bluuebunny/crossref_metadata_2025 huggingface dataset:
Btl, a structural gene for the major 39–44 kDa amyloplast membrane polypeptides
Authors: Cao Heping , Sullivan Thomas D. , Boyer Charles D. , Shannon Jack C.
Published: May 2006

The aim of the present work was to investigate the relationship between theBtlgene(Btl)and the major 39–44 kDa amyloplast membrane polypeptides which were deficient in amyloplast membranes ofbrittlel (btl)kernels of maize (Zea maysL.). A rapid yet gentle procedure for the isolation of amyloplasts from immature kernels is described. These amyloplasts were relatively free of contamination by other cellular components, and immunological studies showed that they contained polypeptides which reacted with antibodies to maize starch branching enzyme and ADP‐Gle pyrophosphorylase. Purified membranes isolated from the amyloplast contained a poly‐peptide which reacted with antibodies to the Pi‐translocator from spinach chloroplasts. However, a cluster of 39–44 kDa polypeptides accounted for about 40% of the total amyloplast membrane protein from W64A kernels. These polypeptides were specifically recognized by antibodies raised against a fusion protein consisting of 56 amino acids of the carboxyl terminus of the BTI protein and glutathione S‐transferase. The BT1 antibodies also reacted with the abundant polypeptides in amyloplast membranes from hybrid kernels (Doebler 66XP and Pioneer 3780), and theshrunkenlandshrunken2mutant genotypes, but no BTl reacting polypeptides were present in amyloplast membranes frombtlmutant kernels. We were unable to detect BTl by the immunoblot procedure in microsomal membranes from embryo and pericarp tissues from the kernel, from seedling roots and shoots, or in membranes from mitochondria and chloroplasts. The same BTl immunoblot pattern was obtained for proteins extracted from microsomal membranes from developing endosperm and from purified amyloplast membranes. A linear relationship between the number of copies ofBtlalleles and the levels of BTl in endosperm microsomal membranes was demonstrated in a gene dosage series. BTl was not extracted from amyloplast membranes by chloroform/methanol or by alkaline buffer at pH 11.5, but was partially extracted by 0.1MNaOH. These lines of evidence support the conclusion thatBtl is the structural genefor the major 39–44 kDa amyloplast membrane polypeptides and that these polypeptides are integral proteins specific to amyloplast membranes from the endosperm.
Growth, gas exchange and ion content in Olea europaea plants during salinity stress and subsequent relief
Authors: Tattini Massimiliano , Gucci Riccardo , Coradeschi Maria Assunta , Ponzio Carlo , Everard John D.
Published: May 2006

Olive (Olea europaea L. cv. Frantoio) plants grown hydroponically in a glasshouse were supplied with half‐strength Hoagland solutions containing 0, 50, 100, and 200 mM NaCl for 4 weeks and subsequently supplied with the standard solution without NaCl to relieve salinity stress. Two complete stress‐relief cycles were repeated on the same plant material during one growing season. Growth was inhibited at all salt levels, but most growth parameters of plants treated with 50 or 100 mM NaCl returned to control levels after 4 weeks of relief. More severely stressed plants (200 mM NaCl) recovered to only 60% of the growth of the controls after 4 weeks. During relief, plants treated with 50 and 100 mM NaCl had net photosynthetic rates and stomatal conductances higher than the controls. Increasing the NaCl concentration of the external solution from 0 to 200 mM decreased both leaf pre‐dawn water potential (from ‐0.3 to ‐1.0 MPa) and osmotic potential (from ‐2.1 to ‐2.7 MPa). The sodium concentration in the leaves of plants treated with 200 mM NaCl reached maximum levels of 211 and 388 mM (expressed on a tissue water basis) at the end of the first salinity and relief periods, respectively. Leaf chloride concentrations were 359 and 223 mM at the same sampling dates. These data indicate that the inhibitory effects of salinization on growth and gas exchange of the salt‐tolerant olive cv. Frantoio can be readily reversed when salinity is relieved, despite the marked accumulation of potentially toxic ions (Na+. Cl) in the leaf.
Plastid development in germinating wheat (Triticum aestivum) is enhanced by gibberellic acid and delayed by gabaculine
Authors: Younis Suhaila , Ryberg Margareta , Sundqvist Christer
Published: May 2006

Etioplast development and protochlorophyllide (Pchlide) accumulation was studied in wheat seedlings (Triticum aestivum L. cv. Walde, Weibull) grown in darkness on gibberellic acid (GA3), gabaculine (3‐amino‐2,3‐dihydrobenzoic acid), or on a combination of the two. The results were compared with the features of seedlings grown on water only. GA3 enhanced shoot growth and promoted etioplast development. A correlation was observed between the appearance of prolamellar bodies (PLBs) and of phototransformable Pchlide. Gabaculine, a known tetrapyrrole biosynthesis inhibitor, delayed growth, slowed down the rate of PLB formation and caused structural alterations of the etioplasts up to 48 h of germination. Gabaculine also delayed the formation of phototransformable Pchlide as well as overall Pchlide biosynthesis, as determined by low‐temperature fluorescence emission in vivo. The spectral blue‐shift of newly formed chlorophyllide (Chlide) was delayed in irradiated dark‐grown gabaculine‐grown seedlings, indicating an inhibited dissociation of Chlide and NADPH‐Pchlide oxidoreductase (Pchlide reductase: EC 1.3.1.33). Thus there is a close correlation between accumulation of Pchlide and etioplast development, also under conditions when development is enhanced or delayed.
Reversibility of photosynthetic acclimation of swiss chard and sugarbeet grown at elevated concentrations of CO2
Authors: Ziska Lewis H. , Sicher Richard C. , Kremer Diane F.
Published: May 2006

Although leaf photosynthesis and plant growth are initially stimulated by elevated CO2 concentrations, increasing insensitivity to CO2 (acclimation) is a frequent occurrence. In order to examine the acclimation process, we studied photosynthesis and whole plant development in swiss chard (Beta vulgaris L. Koch ssp. ciela) and sugarbeet (Beta vulgaris L. ssp. vulgaris) grown at either ambient or twice ambient concentrations of CO2. In an initial controlled environment study, photosynthetic acclimation to elevated CO2 levels was observed in both subspecies 24 days after sowing (DAS) but was not observed at 42 and 49 DAS for sugarbeet or at 49 DAS for swiss chard. Although sugarbeet and swiss chard differed in root size and morphology, this was not a factor in the onset of photosynthetic acclimation. The reversal of photosynthetic acclimation that was observed in older plants grown at elevated CO2, concentrations was associated with a rapid increase in root development (i.e. increased root: shoot [R/S] ratio), increased sucrose levels in sinks (roots) and no differences in total soluble leaf protein of either subspecies relative to the ambient CO2 condition. In a second set of experiments, swiss chard and sugarbeet were grown in outdoor Plexiglass chambers at different times of the year (i.e. summer and early fall). Average 24‐h temperature was 30.7 and 19.4°C for the summer and fall plantings, respectively. In agreement with the controlled environment study, lack of photosynthetic acclimation, determined from the response of photosynthesic rate to internal CO2 concentration, was correlated with increased root biomass and sucrose concentration relative to the ambient condition. However, photo‐synthetic acclimation was observed depending on the season, i.e. summer (swiss chard) or fall (sugarbeet), suggesting that acclimation was affected by environmental factors, such as temperature. Data from both experiments suggest that continued long‐term photosynthetic stimulation may be dependent upon the ability of increased CO2 to stimulate new sink development which would allow full utilization of the additional carbon made available in a high CO2 environment.
The influence of plant age on wound induction of proteinase inhibitors in tomato
Authors: Alarcon J.‐J. , Malone M.
Published: May 2006

Proteinase inhibitors can be induced by wounding in shoots of tomato (Lycopersicon esculentum [L.] Mill. cv. Moneymaker). These inhibitors are toxic to insects, but their ecological importance is not clear. Published work suggests that proteinase inhibitors may be wound‐inducible in tomato only while the plants are young (less than 30 days). In the present investigation the influence of plant age on wound‐inducible proteinase inhibitor was re‐assessed using tomato plants grown in an outdoor polythene tunnel, with natural lighting and without supplementary heat. In contrast to previous findings, proteinase inhibitor was shown to be induced by wounding in plants of all ages. However, the systemic efficacy of wounds was much reduced in mature plants, possibly because such plants have outgrown the range of the wound‐signalling system.
Metabolism of nitrate and ammonium in seedlings of Norway spruce (Picea abies) measured by in vivo 14N and 15N NMR spectroscopy
Authors: Aarnes Halvor , Eriksen Aud B. , Southon Timothy E.
Published: May 2006

In vivo 15N and 14N nuclear magnetic resonance spectroscopy was used to investigate the assimilation of nitrate and ammonium in seedlings of Norway spruce (Picea abies [L.] Karst.). The main objective was to study accumulation of free NH+4 and examine to what extent the nitrogen source affects the composition of the free amino acid pools in roots, stems and needles. NH+4 concentrations in plants growing in the presence of 0.5–50 mM ammonium were quantified using 14N NMR. The NH+4 values in tissues ranged from 6 to 46 μmol (g fresh weight)−1. with highest concentrations in roots and needles. The tissue NH+4 peaked at 5.0 mM NH+4 in the medium. and failed to increase when NH+4 in the medium was increased to 50 mM, indicating metabolic control of the concentration of this cation in tissues. The 14N NMR spectra were used to estimate pH of the NH+4 storage pools. Based on the pH sensitivity of the quintet of 14NH+4 resonance, we suggest that the pH of the ammonium storage compartments in the roots and stems should be 3.7–3.8, and in needles 3.4–3.5, representing extremely low pH values of the tissue. 15N from nitrate or ammonium was first incorporated into the amide group of glutamine and then into α‐amino groups, confirming that the glutamine synthetase/ glutamate synthase cycle is the major route of nitrogen assimilation into amino acids and thus plays a role in lowering the levels of NH+4 in the cytoplasm. NH+4 can also be assimilated in roots in plants growing in darkness. The main 15N‐labelled amino acids were glutamine. arginine and alanine. Almost no 15N signals from needles were observed. Double labelling (δN + w, wN) of arginine is consistent with the operation of the ornithine cycle, and enrichment indicates that this cycle is a major sink of newly assimilated nitrogen. Nitrogen assimilation in roots in the presence of added methionine sulphoximine and glutamate indicated the catabolic action of glutamate dehydrogenase. The 15N NMR spectra of plants grown on 15N‐urea showed a marked increase in the labelling of ammonium and glutamine. indicating high urease activity. Amino acids were also quantified using high pressure liquid chromatography. Arginine was found to be an important transport form of nitrogen in the stem.
Possible involvement of calmodulin in the regulation of ATPase activity in guard cells
Authors: Nejidat Ali
Published: May 2006

Calcium ions play an important role in the regulation of stomatal movement and the mechanism underlying this action is yet to be determined. It is suggested that guard cell plasma membrane ATPase is a target for calcium action and that this effect is mediated by calmodulin. In this study, the effects of calcium and two calmodulin antagonists on ATPase activity in a crude homogenate of Commelina communis L. guard cell protoplasts were examined. The homogenate contained Mg2+‐dependent, K+‐simulated ATPase activity, which was inhibited by CaCl2 while stimulated by the calmodulin antagonists, compound 48/80 and chlorpromazine. The calmodulin antagonists partially reversed the inhibitory effect of calcium ions. The results support the possibility of calmodulin involvement in the regulation of guard cell ATPase activity by calcium ions.
Sequence analysis and hormonal regulation of a dehydrin promoter from barley, Hordeum vulgare
Authors: Robertson Masumi , Cuming Andrew C. , Chandler Peter M.
Published: May 2006

A dehydrin gene (dhn7) was isolated from a barley (Hordeum vulgare L. cv. Himalaya) genomic library. A 2138‐bp fragment of the gene was sequenced and the deduced amino acid sequence showed 99% identity with that of a previously identified cDNA, Dhn 1, which encodes one of a group of closely related proteins induced by dehydration stress. Transient expression assays in barley aleurone protoplasts defined regions of the dhn7 promoter that mediate abscisic acid (ABA) responsive transcription. A fragment (‐935 to +42) of the gene was found to confer concentration‐dependent ABA‐responsiveness measured by expression of a β‐glucuronidase (GUS) reporter gene. Analysis of a 5’deletion series of the promoter defined a region (‐285 to ‐233) that modulated the amplitude of the ABA‐response, whilst ABA‐responsiveness, per se, required a region (‐233 to ‐211) that included a conserved motif containing the G‐box‐like sequence TACGTGG. Gibberellic acid (GA3) antagonised ABA‐induced accumulation of dehydrin mRNA in aleurone cells, but did not antagonise ABA‐induced transcriptional activation as revealed by GUS activity. The antagonistic effect of GA3 on ABA‐induced dehydrin expression might therefore operate post‐transcriptionally.
Analysis of leaf proteins in late flowering mutants of Arabidopsis thaliana
Authors: Tacchini P. , Fink A. , Thiellement H. , Greppin H.
Published: May 2006

Late flowering monogenic mutants of Arabidopsis thaliana (L.) Heynh. at the loci co, gi, fca, fve, fwa, fha, fpa, fy and their corresponding wild type, Landsberg erecta, were analysed by two‐dimensional gel electrophoresis. All plants were grown under continuous light and proteins were extracted from leaves of the same age (20‐day‐old). The polypeptide patterns of the mutants at the loci co, gi, fca, fve, fwa, fha, fpa, and Landsberg erecta were identical. The mutant at the fy locus showed a qualitative difference with Landsberg erecta. Crosses were made between this line and the wild type Landsberg erecta. F2 plants, resulting from autopollination of the hybrid, were analysed and showed no cosegregation between the observed protein and the flowering phenotype, indicating that these two lines differ by more than a single mutation.
The presence of two types of β‐cyanoalanine synthase in germinating seeds and their responses to ethylene
Authors: Hasegawa Ryo , Maruyama Akiko , Nakaya Minoru , Tsuda Sachiko , Esashi Yohji
Published: May 2006

Germinating seeds of many species contain two types of β‐cyanoalanine synthase (CAS, EC 4.4.1.9) that convert HCN to β‐cyanoalanine. One is cytoplasmic CAS (cyt‐CAS), which is precipitated by 50 to 60% (NH4)2SO4 and has a pH optimum of 10.5. Cytoplasmic CAS is present at high levels in dry seed and its activity does not increase during imbibition. The activity of cyt‐CAS is not affected by exogenously applied ethylene (C2H4), except in rice (Oryza sativa cv. Sasanishiki). The second type of CAS found in seed is mitochondrial CAS (mit‐CAS), which is precipitated by 60 to 70% (NH4)2SO4 and has a pH optimum of 9.5. Mitochondrial CAS is present at low levels in dry seed, and its activity increases greatly during imbibition in the seeds of all species tested. Exposure to C2H4 stimulated mit‐CAS activity in seeds of rice, barley (Hordeum vulgare cv. Hadakamugi). cucumber (Cucumis sativus cv. Kagafushinari) and cocklebur (Xanthium pennsylvanicum). The increase in the mit‐CAS activity in cocklebur in response to C2H4 commenced alter a lag period of 2 to 3 h when the duration of soaking was short (16 h), but commenced without a lag period when the seeds were soaked for three months. Application of both chloramphenicol and cycloheximide to the axial and cotyledonary tissues of cocklebur seeds strongly inhibited growth as well as the increase in mit‐CAS activity. It is postulated that the mit‐CAS is synthesized de novo during imbibition and that its activity is regulated by C2H4, CO2 which also promotes seed germination in some species, was ineffective m stimulating mit‐CAS activity in cocklebur seeds.
Fixation induces differential tip morphology and immunolocalization of the cytoskeleton in pollen tubes
Authors: He Yi , Wetzstein Hazel Y.
Published: May 2006

The effects of chemical fixation on tip morphology and immunolocalization of the cytoskeleton in Tradescantia virginiana pollen tubes were evaluated using lour different fixation protocols differing in fixative type/concentration, fixation time, buffer system and additives. Apical regions were much more sensitive to fixation manipulations than more basipetal areas. The presence of the calcium chelator EGTA at 5 mM led to tip rupture and/or swelling in over 80% of germinated grains. However, low or no EGTA levels during fixation resulted in poor immunolocalizations, although lips had more normal morphology. Double fixation in which pollen tubes were first treated for a short period with higher fixative and lower EGTA (0.5 mM) concentrations, followed by lower fixative and higher EGTA (5.0 mM) concentrations, resulted in both improved preservation of pollen lube tip morphology and microfilament/microtubule localizations.
An increase in ethylene sensitivity following pollination is the initial event triggering an increase in ethylene production and enhanced senescence of Phalaenopsis orchid flowers
Authors: Porat R. , Halevy A. H. , Serek M. , Borochov A.
Published: May 2006

Cut Phalaenopsis (Phalaenopsis hybrid, cv. Herbert Hager) flowers usually last about 2 weeks. Following pollination however, there is a rapid acceleration of the wilting process, which is completed within 2 days. The first event detected following pollination was an increase in ethylene sensitivity. This increased sensitivity began about 4 h after pollination and peaked 6 h later. A subsequent increase in ethylene production could only be detected 12 to 14 h after pollination. Treatment of the flowers with silver thiosulfate or 1‐methylcyclopropene, both inhibitors of ethylene action, completely inhibited the pollination‐induced increase in ethylene production and the enhanced senescence of the flowers. This indicates that the pollination‐induced increase in ethylene production is a response to the existing ethylene. Treatment of flowers with calcium and its ionophore A23187, which increased ethylene sensitivity and protein phosphorylation, also promoted ethylene production and senescence of unpollinated flowers, EGTA, a calcium chelator, decreased the sensitivity of pollinated flowers to ethylene and delayed and decreased the pollination‐induced increase in ethylene production. We suggest that the pollination‐induced increase in ethylene sensitivity is the initial pollination‐induced event triggering the enhancement of ethylene production, which leads to enhanced senescence of Phalaenopsis flowers.
Oscillatory growth movements of roots in weightlessness
Authors: Antonsen F. , Johnsson A. , Perbal G. , Driss‐Ecole D.
Published: May 2006

The gravitropic curvature of lentil roots (Lens culinarisL. cv. Verte du Puy), grown in near weightlessness and stimulated on a 1‐g centrifuge for 5 to 60 min was followed by time lapse photography. The experiment was carried out in the frame of the IML 1 Mission of Spacelab. Due to the applied acceleration field, the tip of the roots bent and reoriented with respect to the acceleration vector. However, visual inspection of the data could indicate an oscillatory movement superimposed on the gravitropic reorientation.

We applied two signal processing techniques, fast Fourier transform (FFT) and maximum entropy spectral analysis (MESA), to provide quantitative data about the oscillatory movements of the lentil roots under gravity free conditions. In the case with very few data points in the time series the MESA method is superior to the conventional FFT. In the lentil root movements, the Fourier analysis could not extract and resolve the oscillatory signals present in the time series. The MESA approach revealed oscillations with periods around 35 and 50 min for the present lentil roots.

Circumnutations are, therefore, present in roots also in weightlessness.
A localised decrease of GA1 in shoot tips of Salix pentandra seedings precedes cessation of shoot elongation under short photoperiod
Authors: Olsen J. E. , Junttila O. , Moritz T.
Published: May 2006

By application of a recently developed method allowing analysis of gibberellins (GAs) in mg amounts of tissue, the effect of photoperiod on levels of GAs in shoot tips of individual seedlings of the woody species Salix pentandra was studied. In elongating long day‐grown seedlings, maximum levels of GA1 were found 5–20 mm below the apex, approximately twice the levels in other segments. After exposure of plants to 5 or 15 short days, the levels of GA1 were about 50% lower within this specific region of the stem, as compared with seedlings grown under long days. Short day‐induced cessation of shoot elongation also correlated with overall declines in the levels of GA53, GA19, GA20 and GA8, Within each photoperiodic treatment the levels of these GAs were generally relatively similar throughout the upper 35 mm of stems. No differences in internode lengths or in lengths of pith or epidermal cells were found in plants grown under long days compared with those exposed to 5 short days. In both cases, cells in mitosis were observed in the subapical stem tissues of shoot tips. After 15 short days, stem elongation was completed, and dividing cells were generally not found in the subapical part of the stem. However, short day exposure did not prevent elongation of internodes and cells differentiated before the treatment was started. Thus, the localised decrease in level of GA1 in shoot tips under short days precedes the morphological and anatomical changes connected with the short day‐induced cessation of elongation growth. This supports the hypothesised role for GA1 in photoperiodic control of shoot elongation in S. pentandra.
Effect of sulphur nutrition on redistribution of sulphur in vegetative barley
Authors: Adiputra I Gede K. , Anderson J. W.
Published: May 2006

Barley plants (Hordeum vulgare cv. Clipper) were grown in nutrient solution containing 25 μM sulphate and pulsed for 48 h with [35S]sulphate. The plants were then returned to unlabelled 25 μM sulphate and analysed for sulphur and 35S‐label at various times. The sulphur content of each leaf increased to a maximum as it attained full expansion and then decreased by ca 38–50% over the ensuing 30 days. Expanding leaves had the highest specific radioactivity after the pulse but this declined as the leaves expanded. The first leaf to emerge during the chase also had a high specific radioactivity. The data are consistent with the proposal that the sulphur required for early leaf development is derived from a previously formed leaf. 35S‐Labelled sulphur which was delivered to fully expanded leaves did not equilibrate with endogenous sulphur and was selectively re‐exported. In another experiment, barley plants were grown in 5 μM sulphate, pulsed for 48 h with [35S]sulphate and then grown at 0 (S0), 5 (Ss) or 25 μM (S25) unlabelled sulphate. In S25 plants, the sulphur content of both the fully expanded leaves and the expanding leaves increased indicating that the control of sulphur allocation in these plants differed from that in plants grown continuously in 25 μM sulphate and in plants which were grown at 0 or 5 μM sulphate (sub‐optimal for the growth of leaves L7 and L8). The export of 35S‐label from fully expanded leaves during the chase was not influenced by sulphur nutrition. However, the amount of 35S‐label acquired by leaves which formed during the chase increased with sulphur nutrition. In S25 plants these leaves subsequently underwent net loss of label but the analogous leaves of Sn and S5 plants did not. Collectively, the data indicate that, under sulphur limiting conditions, there is no evidence of a mechanism in barley which enhances the mobilization of sulphur from fully expanded leaves to young expanding leaves.
Regulation of cadaverine and putrescine levels in different organs of chick‐pea seed and seedlings during germination
Authors: Torrigiani Patrizia , Scoccianti Valeria
Published: May 2006

In chick‐pea (Cicer arietinum L.) seed germinated in the presence of 14C‐lysine, the latter is taken up and partly metabolised to cadaverine and TCA‐precipitable molecules. Labelled cadaverine is detectable in seedlings only after 3 days, on a labelled lysine‐containing medium, as confirmed also by the presence of lysine decarboxylase (LDC) activity, measured in the embryo axis and cotyledons of the seed and in the epicotyl, cotyledons, hypocotyl and roots of the seedling on the basis of 14CO2 evolution from the labelled precursor. Putrescine biosynthesis occurred only via arginine decarboxylase (ADC) activities in soaked seeds and via both ADC and ornithine decarboxylase (ODC) activities in seedlings. Both putrescine and cadaverine were present in soaked seed, and accumulated in very large amounts in the different portions of both 3‐ and 8‐day‐old seedlings, while spermidine and spermine titers were maintained at similar levels with respect to the seed. Diamine oxidase activity, measured by evaluating oxygen consumption in the presence of putrescine, was absent in ungerminated seed and appeared in 3‐ and 8‐day‐old seedlings. In order to clarify the metabolic relationships between cadaverine and the more common polyamines, gradients of biosynthesis, accumulation and degradation of putrescine and cadaverine along the seedling axis were compared, indicating that the two diamines behave similarly during seed germination and seedling development. Their conspicuous accumulation (up to 6 mM for putrescine) seems to be regulated mainly via oxidation rather than biosynthesis.
Formation of short‐wavelength chlorophyll(ide) after brief irradiation is correlated with the occurrence of protochlorophyll(ide)636–642 in dark‐grown epi‐ and hypocotyls of bean (Phaseolus vulgaris)
Authors: Mc Ewen Birgitta , Seyyedi Mehdi , Younis Suhaila , Sundqvist Christer
Published: May 2006

Chlorophyll formation capacity along the seedling of bean (Phaseolus vulgaris L. cv. Brede zonder draad) was investigated. After 7 days of irradiation a gradient was formed, where the primary leaf contained ca 300 times more chlorophyll per gram fresh weight than the lower hypocotyl section and ca 20 times more than the epicotyl. Similar chlorophyll gradients but at lower levels were seen when the seedlings were first placed in darkness for 7 days and then irradiated for 1, 2 or 7 days. Ultrastructural investigation of seedlings grown for 7 days in darkness and then irradiated for 24 h revealed a more developed inner membrane system with grana stacks in plastids of cells in the uppermost hypocotyl section compared to plastids of cells in lower hypocoty] sections. The higher up on the seedling the more the ratio increased of protochlorophyll(ide) emitting at 657 nm to short‐wavelength protochlorophyll(ide). After flash irradiation of the different sections, fluorescence emission spectra with maxima at 680 and 690 nm, respectively, were observed, indicating the formation of short‐ and long wavelength chlorophyll(ide) forms. The lower the ratio of protochlorophyll(ide) emitting at 657 nm to the short‐wavelength protochlorophyll(ide), the less long‐wavelength chlorophyll(ide) was formed after irradiation. However, after continuous irradiation long‐wavelength chlorophyll(ide) was formed. In dark grown roots, where only short‐wavelength protochlorophyll forms were present, it was not possible to transform protochlorophyll to chlorophyll by flash irradiation. Possible explanations for this phenomenon are discussed.
Negative regulation of asparagine synthetase in the leaves of maize seedlings by light, benzyladenine and glucose
Authors: Dembinski Edward , Wisniewska Iwona , Zebrowski Jacek , Raczynska‐Bojanowska Konstancja
Published: May 2006

Asparagine synthetase (EC 6.3.5.4) activity was increased 4‐ and 8‐fold when maize (Zea mays L.) seedlings were kept in darkness for 24 h and 7 days, respectively; this increase was abolished by cycloheximide. Irradiation of the dark adapted seedlings with a pulse of red light resulted in a 4‐fold decrease of the enzyme activity within 48 h, which was raised again following a far‐red light pulse. Co‐action of light and benzyladenine, reported for the light‐inducible enzymes, was proved to hold also for the light‐repressible asparagine synthetase. The induction of asparagine synthetase activity in the dark is abolished by glucose, suggesting the possible involvement of the enzyme in the contrae of metabolic fluxes of –carbon and nitrogen through assimilatory pathways.
Mechanisms of potassium absorption by higher plant roots
Authors: Maathuis Frans J. M. , Sanders Dale
Published: May 2006

Potassium, as a plant macronutrient, is accumulated in plant cells from relatively dilute soil solutions and is indispensable for many vital processes. Studies characterising potassium uptake by roots stretch back over many decades. However, it is only with the introduction of modern electrophysiological and molecular techniques that investigations have been possible at a molecular level. Such approaches have confirmed the existence of discrete high and low affinity uptake systems at the root plasma membrane and have greatly enhanced our understanding of the underlying molecular nature of these uptake systems.

High affinity K+ uptake from micromolar external K+ levels is coupled to H+ transport as demonstrated independently by patch clamping of single root protoplasts and by studying the transport system after expression in Xenopus oocytes. The measured coupling ratio between the two ions is 1:1 and is sufficient to account for an accumulation ratio in excess of 106, a value which encompasses experimental observations on K+ accumulation.

Low affinity K+ uptake activates at relatively high external K+ levels in the millimolar range and is ‘passive’ i.e. down the electrochemical gradient for potassium. In two higher plant species single cell inward potassium currents have been identified which are associated with low affinity potassium uptake. Furthermore, specific ion channels which underlie these potassium influxes and form a major constituent of the low affinity potassium uptake pathway have been identified and characterised.
Functional analysis of two bean nitrate reductase promoters in transgenic tobacco
Authors: Jensen Poul E. , Hoff Tine , Stummann Bjarne M. , Henningsen Knud W.
Published: May 2006

Transcription of nitrate reductase (NR) genes is regulated by nitrate as well as a variety of other environmental and developmental factors. Two NR genes have previously been characterized in bean (Phaseolus vulgaris). Both genes are nitrate‐ and light‐inducible and their mRNA expression level displays a circadian rhythm. The two genes, NR1 and NR2, show differences in developmental and tissue‐specific expression. In order to deliniate elements in the NR1 and NR2 promoters that are involved in these expression patterns, eight 5′deleted versions of the NR1 promoter and one fragment of the NR2 promoter were cloned in front of the GUS reporter gene and transformed into tobacco. Approximately 50% of the regenerated transformants expressed detectable levels of GUS activity. For the eight NR1 promoter deletion constructs, differences in promoter strength were observed indicating both positive and negative elements in the promoter. For both the NR1 and the NR2 promoter‐GUS constructs no significant nitrate regulation could be detected in the transgenic plants. A possible explanation for this is that elements needed for proper nitrate regulation of the NR1 and NR2 genes are located outside the analysed 3 500 bp and 1 400 bp promoter regions, respectively. A diurnal rhythm regulation similar to that seen for the endogenous nitrate reductase in bean plants, could be found for the GUS mRNA expression in several of the transformants containing the NR1 and NR2 promoter‐GUS constructs.
Role of putrescine in enhancing shoot elongation in Scirpus mucronatus under submergence
Authors: Lee Tse‐Min , Shieh Yuh‐Jang , Chou Chang‐Hung
Published: May 2006

Changes in polyamine biosynthesis in relation to submergence‐enhanced shoot elongation were determined in shoots of Scirpus mucronatus L. Under submergence, the levels of free putrescine and the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17) increased, but the levels of free spermidine and spermine and the activity of S‐adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50) decreased. The increases in free putrescine and shoot elongation in submerged shoots diminished from the base to the apex. The increase in free putrescine in submerged shoots was coincident with the increase in shoot length. The submergence‐induced increases in free putrescine and shoot elongation were inhibited by both 5 μMa‐difluoromethylarginine and 5 μMa‐difluoromethylornithine, and the inhibitory effects were reversed by 50 μM putrescine. These overall results indicate that ADC‐ and ODC‐mediated putrescine synthesis is essential for the elongation of Scirpus shoots grown under submergence.
Bet v 1 proteins, the major birch pollen allergens and members of a family of conserved pathogenesis‐related proteins, show ribonuclease activity in vitro
Authors: Swoboda Ines , Hoffmann‐Sommergruber Karin , O'Ríordáin Gabriel , Scheiner Otto , Heberle‐Bors Erwin , Vicente Oscar
Published: May 2006

The Bet v. 1 gene family of birch encodes the major pollen allergens as well as pathogenesis‐related (PR) proteins that are induced by microbes in somatic tissues. These PR proteins belong to a group of conserved intracellular defense‐related proteins that have been termed ‘ribonuclease‐like’ PR proteins, on the basis of the partial sequence homology observed between PR1, a Bet v 1‐homologue from parsley, and a recently characterized ginseng ribonuclease. However, this enzymatic activity has not yet been demonstrated, not for any of the members of this family of PR proteins, nor for the related pollen allergens. We have investigated the possible nuclease activity of Bet v 1 using apparently homogeneous preparations of natural Bet v 1 purified from birch pollen, and a recombinant non‐fusion protein purified from E. coli extracts. We report here that Bet v 1 proteins indeed possess an intrinsic ribonucleolytic activity as they can digest different RNA substrates in vitro, but show no activity on single or double‐stranded DNA.
Phenylpropanoid compounds in primary leaf tissues of rye (Secale cereale). Light response of their metabolism and the possible role in UV‐B protection
Authors: Reuber Sebastian , Bornman Janet F. , Weissenböck Gottfried
Published: May 2006

The present study was undertaken in order to investigate the suitability of certain markers for UV plant response. In addition, we attempted to link the internal tissue distribution of specific UV‐absorbing compounds to profiles of radiation gradients within intact primary rye leaves (Secale cereale L. cv. Kustro). Etiolated rye seedlings irradiated with low visible light (LL) and/or UV radiation were used to study enzyme activities of the two key enzymes, phenylalanine ammonia‐lyase (PAL) and chalcone synthase (CHS), together with the tissue‐specific accumulation of soluble phenylpropanoid products. Plants grown under relatively high visible light (HL) with or without supplementary UV‐B radiation were used for further characterization. Apparent quantum yield and fluorescence quenching parameters were monitored to assess potential physiological changes due to UV‐B exposure in HL‐grown seedlings. A quartz fibreoptic microprobe was used to characterize the internal UV‐B gradient of the leaf. The response of the phenylpropanoid metabolism to UV radiation was similar in primary leaves of both etiolated and HL‐treated green plants. The epidermis‐specific flavonoids together with CHS activity turned out to be suitable markers for assessing the effect of UV on the phenolic metabolism. The functional role of phenylpropanoid compounds was strongly implicated in protecting rye from UV‐B radiation.
Inhibition of flowering of cucumber grafted on rooted squash stock
Authors: Satoh Shinobu
Published: May 2006

For the elucidation of the mechanisms of floral transition in indifferent plants, cucumber seedlings (Cucumis sativus cv. Rennsei or cv. Shimoshirazu‐jibai) were grafted onto squash seedlings (Cucurbita maxima Duchesne X C. moschata Duchesne cv. Shintosa‐ichigou) of which the meristems had been removed, and the effect on flower induction on the cucumber scion was examined. In both cultivars, the grafted cucumber bore no flowers, whereas control plants developed flowers above the second to fourth nodes. The inhibition of flower formation on the grafted cucumber scion occurred even when the root of cucumber was left with the squash root on the grafted plant, and flower formation occurred after removal of the squash stock. The inhibitory effect of the squash stock in the presence of the cucumber root was abolished by removal of the squash root. Neither the dry weight of stem plus leaf nor the chlorophyll content of the leaf, as indicators of vegetative growth, were correlated with flower formation on cucumber plants that had been grafted in the presence of cucumber roots on whole, cotyledon‐free or root‐free squash stock. These results indicate that flower formation in cucumber was inhibited by a factor produced by squash roots, an inhibition probably not involved in the modulation of vegetative growth. The root may control floral transition by the production of inhibitory factors in some day‐neutral Cucurbitaceae plants.
Short‐chain saturated fatty acids in the regulation of pollination‐induced ethylene sensitivity of Phalaenopsis flowers
Authors: Halevy Abraham H. , Porat Ron , Spiegelstein Hanna , Borochov Amihud , Botha Louise , Whitehead Charles S.
Published: May 2006

Pollination greatly accelerates petal senescence. The first observed event after pollination is an increase in the flower's sensitivity to ethylene, followed by an increase in ethylene biosynthesis. Our objectives were to study the mode of action of the increase in ethylene sensitivity and the possible involvement of short‐chain saturated fatty acids (SCSFAs) in this process. Application of SCSFAs, ranging in chain length from 7 to 10 carbons onto stigmas of Phalaenopsis (Phalaenopsis hybrid, cv. Herbert Hager) flowers increased their sensitivity to ethylene in the same way as pollination. Following pollination, there was a significant increase in the endogenous content of these fatty acids in the flower's column and perianth, with octanoic acid (C8) being the main SCSFA observed. The increase in SCSFA content was observed as early as 6 h after pollination and began to decline 6 h later. Incorporation of octanoic acid into liposomes or microsomal membranes isolated from Phalaenopsis petals resulted in a decrease in lipid order that was detected by fluorescence polarization of dansyl pyrrolidine (DNSP) but not of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH). At peak ethylene sensitivity, 10 h after pollination, there was a significant decrease in the lipid order of microsomal membranes isolated from Phalaenopsis columns and perianths, again as detected by DNSP but not by DPH. Stigmatic application of octanoic acid mimicked the effect of pollination on membrane lipid order. We suggest that SCSFAs may be the ethylene ‘sensitivity factors’ produced following pollination, and that their mode of action involves a decrease in the order of specific regions in the membrane lipid bilayer, consequently altering ethylene action.
Heat shock proteins do not provide thermoprotection to normal cellular protein synthesis, α‐amylase mRNA and endoplasmic reticulum lamellae in barley aleurone layers
Authors: Lanciloti Daniel F. , Cwik Christopher , Brodl Mark R.
Published: May 2006

Heat shock in barley (Hordeum vulgare L. cv. Himalaya) aleurone layers induces the synthesis of heat shock proteins (hsps) and suppresses the synthesis and secretion of α‐amylase, the principal secretory protein. This is accompanied by the destabilization of α‐amylase mRNA and a concomitant dissociation of ER lamellae. In the absence of heat shock α‐amylase mRNA is extremely stable (Belanger et al. 1986. Proc. Natl. Acad. Sci. USA 83: 1354–1358). In most organisms there is a direct correlation between the synthesis of hsps and thermotolerance. The ability of hsps to provide thermoprotection to secretory protein synthesis, α‐amylase mRNA and ER lamellae was analyzed. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) of pulse‐chased, [35S]‐methionine‐labeled proteins revealed that the half‐life of hsps in barley aleurone cells recovering from heat shock was approximately 12 h. Within approximately 6 h, there was a recovery of α‐amylase mRNA and a reformation of ER lamellae. Heat shock protein synthesis was induced by either heat shock (40°C) or arsenite, the cells were allowed to recover for 8 h, then were re‐exposed to heat shock. Results from SDS‐PAGE showed that, despite the presence of hsps, α‐amylase synthesis was suppressed. Northern blot hybridizations showed that α‐amylase mRNA levels were reduced in heat‐shocked tissues. Transmission electron microscopy demonstrated that ER lamellar structures were dissociated. The synthesis of hsps did not enable barley aleurone cells to sustain the synthesis of any proteins at lethal temperature. In contrast, similar conditions established thermotolerance and provided thermoprotection to protein synthesis in germinating barley embryos. Our findings suggest that the aleurone layer does not become thermotolerant following the induction of hsp synthesis.
Early effects of triadimefon on water relations, sterol composition and plasma membrane ATPase in white spruce (Picea glauca) seedlings
Authors: Sailerova Eva , Zwiazek Janusz J.
Published: May 2006

Seedlings of white spruce (Picea glauca [Moench] Voss.) were treated with triadimefon solution applied to the soil, and their early responses studied from 12 h to 7 days after treatment. Transpiration rates declined and respiration rates increased immediately after the commencement of triadimefon treatment. Photosynthetic rates declined less than transpiration rates, resulting in an increase in water use efficiency, whereas root and shoot water potentials remained unchanged during the first 5 days of triadimefon treatment. Triadimefon decreased root hydraulic conductivity and inhibited the activity of the plasma membrane ATPase. In addition, triadimefon‐treated roots drastically increased the ratios between free sterols and sterol esters and decreased the ratios between sterol esters and acylated sterol glycosides.
A role for cyanide, derived from ethylene biosynthesis, in the development of stress symptoms
Authors: Grossmann Klaus
Published: May 2006

Cyanide is formed as a co‐product of ethylene during the oxidation of 1‐aminocyclo‐propane‐1‐carboxylic acid (ACC) catalyzed by ACC oxidase. A toxic or regulatory function for cyanide in plant metabolism remains controversial. However, recent studies on the mode of action of auxin herbicides in sensitive plants suggest that the accumulation of tissue cyanide, derived ultimately from herbicide‐stimulated ACC synthesis, is implicated in the induction of herbicide phytotoxicity. Furthermore, increases in cyanide levels have been observed during the formation of necrotic lesions in tobacco mosaic virus‐infected tobacco leaves. It thus appears worthwhile to elucidate in more detail a possible role for cyanide in the induction of cell death under stress conditions which coincide with a strong stimulation of ethylene biosynthesis.
Blue light‐induced acidification of the medium of a nitrate‐starved Chlorella mutant
Authors: Kamiya Akio
Published: May 2006

Irradiation with blue light resulted in acidification of the suspension medium of a colorless mutant of Chlorella kessleri (Fott et Novákóva, no. 9.80). Qualitatively red light gave the same result, although to a much lower extent than blue, whereas far‐red had little effect. A pulse of blue light led to a transient acidification of the medium. The light‐induced acidification was particularly pronounced if nitrate‐starved cells were used. Acidification was inhibited by vanadate (V2O5, Na3VO4), so that the phenomenon appears due to proton extrusion from the mutant. The light‐induced acidification was also observed in a yellow mutant and the wild‐type of Chlorella kessleri. The role of light in the acidification of the medium of algal cells is discussed in relation to the earlier findings that blue light enhances the uptake of nitrate in the colorless mutant; and that in Chlorella cells the transport process of nitrate is connected with a proton symport.
Suppression of flash‐induced PSII‐dependent electrogenesis caused by proton pumping in chloroplasts
Authors: van Voorthuysen Tijmen , Bulychev Alexander A. , Dassen Hans H. A. , Snel Jan F. H. , Vredenberg Wim J.
Published: May 2006

Pre‐illumination of the thylakoid membrane of Peperomia metallica chloroplasts leads to a reversible suppression of the flash‐induced electrical potential as measured either with the electrochromic bandshift (P515), microelectrode impalement or patch‐clamp technique. The energization‐dependent potential suppression was not observed in the presence of 1 μM nigericin suggesting the involvement of proton and/or cation gradients. Energization in the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) and N,N,N′,N′‐tetramethylphenylenediamine (TMPD), i.e. cyclic electron flow around photosystem (PS) I, results in the accumulation of TMPD+ in the thylakoid lumen. The reversible suppression of the flash‐induced membrane potential was not observed in these conditions indicating that it is not a general cation‐induced increase of membrane capacitance. Cyclic electron flow around PSI in the presence of DCMU and phenazine methosulfate (PMS) results in the accumulation of PMS+ and H+ in the thylakoid lumen. The absence of reversible suppression of the flash‐induced membrane potential for this condition shows that accumulation of protons does not lead to (1) a reversible increase of membrane capacitance and (2) a reversible suppression of PSI‐dependent electrogenesis. Reversible inactivation of PSII by a low pH in the thylakoid lumen is therefore proposed to be the cause for the temporary suppression of the flash‐induced electrical potential. The flash‐induced PSII‐dependent membrane potential, as measured after major oxidation of P700 in far‐red background light, was indeed found to be suppressed at low assay pH (pH 5) in isolated spinach (Spinacia oleracea) chloroplasts.