophyllous tissues of Zea mays possess a C3‐like metabolism.
Applications of an optimized monocot expression vector in studying transient gene expression and stable transformation of barley
Authors: Maas Christoph , Schell Jeff , Steinbiß Hans‐Henning 
Published: May 2006

Protoplasts of a barley (Hordeum vulgare L. cv. Golden Promise) suspension cell line were used for PEG‐mediated gene transfer. Transient gene expression in barley protoplasts was studied using a chimeric CaMV 35S cat construct, which was only poorly expressed in barley cells. However, insertion of exon 1 and intron 1 of the maize Shrunken‐1 (Sh1) gene in the 5′‐untranslated leader of the construct strongly stimulated gene expression. By using the optimized chimeric cat construction the amount of CAT protein that was reached 19 hours after DNA uptake was 0.5% of total protein, which was calculated from western blot data.As an alternative marker gene for expression studies, we also tested the firefly luciferase gene in barley protoplasts. Low level expression of chimeric CaMV 35S luciferase genes could be highly stimulated when Sh1 exon1 and intron1 were inserted in the 5′‐untranslated leader of the constructs. Enhanced luciferase gene expression by Shrunken‐1 intronic sequences enabled us to monitor gene integration events early after DNA uptake using a promoterless luciferase marker gene, which could only be expressed after integration behind an endogenous promoter.
Degradation of membrane lipid components and antiovidanl levels in Hordeum vulgare exposed to long‐term fumigation with SO2
Authors: Navari‐Izzo. Flavia , Quartacci Mike F. , Izzo Riccardo , Pinzino Calogero 
Published: May 2006

Hordeum vulgare L. (cv. Barberousse) seedlings were continuosly exposed to SO2 (40±5 and 117±20 ppb) for 48 days and compared to control plants exposed to charcoal‐filtered air. Glyco‐and phospolipid amounts were strongly affected by exposure to SO2:, and decreased with increasing SO2, fumigation. The chloroplast membranes of fumigated leaves were characterized by lower quantities of rnonogalacto‐syldiacylglycerol (MGDG) as well as of sulphoquinovosyldiacylglycerol (SQDG). Among the phospholipids a decrease in the phosphatidylglycerol (PG) content was observed, indicating that the chloroplast membranes are affected even by such low concentrations of SO2 as used here. As for the other phospholipids, phosphatidylcholine (PC) and phosphatidylinositol (PI) suffered a reduction and phosphatidylethano‐lairrine (PE) almost disappeared at the highest SO2, concentration, whereas phosphatidic acid (PA) followed the opposite trend. The fatty acids of both glyco‐ and phospholipids fell sharply upon fumigation without any decline in the degree of unsataration. In particuSar, neither linoleic nor linolenic acid showed any evident change in level, suggesting that no lipid peroxidation of polytmsaturated fatty acid tails occurred. Furthermore, the electron spin resonance (ESR) showed no differences in the free radical levels between control and fumigated leaves.The level of malondialdehyde (MDA) decreased, while lipid‐soluble antioxidants, as well as superoxide dismutase (SOD; EC 1.15.1.1) and catalase (EC 1.11.1.6) activities increased with the increase in SO2 concentration, providing evidence that defence mechanisms against oxy‐radical action are activated by the plants at low levels of SO2,. Even if SO2, at low concentrations may not directly oxidize polyunsaturated fatty acids, it may act as a deesterifying factor on each component of both glyco‐ and phospholipids.
Cellular changes in early development of regenerating thin cell layer‐explants of rapeseed analyzed by light and electron microscopy
Authors: Pihakaski‐Maunsbach K. , Nygaard K. Brauner , Jensen K. H. , Rasmussen O. 
Published: May 2006

Cellular changes in thin cell layer (TCL) explants of stem origin of Brassica napus L. cv. Vega were studied from 0 to 15 day by light and transmission electron microscopy. Apical and basal ends of the old explants were analysed separately. Quantitative and qualitative analyses showed that during the first culture day the parenchyma cells enlarged significantly as did the cytoplasm/vacuole ratio. The cytoplasm contained increased rough endoplasmic reticulum (RER), polysomes and dictyosomes associated with both coated and uncoated vesicles. The cell enlargement continued during the first 5 days of culture. The structural organization of the cell wall became somewhat loose and inhomogeneous. Parenchyma in the basal end divided frequently, resulting in several centres of division, while cell division in apical cells was less frequent and cells there remained enlarged. Starch accumulation started on the first day and increased until the third day. i. e. until cell divisions became more frequent. The starch content of dividing cells gradually decreased and starch was almost totally lacking in 15‐day‐old explants. Starch grains remained numerous, however, in the large non‐dividing apical cells, except in those cells adjacent to the medium. Cell divisions started close to medium in explants containing vascular tissue, but closer to the epidermis in the explants without vascular tissue.The results show how rapid (one day) striking changes in the cells take place and suggest that optimal hormone concentration and intertissue relations between epidermis and parenchyma and between parenchyma and vascular tissues as well as intercellular relations among parenchyma cells determine the first cell division sites and planes in the explants. Although the cells change from elongated to spheroid, their original polarity remains as evidenced by the formation of more numerous basal shoot primordia than in apical shoot primordia.