bluuebunny/crossref_metadata_2025 huggingface dataset:
Purification and partial characterization of an aminopeptidase from mung bean cotyledons
Authors: Yamaoka Yoshiko , Takeuchi Michio , Morohashi Yukio
Published: May 2006

An aminopeptidase (EC 3.4.11.‐) was purified to homogeneity, as judged by SDS‐PAGE. from mung bean (Vigna radiata) cotyledons. The molecular mass of this peptidase was estimated as 75 kDa by gel filtration. When an oligopeptide consisting of 5 amino acid residues was used as substrate, amino acids were released in the order of the N‐terminal sequence of the oligopeptide chain. This enzyme apparently requires free sulfhydryl for its activity, as judged by the effects of various proteinase inhibitors. Among aminoacyl‐p‐nitroanilides examined for the availability as substrates of the enzyme, p‐nitroanilides with hydrophobic amino acids were preferred substrates. According to western immunoblot profiles, the enzyme level in cotyledons was high at the early stage of imbibition and declined rapidly after germination.
Native β‐glucuronidase activity in sugarbeet (Beta vulgaris)
Authors: Wozniak Chris A. , Owens Lowell D.
Published: May 2006

β‐Glucuronidase (EC 3.2.1.31) activity, initially thought absent from plants, has been found in a number of plant families. During an analysis of Agrobacterium‐mediated transformation of sugarbeet (Beta vulgaris L.), significant glucuronidase activity was observed in control (non‐transformed) tissues when the fluorogenic substrates 4‐methylumbelliferyl‐β‐d‐glucuronic acid, resorufin glucuronic acid and 3‐carboxyum‐belliferyl‐β‐d‐glucuronic acid were used to quantify β‐glucuronidase activity under standard protocol conditions. Similarly, the colorigenic substrate p‐nitrophenyl‐β‐d‐glucuronide was hydrolyzed by this sugarbeet‐derived glucuronidase. Biochemical and immunological data are presented to indicate significant differences between sugarbeet‐derived glucuronidase and that from Escherichia coli (EC 3.2.1.31) encoded by gusA. These differences provide means of distinguishing between the two activities in extracts that contain a mixture of both. Use of X‐glue, the substrate utilized in histochemical localizations of glucuronidase activity, gave no reaction product (i.e., indigo precipitate) at pH 7.0. However, at pH 3.0, 4.0 and 5.0 formation of the indigo precipitate was evident within 1 h at 37°C in sugarbeet callus and by 4 h in leaves and petioles. The specific activity of sugarbeet glucuronidase was observed to be strongly pH dependent, with an optimum near pH 4.0. The use of various β‐glucuronidase assay techniques as applied to transformation of sugarbeet is discussed.
An extracellular α‐L‐arabinofuranosidase secreted from cell suspension cultures of carrot
Authors: Konno Haruyoshi , Tanaka Reiji , Katoh Kenji
Published: May 2006

Carrot (Daucus carota L. cv. Kintoki) cell cultures secrete an α‐L‐arabinofuranosidase (α‐L‐AFase, EC 3.2.1.55) into their culture medium during growth. The extracellular α‐L‐AFase (α‐L‐AFase‐II) was purified to electrophoretic homogeneity from the concentrated medium using ammonium sulfate precipitation, chromatography on DEAE‐Sepharose CL‐6B, CM‐Sepharose CL‐6B, Sephacryl S‐200HR and Concanavalin A‐Sepharose, and preparative PAGE. The molecular mass of the purified enzyme was estimated to be 84 kDa by Sephacryl S‐200HR gel‐permeation, and 80 kDa by SDS‐PAGE under denaturing conditions. The enzyme contained carbohydrate and protein in a ratio of 1:5 (w/w), and was analyzed for amino acid composition and the sequence of the first 21 amino acids of the N‐terminus. The isoelectric point was pH 5.6, the pH optimum 3.8, and the temperature optimum 55°C. The activity was inhibited by Zn2+, Ag2+, Cu2+, Hg2+ and p‐chloromercuribenzoate. The Km and Vmax values for p‐nitrophenyl‐α‐L‐arabinofuranoside were 0.22 mM and 0.11 mmol (mg protein)−1 h−1, respectively. The enzyme acted on beet arabinan in an exo‐fashion, and was capable of hydrolysing arabinose‐rich polymers purified from pectic polysaccha‐rides of carrot cell cultures. However, even after an exhaustive reaction, the enzyme had little or no effect on cell walls from carrot cell cultures.
Effects of osmotic shock and calcium on growth and solute composition of Phaseolus vulgaris plants
Authors: Ortiz Antonio , Martínez Vicente , Cerdá Antonio
Published: May 2006

Identification of the primary response to salinity is of great importance in order to develop salt tolerant species. In this work the effect of a NaCl osmotic shock on leaf elongation of Phaseolus vulgaris L. cv. Contender has been studied. After establishing an osmotic shock by adding NaCl to the root medium, three consecutive events could be distinguished. First, there was a sudden interruption of leaf growth, followed by a period of retardation of growth, and then by a restoration of growth to reach the steady‐state growth rate. High calcium (5 mM) in the growth medium diminished the initial loss of water in the roots and kept the water content higher upon restoration of leaf growth, as compared to low calcium levels (0.5 mM). During the low calcium treatment, leaf malate started to increase already 3 h after the start of the osmotic treatment, showing a maximum concentration at around 9 h, then decreasing and approaching the value of control plants. At high calcium, malate concentration remained unchanged with time. Plants grown in the presence of low calcium showed an increase in the concentration of total amino acids upon NaCl shock. It is estimated that organic metabolites, if confined to the cell cytoplasm, contribute significantly to the osmotic adjustment, together with inorganic ions. Our results support the hypothesis that water shortage in the roots is responsible for the initial inhibition of leaf elongation. The beneficial effect of calcium on restoration of growth after the NaCl shock is a consequence of short‐term, energetically expensive osmotic adjustment, in which mainly organic metabolites are involved. Under steady state conditions, high calcium treatment results in a faster growth rate than low calcium. In a process of osmotic adjustment, in which inorganic ions are principally involved, this is the result of a decrease in leaf Na+ concentration in expanding leaves, together with an increase in K+ and Ca2+.
Modification of the gravitropic response of seedling roots of raneseed (Brassica napus) transformed by Agrobacterium rhizogenes A4
Authors: Legué V. , Vilaine F. , Tepfer M. , Perbal G.
Published: May 2006

We have examined the growth and gravitropic response of seedling roots of rapeseed (Brassica napus. CrGC5–1) transformed by Agrobacterium rhizogenes A4, in order to evaluate if this could constitute a new model system for the study of gravitropism. The transformed clone chosen for study had integrated full‐length TL‐ and TR‐DNA from pRi (the root inducing plasmid), and thus included all of the agrobacterial genes potentially involved in the modified phenotype of transformed plants. In the vertical position, the growth rate of transformed roots was higher than controls. During 24 h of continuous stimulation, the optimal angle for gravitropic bending in normal roots was 135° (with respect to the gravity axis), with decreasing response at 90° and 45°. For transformed roots, slight curvature developed at 45° and at 90°, and stronger curvature was observed at 135°, though transformed roots tips never reached the vertical position. The minimum stimulation time necessary to elicit a response (presentation time) was also determined: it was signficantly shorter in normal roots (80 s) than in transformed ones (120 s). The results show that pRi transformed roots are less sensitive to gravity than normal roots.
Accumulation of a 22‐kDa protein and its mRNA in the leaves of Raphanus sativus in response to salt stress or water deficit
Authors: Lopez Félicie , Vansuyt Gérard , Fourcroy Pierre , Casse‐Delbart Francine
Published: May 2006

The response of 10‐day‐old seedlings of Raphanus sativus L. cv. Fakir to salt stress (100 mM to 200 mM NaCl) was investigated. Three weeks after initiation of salt treatment, the fresh weight of the shoots of salt‐treated plants was half that of untreated plants. The salt stress resulted in the accumulation of Na+, preferably in the old leaves. The K+ level was reduced by as much as 50% in the old leaves of NaCl‐treated plants, whereas this reduction was only 20–25% in the young leaves. Free proline accumulated in all aerial organs, and the highest levels were found in the young leaves. Patterns of total proteins extracted from the leaves of control or salt‐treated plants were compared. The most obvious change concerned a 22‐kDa, pl 7.5 polypeptide, which accumulated after exposure of the plants to NaCl. The appearance of this polypeptide was also mediated by a rapid drought stress, and sequencing indicated that it is related to the Künitz protease inhibitor family. A cDNA clone corresponding to the radish 22‐kDa polypeptide was obtained and sequenced. Northern blot analysis showed that salt stress induces a large accumulation of this mRNA in the leaves of radish.
Endoribonuclease of Vicia faba ssp. minor radicles, and enhancement of its activity by chilling stress or abscisic acid
Authors: Kazmierczak Andrzej , Knypl J. Stan
Published: May 2006

Endoribonuclease in roots of 3‐day‐old seedlings of Vicia faba L. ssp, minor is a citrate activated glycoprotein of 35 kDa, with pH and temperature optima of 6.0 and 50°C. The same holds for endoribonuclease from seedlings treated with abscisic acid or exposed to a chilling stress of ‐3°C for 24 h, except that the temperature optimum was decreased to 40°C. The enzyme(s) preferentially hydrolysed poly (A) and poly (U). RNase activity in the radicles was enhanced by chilling stress or abscisic acid. ABA did not potentiate the effect brought about by chilling but slowed down the decrease in RNase activity in chill‐stressed seedlings upon transfer to 25°C. Both factors modified the pattern of the isoelectric‐points of the molecular forms of RNase.
Allelopathic potential of the phenolics from the roots of Pluchea lanceolata
Authors: Inderjit  , Dakshini K.M.M.
Published: May 2006

Aqueous leachates of roots of the perennial weed Pluchea lanceolata (DC.) C. B. Clarke, its root‐incorporated soil and rhizosphere soil, interfered with the seedling growth of certain plant species. The soils from the rhizosphere zone of this plant had significantly higher total phenolics and HPLC analysis revealed that phenolic fractions represented by retention times of 1.6, 1.9, 2.5 (simple phenol, chlorogenic acid and phloroglucinol respectively), 3.7 and 4.3 min were contributed by roots of the weed to the soil. The phenolic fraction represented by the retention time 3.3 (formononetin 7‐O‐glucoside) was detected in the weed's rhizosphere soils and not in the rootincorporated soils. UV spectral studies established the presence of phloroglucinol, simple phenol, chlorogenic acid, formononetin 7‐O‐glucoside, and methylated coumarins in the root leachate, which affect the seedling growth of mustard (Brassica juncea). Present research established the allelopathic potential of P. lanceolata roots, and the possible involvement of allelopathy in its interference success.
Photooxidative stress in plants
Authors: Foyer Christine H. , Lelandais Maud , Kunert Karl J.
Published: May 2006

The light‐dependent generation of active oxygen species is termed photooxidative stress. This can occur in two ways: (1) the donation of energy or electrons directly to oxygen as a result of photosynthetic activity; (2) exposure of tissues to ultraviolet irradiation. The light‐dependent destruction of catalase compounds the problem. Although generally detrimental to metabolism, superoxide and hydrogen peroxide may serve useful functions if rigorously controlled and compartmentalised. During photosynthesis the formation of active oxygen species is minimised by a number of complex and refined regulatory mechanisms. When produced, active oxygen species are eliminated rapidly by efficient antioxidative systems. The chloroplast is able to use the production and destruction of hydrogen peroxide to regulate the thermal dissipation of excess excitation energy. This is an intrinsic feature of the regulation of photosynthetic electron transport. Photoinhibition and photooxidation only usually occur when plants are exposed to stress. Active oxygen species are part of the alarm‐signalling processes in plants. These serve to modify metabolism and gene expression so that the plant can respond to adverse environmental conditions, invading organisms and ultraviolet irradiation. The capacity of the antioxidative defense system is often increased at such times but if the response is not sufficient, radical production will exceed scavenging and ultimately lead to the disruption of metabolism. Oxidative damage arises in high light principally when the latter is in synergy with additional stress factors such as chilling temperatures or pollution. Environmental stress can modify the photooxidative processes in various ways ranging from direct involvement in light‐induced free radical formation to the inhibition of metabolism that renders previously optimal light levels excessive. It is in just such situations that the capacity for the production of active oxygen species can exceed that for scavenging by the antioxidative defense systems. The advent of plant transformation, however, may have placed within our grasp the possibility of engineering greater stress tolerance in plants by enhancement of the antioxidative defence system.
Regulation of a petal‐specific ethylene‐induced 70‐kDa protein from Dianthus caryophyllus
Authors: Jiang Wei Bo , Mayak Shimon , Weiss David , Halevy Abraham H.
Published: May 2006

Ethylene enhances senescence of carnation (Dianthus caryophyllus L.) flowers. Sephacryl S‐200 gel filtration followed by SDS‐PAGE of extracts of petals exposed to ethyiene revealed the increase or appearance of proteins with molecular masses of 70, 60, 35 and 33 kDa, and a concomitant decrease in proteins with molecular masses of 62. 45. 34. 30 and 26 kDa.

The 70‐kDa protein, which was not detected in untreated flowers, was isolated and polyclonal antibodies were prepared against it. Its N‐terminal sequence (20 amino acids) was identical to that of a portion of the deduced protein encoded by cDNA clone pSR 12. recently isolated by others from carnation petals. Western blot analyses of petal extracts after various exposure times to ethylene alone or in the presence of translation or transcription inhibitors suggested that accumulation of the 70‐kDa protein is due primarily to ethylene‐induced synthesis. The apparent induction by ethyiene was further supported by data indicating that the protein is not formed in flowers pre‐treated with silver thiosulfale. an inhibitor of ethylene action, prior to exposure to ethylene. Ethylene induction of the protein was found only in petal tissue, and the protein was not detected in other carnation plant organs. Immunological studies revealed that the protein is specifically expressed in carnation petals and not in petals of several other flowers. Southern and northern analyses using an SRI2 cDNA probe indicated that the genomic DNA of petunia, carnation, and gerbera contain fragments homologous to SRI2. Gene expression products were however, only detected in petals of ethylenetreated carnation flowers.
Enzymes of ammonium metabolism in ectendomycorrhizal and ectomycorrhizal symbionts of pine
Authors: Rudawska Maria , Kieliszewska‐Rokicka Barbara , Debaud Jean‐Claude , Lewandowski Andrzej , Gay Gilles
Published: May 2006

Ammonium assimilation enzymes from several strains of ectendo‐ and ectomycorrhizal fungi were assayed after three weeks culture on a buffered synthetic medium containing ammonium as sole nitrogen source. Activity of NADP‐dependent glutamate dehydrogenase (GDH, EC 1.4.1.4) of ectomycorrhizal strains was very low despite excellent mycelial growth. Only ectendomycorrhizal fungus MrgX isolated from roots of Pinus sylvestris showed high GDH activity. Similar results were obtained when the enzyme extracts were subjected to starch gel electrophoresis. Growth of the fungi, except ectendomycorrhizal MrgX, was arrested when inhibitors of glutamine synthetase (GS, EC 6.3.1.2) or glutamate synthase (GOGAT. EC 1.4.7.1) (methionine sulphoximine or albizine, respectively) were included in the culture medium. Glutamine synthetase activity was found in all fungi tested. The results suggest that the GS pathway for ammonium assimilation is potentially operative in ectomycorrhizal fungi and imply only a minor role for GDH in ammonium assimilation by the studied ectomycorrhizal symbionts of pine. Some physiological and ecological implications of these results are discussed.
Experimental control of floral reversion in isolated shoot apices of the long‐day plant Silene coeli‐rosa
Authors: Donnison Iain Simon , Francis Dennis
Published: May 2006

The fate of shoot meristems of the long day (LD) plant Silene coeli‐rosa in culture was examined (complete, reverted or arrested flowers) to establish whether these different patterns were related to a particular stage of morphogenesis and the extent to which the fate of the pattern was regulated by either added plant growth regulators (PGRs) or changing the carbohydrate source in the medium. In particular, the frequency of reversion was measured to test the stability of the determined state for each whorl. The plants were given various inductive treatments (4–7 LD, 7 LD + 1 to 3 SD) and the apices were explained onto Murashige‐Skoog medium supplemented with 3% sucrose (controls) ± IAA, ± kinetin, ± GA3 or onto the basal medium containing 1 or 3% sucrose, glucose or fructose or 7% sucrose. The apices were examined 12 weeks later. When the data were pooled from all inductive treatments, IAA resulted in more reversions, GA3 caused more arrested flowers while kinetin hardly affected the pattern of meristem fate compared with the controls. However, each PGR treatment did not perturb the pattern of organ formation for those apices that formed either arrested or complete flowers. The time for determination (days) of the earlier formed whorls (determination times for the controls in brackets): sepals (2), stamens 1–5 (3) and petals (3), was shortened by about a day in all PGR treatments whereas the corresponding times for the later formed whorls: stamens 6–10 (4) and carpels (4), were either lengthened to 5 days or unaffected. The response of the apices to the various sugars was simply a reflection of concentration. Hence, more complete flowers formed at 7 or 3% and more flowers were arrested at 1 % regardless of the sugar moiety. However, the frequency of reversion was similar on each of the media. Pooling all data from all treatments enabled a statistical analysis of the pattern of reversion and the pattern of arrest. Reversion was more common from apices which exhibited the later‐formed whorls (stamens 6–10 and carpels) than from the earlier whorls. Moreover, the stronger the inductive treatment the less frequent was reversion. The most common stage of arrest was at the stamen 6–10 whorl and this was particularly so for the GA3 treatment. The data indicated that reversion could occur from any whorl, which suggests that determination of each whorl is independent of the next. This conclusion is underlined by the more frequent occurrence of reversion from the carpel whorl. However, the longer the inductive treatment the less likelihood of reversion; this suggests that in Silene, the floral stimulus is required continuously to stabilise the determined state of each whorl and to ensure smooth completion of floral morphogenesis.
High CO2 levels reduce ethylene production in kiwifruit
Authors: Rothan Christophe , Nicolas Jacques
Published: May 2006

The effects of CO2 on ethylene production rates and on the conversion of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) to ethylene have been investigated in kiwifruit [Actinidia deliciosa (A. Chev.) Liang and Ferguson, cv. Hayward] pericarp tissues. Carbon dioxide concentrations up to 10% notably reduced ethylene production rates but did not affect ACC levels. Carbon dioxide levels from 10 to 28.5% slightly reduced wound‐induced ACC accumulation but resulted in only a slight additional reduction in ethylene production. However, in the presence of saturating amounts of ACC, ethylene formation was stimulated by high CO2: levels. The apparent Vmax and Km for ACC of the in vivo conversion of ACC to ethylene were both increased by high CO2 although to a different extent. When CO2 concentrations were increased from 0.2 to 28.5%, the Vmax varied from 50 to 90 nl g–1 h–1 while the Km for ACC increased from 15 to 72 μM. Thus, the Vmax over Km ratio, which represents the efficiency of ACC conversion to ethylene when ACC concentrations are very low, was reduced by 40% in the presence of 5% CO2 and by 60% in the presence of 28% CO2. The concentrations of ACC, at which ACC, oxidase was inhibited by high CO2 are comparable to the concentrations found in the fruit. It is therefore suggested that the reduction of ethylene production rates in fruits by high CO2 might be exerted at least partially at the level of the conversion of ACC to ethylene.
Adaptation versus shock response to polyethylene glycol‐induced low water potential in cultured potato cells
Authors: Leone Antonella , Costa Antonello , Tucci Marina , Grillo Stefania
Published: May 2006

We compared long‐term adaptation versus short‐term or shock response of potato (Solanum tuberosum) cells to polyethylene glycol (PEG)‐induced low water potential. Potato cells, which were allowed to adapt gradually to a decreasing water potential, were able to grow actively in a medium containing 20% PEG. In contrast, no appreciable gain in dry weight was observed in potato cells shocked by abrupt transfer to the same medium. PEG‐adapted cells were also salt‐tolerant, as they were able to proliferate in a medium supplemented with 200 mM NaCl. No visible ultrastructural changes of mitochondria or proplastids were observed in adapted cells at values of low water potential (about −2.0 MPa), which caused membrane disruption and appearance of lipid droplets in unadapted cells. ABA cellular content increased 5‐fold in PEG‐shocked cells but no significant increase was found in PEG‐adapted cells. The intracellular content of free proline increased 12.5 times over the basal level in PEG‐adapted cells and 6.5 times in PEG‐shocked cells. As shown by in vivo protein labeling, shock conditions strongly inhibited protein synthesis, which was completely recovered in PEG‐adapted cells. Osmotin, a protein associated with salt adaptation in tobacco, was constitutively expressed at a high level in PEG‐adapted cells and accumulated in PEG‐shocked cells only three days after the transfer in a medium supplemented with 20% PEG. Proline and osmotin accumulation were coincident with the increase in cellular ABA content in PEG‐shocked cells, but not in PEG‐adapted cells. These data suggest that this hormone is mainly involved in shock response rather than long‐term adaptation.
Changes in polyamine synthesis during anther development and pollen germination in tobacco (Nicotiana tabacum)
Authors: Chibi Fatiha , Matilla Angel Jesús , Angosto Trinidad , Garrido Dolores , Bornman C. H.
Published: May 2006

Changes in polyamine levels and in the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and omithine decarboxylase (ODC. EC 4.1.1.17) were studied during anther development in Nicotiana tabacum as well as during the first 120 min of dry pollen germination in vitro. Arginine decarboxylase activity was more abundant than that of ODC in the whole anther and isolated pollen: activities of both enzymes reached a maximum at the binucleate stage of pollen development and increased with elongation of the pollen tube. During anther development, no alteration in free putrescine (Put) or in free spermidine (Spd) was found from the microspore to the binucleate stage. However, during maturation, free Put decreased, probably because of its transformation into Spd. Bound polyammes were more abundant than the free polyamines during anther development. The presence of a‐amanitin. on inhibitor of transcription, did not affect ADC activity during the germination process, whereas cycloheximide. on inhibitor of protein synthesis, had a strong inhibitory effect. Compared to their levels in dry pollen, free Put. Spd and spermine (Spm), and bound Put were present at increased levels during pollen tube elongation. However, in the presence of cycloheximide. which had little effect on elongation of the pollen tube, free polyamine synthesis was inhibited. In light of the results obtained with cycloheximide and difluoromethvlargi‐nine. An inhibitor of arginine decarboxylase. which inhibited elongation but not emergence of the pollen tube, we propose that the endogenous polyamine liter in dry pollen was sufficient to contribute to the emergence of the pollen tube and. once emergence was established, that pre‐existent ADC and ODC were responsible for the synthesis of those polyaraines related to tube elongation, since the polyamine levels of the dry pollen appeared to be insufficient.
Effect of partial deglycosylation on catalytic characteristics and stability of an avocado peroxidase
Authors: Sánchez‐Romero Carolina , García‐Gómez María L. , Pliego‐Alfaro Fernando , Heredia Antonio
Published: May 2006

An isoperoxidase (EC 1.11.1.7) purified from avocado (Persea americana Mill. cv. Topa Topa) leaves, lost 35% of its glycosidic moiety after incubation with glycopeptidase F (EC 3.2.2.18). The partial removal of carbohydrate chains caused a decrease in the Km for reductor substrates tguaiacol, syringaldazine and indole‐3‐acetic acid) and favoured the enzyme activation by Ca2+. A decrease in stability against temperature was also observed. Our results are consistent with the hypothesis that the carbohydrate moiety located on the surface of the peroxidase molecule acts as a molecular shield.
Growth rate, plant development and water relations of the ABA‐deficient tomato mutant sitiens
Authors: Nagel Oscar W. , Konings Henk , Lambers Hans
Published: May 2006

Given the close relationship between a plant's growth rate and its pattern of biomass allocation and the effects of abscisic acid (ABA) on biomass allocation, we studied the influence of ABA on biomass allocation and growth rate of wildtype tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants and their strongly ABA‐deficient mutant sitiens. The relative growth rate of sitiens was 22% lower than that of the wildtype, as the result of a decreased specific leaf area. The net assimilation rate and the leaf weight ratio were not affected. The mutant showed a much higher transpiration rate and lower hydraulic conductance of the roots. These two factors resulted in sitiens having a significantly lower leaf water potential and turgor. resulting in reduced leaf expansion and, consequently, a lower specific leaf area relative to the wildtype. Addition of ABA to the sitiens roots resulted in phenotypic reversion to the wildtype. We conclude that the influence of ABA‐deficiency on biomass allocation and relative growth rate is the result of altered water relations in the plants, rather than of a direct effect on sink strength of different plant organs.
Protochlorophyllide forms in non‐greening epicotyls of dark‐grown pea (Pisum sativum)
Authors: Böddi Béla , McEwen Birgitta , Ryberg Margareta , Sundqvist Christer
Published: May 2006

Low‐temperature fluorescence emission spectra of 6.5‐day‐old dark‐grown epicotyls of pea (Pisum sativum) revealed the presence of protochlorophyll(ide). The upper part of the epicotyl contained 30% of the protochlorophyll(ide) content per fresh weight found in pea leaves, whereas the lower part contained 3%. Three discrete spectral forms of protochlorophyll(ide) were clearly distinguished after Gaussian deconvolution of fluorescence excitation and emission spectra. Adding the satellite bands of the Qy(0‐0)transitions (the emission vibrational (Emv) bands with correlated amplitudes, gave the following delineation: Ex439–Em629–Emv684, Ex447–Em636–Emv700 and Ex456–Em650–Emv728. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE) followed by immunodetection of whole tissue extracts of the epicotyl indicated the presence of NADPH‐protochlorophyllide oxidoreductase (EC 1.3.1.33). Electron micrographs showed prolamellar bodies in at most 11 % of the plastid profiles of the epicotyl cells. These prolamellar bodies were smaller, and many of them showed less regular structure than those of the leaves. Taken together, the results indicate that the protochlorophyll(ide) in epicotyls is arranged in a different way than in leaves.
Photoinhibition of photosynthesis in vivo: The role of protein turnover in photosystem II
Authors: Critchley Christa , Russell A. Wendy
Published: May 2006

Divergent theories on the mechanism behind, and the nature of, photoinhibition are discussed, especially in relation to observations made in higher plant leaves. Comparisons are made with ‘lower’ plant groups and results of in vivo and in vitro experiments are considered. Irradiance‐induced mechanisms involved in the regulation of PSII function and structure are discussed in connection with turnover of the DI protein. A model is presented in which a structural change in DI protein facilitates the formation of a population of dissipative PSII centres that do not participate in linear electron transport to PSI. We suggest a sophisticated regulatory mechanism whereby this variable PSII function is controlled with respect to both incident light and biochemical demand, a control which relies on feedback from both light and dark reactions.
Growth cessation and bud dormancy in relation to ABA level in seedlings and coppice shoots of Betula pubescens as affected by a short photoperiod, water stress and chilling
Authors: Rinne Päivi , Saarelainen Annikki , Junttila Olavi
Published: May 2006

Seedlings and coppice shoots of Betula pubescens Ehrh. were grown under controlled conditions designed to simulate the annual growth cycle, and a water stress was introduced during the short day (SD). Alleviation of hud dormancy after increasing periods at chilling temperatures was tested under long day (LD) conditions. Abscisic acid (ABA) was analysed in leaf and bud samples by gas chromatography‐mass spectrometry using [2H4]ABA as the internal standard. Elongation growth of coppice shoots was faster than that of seedlings under both LD and SD conditions, while the final growth cessation occurred in a similar manner and was not affected by water stress, which significantly reduced growth rate in both plant types. Bud dormancy gradually decreased with increasing length of chilling, starting from the basal parts of the plant axis. Water stress did not retard hudhurst. but rather improved it in the chilled coppice shoots and in the non‐chilled and partially chilled seedlings. Water content of buds was higher in coppice shoots than in seedlings, but after exposure to SD. it gradually decreased to 45% in both plant types and was not affected by water stress or chilling. The ABA level in both leaves and buds increased during SD treatment and was” enhanced by water stress. No clear differences in bud ABA level were found between the seedlings and coppice shoots under SD conditions, although coppice shoots had less ABA during the preceding LD conditions. There was, in general, no clear effect of chilling on bud ABA level. Budbursl in chilled, single‐node cuttings was inhibited by external ABA treatment, which raised the internal ABA levels 10 to 150 times above normal. The observed correlation between ABA level and water content in buds during induction of dormancy under SD and water stress conditions indicates a possible role for ABA in the regulation of dormancy.
Translocation of N to and from barley roots: its dependence on local nitrate supply in split‐root culture
Authors: Agrell David , Oscarson Petter , Larsson Carl‐Magnus
Published: May 2006

The relationship between availability of external nitrate and N translocation between root and shoot was studied in N‐limited barley (Hordeum vulgare L. cv. Golf). Nitrate‐N was added at a relative rate (i.e. N added per unit time and unit N in plant biomass) of (1.09 da‐1, and distributed between the subroots at ratios of 50:50 or 80:20. The plants were grown for 13 days under these conditions of nitrate nutrition, and for another three days with the nitrate distribution reversed from 80:20 to 20:80. The nitrale‐N doses thus experienced by individual subroots ranged from 2 to 11 mg N g‐1 root dry weight day‐1 . 15N‐Nitrate labellings were performed after 2 to 3 and 12 to 13 days of nitrate nutrition. and 2 to 3 days after reversal of nitrate additions. For all treatments, between 60 and 82% of the absorbed label initially left the root, and between 25 and 55% of the label recovered in roots had been supplied (cycled) via the shoot. Labelling of xylem N at the end of the 24‐h labelling period ranged from to 36 to 46% indicating that a substantial fraction of the N in the xylem had been absorbed by the plant prior to labelling. It is concluded that cycling of N to roots, and cycling of N in the plant as a whole, is substantial also during N‐limited growth. N allocation to roots increased with external nitrate dose. An increased utilization of non‐translocated N as well as an increased translocation of N from the shoot contributed to this effect. Thus, the results indicate that increased external availability of N also increased the sink strength of the root for cycling N.
Field photosynthetic activity of lichens in the Windmill Islands oasis, Wilkes Land, continental Antarctica
Authors: Hovenden M. J. , Jackson A. E. , Seppelt R. D.
Published: May 2006

In order to ascertain whether the major species of continental antarctic macrolichens are photosynthetically active during summer conditions, the chlorophyll fluorescence of three lichen species [Umbilicarin decussata (Vill. Zahlbr., Pseudephebe minuscula (Ny‐l. ex Arnold) Brodo and Hawksw. and Usnea sphacetala R. Br.] was monitored in the vicinity of Casey Station. Wilkes Land, continental Antarctica using a PAM‐2000 modulated fluorescence system. Lichens were studied when in equilibrium with the atmosphere as well as when moistened by snow showers. Photochemical quantum yield was estimated as ΔF/F′m and related to thallus water content as well as microclimatic conditions. Lichens were photosynthetically active only when moistened by snow fall or by run‐off from snow melt. The levels of photosynthetic activity in the field for all species were influenced by microenvironmental conditions and patterns in response were site and species specific. Highest levels of photosynthetic efficiency occurred when thalli were at intermediate water contents. Photosynthetic activity was reduced by cold as well as warm, bright conditions. Highest thallus water contents occurred during the middle of the day after substantial “falls of snow. P. minuscula maintained highest thallus water contents at all sites and appears to have a high water compensation point which is related to its observed distribution patterns. Umbilicaria decussata studied in the laboratory did not become photosynthetically active even when exposed to 95% relative humidity (RH) for 51 h and. when dehydrating after artificial wetting, showed an optimum thallus water content for photosynthesis of ca 90% dry weight and a thallus water compensation point of about 35% dry weighl. In the field U. decussata did not become pholosynthetically active except when moistened by snow. Usnea sphacelata exposed to the atmosphere had low thallus water contents (ca 30%) which was not related to RH. The results indicate that the lichens are photosynthetically inactive for most of the summer period and are totally reliant on snow as a water supply. This i.s important when modelling carbon gain and growth rates of continental antarctic lichens.
The protective effect of desferrioxamine on paraquat‐treated pea (Pisum sativum)
Authors: Zer Hagit , Peleg Itzhak , Chevion Mordechai
Published: May 2006

Paraquat, a widely used herbicide, is photoreduced by photosystem I to the monovalent cation radical, which in turn, can react quickly and efficiently with molecular oxygen to produce superoxide anion radicals. In the presence of redox‐active iron (or copper) superoxide radicals can serve as a source for the more active species such as hydroxyl radicals. The present sludv investigated the possible mediatory role of iron in paraquat to xicity. The results demonstrate that desferrioxamme (0–150μM) a highiy specific iron chelator, reduces the loss of proteins (by 34–69%) and lipid peroxidation (by 31–96%) in paraquat treated leaf cuts. Dcsferrioxamine also protects malate dehydrogenase (61–70%) hydroxvpyruvate reductase (54–100%), and Ca2+‐dependent ATPase (25–34%) against the paraquat‐induced loss of their activity. It also induces an increase in glutathione reductase activity (by 188%). These results, together with those from other experiments concerning the effect of desferrioxamine on paraquat uptake by the leaf cuts, suggest that the protection by desferrioxamine arises from its specific iron chelanon properties, and lead to the conclusion that nan‐protein‐bound and redoxactive forms of iron pluy a role in the manifestation of paraquat toxicity in plants.
Plasma membrane lipid alterations induced by NaCl in winter wheat roots
Authors: Magdy Mohamed , Mansour F. , van Hasselt Philip R. , Kuiper Pieter J.C.
Published: May 2006

A highly enriched plasma membrane traction was isolated by two phase partitioning from wheat roots (Triticum aestivum L. cv. Vivant) grown with and without 100 mM NaCl. The lipids of the plasma membrane fraction were extracted and characterised. Phosphatidylcholine and phosphatidylethanolamine were the major phospholipids with lesser amounts of phosphandylinositol, phosphatidylglycerol, diphosphalidylglycerol, phosphatidic acid and phosphatidylseriae. NaCl decreased the total phospholipids and the phosphatidylcholine portion of the plasma membranes. Salt treatment had no effect on total sterols and glycolipids. but the relative abundance of the tree sterols was altered: cholesterol, stigma sterol and brassicasterol were significantly increased. Salt treatment resulted in an increase of the more planar/less planar ratio of the free sterols and in introduction of a double bond in the C22 position in the side chain of stigma sterol and brassicasterol. The degree of fatty acid saturation of total phospholipids, phospha‐tidylcholine and phosphatidylethanolamine was increased after salt treatment. These lipid changes are discussed in relation to the salt tolerance mechanism.
Exposure to ultraviolet‐B radiation increases cold hardiness in Rhododendron
Authors: Dunning Chris A. , Chalker‐Scott Linda , Scott James D.
Published: May 2006

The change in the cold hardiness of Rhododendron (cv. English Roseum) following chronic exposure to ultraviolet‐B (UV‐B) radiation (280–320 nm) was studied. Leaf disks removed from UV‐B‐exposed plants exbibited a greater tolerance to freezing temperatures than plants that received no UV‐B exposure. Visual browning and percent phenolic leakage indicated that UV‐B‐exposed leaf disks were killed al ‐11°C. while control disks were killed at ‐8°C. Ultraviolet‐induced production of phenolic compounds may be involved in increasing cold hardiness of Rhododendron leaf tissues.
Differential expression of two β‐amylase genes of rye during seed development
Authors: Rorat Tadeusz , Sadowski Jan , Irzykowski Witold , Ziegler Paul , Daussant Jean
Published: May 2006

The expression of two β‐amylase loci was analysed in the developing seeds of two inbred lines of rye (Secale cereale L.), one of which was a β‐amylase deficient mutant. Enzymatic activity and the contents of enzymatic protein and mRNA specific for each of an endosperm‐characteristic and ubiquitous β‐amylase were determined throughout the course of caryopsis development. Both loci were expressed in the developing normal line caryopses according to different temporal and quantitative patterns. The ubiquitous enzyme‐specific locus β‐Amy 2 was expressed earlier; both mRNA and enzymatic protein accumulated to a maximum extent at 10 to 15 days after pollination. In contrast, the highest content of mRNA for endosperm β‐amylase (encoded by the β‐Amy I locus) was found 20 days after pollination, and the corresponding enzymatic protein accumulated throughout seed development. The expression of the β‐Amy I locus was 30‐ to 40‐fold higher than that of the β‐Amy 2 locus in terms of maximum specific mRNA accumulation. The expression product of only the β‐Amy 2 locus was found in the developing mutant line caryopses. The expression pattern of this locus was similar in the developing normal and mutant line seeds in terms of the temporal accumulation of mRNA and enzymatic protein. However, an approximately 4‐fold higher level of ubiquitous β‐amylase‐specific mRNA was found in the mutant than in the normal line caryopses, and the content of ubiquitous β‐amylase protein decreased to near zero at seed maturity in the mutant line, but not in the normal line, caryopses. The enzymatic activities of both β‐amylases appeared to be regulated at the level of accumulated enzymatic protein.
Enhanced UV‐B radiation alleviates the adverse effects of summer drought in two Mediterranean pines under field conditions
Authors: Petropoulou Yiola , Kyparissis Aris , Nikolopoulos Demosthenis , Manetas Yiannis
Published: May 2006

The effects of enhanced UV‐B (290‐320 nm) radiation on two native Mediterranean pines (Pinus pinea L., Pinus halepensis Mill.) were recorded during a one‐year field study. Plants received ambient or ambient plus supplemental UV‐B radiation (simulating a 15% stratospheric ozone depletion over Patras. Greece, 38.3°N. 29.1°E) and only natural precipitation, i.e. they were simultaneously exposed to other natural stresses. particularly water stress during summer. Supplemental UV‐B irradiation started in early February, 1993 and up to late June, no effects were observed on growth and photochemical efficiency of photosystem II, as measured by chlorophy II fluorescence induction. Water stress during the summer was manifested in the control plants as a decline in the ratio of variable to maximum fluorescence (Fv/Fm), the apparent photon yield for oxygen evolution (φl) and the photosynthetic capacity at 5% CO2 (Pm). In addition, a partial needle loss was evident. Under supplemental UV‐B radiation, however, the decreases in Fv/Fm, φi, and Pm. as well as needle losses were significantly less. Soon after the first heavy autumn rains. photosynthetic parameters in both control and UV‐B treated plants recovered to similar values. but the transient summer superiority of UV‐B irradiated plants resulted in a significant increase in their dry weight measured at plant harvest. during late January. 1994. Plant height. UV‐B absorbing compounds, photosynthetic pigments and relative water content measured at late spring. late summer and at plant harvest, were not significantly affected by supplemental UV‐B radiation. The results indicate that enhanced UV‐B radiation may be beneficial for Mediterranean pines through a partial alleviation of the adverse effects of summer drought.
Development of an assay for Mg‐dechelatase of oilseed rape cotyledons, using chlorophyllin as the substrate
Authors: Vicentini Fabrizio , Iten Felix , Matile Philippe
Published: May 2006

Chlorophyllin (Chlin), the Mg‐chlorin obtained from chlorophyll (Chl) was employed as substrate of Mg‐dechelatase. The release of Mg2+was associated with a shift of absorption from 644 to 687 nm. Changes of absorption at 687 nm were taken as a measure of Mg‐dechelatase activity present in preparations of oilseed rape thylakoids. Absorption changes were correlated linearly with enzyme dose. The pH optimum of Mg release from Chlin was ca 9 with a broad flank down to pH 7. The reaction showed saturation kinetics with an apparent Kmvalue of ca 17 nM. The activity was inhibited in the presence of cysteamine or reduced glutathion. There was no effect of the thiol reagent N‐ethyl maleimide. The bulk of dechelatase activity was associated with the chloroplast membranes. The enzyme is partially latent and the appearance of full activity requires the solubilization of thylakoids with detergent. The highest activities were detected in mature green rape cotyledons. During dark‐induced senescence the activity declined at roughly the same rate as Chl was lost in the leaf tissue.
The Maillard reaction and oxidative stress during aging of soybean seeds
Authors: Sun Wendell Q. , Leopold A. Carl
Published: May 2006

The chemical reactions that may lead to the loss of seed viability were investigated both during the accelerated aging and natural aging of soybeans (Glycine max Merrill cv. Chippewa 64). Under conditions of accelerated aging (36°C and 75% RH), fluorescence of soluble proteins accumulated, which was closely correlated with the loss of seed germinability and vigor. We were able to show this correlation by using partially purified proteins for the assay. Fluorescence also increased in seeds under good storage conditions (5°C for up to 21 years), although there was a less significant correlation between seed viability and the accumulation of fluorescent products during the time of natural aging. The rise in protein fluorescence is interpreted as an increase of Maillard products. The carbonyl content of soluble proteins (a measure of the oxidative damage) did not change significantly during either accelerated aging or natural aging: however the elimination of carbonyls during germination seemed to be hindered in seeds that had poor germination. The Maillard reaction may be a consequence of the formation of reducing sugars through a gradual hydrolysis of oligosaccharides during aging. Preliminary evidence from the natural aging study showed that, when seeds were in the glassy state, the sugar hydrolysis was inhibited. These results suggest that the Maillard reaction and oxidative reaction may play an important role in seed deterioration.
Development of galactomannan‐hydrolyzing activity in the micropylar endosperm tip of tomato seed prior to germination
Authors: Nomaguchi Masako , Nonogaki Hiroyuki , Morohashi Yukio
Published: May 2006

Development of galactomannan‐hydrolyzing activity, that is involved in the weakening of the mechanical restraint of the endosperm, was followed at pre‐germinative stages in tomato (Lycopersicon esculentum) seed. Prior to germination the activity developed exclusively in the endosperm portion just adjacent to the radicle tip. In other parts of the endosperm, the activity developed only after germination occurred. Under the conditions where germination was suppressed (far‐red light‐ or ABA‐treatment). no activity was detected in the endosperm at the pre‐germinative stages. Under the conditions where the inhibition of germination was alleviated (far‐red + red or ABA + GA3), the activity developed prior to germination in the endosperm part in front of the radicle tip. Thus, a clear parallel relationship was observed between germinability of the seed and the pre‐germinative development of activity in the part of the endosperm portion adjacent to the radicle tip.