bluuebunny/crossref_metadata_2025 huggingface dataset:
[14C]‐Assimilate partitioning in photoperiodically induced seedlings of Pharbitis nil. The effect of benzyladenine
Authors: Abou‐Haidar Sana S. , Miginiac Emile , Sachs Roy M.
Published: April 2006

Partitioning of [14C]‐labeled assimilates was studied in relation to photoperiodic floral induction and evocation in one‐week‐old Pharbitis nil Choisy cv. ‘Violet’ seedlings. In plants kept under 16 h photoperiods, one 15 h night induced 100% axillary flowering whereas a 24 h night induced both terminal and axillary flowering. A 15 min night break of red light given 8 h after the beginning of the dark period inhibited flowering. Total [14C]‐assimilate distribution among major sinks (plumules + epicotyl and roots + hypocotyl) from a single source cotyledon was unchanged by one inductive night; however, import of [14C]‐assimilates into shoot apices was increased in induced plants compared to vegegative controls. This increase was several‐fold in plants subjected to a 24 h night. N6‐Benzyladenine (BA) application to cotyledons or plumules under non‐saturating night lengths increased the number of floral buds per plant without affecting the position of the first floral bud (i.e. the speed of induction). The same treatment caused increased label accumulation in induced apices, while it only slightly affected non‐induced ones. The mode of action of BA on flowering through growth stimulation and resulting assimilate mobilization is discussed.
Thigmomorphogenesis: The induction of callose formation and ethylene evolution by mechanical perturbation in bean stems
Authors: Jaffe Mordecai J. , Huberman Moshe , Johnson James , Telewski Frank W.
Published: April 2006

Mechanical perturbation by rubbing of the first internode of 11–12 day old plants of Phaseolus vulgaris L. cv. Cherokee wax induces the rapid deposition of callose in the cells of phloem and other tissues. Callose deposition begins immediately after mechanical perturbation, and shows a minor transient peak 1.5 h, and a major peak 6 h later. The callose gradually disappears and is gone after 3 days. If the stems are perturbed every day, the amount of callose decreases by day 2 but then gradually increases again through day 12. Both the top and bottom of the internode produce callose in response to mechanical perturbation. The evolution of ethylene in response to mechanical perturbation begins after 1 h, peaks at 2–3 h and is gone by 5–6 h. A spray of 10−2M 2‐deoxy‐D‐glucose (DDG) completely blocks stem thickening, callose deposition and ethylene evolution due to mechanical perturbation. DDG at 10−5 to 10−4M blocks callose production in mechanically perturbed stem segments and increases ethylene evolution from unperturbed stem segments to greater levels than those obtained by mechanically perturbed segments. It is concluded that mechanical perturbation of bean stems tissue induces deposition of callose more rapidly than it induces evolution of ethylene and that DDG can block both processes.
Antagonistic effect of silver thiosulphate or 2,5‐norbornadiene on 1‐aminocyclopropane‐1‐carboxylic acid‐stimulated growth of pistils in carnation buds
Authors: Veen H.
Published: April 2006

Growth promotion of pistils in carnation buds (Dianthus caryophyllus L., cv. White Sim) by 1‐aminocyclopropane‐1‐carboxylic acid (ACC) can be reversed by administering silver thiosulphate via the stem or 2,5‐norbornadiene in the ambient atmosphere. Double reciprocal plots of relative style growth versus ACC concentration at different inhibitor concentrations suggest the inhibition to be competitive in both cases.
Uptake of glycine by excised pulvini of Mimosa pudica in relation to proton pump activity
Authors: Otsiogo‐Oyabi Hyacinthe , Roblin Gabriel
Published: April 2006

Uptake of [3H]‐glycine by sections of Mimosa pudica L. pulvini is pH dependent (maximum at pH 5.5) and exhibits biphasic saturation kinetics in the range of concentrations tested (1–75 mM). Effects of compounds which increase [fusicoccin (FC)] or decrease (uncouplers, ATPase inhibitors) the proton‐motive force were tested both on the pH variations induced in the incubation medium and on glycine uptake by the pulvinar tissues: there is a close relationship between the time required for the effect of these compounds on the acidification (for FC) and the pH rise (for the inhibitors) of the medium and that needed respectively for promotion and inhibition of glycine uptake. Experiments with sulfhydryl‐reacting compounds show that N‐ethylmaleimide induces a large rise in pH in the incubation medium and strongly inhibits glycine uptake, whereas p‐chloromercuribenzenesulfonic acid has less effect on these processes. These results argue for a proton‐glycine symport mechanism in the pulvinar tissue and thus support the previously postulated involvement of a proton pump in the regulation of pulvinar movement.
Vacuolar localization of the enzymatic synthesis of hydroxycinnamic acid esters of malic acid in protoplasts from Raphanus sativus leaves
Authors: Strack Dieter , Sharma Vinay
Published: April 2006

Protoplasts from leaves of radish (Raphanus sativus L. var. sativus) were examined for the subcellular localization of p‐coumaric, caffeic, ferulic and sinapic acid esters of malic acid and the enzyme(s) involved in their syntheses. Vacuoles isolated from leaf protoplasts contained all the hydroxycinnamic acid esters as well as all the dependent enzyme activities. Protein from leaf vacuoles was shown to form the hydroxycinnamoylmalic acids, using the corresponding hydroxycinnamic acid glucose esters (1‐O‐acyl glucosides) as acyl donors. It is proposed that the vacuole is the cell compartment for synthesis and deposition of the hydroxycinnamoylmalic acids.
Changes in catalase activity and hydrogen peroxide concentration in plants in response to low temperature
Authors: MacRae E. A. , Ferguson I. B.
Published: April 2006

Taxicity of oxygen species such as free radicals and H2O2 has been invoked to explain a number of degradative processes in plants, most involving photo‐oxidation. Since catalase is a major protectant against accumulation and toxicity of H2O2, we examined alterations in catalase activity in several plant species (Pisum sativum L. cv. Greenfeast, Vigna radiata (L.) R. Wilcz, Cucumis sativus L. cv. Heinz Pickling, and Passiflora spp.) during chilling, and compared this change to change in H2O2 content. Catalase activity was reduced in a range of chilling sensitive and tolerant species by exposure to low temperature. This reduction in catalase activity correlated better with the onset of visible symptoms than with the treatment itself. Visible injury in turn was dependent on light and temperature differences. Hydrogen peroxide concentrations invariably decreased with low temperatures.

Reduction in catalase activity therefore does not necessarily imply accumulation of H2O2 to damaging levels. The absence of a clear inverse relationship between catalase activity and H2O2 concentration suggests the continued activity of other reactions that remove H2O2 and these may be important in the tolerance of plants to oxidative attack. Loss of catalase activity may result from the inability of damaged peroxisomal membranes to transport catalase precursors into the peroxisome.
Endogenous ethylene formation and the development of the alternative pathway in potato tuber discs
Authors: Gude Henk , van der Plas Linus H. W.
Published: April 2006

Callus‐forming discs from potato (Solanum tuberosum L. cv. Bintje) tubers grown on a nutrient medium containing an auxin and a cytokinin show both a higher ethylene formation and a higher capacity of the mitochondrial alternative pathway than nongrowing discs (on the same medium without auxin and cytokinin). Addition of 1‐ami‐nocyclopropane‐1‐carboxylic acid (ACC) to the nutrient medium of non‐growing discs results in an enhancement of the ethylene formation as well as the alternative pathway capacity. In callus‐forming tissue, the levels of both these parameters can be suppressed by adding aminoethoxyvinylglycine (AVG) to the nutrient medium without affecting growth. The effects on state 3‐respiration of ACC (increase) and AVG (decrease) are relatively small. These results suggest that the alternative pathway capacity is controlled to a considerable extent by the endogenous ethylene formation of the tissues.
Treatment of bean cuttings by chestnut extracts during rooting modifies their IAA‐oxidase activity
Authors: Mato M. C. , Vázquez A. , Gesto M. D. V.
Published: April 2006

The IAA‐oxidase activity in bean cuttings (Phaseolus vulgaris L. cv. Contender) treated with extracts from juvenile and adult chestnut (Castanea sativa Mill.) was studied in the light of the effect of the extracts on the rooting activity of some auxins. Extracts from adult chestnut increased IAA‐oxidase activity in bean cuttings. Extracts from juvenile chestnut inhibited IAA‐oxidase activity only slightly, but substantially reduced the IAA‐oxidase activity of bean cuttings pre‐treated with adult chestnut extracts. These findings provide evidence that there is a relationship between the IAA‐oxidase system and the effect of chestnut extracts on IAA‐induced rhizogenesis in bean cuttings.
Changes in glucan synthase activities during the cell cycle in a synchronous culture of Catharanthus roseus
Authors: Amino Shin‐ichi , Yoshihisa Tohru , Komamine Atsushi
Published: April 2006

Glucan synthase activities were determined during the cell cycle in a synchronous culture of Catharanthus roseus (L.) G. Don. Using radio gas chromatography, it was confirmed that glucans produced by a crude particulate extract from 1 μM UDP‐glucose were rich in 4‐linked glucose residues, and that those formed from 1 mM UDP‐glucose contained mostly 3‐linkages. Glucan synthase activity with 1 mM UDP‐glucose increased prior to cytokinesis. In the G1 phase after cell division, glucan synthase activities with both 1 μM and 1 mM UDP‐glucose were high, which may correlate with the maximal active synthesis of cell wall polysaccharides in this period of the cell cycle as reported by S. Amino et al. (Physiol. Plant. 60: 326–332, 1984).
Effects of NaCl on the properties of phosphoenolpyruvate carboxylase from Suaeda monoica and Chloris gayana
Authors: Shomer‐Ilan Adiva , Moualem‐Beno Delila , Waisel Yoav
Published: April 2006

The effects of NaCl on the kinetic properties of desalted phosphoenolpyruvate carboxylase (PEP carboxylase, EC 4.1.1.31) from two halophytes, Suaeda monoica Forssk. ex. J.F. Gmel and Chloris gayana Kunth. were investigated. The tolerance of PEP carboxylase to NaCl in the reaction medium depends on the enzyme pre‐conditioning as well as on the concentration of its substrate PEP in the assay medium. Addition of PEP to the extraction and the storage medium, stabilizes the enzyme. Such a pre‐treated enzyme is inhibited by NaCl in the presence of low concentrations of PEP in the assay medium but is activated by NaCl in the presence of PEP at concentrations above 1.0 mM. NaCl modifies the nH value, K’ and Vmax, and seems to act as an allosteric effector.
Leaf aging and lipid peroxidation: The role of the antioxidants vitamin C and E
Authors: Kunert Karl Josef , Ederer Martina
Published: April 2006

To study age‐related peroxidation in annual beech (Fagus silvatica Mill.) leaves and perennial fir (Abies alba Mill.) needles, the concentration changes of the antioxidants vitamin C (ascorbic acid) and vitamin E (α‐tocopherol) present in leaves and needles were determined, and the formation of thiobarbituric acid reactants was measured as an index of age‐related lipid peroxidation. With age, the content of the lipid‐soluble antioxidant vitamin E increased, and the increase was higher in beech leaves than in fir needles. A comparable age‐dependent increase of the vitamin C content was found neither in leaves nor in needles. The concentration ratio of the vitamin C to the vitamin E present in leaves and needles, which determines the potency of the anti oxidative system consisting of both vitamins, declined with age. This decline was directly related to a higher peroxidation of lipids. The extent of age‐related peroxidative damage of cells seems to be controlled by the potency of anti oxidative systems.
Metabolic changes in cherry flower buds associated with breaking of dormancy in early and late blooming cultivars
Authors: Wang S. Y. , Faust M. , Steffens G. L.
Published: April 2006

Changes of metabolic activities during dormancy and breaking of dormancy in the cherry flower buds of early blooming (EB) cultivar (Prunus avium L. cv. Coeur de Pigeon) and late blooming (LB) cultivar (Prunus serrulata Lindl. cv. Kwanzan) were determined. The LB buds had higher polyamines, protein and 1‐(malonylamino) cyclopropane‐1‐carboxylic acid (MACC) content than the EB buds. During the dormant state, the DNA, RNA, protein and polyamines in the EB buds were low but increased slowly and steadily, whereas those in the LB buds remained at a consistently higher level. The transition from dormancy to the active state in both cultivars was characterized by a sharp increase in DNA, RNA, protein, polyamines, S‐adenosyl‐methionine (SAM), 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and MACC. After initial swelling and development of flowers, the levels of all these components decreased. Polyamine and ethylene biosyntheses did not seem to be competing for their common substrate, SAM, during flower bud development.
Energetics of membrane transport in protoplasts
Authors: Lin Willy
Published: April 2006

Examples are given to illustrate the recent use of isolated protoplasts in the study of membrane transport with the emphasis on the energetics of solute transport. A model is also presented for the mechanism of active solute transport at the plasmalemma.
Inhibition of photosynthesis by freezing temperatures and high light levels in cold‐acclimated seedlings of Scots pine (Pinus sylvestris). – II. Effects on chlorophyll fluorescence at room temperature and 77 K.
Authors: Strand Martin , Öquist Gunnar
Published: April 2006

Shoots of cold‐acclimated seedlings of Pinus sylvestris L. were exposed to a temperature of –7°C for 4 h, in darkness or at a photon flux density of 1 300 μmol m‐2s‐1. Before and after freezing, fluorescence kinetics of intact needles and isolated chloroplast membranes were measured at both room temperature and 77 K. Maximum and variable fluorescence yield of photosystem II both at room temperature and 77 K decreased strongly after freezing in light, whereas the initial fluorescence yield was little affected. Quenching of maximum and variable fluorescence of photosystem I at 77 K also occurred. The results show that freezing in light damages photosystem II, thereby increasing the radiationless decay at the reaction centres of photosystem II. This is a typical symptom of photoinhibition of photosynthesis. Freezing in darkness did not significantly reduce fluorescence yield of photosystem II or photosystem I. Moreover, electron transport capacity was not significantly affected. We therefore suggest that the inhibition of the CO2 assimilation in pine seedlings by freezing alone does not involve thylakoid inactivation.
Differential response of Trifolium species to 4‐(2,4‐dichlorophenoxy)butyric acid treatments
Authors: Smith Albert E.
Published: April 2006

The differential response of white clover (Trifolium repens L. cv. Regal Ladino) and berseem clover (Trifolium alexandrinum L. cv. Mississippi ecotype) was investigated by treating greenhouse cultured plants with 4‐(2,4‐dichlorophenoxy)butyric acid (2,4‐DB). Berseem clover plants were significantly injured by a treatment concentration of 0.6 kg ha‐1 of 2,4‐DB, whereas white clover plants were not injured by treatment levels below 2.4 kg ha‐1. The metabolism of 2,4‐DB in cell suspension cultures of white clover and berseem clover was investigated using [ring‐14C]‐2,4‐DB and non‐labeled 2,4‐DB. White clover cell cultures metabolized ca 4‐fold more 2,4‐DB than berseem cultures over a 44‐h treatment period. The decrease in berseem cell population was 4‐fold greater than the decrease in white clover cell population in response to the 8 μM 2,4‐DB treatment. The herbicide and its [ring‐14C]‐labeled metabolites were isolated from treated cells and medium after 44 h by partition and thin‐layer chromatography. White clover cells metabolized 90% of the [14C]‐2,4‐DB and berseem clover cells metabolized 22% of the herbicide. The major portion of the radiolabel was in the glycoside fractions from extracts of both species. The differential response of Trifolium species to 2,4‐DB is implied to be due to the differential rate of 2,4‐DB metabolism to a glycoside by the clover plants.
Methods to extract NAD+‐malate dehydrogenase efficiently from white spruce needles
Authors: Pitel J. A. , Cheliak W. M.
Published: April 2006

The spectrophotometrically‐determined activity of NAD+‐malate dehydrogenase (MDH, EC 1.1.1.37) from white spruce [Picea glauca (Moench) Voss] needles was assayed with NADH and oxaloacetate. Activity was very low when extracted with only acetate buffer (pH 5.4), phosphate buffer (pH 6.8), or Tris‐HCl buffer (pH 8.0). However, activity increased from 1 to over 200 μmol (g dry weight)‐1 min‐1 with the addition of polymers such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) and the detergents, Tween 80, Tergitol 15‐S‐9 and Triton X‐100. Best activity was observed when extracted in a buffer at pH 6.8 and with 1% (v/v) for the three detergents and PEG, and 6% (w/v) for PVP.

MDH activity decreased with age of the needles on the tree. Six‐year‐old needles contained only about one‐fifth of the activity of current year, fully‐expanded needles. The main decrease in enzyme activity was observed in one‐year‐old needles. Protein content obtained from needles extracted with just phosphate buffer (pH 6.8) was very low, but increased greatly when the above chemicals were added to the buffer. In contrast with needles, extracts of vegetative buds contained much higher levels of MDH and protein when extracted with only phosphate buffer (pH 6.8). Although MDH activity in needle extracts declined with storage of the extracts at 4°C in the dark for 6 days, the decrease was least for buffers containing a combination of different protective agents.
Inhibition of brassinosteroid‐induced epinasty in tomato plants by aminooxyacetic acid and Co2+
Authors: Schlagnhaufer Carl D. , Arteca Richard N.
Published: April 2006

The inhibitory effects of aminooxyacetic acid (AOA) and cobalt chloride (CoCl2) on brassinosteroid (BR)‐induced epinasty in tomato plants (Lycopersicon esculentum Mill. cv. Heinz 1350) are evaluated. CoCl2 dramatically decreases petiole bending and ethylene production as the concentration increases from 50 to 200 μM. The content of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) in the petiole, instead of accumulating, is reduced and does not change over the concentration range tested. Inhibition of BR‐induced epinasty by AOA results from inhibition of ACC synthesis. There are dramatic reductions in petiole bending, ethylene and ACC production as the concentration of AOA is increased from 50 to 200 μM. Maximum inhibition occurs when the plants are pretreated with the inhibitors. The degree of inhibition increases as the length of pretreatment increases from 1 to 4 h. The response of BR‐treated plants to AOA and CoCl2 is similar to the effect of auxin, indicating the integral relationship between BR and auxin.
Changes in ATP in relation to floral induction and initiation in Pharbitis nil
Authors: Thigpen Stephen P. , Sachs Roy M.
Published: April 2006

No changes in metabolism of adenosine phosphates as a function of short day induction were detected in cotyledons of Pharbitis nil Chois strain Violet. A gradual increase in ATP level was detected throughout the dark period in plumules. A rapid decline of ATP pool size was observed in induced plumules shortly after floral induction. The decline occurred close to the 14th hour of the dark period, 1 to 1.5 h after the dark period length required for a 90% flowering response, which is thought to be the minimum time required for transport of the floral stimulus (and assimilates) from the induced cotyledons to the plumule. Transport of the major adenylates from the cotyledons was verified using [14C]‐adenine. Estimates of the amount, and rate, of adenylate transport suggest that the cotyledons could be an important source of adenylates to re‐establish the ATP pool size in evoked plumules.
Regulation of ethylene biosynthesis during senescence of oat leaf segments
Authors: Preger Ronit , Gepstein Shimon
Published: April 2006

The evolution of endogenous ethylene, the conversion of 1‐aminocylopropane‐1‐car‐boxylic acid (ACC) to ethylene and the amounts of ACC (free and conjugated) have been followed during the senescence of oat (Avena sativa L. cv. Victory) leaf segments. During the first three days of incubation of leaf segments in darkness, endogenous ethylene evolution and ACC‐dependent ethylene production displayed a close relationship, both showing an increase followed by a decrease to the basal rate. However, unlike ethylene production, the level of ACC increased during the five days of incubation in the dark without any decline. It is concluded that ACC synthesis does not limit ethylene production, at least in the last stages of leaf senescence when ethylene production markedly decreased. The level of conjugated ACC increased and reached a plateau already at the first day of incubation. Yet, at the progressive stages of senescence, when the level af ACC gradually increased, no further conjugation of ACC could be detected. Thus, conjugation of ACC cannot account for ethylene drop at the last stages of oat leaf senescence.
Anatomical and chemical studies of vitrified shoots of chestnut regenerated in vitro
Authors: Vieitez A. M. , Ballester A. , San‐José M. C. , Vieitez E.
Published: April 2006

Vitrified shoots were produced in multiplication cultures of Castanea sativa Mill. when Murashige and Skoog mineral medium was used during successive subcultures, whereas normal shoots were obtained when Heller's macronutrient formula was used with or without addition of 1 mM (NH4)2SO4. Vitreous and normal plantlets were compared both anatomically and chemically. Xylem and sclerenchyma tissues are less differentiated and lignified in vitrified than in normal shoots. On the other hand, there is a hypertrophy in the cortical and pith parenchyma. Leaves of vitrified shoots are characterized by the lack of clear differentiation between the palisade and spongy mesophyll, where a system of large intercellular spaces develops. The cytohistological zonation of vitrified apices is characterized by the comparatively small meristem tissue in the apical dome. Phenolic content of explants, assayed by high pressure liquid chromatography, was lower in vitreous than in normal cultures. Gallic acid was identified in both types of cultures.
Nitrate and nitrite reduction in the plant fraction of alfalfa root nodules
Authors: Becana M. , Aparicio‐Tejo P. M. , Sanchez‐Diaz M.
Published: April 2006

The plant fraction of alfalfa (Medicago sativa L. cv. Aragon) nodules contained both nitrate reductase (NR) and nitrite reductase (NiR). Specific activity of NADH‐NR from the cytosol of nodules not treated with NO3‐ was about 30 nmol (mg protein)‐1‐h‐1 and was not basically affected by NO3 addition. In contrast, typical specific activity for cytosolic NiR was 1.5 umol (mg protein)‐1h‐1 using methyl viologen as electron donor. This activity strongly increased with NO3 concentration, probably due to substrate induction. Maximal activity was 3.5 μmol (mg protein)‐1h‐1 at 50 to 200 mM NO3.

Estimates indicate that the contribution of cytosol to the overall NR and NiR activities of alfalfa nodules is distinctly different: less than 10% and about 70%, respectively. The increasing amounts of NO2 accumulating in the cytosol upon NO3, supply, and the different response to NO3 of bacteroid and cytosolic NRs support the concept that most of this NO2 comes from the bacteroids.
Isolation and characterization of a DCMU (3–(3,4–dichlorophenyl)‐1,1–dimethylurea) resistant strain of a marine alga, Dunaliella bioculata
Authors: Grizeau D. , Jeanne N. , Calvayrac R.
Published: April 2006

A DCMU‐resistant strain was isolated from cell cultures of a wall‐less alga, Dunaliella bioculata (Butcher 19/4 CCAP). This variant strain is essentially characterized by its ability of grow autotrophically in the presence of 4 μM DCMU and by the stability of this property even after numerous subcultures in the absence of the herbicide.

Chloroplastic structures and photosynthetic activities of whole and fragmented cells of the wild and the variant strains were compared for their respective sensitivities towards DCMU. The DCMU‐resistant strain was also insensitive to other photosynthetic inhibitors such as chloroxuron, but not to atrazine. The results suggest that the DCMU‐resistance could be due to some modified plastid property.
The site of 1‐aminocyclopropane‐1‐carboxylic acid synthesis in senescing carnation petals
Authors: Mor Yoram , Halevy Abraham H. , Spiegelstein Hanna , Mayak Shimon
Published: April 2006

To study the cause of the uneven production of ethylene by upper and basal portions of detached petals of carnation (Dianthus caryophyllus L. cv. White Sim), the petals were divided and exposed to ethylene (30 μl 1‐1 for 16 h). The treatment induced rapid wilting and autocatalytic ethylene production in the basal portion similar to that induced in entire petals. In contrast to the response in entire petals and the basal portions, the upper portions responded to ethylene by delayed wilting and much lower ethylene production. Aminocyclopropane carboxylic acid (ACC)‐synthase activity in the basal portion of the petals was 38 to 400 times that in the upper portion. In untreated detached petal pieces from senescing carnation flowers, ethylene production by the upper portion declined after 6 h while the basal portion was still producing ethylene at a steady rate 18 h later. Application of ACC to the upper portion of senescing petals increased their ethylene production. α‐Aminooxyacetic acid (0.5 mM), reduced the ethylene production of the senescing basal portion more than that of the upper portion. Endogenous ACC content in basal portions of senescing carnation petals was 3 to 4 times higher than in the upper parts. When detached senescing petals were divided immediately after detaching, the endogenous ACC levels in upper portions remained steady or declined during 24 h after division, while in the basal portions the ACC level rose steadily as in the intact petals. There was no change in the conjugated ACC in either portion after 24 h. Benzyladenine (BA) applied as a pretreatment to entire preclimacteric petals greatly reduced the development of ACC‐synthase activity of the basal portion, but had little effect on the activity in the upper portion of the petal. In both portions, however, BA effectively reduced the conversion of ACC to ethylene.
Seasonal changes in tissue elasticity in chaparral shrubs
Authors: Bowman William D. , Roberts Stephen W.
Published: April 2006

An important physiological feature of chaparral shrubs is the development of low water potentials during periods of drought characteristic of southern Californian summers. Changes in tissue elasticity may be an important characteristic allowing these low water potentials to be reached and maintained without the development of detrimental water deficits. To examine this possibility, seasonal changes in tissue elasticity were measured in 3 species of chaparral shrubs, Arctostaphylos glandulosa Eastw., Quercus dumosa Nutt. and Ceanothus greggii Gray., by the pressure‐volume method. Tissue elasticity was characterized using graphs of the modulus of elasticity plotted as a function of turgor pressure, and maximum values of the elastic modulus. The moduli of elasticity of the shrubs increased following leaf emergence in the spring, were highest during periods of low soil water potential, and tended to decrease following the summer‐fall drought period. Increases in tissue elasticity facilitate water uptake from drying soils, but result in greater turgor loss during tissue dehydration.
A developmental study of Glycine max cell and protoplast isolation in relation to leaf age and photosynthetic competence
Authors: Rees Richard T. , Cobb Andrew H. , Pallett Kenneth E.
Published: April 2006

Leaf mesophyll cells were isolated from developing first trifoliate leaves of Glycine max (L.) Merr cv. Fiskeby V using a mechanical isolation procedure combined with low speed centrifugation. Cell yields of 17 ± 1.7% were routinely obtained with 55–75% intactness, as assessed by staining techniques, fluorescence transients and the ability of cells to convert to protoplasts after enzyme treatment. Rates of leaf photosynthesis were maximal in 27‐day‐old plants [280 μmol O2 evolved (mg chlorophyll)‐1h‐1], from which isolated cells and protoplasts gave rates of up to 140 μmol O2 evolved (mg chlorophyll)‐1 h‐1. Results are discussed in relation to leaf development and cell status during the attainment of photosynthetic competence.
Effects of gibberellic acid on patterns of carbohydrate distribution and acid invertase activity in Phaseolus vulgaris
Authors: Morris David A. , Arthur Edwin D.
Published: April 2006

The application of gibberellic acid (GA3,10 μM) as a root drench to 16‐day‐old plants of Phaseolus vulgaris L. cv. Masterpiece stimulated growth of the stem internodes and reduced root growth. GA3 treatment did not affect the export of 14C from a primary leaf to which [14C]‐sucrose was applied, but greatly increased upward translocation to the elongation region of the stem at the expense of transport to the hypocotyl and root system. The observed changes in the patterns of growth and [14C]‐labelled assimilate distribution were correlated with an increase in the specific activity of acid invertase in the elongating stem internodes and a decrease in invertase activity in the hypocotyl and root. Sucrose concentration in the elongating internodes fell substantially after treatment with GA3 while the concentration of hexose sugars increased. We suggest that by stimulating acid invertase synthesis in the elongating internodes, GA3 acts to establish a more favourable sucrose gradient between these sinks and source leaves. Under source‐limiting conditions this, in turn, will lead to a reduced rate of assimilate translocation to competing sinks in the root system.
Effects of irradiation level on leaf growth of sunflower
Authors: Pieters George A.
Published: April 2006

Sunflower, Helianthus annuus L. cv. INRA 6501, plants were grown in a gravel culture subirrigated with Hoagland nutrient solution, at photosynthetically active radiation levels of 15, 30 and 60 W m‐2 at a daylength of 16 h, a temperature of 20°C and a relative humidity of 60% throughout. Development of the plant and growth of the leaves were measured. High irradiance accelerated development proportionally in all phases from germination, through leaf initiation, primordial flower formation and the maturation of all plant organs until anthesis. High irradiance levels stimulated the expansion of the growing shoot, which produced more and larger primordia. Under constant conditions the ratio between leaf initiation rate and mature length of a leaf remained constant, although the growth patterns [relationship between relative growth rate (RGR) and organ age] of successive leaves were not similar. Consequently, it may be assumed that, as in poplar, the increasing size of the growing shoot reflects the increase of the vascular system of sunflower. The growth patterns of the leaves depend on the developmental stage of the plant and, in the young primordial stage, also on irradiance level. In the linear phase of growth the growth pattern is independent of irradiance level.
Age‐related contents of polymerized lipids in the ectohydric forest mosses Pleurozium schreberi and Hylocomium splendens
Authors: Kälviäinen Eeva , Karunen Pirjo , Ekman Rainer
Published: April 2006

Cell wall preparations of the ectohydric forest mosses, Pleurozium schreberi (Brid.) Mitt. and Hylocomium splendens (Hedw.) B. S. G. contain polymerized lipids consisting of hydroxy acids, dicarboxylic acids, fatty acids, fatty alcohols and unidentified components. The finding of polymerized lipids in ectohydric mosses, which have highly permeable cell walls, indicates that the polymers do not form an effective barrier against water and nutrients, at least not in the cell walls of these mosses. The youngest parts of P. schreberi and H. splendens contained 2.0 and 1.6 mg polymerized lipids, respectively, on a dry cell wall weight basis. In the senescent, greyish‐green parts of P. schreberi and in the one‐year‐old shoot tissue of H. splendens the corresponding amounts were about 1.5‐fold. In both species the increase was due to increases in hydroxy acids, particularly dihydroxyhexadecanoic acids, dicarboxylic acids, unknown components and, in the case of H. splendens, also an increase in fatty acids. The increase may be related to the maturation of the cell walls. In still older shoot parts the amounts of polymerized lipids decreased in both species, and remained low until final decay of the tissues into small particles. A slight increase in the amount of the polymerized lipid monomers was found in the oldest and most decomposed parts of H. splendens, probably indicating a better resistance to decay than for other cell wall components. These findings are discussed in relation to what is known from the ectohydric peat‐forming Sphagnum mosses.
Distribution and remobilization of symbiotically fixed nitrogen in soybean (Glycine max)
Authors: Warembourg F. R. , Fernandez M. P.
Published: April 2006

Partitioning of nitrogen by soybeans (Glycine max L. Merr. cv. Hodgson) grown in natural conditions was studied by successive exposures of root systems to 15N2 and periodical measurements of 15N distribution. Nitrogen derived from the atmosphere was mainly found in the aerial parts of the plants, and the stage of development exerted a strong influence on the initial 15N distribution (measured one week after incorporation). Until day 69 after sowing, leaf blades contained 47 to 57% of the fixed N. After that, reproductive structures attracted increasing proportions, 10 to 60% between days 69 and 92. Around day 82, stems and petioles stored up to 30% of the newly fixed N. During pod development and pod filling and until maturity, fixed N was remobilized from vegetative tissues and pod walls to seeds. These transfers first concerned the newly incorporated N, but at maturity 80 to 90% of the total was recovered in the seeds. The high mobility of N originating from the atmosphere as compared to that coming from the soil (vegetative tissues exported only 50% of their total N) seems to indicate that fixed N was at least partially integrated in a special pool. This was certainly the case at the later stage of N2 fixation, when a large portion of fixed N accumulated in the stems and petioles, probably in the form of storage compounds such as ureides for later transfer to the developing seeds. Further research is needed in order to investigate the nature and role of this pool in the nitrogen nutrition of soybeans.
Temperature‐induced absorbance changes in developing barley chloroplasts
Authors: Singh Bal Ram , Singhal Gauri S.
Published: April 2006

Absorbance changes on cooling and heating of barley (Hordeum vulgareL. cv. IB65) chloroplasts greened for 12, 48 and 72 h were investigated to understand the structural changes during biogenesis of chloroplast membranes. Upon cooling the chloroplast suspension from 24 to 8°C, a positive absorbance change occurred at 678, 435 and 495 nm in 12, 48 and 72 h greened chloroplasts. During heating from 24 to 45°C negative absorbance changes were observed with some shifts in positions in different chloroplast preparations and a simultaneous increase in absorbance between 690 and 735 nm. For chloroplasts developed for 12, 48 and 72 h the changes in absorbance on cooling were 3.8, 3.3 and 1.9% at 678 nm, and on heating, 8.9, 8.3 and 4.1% at 680 nm.

The differences in absorbance changes are considered as an indication of variations in the structural organization and composition of developing chloroplasts. The reversibility of the absorbance changes was maximum in chloroplasts greened for 72 h and minimum in chloroplasts greened for 12 h. This would suggest that fully developed chloroplasts have more flexibility towards temperature‐induced changes in the membranes.
Effect of auxin on alkaloids, K+ and free amino acid content in cultured tobacco callus
Authors: Piñol Ma T. , Palazón J. , Altabella T. , Cusido R. , Serrano M.
Published: April 2006

Callus cultures derived from the petiole of Nicotiana tabacum L. cv. Burley 21 were grown at 25°C in the dark on two different basal media containing: (1) 11.5 μMα‐naphthaleneacetic acid and 1 μM kinetin, and (2) 1 μMα‐naphthaleneacetic acid and 1 μM kinetin. The contents of alkaloids, K+ and free amino acids of callus tissues were determined. The tissues were also examined microscopically for organization when organogenesis was not apparent. The first medium limited nicotine synthesis and stimulated its N‐demethylation to nornicotine. The second medium stimulated nicotine synthesis and limited tissue growth. Although significantly higher concentrations of K+ were observed in calli grown on the high‐auxin medium, both cultures were K+ deficient. The fact that the low‐auxin medium limited K+ uptake to a higher degree would account for the lower growth observed in calli cultured on this medium, and it is possible that the effect of auxin concentration on nicotine production may be mediated through its effects on K+ uptake by cells of the culture. The free amino acid concentration increased in the calli grown on the low‐auxin medium. Glutamic acid and proline, known as initial precursors of nicotine, increased significantly. Histological examination showed that the occurrence of meristematic areas in calli without organogenesis promoted nicotine synthesis. The relation between the accumulation of nicotine and formation of roots or shoot‐buds is discussed.
Methanol production from lignin‐related substances by Phanerochaete chrysosporium
Authors: Ander Paul , Eriksson Mats E. R. , Eriksson Karl‐Erik
Published: April 2006

Methanol production resulting from the demethoxylation of lignin‐related substances by Phanerochaete chrysosporium K‐3 was studied in the presence or absence of glutamic acid in order to determine if methanol formation involved the ligninolytic system of the fungus. The general pattern was that methanol formation, calculated as percentage of theoretical yield, decreased in the order guaiacyl > syringyl > veratryl (3,4‐dimethoxy) compounds. Methoxyhydroquinone and vanillic acid were most easily demethoxylated, while methanol production decreased with increasing molecular weight for the same type of structure (i.e. guaiacyl). Glutamic acid inhibited the demethoxylation of many of the compounds tested. The demethoxylation of the 4‐methoxy group of veratric acid was particularly inhibited by glutamic acid suggesting a participation of the ligninolytic system, while the 3‐methoxy group was influenced to a lesser extent.

The demethoxylating enzyme acting on lignin‐related phenols is probably a peroxidase, while the identity of the enzyme demethoxylating dimethoxy compounds is not known with certainty, although a peroxidase type of enzyme reaction is anticipated also here.
Patterns of carbon allocation above ground in a deciduous (Vaccinium uliginosum) and an evergreen (Vaccinium vitis‐idaea) dwarf shrub
Authors: Karlsson P. S.
Published: April 2006

The carbon allocation to current‐year shoots of the deciduous Vaccinium uliginosum L. and the evergreen V. vitis‐idaea L. was studied in a field experiment using 14C. During the first week after labelling, 0–50% and 30–80% of the initially assimilated 14C was lost in V. vitis‐idaea and V. uliginosum respectively. Later on, the losses were smaller. After leaf fall in V. uliginosum, 30, 10 and 8% of the initially assimilated 14C was recovered in the abscised leaves, in plants labelled 1 July, 1 August and 1 September, respectively. The amounts found in the old V. vitis‐idaea leaves the year after labelling were 33, 20 and 10%. Only traces of past‐year assimilates were found in the current‐year V. vitis‐idaea leaves, while it was estimated that the V. uliginosum leaves contained 10–15% of the past‐year label. It is concluded that V. vitis‐idaea is mainly dependent on early summer assimilates ‐ produced by leaves that have overwintered – for the current year shoot growth, while past‐years' assimilates probably make an important contribution to the leaf expansion in V. uliginosum. When fruits occurred, a large fraction of the 14C assimilates was allocated to them.
Apparent transinhibition of peptide uptake in the scutellum of barley grain
Authors: Sopanen Tuomas , Sinervo Tuija , Mikola Juhani
Published: April 2006

The uptake of glycylsarcosine (Gly‐Sar) into scutella separated from germinating grains of barley (Hordeum vulgare L. cv. Himalaya) is inhibited by other peptides; in most cases the inhibition is not purely competitive but of a mixed type (simultaneous increase in the apparent Km and decrease in Vmax) (Sopanen, T. 1979. FEBS Lett. 108: 447–450). The aim of the present experiments was to elucidate the mechanism of the mixed inhibition by studying how peptides already taken up into the cells affect the uptake of Gly‐Sar.

When scutella were preincubated in the presence of various peptides, 11 of the 13 peptides tested inhibited the subsequent uptake of Gly‐Sar by 10 to 45%. The inhibition, studied in detail with leucylleucine and prolylproline, was due to a decrease in Vmax. The two peptides having no effect were glycylglycine and D‐alanyl‐L‐alanine which are the only peptides known to date acting as purely competitive inhibitors when present together with the substrate Gly‐Sar.

Preincubation with leucine, proline and alanine was not inhibitory, although preincubation with the corresponding dipeptides was. This result, together with the demonstration of intact leucylleucine in the scutella after preincubation with leucylleucine, indicates that the inhibition was caused by the intact peptides.

The results support the notion that in the mixed type inhibition the increase in the apparent Km is due to competition for the carrier at the outside of the membrane, while the decrease in Vmax is due to peptides taken up and binding to the carrier at the inside of the membrane.
Metabolism of Urtica dioica as dependent on the supply of mineral nutrients
Authors: Hofstra Rinie (J. J.) , Lanting Lineke , de Visser Ries
Published: April 2006

Plants of Urtica dioica L., a very nitrophilous species, were grown in a nutrient solution containing either high (100%) or low (2%) nutrient supply. Part of these plants were subjected to a sudden switch from 100% to 2% or vice versa. Plant weight, sugar and organic nitrogen (both soluble and insoluble) and nitrate content were measured during growth. The activities of two nitrogen assimilating enzymes, nitrate reductase (NR) and glutamine synthetase (GS) were determined.

Growth of Urtica dioica was retarded at low nutrient supply. Root growth was limited by another factor than nitrogen. This was shown by a higher protein content. In the first period after a switch from 100% to 2%, redistribution of nitrogen from shoot to root could be demonstrated, and leakage from the root into the nutrient solution. It is suggested that in these conditions GS in the root reacted to this downward flux. Comparison with earlier findings on the less nitrophilous Plantago lanceolata showed that at 100% nutrient supply a correlation occurs between nitrate reduction and glutamine synthetase activity in that plant part which exported reduced nitrogen: the root in P. lanceolata and the shoot in U. dioica. In the importing plant part, glutamine synthetase was influenced by nitrate reduction as well as by imported reduced nitrogen.
Glycerate kinase from spinach leaves: Partial purification, characterization and subcellular localization
Authors: Chaguturu Rathnam
Published: April 2006

Spinach (Spinacia oleracea L. cv. Melody hybrid) leaf glycerate kinase (EC 2.7.1.31) was partially purified and characterized. The enzyme did not exhibit any absolute stereospecificity towards the two enantiomers of glycerate, but the affinity for the D‐isomer was 15‐fold greater. The enzyme exhibited a broad pH optimum of 7.5–9.0 and a requirement for divalent cation, satisfied by Mg2+. The reaction product was identified as 3‐phosphoglyceric acid. The observed high glycerate kinase activity together with its strategic localization exclusively in the chloroplast stroma are considered adequate for an efficient coupling of photosynthetic and photorespiratory carbon pathways.
Root hair deformation in the white clover/Rhizobium trifolii symbiosis
Authors: Bhuvaneswari T. V. , Solheim Bjorn
Published: April 2006

Rhizobium trifolii most frequently infects its host white clover (Trifolium repens L.) by means of infection threads formed in markedly curled root hairs. Rhizobium infections are classified as either lateral or apical based on whether they originate in the branches or at the apex of the root hairs. A quantitative estimate of lateral and apical infection in the region of the host root (Trifolium repens L. cv. Regal Ladino) that possessed mature and immature root hairs at the time of inoculation with Rhizobium trifolii TAI (CSIRO, Canberra City, Australia) indicated that lateral infection occurred more frequently in the mature root hair region of the root. Apical infections were more common in the immature root hair region. Cell free filtrates collected from R. trifolii cultured in association with the host roots induced branching in white clover root hairs. A partially purified preparation of the branching factor was obtained from freeze‐dried filtrates by ethanol extraction and ion exchange chromatography. Preliminary studies on the characteristics of these substances suggest that some are dialyzable and heat stable white others are non‐dialyzable and heat labile. The dialyzable, heat‐stable compounds contain neutral sugars and range between 1200 to 10000 daltons in size. In roots that were exposed to low concentrations (6–25 μg‐ml−1) of these partially purified deformation factors before inoculation, the developmentally mature root hairs were deformed at the time of inoculation. Nodules appeared in the mature and immature root hair region of these plants at the same time. In plants exposed to water, nodules were observed in the immature root hair region and mature root hair regions 3 and 5 days after inoculation, respectively. Based on these results, we conclude that the nodule development was hastened in the plants exposed to the root hair‐deforming substances because the mature root hairs of these plants were made infectible at the time of inoculation by this exposure.
Experimental control of flowering and vivipary in timothy (Phleum pratense)
Authors: Junttila Olavi
Published: April 2006

Environmental and hormonal control of flowering and vivipary in four Norwegian timothy (Phleum pratense L.) cultivars has been studied in phytotron and by aseptic culture of inflorescence explants. The critical photoperiod for flowering increased with increasing temperature (12–18°C) and it was 13 to 15 h for the southern and 14 to 16.5 h for the northern cultivars. Diurnal temperature fluctuation significantly stimulated flower formation compared to the corresponding constant temperature treatment. Plants grown in 16‐h photoperiod contained normal sexual flowers, but a high percentage of spikes developed in 12‐ or 14‐h photoperiod contained viviparous plantlets. One‐ to four‐weeks in continuous light before treatment with 12‐h photoperiod increased the number of spikes per plant, but did not enhance the frequency of vivipary. Experiments with aseptic cultures showed that generative versus vegetative development of timothy inflorescence was affected by plant hormones. Kinetin stimulated the vegetative development and induced proliferation both in inflorescence initials and in spikelets isolated at heading time.