bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of NaCl, Cd(NO3)2 and air humidity on transpiration of Tamarix aphylla
Authors: Hagemeyer Jürgen , Waisel Yoav
Published: May 2006

Transpiration rates of young Tamarix aphylla (L.) Karst, plants grown in hydroponics were measured under NaCl‐ and Cd(NO3)2‐stress. Transpiration rates were negatively correlated with the relative humidity of the ambient air at all NaCl concentrations investigated. Low and intermediate concentrations of Cd2+ (45 and 90 μM, respectively) in the medium caused an increase in transpiration rates. This was particularly pronounced at low levels of relative humidity. At 180 μM Cd2+, transpiration rates dropped, probably as a result of root damage due to Cd2+ toxicity. Since the transpiration rates differed by a factor of ca 3 between day and night, it is concluded that the stomata did not lose their ability to regulate transpiration under the influence of NaCl or of Cd(NO3)2. The transpiration behaviour of T. aphylla indicates that the effect of water vapour pressure (presented as relative humidity) on the degree of stomatal opening is small. Under conditions of ample water supply transpiration follows the evaporative demand of the ambient air and is influenced by the water uptake capacity of the root system as well as by other environmental factors, e.g. light.
Effect of nitrogen starvation on ammonium assimilation by Chlamydomonas reinhardtii
Authors: Menacho Alberto , Vega José M.
Published: May 2006

In nitrogen‐starved Chlamydomonas reinhardtii, wild type, strain 21 gr cells, consumption of nitrate, nitrite and ammonium may occur in the dark in the absence of an added carbon source. Consumption of ammonium in the dark was about 25% higher than in the light, while consumption of nitrate or nitrite in the dark was lower than in the light.

N starvation produced a linear increase with time in the intracellular level of glutamine synthetase (GS, EC 6.3.2.1) and glutamate synthase (NADH‐GOGAT, EC 1.4.1.14 and ferredoxin‐GOGAT, EC 1.4.7.1) activities in C. reinhardtii. The effect on GS1 (3‐fold) and NADH‐GOGAT (4.5‐fold) was higher than that on GS2 (1.5‐fold) and ferredoxin‐GOGAT (1.5‐fold).

Experiments with methylammonium, L‐methionine‐D, L‐sulfoximine (MSX) and azaserine suggest that: 1) Ammonium itself decreases the intracellular levels of glutamine synthetase and ferredoxin‐glutamate synthase activities; and 2) a metabolite resulting from ammonium assimilation by the alga may be a negative modulator of NADH‐glutamate synthase activity.
Fiber development in preanthesis cotton ovules
Authors: Davidonis Gayle H.
Published: May 2006

A tissue culture method was developed to investigate the production of cotton (Gossypium hirsutum L. cv. Texas Marker‐1) fibers in vitro. Ovules were excised from 3, 5, 7 and 9 days preanthesis ovaries and placed on an agar‐solidified, modified Murashige and Skoog medium containing 2.3 μM kinetin and 0.45 μM–2,4–dichlo‐rophenoxyacetic acid or 2.3 μM kinetin and 10.7 μM naphthaleneacetic acid. Ovules formed fibers and callus tissue. Fibers formed in vitro were up to 10 mm long, 10–22 μ wide and the cell wall was 1–3 μM thick. Callus tissue cells were subcultured for over 25 weeks and their degree of elongation was monitored. The ability of ovule‐derived cells to direct expansion in a longitudinal direction diminished, while lateral expansion increased with time in culture.
An analysis of the light‐induced unrolling of the grass leaf
Authors: Virgin Hemming I.
Published: May 2006

The light‐induced unrolling of primary leaves of dark‐grown wheat (Triticum aestivum L. cv. Weibull's Folke) and barley (Hordeum vulgare L. cv. Weibull's Ida) does not follow the reciprocity law but shows maxima and minima like the phototropic dose‐response curve. These fluctuations of the unrolling can be explained by differences and non‐synchronizations of the growth in width of the two sides of the leaves. As the thickness of the leaves is small, even minute differences between the widths of the two sides will give rise to great changes in the unrolling and thus in the projection values.
Occurrence and activity of hydrogenase in symbiotic Frankia from field‐collected Alnus incana
Authors: Sellstedt Anita
Published: May 2006

Occurrence and activity of the hydrogen uptake enzyme were studied in root nodule homogenates made from plants of Alnus incana (L.) Moench collected from field sites in the northern part of Sweden. Nitrogenase (EC 1.7.99.2) activity (estimated by acetylene reduction) and hydrogen evolution were studied in excised nodules. All Frankia sources showed acetylene reduction activity, and possessed a hydrogen uptake system. Hydrogen uptake in nodule homogenates from the Frankia sources measured at 23.8 μM H2 ranged from 0.04 to 5.0 μmol H2 (g fresh weight nodule)−1 h−1. The H2 uptake capacity of nodule homogenates from one of the Frankia sources was almost 8 times higher than the hydrogen evolution from nitrogenase, both expressed on a nodule fresh weight basis. Frankia sources from field sites 6 and 11 showed Km for H2 of 13.0 and 23.6 μM H2, respectively. This indicates similarities in the hydrogen uptake enzymes in the two Frankia sources. It is concluded that hydrogen uptake is a common characteristic in Frankia.
Effects of aluminium on growth and kinetics of K+(86Rb) uptake in two cultivars of wheat (Triticum aestivum) with different sensitivity to aluminium
Authors: Pettersson Sune , Strid Håkan
Published: May 2006

Two cultivars of wheat (Triticum aestivum L. cvs Kadett and WW 20299) were grown for 9 days with 20% relative increase in nutrient supply per day at pH 4.1. Aluminium at 50 μM retarded the growth of roots more than that of shoots in both cultivars, thus decreasing the root/shoot ratio. The inhibition was largest in WW 20299. With long term Al treatment (9 days), Km for K+(86Rb) influx increased five times in both cultivars and Vmax decreased in WW 20299. Efflux of K+(86Rb) was little affected. When the roots were treated with aluminium for two days, only relative growth rate of roots was retarded, while growth of shoots was unaffected and influx of K+(86Rb) adjusted to the actual K+ demand of the plants. It is concluded that the effects of aluminium on K+ uptake in these wheat cultivars are not primary factors contributing to aluminium sensitivity. However, in soil with Al the demand for a comparatively high concentration of K+ to maintain an adequate K+ uptake rate, in combination with a slow growth rate of the roots, may secondarily lead to K+ deficiency in the plants.
Ultrastructural changes arising from freezing of leaf blade cells of rye (Secale cereale): an investigation using freeze‐substitution
Authors: Harvey Diana M.R. , Pihakaski Kaarina
Published: May 2006

The survival at sub‐zero temperatures of leaf blade cells of rye (Secale cereale L. cv. Voima), which had not been cold acclimated, was determined by measuring the efflux of ninhydrin‐positive substances: 50% of the cells were dead at −4°C (LT50) and none survived at −12°C or below. Examination of ultrastructural changes during cold hardening and freezing injury requires frozen tissues prepared for transmission electron microscopy without thawing. Specimens were prepared from leaf blade segments at room temperature, −4°C or −12°C by plunge freezing at 3 m s−1 into a cooling medium at −170°C followed by freeze‐substitution in acetone with OsO4 fixation. Comparisons of room temperature specimens were made with those prepared by chemical fixation using glutaraldehyde/paraformaldehyde/tannic acid. On freezing to −12°C, the cells were severely dehydrated and distorted, the vacuoles severely shrunken and the cytoplasm and mitochondria disorganized whereas the chloroplasts were little affected. On freezing to −4°C, some cells were as disorganized as those at −12°C, others were relatively intact, and some showed evidence of intracellular ice crystal formation.
Recovery of sulfate transport into heterotrophic tobacco cells from inhibition by reduced glutathione
Authors: Rennenberg Heinz , Kemper Oliver , Thoene Barbara
Published: May 2006

In heterotrophic tobacco cells (Nicotiana tabacum L. cv. Samsun) inhibition of sulfate transport by reduced glutathione (GSH) is a reversible process. When GSH was removed from the culture medium subsequent to a 10‐h treatment with 1 mM GSH, sulfate transport began to recover after a lag period of ca 4 h and reached the transport rates of controls without GSH within another 3–4 h. Recovery was prevented when inhibitors of protein synthesis, i.e. cycloheximide or puromycin, were added to the medium upon removal of GSH, even if low concentrations (cycloheximide 1 μM; puromycin 250 μM) were applied. At these low concentrations the rate of synthesis of sulfate transport entities was maintained at the rate of degradation in the absence of GSH. The post‐transcriptional polyadenylation inhibitor cordycepin and the transcription inhibitor α‐amanitin only slightly reduced recovery of sulfate transport from inhibition by GSH. Apparently, protein synthesis is required for this recovery, suggesting that inhibition of synthesis of sulfate carrier entities is the mechanism of action of GSH on sulfate transport in heterotrophic tobacco cells. An initial rate of net increase in sulfate transport during recovery from inhibition of GSH of 3.6±0.2 U h−1 was calculated [1 U=1 nmol sulfate (g DW)−1 min−1]. This rate of increase is small compared with the rate of decrease in sulfate transport at maximum inhibition by cycloheximide (110±3 U h−1). However, with increasing time of exposure without GSH, the net increase in sulfate transport was enhanced to a maximum rate of 96±3 U h−1, measured 5–7 h after GSH had been removed from the media. Apparently, the rate of synthesis of sulfate transport entities in heterotrophic tobacco cells is about twice its rate of degradation.
Effects of glutamine and K‐glutamate on assimilation of [15N]‐nitrate during auxin treatment for root formation in vitro (Pinus pinaster)
Authors: Faye M. , Ourry A. , Saidali‐Savi C. , Dargent R. , Boucaud J. , David A.
Published: May 2006

In order to establish the relationship of nitrogen nutrition to root formation in vitro, efficiency of various forms of nitrogen supply was investigated in micropropagated shoots of Pinus pinaster. Nitrate (3.3 mM as N) containing medium supplemented with glutamine (2 mM as N) resulted in optimal rooting (control medium) whereas the rooting response was inhibited by the presence of glutamate (2 mM as N) in the medium. Study of 15NO−3 behaviour in shoots cultured on the control medium showed a marked increase of 15N incorporation during the second half of a period of auxin treatment (total duration 16 days). The majority of the nitrogen incorporated from the medium was accumulated into protein in the rooting zone. Autoradiography of [3H]‐thymidine in this reacting zone showed strong DNA synthesis at this time. Addition of glutamate both prevented the root formation process and resulted in a marked slowdown of nitrate uptake and decrease of protein synthesis.
Effects of abscisic acid and proline on adaptation of tobacco callus cultures to salinity and osmotic shock
Authors: Eberhardt H.‐J. , Wegmann K.
Published: May 2006

Tobacco callus (Nicotina tabacum cv. Badischer Geudertheimer) took up sorbitol rapidly and without a lag period from media with up to 0.7 M of the polyol. Accumulation of proline was greatly enhanced under these conditions and was proportional to the absorbed sorbitol, while the viability of the callus cultures was quite low after a few hours of incubation. Under moderate conditions (0.1 M sorbitol) as well as under severe osmotic shock (0.7 M sorbitol), the cells adapted by adjusting the sorbitol/proline ratio to ca 3. NaCl (0.1 M) had the same effect as sorbitol (0.7 M) on the survival rate, but only slightly affected proline synthesis in the first hours of incubation. Addition of 107 or 10 5M abscisic acid (ABA) did not increase the proline content, but 10 7M ABA delayed the deleterious effect of NaCl and improved the state of the cells. No influence of abscisic acid during the incubation with sorbitol could be detected. Two different strategies for the adjustment of tobacco callus to salinity and sorbitol are suggested: Non‐ionic stress is controlled by the accumulation of proline, whereas ABA could be involved in the adaptation to ionic stress.
The effect of salt stress on polyamine biosynthesis and content in mung bean plants and in halophytes
Authors: Friedman Ra'anan , Altman Arie , Levin Nitsa
Published: May 2006

The activity of L‐arginine decarboxylase (EC 4.1.1.19) and L‐ornithine decarboxylase (EC 4.1.1.17), polyamine content, and incorporation of arginine and ornithine into polyamines, were determined in mung bean [Vigna radiata (L.) Wilczek] plants subjected to salt (hypertonic) stress (NaCl at 0.51–2.27 MPa). Changes in enzyme activity in response to hypotonic stress were determined as well in several halophytes [Pulicaria undulata (L.), Kostei, Salsola rosmarinus (Ehr.) Solms‐Laub, Mesembryanthemum forskahlei Hochst, and Atriplex halimus L.].

NaCl stress, possibly combined with other types of stress that accompanied the experimental conditions, resulted in organ‐specific changes in polyamine biosynthesis and content in mung bean plants. The activity of both enzymes was inhibited in salt‐stressed leaves. In roots, however, NaCl induced a 2 to 8‐fold increase in ornithine decarboxylase activity. Promotion of ornithine decarboxylase in roots could be detected already 2 h after exposure of excised roots to NaCl, and iso‐osmotic concentrations of NaCl and KCl resulted in similar changes in the activity of both enzymes. Putrescine level in shoots of salt‐stressed mung bean plants increased considerably, but its level in roots decreased. The effect of NaCl stress on spermidine content was similar, but generally more moderate, resulting in an increased putrescine/spermidine ratio in salt‐stressed plants. Exposure of plants to NaCl resulted also in organ‐specific changes in the incorporation of both arginine and ornithine into putrescine: incorporation was inhibited in leaf discs but promoted in excised roots of salt‐stressed mung bean plants.

In contrast to mung bean (and several other glycophytes), ornithine and arginine decarboxylase activity in roots of halophytes increased when plants were exposed to tap water or grown in a pre‐washed soil—i.e. a hypotonic stress with respect to their natural habitat. NaCl, when present in the enzymatic assay mixture, inhibited arginine and ornithine decarboxylase in curde extracts of mung bean roots, but did not affect the activity of enzymes extracted from roots of the halophyte Pulicaria.

Although no distinct separation between NaCl stress and osmotic stress could be made in the present study, the data suggest that changes in polyamines in response to NaCl stress in mung bean plants are coordinated at the organ level: activation of biosynthetic enzymes concomitant with increased putrescine biosynthesis from its precursors in the root system, and accumulation of putrescine in leaves of salt‐stressed plants. In addition, hypertonic stress applied to glycophytes and hypotonic stress applied to halophytes both resulted in an increase in the activity of polyamine biosynthetic enzymes in roots.
Modification of polyuronides and hemicelluloses during muskmelon fruit softening
Authors: McCollum T. Gregory , Huber Donald J. , Cantliffe Daniel J.
Published: May 2006

The loss of flesh firmness during muskmelon (Cucumis melo var. reticulatus L. Naud. cv. Galia) fruit ripening was related temporally to modifications of pectic and hemicellulosic polysaccharides, and a net loss of non‐cellulosic neutral sugars. An increase in solubility and a decrease in molecular size of polyuronides occurred during ripening; however, the decrease in molecular size was apparently not the result of polygalacturonase (EC 3.2.1.15) activity. Molecular size of hemicelluloses shifted from larger to smaller polymers during ripening, and this decrease was accompanied by changes in neutral sugar composition. Galactose, glucose, and xylose were the predominant neutral sugars in the hemicellulosic polymers. On a mol% basis there were decreases in galactose and glucose in large hemicellulosic polymers with ripening. Relative xylose content approximately doubled in the large polymers during ripening; xylose was the predominant neutral sugar in the small polymers and remained fairly constant.
Unusual regulatory properties of sucrose‐phosphate synthase purified from soybean (Glycine max) leaves
Authors: Nielsen Tom H. , Huber Steven C.
Published: May 2006

Sucrose‐phosphate (SPS) from source leaves of soybean (Glycine max (L.) Merr. cv. Ransom II) was purified 74‐fold to a final specific activity of 1.8 U (mg protein)1. The partially purified preparation was free from phosphoglucoseisomerase (EC 5.3.1.9), pyrophosphatase (EC 3.6.1.1), phosphoenolpyruvate‐phosphatase (EC 3.1.3.‐), phosphofructokinase (EC 2.7.1.11), and uridine diphosphatase (EC 3.6.1.6), and was used for characterization of the kinetic and regulatory properties of the enzyme. The enzyme showed hyperbolic saturation kinetics for both fructose‐6‐phosphate (Km=0.57 mM) and UDPGlucose (UDPG) (Km=4.8 mM). The activity of SPS was inhibited by the product UDP. In vitro this inhibition could be partially overcome by the presence of Mg2+. Inorganic orthophosphate was only slightly inhibitory (35% inhibition at 25 mM phosphate). Glucose‐6‐phosphate (up to 20 mM) had no effect on activity, and did not show any significant interaction with phosphate inhibition. A range of potential effectors was tested and had no effect on SPS activity: Glucose‐1‐phosphate, fructose‐1, 6‐bisphosphate, α‐glycero‐phosphate, dihydroxyacetone‐phosphate, 3‐phosphoglyceric acid, (all at 5 mM), sucrose at 100 mM and pyrophosphate at 0.1 mM. The apparent lack of allosteric regulation of soybean SPS makes this enzyme markedly different from SPS previously characterized from spinach and maize.
Asparagine and regulation of photoinduced rhythm in Penicillium claviforme
Authors: Piskorz‐Binczycka B. , Jerebzoff S. , Jerebzoff‐Quintin S.
Published: May 2006

A photosensitive reaction involved in the expression and regulation of the endogenous sporulation rhythm in Penicillium claviforme Bainier CBS 126‐23 has been described earlier by our team. The present work shows that asparagine plays a central role in this periodic system. The 24–26 h periodicity, which becomes desynchronized over a few days, was affected by supplying asparagine (1 to 25 mM). a) The rhythm remained synchronized for at least 3 weeks, for all the asparagine concentrations used, b) The period increased successively from one cycle to the next (from 35±3 h to 73±8 h over 6 cycles) for 1 mM asparagine. This period lengthening became less and less accentuated as the asparagine concentration was increased. At ≥10 mM, the period was stable; it was 33±5 h for 10 mM and 22±1.5 h for 25 mM asparagine. Otherwise asparagine could not elicit rhythmicity in darkness or in dim continuous light (≤5 μW m−2).
Binding of 124‐kilodalton oat phytochrome to liposomes and chloroplasts
Authors: Singh Bal Ram , Choi Jung‐Kap , Kim In‐Soo , Song Pill‐Soon
Published: May 2006

Binding of the radio‐iodinated 124‐kDa oat (Avena sativa L. cv. Garry) phytochrome to liposomes and chloroplasts was investigated as a model system in order to understand the molecular affinity of phytochrome toward cellular organelles in plants. The binding of intact (124 kDa) phytochrome to liposomes and chloroplasts is hydrophobic in nature, as in the case of the degraded (118/114 kDa) phytochrome, but electrostatic interactions play a greater role in the intact phytochrome. The physiologically active Pfr form of the intact phytochrome showed a binding preference over the inactive Pr form with neutral liposomes and chloroplasts. However, the Pfr form of intact phytochrome exhibits smaller binding preference than the Pfr form of degraded phytochrome over their respective Pr forms (see Kim, I.‐S. and Song, P.‐S. 1981, Biochemistry 20: 5482–5489, for degraded phytochrome binding). These results indicate that the 6/10 kDa N‐terminus segment, which is lost in the degraded phytochrome, plays an important role in determining the protein surface properties of the intact phytochrome. A competitive binding study on phytochrome also suggested that the Pfr form had a greater binding affinity for chloroplasts than the Pr form. However, the physiological activity of the Pfr form may not be explained simply by the observed difference in binding affinity between the two forms of phytochrome.
Porphyrinogenesis in maize as affected by bidentate chelators of iron
Authors: Hodgins R. R. W. , van Huystee R. B.
Published: May 2006

Etiolated maize (Zea mays L. cv. Senesca Chief hybrid sweet) leaves incubated in darkness with bidentate chelators of iron are shown to accumulate protoporphyrin and Mg‐porphyrins to concentrations higher than controls. The accumulation of 5‐aminolevulinic acid in vivo is inhibited by chelators. The heme content of the chelator treated tissues was not decreased relative to the controls. The presence of bidentate chelators inhibited the metabolism of porphobilinogen in crude extracts of maize. The porphyrinogenic effect of chelators in maize is different than that reported for bean. It is suggested that enhancement of porphyrin accumulation in maize in the presence of bidentate chelators of iron is the result of an increased stability of endogenous porphobilinogen.
Diagnostic parameters for selecting against novel spruce (Picea abies) decline: III. Response of photosynthesis and transpiration to O3 exposures
Authors: Saxe Henrik , Murali N. S.
Published: May 2006

The dose‐ and time‐response effects of single 4 h day‐time exposures of 0.064, 0.166, 0.336, 0.452 or 0.693 μl l−1 (ppm) O3 followed by single 4 h night‐time exposures of 0.078, 0.198, 0.378, 0.502 or 0.747 μl l−1 O3 on photosynthesis, transpiration and dark respiration were examined for nine Carpatho‐Ukrainian (‘Rachovo’) half‐sib families and for two populations. ‘Westerhof’ from the FRG and ‘Schmiedefeld’ from the GDR, of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season. Needles were scorched by 4 h exposures to 0.336 μl l−1 O3 and higher.

The lag before photosynthesis and transpiration responded significantly to O3 decline took from a few minutes at the highest concentration to several hours at the lower concentrations. Recovery of photosynthesis and transpiration was absent or extremely slow. Photosynthesis of the different spruce types was affected significantly differently, the most sensitive spruce having its photosynthesis suppressed 1.9 times and its transpiration 1.6 times more than the most tolerant spruce. The physiological responses of ‘Westerhof’ were less sensitive than the average ‘Rachovo’ half‐sibs. Neither night transpiration nor dark respiration were affected by high doses of night O3, preceded by day O3 exposures.

The gradients of different photosynthesis and transpiration sensitivities of the young half‐sibs (and ‘Westerhof’) demonstrated a significant, positive, mutual correlation, and significant positive correlations with the gradient of novel decline symptoms of their parents growing in Danish forests. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters in laboratory tests for selection against novel spruce decline.
ATPase activity of isolated plasma membrane vesicles of leaves of Elodea as affected by thiol reagents and NADH/NAD+ ratio
Authors: Elzenga J. Theo M. , Staal Marten , Prins Hidde B. A.
Published: May 2006

The goal of this study was to test the hypothesis that the plasma membrane‐bound ATPase activity is influenced by the redox poise of the cytoplasm. Purified plasma membrane vesicles from leaves of Elodea canadensis Michx. and E. nuttallii (Planch.) St. John were isolated using an aqueous polymer two‐phase batch procedure. The distribution of marker enzyme activities confirmed the plasma membrane origin of the vesicles. The vesicles exhibited NADH‐ferricyanide reductase activity, indicating the presence of a redox chain in the plasma membrane. The K+, Mg2+‐ATPase activity associated with these vesicles was inhibited by the sulfhydryl reagents N‐ethylmaleimide and glutathione (GSSG). Furthermore the activity was inhibited by NAD+. This inhibition by NAD+ was relieved by increasing the NADH/NAD+ ratio. The possibility that the ATPase activity is regulated by the cytoplasmic NAD(P)H/ NAD(P)+ ratio is discussed, as well as the role of a plasma membrane‐bound redox chain.
Impairment of photosystem 2 activity at the level of secondary quinone electron acceptor in chloroplasts treated with cobalt, nickel and zinc ions
Authors: Mohanty Narendranath , Vass Imre , Demeter Sándor
Published: May 2006

The toxicity of heavy metals on photosystem 2 photochemistry, was investigated by monitoring Hill activity, fluorescence, and thermoluminescence properties of photosystem 2 (PS 2) in pea (Pisum sativum L. cv. Bombay) chloroplasts. In Co2+‐, Ni2+‐ or Zn2+‐treated chloroplasts 2,6‐dichlorophenolindophenol‐Hill activity was markedly inhibited. Addition of hydroxylamine which donates electrons close to PS 2 reaction center did not restore the PS 2 activity. Co2+‐, Ni2+ or Zn2+ also inhibited PS 2 activity supported by hydroxylamine in tris (hydroxymethyl)aminomethane (Tris)‐inactivated chloroplasts. These observations were confirmed by fluorescence transient measurements. This implies that the metal ions inhibit either the reaction center or the components of PS 2 acceptor side. Flash‐induced thermoluminescence studies revealed that the S2Q−A charge recombination was insensitive to metal ion addition. The S2Q−B charge recombination, however, was inhibited with increase in the level of Co2+, Ni2+ or Zn2+. The observed sensitivity of S2−B charge recombination in comparison to the stability of S2Q−A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. QB. We suggest that Co2+, Ni2+ or Zn2+ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify QB site, leading to the loss of PS 2 activity.
Red‐light and blue‐light photoreceptors controlling chlorophyll a synthesis in the red alga Porphyra umbilicalis and in the green alga Ulva rigida
Authors: Lopez‐Figueroa F. , Niell F. X.
Published: May 2006

Chlorophyll synthesis is stimulated by red light in the green alga Ulva rigida C. Ag. and in the red alga Porphyra umbilicalis (L.) Kützing. Because the effect of red light showed some far‐red reversibility in successive red and far‐red light treatments, the involvement of phytochrome or a phytochrome‐like photoreceptor is suggested. The extent of the response is dependent on exposure and photon fluence rate of red‐light pulses. In addition to the effect of red light, a strong stimulation of chlorophyll synthesis by blue light was only observed in Ulva rigida. The effect of blue light shows also some far‐red reversibility. In the green alga the accumulated chlorophyll is higher after blue light pulses than after red light pulses. In Porphyra umbilicalis, however, the contrary is observed. In Ulva rigida the involvement of a blue light photoreceptor in addition to phytochrome or a phytochrome‐like photoreceptor is proposed. The different responses to red and blue light in both algae are explained in terms of their adaptation to the natural light environment.
On the possible control of ultraviolet‐B induced response in growth and photosynthetic activities in higher plants
Authors: Kulandaivelu G. , Maragatham S. , Nedunchezhian N.
Published: May 2006

When Vigna sinensis L.cv. Walp seedlings were grown under control (from four 40 W white fluorescent tubes) and enhanced ultraviolet‐B (UV‐B) radiation (four 40 W white fluorescent tubes plus one Philips 20W/12 sun lamp) a large inhibition in seedling growth, particularly shoot eelongation and leaf expansion, was observed under enhanced UV‐B radiation. The UV‐B radiation also reduced the overall photosynthetic activity as measured by chlorophyll fluorescence induction. In order to check whether UV‐B causes any destruction of auxins, seedlings with either their shoot tip or primary leaves were covered with black paper and kept under both light conditions. Both the fully exposed and shoot tip‐covered seedlings showed a similar negative response on growth characteristics and physiological activities. Leaf‐covered seedlings showed well preserved photosynthetic activity under both light conditions. However, in these seedlings the pigment content decreased more than under other treatment conditions.

Our experiments provide evidence for distinguishing between the UV‐B induced responses on growth and physiological activities; while the former may be controlled through auxins, the latter is probably by direct action on the organelles.
Biochemical and histochemical detection of endoproteolytic activities involved in ovary senescence or fruit development in Pisum sativum
Authors: Vercher Yolanda , Carrasco Pedro , Carbonell Juan
Published: May 2006

The appearance of endoproteolytic activities related to the senescence of unpollinated pea (Pisum sativum L. cv. Alaska) ovaries, or with fruit development induced by gibberellic acid (GA3), was examined simultaneously by biochemical and histochemical techniques using gelatin as substrate. Biochemical detection was carried out by gelatin‐containing sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis. Histochemical detection was performed using a gelatin film technique. No differences in endopeptidase activity were found in extracts from non‐treated or developing ovaries during the two first days post‐anthesis. After day 3 non‐treated ovaries showed a marked increase in activity as well as two new bands with proteolytic activity, associated with the beginning of the senescence. At the same time a new activity was also located at the endocarp. In developing ovaries activity was only observed around vascular cells of the mesocarp at the end of the period studied (4–5 days post‐anthesis). Activity detected in the ovules was essentially the same in both GA3‐treated and non‐treated ovaries.
Wound‐induced ethylene production, phenolic metabolism and susceptibility to russet spotting in iceberg lettuce
Authors: Ke Dangyang , Saltveit Mikal E.
Published: May 2006

Mechanical wounding by cuts or punctures caused a brief increase in ethylene production by iceberg lettuce (Lactuca sativa L.) leaf tissue. Wounding increased phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5) activity, which was a function of the degree of injury. Wound‐induced PAL activity appeared after 4 h and reached maximum activity in about 24 h before slowly declining to normal levels in about a week. A signal for PAL induction was transmitted at about 0.5 cm h−1 from the site of injury to cells up to 2.5 cm away. Treatment with 100 μ2‐aminoethoxyvinylglycine prevented wound‐induced ethylene production but did not affect induced PAL activity. Injury increased the concentration of several soluble phenolic compounds that were easily oxidized to brown substances by polyphenol oxidase (EC 1.10.3.2) isolated from lettuce tissue. Wounding also increased peroxidase (EC 1.11.1.7) activity and lignin content, with cell wall lignification localized in wounded and adjacent cells. Although wounding alone did not induce russet spotting, it did greatly increase susceptibility to ethylene‐induced russet spot development. In the presence of 3 μ1−1 ethylene, the russet spot score increased as the degree of injury increased.
Respiration rate in maize roots is related to concentration of reduced nitrogen and proliferation of lateral roots
Authors: Granato Tom C. , Raper C. David , Wilkerson Gail G.
Published: May 2006

The relationship between specific rate of respiration (respiration rate per unit root dry weight) and concentration of reduced nitrogen was examined for maize (Zea mays L.) roots. Plants with 2 primary nodal root axes were grown for 8 days in a split‐root hydroponic system in which NO‐3 was supplied to both axes at 1.0 mol m−3, to one axis at 1.0 mol m−3 and the other axis at 0.0 mol m−3 or to both axes at 0.0 mol m−3 Respiration rates and root characteristics were measured at 2‐day intervals. Specific rate of respiration was positively correlated in a nonlinear relationship with concentration of reduced nitrogen. The lowest specific rates of respiration occurred when neither axis received exogenous NO−3 and the concentration of reduced nitrogen in the axes was less than 9 mg g−1. The greatest rates occurred in axes that were actively absorbing NO−3 and contained more than 35 mg g−1 of reduced nitrogen. At 23 mg g−1 of reduced nitrogen, below which initiation of lateral branches was decreased by 30–50%. specific rate of respiration was 17% greater for roots actively absorbing NO−3 than for roots not absorbing NO−3 Increases in specific rate of respiration associated with concentrations of reduced nitrogen greater than 23 mg g−1 were concluded to be attributable primarily to proliferation of lateral branches.
Effect of UV‐B (290–320 nm) irradiation on growth and metabolism of cucumber cotyledons
Authors: Takeuchi Yuichi , Akizuki Megumi , Shimizu Hideyuki , Kondo Noriaki , Sugahara Kiyoshi
Published: May 2006

Cucumber (Cucumis sativus L. cv. Natsusairaku 3) seedlings were grown in a growth cabinet under UV‐B (290–320 nm) irradiation (equivalent to the UV‐B radiation normally incident at Tokyo, 36°N latitude, during clear sky conditions in mid‐april on a weighted daily fluence basis) and a UV‐B‐free control condition. UV‐B irradiation inhibited the growth of the cotyledons, i.e. the increase in area, and increase in fresh and dry weights of the cotyledons. The greatest inhibition rate was observed in the increase in area, causing a significant increase in specific leaf weight (the ratio of weight to area). UV‐B irradiation had no significant effect on DNA and RNA contents in the cotyledons, but decreased protein content slightly. In contrast, the irradiation reduced the amounts of organic acids and soluble sugars, indicating that primary carbon metabolism was very sensitive to UV‐B radiation. UV‐B irradiation lowered the photosynthetic activity in the cotyledons without any effect on chlorophyll content and respiratory activity. These results indicate that UV‐B radiation at the ambient level may act as a physiological stress in some UV‐sensitive plants.
Preparatory studies for the use of plant protoplasts in space research
Authors: Rasmussen Ole , Baggerud Carolyn , Iversen Tor‐Henning
Published: May 2006

An experiment using plant protoplasts has been accepted for the IML‐1 mission to be flown on a space shuttle in 1991. Preparatory experiments include studies of cell wall formation, cell division, the effect of simulated weightlessness using fast and slow rotating clinostats, and the development and testing of hardware for the IML‐1 mission. After 24 h at 25°C, protoplasts isolated from hypocotyls or leaves of rapeseed seedlings, or from carrot suspension cells, show 60, 20 and 15% cell wall formation, respectively. The time course of formation of the cell wall and cell division could be delayed by treatment at low temperatures or immobilization in alginate or agarose. This aspect is of importance in connection with problems of late access to the space shuttle before launch. At 4°C only 18% of the rapeseed hypocotyl protoplasts had formed cell walls after 24 h. Protoplasts immobilised in agarose or alginate gradually regain their cell division capacity and after 72 h the frequencies are 51 and 26%, respectively, compared to non‐immobilised control protoplasts. A significant decrease in cell division activity is observed after rotation for 6 h on the slow clinostat. A similar effect is not observed on the fast clinostat. Protoplasts, cultured in the specially designed plant chamber for up to 14 days established cell aggregates which have further developed into plants.
Oxygen toxicity and superoxide dismutase as an antioxidant in physiological stress
Authors: Monk Lorna S. , Fagerstedt Kurt V. , Crawford Robert M. M.
Published: May 2006

Although oxygen is vital for all aerobic life forms, excessive levels of oxygen free radical production can lead to potentially lethal oxidative reactions. The role of superoxide dismutase is examined as an integral part of the defence against oxidative injury resulting from various physiological stresses.
Temperature‐dependent changes in Photosystem II heterogeneity of attached leaves under high light
Authors: Aro Eva‐Mari , Tyystjärvi Esa , Nurmi Arja
Published: May 2006

Attached leaves of pumpkin (Cucurbita pepo L. cv. Jattiläismeloni) were exposed to high light intensity at room temperature (ca 23°C) and at 1°C. Fluorescence parameters and electron transport activities measured from isolated thylakoids indicated faster photoinhibition of PSII at low temperature. Separation of the α and β components of the complementary area above the fluorescence induction curve of dichlorophenyl‐dimethylurea‐poisoned thylakoids revealed that at low temperature only the α‐centers declined during exposure to high light intensity while the content of functional β‐centers remained constant. Freeze‐fracture electron microscopy showed no decrease in the density of particles on the appressed exoplasmic fracture face, indicating that the photoinhibited α‐centers remained in the appressed membranes at 1°C. Because of the function of the repair and protective mechanisms of PSII, strong light induced less photoinhibition at room temperature, but more complicated changes occurred in the α/β‐heterogeneity of PSII. During the first 30 min at high light intensity the decrease in α‐centers was almost as large as at 1°C, but in contrast to the situation at low temperature the decrease in α‐centers was compensated for by a significant increase in PSIIβ‐centers. Changes in the density and size of freeze‐fracture particles suggest that this increase in β‐centers was due to migration of phosphorylated light‐harvesting complex from appressed to non‐appressed thylakoid membranes while the PSII core remained in the appressed membranes. This situation, however, was only transient and was followed by a rapid decrease in the functionalβ‐centers.
Assessment of the potential of the blue light gradient in soybean pulvini as a leaf orientation signal
Authors: Donahue Raymon A. , Berg Virginia Seymour , Vogelmann Thomas C.
Published: May 2006

Blue light gradients in the pulvini of soybean (Glycine max var. Northrup King S1346) leaves with different laminar orientations were examined with a fiber optic microprobe. The gradients changed markedly as a function of both incident light angle and leaf position and were determined largely by the amount of light present in the adaxial side of the pulvinus. The steepest gradient for inclined leaves was with light incident at 90° whereas for declined leaves it occurred when the light was incident at 150°. A proposed pulvinar mechanism which allows for the detection of light direction and leaf position by using the blue light gradient as an orientation signal could account for solar tracking by soybean.
Tissue to tissue symplastic communication in the shoots of etiolated corn seedlings
Authors: Epel Bernard L. , Bandurski Robert S.
Published: May 2006

Carboxyfluorescein, a symplastic probe, was applied to the cut mesocotyl base or coleoptile apex of etiolated Zea mays cv. Silver Queen seedlings and its transport measured and tissue distribution determined. Long‐distance longitudinal symplastic transport of the carboxyfluorescein was mainly in the vascular stele. It moved laterally from the mesocotyl stele to the mesocotyl cortex but the presence of a weak barrier limited the movement. A partial symplastic barrier was also present near the coleoptile‐mesocotyl node.
Distribution of isoflavones in lupin hypocotyls. Possible control of cell wall peroxidase activity involved in lignification
Authors: Ferrer M. Angeles , Pedreño M. Angeles , Calderón Antonio A. , Muñoz Romualdo , Ros Barceló Alfonso
Published: May 2006

The distribution of 4 key isoflavones (luteone, genistein, 2′‐hydroxygenistein and wighteone) in lupin (Lupinus albus L. cv. multolupa) hypocotyls shows a gradient that diminishes from young to old tissues. A spatial gradient occurs within the hypocotyl, and a temporal gradient in both the outermost vascular and epidermal tissues. Not only does a gradient exist in respect to the quantity of isoflavones, but there is also a gradient in respect to the type of isoflavone. Thus, wighteone is mainly associated with the non‐meristematic zones of the lupin hypocotyl. A close relationship was found between the distribution and the localization in the walls of phloem cells of both peroxidase (EC 1.11.1.7) and isoflavones. This observation suggests an in vivo peroxidase‐isoflavone interconnection. In fact, lupin isoflavones are able to inhibit the peroxidase‐catalyzed oxidation of the lignin precursor coniferyl alcohol, probably due to the co‐oxidation of isoflavones in the reaction media. The results are discussed on the basis of a possible role for isoflavones in controlling cell wallperoxidase activity involved in the lignification of phloem cells.
Photoinhibition at chilling temperatures and effects of freezing stress on cold acclimated spinach leaves in the field. A fluorescence study
Authors: Somersalo Susanne , Krause G. Heinrich
Published: May 2006

The role of high light stress in a natural environment was studied on spinach plants (Spinacia oleracea L. cv. Wolter) grown in the field during the winter season. Fluorescence induction (at 293 K and 77 K) of leaves was used to characterize the stress effects. Night frost with minimum temperatures between – 1.5°C and –7.5°C (i.e. above the‘frost killing point’at ca. –11.5°C) led to impaired photosynthesis. This was seen as increased initial fluorescence (Fo), decreased ratio of variable to maximum fluorescence (FV/FM) and lowered rates of O2 evolution. The freezing injury was reversible within several frostless days. Exposure to high light (about 900 mol m–2 s–1) at chilling temperatures in the field caused photoinhibition, manifested as decreased variable fluorescence (FV) and FV/FM ratio without changes in FO. The photoinhibitory fluorescence quenching was not stronger after frost than after frostless nights; synergism between light stress and preceding freezing stress was not observed. Fluorescence induction signals at 77 K showed that FV of photosystems I and II decreased to the same extent, indicating increased thermal deactivation of excited chlorophyll. Photoinhibition was fully reversible at +4°C within 1 h in low light, but only partially in moderate light. Preceding night frosts did not affect the recovery. The photoinhibition observed here is regarded as a protective system of thermal dissipation of excess light energy.
Purification of an anionic isoperoxidase from peach seeds and its immunological comparison with other anionic isoperoxidases
Authors: Quesada Miguel A. , Tigier Horacio A. , Bukovac Martin J. , Valpuesta Victoriano
Published: May 2006

A soluble anionic isoperoxidase (EC 1,11,1,7) was purified from peach (Prunus persica L. Batsch cv. Merry) seeds. Purification was achieved by DEAE‐Sephacel, Sephacryl S‐300 and CM‐cellulose chromatography. The purified isoperoxidase de‐carboxylated indole‐3‐acetic acid (S0.5 0.13 mM, Hill coefficient 1.7). Molecular mass, determined by gel filtration and sodium dodecyl sulfate polyacrylamide gel electrophoresis, was ca 60 kDa. Polyclonal antibodies were raised in rabbit against this isoperoxidase. Using immunoprecipitation this isoenzyme was found to be immunologically different from other soluble anionic isoperoxidases isolated from peach seeds.
Failure to corroborate claims that the developing endosperm of wheat (Triticum aestivum) contains significant activities of fructose‐1,6‐bisphosphatase
Authors: Entwistle Gail , ap Rees Tom
Published: May 2006

This work was done to test claims (Sangwan and Singh, Physiol. Plant. 73: 21–26) that the developing endosperm of wheat (Triticum aestivum L.) contains a cytosolic and a plastidic fructose‐ 1,6‐bisphosphatase (EC 3.1.3.11; FBPase). Repetition of the procedure of Sangwan and Singh with extracts of developing endosperm of Triticum aestivum cv. Mercia produced two peaks of apparent FBPase activity on elution from DEAE‐cellulose. Both peaks showed high activity of pyrophosphate:fructose‐6‐phos‐phate 1‐phosphotransferase [EC 2.7.1.90; PFK(PPi)]. The apparent FBPase activity in both peaks was stimulated by 20 μM fructose‐2,6‐bisphosphate and inhibited by antibodies to PFK(PPi). Antibody to plastidic FBPase did not react positively in an immunoblot analysis with any protein of Mr comparable to that of known FBPase in either peak. It is argued that the ability of each peak to convert fructose‐1,6‐bisphosphate to fructose‐6‐phosphate was due to PFK(PPi). and that there remains no substantiated evidence for the presence of a plastidic FBPase in the developing endosperm of wheat.
Plastid microtubule‐like structures in wheat are insensitive to microtubule inhibitors
Authors: Artus Nancy N. , Ryberg Margareta , Sundqvist Christer
Published: May 2006

The effects of microtubule inhibitors on the spectral properties of leaves of wheat (Triticum aestivum L. cv. Walde) and on the presence of plastid microtubule–like structures (MTLS) during etioplast to chloroplast transformation were examined. Amiprophos‐methyl (APM, 0.1 mM), fed to leaf sections of 7‐day‐old dark‐grown wheat, reduced the ration of phototransformable to non‐phototransformable proto‐chlorophyllide (PChlide), decreased the rate of the Shibata shift, and inhibited chlorophyll accumulation and grana stacking. The spectral properties of isolated etioplasts were not affected by APM. Colchicine (10 mM), fed to leaf sections, inhibited greening but had no effect on the PChlide ratio or the Shibata shift. MTLS were still visible on electron micrographs after treatment with APM or colchicine at frequencies similar to controls. A third inhibitor, vinblastine, had no effect on the spectral properties of non‐irradiated or irradiated etiolated leaves except at concentrations that produced visible tissue damage before the irradiation. The effects of APM and colchicine may reflect inhibitions of respiration and protein synthesis, respectively. It is concluded that MTLS are insensitive to microtubule inhibitors and thus are probably not composed of tubulin.
[14C]‐Assimilate translocation in the light and dark in celery (Apium graveokns) leaves of different ages
Authors: Davis Jeanine M. , Loescher Wayne H.
Published: May 2006

The 2 major photosynthetic products and translocated carbohydrates in celery (Apium graveolens L.) are sucrose and the sugar alcohol, mannitol. Sucrose is produced and utilized in leaves of all ages. Mannitol, however, is synthesized primarily in mature leaves, utilized in young leaves and stored in all leaves. Here we show that mannitol export was lower from young, expanding leaves than from older leaves. After a 10 min pulse of 14CO2 and a 2 h chase in the light or dark there was more radioactivity in sucrose than in mannitol in petiole tissues from leaves of all ages. However, after a chase of 15 h in the dark or 6 h in the light followed by 9 h in the dark, mannitol was the predominant [14C]‐labeled carbohydrate remaining in all leaf and petiole tissues. Thus, newly synthesized sucrose was apparently exported at a faster rate than mannitol and more mannitol was partitioned into vacuolar storage pools than was sucrose. It also appears that in the light both sucrose and mannitol were exported, but in the dark, once sucrose pools were depleted, mannitol remained as the predominant substance translocated. Both mannitol and sucrose were unloaded into petiole storage parenchyma tissue, but sucrose was hydrolyzed prior to storage.