bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnal variations of amino acids and organic acids in xylem fluid from Lagerstroemia indica: an endogenous circadian rhythm
Authors: Andersen P. C. , Brodbeck B. V. , Mizell R. F.
Published: May 2006

Diurnal variations in the concentrations of major organic compounds occurred in xylem fluid extracted from Lagerstroemia indica L. The concentration of amino acids and the N/C ratio was at a maximum and that of organic acids was at a minimum between 1230 and 2030 h. Since the concentrations of total organic nitrogen, total amino acids and most individual amino acids (but not organic acids or sugars) were also proportional to xylem tension two experiments were performed to discern whether variations in chemistry were a consequence of diurnal changes in moisture stress. In the first experiment, L. indica, exposed to variable levels of moisture stress during midday, manifested an increase in organic acids and a reduction in the N/C ratio. In the second experiment, chemical profiles of xylem fluid were collected and compared for plants exposed to a natural photoperiod, constant darkness or continuous light at noon and midnight. After 1 day amino acids increased in concentration during midday for all treatments; the variation was greatest (10‐fold) for plants in constant darkness where xylem tension varied from 0.20 to 0.25 MPa. Only plants exposed to continuous light lost a diurnal rhythm after 3 days. Thus, the circadian rhythm was endogenous, terminated in continuous light and was not mediated by changes in moisture stress. Glutamine accounted for most of the diurnal variation in total amino acids, organic nitrogen and the N/C ratio in xylem fluid.
Redox state of ascorbic acid in the apoplast of stems of Kalanchoë daigremontiana
Authors: Takahama Umeo
Published: May 2006

The aqueous phase of cell walls in stems of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie (apoplast) contained ascorbic acid (AA) and dehydroascorbic acid (DHA). Ratios of AA/(AA + DHA) were 0.31 ± 0.12 (SD, n = 4), whereas those of whole stems (tissues plus apoplast) were >0.9. The amounts of (AA + DHA) in the stems were 1970 ± 190 (SD, n = 4) nmol g−1 fresh weight and those in the apoplast were 14 ± 2 (SD, n = 4) nmol g−1 fresh weight of stems. Ratios of AA/(AA + DHA) differed in different tissues of the stems. The ratios of AA/(AA + DHA) of apoplast plus symplast were in the following order: pith ⋍ epidermis plus cortex > vascular bundle system, and those of apoplast were: pith > epidermis plus cortex > vascular bundle system. Ratios of AA/(AA + DHA) in the apoplast of the different tissues decreased to about 1/3 of the original values after wounding, while the amounts of (AA + DHA) remained largely unaffected. In contrast, soluble apoplastic peroxidase activities increased 30‐ to 70‐fold on wounding. Hydrogen peroxide infiltrated into stems caused a rapid oxidation of AA. Coniferyl alcohol was oxidized by peroxidase in intercellular washing fluid and by cell wall‐bound peroxidase. The oxidation of coniferyl alcohol by peroxidase in intercellular washing fluid was completely inhibited as long as AA was present in reaction mixtures. The oxidation of the coniferyl alcohol by cell wall‐bound peroxidase was partially inihibited by AA and the degree of inhibition was dependent upon the concentration of AA. The possible functions of AA in the apoplast are discussed in relation to the control of peroxidase‐dependent oxidation of phenolics.
Characterization of a rice mutant having an increased susceptibility to light stress at high temperature
Authors: Fuse Takuichi , Iba Koh , Satoh Hikaru , Nishimura Mitsuo
Published: May 2006

The effect of light irradiation at high temperature was investigated in a rice mutant, spl‐2, which is sensitive to solar radiation. Dead spots appeared on the mutant leaves when cultured at a high temperature (40°C) under strong white‐light illumination (15 W m−2). A similar damage was also observed in the wild‐type leaves under the same conditions when the plants were preincubated in the dark for one day. Preillumination with weak light (6 W m−2) lessened the irradiation‐induced damage in the wild‐type. These observations suggest that in rice plants the acclimatization to weak light has a protective effect against strong irradiation at high temperature, and the spl‐2 locus participates in the mechanisms of the acclimatization. The action spectrum for the irradiation‐induced damage at the high temperature (40°C) in the spl‐2 leaves indicated that the maximum damage occurred at around 480 nm and, in a lesser extent, at around 680 nm. Activity of the O−2− and H2O2−scavenging enzymes in the spl−2 leaves were almost the same or somewhat higher than those in the wild‐type after irradiation with strong white light (15 W m−2) at 40°C, whereas the content of ascorbic acid in the spl−2 decreased significantly compared with the wild type.
Drought tolerance, abscisic acid and electrolyte leakage in fast‐and slow‐growing black spruce (Picea mariana) progenies
Authors: Tan Weixing , Blake Terence J.
Published: May 2006

To investigate the role that drought tolerance plays in growth, abscisic acid (ABA) accumulation and electrolyte leakage during water stress were compared in fast‐ and slow‐growing black spruce (Picea mariana [Mill.] B. S. P.) progenies. Changes in the ABA content of the needles were quantified using an indirect enzyme‐linked immuno‐sorbent assay validated by gas chromatography electron capture detection. Needle electrolyte leakage was estimated using a conductivity bridge. Seedlings were stressed using (1) osmotic stress, induced by a stepwise increase in concentrations of polyethylene glycol 3 350 (PEG) for ABA study and (2) air drying for electrolyte leakage study. Progenies did not differ in ABA levels under unstressed conditions, but progeny differences were observed under osmotic stress. Needle ABA content increased up to 500% under osmotic stress. Slow‐growing black spruce progenies (25 and 46) accumulated more ABA under moderate (18% PEG), but not severe (25% PEG), osmotic stress. The slow‐growing progenies also leaked more electrolytes under moderate to severe water stress and lost 50% electrolytes at a higher xylem tension, suggesting they suffered more injury and were less dehydration tolerant. Our previously‐published results showed that slow‐growing progenies lost their photosynthesis and stomatal conductance more quickly during osmotic stress and recovered more slowly after rehydration. Therefore, tolerance of dehydration leading to a maintenance of physiological integrity during drought stress could explain the fast growth rates of more vigorous black spruce progenies.
Soluble and insoluble invertase activity in elongating Tulipa gesneriana flower stalks
Authors: Lambrechts H. , Kollöffel C.
Published: May 2006

Previously ‘frozen’Tulipa gesneriana L. bulbs cv. Apeldoorn, were planted and grown at higher temperatures to study the role of invertase (EC 3.2.1.26) in the cold‐induced elongation of the flower stalk internodes. After planting, flower stalks were left intact, or, the leaves and flower bud were both removed to inhibit internode elongation. In intact flower stalks, elongation of the internodes was accompanied by an accumulation of glucose and an initial decrease in the sucrose content g,−1 dry weight. Insoluble invertase activity g,−1 dry weight hardly changed, but soluble invertase activity showed a peak pattern, that was related, at least for the greater part, to the changes in the sugar contents. Peak activities of soluble invertase were found during (lower‐ and uppermost internodes) or around the onset of the rapid phase of internode elongation (middle internodes). Internode elongation and glucose accumulation immediately ceased when the leaves and flower bud were removed. Insoluble invertase activity g,−1 dry weight remained at its initial level (lowermost internode) or increased more towards the upper internodes. Soluble invertase activity did not further increase (uppermost internode) or decreased abruptly to a low level. It is concluded that soluble invertase may be one of the factors contributing to glucose accumulation and internode elongation in the tulip flower stalk.
An analysis of soluble starch synthase isozymes from the developing grains of normal and shx cv. Bomi barley (Hordeum vulgare)
Authors: Tyynelä Janna , Schulman Alan H.
Published: May 2006

Soluble starch synthase (SSS, EC 2.4.1.21) catalyzes formation of the α‐1,4 bonds of amylopectin. It occurs in multiple isozymes which are either type I, primer‐independent in the presence of citrate, or type II. always primer‐dependent. To analyze the enzyme. a sensitive native gel assay was developed, monitoring ADP‐[14C]glucose incorporation into insoluble α‐glucan in the presence of either sodium citrate or glycogen primer or both. Using this system, we observed multiple type I and type II forms in developing grains of barley (Hordeum vulgare L.) cv. Bomi, the relative activities of which vary with seed development. At least one form comigrates in native gels with starch branching enzyme. Assays of the shx mutant, which is severely reduced in starch accumulation and in type I SSS activity, indicate that one type I isozyme becomes primer‐dependent.
Transient expression of electroporated gene in leaf protoplasts of indica rice and influence of template topology and vector sequences
Authors: Chaudhury A. , Maheshwari S. C. , Tyagi A. K.
Published: May 2006

Electroporation was used for gene delivery and evaluation of various parameters affecting transient expression of a gene for β‐glucuronidase (gus) in leaf protoplasts of Oryza sativa var. Basmati‐370. Transient expression was found to be dependent on voltage, capacitance, amount of plasmid and carrier DNA as well as period of culture. Maximum GUS activity was obtained when a 150 ms pulse at 300 V cm‐1 and 200 μF was applied to the protoplasts (l–2×106ml−1) in an electroporation buffer containing 20 μg of plasmid and 30 μg of calf thymus DNA, assayed 48 h after electroporation. DNA topology did not influence expression of the gene as both linear and supercoiled templates resulted in similar activities, but a 4‐fold decrease in expression was observed if the gene was excised, reflecting the positive influence of vector sequences on gene expression.
Time‐course of the phosphinothricin effect on gas exchange and nitrate reduction in Medicago sativa
Authors: Lacuesta M. , González‐Moro B. , González‐Murua C. , Muñoz‐Ruedu A.
Published: May 2006

The long‐time effect of phosphinothricin (PPT) on gas exchange and nitrate metabolism in intact plants of lucerne (Medicago sativa L. cv. Aragón) was investigated. Photosynthetic CO2 uptake, stomatal conductance, and transpiration were measured with an Infra‐Red Gas Analyzer (IRGA). Under photorespiratory conditions, CO2 uptake continuously decreased after PPT treatment. The decrease of photosynthesis led to an increase in the internal CO2 concentration, which in turn caused stomatal closure and a reduction of transpiration rate. Nitrate reduction from plants sprayed with PPT was assayed both in vitro and in vivo. In vivo nitrate reductase was measured with and without nitrate in the infiltration medium. Both types of nitrate reductase assays indicated that the enzyme was inhibited in plants treated with PPT; however, the enzyme appeared more affected when the in vivo assay was used than when the one in vitro was applied. The nitrate reduction was pronouncedly affected after 24 h of PPT treatment, when glutamine synthetase (GS, EC 6.3.1.2.) activity and gas exchange were inhibited by more than 60%. The data suggest that the inhibition of GS leads to inhibition of photosynthesis, which, in turn, means lack of NADPH and nitrate, the substrates for nitrate reductase. The inhibition of GS also leads to a high ammonia level, which will produce a secondary inhibition of nitrate reductase activity.
Light quality during growth of Tradescantia albiflora regulates photosystem stoichiometry, photosynthetic function and susceptibility to photoinhibition
Authors: Liu Li‐Xia , Chow W. S. , Anderson Jan M.
Published: May 2006

Tradescantia albiflora (Kunth) was grown under two different light quality regimes of comparable light quantity: in red + far‐red light absorbed mainly by photosystem I (PSI light) and yellow light absorbed mainly by photosystem II (PSII light). The composition, function and ultrastructure of chloroplasts, and photoinhibition of photosynthesis in the two types of leaves were compared. In contrast to regulation by light quantity (Chow et al. 1991. Physiol. Plant. 81: 175–182), light quality exerted an effect on the composition of pigment complexes, function and structure of chloroplasts in Tradescantia: PSII light‐grown leaves had higher Chl a/b ratios, higher PSI concentrations, lower PSII/PSI reaction centre ratios and less extensive thylakoid stacking than PSI light‐grown leaves. Light quality triggered modulations of chloroplast components, leading to a variation of photosynthetic characteristics. A larger proportion of primary quinone acceptor (QA) in PSI light‐grown leaves was chemically reduced at any given irradiance. It was also observed that the quantum yield of PSII photochemistry was lower in PSI light‐grown leaves. PSI light‐grown leaves were more sensitive to photoinihibition and recovery was slower compared to PSII light‐grown leaves, showing that the PSII reaction centre in PSI light‐grown leaves was more easily impaired by photoinhibition. The increase in susceptibility of leaves to photoinhibition following blockage of chloroplast‐encoded protein synthesis was greater in PSII light‐grown leaves, showing that these leaves normally have a greater capacity for PSII repair. Inhibition of zeaxanthin formation by dithiothreitol slightly increased sensitivity to photoinhibition in both PSI and PSII light‐grown leaves.
Dormancy‐associated embryonic mRNAs and proteins in imbibing Avena fatua caryopses
Authors: Dyer William E.
Published: May 2006

The mechanisms controlling seed dormancy maintenance and release are not understood. To characterize the molecular events accompanying dormancy release, two‐dimensional gel electrophoresis was used to monitor changes in soluble proteins and in vitro translation products of embryonic mRNA populations during imbibition of dormant and nondormant (after‐ripened) Avena fatua L. caryopses. No differences were observed between in vitro translation products of mRNA extracted from dry dormant and nondormant embryos. However, the expression patterns of several imbibition‐ and germination‐associated mRNAs were temporally modulated during the first 24 h of imbibition. Two dormancy‐associated mRNAs, represented by polypeptides D1 and D2, were differentially overexpressed in dormant embryos after 3 h of imbibition. mRNA levels for D1 and D2 were about 8‐ and 3‐fold higher, respectively, in dormant embryos than in nondormant embryos after 3 h of imbibition. Overexpression of D1 continued through 12 h of imbibition, while expression of both mRNAs fell to low and equivalent amounts in dormant and nondormant embryos after 24 h. Similar dormancy‐associated changes in two soluble proteins were observed during imbibition. The results demonstrate that steady‐state levels of specific mRNAs and proteins change during early imbibition of dormant and nondormant A. fatua embryos and indicate that these changes may be associated with differential gene expression responsible for the maintenance of dormancy.
Soybean (Glycine max) modulation and N2‐fixation as affected by exposure to a low root‐zone temperature
Authors: Lynch D. H. , Smith D. L.
Published: May 2006

Low root‐zone temperatures (RZTs) are known to reduce soybean N2‐fixation. However, the relative sensitivity of the various stages of symbiosis establishment and function (N2‐fixation) to suboptimal RZTs is unresolved. We conducted experiments to examine the effect of exposure to a RZT of 15°C on nodulation. The control RZT was 25°C. Root temperatures were controlled by circulating cooled water around pots on a growth bench. Soybean seedlings [Glycine max (L.) Merr. cv. Maple Arrow] were inoculated with 1 ml of a log‐phase culture (approximately 10−8 cells) of Bradyhizobium japonicum strain 532C. They were then (1) maintained continuously at RZTs of 15 or 25°C, transferred to 15 or 25°C from the alternate temperature 7 days after inoculation (DAI), or transferred to 15 or 25°C at 14 DAI, and (2) maintained at 15 or 25°C, or transferred at either 1, 4 or 7 DAI. When seedlings were maintained at a RZT of 25°C nodule primordia (<1 mm) were visible at 7 DAI and N2‐fixation commenced at 14 DAI. Nodule function (N2‐fixation) appeared to be relatively insensitive to low RZTs since exposure of plants to 15°C following the onset of N2‐fixation (14 DAI) resulted in 68% of the N fixed and 78% of the dry weight of the 25°C RZT, although N partitioning to shoot tissues was reduced. In contrast, exposure to the low RZT shortly after inoculation declayed the onset of N2‐fixation for 4 to 6 weeks, primarily by inhibiting the early stages of nodulation. This resulted in fixed N and dry weight levels of 9% and 22% of controls, respectively.
Immunogold localization of phytoene desaturase in higher plant chloroplasts
Authors: Linden Hartmut , Lucas M. Mercedes , de Felipe Maria Rosario , Sandmann Gerhard
Published: May 2006

In situ location of phytoene desaturase, a key enzyme in the carotenoid biosynthesis pathway, has been investigated in chloroplasts from higher plants. For this purpose, an antiserum has been raised against the phytoene desaturase from the cyanobacterium Synechococcus PCC 7942 overexpressed in E. coli. The specifity of this antiserum was demonstrated by inhibition of the enzymatic desaturation reaction in vitro. The antiserum was further purified and immunoabsorbed with E. coli proteins. The resulting IgG‐fraction was tested by western blotting against membrane proteins from chloroplasts of tobacco (Nicotiana tabacum L. cv. Samsun) and spinach (Spinacia oleracea L. cv. Atlanta). Apparent molecular masses of immunoreactive proteins were 62 and 64 kDa. A western blot of different membrane fractions of spinach chloroplasts (inner and outer envelopes, and thylakoids) indicated a localization of the phytoene desaturase in thylakoids. A post embedding immunogold microscopy procedure was employed. In these experiments the main labelling (79%) was associated with thylakoid membranes of tobacco chloroplasts. Of the counted colloidal gold particles, 16% were found in the stroma. Only 5% were detected in the envelope membranes. These results give clear evidence that at least the majority of phytoene desaturase molecules is localized within thylakoid membranes of higher plant chloroplasts and that the presence of the enzyme in the envelope is of minor significance.
The regulation of respiration in cell suspensions of Petunia hybrida, studied by inhibiting mitochondrial protein synthesis with chloramphenicol
Authors: van Emmerik Willie A. M. , Wagner Anneke M. , Zwiers Johanneke H. , van der Plas Linus H. W.
Published: May 2006

When Petunia hybrida L. cv. Rosy Morn Fertile suspension cells were inoculated in fresh medium with chloramphenicol (CAP), the activity of cytochrome C oxidase (EC 1. 9. 3. 1), and the respiration via the cytochrome pathway of isolated mitochondria decreased, while in untreated cells these parameters more than doubled in 2–3 days. However, the in vivo respiratory activity of the cytochrome pathway of CAP‐treated cells showed a similar course in time as that of untreated cells, even in the presence of an uncoupler, a large rise during the first 2–3 days followed by a decline. This leads to the conclusion that the respiration via the cytochrome pathway, even when measured in the presence of an uncoupler, is not the capacity of this pathway. Furthermore, the results suggest that, although new‐synthesis of proteins occurs directly after in‐oculation, a large overcapacity must be present of cytochrome pathway elements (at least of those that are mitochondrial encoded). CAP had little effect on the uninhibited respiration and the cyanide‐resistant, alternative pathway of the Petunia cells. However, the engagement of the alternative pathway (in the presence or absence of uncoupler) was increased in CAP‐treated cells, especially after day 3 of the batch cycle, possibly as an effect of higher sugar degradation in combination with substrate phosphorylation to compensate the loss of ATP‐synthesizing ability of the cytochrome pathway. It will be discussed that in general one should be careful using the term ‘capacity’ for the respiratory pathways.
Transient expression of photosynthetic genes in transfected albinoid petunia protoplasts and correct processing of newly synthesized chloroplast‐destined polypeptides
Authors: Broido Shimsbon , Loyter Abraham , Vainstein Alexander
Published: May 2006

Protoplasts prepared from cultured albinoid cells of petunia do not express photosynthetic genes, such as those coding for chlorophyll a/b‐binding (Cab) proteins or ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco). They therefore provide a convenient system for expressing recombinant photosynthetic genes, without background interference. Transfection of petunia protoplasts with vectors bearing the Lhcbl*1 Cab gene under the control of the 35S promoter of cauliflower mosaic virus (CaMV) resulted in the appearance of significant amounts of the specific transcripts, but not of the corresponding polypeptides, as inferred from northern and western blot analysis, respectively. The use of an expression vector carrying the translational enhancer Ω of tobacco mosaic virus (TMV) strongly enhanced the appearance of transfected gene products: western blot analysis of transfected protoplasts clearly revealed the appearance of Lemna gibba Lhcbl*1 and Lhcb2*1, tomato Lhcb2*1 and psaD, and pea rbcS gene products. Molecular weight estimations of the newly synthesized polypeptides indicated that each was promptly processed into its mature‐cleaved form within the transfected albinoid protoplasts. This occurred despite a lack of chlorophyll and the absence of a thylakoid network.
Purification and characterization of a thiol‐protease induced during senescence of unpollinated ovaries of Pisum sativum
Authors: Cercós Manuel , Carbonell Juan
Published: May 2006

A senescence‐specific protease has been purified from senescent unpollinated ovaries of Pisum sativum L. cv. Alaska by acidic extraction. (NH4)2SO4 fractionation, ion exchange chromatography on CM‐Sephadex, and affinity chromatography on ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco)‐Sepharose. Characterization of the purified protease indicated that it is a thiol‐endoprotease (EC 3. 4. 22 class) active over a wide pH range. Purified antibodies against this protease inhibit the degradation of Rubisco in autodigested extracts of senescent ovaries, suggesting that Rubisco might be a substrate for the protease in senescent pea ovaries. The relative levels of the protease were determined by an enzyme‐linked immunosorbent assay (ELISA) along the processes of ovary senescence and gibberellic acid (GA)‐induced fruit development, indicating its induction at the beginning of senescence and the suppression of its synthesis by GA treatment.
Immunolocalization of a thiol‐protease induced during the senescence of unpollinated pea ovaries
Authors: Cercós Manuel , Harris Nick , Carbonell Juan
Published: May 2006

A thiol‐endoprotease induced during the senescence of unpollinated ovaries of Pisum sativum L. cv. Alaska has been localized at both cellular and subcellular levels using purified antibodies. Immunoblot analysis showed a single band of 30 kDa in extracts from senescent ovaries 3 and 4 days post‐anthesis. Immunolocalization showed the accumulation of the protease within the exocarp and in the outer cell layers of the mesocarp of the senescent ovaries, although with an asymmetric distribution as illustrated in transverse sections. Ultrastructural localization indicates that the protease is associated with the tonoplast and with electron dense materials within the vacuole, where lysis of cell components occurs in senescent ovaries.
Occurrence of two endoproteinases in wheat leaf intercellular washing fluid
Authors: Pinedo Marcela L. , Segarra Carmen , Conde Ruben D.
Published: May 2006

The presence of endoproteinases in the intercellular washing fluid of the first wheat (Triticum aestivum) leaf 13 days after sowing was investigated. Two activities were detected after separation of the intercellular fluid proteins by SDS‐PAGE using slab gels containing gelatin as substrate. Their sizes were 70 and 100 kDa. Both enzymes hydrolyzed gelatin and casein. They also seem to be involved in the degradation of a 40 kDa protein component of the intercellular fluid. These results indicate that both enzymes are endoproteinases. They were also obtained from leaves previously sumitted to intercellular fluid extraction. However, the 100 kDa enzyme yield was low, indicating that it is mainly located in the intercellular washing fluid. Assays performed with either specific substrates or inhibitors indicate that both enzymes are serine proteinases.
Symbiotic dinitrogen fixation and host‐plant growth during development of and recovery from phosphorus deficiency
Authors: Israel Daniel W.
Published: May 2006

Characterization of nodule growth and function, phosphorus and nitrogen status of plant tissues and host‐plant growth of nodulated soybean (Glycine max L. Merr.) plants developing and recovering from phosphorus deficiency was used to evaluate the role of phosphorus in symbiotic dinitrogen fixation. The sequence of physiological responses during recovery from phosphorus deficiency was; (1) rapid uptake of phosphorus, (2) rapid increases in the phosphorus concentration of leaves and nodules, (3) enhanced growth and function of nodules, (4) increased nitrogen concentrations in all plant organs and (5) enhanced plant growth. The sequence of physiological responses to onset of phosphorus deficiency was; (1) decreased phosphorus uptake, (2) decreased phosphorus concentrations in leaves and nodules, (3) decreased nodule function, (4) decreased nitrogen concentration in plant organs and (5) decreased plant growth. These results, in conjunction with previously published data (Sa and Israel, Plant Physiol. 97: 928–935, 1991), support an interpretation that the total response of symbiotic dinitrogen fixation in soybean plants to altered phosphorus supply is a function of both indirect effects on host‐plant growth and more direct effects on the metabolic function of nodules.
Gibberellin‐enhanced sugar accumulation in growing subhooks of etiolated Pisum sativum seedlings. Effects of gibberellic acid, indoleacetic acid and cycloheximide on invertase activity, sugar accumulation and growth
Authors: Miyamoto Kensuke , Ueda Junichi , Kamisaka Seiichiro
Published: May 2006

The possible involvement of invertase in the action of gibberellic acid (GA) on stimulating sugar accumulation in growing subhooks of Alaska pea (Pisum sativum L. cv. Alaska) was studied. GA and indoleacetic acid (IAA) stimulated elongation growth to a similar extent. GA, in contrast to IAA, increased the amount of soluble sugars in the subhook. GA substantially increased invertase activity whereas IAA did not. These results suggest that the mode of action of GA and IAA differs, although both stimulate pea subhook growth.

Cycloheximide (CH) inhibited the effect of GA on invertase activity, accumulation of soluble sugars, and elongation growth. Good correlations were found between invertase activity, the amount of soluble sugars and growth. The results suggest that GA‐induced enhancement of sugar accumulation in the subhook cells is dependent on increased invertase activity. The sugar accumulated in the subhook may be involved in growth promotion by GA.
Extracellular proteins in embryogenic suspension cultures of Norway spruce (Picea abies)
Authors: Egertsdotter Ulrika , Mo Lars H. , von Arnold Sara
Published: May 2006

Embryogenic cell lines of Norway spruce (Picea abies) varying in growth habit and morphology were compared as regards profiles of extracellular proteins. Similar proteins were detected in the culture medium by SDS PAGE and in vivo labeling experiments, indicating that the proteins were secreted. Approximately 20 protein bands could be detected in the medium of each cell line. Three of the bands represented glycosylated proteins, as revealed by Concanavalin A staining. Some of the secreted proteins were similar for all tested embryogenic lines of Norway spruce, others were either specific for a group of cell lines or for individual cell lines. A correlation was observed between the morphology of the somatic embryos in a cell line and the presence of secreted proteins. The embryogenic cell lines of Norway spruce can be divided into two main groups. A and B, where A is characterized by somatic embryos with dense embryoheads and B by somatic embryos with loosely aggregated cells in their embryoheads. When proteins secreted from a cell line belonging to group A were added to cell lines belonging to group B, the somatic embryos of the B type developed further and became more similar in morphology to A‐type embryos. These observations indicate that cell lines belonging to group A secrete certain proteins to the culture medium that are essential for the development of somatic embryos of Norway spruce.
Seasonal CO2 exchange patterns of developing peach (Prunus persica) fruits in response to temperature, light and CO2 concentration
Authors: Pavel E. W. , DeJong T. M.
Published: May 2006

CO2 exchange rates per unit dry weight, measured in the field on attached fruits of the late‐maturing Cal Red peach cultivar, at 1200 μmol photons m−2S−1 and in dark, and photosynthetic rates, calculated by the difference between the rates of CO2 evolution in light and dark, declined over the growing season. Calculated photosynthetic rates per fruit increased over the season with increasing fruit dry matter, but declined in maturing fruits apparently coinciding with the loss of chlorophyll. Slight net fruit photosynthetic rates ranging from 0. 087 ± 0. 06 to 0. 003 ± 0. 05 nmol CO2 (g dry weight)−1 S−1 were measured in midseason under optimal temperature (15 and 20°C) and light (1200 μmol photons m−2 S−1) conditions. Calculated fruit photosynthetic rates per unit dry weight increased with increasing temperatures and photon flux densities during fruit development. Dark respiration rates per unit dry weight doubled within a temperature interval of 10°C; the mean seasonal O10 value was 2. 03 between 20 and 30°C. The highest photosynthetic rates were measured at 35°C throughout the growing season. Since dark respiration rates increased at high temperatures to a greater extent than CO2 exchange rates in light, fruit photosynthesis was apparently stimulated by high internal CO2 concentrations via CO2 refixation. At 15°C, fruit photosynthetic rates tended to be saturated at about 600 μmol photons m−2 S−1. Young peach fruits responded to increasing ambient CO2 concentrations with decreasing net CO2 exchange rates in light, but more mature fruits did not respond to increases in ambient CO2. Fruit CO2 exchange rates in the dark remained fairly constant, apparently uninfluenced by ambient CO2 concentrations during the entire growing season. Calculated fruit photosynthetic rates clearly revealed the difference in CO2 response of young and mature peach fruits. Photosynthetic rates of younger peach fruits apparently approached saturation at 370 μl CO21−2. In CO2 free air, fruit photosynthesis was dependent on CO2 refixation since CO2 uptake by the fruits from the external atmosphere was not possible. The difference in photosynthetic rates between fruits in CO2‐free air and 370 μl CO2 1−1 indicated that young peach fruits were apparently able to take up CO2 from the external atmosphere. CO2 uptake by peach fruits contributed between 28 and 16% to the fruit photosynthetic rate early in the season, whereas photosynthesis in maturing fruits was supplied entirely by CO2 refixation.
Estimating the photosynthetic contribution of developing peach (Prunus persica) fruits to their growth and maintenance carbohydrate requirements
Authors: Pavel E. W. , DeJong T. M.
Published: May 2006

CO2 exchange rates (CO2 evolution) of late‐maturing cv. Cal Red peaches, exposed to different photon flux densities, were simulated from 24 days after flowering (DAF) until harvest by using light and temperature response curves measured on attached fruits in the field at biweekly intervals. The daily patterns of dark respiration rates per unit dry weight indicated their dependence on temperatures. Fruit CO2 exchange rates in light were also affected by photosynthetic photon flux densities. Daily photosynthetic rates per unit dry weight and per fruit were significantly lower in shaded fruits receiving 7% of the full daily sunlight compared to fruits exposed to 35% sunlight. However, the difference in photosynthetic rates in peach fruits receiving 21 and 35% of total daily sunlight was small. Within the last 4 weeks before harvest, weekly carbohydrate requirements for the production of dry matter rose rapidly in cv. Cal Red peaches and were related to high carbohydrate accumulations, especially of sucrose, in the peach mesocarp. Weekly photosynthetic contribution of late‐maturing cv. Cal Red peaches to these carbohydrate accumulations increased up to 115 DAF. A decline in photosynthetic contributions between 115 DAF and harvest was related to decreasing photosynthetic activities in association with declining chlorophyll contents. Photosynthesis of late‐maturing cv. Cal Red peaches provided 3–9% of the weekly fruit carbohydrate requirements early in the season and 8–15% in the midseason depending on fruit exposure to light. Photosynthesis of mature fruits contributed 3–5% of the total fruit carbohydrate requirements. Since fruit photosynthetic rates approach saturation at a photosynthetic photon flux density of about 600 μmol m2 s−2, the difference in weekly photosynthetic contributions was small between exposed and partially exposed (35 and 21% sunlight, respectively) peach fruits. However, a shaded fruit (7% sunlight) supplied significantly less of its weekly carbohydrate requirements through photosynthesis compared to exposed fruits. During the growing period of 24 DAF until harvest, dry matter accumulation of latematuring cv. Cal Red peaches accounted for 78% of the total carbohydrate requirements and 22% was used in respiration. Fruit photosynthesis of shaded peach fruit, partially exposed fruit and exposed fruit (receiving 7. 21 and 35% of full sunlight over the day, respectively) contributed 5. 8 and 9%, respectively, of the total growth and maintenance carbohydrate requirements during the growing season.
Variability in antifungal proteins in the grains of maize, sorghum and wheat
Authors: Darnetty  , Leslie John F. , Muthukrishnan Subbaratnam , Swegle Mark , Vigers Alison J. , Selitrennikoff Claude P.
Published: May 2006

Crude protein extracts were made from kernels of 12 cultivars each of maize, sorghum and wheat. These preparations were fractionated on sodium dodecyl sulfate (SDS)‐polyacrylamide gels and subjected to Western blot analyses. Bands corresponding to chitinases and β‐glucanases were identified immunologically (Western blots) and on activity gels. Ribosome Inactivating Protein(s) (RIP) and permatins were identified immunologically. In maize, two chitinase bands (25–29 kDa) were seen in all cultivars, and a third band of about 23 kDa was detected in 7 of the 12 cultivars. Two or three β‐glucanase bands of sizes between 24 and 36 kDa (probably a mixture of 1,3–β‐ and 1,3–1,4‐β‐glucanases) were detected in blots of SDS gels, and one band was detected in activity gels (1,3‐β‐glucanase). In sorghum, one chitnase band of approximately 29 kDa, and two or three additional bands ranging in size from 21–24 kDa were observed. Only one β‐glucanase band was identified, with an estimated molecular weight of 30 kDa. All bands that appeared on Western blots of SDS gels corresponded to bands detected on activity gels. In wheat, one chitmase band of around 20 kDa, one β‐glucanase band of about 30 kDa and one RIP band of about 30 kDa were identified. Permatins (molecular weight about 22 kDa) were identified in maize, sorghum and wheat, with the different cultivars having varying amounts of permatins.
UV‐B response of cucumber seedlings grown under metal halide and high pressure sodium/deluxe lamps
Authors: Krizek Donald T. , Kramer George F. , Upadhyaya Abha , Mirecki Roman M.
Published: May 2006

UV‐B‐sensitive (Poinsett) and ‐insensitive (Ashley) cultivars of cucumber (Cucumis sativus L.) were grown in growth chambers at 600 μmol m−2s−1 of photosynthetically active radiation provided by metal halide (MH) or high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradiated 15 days from seeding for 6 h per day under 18. 2 kJ m−2 day−1 of biologically effective UV‐B (UV‐BBE) radiation. One of the most pronounced effects of UV‐B was a 27 to 78% increase in phenylalanine ammonialyase (PAL) activity. UV‐B also increased total polyamines. Catalase and superoxide dismutase varied greatly in their response to UV‐B. There were no interactive effects on PAL or catalase activity, or total polyamines. There was a UV × PAR source interaction for superoxide dismutase activity. UV‐B increased chlorosis and decreased height, dry weight and leaf area. Stem elongation, biomass production, leaf enlargement and chlorosis were greater under HPS/DX lamps than under MH lamps. Chlorosis was greater in Poinsett than in Ashley and in lower leaves than in upper ones. Aside from chlorosis, there were no interactive effects of UV‐B, PAR source or cultivar on any of the growth parameters measured, suggesting that the growth response of cucumber seedlings to UV‐B is unaffected by PAR source or cultivar. Similarly, except for SOD activity, the biochemical response to UV‐B was also not influenced by PAR source or cultivar.
Ethylene biosynthesis and strigol‐induced germination of Striga asiatica
Authors: Babiker Abdel Gabbar T. , Ejeta Gebisa , Butler Larry G. , Woodson William R.
Published: May 2006

Germination of witchweed [Striga asiatica (L.) Kuntze], an important parasite on cereal crops, is stimulated by several natural and synthetic compounds. In the present study the role of ethylene in germination of Striga asiatica in response to strigol was examined. Unconditioned seeds and those conditioned for 3 days produced negligible amounts of ethylene in response to strigol. However, extending the conditioning period to 5 and 8 days increased ethylene evolution by more than 10‐fold. Ethylene production preceded radicle protrusion and was detectable within 3h after treatment. No germination was observed in the first 6 h of exposure to strigol. Germination and ethylene production increased with strigol concentration. Strigol‐induced germination was considerably reduced by the ethylene action inhibitors. 2. 5‐norbornadiene, silver thiosulphate and CO2. The ethylene precursor 1‐aminocyclopropane‐1‐carboxyac acid (ACC) at 5 to 200 μM elicited neither germination nor ethylene production. However, a combination of strigol and ACC resulted in a high germination rate and copious ethylene production. Both germination and ethylene production were reduced by CoCl2 and cyclobeximide, inhibitors of the ethylene‐forming enzyme and of protein synthesis, respectively. The results are consistent with a model in which conditioning and strigol are required to remove a restriction on the ethylene biosynthetic pathway and in which the ethylene‐forming enzyme is rate limiting.
Photosystem I and its bacterial counterparts
Authors: Lockau Wolfgang , Nitschke Wolfgang
Published: May 2006

Photosynthetic reaction centres of green sulphur bacteria and of heliobacteria show a remarkable similarity to photosystem 1 of O2‐evolving photosynthesis. Three features are common to this ‘reaction centre 1‐type’. (1) A redox potential negative enough to reduce ferredoxin is generated. (2) Iron‐sulphur centres are constituents of the bound electron acceptor complex. (3) A dimer of large, very hydrophobic protein subunits not only binds the redox centres that are involved in the initial steps of charge separation, but also binds the pigments of the inner light antenna. This protein dimer is a heterodimer in photosystem I, but appears to be a homodimer in reaction centres of green sulphur bacteria and of heliobacteria. The dimer‐forming proteins contain a highly conserved dodecapeptide to which one of the iron‐sulphur centres is bound.
Axillary bud flowering after apical decapitation in Pharbitis in relation to photoinduction
Authors: Ono Michiyuki , Ono Kimiyo Sage , Yamada Koichiro , Yasui Masaru , Okazaki Mitsuo
Published: May 2006

The flowering response of axillary buds of seedlings of Pharbitis nil Choisy, cv. Violet, was examined in relation to the timing of apical bud removal (plumule including the first leaf or second leaf) before or after a flower‐inductive 16‐h dark period. When the apical bud was removed well before the dark period, flower buds formed on the axillary shoots that subsequently developed, but when removed just before, or after, the dark period, different results were observed depending on the timing of the apical bud removal and plant age. In the case of 8‐day‐old seedlings, fewer flower buds formed on the axillary shoots developing from the cotyledonary node when plumules were removed 20 to 0 h before the dark period. When the apical bud was removed after the dark period, no flower buds formed. Using 14‐day‐old seedlings a similar reduction of flowering response was observed on the axillary shoots developing from the first leaf node when the apical bud was removed just after the dark period. To further elucidate the relationship between apical dominance and flowering, kinetin or IAA was applied to axillary buds or the cut site where the apical bud was located. Both chemicals influenced flowering, probably by modulating apical dominance which normally forces axillary buds to be dormant.
Lipid changes in tobacco cell suspensions following treatment with cellulase elicitor
Authors: Moreau Robert A. , Preisig Carol L.
Published: May 2006

Tobacco (Nicotians tabacum) KY14 cell cultures have previously been reported to produce capsidiol and other stress metabolites when treated with fungal elicitor or cellulase. Using a new high performance liquid chromatographic technique, we have measured the changes in sesquiterpene phytoalexins and membrane lipid classes thai occur upon elicitation of tobacco cell cultures with cellulase. Measurable levels of capsidiol and debneyol were found in the tobacco cells and in the culture medium after 8 h of elicitor treatment, with levels continuing to increase for up to 24 h. For the duration of the experiments, the levels of most of the galactolipids and phospholipids were found to decrease in elicited cells and increase in control cells. The most striking change was a rapid decrease in the level of digalactosyldiacylglycerol in elicited cells, to less than 10% of the level in control cells. Among the sterol lipid classes, the most notable changes occurred in the levels of sterol esters and acylated sterol glycosides, which increased significantly in elicited cells within 2 to 4 h after addition of cellulase, but remained unchanged in control cells. Free sterols and sterol glycosides declined slightly, while free fatty acids dropped to low levels 24 h after treatment of cells with cellulase. The present results and those of previous studies indicate that esterification of phytosterols may be a widespread response to environmental or chemical stress.
Changes in maize‐stalk proteins during ear development
Authors: Ta T. Chanh , Roeske Chrissl A. , Eaglesham Allan R. J.
Published: May 2006

Although the stalk of maize (Zea mays L.) functions as a reservoir for N, little is known of qualitative changes which accompany the remobilization of N to the developing ear. SDS‐PAGE analysis revealed that certain stalk proteins were lost, whereas others were not. The removal of ears and the prevention of pollination eliminated the selective protein loss. The use of 15N labelling showed that some stalk‐protein fractions turned over faster with ear development, whereas the turnover of others was unchanged or slowed. The data indicate that at least 7 proteins function as temporary storage forms of N in the stalk, and that they are degraded during the first 3 weeks after silking to provide organic N for ear development.
Inhibition of internode growth due to mechanical stress in Bryonia dioica: relationship between changes in DNA methylation and ethylene metabolism
Authors: Galaud Jean‐Philippe , Gaspar Thomas , Boyer Nicole
Published: May 2006

Changes in the level of cytosine methylation were assessed by HPLC in mechanically stressed Bryonia dioica. Rubbing young internodes. which results in growth inhibition and ethylene production, induced a rapid and transient decrease of cytosine methylation in DNA. The level of cytosine methylation was about 25% in young internodes and dropped to nearly 0% in less than 1 h before increasing to the normal level within 3 h. A decreasing gradient of DNA methylation occurred naturally along the plant, from the apex to the base. The pool of S‐adenosylmethionine was also measured in order to establish a possible relationship between ethylene metabolism and DNA methylation. The role of DNA methylation in gene regulation is discussed and different mechanisms for methylation are considered.
Separation of membranes from semiprotoplasts of suspension‐cultured sycamore maple (Acer pseudoplatanus) cells
Authors: White Alan R. , Xin Yi , Pezeshk Vida
Published: May 2006

Semiprotoplasts were produced from suspension‐cultured Acer pseudoplatanus (sycamore maple) cells prior to cell disruption by passing them through a 60 μm nylon screen. Cell membranes from homogenates were separated by ultracentrifugation on linear sucrose density gradients. Samples were collected by gradient fractionation and subcellular fractions were assayed for membrane markers and glycosyl transferase activities. Results of standard marker assays (cytochrome c reductase for endoplas‐mic reticulum. uridine and inosine diphosphatases for Golgi. and eosin‐5′‐maleimide binding for plasma membrane) showed partial separation of these three membrane types. Golgi and plasma membrane markers overlapped in most gradients. Incorporation of 14C‐labeled sugars from UDP‐glucose and UDP‐xylose into ethanol precipitated polysaccharides was used to detect glucan synthases I & II (glucosyl transferases) and xylosyl transferase activities in Golgi membrane fractions. All three glycosyl transferases overlapped in fractions corresponding to both Golgi and plasma membrane markers, although peak activities for all three occurred in different fractions. More than one peak of glucan synthase I activity was found. Glucan synthase II, associated with ß‐l.3 glucan (cullose) synthesis in plasma membranes, was also detected and exhibited a 10‐fold stimulation in the presence of Ca2+.