bluuebunny/crossref_metadata_2025 huggingface dataset:
Partial floral evocation by high irradiance in the long‐day plant Sinapis alba
Authors: Havelange A. , Bernier G.
Published: April 2006

Previous work has shown that increased irradiance promotes flower initiation in the long‐day plant Sinapis alba when given during the first half of a single, suboptimal long day. It is without flower‐promoting effect, however, when given during a single short day. In the present work it is shown that, in the apex of plants exposed to a single short day at high irradiance, some changes occur that are normally observed during the transition to flowering (full evocation), e.g., elevated soluble sugar and starch levels, increased numbers of mitochondria and changed nucleolus structure. These changes are of similar magnitude and follow the same sequence as the corresponding changes during full evocation. Other changes, normally associated with full evocation, e.g., increased mitotic activity, are not caused by one short day at high irradiance. This treatment thus produces only what we call “partial evocation”.
Monitoring of membrane‐bound divalent cations in plant mitochondria using chlorotetracycline fluorescence
Authors: Meller Ian M.
Published: April 2006

Chlorotetracycline (CTC) shows a strongly enhanced fluorescence upon addition of mitochondria isolated from Jerusalem artichoke (Helianthus tuberosus L.) tubers in a low‐cation medium. This indicates the presence of membrane‐bound divalent cations. The chelation by CTC of the membrane‐bound divalent cations does not affect the oxidation of exogenous NADH significantly. The removal of the bound divalent cations using ethyleneglycol‐bis‐(β‐aminoethylether)‐N,N′‐tetraacetic acid (EGTA) and EDTA causes an 80% decrease in CTC fluorescence. Titration of CTC fluorescence (a direct measure of bound divalent cations) and 9‐aminoacridine fluorescence (a measure of surface potential) with EGTA and EDTA gives similar curves, although CTC fluorescence responds more slowly to the addition of chelators. The same bound divalent cations appear to be monitored by CTC fluorescence or by 9‐aminoacridine fluorescence.
Pathogen‐induced vascular gels: Ethylene as a host intermediate
Authors: VanderMolen G. E. , Labavitch John M. , Strand Larry L. , DeVay James E.
Published: April 2006

A cell free culture filtrate from 6‐day cultures of Fusarium oxysporum f. sp. cubense was processed to give: (1) a heterogeneous enzyme mixture, (2) purified polygalacturonase (PG), (3) partially‐purified polygalacturonate lyase and (4) β‐1,4‐xylanase. When introduced into explanted castor bean leaves each of these preparations was able to promote the formation of vascular system‐obstructing gels. Exposure of castor bean leaves to ethylene (3 ppm) also triggered gel formation. Explanted leaves produced ethylene in response to the enzyme mixture and PG. Vascular gel formation did not occur when ethylene production in response to enzymes was prevented.
Mycochrome system and the effect of molecular oxygen in the reversible photoinduction of conidiation in the fungus, Alternaria cichorii
Authors: Kumagai Tadashi
Published: April 2006

Coniditation the fungus, Alternaria cichorii Nattras (IMI 225641), was repeatedly induced and inhibited by alternating doses of near ultraviolet and blue radiation. The final response largely depended on the last kind of radiation administered. When the final radiation was near ultraviolet, conidiophore formation was induced, and conidia were then produced in the subsequent dark period; when it was blue, the induction of conidiation was suppressed. The inductive effect of near ultraviolet was promoted by anaerobiosis, but the reversing effect by blue radiation was not influenced by molecular oxygen. Thus, the “mycochrome” system apprears to control induction of conidiation in Alternaria cichorii, and oxidation‐reduction processes may be involved in its function.
Cold stratification and growth of radicles of loblolly pine (Pinus taeda) embryos
Authors: Carpita N. C. , Skaria A. , Barnett J. P. , Dunlap J. R.
Published: April 2006

The mechanism of germination enhancement by cold stratification was examined in seeds of loblolly pine (Pinus taeda L.), Removal of the seed coat permitted elongation of radicles from unstratified embryos, but both rates of germination and radicle elongation were increased by stratification. Radicles of both stratified and unstratified embryos excised from the megagamethophyte elongated only when in contact with solid incubation media supplemented with sucrose. Stratification of embryos either in the presence or absence of the megagametophyte resulted in similar enhancement of radicle elongation. Elongation rates of radicles were increased after stratification independent of sucrose concentration, and changes in sucrose content in the megagamethophyte during stratification or incubations subsequent to stratification were insufficient to regulate radicle growth. Our results support the hypothesis that the embryos of pine seeds perceive the low temperature stimulus directly and this stimulus results in a growth potential increase in the embryonic axes. We propose that this growth potential increase enables the embryos to overcome the mechanical restraint of the seeds coats and to germinate.
Photosynthetic development of Ocimum basilicum cells on transition from phosphate to fructose limitation
Authors: Dalton C. C.
Published: April 2006

Continuous culture was used to establish a steady state in fructose excess. Phosphate in the Murashige and Skoog type medium was found to be limiting growth; when phosphate concentration in the medium feed was doubled, the concentration of dry biomass and of all biomass elements increased After doubling the phosphate concentration fructose became limiting. Ocimun basilicum cells responded to the transition from phosphate limitation to fructose limitation by becoming greener and more photosynthetic; consequently, the yield on fructose increased.
Regulation of cell wall synthesis by auxin and fusicoccin in different tissues of pea stem segments
Authors: Brummell D. A. , Hall J. L.
Published: April 2006

Cell wall synthesis was studied by determining the incorporation of [14C]‐glucose into epidermal and cortical cell walls of etiolated Pisum sativum L. cv. Alaska stem segments. Walls were fractionated into the matrix and cellulose components, and incorporation into these components assessed in terms of the total uptake of label into that tissue. When segments were allowed to elongate, the stimulation of total glucose uptake by indole‐3‐acetic acid (IAA) and fusicoccin (FC) was greater than their stimulation of incorporation. IAA and FC thus did not stimulate precursor incorporation in elongating segments. When elongation was inhibited by calcium, however, IAA and FC significantly promoted wall synthesis in the cortex and vasular tissue (which shows almost no growth or acidification response to auxin). In these tissues incorporation into matrix and cellulose was promoted approximately equally. In the epidermis (thought to be the tissue responsive to auxin in the control of growth), FC promoted a significant increase in wall synthesis, although less than that in the cortex, while there was some evidence of a similar promotion by IAA. Both IAA and FC had a greater effect on incorporation into the matrix component of the wall than into cellulose. The results that FC caused a substantial promotion of cell wall synthesis which was not due solely to elongation, and that the inner non‐growth responsive cortical tissues can respond to IAA. Moreover, a comparison of the effects of IAA and FC on the different components of the wall suggests that the response in the epidermis differs from that in the other tissues.
Photosynthesis and transpiration by young Larix kaempferi trees: C3 responses to light and temperature
Authors: Crane J. L. , Dickmann D. I. , Flore J. A.
Published: April 2006

The effects of photon flux density and temperature on net photosynthesis and transpiration rates of mature and immature leaves of three‐year‐old Japanese larch Larix kaempferi (Lamb.) Sarg. trees were determined with an infrared, differential open gas analysis system. Net photosynthetic response to increasing photon flux densities was similar for different foliage positions and stage of maturity. Light compensation was between 25 and 50 μmol m−2 s−1. Rates of photosynthesis increased rapidly at photon flux densities above the compensation level and became saturated between 800 and 1000 μmol m−2 s−1. Transpiration rates at constant temperature likewise increased with increasing photon flux density, and leveled off between 800 and 1000 μmol m−2 s−1. Photosynthetic response to temperature was determined in saturating light and was similar for all foliage positions; it increased steadily from low temperatures to an optimum range betweeen 15 and 21°C and then decreased rapidly above 21°C. Transpiration rate, however, increased continuously with rising temperature up to the experimental maximum. CO2 compensation concentrations for mature foliage varied between 58 and 59 μl l−1; however, foliage borne at the apex of the terminal leader compensated at 75 μl l−1. None of these data support the claim that Japanese larch possesses C4 photosynthetic characteristics.
Isolation and characterization of cytoplasmic NADP+‐malic enzyme from Lupinus luteus leaves
Authors: Tomaszewska Barbara , Schramm Ryszard W. , Kokot Anna , Mazurowa Hanna
Published: April 2006

NADP+‐dependent malic enzyme (L‐malate : NADP+ oxidoreductase, decarboxylating, EC 1.1.1.40) was extracted from the leaves of yellow lupine. The purification procedure included fractionation with (NH4)2SO4 and Sephadex G‐25 chromatography, followed by purification on DEAE‐cellulose and Sephadex G‐200 columns. The enzyme was purified 122‐fold. The enzyme affinity towards L‐malate was found to be significantly higher with Mn2+ than with Mg2+. The Hill coefficient for Mg2+ depended on concentration and was 1.6 for the lower and 3.9 for the higher concentrations. The dependence of the enzyme activity on NADP+ followed a hyperbolic curve. Km values and Hill coefficients for NADP+ were similar with both Mn2+ and Mg2+. The enzyme activity was strictly dependent on divalent cations and followed a sigmoidal curve at least for Mg2+. The enzyme had 4‐fold higher affinity towards Mn2+ than towards Mg2+, the Km values being 0.3 and 1.15 mM respectively. Of several tested organic acids, oxalate was the most effective inhibitor followed by oxaloacetate while succinate was the strongest activator.
The role of ethylene in photoperiodic control of bulbing in Allium cepa
Authors: Lercari Bartolomeo
Published: April 2006

Bulb formation in Allium cepa L. cv. Dorata di Parma, was promoted by ethylene (Ethrel 120 mg l−1) treatments. Application of the antiethylene complex silverthiosulphate (0.01 mM) inhibited ethylene‐induced bulb formation, but did not affect photoperiod‐induced bulb formation. When the inhibitor of ethylene biosynthesis, aminoethoxyvinylglycine, was applied at 0.04 to 4 mg l−1 to onion plants under inductive photoperiodic conditions the bulb promotion was unaffected. Therefore, Ethrel‐induced bulb formation does not appear to be related to endogenous control of bulbing.
The response to NaCl of excised fully differentiated and differentiating tissues of the cultivated tomato, Lycopersicon esculentum, and its wild relatives, L. peruvianum and Solanum pennellii
Authors: Taleisnik‐Gertel E. , Tal M. , Shannon M. C.
Published: April 2006

The responses to NaCl of cultured leaf discs and leaflets derived from fully differentiated leaves and of shoot apices excised from the cultivated tomato Lycopersicon esculentum Mill. and its wild salt‐tolerant relatives L. peruvianum (L.) Mill, and Solanum pennellii Cor were compared. The results suggest that the tolerance of the whole plant to salt depends largely on the tolerance of plant organs containing meristematic tissues rather than on tissues already differentiated. This suggestion is based on the positive correlation found between the response to NaCl of shoot apices and of the whole plant, i.e. both whole plants and apices of the wild species were more resistant to salt than those of the cultivated species. No difference was found among the species with respect to the responses of the fully differentiated parts. The ion balance (K+/Na+ and Cl−/Na+) in detached leaves and apices exposed to salt was different from the balance in the same parts while attached to the salt‐treated plant. This difference may be due to the severance of the excised parts from the major sites controlling the balance of ions in the whole plant.
Distribution of [14C]‐labeled photosynthates within intensively cultured Populus clones during the establishment year
Authors: Isebrands J. G. , Nelson N. D.
Published: April 2006

Seasonal patterns of [14C]‐labeled photosynthate distribution within two intensively cultured Populus clones with contrasting phenology (P. tristis × P. balsamifera cv. ‘Tristis no. 1′; P. × euramericana cv. Eugenei) were investigated during the establishment year. During active shoot elongation upper mature leaves exported 14C acropetally to the expanding leaves and elongating internodes, and basipetally to the stem. Little 14C was exported to lower mature leaves or lateral branches. At budset the 14C export pattern shifted dramatically in the basipetal direction, i.e., to the lower stem, hardwood cutting, and roots. The timing of budset was the primary factor determining the differences between the clones, except that in all cases Tristis exported more 14C to the roots than Eugenei. After budset lower mature leaves had a similar export pattern to upper leaves, but the quantity of 14C exported to the roots was slightly higher. The results confirm the importance of autumn foliage for root growth in poplar. Clonal differences in seasonal patterns of photosynthate distribution offer potential for the poplar breeder seeking to match a clone's growth pattern with the specific growing season of the site.
Sulfide‐induced oxygen uptake by isolated spinach chloroplasts catalyzed by photosynthetic electron transport
Authors: de Kok L. J. , Thompson C. R. , Kuiper P. J. C.
Published: April 2006

In addition to an inhibitory effect on the photoreduction of NADP+ by isolated spinach chloroplasts (Spinacea oleracea L. cv. Melody Hybrid), sulfide initiated oxygen uptake by chloroplasts upon illumination, both in presence and absence of an electron acceptor. Sulfide‐induced oxygen uptake was sensitive to DCMU demonstrating the involvement of photosynthetic electron transport. Addition of superoxide dismutase to the chloroplast suspension prevented the sulfide‐induced oxygen uptake, which indicated that sulfide may be oxidized by the chloroplast, its oxidation being initiated by superoxide formed upon illumination (at the reducing side of PSI). Tris‐induced inhibition of NADP+ photo‐reduction could not be abolished by sulfide, which indicated that sulfide could not act as an electron donor for PSI.
A long‐wavelength absorbing form of protochlorophyll and crystalloids in the inner seed coat of Luffa cylindrica
Authors: Sundqvist Christer , Ryberg Hans
Published: April 2006

The inner seed coat of seeds of Luffa cylindrica (L.) Roem. (cv. Luffa sponge vine) was used to study the development of the protochlorophyll‐containing plastids during different stages of maturity of the fruits. The inner seed coats had an absorption spectrum with a main peak in the red region at 675 nm and a shoulder at 630 nm. The fourth derivative spectrum gave a clear peak at 630 nm and also a small additional peak at 650 nm. An acetone extract showed a peak at 626 nm and a Soret band at 440 nm indicating that the main pigment in the seed coat was protochlorophyll. The ultrastructure of the protochlorophyll‐containing plastids changed during maturation of the seed. In the young stage an elaborate membrane system was present. In a more mature stage the membrane system degenerated and crystalloids were formed. Some of these crystalloids seemed to develop into plastoglobuli in the most mature stage.
Release of ethane from immobilised plant cell protoplasts in response to chemical treatment
Authors: Schnabl H. , Elbert Chr. , Youngman R. J.
Published: April 2006

In isolated protoplasts ofVicia fabaL. (cv. Weißkernige Hangdown) which were immobilised in a cross‐linked alginate matrix, ethane production and ribulose bisphosphate carboxylase (RuBP carboxylase) aetivity were determined after treatment of the alginate strips with various chemical substances.

The stimulation of ethane formation and the inhibition of RuBP carboxylase activity by the toxic materials might provide the basis for a simple, rapid and sensitive system for the determination of chemicals in the environment.
In vitro study of the xanthine dehydrogenase from illuminated or darkened leaves
Authors: Nguyen J. , Nato A.
Published: April 2006

The activity of xanthine dehydrogenase (XDH; EC 1.2.3.37), a key enzyme of purine catabolism leading to the synthesis of ureides, was investigated in cell‐free extracts of illuminated or darkened tobacco (Nicotiana tabacum L. cv. xanthi) leaves. Whereas the in vivo enzyme activity measured on leaf discs was lower in light than in darkness, cell‐free extracts from illuminated or darkened leaves exhibited the same maximum velocity around 30 pmol (mg fresh weight)‐1 h‐2. The kinetic constants of the enzyme for the substrate and for the cofactor did not change in relation to illumination of leaves, the Km for hypoxanthine being about 30 μM and that for NAD+ 13 μM. Extracts run on polyacrylamide gel electrophoresis showed only one band of XDH activity which was identical whether the plants were illuminated or not. The molecular weight of the native enzyme from both extracts was estimated to be 320 000 dalton. Dithiothreitol treatment of leaf extracts could not mimick the effect of light on XDH activity in leaves. A direct effect of light on the activity of that flavoprotein could not be observed specifically in relation to the light treatment of cotyledons of Pharbitis nil prior to the enzyme extraction. A cycloheximide‐trealment of cotyledons of Pharbitis nil decreased the in vivo XDH activity. But the inhibition of the enzyme activity was similar whether the plants were in conditions inducing an increase of activity or not, indicating that quantitative changes of the enzyme protein are not involved in the variations of the in vivo enzyme activity. The results are discussed in relation to the conditions prevailing in the in vitro and the in vivo enzyme activity measurements. It is suggested that light might affect the XDH activity in leaves through the modifications of cell environment.
Interactions between hydrogen cyanide, gibberellin, abscisic acid and red light in germination of lettuce seeds
Authors: Zagorski Slawomir , Lcwak Stanisiaw
Published: April 2006

Germination of lettuce (Lactuce sativa L. cy. Grand Rapids) seeds was promoted by red light and by pulse treatments with gibbercllie acid (GA3) or hydrogen cyanide, whereas it was inhibited by short exposure of seeds to absusic acid (ABA). The eflects of unsalLirating red light and of 10 μM GA3 on lettuce germination were completely reversed the effect of ABA (100 μM). In contrast, hydrogen cyanide did not reverse the effect of 100 μM ABA and only partly eliminated the effect of 10μM ABA, independently of the sequence of treatments. Possible interactions between HCN GA3, ABA and red light were discussed. It was concluded thai light GA3 and HCN affect different mechanisms involved in lettuce germination: ABA counteracts the stimulatory action of all these faclors. being the most effective against cvanide Additional key words ‐ Lactuca sativa, pholodormancy, phylohormoncs.
Spectrophotometric quantitation of protochlorophyll(ide): Specific absorption and molar extinction coefficients reconsidered
Authors: Kahn Albert
Published: April 2006

To allay doubt about how to calculate molar extinction eoeffieients from the specific absorption coefficients of protoehlorophyll(ide), dark‐grown leaf segments and saponin protochlorophyll(ide) holochrome subunits frotn barley (Hordeum vulgare L.) and cotyledons of cucumber (Cucumis sativus L.) were extracted with acetone without or following prior, brief illumination. Absorbance data and eoeffieients of chlorophyll a were used to derive extinetion eoeffieients of protoehlorophyll(ide); 626 nm (range: 30 to 35 1 mmol‐1 cm‐1) without recourse to published coefficients c protochlorophyll(ide). These results combined with evaluation of how the origin; coefficients were obtained, argue for using the molecular weight of protochlorophy rather than protochlorophyllide to calculate molar extinction eoeffieients from th specific absorption coefficients.
Cytokinin‐controlled polyribosome formation and protein synthesis in cucumber cotyledons
Authors: Gwóźdź Edward A. , Woźny Adam
Published: April 2006

An increased proportion of ribosomes forming polyribosomes and an increased activity of polyribosomes in protein synthesis in vitro were found in dark‐grown kinetin‐treated cucumber cotyledons (Cucumis sativus L. cv. Monastyrski) as compared with untreated controls. The stimulation occurred also under an osmotic stress which suppressed the kinetin stimulation of the cotyledon growth, indicating an independence of the effect from the promotion of growth. Analysis of the ribosomal profiles as well as experiments with [3H]‐adenosine showed that kinetin neither changed the total amount of ribosomal material nor enhanced the label incorporation into the polyribosomes. Inhibitors of transcription and of polyadenylation did not affect the kinetin stimulation of the polyribosome level. Aurin tricarboxylic acid (inhibitor of initiation) markedly suppressed the stimulatory effect of kinetin on the polyribosome formation. It is suggested that the increase in polyribosomes in response to kinetin results from the kinetin effect at the translational level by increasing the rate of initiation through an enhancement of the affinity of ribosomes for the messenger RNA.
Effects of long‐chained aliphatic amines on photosynthetic reactions in isolated spinach chloroplasts
Authors: Blanck Hans , Egnéus Hans
Published: April 2006

The effect of six long‐chained aliphatic amines on 14CO2‐reduction, electron transport and the 515 nm absorbance change and shrinkage in isolated intact and broken chloroplasts from spinach (Spinacia oleracea L. cv. Weibulls Medania) was investigated. Five of the six investigated amines affected photosynthesis in intact chloroplasts by inhibiting 14CO2‐reduction. In broken chloroplasts the same amines uncoupled electron transport. When added to intact chloroplasts the five amines induced a light‐dependent oxygen uptake leading to (he formation of hydrogen peroxide. The oxygen uptake was not due to the amines acting as Mehler reactants. The mode of action, different from that of simple aliphatic amines, was an effect on membrane integrity, first affecting the membrane potential. At higher amine concentrations a more general effect on the ion conditions in the thylakoids was evident.
Effect of chelating agents on bud induction and accumulation of iron and copper by the moss Bartramidula bartramioides
Authors: Rahbar Kavita , Chopra R. N.
Published: April 2006

The chelating agents, EDDHA, its iron salt, EDTA, and salicylic acid enhance bud formation in Bartramidula bartramioides (Griff.) Wijk & Marg. Salicylic acid elicits optimal response at 10–4M, whereas the other substances do so at 10–7M. Increased concentration of ferric citrate and cupric sulphate also stimulate bud induction. The accumulation of Fe3+ and Cu2+ is facilitated by chelators. The endogenous iron content is maximum at 10–7M EDDHA or EDTA, which is also the concentration optimal for bud induction.
Effect of ABA on the water relations of winter‐wheat cultivars varying in drought resistance
Authors: Kirkham M. B.
Published: April 2006

Water and osmotic potentials were measured in leaves of a drought‐sensitive (‘Ponca’) and a drought‐resistant (‘KanKing’) cultivar of winter wheat (Triticum aestivum L. em. Thell.) to determine if the potentials of the drought‐sensitive cultivar could be made similar to those of the drought‐resistant cultivar through application of abscisic acid (ABA). Stomatal resistance was also measured. Plants were sprayed with ABA and grown in soil, which was watered or allowed to dry. In well‐watered plants, ABA closed the stomata of both cultivars. Stomatal resistance of plants grown without added water and with ABA was less than that of plants grown without added water and without ABA. Under ample water supply, ABA decreased water and osmotic potentials of the drought‐sensitive cultivar (Ponca), but had no effect on these potentials in the drought‐resistant cultivar (KanKing). Under water‐deprived conditions, ABA increased water and osmotic potentials of Ponca, but did not change these potentials in KanKing. The overall effect of ABA was to decrease the differences in the water and osmotic potentials between the two cultivars.
The effect of abscisic acid on cell growth, cell division and DNA synthesis in the maize root meristem
Authors: Barlow Peter W. , Pilet Paul‐Emile
Published: April 2006

Cis‐abscisic acid (ABA), when applied to maize (Zea mays L. cv. LG 11) roots, decreases the rates of cell growth and cell division in the meristem. It also decreases the rate at which nuclei become labelled with [3H]‐thymidine and enter mitosis. Removing the root cap accelerates the entry of nuclei into the DNA synthetic phase of the mitotic cycle and enhances the rate of cell proliferation in the quescent centre. ABA diminishes these effects, but does not suppress them. Thus, ABA cannot wholely substitute for the presence of a cap. One of the primary effects of applied ABA is to retard cell enlargement which may in turn affect the rate of cell division; natural endogenous ABA may act similarly. ABA might in this way assist in maintaining the quiescent centre in intact roots, but cannot be the sole agent involved.
The subcellular distribution of carotenoids in light‐grown Verticillium agaricinum
Authors: Hsiao Ke‐cheng , Møller Ian M.
Published: April 2006

Hyphae of light‐grown V. agaricinum (Link) Corda contain many lipid bodies. The hypae were disrupted and the membranes immediately pelleted by a 48 000 g spin for 30 min. The major part (90%) of the carotenoids was found in a lipid layer on top of the supernatant. Carotenoids extracted from the lipid layer in diethyl ether had an absorption maximum at 488 nm. On the basis of spectra in different organic solvents the main component was tentatively. Thin layer chromatography of extracted and saponified carotenoids revealed the presence of one major and one minor component.

The 48 000 g pellet contained 80% of the NAD+‐dependent malate dehydrogenase (marker for mitrochondria), 25% of the antimycin‐resistant NADH‐cytochrome c reductase (marker for mitochodria and endoplasmic reticulum) and 10% of the proteins and the carotenoids. The latter were different from the carotenoids in the lipid layer in that the absorption maximum was at 471 nm in diethyl ether.

Further fractionation of the 48 000 g pellet showed the presence of carotenoids in both mitochondria and endoplasmic reticulum (ER) all with an absorption maximum at 471 nm. On a thin layer plate these carotenoids migrated in one band coinciding with the minor band of the lipid layer. On a continous Percoll gradient two main areas of mitochodrial activity (1.068 and 1.063 g ml−1) were clearly separated from the ER (1.059 g ml−1). The carotenoid content was about 0.6 and 0.7–1.0 μg (mg protein)−1 for mitochondria and ER, respectively, equivalent to 1–2 carotenoid molecules per 1000 lipid molecules. The possible role of these membrane‐bound carotenoid molecules is discussed.
Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. I. Photosynthesis in vivo
Authors: Ögren Erling , Öquist Gunnar , Hällgren Jan‐Erlik
Published: April 2006

The floating angiosperm Lemna gibba L. was exposed for 2 h to various combinations of photosynthetic photon flux densities and temperature. The extent of photoinhibition of photosynthesis was assayed by measuring the net CO2 uptake before and after a photoinhibitory treatment, and the time course for photoinhibition was studied. It was found that the maximum quantum yield and the light‐saturated rate of CO2 uptake were affected by the interaction between light and temperature during the photoinhibitory treatment. At a constant photon flux density of 650 μmol m−2 s−1 the extent of photoinhibition increased with decreasing temperature showing that even a chilling‐resistant plant like L. gibba is much more susceptible to photoinhibition at chilling temperatures. About 60% photoinhibition of the quantum yield for CO2 uptake could be obtained either by a high photon flux density of 1 750 μmol m−2 s−1 and 25°C or by a moderate photon flux density of 650 μmol m−2 s−1 and 3°C. The time courses of recovery from 60% photoinhibition produced by either of these two treatments were similar, indicating that the nature of the photoinhibition was intrinsically similar. The extent of photoinhibition was related to the amount of light absorbed in excess to what could be handled by photosynthesis at that temperature. The vital importance of photosynthesis in alleviating photoinhibition is discussed.
Auxin‐induced cell expansion of potato tuber and chicory root: Role of hydroxyproline synthesis
Authors: Shannon P. R. M. , Flood A. E. , Wain R. L.
Published: April 2006

We have reinvestigated the role of protein‐bound hydroxyproline (extensin) in auxininduced cell enlargement using discs excised from tubers of Solanum tuberosum L. cv. Pentland Crown and from roots of Cichorium intybus L. cv. Magdeburg. Extensin increases markedly in potato tuber discs treated with water and auxin, and the hydroxyproline is primarily in the cell wall. 2,2′‐Dipyridyl totally inhibits both hydroxyproline synthesis and auxin‐induced cell expansion in potato with the inhibitions being reversed in parallel by Fe2+. Free hydroxyproline also totally prevents induced cell enlargement. Pretreatment with gibberellic acid totally inhibits subsequent auxin‐induced cell expansion but does not inhibit hydroxyproline synthesis. Therefore, the level of hydroxyproline does not control auxin‐induced cell enlargement in potato tuber discs. Other interpretations are discussed but we conclude that extensin biosynthesis is necessary for auxin‐dependent cell expansion as inhibition of the synthesis prevents the induced expansion. Dipyridyl and free hydroxyproline partially inhibit auxin‐induced cell enlargement in chicory root discs. Thus a component of the auxin‐dependent cell enlargement in chicory is also dependent on extensin synthesis.
Effect of root temperature on the amino‐nitrogen composition of leaves in successive segments of apple shoots
Authors: Tromp J. , Ovaa J. C.
Published: April 2006

Young apple trees (Malus pumila Mill. cv. Cox's Orange Pippin) given nitrogen either at or 40 days after bud‐break were kept at a root temperature of 6, 18 or 30°C under otherwise constant conditions. Twelve weeks after the start of the experiment leaves from successive shoot segments and roots were collected and in most cases analysed to assess total nitrogen, protein nitrogen, and the main amides and amino acids. The percentage composition of the amino‐nitrogen fraction of the roots was not or was hardly at all affected by the treatments; asparagine predominated, followed by arginine. In contrast, in the leaves the share of arginine dropped from about 90% at 6°C to about 30% at 30°C in favour of especially asparagine. This pattern was mainly attributable to the situation in the basal sections of the shoot. In the middle and top segments the temperature effects were small. In general, a high level of amino nitrogen corresponded to a high contribution of arginine. Soluble nitrogen was higher after the late than after the early application of nitrogen. Shoot growth was reduced at 6°C root temperature, but little difference was seen between 18 and 30°C. It was concluded that with respect to nitrogen metabolism roots and shoots function more or less independently of each other. The hypothesis that the roots affect leaf nitrogen metabolism via the supply of growth substances produced in the roots, presumably cytokinins, is discussed.
Aging and flowering of the apex in young Bidens radiata
Authors: Poulhe Robert , Arnaud Yolande , Miginiac Emile
Published: April 2006

The response of Bidens radiata Thuill., a short‐day plant, to conditions for flower induction changes during the first 96 h after germination: the earlier the induction, the better the flowering response. Flowering is observed without previous vegetative development. An histological study shows that failure to flower is correlated with the development of the primordia of the second node leaves. The antagonism between vegetative and floral development is discussed.
Peroxidase and catalase activity in leaves of Halimione portulacoides exposed to salinity
Authors: Kalir Arie , Omri Gila , Poljakoff‐Mayber Alexandra
Published: April 2006

The effect of high NaCl concentrations on the activity of catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7) and malate dehydrogenase (NAD+‐linked; EC 1.1.1.37) from leaves of Halimione portulacoides (L.) Aellen was studied. The plants were exposed to high salinity during growth and enzyme activity was measured either in the absence or in the presence of various concentrations of NaCl. Increasing salinity in vitro induced three types of effects: (1) an increase in activity (peroxidase); (2) a decrease in activity (catalase); (3) stimulation by low salt concentration but inhibition by higher concentrations (malate dehydrogenase). Salinity in vivo induced a marked decrease in catalase and malate dehydrogenase activities. However, peroxidase in vivo showed an optimum curve of activity vs external NaCl concentration, with an optimum at ca 1 M NaCl. Exposure of plants to salinity induced changes in the properties of the enzyme proteins: they precipitated at a higher (NH4)2SO4 concentration, were eluted later during Sephadex G‐200 filtration, and showed a shift in the maximal, minimal and optimal temperatures. These data are interpreted as evidence for conformational changes in the enzymes due to prolonged exposure to high salinity stress; such changes could be disruption into monomers (catalase and malate dehydrogenase), or changes in molecular shape (in the peroxidase).
Vegetative growth in plants: A dynamic model
Authors: Zelawski Wlodzimierz , Szlenk Wieslaw
Published: April 2006

On the basis of data for accumulation and distribution of dry matter in seedlings of scots pine (Pinus sylvestris L.) a mathematical model for vegetative plant growth is formulated. It is assumed that the total growth of a plant results from the mutually dependent growth of assimilatory and non‐assimilatory organs whereas the relative size of these organs reflects phenotypical adaptation to environmental conditions. The mathematical description of vegetative growth is carried out in terms of two‐dimensional difference equations (a discrete dynamic system of a two‐dimensional open domain into itself). The model covers different types of growth curves. These curves can be modelled in terms of a departure from initially exponential to linear, sigmoidal, or even quite irregular growth, depending on environmental conditions which affect both unit leaf rates and partitioning coefficients. The results of a simulation procedure are consistent with the experimental data.
The preparation and activity of a phenylanine ammonia‐lyase inactivator from sunflower leaves
Authors: Gupta Subhash C. , Creasy Leroy L.
Published: April 2006

Isolated plastids from crude extracts of sunflower (Helianthus annuus L. cv. Sungold) leaves released a factor on extraction with Triton X‐100 that inactivated Rhodotorula glutinis L‐phenylaine ammonia‐lyase (PAL; EC 4.3.1.5) in vitro. This PAL‐inactivating factor (PAL‐IF) was found to be proteinaceous in nature when tested with pronase (EC 1.11.1.6), peroxidase (EC 1.11.1.7) and nitrate reductase and the protection of PAL from PAL‐IF by ligands indicated its specificity towards PAL. The inactivated PAL inhibitors reported earlier. It is suggested that inactivation may play an important role in in vivo regulation of L‐phenylalanine ammonia‐lyase activity and phenolic biosynthesis.
Benzyladenine‐induced stimulation of two components of chlorophyII formation in etiolated cucumber cotyledons
Authors: Dei Mitsuru
Published: April 2006

Excised etiolated cotyledons of cucumber (Cucumis sativus L. cv. Aonagajibai) were continuously irradiated under various intensities of white light. The rate of chlorophyII (Chi) formation during the lag phase reaches a plateau at fluence rates above 1.4 urmol m−2 s−1. This is true in both water‐control and benzyladenine (BA)‐pretreated cotyledons. In cotyledons pretreated for 14 h with BA in darkness (in which case, Chl formation is stimulated by BA during both the lag and the steady‐state phases), the increase in the steady‐state rate of Chl formation with increasing light in tensity is stimulated compared to that of the water control over the range of fluence rates, 0. 25‐43 urmol m−2 s−1. In cotyledons pretreated for 6 h with BA in darkness (only Chl formation during the lag phase is stimulated), only an increase in fluence rate from 0.25 to 1.4 umol m−2 s−1 causes a higher increase in the Chl formation in the BA‐treated cotyledons than in the water control. The time course of Chl formation shows that the BA‐induced late‐appearing effect (stimulation of the steady‐state rate) is almost absent at low intensity illumination, but the BA‐induced fast‐appearing effect (elimination of the lag phase) is effective at all intensities. From this evidence, the Chl‐forming process apparently consists of two components, whose periods of operation or light‐intensity requirements are different. BA stimulates the rates of the respective components in both the fast and the late‐appearing effects.
Effect of Mg2+ and Ca2+ on the response to nickel toxicity in a serpentine endemic and nickel‐accumulating species
Authors: Gabbrielli R. , Pandolfini T.
Published: April 2006

The effect of Ca2+, Mg3+ and Ni2+ on root elongation was studied in Alyssum bertolonii Desv., a nickel‐accumulating and serpentine endemic species. The results confirm the detoxifying action of Ca2+ which reduces the toxic effect of Mg2+ and Ni2+ on root development. In addition, Ca2+ and Mg2+ interact positively in depressing Ni2+ uptake. The combined effect of these two ions is of relevance for the mechanism of nickel tolerance in A. bertolonii.
Metabolism of (±) 2‐[14C]‐abscisic acid in Lactuca sativa achenes
Authors: Orlandini M. , Barthe Ph. , Bulard C.
Published: April 2006

Achenes ofLactuca sativa L. cv. Grand Rapids were treated with (±) 2‐[14C]‐abscisic acid (ABA) at 105 ‐ or 2‐106 M for 6, 12, 24, 48 or 96 h in darkness at 24°C. They were then extracted in 80% ethanol. Two acidic diethyl ether phases which contained the free acids and the acids released after mild alkaline hydrolysis respectively, were analyzed as well as the radioactivity which remained in the final aqueous phase. For treatment durations between 6 and 96 h, the major part of the radioactivity was found in the free phase, in the form of ABA. For treatment durations up to 48 h, no radioactivity was detected at the Rf of phaseic acid or dihydrophaseic acid (free and hydrolysed phases). After 96 h culture on 105 M ABA, dihydrophaseic acid was present, but only in very small quantities. Two ABA metabolites were detected. One was characterized as β‐d‐glucopyranosyl abscisate since its Rf was the same as that of an authentic sample in three different solvent systems and also since it released ABA on mild alkaline hydrolysis. It increased steadily with time and represented the main metabolite. The other metabolite found in the aqueous phase after mild alkaline hydrolysis and extraction with ether at pH 3 was a very polar compound, resistant to alkaline hydrolysis in the presence of concentrated ammonia and to methylation. It was, however, metabolized by apple embryo, yielding essentially dihydrophaseic acid and an ester which released dihydrophaseic acid on mild alkaline hydrolysis. These results indicate that under the conditions tried, the metabolism of [14C]‐ABA by lettuce achenes leads almost exclusively to the formation of conjugates, oxidative metabolism of ABA being almost non‐existent. Separate analysis of the integuments and of the endosperm plus embryo after culture of whole achenes for 48 h in the presence of 105 M [14C]‐ABA showed that ABA metabolism occurred only in the endospermembryo tissue.
Ultrastructural changes in naturally aged Pinus pinea seeds
Authors: García de Castro Margarita Fernández , Martinez‐Honduvilla Carlos J.
Published: April 2006

The decline of germination observed after storage of Pinus pinea L. seeds up to 35 years at room temperature was accompanied by an increase in their ability to leak reducing sugars, probably as a consequence of membrane alterations due to senescence. Results of studies of the cell ultrastructure of viable and non‐viable seeds before and after imbibition indicate that such is the case. Noticeable changes occurred in the ultrastructure of endosperm and embryo cells with germinability loss, even in the unimbibed condition. The main alterations were spherosome coalescence, plasmalemma separation from the cell wall and chromatin aggregation.
Hormonal changes associated with leaf senescence in cotton (Gossypium barbadense)
Authors: Elkinawy Mahasen
Published: April 2006

To study the hormonal regulation of foliar senescence in cotton (Gossypium barbadense L. cv. Giza 68, long staple), the sequential changes in gibberellins (GAs), indoleacetic acid (IAA) and abscisic acid (ABA) were examined in the cotyledons from the completion of expansion through senescence (days 12‐24 after sowing). The onset of senescence could be detected on day 20, the stage of maximum accumulation of leaf metabolites. At this stage, free GAs quickly lost more than 40% of their initial activity. Further decrease of free GAs was then characteristically observed in the senescent leaves. A remarkable increase in free IAA and free ABA between days 18 and 20 immediately followed by nutrient depletion, suggests the contribution by both hormones to the senescence system. The definite drop in free IAA below its initial level occurred on day 24, when most of the leaf protein and chlorophyll were already broken down.
Non‐electrolyte permeability of plant cuticles: A critical evaluation of experimental methods
Authors: Kerler Franz , Riederer Markus , Schönherr Jörg
Published: April 2006

A method for measurement of non‐electrolyte transport through enzymatically isolated cuticles of Ficus elastica Roxb. var. decora is presented. Permeance coefficients and hold‐up times are determined under steady‐state conditions. The transport system consists of two small reservoirs separated by the cuticle. The compounds tested (4‐nitrophenol and pentachlorophenol) differ widely in lipid solubility and enable a critical evaluation of the apparatus used. The sorption capacity of the cuticle for lipophilic compounds is related to their cuticle/water partition coefficients. The problems of unstirred layers and of membrane integrity are discussed. The permeances measured ranged from 10−11 to 10−5 m s−1, the hold‐up times from 50 s to 22 h.
Changes in protein synthesis during the development of Agrostemma githago seeds
Authors: de Klerk Geert Jan
Published: April 2006

The transition from the growth to the maturation phase in developing seeds of Agrostemma githago L. was found to coincide with major changes in the rate of protein synthesis, the kinds of proteins synthesized, and the composition of the non‐proteinbound amino acid pool. Coincident changes were observed in viability and the ability to withstand desiccation. Desiccated mature Agrostemma seeds are dormant and need at least three months of after‐ripening. In imbibed dormant and after‐ripened seeds no synthesis of storage proteins was observed with the exception of one particular set of storage proteins. Dormant and after‐ripened seeds synthesized the same kinds of proteins during early imbibition, indicating an almost identical metabolic state which differs considerably from that of developing seeds.
Citrate synthases from germinating castor bean seeds – I. Purification and properties
Authors: Zehler Heinz , Thomson Klaus‐Sten , Schnarrenberger Claus
Published: April 2006

The mitochondrial and glyoxysomal citrate synthase (EC 4.1.3.7) from the endosperm of germinating castor beans (Ricinus communis L., type Sanzibaricnsis) were purified to a final specific activity of 76 and 78 U (mg protein)−1, respectively. Both citrate synthases could be bound to ATP‐Sepharose. However, only the mitochondrial enzyme could be eluted by either 100 μM oxaloacetate or 100 μM coenzyme A (indicative of affinity chromatography), while the glyoxysomal enzyme was only eluted by 0.5 M KCI (indicative of ion‐exchange chromatography). Many properties of the two isoenzymes were similar including the pH dependence and temperature dependence of activity, the pH stability, and the inactivation of the enzyme at elevated temperatures. The most pronounced differences between the two citrate synthases were the isolelectric points of pH 5.9 for the mitochondrial and of pH 9.1 for the glyoxysomal enzyme. Both citrate synthases are dimers in the native form with a molecular weight of 95000 each, as determined by gel filtration on Sepharose CL‐6B and by polyacrylamide gel electrophoresis in the presence of 0.1% sodium dodecyl sulfate. However, the glyoxysomal citrate synthase existed also as a tetramer with a molecular weight of 200000 in the presence of 10 mM MgCl2.
Citrate synthases from germinating castor bean seeds – II. Time course of synthesis and immunochemical comparison
Authors: Zehler Heinz , Schnarrenberger Claus
Published: April 2006

The time course of total citrate synthase activity in castor bean (Ricinus communis L., type Sanzibariensis) endosperm showed a 7‐fold increase during the initial 5 days of germination and a decrease thereafter. All citrate synthase activity in the ungerminated seeds was due to the mitochondrial isoenzyme. After two days of germination the glyoxysomal isoenzyme began to appear. After 5 days the glyoxysomal citrate synthase represented 50 to 55% of the total activity and the mitochondrial enzyme the remainder. This was estimated from (a) inactivation of the glyoxysomal citrate synthase by 5,5′‐dithiobis(2‐nitrobenzoic acid); (b) solid phase adsorption of the glyoxysomal synthase by a specific antiserum; (c) separation of isoenzymes by (NH4)2SO4 gradient solubilization.

The increase of both citrate synthases during the initial 4 days of germination could be prevented by 10 μg cycloheximide ml−1, but not by 40 or 400 μg chloramphenicol ml−1, indicating a synthesis on 80 S ribosomes. Actinomycin D completely inhibited the appearance of the glyoxysomal enzyme while the mitochondrial enzyme was not affected. Antisera against the two isoenzymes revealed major structural differences between two citrate synthases, however, also some common determinants. No cross‐reaction was observed with the citrate synthase from pig heart or E. coli.