bluuebunny/crossref_metadata_2025 huggingface dataset:
Isoprene emissions and photosynthesis in three ferns – The influence of light and temperature
Authors: Tingey David T. , Evans Rosemary C. , Bates Emily H. , Gumpertz Marcia L.
Published: May 2006

A study was designed to determine the rates of isoprene emission and photosynthesis in three fern species [Dicksonia antarctica Labill., Thelypteris decursive‐pinnata (Van Hall) Ching and Thelypteris kunthii (Desv.) Morton] and the independent influence of light and temperature on these processes. The plants were conditioned in a growth chamber and then transferred to a controlled environment gas‐exchange chamber. Samples of the chamber atmosphere were collected; isoprene was concentrated cryo‐genically and measured by gas chromatography. Only small amounts of isoprene were detected around the ferns in the dark. Isoprene emissions increased with increasing levels of photosynthetic photon flux density (PPFD) in all three species; 50% of the maximum emission occurred at PPFD levels of 130 to 500 μmol m−2 s−1. Maximum isoprene emissions occurred between 35 and 39°C which is a lower temperature maximum than reported for angiosperms and gymnosperms. The increased emissions with temperature were primarily associated with increased biosynthetic rates for isoprene. Carbon lost through isoprene accounted for 0.02 to 2.6% of the carbon fixed during photosynthesis, depending on the PPFD level, temperature and fern species.
Interactions between myo‐inositol and cytokinins: Their basipetal transport and effect on peach roots
Authors: Gur Arye , Altman Arie , Stern Rafael , Sigler Tomy , Wolowitz Brenda
Published: May 2006

Root growth of partly defoliated young peach seedlings [Prunus persica (L.) Batsch. cv. Lovell] was significantly promoted by application of myo‐inositol to the cut surface of the stem. Addition of benzylaminopurine (BA) combined with sucrose enhanced the promotive effect of myo‐inositol on root growth, but addition of sucrose alone, suppressed it. Spraying rooted peach cuttings (nectarine cv. Sunred) with myo‐inositol and defoliating them after 5 days increased the incorporation of amino acids into proteins in excised roots, obtained from the sprayed plants, as compared with roots from plants sprayed with water, or sucrose, or sucrose + myo‐inositol. Myo‐inositol applied in combination with kinetin or BA to stems of young peach seedlings (cv. Lovell) or rooted peach cuttings (cv. Almog) promoted the basipctal translocation of the two cytokinins in the stem and acropetally into the small lateral roots. Addition of sucrose voided this effect on the cytokinins. BA, when applied together with myo‐inositol, was partly converted into an additional cytokinin‐active compound in the roots.

Application of BA to either roots or tops of rooted peach cuttings (cv. Almog) resulted in the accumulation of myo‐inositol (supplied through the cut surface of the stem) in the plant part to which BA had been applied.
Freeze‐induced phase transitions in the plasma membrane of isolated protoplasts
Authors: Pihakaski Kaarina , Steponkus Peter L.
Published: May 2006

Protoplasts were enzymically isolated from 2‐week‐old non‐acclimated rye (Secale cereale L. cv. Puma) seedlings. They were resuspended in isotonic sorbitol with different concentrations (0–10%) of dimethyl sulfoxide (DMSO). The survival of the protoplasts frozen in isotonic sorbitol solutions declined at temperatures below the freezing point with the LT50 being ‐8°C. Addition of DMSO to the osmoticum increased survival at freezing temperatures. The optimum concentration of DMSO was 4% and lowered the LT50 to ‐19°C. Freeze‐fracture studies of the plasma membrane revealed aparticulate lipid lamellae at ‐4°C, but the first appearance of lateral phase separations, striations and inverted cylindrical micelles (hexagonal11‐type structures) occurred at ‐6°C. At lower temperatures, ‐8 and ‐10°C, the occurrence of nonbilayer structures became more common. The addition of DMSO decreased the incidence of the ultrastructural changes. With 2 or 4% DMSO, non‐bilayer structures were not observed at temperatures above ‐10°C. Instead, striations and H11‐type structures were observed at ‐ 15 and ‐20°C.
Isolation, culture and plant regeneration from mesophyll protoplasts of Digitalis obscura
Authors: Brisa María C. , Segura Juan
Published: May 2006

High yields of protoplasts were obtained from mesophyll tissue of Digitalis obscura L. Osmotic potential of the isolation medium and Ca2+ were important in obtaining a high viability of the preparations. In different culture techniques employed, liquid‐over‐agar‐solidified medium was superior to liquid medium alone. Agar plating technique was ineffective. On Murashige and Skoog modified medium with casein hydrolysate and several indoleacetic acid and benzyladenine combinations, isolated protoplasts underwent sustained mitotic division and produced calli. The calli formed shoots when transferred to regeneration media. Regenerated shoots could be easily rooted and developed into whole plants on half‐strength Murashige and Skoog hormone‐free medium.
Determination of the surface area of fine tomato roots via cation uptake experiments
Authors: Wolterbeek H. T.
Published: May 2006

A method is described by which the surface area of a root is estimated from cation uptake data. 24Na+ was supplied to excised roots of tomato (Lycopersicon esculentum Mill, cv. Tiny Tim) seedlings at 3 μM in unstirred solution. Coarse roots, for which external surface area and specific gravity could be measured accurately, were used to estimate the thickness (dN) of the Nernst boundary layer at the root surface. 24Na+ uptake (J1) was measured by γ‐ray spectroscopy. Jt and dN were used to calculate the total surface area for ion absorption in fine roots, assuming that Na uptake rate was diffusion‐limited. The results were compared to data obtained by conventional methods and indicated the usefulness of the cation uptake technique for quantitative estimates of root surfaces.
Photoacoustic spectra of needles as an indicator of the activity of the photosynthetic apparatus of healthy and damaged conifers
Authors: Nagel Eckehard M. , Buschmann Claus , Lichtenthaler Hartmut K.
Published: May 2006

Photoacoustic spectra were measured at chopping frequencies of the excitation light at 22 and 515 Hz in order to detect differences between needles from healthy and damaged conifers (Abies albaMill, andPicea abiesKarst.) with respect to pigment distribution and possibly also to photosynthetic activity. Fully green needles of healthy trees exhibit photoacoustic spectra at 22 Hz with a maximum in the red absorption region of the chlorophyll. This maximum is lost with increasing damage to needles and chlorophyll breakdown. The photoacoustic spectra at 22 Hz of the damaged needles therefore are characterized by a higher signal in the blue‐light region as compared to that in the red‐light region. This can be quantified by forming the ratio of the photoacoustic signals at 675 and 475 nm (ratio PA 675/475). The needles of the damaged trees possess a lower photosynthetic activity, as seen from the CO2fixation rate and the variable fluorescence (Rfd‐values). It is assumed that the changes in the PA‐spectra of the needles from damaged trees are the result of this decline of the photosynthetic apparatus and its function. In contrast to the PA‐spectrum at 22 Hz the PA‐spectra at 515 Hz, where the PA‐signals primarily emanate from the epidermal layer, exhibit a different shape with a maximum near 550 nm. In the needles from the damaged trees the PA‐signals are higher, particularly in this maximum range of the spectrum, than those of fully green needles from healthy trees.
Gene expression during leaf development in Lolium temulentum: Patterns of protein synthesis in response to heat‐shock and cold‐shock
Authors: Ougham Helen J.
Published: May 2006

At an optimal growth temperature of 20°C, expending 4th leaves of Lolium temulentum L. synthesised a broad spectrum of polypeptides which altered with the maturity of the leaf tissue. Elevation of the temperature to 35°C, or above, induced synthesis of heat‐shock proteins (hsp), and all parts of the 4th leaf were capable of this response. The threshold temperature for induction of hsp synthesis was little affected by the growth temperature (5 or 20°C). In contrast, a sudden 15–18°C decrease in temperature did not result in a marked alteration of protein synthesis patterns. It is concluded that in this species adaptation to rapid temperature reduction is not mediated by stress protein synthesis.
Isolation and characterization of the enzymes involved in disintegration of the cell wall of Chlorella fusca
Authors: Walter J. K. , Aach H. G.
Published: May 2006

Using different chromatographical methods we have isolated an enzyme from the sporangia of Chlorella fusca Shihira et Krauss var. vacuolata, strain SAG 211–8b, which is responsible for the partial disintegration of the sporangium wall. We refer to it as carbohydrate‐releasing activity (CRA). It is an endoenzyme and splits oligosaccharides from the inner layer of the cell wall. In appropriate tests it shows β‐d‐fucosidase activity (EC 3.2.1.,38): The protein has a molecular weight around 45 kDa and an isoelectric point of pH 4.3; maximum activity is found at pH 5.4 and 60°C, although this temperature inactivates the enzyme quickly. β‐d‐Mannosidase (EC 3.2.1.25) and β‐d‐glucosidase (EC 3.2.1.21) were also found in the presence of CRA. These glycosidases were identified as exoenzymes. They are involved in the further degradation of the liberated obligosaccharides.
Photoperiodic control of flowering in Dactylis glomerata, a true short‐long‐day plant
Authors: Heide O. M.
Published: May 2006

Flowering requirements of three Scandinavian cultivars of Dactylis glomerata L. have been studied in controlled environments. At temperatures ranging from 9 to 21°C optimal flowering required 10 weeks of exposure to short days (SD) followed by exposure to long days (LD). Only a few plants flowered in continuous LD and no primary induction took place in any daylength at 24 or 27°C. However, at a temperature of 3°C primary induction occurred also in 24 h LD, but more than 20 weeks of treatment were required for 100% flowering. The critical photoperiod for secondary induction was about 12–13 h, depending on the latitude of origin of the cultivar. A critical number of 12 to 16 LD cycles was required for 100% flowering, although some plants flowered after only 4 LD. A high proportion of viviparous proliferation resulted from marginal LD induction. Initiation of floral primordia did not take place in SD but required a transition from SD to LD. These results demonstrate that D. glomerata is a true short‐long‐day plant.
Accelerated ethylene production as related to changes in lipids and electrolyte leakage during senescence of petals of cut carnations (Dianthus caryophyllus)
Authors: Sylvestre I. , Paulin A.
Published: May 2006

Conditions inhibiting the action of (supply of silver thiosulfate) or the synthesis of (supply of α‐aminooxyacetic acid) ethylene, prolonged the vase‐life of carnation (Dianthus caryophyllus L. cv. Ember) flowers. On the other hand, conditions which provoked an advance in the time of appearance of the ethylene rise (previous exposure to exogenous ethylene), accelerated senescence. This action on the morphological changes was accompanied by an effect on the efflux of electrolytes, which was advanced or delayed depending on the type of treatment, in comparison with the control.

The various factors acting on ethylene production also affected membrane lipids. Those which suppressed or delayed the ethylene rise, slowed down the degradation of the total and free fatty acids and the increase in the level of saturation of the chains. The opposite was observed when the ethylene peak occurred early. There was no correlation between the time of appearance of the burst of ethylene and the time of onset of lipid breakdown.

A 48 h water stress provoked neither an advance in the time of appearance of the ethylene peak nor an acceleration in lipid breakdown on return to normal conditions.
Phosphatase induction in roots of winter wheat during adaptation to phosphorus deficiency
Authors: Szabó‐Nagy Andrea , Oláh Zoltán , Erdei László
Published: May 2006

The effect of phosphate supply during the first 4 weeks of the life cycle of wheat (Triticum aestivum L. cv. Martonvásári‐8) was investigated by following growth of seedlings, P levels in roots and shoots, changes of soluble phosphatases in roots and alteration of Ca2+ ‐ and Mg2+‐ATPase activity in the microsomal fraction. Plants were grown in complete nutrient solution supplemented with different levels of phosphate. Maximal growth rate was attained at 0.2 mM phosphate. The total P level in plants increased with increasing phosphate concentration in the growth solution, however, it decreased with age. Microsomal ATPase activity in 14‐day‐old plants increased with phosphorus deficiency. Using phosphocellulose column chromatography, a phosphatase (EC 3.1.3.2) induced by phosphorus deficiency was purified and partially characterized from the 30 000 g supernatant from roots of 14‐ to 30‐day‐old wheat plants. Na‐pyrophosphate, p‐nitrophenylphosphate, ATP, ADP, AMP, O‐phosphoryl‐l‐serine and glucose‐6‐phosphate were all substrates for the enzyme. Its native molecular weight was 42 kDa as determined by Sephadex G‐200 column chromatography. Readdition of phosphate to the growth solution resulted in a gradual decrease of the phosphatase activity, probably due to repression of its synthesis. We hypothesize that the extra phosphatase may participate in the adaptation mechanism under phosphorus‐deficient conditions.
Free radical production, catalase and superoxide dismutase activities and membrane integrity during senescence of petals of cut carnations (Dianthus caryophyllus)
Authors: Droillard M. J. , Paulin A. , Massot J. C.
Published: May 2006

There is a sudden increase in free radical levels, measured from the electron spin resonance (ESR) signal, in cut carnation (Dianthus caryophyllus L. cv. Ember) petal powders between the end of blooming and the onset of withering. There is also an increase in the microsomal generation of superoxide radicals (measured from the ESR‐Tiron signal). These increases correspond to a decrease of polar lipids content, a slight increase in peroxides and to the onset of a sudden efflux of electrolytes. A correlation is established between free radical production and the loss of membrane integrity. Catalase (EC 1.11.1.6) activity increases progressively until complete withering and an hypothesis concerning the action of this enzyme is proposed. The changes in superoxide dismutase (EC 1.15.1.1) activity appear to be independent of the amplitude of the ESR‐Tiron signal.
Invertases of carnation petals. Partial purification, characterization and changes in activity during petal growth
Authors: Woodson W. Randolph , Wang Hong
Published: May 2006

Carnation (Dianthus caryophyllus L. cv. White Sim) petals contained two distinct invertases (EC 3.2.1.26) based on chromatographic behavior on DEAE‐cellulose. Both are soluble in 20 mM sodium phosphate buffer (pH 6.5) and exhibit acid pH optimum of 5.5. Extraction of a cell wall preparation from petals with 1 M NaCl released little additional activity. Furthermore, only traces of activity remained associated with the NaCl‐extracted cell wall preparation. One of the soluble invertases, representing over 75% of the total activity, was partially purified by (NH4)2SO4 fractionation and sequential chromatography over diethylaminoethyl‐cellulose, concanavalin‐A sepharose and polyacrylamide P‐200. The enzyme was purified 38‐fold with a recovery of 12%. It had an apparent native molecular weight of 215 kDa. The partially purified invertase is a β‐fructofuranosidase (EC 3.2.1.26) based on its specificity for sucrose. The Km for sucrose was 3.3 mM. Accumulation of reducing sugars and increased invertase activity during expansive petal growth indicates that sucrose is the major source of carbon for petal growth.
Effects of sucrose on betacyanin accumulation and growth in suspension cultures of Phytolacca americana
Authors: Sakuta Masaaki , Takagi Tsutomu , Komamine Atsushi
Published: May 2006

The effects of sucrose on betacyanin accumulation and growth in suspension cultures of Phytolacca americana L. were investigated. Maximal betacyanin accumulation was observed at 88 mM sucrose on cell number basis and at 175 mM sucrose on fresh weight basis. This is because cell size decreased as the initial sucrose concentration was increased. Supplementary studies using mannitol indicated that sucrose itself caused increased cell number and that cell size was affected by both sucrose concentration and water potential. Betacyanin accumulation per cell and per fresh weight at a constant concentration of sucrose (88 mM) decreased with decreasing water potential. When sucrose concentration increased at a constant water potential (–0.7 MPa), betacyanin accumulation per fresh weight increased up to 88 mM and remained at constant level at higher concentrations, while betacyanin accumulation per cell decreased remarkably, due to a dramatic increase in cell number.
Ion movements during stomatal opening in darkness after illumination under nitrogen
Authors: Vavasseur A. , Lascève G. , Couchat P.
Published: May 2006

In Zea mays L., Bryophylum laxiflorum Bak., Gossypium hirsutum L., Helianthus annuus L., Oryza sativa L. and Vigna radiata L., a pre‐illumination in nitrogen causes transient stomatal opening upon returning the plant to darkness and normal air. In Zea mays L. hybrid INRA 508, K+ and Cl− fluctuations in the stomatal complex during this stomatal opening in darkness were similar to those observed during a light‐induced opening in normal air. These results are consistent with a two‐phase mechanism for stomatal opening: a light phase that may occur in the absence of oxygen and carbon dioxide, and a dark phase during which oxygen is necessary for ion accumulation and other mechanisms of osmotic adjustment.
Frost resistance of winter rape leaves as related to the changes in water potential and growth capability
Authors: Kacperska Alina , Kulesza Leszek
Published: May 2006

Differential thermal analysis indicated that the frost resistance of winter rape leaves (Brassica napus L. var. oleifera L. cv. Gòrczanski), collected from plants grown in the cold (5/2°C), relies mainly on their ability to supercool to −9 to −11°C, i.e. consists in freezing avoidance. Initiation of ice formation in the cold‐acclimated leaves resulted in the death of more than 50% of the cells as determined with a conductivity method. The development of freezing tolerance appeared to be an attribute of the second stage of plant hardening and was induced by the exposure of plants to a slightly subzero temperature (−5°C) for 18 h. Such a treatment brought about a sudden and persistent water potential decrease in the leaves, despite the fact that they had reabsorbed water from the medium prior to water potential measurements. Water potential changes were associated with a higher growth capability of the leaves as checked by determinations of disk area increments. It is suggested that the increased frost tolerance of the cold‐grown winter rape leaves, subjected to subfreezing temperature, is related to the decreased water potential of the tissue caused by changes in turgor and/or in osmotic pressures of the cells.
Changes in protein and mRNA populations during the senescence of carnation petals
Authors: Woodson W. Randolph
Published: May 2006

Developmental changes in polypeptide and mRNA popultions in carnation (Dianthus caryophyllus L. cv. White Sim) petals were investigated during the senescence of harvested flowers. Total proteins were extracted from flower petals at various stages of senescence and subjected to separation by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Analysis of the Coomassie blue stained gels revealed polypeptides with apparent molecular weights of 76, 62, 35.5 and 24 kDa which increased, while those with molecular weights of 70.5, 67.5, 46.5 and 31 kDa decreased during petal senescence. Changes in mRNA populations were investigated by translating poly (A)+RNA, isolated from carnation petals, in vitro using the rabbit reticulocyte lysate system. Polypeptides synthesized in vitro were separated by one‐ and two‐dimensional gel electrophoresis and visualized by fluorography. Three classes of mRNA's were associated with the senescence of carnation petals. The majority of the mRNA's were constitutive at all stages of senescence. Another class of mRNA's increased with the climacteric rise in ethylene production, which accompanied the onset of senescence. Their translation products were 81, 58, 42, 38 and 35 kDa. In addition, several mRNA's appeared to decrease in abundance during the course of petal senescence. These results indicate that senescence of carnation flower petals is associated with changes in gene expression.
Effect of ultraviolet radiation on accumulation and leakage of 86Rb+ in guard cells of Vicia faba
Authors: Negash Legesse , Jensén Paul , Björn Lars Olof
Published: May 2006

The effects of UV‐C (254 nm), UV‐A (365 nm) and broad‐band UV (280–380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 μmol m−2 s−1). UV‐C (7 μmol m−2 s−1) was found to cause leakage of 86Rb+ from guard cells, while UV‐A (0.3 μmol m−2 s−1) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad‐band UV (3 μmol m−2 s−1) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of 86Rb+ from guard cells continued despite the removal of UV‐C and an increase in the amount of white light from 450 to 1500 μmol m−2 s−1, suggesting that membranes were irreversibly damaged. Irradiation of guard cells with UV‐C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV‐C irradiation.
Abscisic acid metabolism in Ceratocystis coerulescens
Authors: Kettner Jens , DörfOing Karl
Published: May 2006

The fungus Ceratocystis coerulescens Bakshi (strain RWD 390) has been shown to produce the plant hormone, abscisic acid (ABA). The production of ABA in defined liquid medium during a culture period of 50 days was measured by gas‐liquid chromatography. A considerable accumulation of ABA occurred in the stationary phase. Maximum ABA contents were 3.5 ng ml−1 in culture media and 218 ng (g dry weight)−1 in mycelial extracts.

The ABA‐metabolizing capability of the fungus was investigated. Dihydrophaseic acid, and phaseic acid, ABA metabolites in higher plants, were not present in cultures of Ceratocystis coerulescens. When [2‐14C]‐ABA was fed to the fungus, the formation of [2‐14C]‐2‐trans, 4‐trans‐ABA and a second metabolite, less polar than ABA, was observed. This suggests a different metabolic pathway of ABA in the fungus.
Effect of NaCl salinity in vivo and in vitro on ribonuclease activity in the halophyte Suaeda maritima
Authors: Rouxel M. F. , Billard J. P. , Boucaud J.
Published: May 2006

Ribonuclease (EC 2.7.7.17) activity in the obligate halophyte Suaeda maritima (L.) Dum. var. macrocarpa Moq. was studied in relation to salinity (increasing concentrations of NaCl) of incubation and growth media. In vitro, the addition of 50 to 400 mM NaCl did not affect ribonuclease activity. This result, which was also found for Phaseolus vulgaris, indicates that the hydrolase is insensitive to high saline concentrations. The subcellular distribution of RNase activity did not change significantly with the salinity of the medium or with the age of the plant. The microsomal ribonuclease activity expressed on a fresh weight basis represented in every case less than 6% of the total activity. After 23 days of culture, the absence of salt stimulated the activity of soluble ribonuclease in aerial parts of Suaeda; inversely, the capacity of the enzyme was lower under optimal saline conditions (130 mM NaCl). This was also evidenced by transfer of whole plants from a non‐saline to a saline medium. Such a saline shock caused a decrease followed by a stabilization of the capacity of ribonuclease from Suaeda. The influx of NaCl in the tissues lowered the activity of the hydrolase.
Fructose 6‐phosphate metabolism in plants
Authors: Dennis David T. , Greyson Maureen F.
Published: May 2006

The kinetic and regulatory properties of the ATP‐dependent phosphofructokinase from various plant tissues are reviewed. Particular attention is given to the differences in properties between the plastid and cytosolic isozymes of this enzyme. A model for fructose 6‐phosphate utilization in plants is presented which incorporates a role for the pyrophosphate‐dependent phosphofructokinase.
Distribution of 14C assimilates in the storage root of sugar beet plants after import from leaves of different age
Authors: Haeder H. E. , Beringer H.
Published: May 2006

In the sugar beet plant (Beta vulgaris L. ssp. altissima) the vascular bundles of old leaves lead to the center and those of young leaves to the periphery of the storage root. Whether the flux of assimilates follows these anatomical routes was tested by applying 14CO2 for 4 h to either an old (10th) or a young (20th) leaf in intact sugar beet plants. Four‐month‐old plants, which had about 30 leaves, were used in the experiment. The 14C distribution in the storage root was measured by autoradiography and counting in about 20 cross and longitudinal sections per root.

About 37% of assimilated 14C from an old leaf and 23% from a young leaf were exported within 24 h. Although some 14C moved into younger leaves, most was exported into the storage root. During its rapid movement towards the root tip, which took place perferentially in the orthostichon belonging to the [14C]‐treated leaf, the label spread laterally.

The autoradiograms indicate that the distribution of assimilates within the storage root is roughly determined by the course of the vascular bundles extending from the source leaf. The fine distribution, however, seems to be controlled by sucrose gradients between storage cells.
Immunological cross‐reactivity between the light‐harvesting chlorophylla/b‐proteins of a marine green alga and spinach
Authors: Anderson Jan M. , Evans Paula K. , Goodchild David J.
Published: May 2006

Immunoblotting was used to probe the reactivity of rabbit polyclonal antibodies against PS1I and PSI light‐harvesting chlorophyll a/b‐proteins of spinach (Spinacea oleraceaL.) with the light‐harvesting complexes of a siphonaceous marine alga,Codium, that have more chlorophyll b, siphonaxanthin and siphonein instead of the lutein. The spinach LHCII antibodies cross‐reacted only with the apoproteins of Cod‐ium LHCII. Antisera against the spinach LHCI apoproteins showed strong affinity for the apoproteins ofCodiumLHCI, and also reacted with the polypeptides of spinach LHCII and Codium LHCII. Our results indicate some similarities in the amino acid sequences between theCodiumsiphonaxanthin‐Chl a/fe‐proteins of LHCII and LHCI and the corresponding spinach lutein‐chlorophyll a/b‐proteins.
Sterols and sterylglycosides of oats (Avena sativa). Distribution in the leaf tissue and medium‐induced glycosylation of sterols during protoplast isolation
Authors: Kesselmeier Jürgen , Eichenberger Waldemar , Urban Birgit
Published: May 2006

Sterols, sterylglycosides (SG), acylated sterylglycosides (ASG) and steroidal saponins of primary leaves of oat (Avena sativa L. cv. Flämingskrone) were analyzed by thin‐layer chromatography, gas‐liquid chromatography and high‐performance liquid chromatography. Intact leaves, epidermis preparations, epidermis‐stripped leaves, isolated protoplasts and chloroplasts were compared. The mesophyll contained 79% of the total leaf sterols, 80% of the SG and 78% of the ASG, but only 33–67% of the saponins. Free sterols, SG and ASG were mainly localized within the mesophyll, whereas steroidal saponins were localized in the epidermis to a significantly higher extent. The sterol parts consisted mainly of sitosterol, stigmasterol. cholesterol. Δ5‐avenasterol, Δ7‐avenasterol, campesterol and Δ7‐cholestenol, and were quantitatively different in different sterol groups. A higher percentage of sitosterol at the expense of stigmasterol was typical for SG and ASG as compared to free sterols. Only minor differences in the sterol composition were found in a given sterol group when isolated from different tissues. Isolated protoplasts contained only 5–9% of the sterols present in mesophyll cells, indicating that the major part of the free sterols was lost during isolation. Exposure of radioactively labelled leaf segments to either buffer or digestion medium induced rapid transformation of sterols to SG and ASG as shown by the shift of radioactivity from free sterols to the glyeosides. This suggests that two sterol pools exist in the cell: one in the plasmalemma, which is accessible to medium‐induced transformation, and a second non‐accessible pool in the interior membranes (e.g. chloroplasts) of the cell.
Ribulose‐l,5‐bisphosphate carboxylase activity and influence of air pollution in spruce
Authors: Weidner Manfred , Kraus Monika
Published: May 2006

Methods were established, which render possible a simultaneous determination of ri‐bulose‐l,5‐bisphosphate (RuBP) carboxylase (EC 4.1.1.39) activity and chlorophyll content of Norway spruce (Picea abies Karst.) needles from a detergent‐containing aqueous crude extract. Spruce RuBP carboxylase was tentatively characterized with regard to kinetic properties. Recovery experiments employing purified wheat RuBP carboxylase proved quantitative extraction of the enzyme from spruce foliage. Five timber stands consisting of 35–62 years old spruce, two of which exhibited the typical symptoms of recent spruce decline, were compared. For the needle generations 1 to 4 the enzyme activities as well as chlorophyll and protein concentrations were determined. The results do not indicate an involvement of RuBP carboxylase in spruce decline.
Shoot growth in willow (Salix viminalis) in relation to abscisic acid, plant water status and photoperiod
Authors: Barros Raimundo S. , Neill Steven J.
Published: May 2006

The decline in growth rate of field‐grown willow trees in Aberystwyth, U.K., began in mid‐summer and was followed by the senescence and abortion of shoot tips. These events were not triggered by a decline in the length of the natural photoperiod but were coincident with low leaf water potentials that developed in summer. Transient increases in the abscisic acid (ABA) content of shoot tips were observed during the period of declining water potential. These increases were roughly coincident with the onset of growth decline and preceded abortion and senescence of shoot tips. Under controlled conditions growth of both rooted cuttings and potted plants was arrested by short days (8 h) without any increase in tip ABA levels. Growth of rooted cuttings under long days (16 h) was inhibited by exogenous ABA; this inhibition could be relieved by addition of gibberellic acid (GA3) to the nutrient solution. Growth of aseptically cultured apices was also inhibited by ABA; this inhibition was relieved by joint application of GA9 and zeatin riboside.
Plant responses to H2S and SO2 fumigation. I. Effects on growth, transpiration and sulfur content of spinach
Authors: Maas Frank M. , de Kok Luit J. , Hoffmann Ingrid , Kuiper Pieter J. C.
Published: May 2006

Exposure of spinach (Spinacia oleracea L. cv. Monosa) to 0.25 μl l−1 H2S reduced the relative growth rate by 26, 47 and 60% at 15, 18 and 25°C, respectively. Shoot to root ratio decreased in plants fumigated at 18 and 25°C. Growth of spinach was not affected by a 2‐week exposure to 0.10 or 0.25 μl l−1 SO2.

Both H2S and SO2 fumigation increased the content of sulfhydryl compounds and sulfate. A 2‐week exposure to 0.25 μl l−1 H2S resulted in an increase in sulfhydryl and sulfate content of 250 to 450% and 63 to 248% in the shoots, respectively, depending on growth temperature. Exposure to 0.15 and 0.30 μl l−1 H2S at 20°C for 2 weeks resulted in a 46% increase in sulfate content of the shoots at 0.30 μl l−1 and no detectable increase at 0.15 μl l−1 H2S; the sulfate content of the roots increased by 195 and 145% at 0.15 and 0.30 μl l−1 H2S, respectively. Fumigation with 0.25 μl l−1 SO2 at 20°C for 2 weeks resulted in an increase in sulfhydryl content and sulfate content in the shoots of 285% and 300 to 1100%.

H2S fumigation during the 12 h light period or only during the dark period resulted in identical growth reduction and accumulation of sulfhydryl compounds; they were about 50 and 67% of those observed in continuously exposed plants.

H2S‐ and SO2‐exposed plants showed an increased transpiration rate, which was mainly caused by an increased dark‐period transpiration. No effect of H2S and SO2 on the water uptake of the plants and the osmotic potential of the leaves was detected. Plants fumigated with 0.25 μl l−1 H2S for 2 weeks were smaller and differed morphologically from the control plants by slightly more abaxially curved leaf margins. Cross sections of the leaves showed smaller cells at the margins and smaller and fewer air spaces. The increased transpiration in the H2S‐exposed plants is discussed in relation to the observed morphological changes.
Peroxisomes of soybean (Glycine max) root nodule vascular parenchyma cells contain a “nodule—specific” urate oxidase
Authors: Vaughn Kevin C. , Stegink Steven J.
Published: May 2006

The cortex of soybean (Glycine max L. cv. Centennial) nodules contain an organellerich layer of vascular parenchyma tissue, which encircles the elaborate vascular tissue of the nodule. Peroxisomes with small, electron‐opaque nucleoids are found in the vascular parenchyma cells. Positive cytochemical staining for catalase (EC 1.11.1.6) confirms their morphological identification as peroxisomes. Activities of both glycolate oxidase (EC 1.1.3.1) and urate oxidase (EC 1.7.3.3) were detected cytochemically in these peroxisomes. Nodule‐specific urate oxidase was localized principally in the nucleoid region of these vascular parenchyma peroxisomes, as indicated by immunogold labelling using antibodies against nodulin‐35, the nodule‐specific urate oxidase. The density of urate oxidase immunogold labelling in the vascular parenchyma peroxisome nucleoid is similar to that of the more well‐characterized interstitial cell peroxisomes of the infected zone. These results show that the induction of nodule‐specific urate oxidase may be induced in tissue outside of the infected zone.
Gibberellic acid effects on the ultrastructure of endocarp cells of unpollinated ovaries of Pisum sativum
Authors: Vercher Yolaanda , Molowny Asunción , Carbonell Juan
Published: May 2006

Ultrastructural changes of endocarp cells of unpollinated pea (Pisum sativum L. cv. Alaska) ovaries treated and non‐treated with gibberellic acid (GA3) were studied. Following treatment with GA3, the differentiation of cells of the middle zone of the endocarp into sclerenchyma occurred in 3 phases: initial, elongation and maturation. In the initial phase a proliferation of endocarp cells was produced in both GA3treated and non‐treated ovaries. Changes in the cell membrane system (Golgi apparatus, endoplasmic reticulum, plasmalemma) and the formation of primary and secondary cell wall were observed in the 2nd and 3rd phases of treated ovaries. In nontreated ovaries senescence followed the initial phase. These results indicate that GA3 induced the processes involved in the elongation and maturation phases.
Relationship between polar basipetal auxin transport and acropetal Ca2+ transport into tomato fruits
Authors: Banuelos Gary S. , Bangerth Fritz , Marschner Horst
Published: May 2006

The dependence of acropetal Ca2+ transport on polar basipetal indoleacetic acid (IAA) transport was investigated in excised tomato fruits (Lycopersicon esculentum L. Mill.) using an in vitro fruit system. Auxin transport inhibitors like triiodobenzoic acid (TIBA), chlorofluorenolmethyl ester (CME) and naphthylphthalamic acid (NPA) were used in order to investigate the effect of restricted polar basipetal auxin transport on the acropetal transport of 45Ca2+, 86Rb+ and 98Sr2+ into the same fruits. TIBA and CME inhibited basipetal transport of IAA. particularly in 10‐ to 12‐day‐old tomato fruits, and simultaneously restricted the acropetal transport of 45Ca2+. The auxin transport inhibitors failed to significantly reduce the upward transport of 86Rb+ and the transport of 96Sr2+ was less inhibited than that of 45Ca2+. TIBA and CME did not significantly affect the acropetal transport of labelled water into the fruit, nor the cation‐exchange capacity or K+ and Mg2+ concentrations in the tomato fruit. These results support the view that a part of the Ca2+‐specific acropetal transport into tomato fruits is associated with the polar basipetal IAA transport. This Ca2+ transport is independent of the transpiration stream into the fruit and the cation exchange capacity of the fruit tissue.
Release of dormancy during after‐ripening of Agrostemma githago seeds
Authors: de Klerk Geert Jan
Published: May 2006

Freshly harvested seeds of Agrostemma githago L. do not germinate when they are imbibed at 20°C. The block is located in the embryo and is relased by dry storage at 20°C (after‐ripening). Freshly harvested seeds complete only a small part of the processes that occur in after‐ripened seeds during the lag phase prior to germination (radicle protrusion). After‐ripening removed the block on lag phase processes much faster than the block on germination. This was shown both by direct determinations of the completion of lag phase processes and by measurements of the rate of axial protein synthesis, which approximately doubles when seeds are progressing through the lag phase. It is concluded that the percentage germination does not adequately reflect the extent to which the dormancy mechanism has been overcome.
Purification and characterization of glutathione reductase from corn mesophyll chloroplasts
Authors: Mahan James R. , Burke John J.
Published: May 2006

Differences in the apparent molecular weights of the subunits of glutathione reductase (EC 1.6.4.2) from pea chloroplasts and corn mesophyll chloroplasts have been recently reported. In order to more fully describe the differences between the enzymes from these two sources, glutathione reductase from the mesophyll chloroplasts of corn seedlings (Zea mays L. cv. G‐4507) has been purified 200‐fold by affinity chromatography using adenosine 2′,5′‐disphosphate agarose. The purified enzyme had a specific activity of 26 μmol NADPH oxidized (mg protein)‐1 min‐1. The native enzyme had a relative molecular weight of 190 ± 30 kDa and exhibited polypeptides of 65, 63, 34, and 32 kDa when separated on sodium dodecylsulfate‐polyacrylamide gels. Comparisons of the results from electroblotting, native molecular weight and subunit molecular weight analyses suggest that the enzyme exists as a heterotetramer. Optimal enzyme activity was obtained at pH 8 in N‐2‐hydroxyethyl‐piperazine‐N′‐2‐ethanesulfonic acid (HEPES‐NaOH) buffer. The sulfhydryl reagent, n‐ethylmaleimide, inhibited enzymatic activity when incubated in the presence of NADPH while no inhibition was detected with oxidized glutathione in the incubation mixture. Reduced glutathione (5 mM) inactivated the enzyme by 50%. This inactivation followed first order kinetics with a rate constant of 0.0028 s‐1. The enzyme was also inactivated by NADPH. The inactivation reached ca 90% within 30 min and followed first order kinetics with a rate constant of 0.0015 s‐1.
Lack of active K+ uptake in aeroponically grown wheat seedlings
Authors: Zsoldos Ferenc , Vashegyi Ágnes , Erdei László
Published: May 2006

The K+ (86Rb+) uptake and the growth of intact wheat seedlings (Triticum aestivum L. cv. GK Szeged) grown in 0.5 mM CaCl2 solution and of seedlings grown on wet filter paper in Petri dishes were compared under different experimental conditions. Aeroponic (AP) and hydroponic (HP) conditions brought about striking differences in the growth of the roots, whereas the shoot growth was not influenced. The dry weight of the roots was higher for the AP plants than for the HP plants. The AP grown seedlings exhibit a low rate of K+ uptake, which seems to be a passive process. The effect of 2, 4–dinitrophenol (2, 4–DNP) clearly shows the absence of an active component of the K+ uptake in roots grown in air with a high relative humidity. In plants grown under AP conditions the effect of Ca2+ on the K+ uptake is unfavourable, i.e. there is an inhibition (negative Viets effect). Results relating to the effect of 2,4–DNP suggest that the “negative Viets effect” is a feature of the passive K+ uptake. The data suggest that the AP growth conditions play a very important role in the induction and/or development of the ion transport system(s), which becomes impaired under the AP conditions.
Short‐term effects of aphid feeding on photosynthetic CO2exchange and dark respiration in legume leaves
Authors: Hawkins C. D. B. , Aston M. J. , Whitecross M. I.
Published: May 2006

Net CO2exchange rates and dark respiration rates were determined for single attached legume leaves (leaflets) after 6 to 9 days of aphid infestation. Plant‐aphid combinations used were broad bean (Vicia fabaL. cv. Aquadulce) and cowpea [Vigna unguiculata(L.) Walp. cv. Caloona)] infested with cowpea aphids (Aphis craccivoraKoch) and broad bean and garden pea (Pisum sativumL. cv. Victory Freezer) infested with pea aphids [Acyrthosiphon pisum(Harris)]. Leaves from all aphid‐infested plants had significantly greater net CO2exchange rates in the light than their respective controls and rates of dark respiration of leaves from infested cowpea and garden pea were also significantly greater than those of controls. Dark respiration, as a percentage of net CO2exchange rates in the light, was greater in aphid‐infested than in control plants. When the mean net daily carbon gain was calculated for the leaves of each plant‐aphid combination, leaves from aphid‐infested plants had the greatest gain. It is proposed that net CO2, exchange rates increased due to increased sink demand and dark respiration rates increased to meet the increased energy requirements of phloem loading and cellular maintenance associated with aphid feeding. The apparent compensatory carbon gain of infested leaves was consumed by the aphids.
NADP+‐malate dehydrogenase in C3‐plants: Regulation and role of a light‐activated enzyme
Authors: Scheibe Renate
Published: May 2006

The thioredoxin‐dependent light/dark modulation system of the chloroplast is described as a prerequisite enabling the flexible control of fluxes through the various parts of the CO2‐fixation pathway. Both the rapid turnover of the reduced thiol‐containing form of the respective target enzyme, and the metabolite effect upon the reductive enzyme modulation, allow rapid adjustment of the amount of active species to the actual requirements. The structural basis of the regulation of chloroplast NADP+‐malate dehydrogenase (EC 1.1.1.82) is described in more detail. The modulable plastid enzyme is characterized by two sequence extensions not present in any other known NADP+‐ and/or NAD+‐specific malate dehydrogenase. The NADP+‐malate dehydrogenase of C3‐plants is part of the “malate valve”, which catalyzes the export of reducing equivalents in the form of malate from the chloroplast only when the NADPH to NADP+ ratio is high, thus poising the NADPH to ATP ratio required for optimal carbon reduction in the light. The mode of regulation of other light/dark modulated enzymes is discussed.
Chlorophyll content and the light response curve of shade‐adapted conifer needles
Authors: Leverenz Jerry W.
Published: May 2006

Rates of photosynthesis were measured for shade‐adapted conifer needles [Picea abies(L.) Karst.,Picea glauca(Moench) Voss,Picea mariana(Mill.) B. S. P.,Picea sitchensis(Bong.) Carr.,Pinus sylvestrisL.] illuminated on i) their top surface, ii) their top and bottom surfaces simultaneously, or iii) uniformly in a light integrating sphere. The rate of bending of the light response curve of photosynthesis was strongly correlated with the amount of chlorophyll per unit of illuminated leaf area, when the amounts of chlorophyll were above 200 mg m−2. Below 200 mg m−2only small differences in the rate of bending occurred and the light response curves took the form of a quasi‐Blackman response. At chlorophyll contents below 200 mg m−2the rate of bending of the light response curves was insignificantly different from a mean published value for enzymatically isolated cells of angiosperm leaves (I. Terashima and T. Saeki. Ann. Bot. 56: 489–499, 1985). The apparent quantum yield of photosynthesis (based on incident light) also showed a response to chlorophyll content not different from the pattern reported for angiosperm leaves (E. K. Gabrielsen. Physiol. Plantarum 1: 5–37, 1948). Neither CO2nor O2concentration significantly affected the rate of bending of the light response curves. It is concluded that the light response curve of individual chlorenchyma cells is a quasi‐Blackman response and that the rate of bending of the light response curve of intact leaves is a strong function of the development of gradients of light and thus the chlorophyll content of leaves.
Seasonal variations in the properties of ribosome assemblies from vegetative buds of Scots pine
Authors: Kupila‐Ahvenniemi Sirkka , Lindfors Aija , Häggman Hely
Published: May 2006

The amount of total ribosome assemblies extractable from the vegetative buds of 2 m high Scots pine (Pinus sylvestrís L.) plants remained more or less constant throughout the sampling period from September to May. The stability of the ribosomes, the shape of the polysome profiles obtained after sucrose density gradient centrifugation and the clustering of material as seen in the scanning electron micrographs suggested the presence of storage formations during the winter.

All samples of isolated ribosomes were able to synthesize proteins in vitro. During midwinter the translation capacity, when calculated on a ribosome unit basis, was about one third of that found in September and May. This reflects not only the occurrence of storage formation during the winter, but also the amount of initiated translation processes at any given time. The decrease in the in vitro translation capacity in the autumn ceases around the end of November. Ribosome activity starts to increase as early as the end of January or beginning of February. It seems that the reactions are triggered either by an endogenous clock or by the change in the daylength.
Nitrogen fixation (C2H2 reduction) by Medicago nodules and bacteroids under sodium chloride stress
Authors: Bekki Abdelkader , Trinchant Jean‐Charles , Rigaud Jean
Published: May 2006

Medicago ciliaris (L.) All., a salt‐tolerant legume, was not nodulated by Rhizobium meliloti (2011), a strain commonly used for field inoculation of alfalfas. A strain of Rhizobium meliloti (ABS7) was isolated from saline Algerian soils. It is generally more salt‐resistant than strain 2011, exhibits a higher rate of growth and induces the formation of nodules on M. ciliaris. C2H2 reduction activity of M. ciliaris nodules was inhibited by 50% in the presence of 200 mM NaCl in the culture medium. whereas 100 mM NaCl was sufficient to inhibit the activity of nodules of M. sativa (L. cv. Europe). C2H2 reduction by bacteroids, isolated from nodules of the two species of alfalfa, was directly inhibited by the presence of NaCl in the incubation medium. In both cases, glucose could support bacteroid nitrogen fixation, but only in a narrow range of O2 tensions. Bacteriods from M. ciliaris were more tolerant to salt than M. sativa ones. The salt resistance of bacteroids from nodules of plants watered with NaCl solutions was not improved in either species. Salt directly added to the incubation mixture of bacteroids or to the culture medium of plants inhibited O2 uptake of bacteroids isolated from nodules of both M. ciliaris and M. sativa. The depressive effect of NaCl on bacteroid C2H2 reduction could be directly related to the drop in bacteroid respiration. The nitrogen fixation capacity of the M. ciliaris‐Rhizobium meliloti (ABS7) symbiosis under saline conditions leads us to recommend the introduction of this association in salt‐troubled areas.