bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniconazole‐induced thermotolerance in wheat seedlings is mediated by transpirational cooling
Authors: Booker H. M. , Gillespie T. J. , Hofstra G. , Fletcher R. A.
Published: May 2006

Seed treatment of thermotolerant and sensitive cultivars of wheat (Triticum aestivum L. cv. Frederick and Glenlea, respectively) with uniconazole reduced shoot and increased root fresh and dry weights. When subjected to 48°C for 6 h, treated seedlings had lower leaf‐temperatures and overall higher rates of evapotranspiration. Percent survival 11 days after high temperature incubation in untreated seedlings was 53% in Frederick and 30% in Glenlea, whereas in uniconazole‐treated seedlings it was 94% and 80%, respectively. Transpiration resistance markedly increased in the control cultivars after 4 h of high‐temperature incubation, but remained relatively unchanged in the treated cultivars. The increased root to shoot ratio exhibited in treated plants may have alleviated guard cell stress, even under high evaporative demand. Chlorophyll fluorescence measurements on leaves of heat‐stressed seedlings indicated that increased photosynthetic metabolism in treated seedlings was correlated with lower leaf temperatures. High‐temperature stress resulted in a dramatic decline in pigments and proteins in thylakoid extracts of control seedlings but not in extracts from treated seedlings. Integrity of thylakoid pigment protein complexes, as illustrated by reduced relative amounts of free pigment, was maintained after exposure to high temperatures in treated seedlings. Furthermore, the treated Glenlea seedlings displayed a reduction in the monomeric form of Sight‐harvesting chlorophyll protein II (LHCP II) compared to control and Frederick seedlings. The heat‐tolerant Frederick cultivar showed a greater protective effect from uniconazole treatment than the sensitive Glenlea cultivar. Uniconazole treatment did not affect heat‐shock protein (HSP) synthesis in mesocotyl tissue.
Changes in protein synthesis and translatable messenger RNA populations associated with ABA‐induced cold hardiness in potato (Solatium commersonii)
Authors: Tseng M. J. , Li P. H.
Published: May 2006

Plantlets of Solanum commersonii Dun, PI 458317 stem‐culture were treated with abscisic acid (ABA) (3.78 to 113.5 μM) at a 20°/15°C day/night temperature regime for 14 days. Cold hardiness increased from—3.3°C to—8.4°C (killing temperature) after 7 days of ABA treatment and remained at this level thereafter. During the course of treatment (14 days), the synthesis of polypeptides was investigated and poly(A+)‐RNA was isolated. Translation products of poly(A+)‐RNA in a rabbit reticulocyte lysate system were then analyzed by 2‐D polyacrylamide gel electropho‐resis. During the 14 days of ABA treatment, 30 ABA‐induced polypeptides were identified. The synthesis of one group of polypeptides was stable and prominent throughout the treatment period. The other group was transient. The most prominent and stable polypeptides had molecular weights of 21 (pi 6.0, 6.3), 22 (pI 6.0, 6.3), 31 (pi 4.5) and 83 (pi 5.4, 5.5, 5.6) ItDa. About one‐third of the new polypeptides appeared after cold hardiness reached a maximum (after 7 days of ABA treatments.

ABA treatment alters translatable mRNA populations during the development of cold hardiness. Several mRNAs, encoding in vitro translation products at 26 (pi 6.0, 6.3, 6.4), and 27 (pi 6.0, 6.3, 6.4), 40 (pi 6.4) and 50 (pi 4.5) kDa were identified during course of the ABA treatment. These proteins may play important roles for the development of cold hardiness in tuber‐bearing S. commersonii.
Hydration, protons and onset of physiological activities in maize seeds
Authors: Bruni Fabio , Leopold A. Carl
Published: May 2006

Dry maize (Zea mays L.) seed components, namely, embryo and endosperm, provide model materials for studies on water‐dependent mechanisms in cellular function. We explored the thermodynamics of hydration for both tissues, along with their dielectric behavior, as a function of water content. In addition, we evaluated the direct current (DC) conductivity due to water protons. Our data on embryo tissue show large enthalpic and entropic peaks at water content [h, in g H2O (g dry sampie)−1] around 0.08 g g−1, indicating very tight binding and ordering of water molecules. With increasing water content both enthalpy and entropy decrease, and the completion of primary hydration requires h ∼ 0.26 g g−1. Data for endosperm tissue show the absence of such an enthalpic peak and a reduced degree of ordering for h < 0.10 g g−1. The DC protonic conductivity shows explosive growth above a threshold hydration level hc= 0.082 g g−1 and hc= 0.12 g g−1, for embryo and endosperm, respectively. Protonic conduction can be considered within the framework of a percolation modell characterized by a hydration threshold and by a power law increase in conductivity with further hydration. The critical exponent of the power law is in agreement with theory for a two‐dimensional percolative process. This percolative water‐assisted behavior reflects the presence of an extended network of water molecules adsorbed on the surface of proteins and/or membranes inside cells. We consider this percolative protonic conduction as being a prerequisite to respiration processes.
Lincomycin‐induced alteration in the contents of chlorophyll‐protein complexes of dimorphic maize chloroplasts and its effect on the temperature‐induced spectral changes
Authors: Singh Bal Ram , Sarvari Eva , Agnihotri Abha , Singhal Gauri S.
Published: May 2006

The difference spectroscopy technique has been utilized to investigate the temperature‐induced spectral changes in mesophyll and bundle sheath chloroplasts of maize (Zea maysL. cv. Ganga‐5) in order to assess the role of different pigment‐protein complexes in the manifestation of temperature effect on the chloroplast membranes. Cooling and heating of both mesophyll and bundle sheath chloroplasts resulted in absorbance difference (AA) bands at similar wavelengths but the degree of absorb‐ance changes were significantly higher in bundle sheath chloroplasts. For example, upon cooling to 7‐8°C, positive AA bands were observed at 440, 490 and 680 nm in mesophyll chloroplasts and at 440, 495–500 and 680 nm in bundle sheath chloroplasts but the absorbance change at 680 nm was ca 2% in mesophyll chloroplasts, whereas it was ca 5% in bundle sheath chloroplasts, which have a lower content of light‐harvesting pigment‐protein complex. The role of chlorophyll‐protein complexes was further investigated by monitoring the temperature‐induced spectral changes of mesophyll and bundle sheath chloroplasts isolated from lincomycin‐treated maize plants where lincomycin selectively inhibits the biosynthesis of specific chlorophyll‐protein complexes. Results indicated that depletion of certain pigment‐protein complexes in mesophyll chloroplasts made them more susceptible (a ca 4% vs ca 2% absorbance change upon cooling and a ca 6% vs ca 4% absorbance change upon heating) and less tolerant to temperature variation (a 76% vs 39% reversibility during ambient→Cooling→ambient temperature cycle). The data indicate that pigment‐protein complexes play a significant role in protecting the chloroplast membranes against temperature variation.
Distribution of lead in mycorrhizal and non‐mycorrhizal Norway spruce seedlings
Authors: Jentschke Georg , Fritz Eberhard , Godbold Douglas L.
Published: May 2006

Non‐mycorrhizal spruce seedlings(Picea abies Karst.) and spruce seedlings colonized with Lactarius rufus (Scop.) Fr. or two strains of Paxillits involutus (Batsch) Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization, the seedlings were exposed to 1 μM PbCI2 for 19 weeks. The degree of infection in all of the mycorrhizal treatments approached 100% during the experiment and was not affected by exposure to Pb. However, the number of root tips per root dry weight and the shoot: root ratio, both in the non‐mycorrhizal and the mycorrhizal seedlings, had decreased after the 19 week treatment with PbCl2 Using X‐ray microanalysis, the distribution and concentration of Pb in the tissues of mycorrhizal and non‐mycorrhizal root tips were compared. In the mycorrhizae of seedlings exposed to Pb no significant accumulation of Pb in the hyphal mantle or in fungal cell walls of the Hartig net were detected. Lead accumulated primarily in the cortex cell walls both of non‐mycorrhizal and mycorrhizal root tips. No significant difference of Pb concentrations in root cortex cell walls of non‐mycorrhizal and mycorrhizal seedlings was found; except for seedlings colonized with Paxillus involutus strain 537. However, at the endodermis no effect of mycorrhizal fungal colonization on the Pb tissue concentration was detected. The presence of the fungal sheath did not prevent Pb from reaching the root cortex. The endodermis acted as a barrier to Pb radial transport in both mycorrhizal and non‐mycorrhizal seedling roots.
The iron‐quinone electron‐acceptor complex of photosystem II
Authors: Diner Bruce A. , Petrouleas Vasili , Wendoloski John J.
Published: May 2006

The iron quinone‐complex of the reaction centers of photosystem II and the purple non‐sulphur photosynthetic bacteria contains two quinones, QAand QBconnected in series with respect to electron transfer, and separated by a non‐heme iron coordinated by amino acid residues. It is the site of inhibition of many of the common photosynthetic herbicides, which act by displacing QBfrom the center. The complex is responsible for reducing QBto QBH2in two successive one‐electron photo acts. OBH2dissociates from the center, to be replaced by a new QBmolecule and reduces the following membrane‐bound electron‐transfer complex (cytochromeb6/for b/c1). The energetic, kinetics and mechanism of complex function are reviewed here. Recent crystallographic, spectroscopic and molecular biological evidence has produced a considerable quantity of structural information on this complex. These data have given a less formal and more molecular view of how the complex functions. They have also revealed fundamental differences between the photo system II and bacterial complexes, particularly with respect to the coordination of the iron and its chemistry. The comparative anatomy of the complexes is reviewed and its implications for function discussed.
Between DNA and protein – RNA editing in plant mitochondria
Authors: Schuster Wolfgang , Wissinger Bernd , Hiesel Rudolf , Unseid Michael , Gerold Ernst , Knoop Volker , Marchfelder Anita , Binder Stefan , Schobel Werner , Scheike Rupert , Granger Petra , Ternes Rainer , Brennicke Axel
Published: May 2006

Higher plants contain the largest mitochondrial genomes found so far. Several factors contribute to this expansion in size, notably integrated plastid and nuclear sequences; numerous repeats, some of which are active in recombination and sequence rearrangements; introns of more than 3 400 nucleotides and several genes unique to plant mitochondrial DNA. Genes are transcribed into mono and polycistronic mRNAs and translated by the standard genetic code. However, mRNAs are altered from the DNA encoded sequence by RNA editing with mostly cytidine to uridine and occasionally uridine to cytidine transitions. Edited mRNAs specify different polypeptides than those predicted by open reading frames in the DNA. Partially edited mRNA molecules raise the question of which proteins are actually synthesized. RNA editing of mitochondrial transcripts appears to occur in all higher plants and may date back to the common ancestors of modern plants.
Light control of porphyrin accumulation in acifluorfen‐methyl‐treated Lemna pausicostata
Authors: Becerril José M. , Duke Mary V. , Nandihalli Ujjana B. , Matsumoto Hiroshi , Duke Stephen O.
Published: May 2006

In Lemna pausicostata Hegelm. 6746, light is required for sufficient acifluorfenmethyl (AFM) stimulation of protoporphyrin IX (Proto IX) accumulation to cause significant herbicidal action. In darkness, AFM causes Proto IX levels to increase for about 2 h, after which Proto IX content is stable at levels significantly lower than those accumulated in light. In darkness, sucrose cannot increase levels of AFM‐induced Proto IX. However, addition of δ‐aminolevulinic acid (ALA) increases Proto IX levels in AFM‐treated plants in darkness, demonstrating that the herbicide blocks the porphyrin pathway in darkness as it does in the light. Thus, Proto IX accumulation in darkness appears to be limited by ALA availability. This is supported by the finding that dioxoheptanoic acid caused more ALA to accumulate in light than in darkness. Heme is a feedback inhibitor of ALA synthesis, and heme synthesis is inhibited by AFM. However, total extractable heme levels were reduced by AFM by about the same amount in both light and darkness. Exogenously supplied hemin reduced AFM‐caused Proto IX accumulation and herbicidal damage in the light and also reduced Proto IX accumulation caused by AFM or AFM plus ALA in darkness. AFM‐stimulated Proto IX accumulation was inversely proportional to the log of the photon flux density between 5 and 500 μmol in m−2 s−1. Reduced effects of higher photon fluxes on AFM‐stimulated Proto IX accumulation are probably due to both increased photobleaching of Proto IX and reduced porphyrin synthesis because of herbicidal damage. AFM‐stimulated Proto IX accumulation in darkness could not be demonstrated to be under phytochrome control, but it appeared to be under the negative influence of protochlorophyllide levels.
Modification of matrix polysaccharides during avocado (Persea americana) fruit ripening: an assessment of the role of Cx‐cellulase
Authors: O'Donoghue E. M. , Huber D. J.
Published: May 2006

The role of Cx‐cellulase (EC 3.2.1.4) in fruit ripening and softening is unknown. In the present study, avocado (Persea americana) fruit, a rich source of Cx‐cellulase, were examined to determine if the enzyme plays a role in ripening‐related hemicellulose metabolism. Hemicelluloses (4 M alkali‐soluble) from avocado fruit exhibited a very broad distribution of polymer sizes and an overall decrease in Mr during ripening. Polymers affected were primarily those of large Mr (relative molecular mass). The characteristic total hemicellulose Mr distribution and changes with ripening were also evident for xyloglucan (XG), a putative substrate for avocado Cx‐cellulase. Hydrolytic activity toward hemicelluloses from preripe fruit was detected in crude buffer‐soluble protein extracts derived from ripe avocado mesocarp tissue. XG was also degraded, and in a pattern similar to that observed during ripening. Purified Cx‐cellulase also exhibited activity against specific components of isolated hemicelluloses; however, in contrast to the crude protein. Cx‐cellulase alone was without influence on the Mr distribution of avocado XG. Protein depleted of Cx‐cellulase was capable of moderate XG depolymerization. We conclude from the present studies that the enzyme Cx‐cellulase is not involved in the ripening‐related depolymerization of XG in avocado fruit.
Effects of 2,6‐dichlorobenzonitrile on differentiation to tracheary elements of isolated mesophyll cells of Zinnia elegans and formation of secondary cell walls
Authors: Suzuki Kaoru , Ingold Edgar , Sugiyama Munetaka , Fukuda Hiroo , Komamine Atsushi
Published: May 2006

The influence of 2,6‐dichlorobenzonitrile (DCB), an inhibitor of the synthesis of glucans, on the differentiation to tracheary elements of isolated mesophyll cells of Zinnia elegans and the formation of secondary cell walls was investigated. DCB caused a decrease in viability of the cells. The number of tracheary elements and the amount of lignin decreased with increasing concentrations of DCB in the medium. However, lignified tracheary elements were observed even in the presence of 5 μM DCB. In the presence of DCB, peroxidase activity and deposition of lignin were not always restricted to secondary cell‐wall thickenings but were observed all over the walls of tracheary elements. In addition, some of the cells without any obvious cell‐wall thickening were also lignified. The amount of total carbohydrate in cell walls decreased in the presence of DCB but the amount of uronic acids was barely affected. The amount of extracellular polysaccharide (ECP) increased in the presence of DCB. The effect of DCB on the incorporation of radiolabel from [14C]‐glucose into cell‐wall polysaccharides was examined. DCB specifically inhibited the synthesis of cellulose. These results suggest that the increase in the amount of ECP and the aberrant deposition of lignin caused by DCB were results of the perturbation of the assembly of cell‐wall materials caused by interference by DCB in the synthesis of cellulose.
Light‐ and phytochrome‐mediated gene expression in Douglas‐fir seedlings
Authors: Alosi M. Carol , Neale David B.
Published: May 2006

In dark‐grown Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings, the steady‐state level of the major light‐harvesting chlorophyll a/b binding proteins mRNA (cab mRNA) was about 25% of the level that accumulated in light‐grown seedlings. A single, 5‐min irradiance with red light up‐regulated expression transiently, so that cab mRNAs accumulated to a Jevel approaching that determined for light‐grown seedlings. The response was reversible by far‐red light to the dark level, indicating that the up‐regulation was a phytochrome‐mediated response. Phytochrome action also up‐regulated genes that encode ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rbcS) in Douglas‐fir seedlings, but the maximal rbcS mRNA level that was attained after the red light treatment was several‐fold lower than the expression level deternined for light‐grown seedlings. Genes that produce ubiquitin and ubiquitin‐fusion transcripts were differentially expressed in dark‐ and light‐grown seedlings, but the genes did not appear to be phytochrome regulated.
Chromatin structure of heat‐shock‐inducible genes and abscisic acid‐inducible genes in wheat
Authors: Loer Deborah S. , Spiker Steven
Published: May 2006

We have asked if the induction of gene expression by heat shock or by the phytohormone abscisic acid is accompanied by a change in chromatin structure as assayed by general DNase I sensitivity of the coding region of the responsive genes in wheat (Triticum aestivum L. cv. Stephens). Using nuclei isolated from wheat seedlings, we show by Southern blot hybridization that members of the WHSP 17 gene family (encoding a low‐molecular‐weight heat‐shock protein) become more sensitive to DNase I upon heat shock. This result indicates that the induction of heat‐shock genes is accompanied by a change in chromatin conformation in plants, as has been previously demonstrated in animal systems. Abscisic acid has previously been shown to induce the transcription of a 7S globulin gene and inhibit the expression of ribulose 1,5‐bisphate carboxylase/oxygenase small subunit genes in wheat seedlings. We found both of these genes to be sensitive to DNase I before abscisic acid treatment, and we found no change upon treatment.
Effects of chloride and sodium on gas exchange parameters and water relations of Citrus plants
Authors: Bañuls J. , Primo‐Millo E.
Published: May 2006

Gas exchange parameters, water relations and Na+/Cl‐ content were measured on leaves of one‐year‐old sweet orange (Citrus sinensis [L.] Osbeck cv. Hamlin) seedlings grown at increasing levels of salinity. Different salts (NaCl, KCl and NaNO3) were used to separate the effects of Cl− and Na+ on the investigated parameters. The chloride salts reduced plant dry weight and increased defoliation. Accumulation of Cl− in the leaf tissue caused a sharp reduction in photosynthesis and stomatal conductance. By contrast, these parameters were not affected by leaf Na+ concentrations of up to 478 mM in the tissue water. Leaf water potentials reached values near −1.8 MPa at high NaCl and KCl supplies. This reduction was offset by a decrease in the osmotic potential so that turgor was maintained at or above control values. The changes in osmotic potential were closely correlated with changes in leaf proline concentrations. Addition of Ca2+ (as calcium acetate) increased growth and halved defoliation of salt stressed plants. Furthermore, calcium acetate decreased the concentration of Cl− and Na+ in the leaves, and increased photosynthesis and stomatal conductance. Calcium acetate also counteracted the reductions in leaf water and osmotic potentials induced by salinity. In addition, calcium acetate inhibited the accumulation of proline in the leaves which affected the reduction in osmotic potential. These results indicate that adverse effects of salinity in Citrus leaves are caused by accumulation of chloride.
Light, temperature and nutrients as factors in photosynthetic adjustment to an elevated concentration of carbon dioxide
Authors: Bunce James A.
Published: May 2006

The short‐term stimulation of the net rate of carbon dioxide exchange of leaves by elevated concentrations of CO2 usually observed in C3 plants sometimes does not persist. Experiments were conducted to test whether the patterns of response to the environment during growth were consistent with the hypotheses that photosynthetic adjustment to elevated CO2 concentration is due to (1) feedback inhibition or (2) nutrient stress. Soybean [Glycine max (L.) Merr. cv. Williams] and sugar beet (Best vulgaris L. cv. Mono Hye‐4) were grown from seed at 350 and 700 μl− CO2, at 20 and 25°C, at a photon flux density of 0.5 and 1.0 mmol m−2 S−1 and with three nutrient regimes until the third trifoliolate leaf of soybean or the sixth leaf of sugar beet had finished expanding. Net rates of CO2 exchange of the most recently expanded leaves were then measured at both 350 and 700 μl 1−1 CO2. Plants grown at the elevated CO2 concentration had net rates of leaf CO2 exchange which were reduced by 33% in sugar beet and 23% in soybean when measured at 350 μl 1−1 CO2 and when averaged over all treatments. Negative photosynthetic adjustment to elevated CO2 concentration was not greater at 20 than at 25°C, was not greater at a photon flux density of 1.0 than at 0.5 mmol m−2 S−1 and was not greater with limiting nutrients. Furthermore, in soybean, negative photosynthetic adjustment could be induced by a single night at elevated CO2 concentration, with net rates of CO2 exchange the next day equal to those of leaves of plants grown from seed at the elevated concentration of CO2. These patterns do not support either the feedback‐inhibition or the nutrient‐stress hypothesis of photosynthetic adjustment to elevated concentrations of CO2.
Shoot growth in aseptically cultivated daylily and haplopappus plantlets after a 5‐day spaceflight
Authors: Levine Howard G. , Krikorian A. D.
Published: May 2006

Plantlets of daylily (Hemerocallis cv. Autumn Blaze) regenerated from cell suspensions, and 4 clonal populations of Haplopappus gracilis were aseptically cultivated aboard the Shuttle “Discovery’’ during a 5‐day mission within NASA's Plant Growth Unit (PGU) apparatus. Daylily was selected as a representative herbaceous perennial monocotyledon and the haplopappus clones represented an annual dicotyledon. The latter included 4 strains with different physiological and morphological characteristics: two aseptic seedling clones (each generated from a single seedling) and two tissue culture‐derived lines. Mean daily growth rates for the primary shoots of all plantlets averaged 4.13 mm day−1 (sd = 2.20) for the flight experiment and 4.68 mm day−1 (sd = 2.59) for the ground control. Comparable growth rates calculated by summing both the primary and secondary shoots for all plantlets were 5.94 mm day−1 (sd = 2.89) for the flight experiment and 6.38 mm day−1 (sd = 3.71) for the control. Statistically significant differences existed between: (1) flight vs control primary shoot growth (the controls growing more than plantlets subjected to spaceflight conditions), (2) the different populations (the daylily gaining more shoot material than any of the haplopappus populations and the haplopappus seedling clones outperforming the tissue culture‐derived haplopappus lines), and (3) the individual Plant Growth Chambers contained within the PGU. The data suggest that some spaceflight‐associated factor(s) increased the tendency for primary shoot apices to degrade or senesce, resulting in the release of apical dominance and permitting the emergence of axillary branches, which subsequently partially compensated for the reduced primary axis growth. In addition to spaceflight‐associated factors, the physiologically diverse nature of the experimental material as well as environmental heterogeneities within the culture apparatus contributed to the variation in growth results. The findings could explain some discrepancies reported from various plant culture experiments conducted in space.
Seasonal changes in some photosynthetic properties of Ceratonia siliqua (carob tree) leaves under natural conditions
Authors: Nunes Maria Antonieta , Cochicho Ramalho José Domingos , Silva Rijo Paula da
Published: May 2006

Rates of photosynthesis and leaf conductance of the leaves of carob trees (Ceratonia siliqua L.) growing in natural conditions were measured during the course of the seasons to define the effects of the main climatic factors limiting growth in the region: temperature during the winter and water in the summer. The highest photosynthetic rates were measured in spring and autumn and could reach 25 μmol m−2 s−1 with optimal temperature and available water. Due to lower temperatures (4 to 6°C in the night) these values were frequently around 15 μmol m−2 s−1 during winter, but the strongest depression was due to prolonged drought in summer. However a reduction in photosynthesis rate down to 5 μmol m−2 s−1 occurred only after depletion of all the available water in the soil layer up to a depth of 50 cm. In the end of the summer, leaf conductance and water potential were in the order of 20 mmol m−2 s−1 and −3 MPa respectively. Compared to other trees that make up the Mediterranean sclerophyll forest, the photosynthetic activity of carob is high, and the tree tolerates a considerable depletion of soil water.
Effect of ethylene on enzymatic activities involved in the browning of Hevea brasiliensis callus
Authors: Housti Fatima , Coupé Michel , D'Auzac Jean
Published: May 2006

Browning, which is of varying intensity depending on species, develops in Hevea brasiliensis callus in vitro and can affect somatic embryogenesis. Endogenous ethylene appears to be involved since application of aminocyclopropane carboxylic acid (ACC) strongly enhances this browning. At the same time, peroxidases (EC 1.11.1.7), bonded polyphenol oxidase (EC 1.10.3.1) and NADH‐quinone reductase (EC 1.6.99.5) are enhanced by ACC whereas superoxide dismutase (SOD: EC 1.15.1.1) and ascorbate peroxidase (EC 1.11.1.11) are decreased. In contrast, application of aminoacetic acid (AOA) causes spectacular decreases in bound and soluble polyphenol oxidase, peroxidase and NADH‐quinone reductase activities whereas SOD and ascorbate peroxidase activities increase. Enzymatic activities in the control callus present a medium value, probably due to a considerable ethylene production in the culture medium. After 47 days culture. the initial catalase activity (EC 1.11.1.6) in the explants had disappeared completely. In contrast, after only 22 days, the silver nitrate and especially AOA treatments promoted considerable activities of catalase. The beneficial effect of the inhibitors of ethylene synthesis was reflected in the enhanced formation of embryogenic tissue, which varied from 1% (control or ACC) to 34% (AOA treatment).
Acclimatizing micropropagated black cherry by comparison with half‐sib seedlings
Authors: Drew A. P. , Kavanagh K. L. , Maynard C. A.
Published: May 2006

Black cherry (Prunus serotina Ehrh.) plantlets were cultured in vitro, transferred to potting mixture and evaluated for 8 weeks for acclimatization to a varying, but controlled environment. Whole plantlet growth and water relations were monitored and compared to seedlings of comparable size of the same maternal genotype grown under different conditions, but given the same pretest environment. At one week ex vitro. gravimetrically determined leaf conductance of plantlets was high, but became closer to that of seedlings in both magnitude and diurnal pattern as acclimatization progressed. By 8 weeks, leaf conductance of plantlets was nearly identical to that of seedlings, but the xylem water potential of the plantlets was significantly less. Logarithmic regressions of shoot vs root dry weight indicated that seedlings were allocating twice as much dry matter to shoot than to root growth compared to 4‐ and 8‐week plantlets. Over the same period, stomatal densities of both seedlings and plantlets decreased and stomatal pore lengths increased. Multiple adventitious roots of plantlets emerged from a single site just below the root collar whereas secondary or lateral roots of seedlings originated acropetally along the central root axis. Leaf conductance of plantlets at 8 weeks was similar to that of seedlings indicating satisfactory acclimatization. The larger relative root growth rate of plantlets compared to the shoot, however, was associated with lower stem xylem water potential. The anomaly may be a consequence of the method of in vitro root formation. Plantlet growth rates were lower than growth rates of seedlings and their leaf area was correspondingly less.
The state of water in acclimating vegetative buds from Malus and Amelanchier and its relationship to winter hardiness
Authors: Vertucci Christina W. , Stushnoff Cecil
Published: May 2006

The relationship between freezable water and cold hardiness during acclimation was studied using vegetative buds from several apple (Malus domestica Borkh) cultivars and from one saskatoonberry (Amelanchier alnifolia Nutt. cv. Smoky) cultivar. According to leakage data and visual assessments of cortical browning, vegetative buds of all cultivars were most tolerant to subfreezing temperatures in January. The hardy condition was also associated with maximum tolerance to desiccation. Qualitative features of freezing exotherms (number of peaks and temperature of the transition) were not correlated with the hardy condition in the tissues. However, the amount of unfrozen water, determined by quantifying the energy of the exotherms, increased with increasing hardiness. In buds that survived exposure to −45°C, freezing reduced the intracellular water content, but only to levels above the critical moisture content for desiccation damage. In buds that did not survive exposure to −45°C, freezing reduced the water content to levels equal to or less than the critical moisture content for desiccation damage. These observations suggest that the freezing of water in nonhardy tissue dried the tissue to moisture levels at which severe dehydration damage occurred. It appears that acclimation of vegetative apple buds involves at least two processes: (1) an increase in tolerance to dehydration and (2) an increase in the level of unfreezable water.
Bacterial phytotoxins, syringomycin, syringostatin and syringotoxin, exert their effect on the plasma membrane H+‐ATPase partly by a detergent‐like action and partly by inhibition of the enzyme
Authors: Che Fang‐Sik , Kasamo Kunihiro , Fukuchi Naoyuki , Isogai Akira , Suzuki Akinori
Published: May 2006

Syringostatin is a newly discovered phytotoxin produced by a phytopathogenic bacterium Pseudomonas syringae pv. syringae lilac isolate. The effects of syringostatin and the similar phytotoxins, syringomycin and syringotoxin, on H−‐ATPase activity were investigated using cultured mung bean (Vigna radiata L. cv. Ryokuto) cells or plasma membrane vesicles isolated from mung bean hypocotyls. 31P‐NMR analysis of cultured cells treated with syringostatin revealed that the cytoplasmic pH was decreased. When plasma membrane was prepared by a two‐step method (Dextran gradient followed by a sucrose gradient). syringostatin, syringomycin and syringotoxin inhibited the H+‐ATPase activity in a dose‐dependent manner. In contrast, these toxins stimulated H+‐ATPase activity when plasma membrane was prepared by a one‐step method (sucrose gradient). While these toxins inhibited the H+‐ATPase activity of inside‐out plasma membrane vesicles, the H+‐ATPase activity of right‐side‐out vesicles was stimulated. The detergent. Triton X‐100, abolished this stimulatory effect of the toxins on the H+‐ATPase of right‐side‐out vesicles and of one‐step purified plasma membrane. The toxins also inhibited the activity of the plasma membrane H+‐ATPase solubilized with deoxycholate and Zwittergent 3–14. Taken together, these results indicate that these toxins exert their effects partly by a detergent‐like action on the plasma membrane and partly by inhibition of the enzyme.
Physiological effects of a long term exposure to low concentrations of NH3, NO2 and SO2 on Douglas fir (Pseudotsuga menziesii)
Authors: van Hove L. W. A. , Bossen M. E. , Mensink M. G. J. , van Kooten O.
Published: May 2006

The above‐ground parts of two years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed to filtered air, NH3, NO2+, SO2 (66, 96 and 95 μg m−3, respectively), to a mixture of NO2+NH3 (55 + 82 μg m−3) or SO2+NO2 (128 + 129 μg m−3), for 8 months in fumigation chambers. Both chlorophyll fluorescence and gas exchange measurements were carried out on shoots which had sprouted at the beginning of the exposure period. The chlorophyll fluorescence measurements were performed after 3 and 5 months of exposure (average shoot age 70 and 140 days, respectively). Light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. In addition, light response curves of net CO2 assimilation were determined after 5 months of exposure. After 3 months of exposure (average shoot age 70 days) all exposure treatments showed a lower maximum electron transport rate (Jmax) as compared to the control shoots (filtered air). A large reduction (45%) was observed for shoots exposed to SO2+NO2. During the exposure period between 3 and 5 months (average shoot age 70 and 140 days, respectively) a decrease of Jmax was observed for all treatments. Jmax had further declined some time after termination of the exposure, when average shoot age was 310 days.

Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum net CO2 assimilation (Pmax) as compared to the control shoots. However, shoots exposed to NO2 showed no reduction and even a higher Pmax was observed for shoots exposed to NH3 or NO2+NH3. Needles of these treatments also showed a higher chlorophyll content which might explain the contradictory results obtained for these treatments: the increased amount of photosynthetic units counteracts the reduction in Jmax and consequently no reduction in Pmax is measured. Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum stomatal conductance (gs). However, the stomatal opening was larger than could be expected on basis of their (maximum) CO2 assimilation rate. Consequently, water use efficiency of these shoots was lower than that of the control shoots. Also shoots exposed to NO2 had a lower water use efficiency due to a significantly higher maximum gs. Shoots exposed to NH3 showed a high transpiration rate in the dark, indicating imperfect stomatal closure.
Reversible lowering of modulated chlorophyll fluorescence after saturating flashes inHaematococcus lacustris(Volvocales) at room temperature
Authors: Hagen C. , Bornman J. F. , Braune W.
Published: May 2006

During modulated Chl fluorescence kinetics in zoospores of the green algaHaemutococcus lacustrisRostafinski, sudden reversible drops in fluorescence intensity immediately following each saturating light flash occur. In order to characterize the cause of these low‐waves several treatments were applied to modify their expression: (I) inhibition of non‐photochemical quenching by application of uncouplers: (2) application of effectors to the photosynthetic electron transport system: (3) brief chilling treatment and UV‐B irradiation. The results indicate that the phenomenon is not related to oscillations of the trans‐thylakoid pH gradient. The reversible short‐term decrease in fluorescence after a saturating light pulse seems to originate from an imbalance between charge separation capacity of the photosystems and the electron buffering capacity of the intersystem electron transport pool.
Aluminium effects on Scenedesmus obtusiusculus with different phosphorus status. II. Growth, photosynthesis and pH
Authors: Greger Maria , Tillberg Jan‐Eric , Johansson Monica
Published: May 2006

Synchronously dividing cultures of the unicellular green alga Scenedesmus obtusiusculus were cultivated for 24 or 70 h in medium high (1000 μM) or low (60 μM) in phosphorus. Aliquots of AlCl3 (0, 37, 74, 111, 148, 185, or 222 μmol) were added daily to 1 l cell suspension at the end of the cell division phase. Algae were also grown in media with different pH, adjusted with HCl, in the absence of AlCl3.

Effects of Al on cell metabolism vary with the intracellular Al concentration and with the concentration of Al available per cell. When the concentration of phosphorus is low, internal concentrations of Al are high and the chlorophyll content and the net dry matter production per cell increase, whereas the photosynthesis and the cell division are increased. Presence of Al in a low P medium decreases the pH of the medium down to 4.5. There are only small effects of Al in the presence of P, due to precipitation of most of the Al with P in the medium.

Despite the Al‐induced decrease of the pH of the culture medium, effects caused by Al cannot be explained as a pH effect. Instead, the Al effect may, at least to some extent, be related to a decrease in availability of P in the metabolism, due to formation of aluminium phosphate inside the cell.
Benzyladenine‐controlled protein synthesis and growth in apple cell suspensions
Authors: Ordás Ricardo J. , Fernández Belen , Rodríguez Roberto
Published: May 2006

Prolific growth in cytokinin‐requiring apple cell suspensions was achieved during 10 days of culture with appropriate concentrations of benzyladenine (BA). Unlike the controls, BA‐treated cells showed a well developed sub‐cellular organization and protein synthesis. Upon transfer to fresh cytokinin‐free medium, however, these cells exhibited a rapid decrease in polyribosome formation, but with unchanged nuclear and nucleolar activities. Cells lacking added cytokinin showed a reduced metabolic activity and failed to divide. Deficiency in the translation process of cytokinin‐deprived cells was overcome by exogenous BA‐treatment. In cells maintained on a cytokinin‐free medium for 5 days, BA‐treatment enhanced protein synthesis from pre‐existing mRNA in a specific way.
The lysolipid sphingosine modulates pyrophosphatase activity in tonoplast vesicles and isolated vacuoles from a heterotrophic cell suspension culture of Chenopodium rubrum
Authors: Bille Joachim , Weiser Thomas , Bentrup Friedrich‐Wilhelm
Published: May 2006

The proton pumping activity of the tonoplast (vacuolar membrane) H+‐ATPase and H+‐pyrophosphatase (H+‐PPase) has been studied on a tonoplast‐enriched microsomal fraction and on intact vacuoles isolated from a heterotrophic cell suspension culture of Chenopodium rubrum L. in the presence of the lysosphingolipids D‐sphingosine, psychosine (galactosylsphingosine) and lysosulfatide (sulfogalactosyl‐sphingosine). Sphingosine strongly stimulates (Ka= 0.16 μM) the PPase activity, assayed both as ΔpH formation across the tonoplast vesicle membrane, and as reversible clamp current measured by the whole‐vacuolar mode of the patch‐clamp technique. Psychosine showed a minor, and lysosulfatide no stimulatory effect. No effect upon the ATPase activity has been observed. No sphingosine‐induced change could be observed in the affinity of the PPase for its substrate (apparent Km= 10 μM MgPPi). We tentatively conclude that sphingosine, which is known as a potent inhibitor of the protein kinase C in animal cells, may be a regulator of the plant vacuolar PPase.
Evidence for the expression of morphological and biochemical characteristics of C3‐photosynthesis in chlorohyllous callus cultures of Zea mays
Authors: Lavergne D. , Nato A. , Dupuis J.‐M. , Péan M. , Chagvardieff P.
Published: May 2006

A Zea mays callus culture containing chlorophyll was established and grown photomixotrophically. Cell chloroplast structure, and pigment and soluble protein contents were examined. Expression of some key enzymes of C4 carbon metabolism was compared with that of etiolated (heterotrophic) and green photoautotrophic leaves. Chlorophyll content of the callus was 15–20% that of green leaves. Soluble protein content of callus was half that of leaf cells. Electron microscopic observations showed that green callus cells contained only typical granal chloroplasts. Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.38) activities in green callus were ca 30% those of green leaves but 2–3 times higher than in etiolated leaves. Quantitative enzyme protein determination, using antibodies specific to maize leaf Rubisco showed that the chloroplastic carboxylase represented about 7% of total soluble protein in green callus, in parallel to its low chlorophyll content. The specific activity of Rubisco in callus and leaves was unchanged.

Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activity in green callus was about 20% that of green leaves and similar to that measured in etiolated leaves. Apparent Km (PEP) values (0.08 mM) for PEPC isolated from green callus and etiolated leaves were very different from values (0.5 mM) obtained with PEPC from green leaves. These kinetic characteristics together with the absence of inhibition by malate and activation by glucose‐6‐phosphate suggest that the properties of PEPC isolated from green callus and etiolated maize leaves are very similar to those of PEPPC from C3 plants. Using PEPC antibodies specific to green maize leaf enzyme, immunotitration of PEPC preparations containing identical enzyme units allowed complete precipitation of the green leaf enzyme with increasing antibody volumes. In contrast, 60–70% of the activity of PEPC from etiolated and green callus was inhibited, suggesting low affinity for the maize green leaf PEPC antiserum (typical C4 form). Ouchterlony double diffusion tests revealed only partial recognition of PEPC in green callus and etiolated leaves.

NAD‐malate dehydrogenase (NAD‐MDH, EC 1.1.1.37) activity in callus was 2 and 3 times higher, respectively, than in etiolated and green leaves. NADP‐malic enzyme (NADP‐ME, EC 1.1.1.40) activity in callus cultures was much lower than in green leaves. All our data support the hypothesis that cultures of fully dedifferentiated chlorophyllous tissues of Zea mays possess a C3‐like metabolism.
Strategies in the purification of plant proteins
Authors: Weselake Randall J. , Jain Jinesh C.
Published: May 2006

This review focuses on some recent developments in the purification of plant proteins. Topics discussed include chromatographic procedures using immobilized antibodies, protein subunits and metal ions. The use of affinity labeling to facilitate purification is presented along with recent uses of detergents. Some of the methodology has had limited application in plant biochemistry, and where appropriate, the authors have presented examples of results with non‐plant systems.
Purification of two forms of starch branching enzyme (Q‐enzyme) from developing rice endosperm
Authors: Nakamura Yasunori , Takeichi Tetsuo , Kawaguchi Kentaro , Yamanouchi Hiroaki
Published: May 2006

Two isoforms of starch branching enzyme (Q‐enzyme), QEI and QEII, have been purified to honlogeneity from developing rice endosperm. QEI and QEII, with molecular weights of about 80 and 85 kDa, respectively, could be fully separated by anion‐exchange or hydrophobic chromatography. The peptide maps obtained after V8 proteinase digestion were quite different between the two enzymes. Antibodies prepared against QEI showed no immunological cross‐reaction with the QEII protein in Western blot experiments, and anti‐QEII serum did not react with the QEI protein. The data indicate that QEI and QEII are distinct proteins encoded by different genes in rice plants.
Characterization of protochlorophyllide and protochlorophyllide esters in roots of dark‐grown plants
Authors: McEwen Birgitta , Lindsten Agneta
Published: May 2006

The protochlorophyll pools of roots of dark‐grown wheat (Triticum aestivum L. cv. Walde), maize (Zea mays L. cv. Goldcrest) and wrinkledseeded pea (Pisum sativum L. ssp. sativurh cv. Kelvedon Wonder) were investigated by high performance liquid chromatography (HPLC) and low temperature fluorescence spectroscopy. All roots contained protochlorophyllide and esterified protochlorophyllides (protochlorophylls) but with considerably larger relative amounts of the latter compared with etiolated leaves. The alcohol moieties of the 4 detected protochlorophylls were geranylgeraniol (GG), dihydrogeranylgeraniol (DHGG), tetrahydrogeranylgeraniol (THGG) and phytol. The relative amounts of the different protochlorophylls varied between the species. Protochlorophyllide and the 4 protochlorophylls all contained monovinyl forms. The divinyl forms could not be detected by our instruments. Wrinkledseeded pea contained in addition chlorophyll a, some unidentified chlorophylls and negligible amounts of chlorophyllide. Small amounts of carotenoids were found in roots of all investigated species. The carotenoids were the same as those found in green or etiolated leaves, but present in different relative amounts.
The cytosolic isoenzyme of 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate synthase in Spinacia oleracea and other higher plants: extreme substrate ambiguity and other properties
Authors: Doong Ron Lou , Gander John E. , Ganson Robert J. , Jensen Roy A.
Published: May 2006

The cytosolic isoenzyme of 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate (DAHP) synthase (DS‐Co: EC 4.1.2.15) in Spinacia oleracea, Solanum tubersosum and many other higher plants was found to use a diversity of substrates. Diose (glycolaldehyde), triose (D‐glyceraldehyde, L‐glyceraldehyde and DL‐glyceraldehyde 3‐phosphate), tetrose (D‐erythrose, L‐erythrose, D‐erythrose 4‐phosphate, D‐threose and L‐threose), and pentose (D‐ribose 5‐phosphate and D‐arabinose 5‐phosphate) were utilized in combination with phosphoenolpyruvate (PEP) to make the corresponding 2‐keto‐3‐deoxy sugar acids. Glyoxylate was also utilized by DS‐Co. Glycoladehyde exhibited the highest reaction velocity when substrates were tested at 3 mM concentrations. Pentoses were poor substrates except when phsophorylated, an effect which is probably due to an increased fraction of the molecules being in the open‐chain form. Little stereoselective discrimination exists since comparable velocities were demonstrated with the D and L isomers of glyceraldehyde, erythrose or threose. The enzyme is not a reversible aldolase since pyruvate failed to substitute for PEP. The use of D‐erythrose 4‐phsophate or glycolaldehyde resulted in Km values of 1.95 mM and 8.60 mM, respectively. However, glycolaldehyde exhibited the largest VmaxKm ratio, suggesting a greater catalytic efficiency for this substrate. Glycolaldehyde is an ideal substrate for inexpensive assays of DS‐Co that are absolutely selective in the presence of two other plant enzymes which also utilize erythrose 4‐phosphate and PEP. The spinach DS‐Co enzymes required divalent metals for activity. The presence of 20 mM Mg2+, 1 mM Co2+ and 1 mM Mn2+ yielded relative activities of 100, 70 and 15, respectively. The pH optimum was 9.5 and temperature optimum for activity was 49°C. The molecular masses of DS‐Co from spinach, tobacco and pea were all in the range of 400 kDa. The possible roles of DS‐Co in biosynthesis of α‐ketoglutarate and aromatic amino acids, in biosynthesis of components of cell wall and phytotoxin, and in acting as a sink for 2‐and 3‐carbon sugars are discussed.