bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of the lipid body lipase of Pinus eduUs and electrophoretic purification of its 64 kDa subunit
Authors: Hammer Mark F. , Murphy J. Brad
Published: May 2006

Lipase (triacyiglycerol acylhydrolase, EC 3.1.1.3) in oilseeds can be associated with either the lipid body or glyoxysomal membrane and can have various pH optima and substrate specificities. There is conflicting evidence for the subcellular location of lipase in gymnosperms, and little information exists on its activity characteristics. In this report, Pinus edulis (pinyon) was found to have an acid lipase, which was associated with the lipid body fraction and the activity of which increased during germination. Active lipase from the solubilized lipid body membrane was determined by gel permeation chromatography to have a molecular weight of 260 000. Further attempts to purify the active enzyme were unsuccessful. A lipid body membrane protein of 64 kDa which increased in parallel with lipase activity during germination was isolated by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis. excised, and polyclonal antibodies were made against it. Using these antibodies, active lipase was immunoprecipitated from solution, thus indicating that the 64 kDa protein is a subunit of the lipase. Pinus edulis lipase had a pH optimum of ca 4.5. and it exhibited little specificity for triacyiglycerol substrates in vitro. The lipase was specific in activity against fluorometric substrates, with the highest activity against methyl‐umbelliferyl laurale. Lipase activity was inhibited by high concentrations of non‐ionic detergent. This lipid body acid lipase appears to be primarily responsible for lipid hydrolysis during pinyon germination.
Can plants exposed to SO2 excrete sulfuric acid through the roots?
Authors: Kaiser W. M. , Höfler M. , Heber U.
Published: May 2006

Hydroponically grown pea plants (Pisum sativum L., cv. Kleine Rheinländerin) and barley seedlings (Hordeum vulgare L., cv. Gerbel) were fumigated for several days with 1 or 2 μl l−1 SO2. Both species accumulated sulfate during fumigation, although the nutrient medium lacked sulfate. In pea, SO2‐dependent sulfate accumulation in different plant parts accounted for 60 percent of the SO2 sulfur which, as calculated from a determination of boundary and stomatal flux resistances had entered the leaves. Up to 55% of the air‐borne sulfate was translocated from pea leaves to roots during the period of fumigation, but no or only little sulfate was excreted into the nutrient solution. In contrast, barley retained sulfate in the leaves, and sulfate translocation from shoot to the root system could not be observed. In both species, protons were excreted by the roots. In fumigated plants, proton loss was higher than in untreated controls in pea, but not in barley. In pea, SO2‐dependent proton loss into the medium accounted for up to 50% of the sulfuric acid formed from SO2. Proton excretion was strongly dependent on potassium availability in the nutrient medium. Cation uptake by the plants during fumigation was sufficient to compensate for proton loss, suggesting proton/cation exchange at the interface between root and medium. We conclude that by oxidation to sulfuric acid, plants are capable of detoxifying SO2 taken up by the leaves. Depending on plant species, either both protons and sulfate anions can be exported from the leaves, or the proton load on leaf cells can be relieved by proton/cation exchange at the plasmalemma. Finally, the problem of airborne plant acidification may be solved by proton/cation exchange at the level of roots. The burden of acidification is then shifted from the plant to the nutrient medium. Appreciable amounts of sulfate can be excreted neither by pea nor by barley plants.
Effects of calmodulin antagonists on auxin‐stimulated proton extrusion in Avena sativa coleoptile segments
Authors: González‐Darós Francisco , Carrasco‐Luna Joaquin , Calatayud Angeles , Salguero Julio , del Valle‐Tascón Secundino
Published: May 2006

The effect of the 5 calmodulin (CaM) antagonists trifluoperazine (TFP). compound 48/80, N‐(6‐aminohexyl)‐naphthalenesulfonamtde (W‐5), N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalenesulfonamide (W‐7), and calmidazolium on auxin‐dependent medium acidification was investigated in abraded segments of Avena sativa L. cv. Victory I. Buffering capacity, Asn content, and changes in pH of bathing solutions were measured in the presence of these inhibitors. When coleoptiles were treated with TFP or compound 48/80, the Asn content and the buffering capacity increased, thus suggesting that plasma membrane permeability was modified. On the contrary. the effect of calmidazolium, W‐5. and W‐7 on Asn release and buffering capacity was rather low; only small effects being observable at the highest concentration employed. Calmidazolium and W‐7 strongly inhibited auxin‐dependent medium acidification. W‐5 did not affect medium acidification. The specificity of these CaM antagonists and their effects on medium acidification are discussed. The data adduced is consistent with the working hypothesis which postulates an essential role for the Ca2+‐CaM system on auxin‐dependent medium acidification.
Sucrose and fructan metabolism in wheat roots at chilling temperatures
Authors: Santoiani C. S. , Tognetti J. A. , Pontis H. G. , Salerno G. L.
Published: May 2006

Sucrose and fructan metabolism were studied in wheat (Triticuin aotiirum L. cv. Tribal 800) roots during a period at chilling temperature. Enzyme activities related to fructan and sucrose metabolism were measured. Sucrose‐sucrose fructosyl transfer‐ase (EC 2.4.1.99) activity increased more than 25‐fold when plants were cooled to 4°C. Sucrose synthase (EC 2.4.1.13) and sucrose‐phosphate synthase (EC 2.4.1.14) activities also increased, but low temperatures had no significant effect on invertaso (EC 3.2.1.26) or on fructan hydrolase (EC 3.2.1.26) activities. The accumulation pattern of fructan in roots was different to that in leaves. In roots chilling stimulated the synthesis of fructans of high degree of polymerization.
Gaseous diffusive properties of soybean nodules cultured with non‐ambient pO2
Authors: Atkins Craig A. , Hunt Stephen , Layzell David B.
Published: May 2006

Measurements of the short‐term response of nodulated roots of soybean (Glycine max L. Merr, cv. Harosoy: Bradyrhizobium japonicum USDA 16) to rapid changes in surrounding pO2 indicate that their ability to reversibly adjust gaseous diffusive resistance is retained whether plants are cultured in rhizospheres of very low (2.8%) or very high (61.2%) pO2. Thus the capacity for reversible short‐term diffusion adjustment is additional to structural changes in the fixed diffusional barriers of nodules which allow their continued fixation of N2 in unfavourably high or low external pO2. Anatomical evidence, involving quantitative measurement of intercellular spaces in the cortical tissues using electron microscopy of thin sections, indicates that the major fixed diffusional barrier is a boundary layer of cells in the inner cortex which may be as small as one cell thick in nodules from 2.8% O2 to 5 or 6 cells thick, and almost completely devoid of intercellular spaces, in those from 61.2% O2. The data are interpreted to indicate that the variable diffusion harrier is distinct from the boundary layer and is most likely to be a property of cells and/or intercellular spaces inside the boundary layer of the nodule cortex.
Partial purification and characterization of stomatal phosphoenolpyruvate carboxylase from Vicia faba
Authors: Denecke Martin , Schulz Margot , Fischer Christoph , Schnabl Heide
Published: May 2006

Stomatal phosphoenolpyruvate carboxylase (PEPCase EC 4.1.1.31), extracted from abaxial epidermal peels of Vicia faba L. cv. Frühe Weiβkeimige, was partially purified by ammoniumsulfate precipitation, and molecular sieve (Sepharosc S‐400) and ion exchange (DEAE‐Sepharose) chromatography. The partially purified enzyme, essentially free of a PEPCase isoform existing in mesophyll and epidermal cells, had a specific activity of 300 nkat mg‐1 protein at 25°C. Western immunoblot analysis revealed that the stomatal enzyme had two bands (M: of 110000 and 112000), crossreacting with PEPCase antibodies raised against PEPCase from Ka‐lanchoe daigremontiana. The native molecular mass of the enzyme (467000) points to a tetrameric subunit structure. The temperature optimum was found to be 35°C; cold treatments of PEPCase before assaying were accompanied by inactivation. The energy of activation was calculated to 51 kJ mol‐1. The kinetic behaviour of the enzyme at fixed MgCl2 concentrations is characterized by a pH optimum between pH 8.0–8.2 with or without 1 mM malate or 5 mM glucose‐6‐phosphate (Glc‐6‐P), but a combination of both effectors resulted in a shift of the optimum to pH 7.6. The enzyme showed a pH sensitive inhibition by 1 mM malate and an activation by Glc‐6‐P. At low pH (6–7), Glc‐6‐P was able to compensate for the malate induced inhibition of the enzyme. Malate and Glc‐6‐P both affected Km(PEP), drastically and influenced Vmax at pH 7, but not at pH 8.3. The inhibition constant of malate was determined to be 1.2 mM at pH 7. From the Dixon plot, a competitive inhibition of malate was assumed under defined assay conditions.
Regulation of ethylene biosynthesis after short‐term heat treatment in etiolated pea stems
Authors: Steed Candice L. , Harrison Marcia A.
Published: May 2006

Incubation of plant tissues at a constant elevated temperature greatly inhibits both basal and wound ethylene production. However, recovery from heat treatment is relatively rapid and is followed by stimulated ethylene production. The present investigation examines the kinetics of ethylene production after short‐term heal treatment and the regulation of heat‐altered ethylene production. Subapical stem segments of 7‐day‐old etiolated pea L. cv. Alaska) seedlings were analyzed for ethylene production, 1‐aminocyclopropane‐l‐carboxylic acid (ACC) oxidation, and ACC and l‐(malonylamino)cyclopropane‐l‐carboxylic acid (MACC) content after a 2‐min 40°C heat pulse. The short‐term heat pulse transiently inhibited ethylene production and ACC oxidation accompanied by a slight ACC accumulation within a 30‐min time period. Conjugation to MACC did not appear to play an integral role in heat‐regulated ethylene production. It was concluded that the major factor affecting ethylene production after heat treatment is the temporary inactivation of ACC oxidation. The possible roles of ACC synthase, ACC oxidase and lipoxygenase in regulating ethylene production after heat treatment are discussed.
Correlation of betacyanin synthesis with cell division in cell suspension cultures of Phytolacca americana
Authors: Hirano Hiroshi , Komamine Atsushi
Published: May 2006

In suspension cultures of Phytolacca americana, betacyanin accumulation was reduced when cell division was inhibited by treatment with various inhibitors of DNA synthesis or anti‐microtubule drugs. Aphidicolin (APC), an inhibitor of DNA synthesis, reduced the incorporation of radioactivity from labeled tyrosine into betacyanin, but the incorporation of radioactivity from labeled 3,4‐dihydroxyphenylalanine (DOPA) into betacyanin was not affected by similar treatments. Propyzamide, another anti‐microtubule drug, reduced incorporation of radioactivity from tyrosine and DOPA into betacyanin. However, the rate of incorporation from DOPA was higher than that from tyrosine. The results suggest that inhibition of betacyanin accumulation in Phytolacca americana cells by APC and propyzamide is due to suppression of the reaction converting tyrosine to DOPA, which may be closely related to cell division.
Loblolly pine seed dormancy. I. The relationship between protein synthesis and the loss of dormancy
Authors: Schneider Wendy L. , Gifford David J.
Published: May 2006

Embryos from the mature unstratified loblolly pine (Pinus taeda L.) seeds used in this study were nondormant: however, they failed to germinate in situ because of constraints imposed by the surrounding tissues. During a stratification period of 35 days of moist chilling at 2°C, seed germinability increased from 19 to 76%. The total lipid content of the megagametophyte did not change during stratification, whereas the total protein content of both megagametophyte and embryo was more variable. The rate of synthesis of buffer soluble proteins in these two tissues increased and electrophoretic analysis showed that while similar proteins were synthesized during the stratification period, changes in the patterns of synthesis of some proteins did occur. In both the embryo and megagametophyte the synthesis of a set of proteins with molecular masses below 46 kDa decreased markedly after 14 days of chilling (DOC). In the megagametophyte, the synthesis of a more diverse set of proteins with molecular masses ranging from 16 to 78 kDa increased after 14 DOC. It is noteworthy that these changes in the patterns of protein synthesis coincided with the greatest relative increase in seed germinability of 35%.
Methionyl sulfoxide content and protein‐methionine‐S‐oxide reductase activity in response to water deficits or high temperature
Authors: Ferguson David L. , Burke John J.
Published: May 2006

Cellular injury resulting from partially reduced oxygen species (superoxide, peroxides and/or hydroxyl radicals) or singlet oxygen frequently increases during environmental stress. Because protein methionine residues are susceptible to oxidation, we investigated the effects of water‐deficit stress and high temperature stress on the content of oxidized methionyl residues [Met(O)] in leaves. Leaf proteins from water‐deficit‐stressed cotton (Gossypium hirsutum L. cv. Paymaster HS‐26). pea (Pisum sativum L. cv. Progress No. 9). wheat (Triticum aestivum L. em. Thell. cv. Len) and potato (Solanum tuberosum L. cv. Norgold M) and from the leaves of high‐temperature‐stressed pea seedlings were evaluated. The activity of protein methionine‐S‐oxide reductase (PrMSR). an enzyme responsible for re‐reducing oxidized methionyl residues, was also determined. Protein Met(O) content did not change in response to either water‐deficit or high temperature stress. PrMSR activity decreased in pea and cotton leaves, remained unchanged in potato leaves and significantly increased in leaves of water‐deficit‐stressed wheat. The findings demonstrate that these plants have developed protection systems that effectively maintain stable levels of oxidized methionyl residues in leaf proteins despite exposure to severe water and high temperature stress. The findings also suggest that changes in PrMSR activity do not fully account for the observed maintenance of protein methionyl sulfoxide content at constant levels.
Responses of soybean to ammonium and nitrate supplied in combination to the whole root system or separately in a split‐root system
Authors: Chaillou Sylvain , Rideout James W. , Raper C. David , Morot‐Gaudry Jean‐François
Published: May 2006

To address the questions of whether allocation of carbohydrates to roots is influenced by ionic form of nitrogen absorbed and whether allocation of carbohydrates to roots in turn influences proportionality between NH4+ and NO3− uptake from mixed sources, NH4+ and NO3− were supplied separately to halves of a split‐root hydroponic system and were supplied in combination to a whole‐root system. Dry matter accumulation in the split‐root system was 18% less in the NH4+‐fed axis than in the NO3−‐fed axis. This, however, does not indicate that partitioning of carbohydrate between the two axes was different. Most of the reduction in dry matter accumulation in the NH4+‐fed axis can be accounted for by the retransport of CH2O equivalents from the root back to the shoot with amino acids produced by NH4+ assimilation. Uptake of NH4+ or NO3− by the respective halves of the split‐root system was proportional to the estimated allocation of carbohydrate to that half.

When NH4+ and NO3− were supplied to separate halves of the split‐root system, the cumulative NH4+ to NO3− uptake ratio was 0.81. When supplied in combination to the whole‐root system, the cumulative NH4+ to NO3− uptake ratio was 1.67. Thus, while the shoot may affect total nitrogen uptake through the export of carbohydrates to roots, the shoot (common for halves of the split‐root system) apparently does not exert a direct effect on proportionality of NH4+ and NO3− uptake by roots. For whole roots supplied with both NH4+ and NO3−, the restriction in uptake of NO3− may involve a stimulation of NO3− efflux rather than an inhibition of NO3− influx. While only the net uptake of NH4+ and NO3− was measured by ion chromatography, monitoring at approximately hourly intervals during the first 3 days of treatment revealed irregularly occurring intervals of both depletion (net influx) and enrichment (net efflux) in solutions. In the case of NH4+, numbers of net efflux events were similar (21 to 24 out of 65 sequential sampling intervals) whether NH4+ was supplied with NO3− to whole‐root systems or separately to an axis of the split‐root system. In the case of NO3−, however, the number of net efflux events increased from 8 when NO3− was supplied to a separate axis of the split‐root system to between 19 and 24 when NO3− was supplied with NH4+ to whole‐root systems.
Plasma membrane lipid metabolism of petunia petals during senescence
Authors: Borochov A. , Cho M. H. , Boss W. F.
Published: May 2006

The specific activities of 6 enzymes, which are involved in the synthesis and catabolism of membrane lipids, were monitored in plasma membranes isolated from petunia petals during senescence. These included phosphatidylinositol (PI) kinase (EC 2.7.1.67), phosphatidylinositol monophosphate (PIP) kinase (EC 2.7.1.68). diacylglycerol (DAG) kinase (EC 2.7.1.107), phospholipase A (EC 3.1.1.4) and PIP‐ and PIP2‐phospholipase C˙(EC 3.1.4.3). Using endogenous substrate, the [32P]PA and [32P]PIP2 formation increased to 140 and 200%, respectively, of the day 1 value by 4 days after harvest. There was no significant change in [32P]PIP formation during the same time period. On the fifth day the petals wilted and the [32P]PA and [32P]PIP formation declined significantly. In contrast, the [32P]PIP2 formation remained high in the day 5 petals. When the lipid kinase activities were assayed in the membranes in the presence of exogenous substrate the specific activity of all of the enzymes increased. and the changes in [32P]PA production over the 5‐day period were similar to those observed with endogenous substrate. When exogenous PI and PIP were added, however, there was no longer an increase in [32P]PIP2 formation by plasma membranes of day 4 petals and [32P]PIP formation significantly decreased. The relative decrease in PIP and PIP2 formation by day 4 membranes when exogenous substrate was added may have resulted from differences in the lipase activities in the day 1 and day 4 membranes. The plasma membrane A‐type phospholipase activity increased throughout the 5 day period, and phospholipase C activity increased two‐fold between day 1 and day 4. Such changes in the metabolism of the plasma membrane lipids during flower senescence would affect the ability of the petals to use inositol phospholipid‐based signal transduction pathways.
Gene expression and carbohydrate content during stolon to tuber transition in potatoes (Solanum tuberosum)
Authors: Visser Richard G. F. , Vreugdenhil Dick , Hendriks Theo , Jacobsen Evert
Published: May 2006

In using an efficient and synchronised in vitro tuberisation system the transition of axillary buds from stolons to tubers in Solanum tuberosum L. cv. Bintje was followed. After 5 or 6 days on tuber‐inducing medium all axillary buds had formed tubers which increased in size until the experiment was ended at day 10. Concomitantly with the visible appearance of tubers the fresh weight of the axillary buds increased as well as their starch content. Soluble sugar content, notably glucose, increased until tuberisation occurred and dropped after that. In the daily sampled explants gene expression was studied at several levels. RNA was isolated from the different explants during the whole tuberisation experiment and northern blots were probed with cDNAs encoding genes involved in starch‐ and patatin‐biosynthesis. It was shown that in the very early stages of development hardly any transcript could be detected. Only one day before visible swelling occurred were clear signals obtained for all the genes investigated. Although it was evident that coordinate expression of starch biosynthetic genes did occur, it was not in a similar fashion for all the genes. Sucrose synthase and ADPG‐pyrophosphorylase B were expressed in an identical fashion which was different from ADPG‐pyrophosphorylase S, granule‐bound starch synthase and branching enzyme. The RNA levels of these three latter genes reached a maximum at day 5, remaining constant until the experiment was finished. The transcript levels of sucrose synthase and ADPG‐pyrophosphorylase B reached their highest level at day 5 after which they dropped to a lower level at day 10. Patatin gene expression was clearly different from that of the starch biosynthetic genes: it steadily increased from day 4 until the end of the experiment. Enzyme activities of sucrose synthase. ADPG‐pyrophosphorylase and branching enzyme confirmed the RNA expression data and showed that ADPG‐pyrophosphorylase enzyme activity reached a maximum at day 4 after which it dropped. The other two enzyme activities could be detected at or one day after tuberisation occurred and increased until the experiment was ended.
Carbon allocation in developing spruce needles. Enzymes and intermediates of sucrose metabolism
Authors: Hampp Rüdiger , Egger Bernd , Effenberger Susanne , Einig Werner
Published: May 2006

In lyophilized needles of Norway spruce (Picea abies [L.] Karsten) and starting from bud break, we determined enzyme activities (sucrose phosphate synthase [SPS; EC 2.4,1.14]. sucrose synthase [SS; EC 2.4,1.13]. acid invertase [AI; EC 3.2,1.26]) and intermediates (starch, sucrose, glucose, fructose; fructose 6‐phosphate, fructose 2.6‐bisphosphate [F26BP]) of carbohydrate metabolism together with needle weight, shoot length, chlorophyll and protein. For up to 110 days after bud break, samples were taken twice a week from about 25‐year‐old trees under field conditions. At least three periods can be distinguished during needle maturation. During the first period (up to 45 days after bud break) Al showed the highest extractable activity. This coincided with very high levels of F26BP (up to 11 pmol [mg dry weight]−1) and a transient increase of starch in parallel to a decrease of sucrose. The interval between 45 and 70 days after bud break was characterized by high SS activity (ratio of fructose/glucose >1), much decreased levels of F26BP (down to below 1 pmol [mg dry weight]−1), and a pronounced increase in the dry weight/fresh weight ratio. In parallel, starch declined and soluble carbohydrates increased. Finally, needle maturation was characterized by decreasing SS and continuously increasing SPS activities, so that the ratio of SPS/SS increased more than 6‐fold. AI. however, did not decline with maturation. Changes in pool sizes of metabolites and enzyme activities (AI. SPS) are consistent with current concepts on sink/source transition. SS is obviously important with regard to the synthesis of structural polysaccharides.
Effects of gamma irradiation on the plasma membrane of suspension‐cultured apple cells. Rapid irreversible inhibition of H+‐ATPase activity
Authors: Dong Chang‐Zhi , Montillet Jean‐Luc , Triantaphylidès Christian
Published: May 2006

The effects of ionizing radiation, used in post‐harvest treatment of fruit and vegetables. were investigated on cultured apple cells (Pyrus malus L. cv. Royal Red) on a short‐term period. Irradiation (2 kGy) induced an increase of passive ion effluxes from cells and a decrease of cell capacity to regulate external pH. These alterations are likely due to effects on plasma membrane structure and function and were further investigated by studying the effects of irradiation on plasma membrane H+‐ATPase activity. Plasma membrane‐enriched vesicles were prepared and the H+‐ATPase activity was characterized. Irradiation of the vesicles induced a dose dependent inhibition of H+‐ATPase activity. The loss of enzyme activity was immediate, even at low doses (0.5 kGy), and was not reversed by the addition of 2mM dithiothreitol. This inhibition may be the result of an irreversible oxidation of enzyme sulfhydryl moieties and/or the result of changes induced within the lipid bilayer affecting the membrane‐enzyme interactions. Further analysis of the H+‐ATPase activity was carried out on vesicles obtained from irradiated cells confirming the previous results. In vivo recovery of activity was not observed within 5 h following the treatment, thus explaining the decrease of cell capacity to regulate external pH.

This rapid irreversible inhibition of the plasma membrane H+‐ATPase must be considered as one of the most important primary biochemical events occurring in irradiated plant material.
Sensitivity to gravistimulus of lentil seedling roots grown in space during the IML 1 Mission of Spacelab
Authors: Perbal G. , Driss‐Ecole D.
Published: May 2006

The gravitropic curvature of seedlings of lentil (Lens culinaris L. cv. Verte du Puy) grown in microgravity and stimulated on the 1 g centrifuge for 5 to 60 min was followed by time lapse photography in near weightlessness in the frame of the IML 1 Mission of Spacelab. In microgravity, the root tip could overshoot the direction of the 1 g acceleration after bending, whereas roots stimulated on the ground did not reach the direction of the gravity vector. On earth, there is, therefore, a regulation (inhibition of root curvature), which is gravity dependent. In space, the initial rate of curvature as well as the amplitude of curvature varied as a function of the quantity of stimulation (Q, in g min). For a given quantity of stimulation, the rate of curvature remained constant for 80 min. The bending has thus a certain inertia, which is linked to the mechanism of differential growth. The presentation time (Tp) of the lentil root was calculated by extrapolation to zero curvature of the regression line representing either the initial rate of curvature or the amplitude of curvature at 2 h after the end of the stimulation. Tp was estimated to 27 and 26 s. respectively. These results confirm the values of Tp obtained by clinostats, and they also lead to a reconsideration of the causes of the kinetics of root curvature.
Chilling sensitivity of the frost‐tolerant potato Solanum commersonii
Authors: Griffith Marilyn , Boese Steven R. , Huner Norman P.A.
Published: May 2006

Frost tolerance has been reported in the shoots of wild, tuberiferous potato species such as Solanum commersonii when the plants are grown in either field or controlled conditions. However, these plants can survive as underground tubers and avoid unfavorable environmental conditions altogether. As such, leaf growth and photosynthesis at low temperature may not be required for survival of the plants. In order to determine the temperature sensitivity of S. commersonii shoots, we examined leaf growth, development and photosynthesis in plants raised at 20/16°C (day/night). 12/9°C and 5/2°C. S. commersonii leaves grown at 5°C exhibited a marked decrease in leaf area and in total chlorophyll (Chl) content per leaf area when compared with leaves grown at 20°C. Furthermore, leaves grown at 5°C did not exhibit the expected decrease in either water content or susceptibility to low‐temperature‐induced photoinhibition that normally characterizes cold acclimation in frost‐tolerant plants. Measurements of CO2‐saturated O2 evolution showed that the photosynthetic apparatus of 5°C plants was functional, even though the efficiency of photosystem II photochemistry was reduced by growth at 5°C. A decrease in the resolution of the M‐peak in the slow transients for Chl a fluorescence in leaves grown at 12 and 5°C and in all leaves exposed to high light at 5°C indicated that low temperature significantly affected processes on the reducing side of QA, the primary quinone electron acceptor in photosystem II. Thus S. commarsonii exhibits the characteristics of a plant that is limited by chilling temperatures. Although S. commersonii can tolerate light frosts, its sensitivity to chilling temperatures may result in shoot dieback in winter in its native habitat. The plants may avoid both chilling and freezing temperatures by overwintering as underground tubers.
Characterization of an iron‐containing superoxide dismutase from a higher plant, Citrus limonum
Authors: Almansa Maria S. , del Rio Luis A. , Sevilla Francisca
Published: May 2006

An iron‐containing superoxide dismutase (SOD, EC 1.15.1.1) was fully characterized from leaves of the higher plant Citrus limonum R. cv. Verna. This enzyme is the first iron‐containing SOD to be characterized in the plant family Rutaceae. The purified Fe‐SOD has a molecular mass of about 47 kDa and is composed of two non‐covalently joined equal subunits. The amino acid composition determined for the enzyme was compared with that of a wide range of SODs and had highest degree of homology with the Fe‐SODs from Brassica campestris and Nuphar luteum. The enzyme was more labile at high temperatures than some eucaryotic and procaryotic Fe‐SODs. It showed a maximum stability at pH 7.8. The sensitivity of the enzyme to cyanide, hydrogen peroxide and o‐phenanthroline was similar to those reported for other Fe‐SODs. but the lemon enzyme was comparatively resistant to H2O2. By kinetic competition experiments, the rate constant for the disproportionation of superoxide radicals by lemon Fe‐SOD was found to be 1.9 × 109M−1 s−1 at pH 7.8 and 25°C. A comparative study between the molecular properties of this higher plant Fe‐SOD and SODs from different origins is presented.
Development of auxin autotrophy in Nicotiana tabacum callus cultures
Authors: Szabó M. , Köves E. , Somogyi I.
Published: May 2006

Changes of auxin and ethylene metabolism of Nicotiana tabacum var. Xanthi callus were investigated in relation to auxin‐independent growth. During the habituation process, changes occur progressively in hormone metabolism in auxin‐heterotrophic tissues: the potential for the destruction of indoleacetic acid (IAA) increases, the IAA level in the cultures rises slightly, and the auxin sensitivity of the callus becomes modified. Preceding the onset of habituation, ethylene production is enhanced although the tissues retain their ability to undergo regeneration.

Gradual changes in auxin metabolism and ethylene production confirm the epigenetic character of the habituation process.
Enhancement of extractable ethylene at light/dark transition in primary leaves of paclobutrazol‐treated Phaseolus vulgaris seedlings
Authors: Tari Irma , Nagy Maria
Published: May 2006

Paclobutrazol [(2RS,3RS)‐1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1,2,4‐triazol‐1‐yl)pentan‐3‐ol], a triazole growth retardant, increased the 1‐aminocyclopropane‐1‐carboxylic acid (ACC) level and resulted in reduced ethylene production, estimated as ethylene release in a closed system or by vacuum‐extraction, in the primary leaves of Phaseolus vulgaris L. cv. Juliska seedlings exposed to light. At the light/dark transition, a definite enhancement of the endogenous ethylene level was observed by vacuum‐extraction of primary leaves of treated plants and the ethylene deficiency of retardant‐treated leaves ceased. The concentration of ACC after the light/dark transition followed the pattern for ethylene, and the increase in ACC content was paralleled by a decrease in malonyl‐ACC.

It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol‐treated bean plants, but under special environmental conditions in vivo it may reach that of the control.
Molecular responses to photooxidative stress in Pinus sylvestris. I. Differential expression of nuclear and plastid genes in relation to recovery from winter stress
Authors: Karpinski Stanislaw , Karpinska Barbara , Wingsle Gunnar , Hällgren Jan‐Erik
Published: May 2006

Inhibition of photosynthesis plays an important role during winter‐spring stress in evergreen plants such as Scots pine (Pinus sylvestris L.). In this experiment, naturally established three‐year‐old Scots pine seedlings were studied during recovery from winter stress, under natural conditions from May to the beginning of June. A comparison was made between top shoot needles exposed to sun and, prior to winter stress recovery snow‐covered, and thus more shaded side shoot needles. Chlorophyll fluorescence, photochemical and non‐photochemical quenching, pigment composition together with the Lhca2*l, Lhcbl*2, RbcS, rbcL, psbA, nad3 and cox2 gene expression were analysed. During the recovery, a general increase in the Fo/Fm ratio of chlorophyll fluorescence and in pigments was observed for both types of shoots. At the beginning of May, the Fo/Fm ratio of chlorophyll fluorescence showed that exposed top shoot needles were more photoinhibited than the snow‐covered side shoot needles. The levels of chlorophyll a and b, neoxanthin, α‐ and β‐carotene were lower, while the level of zeaxanthin was higher in top shoot needles than in side shoot needles during the whole period. On May 6, significantly higher (two‐fold) mRNA levels for Lhca2*l and Lhcbl*2 genes were detected in top shoot needles than in side shoot needles. The reverse situation for these genes was observed on May 19 with a two‐fold higher level of mRNA in side shoot needles. The transcript level was significantly higher for the Lhcbl*2 gene than for the Lhca2*l gene in both types of shoots only at the beginning of May. The mRNA level for the RbcS gene on May 4 and 6 was two‐ and four‐fold higher, respectively, in top than in side shoot needles. The transcript levels for the plastid‐encoded rbcL and psbA and for the mitochondrion‐encoded nad3 and cox2 genes were constant and similar in top and side shoot needles. The results are discussed in relation to recovery from winter‐spring stress and observed differential expression of nuclear‐ and organellar‐encoded genes.
Comparison of endogenous gibberellins in roots and shoots of elongating Salix pentandra seedlings
Authors: Olsen J. E. , Moritz T. , Jensen E. , Junttila O.
Published: May 2006

Gibberellins GA1, GA8. GA19. GA29. GA20 and GA56 (2‐epi‐GA8). were identified by combined gas chromatography‐mass spectrometry in root extracts of elongating Salix pentandra L. seedlings. The presence of GA8 was also demonstrated for the first time in S. pentandra shoots. The levels of GA1, GA8, GA19, GA20 in shoot tissue and in roots were estimated by selected ion monitoring. While the amounts of GA8 and GA19 were similar in both plant parts. the levels of the biologically active GA1 and its immediate precursor GA20. were found to be much lower in roots than in shoots.
Effects of ethylene and auxin on polyamine levels in suspension‐cultured tobacco cells
Authors: Park Ky Young , Lee Sun Hi
Published: May 2006

The effects of ethylene and auxin on polyamine levels were studied in suspension‐cultured cells of tobacco (Nicotiana tabacum. L). Treatment of 4‐day‐cultured cells with ethylene increased the levels of spermidine and spermine. The activities of arginine decarboxylase (ADC; EC 4.1.1.19), ornithine decarboxylase (ODC: EC 4.1.1.17), and S‐adenosylmethionine decarboxylase (SAMDC: EC 4.1.1.50) rapidly increased between 3 and 12 h. An auxin, indole‐3‐acetic acid (IAA), increased polyamine levels and activities of ADC, ODC and SAMDC. The spermine level continued to increase significantly during a 24‐h incubation with IAA. The increases in polyamine accumulation induced by ethylene were partially offset by an inhibitor of ethylene action, 2,5‐norbornadiene. It is suggested that the auxin‐induced polyamine accumulation occurred directly, without metabolic competition between ethylene and polyamine biosynthesis, and indirectly, through auxin‐induced ethylene formation.
Geibberllin and temperature influence carbohydrate content and flowering in Phalaenopsis
Authors: Chen Wen‐Shaw , Liu Ho‐Yih , Liu Zin‐Huang , Yang Leuan , Chen Wen‐Huei
Published: May 2006

When Phalaenopsis amabilis is grown under high temperature (30/25°C, day/night), flowering is blocked, and this can be reversed by gibberellin A3 (GA3) treatment. Associated with GA3 treatment under high temperature are increases in sucrose, glucose and fructose as compared with warm‐treated plants. Spraying with sucrose solution alone caused leaf epinasty in plants grown under high temperature. Epinasty was released by about 9 days of GA3 treatment. In GA3‐treated plants under high temperatures, sucrose application to the source leaves led to an increase in sugar content in both leaves and inflorescence. In contrast, although in warm‐treated plants sucrose application to the source leaves increased sugar content in the leaves, it did not increase sucrose content in the inflorescence. These results corroborate our hypothesis that in Phalaenopsis GA3 stimulates sink activity in the apical meristem and promotes the translocation of sucrose from source leaves to the apex of the inflorescence, where it accumulates. GA3 treatment led to an increase in sucrose synthase activity and had no effect on invertase activity.
Protochlorophyll(ide) forms in hypocotyls of dark‐grown bean (Phaseolus vulgaris)
Authors: McEwen Birgitta , Sundqvist Christer , Younis Suhila
Published: May 2006

The protochlorophyll(ide) forms and plastid ultrastructure were investigated in hypocotyls of dark‐grown seedlings of kidney bean (Phaseolus vulgaris L. cv. Brede zonder draad). By deconvolution of the fluorescence emission spectra into Gaussian components three protochlorophyll(ide) forms were found with maxima at 633, 642 and 657 nm, respectively. The ratio of protochlorophyll(ide) emitting at 657 nm to protochlorophyll(ide) emitting at 633 nm decreased downwards the hypocotyl. The gradient was established already after 4 days in dark‐grown Phaseolus and was also seen in hypocotyls of 7‐day‐old dark‐grown plants of 8 other species. Ultrastructural observations revealed a plastid developmental sequence along the hypocotyl. Plastids in the upper parts of the hypocotyl contained prolamellar bodies typical of etiolated leaves while those in the lower parts contained only stroma lamellae. Immunological detection of NADPH‐protochlorophyllide oxidoreductase (EC 1.3.1.33) on nitrocellulose membranes after sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDSPAGE) indicated the occurrence of the enzyme in upper, middle and lower sections of hypocotyls and in the root tips.
The relative contribution of elastic and osmotic adjustments to turgor maintenance of woody species.
Authors: Fan Shihe , Blake Terence J. , Blumwald Eduardo
Published: May 2006

To determine how tissue water relations vary and contribute to turgor maintenance in species from contrasting ecological zones, seedlings of jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana [Mill] B.S.P.) and flooded gum (Eucalyptus grandis W. Hill ex Maiden) were subjected to an 8 day drought stress by water withholding with and without prior mild water stress conditioning. Jack pine, a deep‐rooted species from dry, sandy boreal sites, lost turgor at the lowest relative water content (75–65%) and water potential, and had lowest maximum bulk elastic modulus (Emax of 5.2–5.8 MPa). Although this suggests a high inherent dehydration tolerance, jack pine did not further adjust its elasticity when repeatedly stressed. Black spruce, a shallow‐rooted species from predominantly moist sites in the boreal region, lost turgor at intermediate relative water content (86–76%) and water potential, but could adjust its elasticity to maintain turgor in repeatedly stressed tissues. Flooded gum, a deep‐rooted species from moist, warm temperate‐subtropical regions, had a low inherent drought tolerance since it lost turgor at higher relative water content (88–84%) and water potential, but was capable of some adjustment when the stress was repeated. Elastic adjustment (<3.7 MPa) was more important for turgor maintenance than osmotic adjustment (<0.13 MPa), which was statistically nonsignificant. Maximum bulk modulus of elasticity, but not osmotic potentials at full turgor, was significantly correlated with the relative water content and water potential at zero turgor in droughted seedlings. These results highlight the importance of tissue shrinkage for dehydration tolerance. Both the inherent capacity for turgor maintenance of a species under drought and its ability to adjust to repeated drought should be considered in genetic selections for drought tolerance.
Abscisic acid induced electrolyte leakage in woody species with contrasting ecological requirements
Authors: Fan Shihe , Blake Terence J.
Published: May 2006

To determine the relationship between drought, abscisic acid (ABA) levels, and membrane leakage, these aspects were studied in three woody species with contrasting ecological requirements. Physiological comparisons were made, during a 14‐day drought‐recovery cycle, on a drought resistant species, jack pine (Pinus banksiana Lamb.), and two more drought susceptible species, black spruce (Picea mariana (Mill) B.S.P.) and flooded gum (Eucalyptus grandis W. Hill ex Maiden). As the xylem pressure potentials (Ψ), declined under drought, both foliar ABA and electrolyte leakage increased significantly. However, ABA increased prior to the increase in leakage, and there was a significant linear correlation between endogenous ABA and leakage in all 3 species. Addition of exogenous ABA to the bathing solutions also significantly increased leakage of both unstressed and (sorbitol) osmotically‐stressed leaf segments in response to increasing (log) concentrations of (±) cis‐trans ABA [0–10.0 μM]. Electrolyte leakage in black spruce and flooded gum was more sensitive to stress‐induced ABA than in jack pine. The results suggest that drought increases foliar ABA which initiates membrane leakage, and that sensitivity of membranes to ABA accumulation varies, depending on the ecological requirements of a species.
Calmodulin‐stimulated calcium pumping ATPases located at higher plant intracellular membranes: a significant divergence from other eukaryotes?
Authors: Evans David E.
Published: May 2006

The plasma membrane (PM) of all eukaryotes so far investigated contains a P‐type Ca2+‐pumping ATPase responsible for maintaining low cytosolic free calcium concentrations. In animal cells this has been shown to be a type of Ca2+‐pump which is directly stimulated by binding the calcium‐dependent regulator protein calmodulin. These PM Ca2+‐pumps have been named ‘PM‐type’ as they appear to be exclusively located at the PM and not in intracellular membrane (IM) fractions. Recent progress on higher plant cells reveals that they possess calmodulin‐stimulated Ca2+‐pumps of the ‘PM‐type’. However, these calmodulin‐stimulated Ca2+‐pumps appear to be located not only at the PM but also in intracellular membranes, probably the endoplasmic reticulum (ER). The evidence is also convincing that these IM‐located Ca2+‐pumps are directly stimulated by calmodulin (possess a calmodulin‐binding region) and are true ‘PM‐type’ Ca2+‐pumps. This appears to represent a marked divergence between plant and animal cell Ca2+‐pumps. Recently, molecular cloning has revealed that plant cells also contain a Ca2+‐pump which is not directly stimulated by calmodulin and which strongly resembles the mammalian ER/SR type of Ca2+‐pump. The significance of these findings for plant cell function is discussed.
Responses of respiration to increasing atmospheric carbon dioxide concentrations
Authors: Bunce James A.
Published: May 2006

It has been recently recognized that increases in carbon dioxide concentration such as are anticipated for the earth's atmosphere in the next century often reduce plant respiration. There can be both a short‐term reversible effect of unknown cause, and long‐term acclimation, which may reflect the synthesis and maintenance of less metabolically expensive materials in plants grown at elevated carbon dioxide concentrations. Because respiration provides energy and carbon intermediates for growth and maintenance, reductions in respiration by increasing carbon dioxide concentrations may have effects on physiology beyond an improvement in plant carbon balance. As atmospheric carbon dioxide concentration increases, reduced respiration could be as important as increased photosynthesis in improving the ability of terrestrial vegetation to act as a sink for carbon, but it could also have other consequences.
The induction of α‐amylase activity by sucrose starvation in suspension‐cultured rice cells is regulated by polyamines
Authors: Sung Hung‐I , Liu Li‐Fei , Kao Ching Huei
Published: May 2006

When suspension‐cultured rice (Oryza sativa L. cv. Tainan 5) cells were deprived of sucrose, α‐amylase (EC 3.2.1.1) activity in the cells and the culture medium increased markedly. The increase in activity of α‐amylase caused by sucrose starvation in the cells and the medium was strongly reduced in the presence of exogenously added spermine. Putrescine and spermidine also inhibited, though only slightly, the increase in α‐amylase activity caused by sucrose starvation. Preincubation of the enzyme extract or enzyme in the medium with polyamines had no effect on α‐amylase activity. Sucrose starvation resulted in lower polyamine levels in rice suspension cells. D‐Arginine and α‐methylomithine, inhibitors of polyamine biosynthesis, caused reduced levels of polyamines and increased activity of α‐amylase in rice suspension cells cultured in the presence of sucrose. Our results indicate that the induction of α‐amylase activity by sucrose starvation in rice suspension cells is mediated, at least partly, through the internal level of polyamines.
Presence of β‐cyanoalanine synthase in unimbibed dry seeds and its activation by ethylene during pre‐germination
Authors: Hasegawa Ryo , Tada Tomoko , Torii Yuichiro , Esashi Yohji
Published: May 2006

Evolution of HCN from both rice (Oryza sativa) and cocklebur (Xanthium pennsylvanicum) seeds increased during a pre‐germination period and preceded the evolution of (C2H4). These two species were adopted as the representatives of starchy and fatty seeds, respectively. Ethylene promotes seed germination of many species. However, HCN evolution declined abruptly when the radicles emerged and before the peak in C2H4 evolution. More‐over, both rice and soybean (Glycine max) seeds showed some activity of β‐cyanoalanine synthase (CAS, EC 4.4.1.9) even in the unimbibed dry state. The activities of CAS in the lower seed of cocklebur and in soybean seeds increased rapidly after emergence of the radicle. However, the CAS of rice seeds, with high activity in the dry state, exhibited a bimodal change, gradually decreasing until radicle emergence had occurred, but then increaing. It is thus likly that HCN evolution during initial imbibition may be derived from cyanogenic reserves and controlled by both pre‐existing and subsequently‐developing CAS. The exogenous application of C2H4 stimulated the activities of CAS in both rice and upper cocklebur seeds and reduced their cyanogen contents. Therefore, the decline of HCN evolution after germination seems to be due to the increased activities of CAS by endogenously produced C2H4.