bluuebunny/crossref_metadata_2025 huggingface dataset:
α‐Hydroxynitrile lyase in Hevea brasiliensis and its significance for rapid cyanogenesis
Authors: Selmar Dirk , Lieberei Reinhard , Biehl Böle , Conn Eric E.
Published: May 2006

The hydroxynitrile lyase (HNL, EC 4.2.1.‐) of Hevea brasiliensis (Muell.‐Arg.) catalyzes the dissociation of acetone cyanohydrin and mandelonitrile, but shows higher activity towards the natural substrate acetone cyanohydrin. The ratio between the activities of linamarase (β‐glycosidase, EC 3.2.1.21) to HNL was screened for more than 30 Hevea plants. In mixed‐enzyme incubations various ratios of HNL to β‐glucosidase were analyzed for the rapidity of HCN liberation. Addition of HNL increased the rate of HCN liberation up to 20‐fold, thus demonstrating the significance of the HNL for rapid cyanogenesis. Its physiological importance is shown by the fact that only plants possessing high HNL activity are able to liberate HCN efficiently. Cyanogenic plants have been described as being weakly or strongly cyanogenic depending on the total amount of HCN which is potentially liberated. The data presented in this paper suggest that cyanogenic plants should also be differentiated as fast or slow cyanogenic according to the observed velocity of HCN liberation. Thus, for evaluating the repellent action of cyanogenic plants not only the final level of the HCN liberated is important but rather the rate with which this level is reached.
Correlation between profile of ion‐current circulation and root development
Authors: Miller Andrew L. , Gow Neil A. R.
Published: May 2006

The electrical currents associated with developing primary root tips ofTriticum aestivumL. cv. Slejpner,Avena sativaL. cv. Victory I,Lolium perenneL. cv. Melle,Vigna radiata(L.) Wilczek,Arachis hypogaeaL.,Pisum sativumL. cv. Keluedon Wonder,Lonchocarpus leucanthusBurk,Dalbergia nigraFr. Allen andPicea abies(L.) Karst. (U. K. Forestry Commission Number: 85/498/B). and that of the adventitious root tips ofFragaria vescaL.,Solanum tuberosumL. cv. Maris Piper andNeptunia plenaLindl. were examined with a vibrating electrode. Current was found consistently to enter the meristematic and elongating tissues of all the intact growing roots examined. Mature non‐growing root regions were responsible for generating the outword limb of the current loop. Peak inward current densities ranged between 2 mA m−2(Lolium) and 28 mA m−2(Arachis). The point at which the inward current reversed to outward current also varied between species. These results, which are derived from 5 taxonomically diverse families (Graminae, Leguminosae, Rosaceae, Solanaceae and Pinaceae) extend the range of different species that have been shown to generate ion currents that transverse, in a highly polar manner, the growing regions of their root systems. This supports the correlations between endogenous current generation and root development.
Gas exchange in intact isolated chloroplasts from Chlamydomonas reinhardtii during starch degradation in the dark
Authors: Klöck G. , Sültemeyer D. F. , Fock H. P. , Kreuzberg K.
Published: May 2006

During starch degradation in intact isolated chloroplasts from Chlamydomonas reinhardtii gas exchange was studied with a mass spectrometer. Oxygen uptake by intact chloroplasts in the dark never exceeded 1.5% of the starch degradation rate [maximum 15 nmol O2 (mg Chl)−1 h−1 consumed. 1 000 nmol glucose (mg Chl)−1h−1 degraded]. Evolution of CO2 under aerobic conditions [9.8–28 nmol (mg Chl)−1 h−1] was stimulated by addition of 0.1–0.5 mM oxaloacetate [393–425 nmol CO2 (mg Chl)−1 h−1]. Pyridoxal phosphate (5 mM) inhibited starch degradation by more than 80%, but had no effect on O2 uptake. Starch degradation rates and CO2 evolution did not differ under acrobic and anaerobic conditions. Increasing Pi in the reaction medium from 0.5 mM to 5.0 mM stimulated starch degradation by 230 and 260% under aerobic and anaerobic conditions, respectively. A rapid autooxidation of reduced ferredoxin was observed in a reconstituted system consisting of purified Chlamydomonas ferredoxin, purified Chlamydomonas NADP‐ferredoxin oxidoreductase (EC 1.6.7.1) and NADPH. Addition of isolated thylakoids from C. reinhardtii did not affect the rate of O2 uptake. Our results clearly indicate the absence of any oxygen requirement during starch degradation in isolated chloroplasts.
Influence of low temperature on regulation of Rb+ and Ca2+ influx in roots of winter wheat
Authors: Erlandson A. Gunvor I. , Jensén Paul
Published: May 2006

Influx of Rb+(86Rb+) and Ca2+(45Ca2+) was determined in roots of winter wheat (Triticum aestivum L. cv. Weibulls Starke II) after 14 days at 16°C/16 h light, after 1 and 8 weeks of cold acclimation (2°C/8 h light) and at intervals after deacclimation (16°C/16 h light) for up to 14 days. The plants were cultivated at 3 ionic strengths: 100, 10 and 1% of a full strength nutrient solution, containing 3.0 mM K+ and 1.0 mM Ca2+.

K+ concentrations in roots and shoots increased during cold treatment, while Ca2+ in the roots decreased. In the shoots Ca2+ concentrations remained the same. Influx of Rb+ as a function of average K+ concentration in the roots of 14‐day‐old, non‐cold‐treated plants was high at a certain K+ level in the root and decreased at higher root K+ levels (negative feedback). The pattern for Ca2+ influx versus average concentration of Ca2+ in the root was the reverse. Independent of duration of treatment (1–8 weeks), cold acclimation partly changed the regulation of Rb+ influx, so that it became less dependent upon negative feedback and more dependent on the ionic strength of the cultivation solution. After exposure to 2°C, Ca2+ influx increased at high Ca2+ concentrations in the root as compared with influx in roots of 14‐day‐old non‐cold‐treated plants. Under deacclimation, Ca2+ influx gradually decreased again, and reached the level observed before cold treatment within 7–14 days at 16°C; the number of days depending on the exposure time at 2°C. It is suggested that Rb+(K+) influx became adjusted to low temperature and that abscisic acid (ABA) may be involved in this mechanism. It is also suggested that extrusion of Ca2+ was impaired and/or Ca2+ channels were activated at 2°C in roots of plants grown in the full‐strength solution and that extrusion was gradually restored and/or Ca2+ channels were closed under deacclimation conditions.
Abscisic acid physiology and biosynthesis in higher plants
Authors: Creelman Robert A.
Published: May 2006

Abscisic acid (ABA) has been postulated to modulate several aspects of plant growth and development. While it is tempting to attribute changes in growth and development to a specific hormone such as ABA, the reality is that these processes are complex and poorly understood. Since there is so little known about basic biochemical events that occur during growth and development, it is difficult ot unambiguously assign a role for ABA in any process. Becuse of this, many of the cited effects of ABA on growth and development have not been conclusively demonstrated. Howver, it is clear that ABA has a function in ameliorating water‐stress and preventing vivipary. The roles of ABA in bud dormancy and growth still remain unclear. With the use of biosynthesis inhibitors and mutants which block ABA accumulation, it has been shown that ABA does not play a role in gravitropism.

Knowledge of how the levels of any particular growth regulator are modulated is essential for the understanding of its physiology. The use of mutants, inhibitors and heavy isotopes suggests that ABA may be derived from a carotenoid rather than directly from farnesyl pyrophosphate (FPP), and that the cleavage of a carotenoid is the rate limiting step. However, the relative contribution of each pathway (and the role of xanthoxin) in ABA biosynthesis remain unknown.
Physiological and structural effects of phosphorus starvation on the unicellular green alga Scenedesmus
Authors: Tillberg J.‐E. , Rowley J. R.
Published: May 2006

The effects of phosphorus starvation on morphology and intracellular structure and on reactions related to the energy metabolism of the unicellular green alga Scenedesmus obtusiusculus (Chod.) were studied over a period of 96 h by employing transmission electron microscopy and various methods for measurement of physiological reactions. Increase in cell size and shape and in cell wall thickness are dominating features of phosphorus starvation. There is also an increase in number and size of starch granules and lipid globules and the internal structure of the cells appears successively disorganized. Shortage of phosphorus in the medium initially induces an increase of the adenylate pool whereas the energy charge value remains the same as for the controls. The photosynthetic and respiratory activities are high during incipient phosphorus starvation. After 24 h, as shortage of phosphorus becomes critical, the internal phosphorus reaches a low steady‐state value, and this is also true for the adenylate energy charge. The total content of adenylates, however, peaks after 24 h of starvation and then decreases with increasing length of phosphorus starvation. Light‐induced oxygen evolution appears not to be as much inhibited by a low phosphorus content in the cells as by the concomitant starch accumulation. The data indicate that the strategy for survival of the cells in a phosphorus‐poor environment includes morphological and physiological changes that facilitate the transfer and adaption of the cells to environments with a more favourable supply of phosphorus, such as the often oxygen‐poor but phosphorus‐rich bottom zones.
Detection and identification of gibberellins in Sitka spruce (Picea sitchensis) of different ages and coning ability by bioassay, radioimmunoassay and gas chromatography – mass spectrometry
Authors: Moritz Thomas , Philipson J. Julian , Odén Per Christer
Published: May 2006

Gibberellins Al (GA1), GA3, GA4, GA9, and after enzymatic hydrolysis of GA‐conjugate‐like fractions, GA9 and GA15, were identified in shoots of Sitka spruce [Picea sitchensis (Bong.) Carr.] of different ages by combined gas chromatography‐mass spectrometry (GC‐MS). The purification and separation of the GAs involved the use of reverse phase and normal phase high performance liquid chromatography (HPLC). The Tan‐ginbozu dwarf rice bioassay and binding to antibodies raised against GA1, GA4 and GA9 were used for detection of GA‐like substances. The qualitative differences between the three ages of plant material were the presence of GA3 and GA1 in the 48‐year‐old material and the absence of detectable amounts of GA4 in the same material. This indicates a difference in GA metabolism which may reflect the difference in ability to form reproductive buds.
Compartmentation and transport of 1‐aminocyclopropane‐1‐carboxylic acid and N‐malonyl‐1‐aminocyclopropane‐1‐carboxylic acid in barley and wheat mesophyll cells and protoplasts
Authors: Tophof Susanne , Martinoia Enrico , Kaiser Georg , Hartung Wolfram , Amrhein Nikolaus
Published: May 2006

Intracellular compartmentation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and N‐malonyl‐1‐aminocyclopropane‐1‐carboxylic acid (MACC) in wheat (Triticum aestivum L. cv. Kanzler) and barley (Hordeum vulgare L. cv. Gerbel) leaves was studied using different methods: first, the isolation of intact vacuoles from protoplasts and, second, a non‐aqueous fractionation procedure. The two methods gave similar results. ACC concentrations were similar in the extravacuolar space and in the vacuole, whereas MACC was accumulated in the vacuolar space. Transport studies revealed that no specific carrier for ACC exists at the tonoplast. MACC transfer across the tonoplast was enhanced by 120% in the presence of ATP. MACC competitively inhibited malate transport into the vacuole indicating that the same transfer system catalyzes the transfer of the two dicarboxylates.

It is concluded that malonylation of ACC is not a prerequisite for the transport of ACC through the tonoplast.
Effect of paraquat on ethylene biosynthesis by intact green Phaseolus vulgaris seedlings
Authors: Weckx J. , Vangronsveld J. , Van Poucke M.
Published: May 2006

Ethylene production by intact green bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings was investigated in white light and in darkness. In white light both endogenous and 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐induced ethylene production were stimulated. A decrease in the 1‐(malonylamino)cyclopropane‐1‐carboxylic acid (M‐ACC) level and a slight increase in the free ACC concentration could be observed in light. The total amount of endogenous ACC was not changed by light. We related the effect of light to the effect of paraquat on ethylene biosynthesis. Paraquat caused a strong increase of endogenous ethylene production in light. However, the conversion of exogenously applied ACC in light was not influenced by the paraquat treatment, although the presence of the herbicide in the chloroplasts was evident through the inhibition of net photosynthesis. In light, paraquat increased the total ACC content. This was due to an enlargement of the free ACC pool. The effects of white light and paraquat on ethylene biosynthesis can be differentiated from one another: white light exerts its influence on the conversion of ACC to ethylene; it also seems to inhibit the malonylation and may act on the formation of ACC itself. Paraquat influences only ACC synthesis.
Gravitational stress and lignification in aerial vs. submerged shoots of Hippuris vulgaris
Authors: Goliber Thomas E.
Published: May 2006

Hippuris vulgaris L. is a heterophyllic aquatic plant that grows naturally under the different degrees of gravitational stress that are associated with submerged and aerial environments. This characteristic of H. vulgaris was exploited in order to study the interaction of gravitational stress with lignification processes. Lignin content was found to be 4.1% of aerial stem dry weight and 2.6% of submerged stem dry weight. The activity of phenylalanine ammonia‐lyase (E.C. 4.3.1.5), an enzyme early in the lignin biosynthetic pathway, paralleled lignin content and was about 5 times higher in aerial than in submerged stems. Another lignin biosynthetic enzyme, peroxidase (E.C. 1.11.1.7), was studied, and although definite conclusions could not be drawn from measurements of total peroxidase activity, different isozyme patterns were observed in aerial and submerged‐type shoots. Abscisic acid, which can induce the aerial‐type shoot morphology on submerged shoots, probably is not involved in mediating changes in the lignin content of H. vulgaris. These results support the hypothesis that lignin biosynthesis is regulated by gravity.
Interactions of drought and low temperature stress on lipid and fatty acid composition of cucumber genotypes differing in growth response at suboptimal temperature
Authors: Bulder H. A. M. , van der Leij W. R. , Speek E. J. , van Hasselt P. R. , Kuiper P. J. C.
Published: May 2006

The effects of drought stress and/or low temperature stress on total lipid and phospholipid content and fatty acid composition of leaves of cucumber (Cucumis sativus L.) genotypes differing in growth response at suboptimal temperature were studied. Both drought and low temperature resulted in reduced growth, especially in cv. Farbio, the genotype least tolerant to low temperature. Drought resulted in an increase in total lipid and phospholipid per g fresh weight. On a lipid basis no change in phospholipids or fatty acid content was observed. The fatty acid composition was changed by drought and low temperature, resulting in an increase in the degree of unsaturation. The genotype‐specific reaction to treatment for total lipid content and the degree of unsaturation point to the possibility of a genetic origin for drought‐induced lipid changes, which may be used in a breeding program for improved growth at suboptimal temperature.
Translational control of chloroplast protein synthesis during senescence of barley leaves
Authors: Martín Mercedes , Sabater Bartolomé
Published: May 2006

A light‐driven homologous system for the translation of chloroplast mRNA has been prepared from chloroplasts isolated from senescent barley leaves and treated with micrococcal nuclease. We have investigated the potential of this system for studies on translational specificity. Chloroplast mRNAs from senescent and kinetin‐treated leaves have been translated in the homologous system and the products have been compared with the polypeptides synthesized by intact chloroplasts isolated from senescent and kinetin‐treated leaves. Isolated intact chloroplasts from senescent barley leaves specifically synthesized polypeptides of: 80,66,58,50,48 and 35 kDa but did not synthesize the 54 kDa large subunit of ribulose‐1, 5‐bisphosphate carboxylase oxygenase. Chloroplasts isolated from leaves treated for 18 h with kinetin specifically synthesized polypeptides of: 85,75 and 54 kDa. Several polypeptides (40,32,25 and 18 kDa) are synthesized by chloroplasts of both senescent and kinetin‐treated leaves. The homologous translation system derived from senescent chloroplasts synthesized only senescence polypeptides whether it was supplied with chloroplast mRNA from senescent leaves or leaves treated with kinetin for 18 h. The homologous translation system derived from chloroplasts of kinetin‐treated leaves synthesized either senescence polypeptides or kinetin‐induced polypeptides depending on the source of chloroplast mRNA, senescent leaves or leaves treated with kinetin, respectively. The results indicate that kinetin controls chloroplast gene expression in senescent leaves at both the transcriptional and translational level.
Photochromism of the cyanobacterial light harvesting biliprotein phycoerythrocyanin
Authors: Kufer Werner , Björn Gunvor S.
Published: May 2006

The light harvesting biliprotein phycoerythrocyanin isolated from the cyanobacterium Mastigocladus laminosus Cohn was separated into its subunits by isoelectric focusing in a granulated gel in the presence of urea with subsequent renaturation. Smaller amounts of the subunits were obtained from Tolypothrix distorta Kützing var. symplocoides Hansgirg, strain IUCC 424 (now UTEX 424), by chromatography of phycoerythrocyanin on hydroxylapatite. In both cases the isolated α‐subunits showed the photoreversible photochemistry characterizing phycochrome b, a photoreversibly photochromic pigment so far found only in extracts of phycoerythrocyanin‐containing organisms. Light‐induced absorbance changes in the β‐subunit and in phycoerythrocyanin were also studied.
Aromatic amino acid metabolism during organogenesis in rice callus cultures
Authors: Kavi Kishor P. B.
Published: May 2006

The activity during root and shoot initiation of key enzymes involved in aromatic amino acid metabolism was examined in rice (Oryza sativa L. cv. Bala) callus cultures. Increased activities of the enzymes quinate:NAD+ oxidoreductase (EC 1.1.1.24), shikimate kinase (EC 2.7.1.71), chorismate mutase (EC 5.4.99.5), anthranilate synthase (EC 4.1.3.27) and tryptophan synthetase (EC 4.2.1.20) were noticed in organ‐forming callus compared to proliferating callus of rice, especially prior to the visible manifestation of form. These results suggest a correlation between organogenesis and the aromatic amino acid pathway.
Is proline involved in stomata regulation of Commelina communis plants recovering from salinity stress?
Authors: Klein Aviva , Itai Chanan
Published: May 2006

Plants of Commelina communis L. were grown in culture solution to which NaCl was added for 48 h. The solutions were then replaced with normal medium, so that the plants could recover from the stress. The water potential increased almost to that of the controls during 4 h of recovery, but stomatal resistance stayed high. Cytokinin treatment of leaf discs failed to enhance recovery of stomatal aperture, although it enhanced stomatal recovery of identically treated epidermal tissue. Proline levels in leaves correlated well with stomatal resistance. Incubation of epidermal tissue in D‐proline inhibited stomatal opening. NaCl and benzyladenine interacted with the effect of proline, and the effect of abscisic acid and was additive to that of proline.
Picomolar concentrations of tentoxin affect Mg2+‐ and Ca2+‐ATPase activities of plasma membrane vesicles from roots of winter wheat seedlings
Authors: Klotz Martin G. , Bérczi Alajos , Erdei László , Liebermann Bernd
Published: May 2006

Purified plasmalemma vesicles were isolated in the presence of 250 mM sucrose from roots of 14‐day‐old seedlings of winter wheat (Triticum aestivum L. Martonvásári‐8) by phase partitioning of salt‐washed microsomal fractions in a Dextran‐polyethylene glycol two‐phase system, and both Mg2+‐ and Ca2+‐ATPase activities were detected. Orthovanadate‐sensitive Mg2+‐ATPase activity associated with the inside of right side‐out plasmalemma (PM) vesicles (latency 98%) was inhibited 76% by 0.3 mM Ca2+, Ca2+‐dependent ATPase activity located partly on the inside and partly on the outside of plasmalemma vesicles (latency 47%) was not affected by Mg2+.

Mg2+‐ATPase activity was inhibited by 68% and inhibition of Mg2+ activation by 0.3 mM Ca2+ partly disappeared in the presence of 10 pM tentoxin, a fungal phytotoxin. Mg2+‐ATPase activity remained inhibited up to 10 nM tentoxin while at 1 μM tentoxin Mg2+ activation was as high as without tentoxin. K+‐stimulation and vanadate inhibition was increased and decreased, respectively, by 100 pM‐10 nM tentoxin. Ca2+‐dependent ATPase activity was continuously increased by 1 pM‐10 nM tentoxin, but at 1 μM tentoxin the stimulation disappeared. The effects of pM tentoxin on plasma‐lemma Mg2+‐ATPase are discussed in relation to its influence on K+ transport in wheat seedlings.
Antioxidant status of the potato tuber and Ca2+ deficiency as a physiological stress
Authors: Monk Lorna S. , Davies Howard V.
Published: May 2006

The antioxidant status of potato (Solanum tuberosum L.) tubers of two genotypes, cv. Désirée and clone 10337de40 was investigated in relation to susceptibility to internal rust spot (IRS), a Ca2+‐related physiological disorder. Concentrations of total calcium within the perimedulla tissue of tubers, grown with a restricted (1 mM CaCl2) Ca2+ supply, were similar in cv. Désirée (IRS resistant) and clone 10337de40 (IRS susceptible). A range of antioxidants was assayed in order to assess antioxidant status in both genotypes under the two Ca2+ treatments. Although no appreciable differences were detected between low Ca2+ and control treatments, certain antioxidants were present at significantly higher levels in the IRS resistant genotype, cv. Désirée. These included dehydroascorbate reductase (EC 1.8.5.1) activity (more than 100% higher), total glutathione content (ca 40% higher), glutathione reductase (EC 1.6.4.2) activity (almost 50% higher), peroxidase (EC 1.11.1.7) activity (ca 60% higher) and superoxide dismutase (EC 1.15.1.1) activity (almost 80% higher). There was no difference in ascorbate content, ascorbate free radical reductase activity (EC 1.6.5.4), α‐tocopherol levels and catalase activity (EC 1.11.1.6) between the two genotypes. The possible relationship between resistance to IRS and a superior antioxidant status, found in cv. Désirée, is discussed.
The effect of excitation on the rate of respiration in the liverwort Conocephalum conicum
Authors: Dziubińska H. , Trȩbacz K. , Zawadzki T.
Published: May 2006

Simultaneous measurements were taken of the electrical activity and the rate of respiration of thalli of Conocephalum conicum L. stimulated electrically and mechanically (by cutting). The measurements of the rate of respiration employed a modified Warburg apparatus for O2 consumption and an infra‐red gas analyzer with computer recording and data processing for CO2 evolution. The action potential, produced by either a cut (a damaging stimulus) or an electrical stimulus (a non‐damaging stimulus), caused a transient rise in the rate of respiration. The course of changes in the rate of respiration depends on the character of the excitation and the area of the thallus covered by it. If stimulation does not produce excitation, the increase in the rate of respiration does not take place, regardless of the magnitude and type of the stimulus applied.
Proteolysis of the main storage protein of buckwheat seeds at the early stage of germination
Authors: Dunaevsky Yakov E. , Belozersky Mikhail A.
Published: May 2006

The changes in the main storage protein of seeds of buckwheat (Fagopyrum esculentum Moench cv. Shatilovskaya 5), 13S globulin, were studied during seed germination. During the first three days of germination the 13S globulin is subjected to a limited proteolysis, which consists in the splitting of some of its subunits into large polypeptide fragments. Insignificant changes in the sedimentation coefficient of the 13S globulin during the first days of germination as well as immunochemical data, indicate that the limited proteolysis of the 13S globulin does not cause any major changes in its structure.

Dormant buckwheat seeds contain a proteolytic enzyme (a metalloproteinase), which can cause limited proteolysis of 13S globulin. The proteinase hydrolyzed some subunits of the 13S globulin to high molecular weight fragments. In the presence of sodium dodecylsulphate the electrophoretic pattern of 13S globulin, isolated from 3‐day‐old buckwheat seedlings, was almost identical to that of 13S globulin from dormant seeds hydrolyzed with metalloproteinase. It is suggested that the proteolysis of 13S globulin observed in vitro may also take place in vivo in the course of seed germination.
Protective mechanisms of nitrogenase against oxygen excess and partially‐reduced oxygen intermediates
Authors: Becana Manuel , Rodríguez‐Barrueco Claudino
Published: May 2006

Diazotrophic systems have developed a number of strategies to protect nitrogenase (N2ase; EC 1.18.6.1) from O2 excess and active‐oxygen species (AOS). Protection against O2 excess is given by biochemical modifications of N2ase, increased rates of low‐efficiency respiration, temporal segregation of N2 fixation and photosynthesis, physical barriers to O2 diffusion, and hemoglobins. On the other hand, AOS may originate from oxidation of N2ase components, ferredoxins, flavodoxins and hemoglobins; interaction among the AOS themselves, or between H2O2 and hemoglobins; and during reactions catalyzed by hydrogenase (EC 1.18.99.1), xanthine oxidase (EC 1.1.3.22) and uricase (EC 1.7.3.3). Active‐oxygen species are scavenged enzymatically [superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6). peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11)] or through non‐enzymic reaction with low‐molecular‐weight compounds (ascorbate, α‐tocopherol, glutathione).
Regulation of the synthesis of normal cellular proteins during heat shock
Authors: Brodl Mark R.
Published: May 2006

Exposure of plant cells to heat shock temperature results in the synthesis of a set of heat shock proteins and, in many cases, the interruption of normal cellular protein synthesis. In some plant secretory cells the interruption of normal cellular protein synthesis is accomplished by the destabilization of otherwise stable mRNAs, perhaps via the dissociation of the endoplasmic reticulum lamellae upon which these mRNAs are translated. Such a mechanism represents a novel means for the regulation of gene expression.
Removal of the stem terminal and application of auxin change carbohydrates in Pinus banksiana cuttings during propagation
Authors: Haissig Bruce E.
Published: May 2006

This study determined how surgical removal of the stem terminal, with indole‐3‐butyric acid (IBA) treatment, influenced concentrations and partitioning of carbohydrates in Pinus banksiana Lamb, cuttings during propagation. Seedlings and cuttings that originated from 90‐day‐old stock plants were untreated or treated by removing the stem terminal, followed by application of IBA to the severed apical or basal (cuttings only) stem. Fresh and dry weights of the basal 1‐cm stems of cuttings were determined daily for the first 10 days of propagation (i.e., before roots were visible). In addition, basal 1‐cm stems, upper (ca 9‐cm) stems and needles of seedlings and cuttings were analyzed for sucrose, soluble reducing sugar and total non‐structural carbohydrate. Net concentrations of each carbohydrate in cuttings were obtained by subtracting corresponding concentrations for similarly treated seedlings, yielding data directly related to only the physiology of rooting. Data for cuttings indicated that presence of the stem terminal combined with applied IBA positively influenced rooting through processes that increased basal stem fresh and dry weights before root emergence. Removal of the stem terminal influenced accumulation of net total carbohydrate in cuttings, but the major effect was on carbohydrate partitioning. Either type of IBA treatment after removal of the stem terminal usually resulted in different net carbohydrate concentrations in each tissue source of cuttings, compared with only removal of the terminal. Neither basal nor apical IBA treatment of cuttings without stem terminals yielded results for carbohydrate accumulation and partitioning like those obtained with intact cuttings. Removal of the stem terminal, even if followed by IBA treatment, may have lessened rooting potential of cuttings because it resulted in greater reducing sugarstarch concentration ratios in basal stems compared with those in intact cuttings.
Relations between carbohydrate, water status and adventitious root formation in leafy pea cuttings rooted under various levels of atmospheric CO2 and relative humidity
Authors: Davis Tim D. , Potter John R.
Published: May 2006

Three levels of atmospheric CO2 and 2 levels of relative humidity (RH) during the rooting period were tested for their effect on several factors presumed to influence adventitious root formation in leafy pea (Pisum sativum L. cv. Alaska) cuttings. Compared to normal CO2 levels (350 μl l−1), neither 1800 nor 675 μl l−1 CO2 affected the rooting percentage or the number of roots per cutting. However, 1800 μl l−1 CO2 increased root and shoot dry weight, root length, carbohydrate levels in the base of the cuttings and water potential (Ψw) of cuttings compared to normal levels of CO2. Compared to 87% RH. 55% RH decreased all of the above parameters, including the number of roots per cutting. A polyvinyl chloride antitranspirant (which partially blocks stomata and slows photosynthesis) applied simultaneously with 87% RH increased Ψw and root length but lowered all of the other above parameters, compared to 87% RH without antitranspirant. Increasing current photosynthate (products of photosynthetic activity after excision), carbohydrate, or Ψw either alone or together was associated with increased root system size but not necessarily with increased rooting percentage or root number. The data are consistent with a hypothesis that the number of roots per cutting increased with increasing current photosynthate and carbohydrate until some other factor became limiting. Also, the effect of Ψw on rooting percentage and root number was mediated through its effect on current photosynthate and carbohydrate.
Activation of 1,3‐β‐glucan synthase by Ca2+, spermine and cellobiose. – Localization of activator sites using inside‐out plasma membrane vesicles
Authors: Fredrikson Karin , Larsson Christer
Published: May 2006

The plant plasma membrane contains a 1,3‐β‐glucan synthase (EC 2.4.1.34) which has its active site on the cytoplasmic side of the membrane, while the product, the cell wall component callose, is deposited on the apoplastic side of the membrane. This enzyme should therefore be an integral, transmembrane protein. The activity of the enzyme is stimulated by Ca2+, polyamines, and polyols. Using sealed, inside‐out (cytoplasmic side out) plasma membrane vesicles from sugar beet (Beta vulgaris L.) leaves, which permits the activity to be measured without solubilization of the membrane, we have localized the activator sites for Ca2+, spermine, and cellobiose to the cytoplasmic side of the plasma membrane.
Effect of anti‐wall protein antibodies on auxin‐induced elongation, cell wall loosening, and β‐D‐glucan degradation in maize coleoptile segments
Authors: Hoson Takayuki , Nevins Donald J.
Published: May 2006

Antiserum raised against the LiCl extract of maize shoot cell walls suppresses auxin‐induced elongation of maize coleoptile segments. A series of polyclonal antibodies were raised against protein fractions separated from the LiCl extract of maize (Zea mays L. cv. B73 x Mo17) coleoptiles by SP‐Sephadex and Bio‐Gel P‐150 chromatography. To understand the role of cell wall proteins in growth regulation, the effect of these antibodies on auxin‐induced elongation and changes in the cell walls of maize coleoptiles was examined. Four of the fractions prepared reacted with the antiserum raised against the total LiCl extract and effectively suppressed its growth‐inhibiting activity. Only these fractions contained the proteins responsible for eliciting growthinhibiting antibodies. The antibodies capable of growth inhibition of auxin‐induced elongation of segments also inhibited auxin‐induced cell wall loosening (decrease in the minimum stress‐relaxation time of the cell walls) of segments. The antibodies raised against one of the protein fractions separated by SP‐Sephadex inhibited the autolytic reactions of isolated cell walls and the auxin‐induced decrease in (1→3), (1→4)‐β‐D‐glucans in the cell walls. Thus, the degradation of β‐D‐glucans by cell wall enzymes may be associated with the cell wall loosening that is responsible for cell elongation. Because the other antibodies did not influence the auxin‐induced degradation of (1→3), (1→4)‐β‐D‐glucanses, β‐D‐glucanases and other cell wall enzymes may cooperate in regulation of cell elongation in maize coleoptiles.
The Nostoc‐Nephroma symbiosis: localization, distribution pattern and levels of key proteins involved in nitrogen and carbon metabolism of the cyanobiont
Authors: Bergman Birgitta , Rai Amar
Published: May 2006

The qualitative distribution and quantitative estimates of nitrogenase (EC 1.7.99.2), glutamine synthetase (EC 6.3.1.2), phycoerythrin and ribulose 1,5‐bisphosphate carboxylase/oxygenase (EC 4.1.1.39) were studied in the cyanobacterium Nostoc residing in internal cephalodia of the tripartite lichen Nephroma arcticum L. Polyclonal antisera, raised in rabbit against the proteins, and goat anti‐rabbit IgG conjugated to 10 nm gold were used as probes to detect the antigens by transmission electron microscopy. Western blot analyses demonstrated the monospecificity of the antisera. Nitrogenase was localized in heterocysts, with vegetative cells showing a label intensity comparable to the background. Distribution of the antigen within the heterocysts was uniform. Glutamine synthetase labelling was very low, but appeared to be distributed in both cell types. An intense phycoerythrin labelling was associated with the thylakoid region of the vegetative cells, whereas a much lower labelling was observed in the heterocyst. No significant differences were found between cyanobionts in younger and older cephalodia except for the nitrogenase labelling, which was higher in heterocysts of the cyanobiont in younger cephalodia. Most of the ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) label was present in vegetative cells. The Rubisco label was pronounced in the carboxysomes, whereas the label in the cytoplasm, on a unit area basis, was much lower. Heterocysts showed a label intensity similar to that of the vegetative cell cytoplasm. In Nostoc of the bipartite lichen Peltigera canina L., the Rubisco protein showed a comparable distribution pattern, but the average number of carboxysomes per vegetative cell was about 4 times higher.
Comparison of the developmental patterns of mitochondrial malate dehydrogenase between mung bean and cucumber cotyledons during and following germination
Authors: Sugimoto Miho , Morohashi Yukio
Published: May 2006

The development of mitochondrial NAD+‐malate dehydrogenase (EC 1.1.1.37) in mung bean and cucumber cotyledons was followed. using the antibody raised against it, during and following germination. The developmental patterns were quite different between the two. In cucumber, the content of mitochondrial malate dehydrogenase continued to increase through 3–4 days after the beginning of imbibition. This was, at least in part, due to active synthesis of the enzyme protein, and the synthesis seemed to be regulated by the availability of the translatable mRNA for the enzyme. In mung bean, on the other hand, the enzyme was present in dry cotyledons at a rather high concentration, and remained at a constant level between day 1 and day 3 after the reduction of the content to one‐half its initial level during the first day. De novo synthesis of the enzyme could not be detected in mung bean cotyledons by pulse‐labeling experiment.
Effect of cadmium and Phytophthora infestans on polyamine levels in potato leaves
Authors: Stroiński Andrzej , Szczotka Zofia
Published: May 2006

Changes in putrescine, spermidine and spermine concentrations in potato (Solanum tuberosum L.) leaves stressed either with cadmium, with the fungal pathogen Phytophthora infestans Mont. (de Bary) or with both simultaneously were investigated. The leaves of two cultivars, Bintje and Bzura, respectively susceptible and resistant to P. infestans were examined. The level of of putrescine did not change under any stress conditions. Cadmium stress caused at least a 2‐fold increase in spermidine and spermine concentrations in susceptible leaves. In resistant leaves there was a 4‐fold increase in spermidine and a decrease in spermine. The pathogenic stress produced similar changes in polyamine concentrations, i. e. with differences between the cultivars. The double stress induced antagonistic alterations in the concentrations of spermidine and spermine.
The seed proteins of white spruce and their mobilization following germination
Authors: Gifford David J. , Tolley Maralee C.
Published: May 2006

Buffer‐soluble proteins that have subunit molecular weights, in the presence of sodium dodecyl sulphate (SDS), of 47, 31 and 27 kilodaltons (kDa) form the major storage proteins in the mature white spruce [Picea glauca (Moench) Voss] seed. These proteins were found mainly in the megagametophyte. but smaller amounts were identified in the embryo. Following the completion of germination, this reserve was rapidly hydrolyzed in both tissues and probably plays a major nutritional role in the germinated seed. Buffer‐insoluble proteins were also found in megagametophytes and embryos from the mature seed. These proteins were soluble in buffer only if SDS was present. Predominant in this class of proteins were several that have a subunit molecular weight and structure that is characteristic of seed crystalloid storage proteins; the subunits were shown to be heterodimers with polypeptide molecular weights in the 33 kDa to 37 kDa and 23.5 kDa to 25 kDa ranges. This reserve was rapidly hydrolyzed in the germinated seed. Storage protein hydrolysis was accompanied by a significant increase in the soluble amino acid pool in both megagametophytes and embryos. Cell‐free extracts of mature seed megagametophytes and embryos contained leucine‐naphthylamidase (leuNAase) activity. Following germination. this activity was maintained at a constant level in megagametophytes but increased substantially in embryos.
Photosynthetic response of Eragrostis tef to temperature
Authors: Kebede H. , Johnson R. C. , Ferris D. M.
Published: May 2006

Photosynthetic characteristics of leaves of tef, Eragrostis tef (Zucc.) Trotter, plants, grown at 25/15°C (day/night), were measured at temperatures from 18 to 48°C. The highest carbon exchange rates (CER) occurred between 36 and 42°C. and averaged 27 μmol m−2 s−1. At lower or higher temperatures, CER was reduced, but the availability of CO2 to the mesophyll, measured as internal CO2 concentration, was highest when temperatures were above or below the optimum for CER. In addition, CER and stomatal conductance were not correlated, but residual conductance was highly correlated with CER (r = 0.98). In additional experiments, relative 13C composition for leaf tissue grown at 25, 35 and 45°C averaged ‐14.4 per mille, confirming that tef is a C4 grass species. Dry matter accumulation was higher at 35 than at 25, and lowest at 45°C. Leaf CER rates increased hyperbolically with increased light when measured from 0 to 2000 μmol m−2 s−1 PPFD. The highest CER, 31.8 μ‐mol m‐2 s−1, occurred at 35°C and 2000 μmol m−2 s−1 PPFR. At high light, CER at 25 and 35°C were nearly equal because of higher stomatal conductance at 25°C. Residual conductance was, however, clearly highest at 35°C compared to 25 and 45°C treatments. Stomatal conductance and residual conductance were not correlated in either set of experiments, yet residual conductance was always highest when temperatures were between 35 and 42°C across experiments, suggesting that internal leaf photosynthetic potential was highest across that temperature range.
The death hormone hypothesis
Authors: Engvild K. C.
Published: May 2006

The ‘death hormones’ or monocarpic senescence factors are hypothetical substances transported from the fruits to the vegetative parts of the mother plant, where they may stop growth, activate senescence, remobilize nutrients. and finally lead to the death of the plant. Death hormones could well be derivatives of jasmonic acid, 4‐chloroindoleacetic acid, or other chlorine compounds.
Density‐dependent interactions between seedlings of Dactylorhiza majalis (Orchidaceae) in symbiotic in vitro culture
Authors: Rasmussen H. , Johansen B. , Andersen. T. F.
Published: May 2006

Growth of the heterotrophic seedlings of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. (Orchidaceae) in vitro with a symbiotic fungus (Rhizoctonia sp.) is density‐dependent, even at densities that are not high enough to exploit the growth medium fully. Competition was two‐sided; increasing density among seedlings did not increase size inequality between them. The slowly growing and smaller seedlings are normally more likely to die than the bigger ones, but mortality was not increased by higher density within the studied range. Growth depression by neighbouring seedlings is independent of their physical distance but varies with the total number of seedlings sharing the same culture dish and the same mycelium.

Therefore, if the growth‐promoting effects of different fungi or treatments are to be compared in future work, the density of planting in the culture dishes should be comparable.
An exo‐β‐d‐glucanase derived from Zea coleoptile walls with a capacity to elicit cell elongation
Authors: Labrador Emilia , Nevins Donald J.
Published: May 2006

Cell wall proteins were extracted from maize coleoptiles, Zea mays L. B37 x MO 17, with high concentrations of LiCl. Ion‐exchange, chromatofocusing and gel‐filtration chromatography were employed extensively to purify exo‐β‐glucanase activity from the extract. The purified enzyme functioned as an exo‐(1→3)‐β‐glucanase (E.C. 3.2.1.58) and as a glucosidase (E.C. 3.2.1.21) capable of extensive hydrolysis of the native Zea wall (1→3), (1→4)‐β‐d‐glucan, yielding glucose as the final product. The exoglucanase also enhances elongation of maize coleoptile sections in both the presence and absence of exogenous IAA.
Selected cell wall proteins from Zea mays: Assessment of their role in wall hydrolysis
Authors: Labrador Emilia , Nevins Donald J.
Published: May 2006

Coleoptile cell wall proteins from Zea mays L. hybrid B 37 × Mo 17 were extracted and fractionated. Three enzymes identified in that extract were examined to determine their role in cell wall hydrolysis with a goal of evaluating the extent to which they participated in autohydrolytic reactions. Two separate proteins were identified as endo‐ and exo‐glucanases. Incubation of these enzymes with heat inactivated cell walls, liberates products derived from the constitutive (1→3), (1→4)‐β‐d‐glucan. The release of sugars from walls resembles that of cell wall autolysis. A third cell wall protein degraded polysaccharides in a more general manner, releasing carbohydrates containing xylose, arabinose, galactose and glucose. Polyclonal antibodies raised against the exoglucanase protein suppressed autolytic reactions of isolated cell wall.
Interaction of gibberellic acid and photoperiod on leaf sheath elongation in normal and gibberellin‐insensitive genotype of wheat
Authors: Junttila Olavi
Published: May 2006

Effect of gibberellic acid (GA3) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin(GA)‐insensitive (cv. Siete Cerros) genotype of wheat (Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA3 both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA3 was additive, and there was no statistically signficant interaction between photoperiod and GA3 concentrations. Leaf sheath length in cv. Siete Cerros was not significantly affected by GA3 under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin.
Effects of flooding under hydrostatic pressure on the respiratory metabolism of germinated wheat seeds
Authors: Malki Eli , Waisel Yoav , Pesis Edna
Published: May 2006

Germinated wheat seeds (Triticum aestivum L. cv. Barqai) that had been subjected to short hydrostatic pressure treatments (0.3–1.2 MPa) changed their normal metabolism into one which is characterized by a high ethanol production, a low O2 consumption and a low CO2 evolution. Alcoholic fermentation could account for ca half of the CO2 evolved from the pressurized seeds. The level of acetaldehyde was low, though significantly higher in the pressurized seeds than in the controls. Subjection of wheat seeds to osmotic stress under aerobic conditions lowered their O2 uptake and CO2 evolution but did not induce ethanol production. Exposure of pressurized seeds to NaCl stress did not alter their ethanol production beyond that which had been induced by pressure. Ethanol production by pressurized seeds increased following either the addition of sucrose or by excision of the embryos from the endosperms. More electrolytes leaked into the embedding solution from pressurized seeds than from control seeds. Exogenous ethanol was toxic to wheat seeds at concentrations as low as 343 mM. The effects of hydrostatic pressure and of the consequently induced ethanol production on the mortality of flooded seeds is discussed.
Changes in ribosome population and in nucleic acids during breaking of dormancy and development of apple flower buds
Authors: Li Qin‐Bao , Liu Liang‐Huan , Liang Hou‐Guo
Published: May 2006

Changes in ribosome population, RNA species and DNA composition in flower buds of apples (Malus pumila Mill. cvs Ralls and White winter pearmain) were investigated during breaking of dormancy and development. After bursting of flower buds, total ribosomes increased approximately 4‐fold, and the polyribosomal fraction increased from 66% to 94% of total ribosomes. The newly synthesized ribosomes were identified by incorporation of radioactive precursor. The observed decrease in specific radioactivity of the monoribosomes is caused by the recruitment of monoribo‐somes into polyribosomes after breaking of dormancy.

In both cultivars, the 25S and 18S rRNA peaks increased to a high level on April 8. The peaks of low molecular weight RNA were apparently increased after initial swelling of the flower buds. The DNA of flower buds was separated into three bands by electrophoresis. The median band is the main band of nuclear DNAs. The ahead band and the slow‐moving band are satellite components of nuclear DNAs, and they obviously rose after initial swelling of the flower buds. On April 8, when the flower buds had opened, two other small DNA bands could be detected. These results suggest that the changes in level of different ribosome populations, RNA species and DNA composition are related to dormancy breaking development of apple flower buds.