bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical, immunological and kinetic properties of ribulose‐1,5‐bisphosphate carboxylase/oxygenase from fir (Abies alba) and spruce (Picea abies)
Authors: Afif D. , Gérant D. , Cavalié G. , Dizengremel P.
Published: May 2006

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) from fir (Abies alba Mill.) and spruce (Picea abies [L.] Karst.) needles was purified to homogeneity. The enzyme was isolated from crude extracts through quantitative precipitation in 40‐55% and 40‐60% (NH4)2SO4 for fir and spruce. respectively, followed by linear sucrose gradient centrifugation. Using two dimensional gel electrophoresis, the isoelectric points were determined. For the large subunit (LSU) it was 6.7 for both species, and for the small subunit (SSU) it was 7.1 and 7.7 for fir and spruce, respectively. Very few differences in tryptic peptides and amino acid composition of Rubisco LSU were observed between fir and spruce. By contrast, marked differences characterized the same analyses for the Rubisco SSU of the two species. Moreover, substitution of residues was observed in the sequenced N‐terminal region when comparing fir and spruce SSU. The Ouchterlony technique showed no immu‐nochemical difference between Rubisco of fir and spruce when a rabbit antiserum to spinach Rubisco was used. The Eadie‐Hofstee plots of carboxylase activity indicated that the apparent Km(CO2) were 31 and 36 μM for the fir and spruce enzymes, respectively.
Effects of a pregrowth period in Al‐free nutrient solution on macronutrient composition of two upland rice cultivars with various Al sensitivity
Authors: Jan Farid
Published: May 2006

Effects of Al on growth and macronutrient distribution (K. P. Ca and Mg) were examined in two rice (Oryza sativa L.) cultivars (BG35 and IR45) pregrown in a nutrient solution without Al for 21 days followed by 14 days at 0.70. 140 or 280 μM Al (pH 4.2 ± 0.1). Relative growth rate (RGR) of pregrown plants was significantly less hampered by Al compared to their controls, than RGR of plants that were not pregrown. However, a similar ranking of the cultivars for Al sensitivity was obtained irrespective of pregrowth period. The more Al tolerant BG35 consistently outyielded the Al sensitive IR45 under all Al treatments. A comparatively high Al‐retention in roots and low Al transport rate to shoots of pregrown IR45 was the opposite of conditions in non‐pregrown IR45. In BG35, uptake and transport of nutrients to the shoots were efficient at all Al levels. In IR45, particularly the uptake and distribution of P and Mg were disturbed by Al. It is suggested that a pregrowth or nursery period without Al reduces Al toxicity in both BG35 and IR45 at least up to 280 μM Al.
Disturbed nitrogen metabolism associated with the hyperhydric status of fully habituated callus of sugarbeet
Authors: Le Dily Frédérik , Billard Jean‐Pierre , Gaspar Thomas , Huault Claude
Published: May 2006

The content of polyamines and proline was much lower in a normal (N) callus of Beta vulgaris L. than in a fully habituated hyperhydric (H) callus. The H callus also contained more glutamate and had a higher glutamate dehydrogenase activity. The excess of glutamate, in this chlorophyll‐deficient callus, was linked to accumulation of proline and polyamines. Experiments with α‐difluoromethylornithine (DFMO) and α‐difluoromethylarginine (DFMA) showed that both ornithine decarboxylase and arginine decarboxylase participated in the synthesis of polyamines (especially spermidine and putrescine) and removal of ammonia. It is hypothesized that the H callus was subjected to ammonia stress from the start of the culture. Experiments with gabaculine, an inhibitor of ornithine aminotransferase, showed that this enzyme linked proline degradation to polyamine synthesis through the production of ornithine. This disturbed nitrogen metabolism appeared to be characteristic of the fully habituated callus and might explain the low growth of this hyperhydric tissue.
Salinity stress and cytoplasmic factors. A comparison of cell permeability and lipid partiality in salt sensitive and salt resistant cultivars and lines of Triticum aestivum and Hordeum vulgare
Authors: Magdy M. , Mansour F. , Lee‐Stadelmann OK Young , Stadelmann Eduard J.
Published: May 2006

Salinity effects on the cell membranes of four lines of wheat (Triticum aestivum L.). and two cultivars of barley (Hordeum vulgare L.), differing in salt resistance were investigated. Plants were grown for 10 days in 1/4‐strength Hoagland solution and then for 5 more days in 1/4‐strength Hoagland with and without NaCl (100 mM) or (for Hordeum only) polyethylene glycol (PEG). Permeability to three non‐electrolytes (urea, methylurea and ethylurea) of subepidermal cells of leaf sheaths (Triticum) and coleoptiles (Hordeum) was determined and membrane partiality calculated, a parameter which numerically indicates the degree of lipophilicity of a membrane. Non‐electrolyte permeability significantly increased and membrane partiality decreased in the salt sensitive cultivars or lines under salt stress. Neither parameter changed significantly in the salt resistant lines and cultivar in a saline environment. Osmotic stress in Hordeum by PEG 10000 had no significant effect on permeability and thus membrane partiality neither in sensitive nor in resistant cultivars.

The osmotic component of salinity stress did not seem to be a major factor causing injury, rather ion toxicity may be a cause of cell damage. The results indicate differences in the membrane between salt sensitive and salt resistant genotypes. Salt resistance seems to be controlled by genetic factors independent of external salinity levels.
Control of root growth: effects of carbohydrates on the extension, branching and rate of respiration of different fractions of wheat roots
Authors: Bingham I. J. , Stevenson E. A.
Published: May 2006

Rates of extension, numbers of laterals and rates of respiration were measured in different fractions of wheat (Triticum aestivum L. cv. Alexandria) roots following changes in carbohydrate supply. The supply of carbohydrate was varied by selective pruning and exogenously fed sugars. Pruning shoots to a single leaf (leaf‐pruning) reduced the rate of O2 uptake by intact roots. Rates were not stimulated by shortterm feeding of sucrose (25 mM), but were stimulated by the uncoupler p‐trifluoro‐methoxy(carbonylcyanide)phenylhydrazone (FCCP). Feeding glucose to roots of leaf‐pruned and non‐pruned plants for 16–24 h increased the rate of O2 uptake. It is concluded that respiration is under fine control by adenylates and coarse control by carbohydrate supply, with carbohydrates regulating directly the rate of some energy consuming process(es). These energy consuming processes are located in growing tissue fractions. Feeding glucose to leaf‐pruned and non‐pruned plants increased rates of O2 uptake in seminal root tips, the zone of developing lateral primordia and mature root sections with elongating laterals, but had no effect on mature sections from which the laterals had been excised. Leaf‐pruning reduced the extension rate of seminal axes and first‐order laterals when measured over 24 h. Feeding glucose to roots from the time of pruning increased the rate, but did not fully restore it to control values. Pruning roots to a single seminal axis (root‐pruning) and feeding glucose to non‐pruned plants had no effect on the extension rate of the seminal axis or its laterals over this time period, although rates were increased by root‐pruning when measured over 3 days. The number of lateral root primordia was reduced by leaf‐pruning and increased by root‐pruning and feeding glucose. The results are discussed in terms of the role of carbohydrates in the control of root growth and branching.
Response of the maize catalases and superoxide dismutases to cercosporin‐containing fungal extracts: the pattern of catalase response in scutella is stage specific
Authors: Williamson John D. , Scandalios John G.
Published: May 2006

Cercosporin, a photoactivated polyketide toxin produced by fungi of the genus Cercospora, reacts with molecular oxygen to produce oxygen radicals. Using both minus‐and plus‐cercosporin fungal extracts and purified cercosporin, we have analyzed antioxdant defense gene responses in maize scutella at two stages in development. The three maize catalases (CATH2O2: H2O2 oxidoreductase, EC 1.11.1.6) respond differentially to applied cercosporin, and this response varies with developmental stage. Total catalase activity, as well as individual isozyme proteins and their corresponding steady‐state levels of RNA changed in parallel in response to applied cercosporin. In contrast, both toal superoxide dismutase (SOD, O2:O2 oxidoreductase; EC 1.15.1.1) activity and individual isozyme protein levels remained constant in all treatments. Sod transcript accumulation, however, changed dramatically. Comparison of the response of these genes to minus‐ and plus‐cercosporin fungal extracts with their response to purified cercosporin demonstrated that other fungal compounds influence the expression of bothSod and Cat.
The relationship between the activity of various iron‐containing and iron‐free enzymes and the presence of nicotianamine in tomato seedlings
Authors: Pich Axel , Scholz Günter
Published: May 2006

The influence of nicotianamine (NA) and iron on the activities of 4 iron‐containing and two iron‐free enzymes in leaves and roots of the NA‐free tomato mutant chloronerva and its NA‐containing wild‐type (Lycopersicon esculentum Mill. cv. Bonner Beste) was investigated. Aconitase (EC 4.2.1.3) activity in both leaves and roots was much higher in the mutant under normal iron supply (10 μM FeEDTA) and in wild‐type under iron deficiency than in wild‐type supplied with 10 μM FeEDTA. Application of NA to chloronerva leaves led to a decrease of aconitase activity in leaves and roots. NA had no effect on the enzyme activity when added to the assay medium.

Similar results were obtained for the iron‐containing enzymes catalase (EC 1.11.1.6), ascorbate‐dependent peroxidase (EC 1.11.1.11) and guaiacol‐dependent peroxidase (EC 1.11.1.7) in roots. NA treatment of the mutant leaves decreased enzyme activities in roots down to wild‐type values. In vivo NA application had no effect on enzyme activities in leaf extracts.

The activities of the iron‐free enzymes NAD+‐malate dehydrogenase (EC 1.1.1.37) and phosphofructokinase (EC 2.7.1.11) in root and leaf extracts were not influenced by the iron supply to the plants.
The role of the plasmalemma in metal tolerance in angiosperms
Authors: Meharg Andrew A.
Published: May 2006

Evidence for the role of the plasmalemma in metal tolerance of metal resistant ecotypes, cultivars and clones is presented. A range of tolerance mechanisms involving the plasmalemma are discussed including alterations to protein carrier and channel function and synthesis, efflux pumps and maintenance of plasmalemma integrity. Specific examples of such alterations from the literature on Al, As and Cu tolerance, where the plasmalemma has been shown to have a role in tolerance are considered. Tolerance by alterations to plasmalemma function in tolerant ecotypes may also rely on internal metal detoxification mechanisms constitutive in tolerant and non‐tolerant plants.
An unambiguous nomenclature for xyloglucan‐derived oligosaccharides
Authors: Fry Stephen C. , York William S. , Albersheim Peter , Darvill Alan , Hayashi Takahisa , Joseleau Jean‐Paul , Kato Yoji , Lorences Ester Pérez , Maclachlan Gordon A. , McNeil Michael , Mort Andrew J. , Grant Reid J. S. , Seitz Hanns Ulrich , Selvendran Robert R. , Voragen Alphons G. J. , White Alan R.
Published: May 2006

A revised system of abbreviated names is proposed for xyloglucan‐derived oligosaccharides. Each (1→4)‐linked β‐d‐glucosyl residue (and the reducing terminal d‐glucose moiety) of the backbone is given a one‐letter code according to its substituents. The name of the oligosaccharide consists of these code letters listed in sequence from non‐reducing to reducing terminus of the backbone.
Enhancement of ethylene biosynthesis and germination by cytokinins and 1‐aminocyclopropane‐l‐carboxylic acid in Striga asiatica seeds
Authors: Babiker Abdel Gabbar T. , Butler Larry G. , Ejeta Gebisa , Woodson William R.
Published: May 2006

Germination of witchweed (Striga asiatica [L.] Kuntze), an important parasitic weed on several poaceous crops, is stimulated by several synthetic and natural compounds. We investigated the role of ethylene biosynthesis and action in cytokinin‐induced germination. Conditioned Striga seeds treated with distilled water, 1‐aminocyclopro‐pane‐1‐carboxylic acid (ACC) or the cytokinins thidiazuron (TDZ), trans zeatin (TZ), benzyladenine (BA) and kinetin (KIN) produced little ethylene. Treatments with cytokinin‐ACC combinations enhanced ethylene production. The relative order of activity of the cytokinins in elicitation of the phytohormone was TDZ > TZ > BA > KIN. Germination in response to distilled water and ACC treatments was negligible. Induction of germination by cytokinins varied from low (0%) to moderate (52%). Seeds treated with cytokinin‐ACC combinations displayed high rates of germination. The observed germination was positively correlated (γ= 0. 8 and 0. 9) with ethylene production. Germination was reduced by silver thiosulphate (STS) and CoCl2, inhibitors of ethylene action and ACC oxidase, respectively. Aminoethoxyvi‐nylglycine (AVG), an ACC‐synthase inhibitor, reduced TDZ‐induced Striga germination. However, the inhibitory effect of AVG was overcome by addition of ACC. The results are consistent with a model in which Striga germination and embryo growth are limited by low capacity of the seeds to oxidize ACC. The cytokinins promote ACC conversion into ethylene and consequent Striga germination by enhancing ACC oxidase activity and/or synthesis.
Annexin‐mediated secretory vesicle aggregation in plants
Authors: Blackbourn Hugh D. , Battey Nick H.
Published: May 2006

The mechanism by which membranes fuse during vesicle‐mediated secretion is of considerable importance for plant cell growth, but remains unknown. We have identified Ca2+‐dependent phospholipid‐binding proteins (annexins) from maize (Zea mays), that may play a part in this process. An assay for Ca2+‐dependent binding of annexins to liposomes, revealed that the maize proteins (p23, p33 and p35) and annexins from bovine lung, bind over a similar range of Ca2+ concentrations. Turbidity assays further revealed that both maize and bovine annexins induced liposome aggregation and that the plant annexins were also effective at aggregating plant secretory vesicles. This aggregation occurred at levels of free Ca2+ similar to that required for the binding of annexins p33 and p35. We discuss the significance of these results for the plant secretory apparatus.
Episodic whole plant growth patterns in Ligustrum
Authors: Kuehny Jeff S. , Halbrooks Mary C.
Published: May 2006

Episodic growth of Ligustrum japonicum Thunb. plants was determined by measuring total shoot and root fresh weight nondestructively. Episodic growth patterns were apparent in shoot elongation, shoot and root fresh weight as a percent of total fresh weight, shoot and root relative growth rates (RGRs and RGRr) and two‐dimensional measurements of the root system. Increases in root growth and initiation of lateral root branching were coincident with changes in percent of total fresh weight in the root and RGRr. The rate of fresh weight gain of roots, shoots and the whole plant increased continuously throughout two experiments and thus episodic growth patterns were not apparent from these values. Alternating episodes of shoot and root growth, which is shown by percent fresh weight allocation and RGR, did not directly correspond to shoot elongation and cessation of elongation. Continuous, nondestructive measurement of total shoot and root growth reveals important changes in growth which may be obscured by other measurement techniques.
Temporal expression of effects of varying nitrogen supply on canopy growth, photosynthesis and fruit production for Actinidia deliciosa vines in the field
Authors: Buwalda J. G. , Meekings J. S.
Published: May 2006

The effects of varying nitrogen supply on canopy leaf area, response of leaf net photosynthesis (An) to quantum flux density (Q), and fruit yields of kiwifruit vines (Actinidia deliciosa var. deliciosa) were examined in a two‐year field experiment. Vines were grown with 0, 250 or 750 kg N ha−1 year−1. The responses to nitrogen supply were compared with responses to shade, to examine the impact of reduced carbon assimilation on canopy leaf area and fruit yields. Nitrogen supply did not affect significantly any of the measured variables during the first season of the experiment. In the second season, canopy leaf area was reduced significantly where nitrogen supply was limited. The quantum efficiency of photosynthesis (φq) increased from 0. 03 mol CO2 mol−1 Q soon after leaf emergence to more than 0. 05 mol CO2 mol−1 Q during the middle of the growing season. The quantum saturated rate of An (Asat) also increased during the season, from 7–10 μmol CO2 m−2 s−1 soon after leaf emergence, to 15–20 (μmol CO2 m−2 s−1 during the middle of the growing season. φq and Asat increased significantly with nitrogen supply at all measurement times during the second season. For vines with high nitrogen, fruit yields in both seasons were similar, averaging 3. 05 kg m−2. Fruit yields in the second season were reduced significantly where nitrogen supply was limited, due to reduced fruit numbers. The relative effects of reduced leaf area and reduced leaf photosynthesis for carbon assimilation by nitrogen deficient vines were examined using a mathematical model of canopy photosynthesis for kiwifruit vines. Simulations of canopy photosynthesis indicated that effects on leaf area and on leaf photosynthesis were of similar importance in the overall effects of nitrogen deficiency on carbon assimilation. The effects of nitrogen supply on fruit numbers (i. e. flower development) preceded the measured effects on carbon assimilation, indicating that the nitrogen supply affected carbon partitioning to reserves in the first season.
Growth, gas exchange and water use efficiency of the facultative hemiparasite Rhinanthus minor associated with hosts differing in foliar nitrogen concentration
Authors: Seel W. E. , Cooper R. E. , Press M. C.
Published: May 2006

The facultative hemiparasitic angiosperm Rhinanthus minor was grown on 11 different host species, and in the absence of a host. The height of R. minor parasitising the legume Trifolium pratense exceeded that of unattached plants by more than an order of magnitude, with performance on grasses and non‐legume dicotlyedonous hosts between these two extremes. Light saturated rates of photosynthesis in R. minor on different hosts ranged from 1. 5 to 22. 5 μmol g−1 dry weight min−1, and were positively correlated with growth. Foliar nitrogen concentrations in the parasite exceeded those of the hosts. The former were positively related to light saturated rates of photosynthesis, and inversely related to photosynthetic nitrogen use efficiency. There was no relationship between leaf nitrogen concentration and water use efficiency in R. minor. The data are discussed in relation to studies of nitrogen and water use in mistletoes.
Developmental changes of enzymes of malate metabolism in relation to respiration, photosynthesis and nitrate assimilation in peach leaves
Authors: Merlo Lucia , Ferretti Massimo , Ghisi Rossella , Passera Calvino
Published: May 2006

The developmental profile of the activities of some enzymes involved in malate metabolism, namely phosphoenolpyruvate carboxylase (PEPC; EC 4. 1. 1. 31), NAD+‐linked (EC 1. 1. 1. 37) and NADP+‐linked (EC 1. 1. 1. 82) malate dehydrosenase (MDH), NAD+linked (EC 1. 1. 1. 39) and NADP+‐linked (EC 1. 1. 1. 40) malic enzyme (ME), has been determined in leaves of peach [Prunus persica (L.) Batsch cv. Maycrest], a woody C3 species. In order to study the role of these enzymes, their activities were related to developmental changes of photosynthesis, respiration, and capacity for N assimilation. Activities of PEPC, NAD(P)+‐MDH and NADP+‐ME were high in young expanding leaves and decreased 2‐ to 3‐fold in mature ones, suggesting that such enzymes play some role during the early stages of leaf expansion. In leaves of peach, such a role did not seem to be linked to C3 photosynthesis or nitrate assimilation, in that photosynthetic O2 evolution and activities of nitrate reductase (EC 1. 6. 6. 1) and glutamine synthetase (EC 6. 3. 1. 2) increased during leaf development. In contrast, leaf respiration strongly decreased with increasing leaf age. We suggest that in expanding leaves of this woody species the enzymes associated with malate metabolism have anaplerotic functions, and that PEPC may also contribute to the recapture of respiratory CO2.
Induction of elongation in maize coleoptiles by hexachloroiridate and its interrelation with auxin and fusicoccin action
Authors: Lüthen Hartwig , Böttger Michael
Published: May 2006

The demonstration of an auxin‐stimulated NADH‐oxidase in the plasma membrane (Brightman et al. 1988. Plant Physiol. 86: 1264–1269) has led to the suggestion that the plasma membrane redox system is involved in the mechanism of auxin action. To evaluate the relevance of this concept in vivo, the influence of micromolar concentrations of hexachloroiridate (IV), an impermeable electron acceptor for the plant plasma membrane redox system, on elongation growth of excised, abraded maize coleoptile (Zea mays L. cv. Golden Bantam) segments was studied. It was found that the substance induced a rapid growth response if the experiment was carried out in an unbuffered solution. This effect was entirely prevented by a 2 mM phosphate buffer. Nevertheless, the acid‐growth‐theory does not seem sufficient to explain this effect, since proton extrusion is induced without a lag, whereas increased growth rates commence after a lag phase of 40 min.

If growth is stimulated by a pretreatment with fusicoccin or auxin, hexachloroiridate IV transiently inhibits growth. The kinetics of the response are then determined by the concentrations of hexachloroiridate and auxin or fusicoccin. These results are compatible with the view that the plasma membrane redox system is somehow involved in the control of elongation growth.
Influence of photoinhibition on electron transport and photophosphorylation of isolated chloroplasts
Authors: Curwiel Victor B. , van Rensen Jack J. S.
Published: May 2006

The effects of a photoinhibition treatment (PIT) on electron transport and photophosphorylation reactions were measured in chloroplasts isolated from triazine‐resistant and susceptible Chenopodium album plants grown under high and low irradiance. Electron transport dependent on photosystem I (PSI) alone was much less affected by PIT than that dependent on both photosystem II (PSII) and PSI. There was a smaller difference in susceptibility to PIT between the photophosphorylation activitity dependent on PSI alone and that dependent on both PSII and PSI. Because in all cases photophosphorylation activity decreased faster upon PIT than the rate of electron transport, we conclude that photoinhibition causes a gradual uncoupling of electron transport with phosphorylation. Since the extent of the light‐induced proton gradient across the thylakoid membrane decreased upon PIT, it is suggested that photoinhibiton causes a proton leakiness of the membrane. We have found no significant differences to PIT of the various reactions measured in chloroplasts isolated from triazine‐resistant and susceptible plants. We have also not observed any significant differences to PIT of the photophosphorylation reactions in chloroplasts of plants grown under low irradiance, compared with those grown under high irradiance. However, the electron transport reactions in chloroplasts from plants grown under low irradiance appeared to be somewhat less sensitive to PIT than those grown under high irradiance.
Salt‐induced oxidative stress mediated by activated oxygen species in pea leaf mitochondria
Authors: Hernández José A. , Corpas Francisco J. , Gómez Manuel , del Río Luis A. , Sevilla Francisca
Published: May 2006

The effect in vivo of salt stress on the activated oxygen metabolism of mitochondria, was studied in leaves from two NaCl‐treated cultivars of Pisum sativum L. with different sensitivity to NaCl. In mitochondria from NaCl‐sensitive plants, salinity brought about a significant decrease of Mn‐SOD (EC 1. 15. 1. 1) Cu, Zn‐SOD I (EC 1. 15. 1. 1) and fumarase (EC 4. 2. 1. 2) activities. Conversely, in salt‐tolerant plants NaCl treatment produced an increase in the mitochondrial Mn‐SOD activity and, to a lesser extent, in fumarase activity. In mitochondria from both salt‐treated cultivars, the internal H2O2 concentration remained unchanged. The NADH‐ and succinate‐dependent generation of O2.−radicals by submitochondrial particles and the lipid peroxidation of mitochondrial membranes, increased as a result of salt treatment, and these changes were higher in NaCl‐sensitive than in NaCl‐tolerant plants. Accordingly, the enhanced rates of superoxide production by mitochondria from salt‐sensitive plants were concomitant with a strong decrease in the mitochondrial Mn‐SOD activity, whereas NaCl‐tolerant plants appear to have a protection mechanism against salt‐induced increased O2.− production by means of the induction of the mitochondrial Mn‐SOD activity. These results indicate that in the subcellular toxicity of NaCl in pea plants, at the level of mitochondria, an oxidative stress mechanism mediated by superoxide radicals is involved, and also imply a function for mitochondrial Mn‐SOD in the molecular mechanisms of plant tolerance to NaCl.
Heat shock increases chilling tolerance of mung bean hypocotyl tissue
Authors: Collins Graham G. , Nie XunLi , Saltveit Mikal E.
Published: May 2006

The effects of heat shock on the chilling tolerance of mung bean [Vigna radiata (L.) Wilczek] seedling tissue were studied by using two measurements of chilling injury: increased 1‐aminocyclopropane‐1‐carboxylic acid (ACC) oxidase activity and solute leakage. ACC oxidase activity (measured as ACC‐induced ethylene production) of freshly excised mung bean hypocotyl segments was highly dependent on the temperature at which the seedlings were grown. However, this highly temperature‐dependent level of ACC oxidase activity was probably a wound response since it was almost entirely eliminated by incubating the excised segments at 20°C for 3 h. In contrast, heating of excised segments to 40°C for up to 4 h resulted in a time‐dependent increase in ACC oxidase activity which was sensitive to cycloheximide, indicating rapid protein synthesis during the heat treatment. ACC oxidase activity fell sharply during subsequent chilling at 2. 5°C. After 3 days of chilling, all treated segments, regardless of their initial ACC oxidase activity, showed a decline to the same low activity level and ACC oxidase activity continued to fall slowly for up to 9 days at 2. 5°C. Hypocotyl segments excised from seedlings held at 15°C showed no change in solute leakage, but leakage increased rapidly when seedlings were either chilled at 2. 5°C or heated to 32°C (just below the heat shock temperature). Chill‐induced leakage from non‐heat‐shocked segments increased steadily with chilling duration and was unaffected by cycloheximide concentration up to day 6. Within the elevated rate of leakage on day 9, however, leakage was lower from segments exposed to 10 and 50 μM cycloheximide. Solute leakage was markedly reduced for up to 9 days when segments were heat shocked at 40°C for 3 or 4 h with or without 10 M cycloheximide, but the presence of 50 μM cycloheximide caused an initial doubling of solute leakage and a 3‐fold increase after 3 days of chilling. Cycloheximide prevented formation of heat shock protection against chilling from the start at 50 μM and after 9 days at 10 μM. These results indicate that the protection afforded by heat shock against chilling damage is quantitative and probably involves protein synthesis.
The Nostoc‐Gunnera symbiosis: carbon fixation and translocation
Authors: Söderbäck Erik , Bergman Birgitta
Published: May 2006

The in vitro specific activity of ribulose‐1,5‐bisphosphate carboxylase (Rubisco; EC 4. 1. 1. 39) and the dark and light in vivo CO2 fixation activities were determined in the cyanobiont of Gunnera. Compared to the free‐living isolate Nostoc PCC 9231, the in vitro Rubisco activity was high, while the in vivo CO2 fixation was very low. Light did not significantly influence CO2 fixation if the cyanobiont was left in the sliced Gunnera tissues, while a small light stimulation was found for CO2 fixation of the freshly‐isolated cyanobiont. The adjacent non‐infected Gunnera tissue showed a very low CO2 fixation. A rapid translocation of fixed 14CO2 from leaves towards apical parts of the plant was apparent, in particular to the symbiotic tissue. The 14C label appeared mainly in soluble form in this tissue and was rapidly catabolised as shown by 14C chase experiments. Also, short‐term experiments revealed that maximum 14C accumulation occurred in the symbiotic tissue showing the highest rates of nitrogen fixation (Söderbäck et al. 1990), about 10–15 mm from the plant apex. The data were taken to indicate that there is a modification in the photosynthetic light reaction of the cyanobiont and that the cyanobiont lives heterotrophically in the dark on photo‐synthate rapidly delivered from nearby leaves of the host plant.
Antagonistic effects of light I and II on chlorophyll a fluorescence yield and P700 turnover as monitors of carbon dioxide depletion in intact algal and cyanobacterial cells
Authors: Govindjee  , Snel Jan F. H. , De Vos Oscar J. , van Rensen Jack J. S.
Published: May 2006

Depletion of carbon dioxide from cells by formate treatment not only causes a cessation of carbon dioxide fixation, but also a dramatic decrease in the rate of electron transfer between QA, the primary plastoquinone electron acceptor of photosystem II, and the cytochrome b6/f complex. We show here that this latter phenomenon can be conveniently monitored by the antagonistic effects of light absorbed in photosystems I and II on chlorophyll a fluorescence yield and P700 turnover in intact cells of green algae and cyanobacteria.
Accumulation of calcium, potassium and magnesium in apple fruits under various conditions of humidity
Authors: Tromp J. , Van Vuure J.
Published: May 2006

In each of two experiments done under controlled conditions, starting at bloom, 4 humidity treatments were applied to potted trees of apple (Malus pumila Mill. cv. Cox's Orange Pippin), i. e. in experiment 1: (1) high humidity throughout, (2) low humidity throughout, (3) low humidity for 7 weeks followed by high humidity for 6‐7 weeks, and (4) the reverse (first high and then low humidity); in experiment 2: (1) day/night humidity high/high, (2) low/low, (3) low/high, and (4) high/low.

In both experiments high humidity favoured shoot growth appreciably. Change from low to high humidity after 7 weeks resulted in some growth stimulation but in the reverse situation growth was markedly reduced. Shoot growth responded little to different night humidities. In the two experiments fruit growth was little affected by treatments. In experiment 2 irrespective of night humidity, water consumption was higher at low than at high day humidity. In the high/low humidity regime water use during the night was high and leaf water potential low, relatively; during the day water potential was little affected by treatments.

At any time leaf Ca and Mg were clearly highest at low day humidity; night humidity had no effect. Leaf K did not respond to treatments. Fruit Ca at high humidity throughout was lower than at low humidity throughout. Increasing humidity later in the season was ineffective but a decrease at that time tended to reduce fruit Ca slightly. The clearly lowest Ca values occurred in the high/low day/night treatment. Fruit K and Mg were not or hardly affected by treatments.

The findings are discussed in terms of humidity effects on transpiration, shoot and fruit growth, and xylem mineral concentration and ion exchange translocation along the xylem walls.
Altered levels of antioxidant enzymes associated with two mutations in tomato
Authors: Gianinetti Alberto , Cantoni Marco , Lorenzoni Carlo , Salamini Francesco , Marocco Adriano
Published: May 2006

Activity of peroxidase, superoxide dismutase and catalase were examined in leaves, stems and roots of olivacea (oli) and monstrosa (mon) mutants of Lycopersicon esculentum Mill. The extent of the difference between the pattern of oxidative enzyme activities of the wild type (wt) and the mutants was determined. The high peroxidase activity during the developmental stages of the leaves and stems of oli and mon phenotypes is associated with high levels of 4 anodic peroxidases in leaves and of two isozymes in the stem. Leaves of oli exhibit higher activity of the cathodic peroxidase C2, while both mutations have a marked increase of peroxidase C1 in stems. A positive relation between high peroxidase activity and oxidative stress damage was found: in chilling experiments at 5°C, peroxidase level in mutants and wt leaves was negatively correlated with electrolyte leakage. Superoxide dismutase (SOD) activity rises in oli stems around flowering time due to the high activity of the chloroplast forms SOD‐1 and SOD‐2. Catalases (CAT) were detectable only in early stages of plant development; CAT‐2 was nearly absent in wild type tissues but well represented in mon and oli. The oli and mon mutations may affect critical steps of a regulatory pathway controlling various classes of oxidative enzymes in tomato.
Hypoxic metabolism in wild rice (Zizania palustris): enzyme induction and metabolite production
Authors: Muench Douglas G. , Archibold O. William , Good Allen G.
Published: May 2006

Alcohol dehydrogenase (ADH, EC 1. 1. 1. 1), lactate dehydrogenase (LDH, EC 1. 1. 1. 27) and alanine aminotransferase (AlaAT, EC 2. 6. 1. 2) activity in wild rice (Zizania palustris L.) root tissue increased after 4 days of exposure to hypoxic stress. The activities of ADH and AlaAT also increased in leaf tissue under these same conditions, whereas LDH activity did not. Isozyme banding patterns indicate that wild rice has at least two functional Adh genes, only one of which is hypoxically induced in root and leaf tissue. The isozyme profile of LDH also indicates the presence of two functional Ldh genes in wild rice. Two bands of AlaAT activity are visible on native electrophoretic gels of root and leaf tissue. Neither of these bands appears to increase in activity in hypoxic samples, even though spectrophotometric assays indicate an increase in AlaAT activity. Ethanol accumulation was the highest of all the metabolites measured. Alanine and malate also accumulated under hypoxic conditions but only to about one‐fifth the level of ethanol. Succinate, aspartate and lactate showed no observable changes throughout the induction period. These results show that wild rice differs from domesticated rice (Oryza sativa L.) in its metabolic responses to anaerobic stress. The possible role of these responses in conferring flood tolerance is discussed.
Effects of aluminum on membrane fluidity of the mycorrhizal fungus Amanita muscaria
Authors: žel Jana , Svetek Jelka , Črne Helena , Schara Milan
Published: May 2006

The effect of aluminum on the ordering and dynamics of lipid molecules in plasmalemma was studied by electron paramagnetic resonance via the membrane‐inserted reporter spin label molecules (methyl ester of 5‐doxyl‐hexadecanoic acid) in situ in mycelia of the ectomycorrhizal fungus Amanita muscaria. It was found, first, that the plasmalemma is structured into coexistent regions of lipids with different ordering and dynamics, and second, that aluminum stress is accompanied by the corresponding relative decrease of the proportion of the less ordered membrane domains. This effect is opposite to that found previously for Lactarius piperatus, where the membrane responded by an increase of the portion of the less ordered membrane domains. Such qualitatively diverse effects of aluminum at the membrane level is of interest as it coincides with the opposite effect on growth, i. e. inhibition of Amanita muscaria and stimulation of Lactarius piperatus.
Cell wall degrading enzymes in Orobanche aegyptiaca and its host Brassica campestris
Authors: Singh Archana , Singh Madhav
Published: May 2006

Activities of the cell‐wall degrading enzymes cellulase (EC 3. 2. 1. 4). poly‐galacturonase (EC 3. 2. 1. 15) and xylanase (EC 3. 2. 1. 8), and also that of protease (EC 3. 4. 21. 14) have been determined in the parasite Orobanche aegyiptiaca Pers. and in the roots of infected and control host plants of Brassica campestris L. var. rapa Hartm. Shoots, roots and root‐freed tubers of Orobanche showed pronounced activities of these enzymes. When expressed in terms of specific activity, protease, cellulase and polygalacturonase activities were higher and xylanase lower in all parts of Orobanche than in the roots of infected or control host plants. Orobanche roots had higher activities of cellulase, polygalacturonase and protease than tuber or shoot. While xylanase activity was higher in the shoot than in roots or tuber. Infection by Orobanche significantly enhanced the cellulase activity of host roots. Cellulase and polygalacturonase in the Orobanche roots appear as the main enzymes involved in establishing haustorial connection with the host root. Protease might be involved in degrading proteins and lipoproteins of the cell walls and membranes of the host tissues.
Interaction between the effects of phytochrome and gibberellic acid on the senescence of Alstroemeria pelegrina leaves
Authors: van Doorn Wouter G. , van Lieburg Marius J.
Published: May 2006

Chlorophyll loss in the leaves of cut flowering branches of Alstroemeria pelegrina L. cv. Stajello, placed in water in darkness at 20°, was inhibited by irradiation with red light and by the inclusion of gibberellic acid (GA3) in the water. The effects of red light were abolished when it was followed by far‐red light. Effects of GA3 and red light were additive over a range of GA3 concentrations (0. 01–1 μM). Chlorophyll breakdown was increased by the inclusion of AMO‐1618, ancymidol, or tetcyclasis in the water. The effect of these inhibitors of gibberellin synthesis was fully reversed by GA3. The inhibition of chlorophyll breakdown by red light was absent when AMO‐1618, ancymidol or tetcyclasis were included in the water. The results indicate that leaf yellowing is controlled by endogenous gibberellins and that the effect of phytochrome is mediated by gibberellin synthesis.
Dormancy release in beech buds (Fagus sylvatica) requires both chilling and long days
Authors: Heide O. M.
Published: May 2006

Chilling and daylength requirements for dormancy release and budburst in dormant beech (Fagus sylvatica L.) buds have been studied in cuttings flushing in controlled environments after different durations of outdoor chilling. Non‐chilled buds sampled in mid October required long days (LD) only for budburst. Buds chilled until March still required LD for normal budburst, whereas buds sampled in November and December were unable to sprout regardless of daylength conditions and would do so only after a substantial period of chilling. Four ecotypes of distant latitudinal and altitudinal origin responded very similarly with a typical quantitative photoperiodic response. In fully chilled shoots sampled in March only 13 to 40% budburst took place in 8‐h SD and only after three times as long time as in continuous light. It is concluded that this dual dormancy control system ensures optimum winter stability in trees under conditions of climatic warming. In the closely related Carpinus betulus L. budburst was unaffected by daylength.
Biogenesis of petunia and carnation corolla chloroplasts: changes in the abundance of nuclear and plastid‐encoded photosynthesis‐specific gene products during flower development
Authors: Vainstein Alexander , Sharon Ronit
Published: May 2006

To study the biogenesis of the photosynthetic apparatus in corollas, as well as compositional differences between corolla and leaf chloroplasts, the levels of 12 nuclear‐ and plastid‐encoded thylakoid and stromal components were analyzed by western blotting using heterologous antisera. Relative levels of the thylakoid polypeptides analyzed in petunia (Petunia hybrida cv. Hit Parade Rosa) and carnation (Dianthus caryophyllus cv. White Sim) corollas increased, per unit chlorophyll, in parallel to corolla development, peaking at the mature stage in both flower types, with the exception of subunit V of the photosystem I (PSI) core complex, which continued to accumulate even after anthesis. The photosystem II (PSII) major light‐harvesting chlorophyll a/b protein accumulated in corollas to a level, per unit chlorophyll, similar to that in leaves in both petunia and carnation plants. Components of the cytochrome b6/f complex were found to accumulate to higher levels in corolla chloroplasts than in leaves. The opposite trend was found for components of the PSI core complex, as well as for the stromally located small and large subunits of ribulose‐1,5‐bisphosphate carboxylase, which accumulated in corollas to levels ca 2. 5 times lower than their respective levels in leaves. The latter subunits accumulated coordinately in corollas of both plant types during flower development. Data obtained from immunological studies were correlated with those at the mRNA level. Nothern blotting revealed that, in petunia corollas, the steady‐state transcript level of genes coding for the small subunit of ribulose‐l,5‐bisphosphate carboxylase was identical to that of genes coding for the major light‐harvesting chlorophyll a/b protein. Levels of both transcripts, as well as those of plastid‐encoded genes for the PSII reaction center's Dl and D2, were ca two‐thirds of their respective levels in leaves. In contrast, the level of transcript for the large subunit of ribulose‐1,5‐bisphosphate carboxylase was reduced 5‐fold in petunia corollas, as compared to leaves.
Inhibition of cell wall autolysis and auxin‐induced elongation of Cicer arietinum epicotyls by β‐galactosidase antibodies
Authors: Valero Pilar , Labrador Emilia
Published: May 2006

Polyclonal antibodies were raised in response to βIII‐galactosidase purified from cell wall of Cicer arietinum epicotyls. The antibody preparation generated, bound to βIII protein giving a major protein band in the zone corresponding to Mr 45 000, the molecular mass previously estimated for βIII‐galactosidase. These antibodies clearly suppress autolytic reactions in isolated walls of Cicer arietinum epicotyl segments, while the preimmune serum had no effect on autolytic reaction. The results strongly support the idea that the autolytic degradation of the cell wall is carried out by the βIII‐galactosidase.

The antibodies against β‐galactosidase were also able to inhibit cell wall hydrolysis mediated by both total cell wall protein extracted by LiCl and cell wall hydrolysis mediated by βIII‐galactosidase.

Since autolysis is thought to be related to the process of cell wall loosening, the effects of the antibodies against the autolytic enzyme was also tested on epicotyl growth. β‐galactosidase antibodies consistently inhibited IAA‐induced elongation.
A protein similar to PR (pathogenesis‐related) proteins is elicited by metal toxicity in wheat roots
Authors: Cruz‐Ortega Rocio , Ownby James D.
Published: May 2006

An acidic, low molecular weight protein called TA1‐18 (T for Triticum. Al for aluminium and 18 for its approximate molecular weight) is induced in wheat roots that are exposed to growth‐inhibiting concentrations of Al. Enhanced biosynthesis of TA1‐18 began during the period 3 to 6 h after exposure to Al, and reached a maximum after 9 to 12 h of treatment. A protein with the same molecular weight and pl was also elicited during toxicity associated with Cu and Cd, with calcium deprivation, and low (3. 5) pH, but not by heat shock. TA1‐18 was formed in small amounts in triticale, but was not detected in rye during exposure to growth‐inhibiting levels of Al. Amino acid sequencing of trypsin fragments of TA1‐18 revealed strong homology to pathogenesis‐related protein PR2 from parsley cultures, with which TA1‐18 also shares similar molecular weight and pl. Aluminium toxicity appears to have features in common with pathogenesis such that similar proteins are formed in response to both types of stress.
Catabolism of indole‐3‐acetic acid in citrus leaves: identification and characterization of indole‐3‐aldehyde oxidase
Authors: Winer Leo , Riov Joseph , Goren Raphael
Published: May 2006

A new enzyme, named indole‐3‐aldehyde oxidase (IAldO), was identified in citrus (Citrus sinensis L. Osbeck cv. Shamouti) leaves. The enzyme was partially purified by (NH4)2SO4 fractionation. Sephadex G‐200 gel filtration and DEAE‐cellulose ion exchange chromatography. IAldO catalyzes the oxidation of indole‐3‐aldehyde (IAld) to indole‐3‐carboxylic acid (ICA) with the production of H2O2. The enzyme is highly specific for IAld. The apparent KM of the enzyme for IAld is 19 μM. The optimum oxidation of IAld occurs at pH 7. 5. The molecular mass of the enzyme, as determined by Sepharose‐6B gel filtration, is about 200 kDa. Based on inhibitor studies, it is concluded that IAldO is not a flavin‐linked oxidase and there is no requirement for free sulfhydryl groups or divalent cations for maximum activity. The enzyme is strongly inhibited by benzaldehyde. Ethylene pretreatment, wounding and aging of leaf tissues did not affect enzyme activity, suggesting that the enzyme is constitutive in citrus tissues.
Hormone trafficking. A case study of growth regulator dynamics
Authors: Brock Thomas G.
Published: May 2006

When growth is promoted in plants, endogenous hormones may move into or out of the growing tissue, change in concentration through synthesis or degradation, or be chemically converted between active and inactive forms. Furthermore, the sensitivity of the growing tissue itself may change, producing an effective change in hormone level. The complexity of hormone trafficking has been partially unraveled in the case of the leaf‐sheath pulvinus of grasses. In this specialized organ, which grows only when turned on its side, hormones including auxins, gibberellins and ethylene change dynamically through time and space to regulate growth.
Inhibition of anthocyanin synthesis in the first internode of Sorghum bicolor by cobaltous ions. The site of action of cobalt
Authors: Dube Alok , Bharti S. , Laloraya M. M.
Published: May 2006

Cobaltous ions (Co2+) inhibited light‐mediated anthocyanin synthesis and phenylalanine ammonia‐lyase (PAL; EC 4. 3. 1. 5) activity in excised first internodes of Sorghum bicolor (L.) Moench. Ethephon (an exogenous source of ethylene) restored anthocyanin synthesis and PAL activity. Sulfhydryl‐containing compounds like cysteine and glutathione completely restored anthocyanin synthesis and PAL activity. N‐ethylmaleimide (NEM), a sulfhydryl reagent, inhibited anthocyanin synthesis and PAL activity; cysteine or glutathione reversed the effect of NEM. EDTA and other organic acids like citric, malic, oxalic and tartaric acid were also effective in bringing about recovery. It is suggested that the site of action of Co2+ might be at sulfhydryl groups or two adjacent carboxylic groups of a macromolecule that is involved either in anthocyanin or ethylene biosynthesis