bluuebunny/crossref_metadata_2025 huggingface dataset:
Dose responses of auxins
Authors: Nissen Per
Published: April 2006

Published data for the most widely used bioassays for auxins as. well as other auxin‐induced responses, have been analyzed to determine whether the response is ultrasensitive, hyperbolic or subsensitive, i.e. whether the change from 10 to 90% of maximal response requires less than, equal to or more than an 81‐fold increase in external auxin concentration. Auxin‐dependent callus growth is most often ultrasensitive. Other responses, including the curvature of Avena coleoptiles, may show simple Mi‐chaelis‐Menten kinetics. In the majority of cases, however, the response is sub‐sensitive, often very markedly so. The finding of subsensitive responses is consistent with the proposal by A. J. Trewavas that plant development is regulated by changes in the sensitivity to plant growth substances.

Detailed data for subsensitive dose responses, particularly auxin‐induced inhibition of root growth, can often be precisely represented by bi‐ or multiphasic isotherms, with the phases separated by sharp transitions. The relationship to auxin uptake and the relationship, if any, between carriers and receptors for auxins remain to be elucidated.
Carbon dioxide and ethylene evolution in the culture atmosphere of Magnolia cultured in vitro
Authors: De Proft Maurice P. , Maene Ludo J. , Debergh Pierre C.
Published: April 2006

Subcultured explants of Magnolia soulangeana Soul, were incubated in tissue culture containers fitted with different types of closures. Type of closure affected the CO2 concentration, with levels as high as 14% CO2 being detected. The ethylene concentration increased gradually with time, to as much as 2–3 ppm after 9 weeks. There was a large variation in the composition of the atmosphere within the containers of any one type. The way by which a container was closed influenced exchange of the inner gas phase with the surrounding atmosphere and was important in determining the development of the cultured tissues.
Field productivity of a CAM plant, Agave salmiana, estimated using daily acidity changes under various environmental conditions
Authors: Nobel Park S. , Meyer Susan E.
Published: April 2006

Nocturnal acidity increases of the Crassulaceae acid metabolism succulent Agave salmiana Otto ex Salm. ssp. crassispina (Trel.) Gentry were determined for various photosynthetically active radiation (PAR) levels in the field and various day/night temperatures and soil water potentials in the laboratory. When a particular factor was optimal for nocturnal acid accumulation, it was assigned an index value of unity. The product of the three indices was termed the environmental productivity index (EPI), which summarizes the effect of PAR, temperature, and water status on nocturnal acid accumulation. A monthly value for EPI was determined using microclimatic conditions at the field site near Salinas de Hidalgo, San Luis Potosf, Mexico. EPI was highly correlated with the number of leaves unfolding monthly from plants in the field (r2= 0.95), where monitoring of such leaf unfolding is a non‐destructive technique for assessing plant productivity. By using the measured leaf area index for four groups of A. salmiana and a relationship between acid accumulation and net CO2 up‐take, the EPI acidity data were converted to dry weight gain per unit ground area. This measure of productivity closely agreed with the 1.05 kg m−2 year−1 determined by conventional harvesting techniques. The productivity is also in agreement with studies on other desert agaves, but about 10‐fold higher than that generally considered for desert ecosystems.
Use of the scanning electron microscope in the study of isssolated ribosomes and polysomes
Authors: Kupila‐Ahvenniemi Sirkka , Peura Raija , Häggman Hely
Published: April 2006

A procedure is described by which the ribosome assemblies isolated from the buds of Scots pine (Pinus sylvestris L.) as well as the ribosome and polysome fractions purified by sucrose density gradient centrifagation can be prepared for study by scanning electron microscopy. The technique has also been used to illustrate ribosomes extracted froai leaves and roots of Nicotiana tabacum L., from roots of Tuiipa gesneriana hybr. and from commercial wheat germ. The sample under study is spread on a piece of coverslip', frozen and dried at room temperature. The coverslip, with attached material, is taken through the critical point drying procedure, glued on a specimen retainer aod coated with gold‐palladium. The coverslip serves as a sufficiently stable specimen support to allow the study of ribosomes at magnifications of several hundred thousand. Use of the method makes it possible to study the structure of polysomes, to check the purity of fractioned samples and to investigate differences in the ribosome assembly of the developing plant tissues.
Variation in the polysome assembly and incorporation of [3H]‐uridine in the cells of pine buds during the cold season
Authors: Häggman Hely , Hohtola Anja , Kupila‐Ahvenniemi Sirkka
Published: April 2006

The ribosome assemblies isolated from buds of Scots pine (Pinus sylvestris L.) containing microsporangiate strobili varied both quantitatively and qualitatively in samples collected from October to April. The seasonal fluctuation in the amount of ribosonnes was more evident in the cytosolic fraction than in the smaller membrane‐bound fraction. The profiles obtained after sucrose density gradient centrifugation were of two types. One type was commonly obtained from samples collected late in the autumn and early in the spring, and this type was characterized by a relatively high peak for the large subunits, a low or negligible peak for the dimers, and an even or ascending series of peaks for the polymers. The other type was obtained from samples collected during the winter, and was characterized by small peaks for both subunits, a moderate to large peak for the dimers and a descending series of peaks for the polymers. However, the scanning electron microscope investigations indicated that the winter‐time samples did not lack polysomes and clusters of ribosomes. They did not become visible in the polysome profiles because they pelleted too tightly at the bottom of the centrifuge tubes to be removed with gradient fractionation. The au‐toradiographic analyses suggested that the cells were capable of synthesizing mRNA throughout the winter, whereas rRNA synthesis was arrested. On the basis of the above results, we postulate that the synthesis of the enzyme proteins needed for the maintenance of winter‐time metabolism takes place in the cytosolic ribosome fraction. The possible existence of winter‐time polysome stores is also pointed out.
Regulation of urease by urea and its precursors in the lichen Evernia prunmtri
Authors: PérezUrria E. , Vicente C.
Published: April 2006

Thallus samples of £. prunastri (L.) Adi, floated on 40 mM urea developed urease (EC 3.5.1.5.) activity which levelled off after 6h. L‐Arguiine, L‐ornitfaine and patrescine added to the incubation media intitially enhanced the effect of urea, but the urease activity ceased after 4h of incubation in the presence of the latter two compounds or when L‐arginine was used; as the sole source of nitrogen. This decline in activity was observed after 6h when L‐arginine was added to urea‐containing media. The loss of urease activity is thought to result from the synthesis of repressers in the presence of the amino acids, whereas putrescine appears to affect membrane permeability by increasing the uptake of urea by the cells. Declining urease activity in the latter case would then be due to feedback inhibition caused by the excess of ammonia produced in both hydrolysis of urea and oxidation of putrescine.
Weak tentoxin effect on the electrical light response of isolated chloroplasts of Peperomia metallica
Authors: Dahse I. , Bulychev A. A. , Kurella G. A. , Liebermann B.
Published: April 2006

The effect of the cyclic tetrapeptide tentoxin, an energy transfer inhibitor which binds to the chloroplast coupling factor 1, on the light‐induced electric potential and the potential decay in the dark was investigated by means of microcapillary glass electrodes in single isolated chloroplasts of the higher plant Peperomia metallica Lind et Rodig. A proposed K+ carrier property of the toxin could not be observed neither in the light response nor in the dark decay of the membrane potential.
Anaesthetic stimulation of Amaranthus albus seed germination: Interaction with phytochrome
Authors: Chadoeuf‐Hannel Régine , Taylorson Ray B.
Published: April 2006

Exposure to solutions of acetaldehyde, ethanol and n‐propanol ranging from 0.06 to 0.6 M for about 5 h induced photosensitivity in imbibed Amaranthus albus L. seeds which normally would be insensitive. When the seeds were made dormant by pre‐treattnent with continuous incandescent light for 24 h, n‐propanol promoted germination np to 80% provided the active form of phytochrome was present. Pre‐treatment of seeds with continuous incandescent light terminated by far‐red reduced the n‐propanol‐stimulated germination to about 33% which could again be increased by a red irradiation. Red light and n‐propanol also interacted in seeds made insensitive to red treatment by 20°C in darkness. Loss of the n‐propanol stimulation resulted from treatment in continuous far‐red for 2 or more days, even when a red irradiance and n‐propanol treatment were combined. It is suggested that n‐propanol may act at a membrane level.
Actual escape area and lateral escape from the xylem of the alkali ions Na+, K+, Rb+and Cs+in tomato
Authors: Wolterbeek H. Th. , van Luipen J. , de Bruin M.
Published: April 2006

Approximation of the total escape area of the xylem in an inbred line of tomato(Ly‐copersicon escutentumMill. cv. Tiny Tim) with help of the frequency distribution of xylem vessel radii provides the possibility to calculate realistic escape constant values from uptake experiments of several elements into tomato stem segments. Comparison of the lateral escape rates of24Na+,42K+,86Rb+and134Cs+indicate that Na+escape is rate‐limited by its uptake into a rather constant number of surrounding cells, regardless of changes in the total escape area of the xylem vessels. The escape of K+, Rb+and Cs+seems to be proportional to the surface area of the xylem vessels and their escape is apparently controlled by their transport across the cell walls of the transport channels. The calculated small values for the escape rate constants (apparent permeability of the xylem cell walls, ca 2–3 · 10−9m s−7) are probably due to the presence of lignin in the xylem cell walls, the discrimination between ions as a result of differing affinities and selectivities and the presence of other solutes in the applied solution.
Photosynthetic and respiratory electron transport in Cu2+‐deficient Dunaliella
Authors: Sandmann Gerhard
Published: April 2006

Growth inhibition of the green alga Dunalietla parva Lerche has been observed during cultivation in low Cu2+ media. A minimum endogenous Cu concentration for unrestricted growth of 100 to 200 nmol ml−1 packed cell volume was estimated. At lower concentrations, Cu deficiency causes a decrease in photosynthesis and respiration. Assay of photosynthetic electron transport rates as well as the determination of several redox components showed that the target of Cu deprivation in the photosynthetic apparatus is the synthesis of Cu‐containing plastocyanin. Consequently, inhibited formation of plastocyanin resulted in low activities of photosynthetic electron transport. A secondary, indirect effect of Cu deficiency is the reduction of thylakoid formation resulting in an additional decrease of photosynthesis compared to cultures with sufficient Cu2+.

The inhibitory influence of low Cu2+ on respiration was located at the site of cytochrome oxidase. In contrast to blue‐green algae, a strong coordination of the biosynthesis of the cytochrome oxidase complex was evident. During restricted Cu2+ supply the formation of cytochiome aa3, another component besides Cu, was stalled. The resulting low activities of cytochrome oxidase are responsible for decreased respiratory electron transfer activity from NADPH to oxygen. At Cu2+ concentrations which exert only moderate effects on Dunalietla, the cytochrome oxidase reaction was more strongly affected than the photosystem I reaction.
Cold tolerance in tomato. I. Seed germination and early seedling growth of Lycopersicon esculentum
Authors: Scott S. Jeffrey , Jones R. A.
Published: April 2006

Tomato seed germination times were evaluated foi three “cold germinating”Lycopersicon esculentum Mill, accessions, PI 120256, PI 174263 and PI 341988 and a control breeding line, T3, at temperatures of 6 to 20°C. Accelerated failure analysis indicated that although PI 120256, 174263 and 341988 germinated more rapidly than T3 from 20 to 9°C, the minimum temperatures for germination were similar, and germination times of PI 120256 and 341988 were relatively more inhibited by progressively lower temperatures than was T3. Rapid germination of these three Pls at 10°C may not be due to cold tolerance, but to seed characteristics that promote rapid germination. Hypocotyl and root elongation over time were described by a three‐parameter logistic equation; the growth rate parameter for hypocotyl elongation of all four genotypes was greatly inhibited from 20 to 15 and 10°C. Multivariate and univariate analyses of hypocotyl growth parameters indicated significant differences among accessions, but no significant genotype by temperature interaction. Rapid emergence reported for these Pis at 10°C is attributable to early germination, rather than rapid hypocotyl growth.
sse of photosynthetic parameters for the diagnosis of copper deficiency in Pinus radiata seedlings
Authors: Gorgé J. López , Lastra O. , Chueca A. , Lachica M.
Published: April 2006

Six‐month‐old water cultures of Pinus radiataI D. Don seedlings showed optimal growth, and the highest CO2 assimilation and photosystem I‐dependent ascorbate/dichlorophenolindophenol → NADP+ electron flow, at 3.0 uM Cu2+ (excess) in the hydroponic media. In the nine‐month‐old water cultures, when the early Cu deprivation has been overcome, the optimum for plant growth and CO2 fixation shifts to 0.3 uM Cu2+ (normal); at that time, the 3.0 uM Cu2+ water cultures showed toxic symptoms of foliar chlorosis. Under Cu2+ deficient levels (0.03 uM) a clear decrease in the photosystem I‐linked electron transport and CO2 assimilation rates, as well as in the whole plant development, could be observed. Both six‐ and nine‐month‐old water cultures showed a close relationship between the Cu2+ concentration of the media and the foliar Cu content. However, leaf chlorophyll and the Cu content of thylakoid lamellae showed such a correlation only in the Cu2+ deficient and Cu2+ normal water cultures. The conclusion from these results is that the electron transport rate ascorbate/dicblorophenolindophenol → NADP+, and the Cu content of the photosynthetic membranes, can be used to diagnose a Cu deficiency in Pinus radiata plants.
The influence of de‐etiolation on the sensitivity of Avena coleoptiles to the far‐red absorbing form of phytochrome
Authors: Blaauw‐Jansen G. , Post Th. H.
Published: April 2006

In photoresponses regulated by phytochrome the effect of a red irradiation is not always reversed by far‐red. This applies for instance to the influence of red light on the geotropic reactionsof Avena coleoptiles. We could induce red/far‐red reversibility by a short de‐etiolating exposure to red light about 20 h prior to the experimental irradiations. This, was due to a decrease of the sensitivity to the low level of the far‐red absorbing form of phytochrome that is established by far‐red. Since etiolated plants react also to a wavelength of 520 nm (green light), it is advisable to expose the coleoptiles to a de‐etiolating irradiation prior to manipulations in green safelight in order to prevent the plants from reacting to the green light.
Microculture of single protoplasts of Brassica napus
Authors: Spangenberg G. , Koop H.‐U. , Lichter R. , Schweiger H. G.
Published: April 2006

Protoplasts of Brassica napus L. were cultured individually in a microdroplet system using a synthetic medium with survival rates of more than 70% and division frequencies of up to 65%. Microcallus formation occurred at frequencies of up to 50%. Factors affecting the survival and division of individually cultured protoplasts, such as composition and volume of culture medium, pH, buffering system, osmolarity and genotype, were analyzed.
Changes in cuticular transpiration rate and cuticular lipids of oat (Avena sativa) seedlings induced by water stress
Authors: Svenningsson Magnus , Liljenberg Conny
Published: April 2006

Two cultivars of oat (Avena sativa L. cvs Pendek and Stormogul II) were exposed to short periods of water‐deficit stress on five consecutive days. The plants responded to the stress by decreasing their cuticular transpiration rate. After two stress periods the cuticular transpiration rate was reduced by 30% for Pendek and by 47% for Stormogul II, and after another three stress periods by 30% and 20%, respectively. These reductions were correlated neither to changes in the total amount of what is generally called epicuticular lipids, nor to changes in any of the major individual constituents of the epicuticular lipids (alkanes, free and esterified fatty acids or free primary alcohols). After removal of the epicuticular lipids the long chain free primary alcohols of the leaves were extracted and determined. The amount of these presumably intracuticular alcohols increased after stress and changed to shorter chain length. From these results it is concluded that the intra‐ as well as the epicuticular lipids must be taken into consideration when discussing leaf surface lipids as protecting agents against water loss.
Danish Rhizobium leguminosarum strains nodulating ‘Afghanistan’ pea (Pisum sativum)
Authors: Jensen E. S. , Sørensen L. H. , Engvild K. C.
Published: April 2006

A wild pea (Pisum sativum L.) native to Afghanistan normally known to be resistant to nodulation with European strains of Rhizobium leguminosarum was nodulated early and effectively in field soil in Denmark. Isolates from nodules formed effective nodules abundantly on ‘Afghanistan’ on reinfection under aseptic conditions. Five types differing in isoenzyme composition pattern were found among 15 isolates from ‘Afghanistan’ nodules. None were identical with the ‘Tom’ strain from Turkey, which also forms effective nodules with ‘Afghanistan’. The five types were also different with respect to isoenzyme pattern from Rhizobium leguminosarum strains isolated from a modern pea variety cultivated in the same field.
Respiration in mature leaves of Lolium perenne as affected by nutrient supply, cutting and competition
Authors: Pilbeam C. J. , Robson M. J. , Lambers H.
Published: April 2006

The rate of oxygen uptake was measured on sections of mature leaf tissue derived from two populations of Lolium perenne L. cv. S23, selected for contrasting rates of mature leaf respiration. Under conditions of sufficient nutrient supply, GL72 had a lower rate of respiration and a greater yield than GL66. The populations were exposed to important management variables to investigate their effect on the selection criterion, the two variables being nutrient supply and defoliation. Conditions of low nutrient supply were characterized by a similarity in respiration rate and a change in the regulation of respiration. Enzyme levels, rather than adenylates, controlled respiration. Weekly cutting induced activity of the otherwise latent alternative pathway.
Effects of glyphosate [N‐(phosphonomethyl)glycine] on photosynthetic pigments, stomatal response and photosynthetic electron transport in Medicago sativa and Trifolium pratense
Authors: Muñoz‐Rueda Alberto , Gonzalez‐Murua Carmen , Becerril José María , Sánchez‐Díaz Manuel F.
Published: April 2006

Stomatal response, chlorophyll and carotenoid content, and photosynthetic electron transport were investigated in Medicago sativa L. (cv. Aragón) and Trifolium pratense L. (cv. Violeta) after plants were exposed to various glyphosate [N‐(phophonomethyl)glycine] concentrations. The herbicide decreased the content of photosynthetic pigments when applied at concentrations of 0.15, 1.5 and 15 mM, showing a greater effect on chlorophyll pigments than on carotenoids. The chlorophyll a/b ratio increased as a consequence of a major effect on chlorophyll b. Glyphosate treatment (15 mM) led to a closure of stomates after seven days in both species. The results suggest that glyphosate acts as an electron transport inhibitor, because glyphosate pre‐incubated chloroplasts, isolated from control plants, showed reduced photosystem II and photosystem I activities. In general, clover was more sensitive to glyphosate than glyphosate, lucerne.
Localization of RNA‐degrading enzyme activity within vacuoles of cultured tomato cells
Authors: Abel Steffen , Glund Konrad
Published: April 2006

Protoplasts were prepared from cells of a tomato (Lycopersicon esculentum Mill. cv. Lukullus) suspension culture and purified to eliminate the highly active exogenous RNase present in the enzyme mixture used for cell wall digestion. The purified protoplasts were used to determine the location of the endogenous RNase activity (measured at pH 5 with yeast RNA as the substrate). Vacuoles were released by shaking the purified protoplasts in alkaline buffer containing EDTA. RNase was unambiguously shown to be located within the vacuoles by (i) its co‐purification with the vacuoles in a discontinuous gradient and by (ii) the co‐migration of RNase and α‐mannosidase (EC 3.2.1.24), a vacuolar marker, during repeated centrifugation of the vacuoles. Vacuolar RNase was insensitive to EDTA, Mg2+, Mn2+ and Ca2+ but was stimulated by citrate or KH2PO4. It exhibited a pH‐optimum in the range of pH 5–6. Gel electrophoretic analysis revealed one single band for RNase of isolated vacuoles. This activity co‐migrated with an RNase from cells extracted under mild conditions. Thus, it was possible to distinguish the vacuolar RNase from the RNase of extracellular origin. RNA‐degrading activity was present in vacuoles throughout the growth of the culture. The activity in vacuoles gradually increased during exponential growth followed by a dramatic increase in the stationary phase.
Influence of some metal chelators and light regimes on bioaccumulation and toxicity of Cd2+ in duckweed (Lemna gibba)
Authors: Polar Emine , Küçükcezzar Rezzan
Published: April 2006

A factorial culture experiment was designed to investigate the influence of light regimes and of some metal chelators on the accumulation of cadmium by Lemna gibba L. The plants were grown in a complete nutrient solution containing Cd2+ concentrations ranging from 0 to 27 μM with or without EDTA, ethylenediamine‐N,N′‐bis‐(o‐hydroxyphenylacetic acid) (EDDHA) or salicylic acid. Each experiment was run for eight days in 18 h:6 h light:dark or continuous light. An increase in the Cd2+ concentration in plants and a simultaneous drop in accumulation efficiency (ratio of Cd2+ concentration in plants to the initial Cd2+ concentration in the nutrient solution) with increasing ambient Cd2+ levels was best represented by regression power curves. At the lowest Cd2+ concentration which caused a significant decrease in the relative growth rate of duckweed, there was a decrease in manganese and zinc and an increase in the iron level in the plants. EDDHA and EDTA protected in some cases against the toxic action of cadmium without preventing its uptake by plants. It was thus observed that 9 μM or higher levels of Cd2+ were toxic to Lemna gibba depending on the chelator and light regime. Duckweed grown in continuous light produced, in general, more dry matter and hence accumulated more cadmium.
Ammonium‐induced vitrification in cultured tissues
Authors: Daguin F. , Letouzé R.
Published: April 2006

Glassiness of willow (Salix babylonica L.) can be controlled by the amount of ammoniacal nitrogen in the culture medium. In this study, glutamate dehydrogenase (EC 1.4.1.3) activity was observed in the different parts of the plant during induction of the vitrification process. The apparent affinity constants of the enzyme for ammonium were determined. The root enzyme displayed the highest affinity for ammonium (Km 0.70 – 2.25 mM), and correlatively, its activity was linked to the amount of ammonium applied and to the development of the vitreous state. Although it has been shown that ethylene, matric potential and high cytokinin content are implicated in vitrification, the present study shows that a knowledge of the affinity constants for ammonium, when the ammoniacal nitrogen content of the culture medium is taken into account, can predict the risk of the plant material becoming vitreous.
A comparison of regulatory effects of chloride on nitrate uptake, and of nitrate on chloride uptake into Pisum sativum seedlings
Authors: Deane‐Drummond Celia E.
Published: April 2006

Net nitrate uptake, 36ClO−3/NO−3 influx and 36Cl− influx into Pisum sativum L. cv. Feltham First seedlings have been examined following growth in culture medium containing different combinations of chloride and nitrate. When young (6 days old) seedlings, that had been grown in the absence of N were used, nitrate accumulation stimulated net nitrate uptake and 36ClO−3/NO−3 influx (r2= 0.99) while chloride accumulation inhibited nitrate uptake and 36ClO−3/NO−3 influx (r2= 0.65). When nitrate was provided during growth there was no effect of chloride pretreatment on net nitrate uptake and there was little effect of total [NO−3+ Cl−]i on 36ClO−3/NO−3 influx (r2= 0.26). A direct effect of Cl− on 36ClO−3/NO−3 influx was only found when seedlings had been starved of N for more prolonged periods (14 days).

When moderate chloride was supplied during growth, 36Cl− influx was insensitive to nitrate or chloride accumulated, but significantly correlated with loge [NO−3+ Cl−]i (r2= 0.75). When trace amounts of Cl− were supplied during growth 36Cl− influx was inhibited by (a) NO−3 in the external medium and (b) Cl− pretreatment, but was insensitive to NO−3 pretreatment. The sensitivity of 36Cl− influx to external nitrate was not found following Cl− pretreatment in the absence of nitrate. The possibility that there are two populations of chloride carriers which differ in their sensitivity to external nitrate is discussed. Tentative schematic models to account for the regulation of nitrate and chloride uptake are proposed in the context of current hypotheses for regulation of ion transport and control systems theory.
A method for determining the apoplastic water volume of conifer needles
Authors: Beeson R. C. , Montano J. M. , Proebsting W. M.
Published: April 2006

A method for direct estimation of percentage apoplastic water volume (% APO) in conifer needles is described. The method presented here, and designated the pressure‐needle (P‐N) method, measures the relative water content of the needles to develop a curve similar to the pressure‐volume (P‐V) curve. P‐V and P‐N curves were developed for Picea pungens Engelm. cv. Hoopsi, Pinus sylvestris L., Abies gradis (Dougl.) L., and Pseudotsuga menziesii (Mirb) Franco. The % APO estimated by the two procedures varied as much as 2‐fold, while other parameters were similar. The P‐V method generated consistently higher and more variable % APO than the P‐N method, due to the inclusion of the apoplastic water of the stem in the P‐V method. For conifers, the P‐N method offers a more accurate and precise method for determining % APO.
Temperature dependence of the membrane resistance in Characeae cells
Authors: Paszewski Adam , Śpiewla Edward
Published: April 2006

Changes in the electrical resistance of internodal cells of Nitellopsis obtusa (Desv. in Lois) J. Gr. and Lychnothamnus barbatus (Meyen) Leonh., produced by short‐lasting temperature changes (3‐min intervals) in the range of 4⇌48°C were measured. In the whole temperature range examined the electrical resistance of the cell membranes underwent from 5 to 9 distinct changes; the overall changes were approximately hyperbolic, while in certain narrow temperature ranges they were non‐monotonic, and in others linear. Arrhenius plots of these dependencies provide data which suggest a specific, stepwise character of changes in the permeability to ions, produced by temperature alterations and probably connected with corresponding modifications of cell membrane fluidity. This seems to support the view that the cell membranes of the examined plant species may exist in different, discrete, physiological states characteristic of certain temperature ranges.
Effects of alkali ions on the circadian leaf movements of Oxalis regnellii
Authors: Rinnan T. , Johnsson A.
Published: April 2006

The influence of alkali ions on the circadian leaf movements of Oxalis regnellii Mig. was investigated. Ions were given to the oscillating system via the transpiration stream of cut stalks in nutrient medium. Chloride solutions of Rb+, Cs+, Na+ and K+ were tested and the results compared to previously published LiCl‐results.

The period of the circadian leaf movements was unaffected by a continual addition of Na+ or K+ to the nutrient medium (at least up to 40 mM). Rb+, in the concentration of 2.5 or 5 mM, caused a shortening of the period when applied continuously. Rb+ concentrations up to 60 mM were tested. Cs+ ions caused only lengthenings of the circadian period. Cs+ concentrations up to 40 mM were tested. Cs+ resembled Li+ in producing period lengthenings, but was not as effective as Li+ when compared on a concentration basis. Toxicity of the effective ions was in the following order: Li+Cs+Rb+, Rb+ pulses (50 mM, 4 h) phase‐shifted the rhythm and caused advances. A phase response curve was determined and the maximum steady state advances were of the order of 1 h. The dual effect of the Rb+ ions is discussed and is assumed to be due to two counteracting processes, exemplified by Rb+‐sensitive ATPase‐controlled pumping processes and protein synthesis. For comparison, the effects of Rb+ and Li+ in human depressive disorders is also discussed in relation to their influence on circadian systems. It is emphasized that Rb+ and K+ behave differently and are not interchangeable in their action on circadian systems.
In vitro translation capacity of ribosomes isolated from the cells of pine buds during the cold season
Authors: Häggman Hely
Published: April 2006

The cytosolic and membrane‐bound ribosome assemblies were isolated from the microsporangiate strobili of Scots pine (Pinus sylvestris L.). Both assemblies studied were able to incorporate [3H]‐leucine into trichloroacetic acid‐insoluble material throughout the sampling period from October to April, indicating that the isolation procedure employed preserves the ability of the ribosomes to synthesize protein. Samples of identical size, taken from cytosolic as well as from membrane‐bound ribosomes isolated from the same source, behaved similarly in vitro: they were both active, their activity was arrested by ribonnuclease and, as shown by aurintricarboxylic acid treatment, most of their mRNA molecules were complexed with the ribosomes. Variation in translation capacities seemed to depend on the season and physiological stage of the bud tissue.
Fruit effects on photosynthesis in Prunus persica
Authors: DeJong T. M.
Published: April 2006

Seasonal measurements of net CO2 assimilation, leaf conductance and mesophyll conductance were made in the field on mature, fruiting and defruited Prunus persica L. Batsch trees. During early stages of fruit growth there were no significant differences in leaf gas exchange characteristics between fruiting and defruited trees. During the early part of the last stage of fruit growth, CO2 assimilation rates were 11–15% higher in fruiting trees than defruited trees. These increased assimilation rates corresponded with approximately 30% increases in leaf conductance and only minor changes in mesophyll conductances or leaf CO2 assimilation capacity as indicated by leaf nitrogen content. It is concluded that under the field conditions of this study the fruit effect on photosynthesis is primarily related to stomatal behavior.
Changes in gibberellin‐like substances of peach seed during stratification
Authors: Gianfagna Thomas J. , Rachmiel Susan
Published: April 2006

The germination percentage of peach [Prunus persica (L.) Batsch cv. Halford] seeds at 20°C was low (< 20%) after incubation at 5°C for as long as 35 days, but then increased considerably (> 40%) when the seeds were maintained at 5°C for longer than 42 days. Four zones of gibberellin‐like activity were found in partially purified seed extracts. Gibberellin‐like activity remained low in seeds incubated at 5°C for as long as 28 days, but increased significantly in three of these zones after 35 days, and in the fourth zone after 49 days. The increase in gibberellin‐like activity was evident prior to the transfer of the seeds to 20°C. Moreover, seeds maintained at 5°C germinated at this temperature after 63 days. For seeds incubated and germinated at 20°C, both the germination percentage and the gibberellin‐like activity remained low throughout the experimental period. Application of the growth retardant paclobutrazol to seeds after 28 days of a 49 day total incubation period at 5°C did not substantially reduce seed germination, although the increase in gibberellin‐like activity was prevented. Seeds did, however, require a longer time to germinate after transfer to 20°C and were dwarfed in appearance. Application of GA3 to seeds prior to stratification increased the percentage germination of seeds only when they had been incubated at 5°C for at least 35 days. The major changes in gibberellin‐like activity are, therefore, associated not so much with the processes which allow germination to take place in peach, but more with those processes which allow normal growth and development of the seedling.
Photorespiratory nitrogen cycle – A critical evaluation
Authors: Singh Prikhshayat , Kumar P. A. , Abrol Y. P. , Naik M. S.
Published: April 2006

The photorespiratory nitrogen cycle proposed by Keys et al. (Nature 275: 741–743, 1978) involved formation of glycine by transamination of glyoxylate in the peroxisomes utilizing glutamate. Subsequently, glycine is oxidized to ammonia, serine and CO2 in the mitochondria. The ammonia is reassimilated via the GS/GOGAT pathway generating glutamate. In this article, experimental evidence which suggests the occurrence of alternative mechanisms of glycolate and serine synthesis as well as of CO2 and ammonia evolution is discussed. The problem of utilization of NADH coupled to ATP synthesis during photosynthesis is still unresolved, which complicates the glycine oxidation reaction in light. Further, factors are presented that determine the availability of amino donors in the peroxisomes and of amino acids viz., glycine, serine and glutamate for the operation of the photorespiratory N cycle. Recent evidence regarding the role of formate arising out of the reaction of glyoxylate with H2O2 in the regulation of photosynthetic electron flow in the Hill reaction, as well as of photorespiratory substrates functioning as carbon sources for the citric acid cycle in the light or for export to the growing tissues, suggests that the role of photo‐respiration in plant metabolism needs to be reexamined.
ATP synthesis and utilization in the early stage of seed germination in relation to seed dormancy and quality
Authors: Perl M.
Published: April 2006

In addition to the possible activities of the well‐known biochemical cycles, the ATP‐synthesizing system in dry seeds consists of a pathway which oxidizes malate and provides phosphoenolpyruvate (PEP). This system seems to be regulated primarily by the malate dehydrogenase (EC 1.1.1.37) activity, which together with the PEP carboxylase (EC 4.1.1.38) provides PEP and NADH. This latter compound may play a role as the “sparker” for the whole cycle.

Breaking seed dormancy does not seem to be related to the rate of ATP synthesis per se but to facilitate enzyme‐substrate interaction, probably caused by intracellular compartment‐fusion. The compartmentation process is probably a result of the seed ripening and maturation functions.

The ATP accumulated at the early stage of seed germination is a result of ATP synthesis and ATP utilization. Thus, ATP accumulation may result from a high rate of synthesis (high quality seeds) or from a low utilization ability (low‐quality seeds). Also, since 95% of the synthesized ATP is utilized concomitantly with its synthesis, the accumulated amount is relatively insignificant and does not indicate seed quality. This conclusion is also supported by many experimental results in which no such correlation was found.
Control of Na+ and K+ transport in Spergularia manrina. II. Effects of plant size, tissue ion contents and root‐shoot ratio at moderate salinity
Authors: Cheeseman John M. , Wickens Linda K.
Published: April 2006

In this paper we continue our analysis of Na+ and K+ uptake in vegetative Spergularia marina (L.) Griseb. plants growing on 0.2x sea water in solution culture. We consider the relationships between isotope uptake and plant size, root: shoot ratio (RSR) and total ion contents, both individually (with the linear effects of time removed) and in combinations through stepwise multiple linear regression. The results differ from those of other studies, representing in our case inherent variability in a homogeneous population under steady‐state growth conditions. The results were broadly similar for 22Na+ and 42K+. Total uptake was significantly and negatively correlated with RSR and root weight (Wr), and positively with root K+ content (Kr). These 3 variables were mutually correlated, however, and this was reflected in the multiple analyses as a reduction or loss of significance of one or more of the measures. Transport to the shoot was very highly correlated with total uptake (r2 > 0.99 for both isotopes), resulting in nearly identical regression results. In multiple regression analyses of root data alone, accumulation was related only to root contents, but in a manner inconsistent with the allosteric regulation hypothesis, the most significant correlation being positive with Kr. The results were nearly identical for the two isotopes. The results were not consistent with a single factor regulatory system involving only initial root plamalemma ion influx. The observed Na+‐K+ and root‐shoot balances seem to require at least involvement of symplast‐to‐medium and symplast‐to‐xylem transport steps. Though the biochemical and biophysical signalling and transduction steps are not known, a physiological working hypothesis is presented, in which the positive correlation of uptake with root contents is balanced by a negative feedback signal deriving from plant size and by the diluting effects of growth. Considered over the vegetative period, these would produce the observed stability of plant contents during growth. The negative interaction with RSR is postulated to manifest the integrating system required to deliver ions to the shoot at the required rates.
Control of Na+ and K+ transport in Spergularia marina. III. Relationship between ion uptake and growth at moderate salinity
Authors: Cheeseman John M. , Wickens Linda K.
Published: April 2006

In this paper, we continue our analysis of Na+ and K+ uptake by mid‐vegetative Spergularia marina (L.) Griseb. plants growing on 0.2x sea water medium, with attention to the relationship of ion uptake and growth. In the first part of the paper, growth analysis techniques are used to compare relative growth rates (RGR) and relative accumulation rates (RAR) for Na+ and K+. Under constant growth conditions, a high correlation between RGR and RAR indicated that growth and accumulation of both ions were well balanced, resulting in Na+ and K+ concentrations within the plants which were stable after adjustement to the saline medium. The analysis confirmed the existence of a Na+ ‐related growth stimulation in S. marina and an associated increase in the efficiency of K+ utilization for growth. When plants were subjected to more rapid salinization and step changes in the light intensity of the growth chamber, RGR and RAR were again similar, even through the discontinuities in growth conditions, suggesting that growth and ion accumulation were co‐regulated rather than simply correlated.

The growth analysis data were then transformed to give net uptake rates for Na+ and K+ and the results were compared to those of isotope studies under similar growth conditions. In roots, the rates estimated by the two techniques differed substantially; net uptake rates reflected primarily growth, while isotope studies indicated a substantial ion exchange rate between mature cells and the growth medium. The rates of transport of either Na+ or K+ to the shoot were very similar using the two estimation techniques. As the rates measured with isotopes were taken from studies lasting at most a few hours, this suggested a very rapid turnover of the upwardly mobile Na+ and K+ pools in the roots.
Effects of phosphate stress on the rate of phosphate uptake during resupply to deficient tomato plants
Authors: Katz Donald B. , Gerloff G. C. , Gabelman W. H.
Published: April 2006

Plants of Lycopersicon esculentum Mill. P. I. 120262 show an increased phosphate uptake rate per unit dry weight of root after as little as one day of growth in solutions lacking phosphate. The reversibility of this response in plants experiencing various degrees of phosphate stress was investigated by measuring the depletion of phosphate from solutions over 3‐h intervals. Measurements were made at three times in the first 30 h after phosphate was resupplied. Reversibility decreased as the level of phosphate stress increased. The phosphate uptake rate was returned to the level of controls after 30 h of phosphate resupply in plants grown without phosphate for one or three days. Plants grown without phosphate for five or seven days had uptake rates 26 and 40% higher than controls, respectively, after the same period of phosphate resupply. Internal phosphate concentrations after 30 h of phosphate resupply were equal to or greater than the controls in all plants. These results are consistent with a simple reversible feedback of phosphate status on phosphate transport in slightly stressed plants, but such a mechanism seems inadequate to explain the responses observed in more severely stressed plants.
Isolation and electrical characterization of tonoplast vesicles from the Kiwi fruit (Actinidia chinensis)
Authors: Chedhomme Francine , Rona Jean‐Pierre
Published: April 2006

Nomarski interference microscopy technique showed that the cell juice of the Kiwi fruit (Actinidia chinensis Planch.) is rich in membrane vesicles that resemble protoplasts and free vacuoles. These vesicles are obtained without enzyme or chemical treatment and probably arise from the rupture and revesiculation of the tonoplasts that limit the cytoplasmic strands of the cells. Vacuole fragmentation in situ probably causes the tonoplast to recombine around the vacuolar sap as well as around the cytoplasmic strands, which implies either original or inverse orientation of the inner face. Electrophysiological measurements in vesicles judged to have the original membrane orientation showed that their polarization was inside positive, the same as central vacuoles of protoplasts and isolated vacuoles.
Sucrose synthase from wheat leaves. Comparison with the wheat germ enzyme
Authors: Larsen Adriana E. , Salerno Graciela L. , Pontis Horacio G.
Published: April 2006

Sucrose synthase (UDP glucose: D‐fructose‐2‐glucosyl transferase, EC 2.4.1.13) was partially purified from wheat (Triticum aestivum L. cv. San Agustin INTA) leaves and its properties compared with the wheat germ enzyme. The leaf enzyme moved faster in polyacrylamide gel electrophoresis, was more sensitive to SH reagents and crossreacted more slowly with antibody prepared towards the germ enzyme. Kinetic constants were of the same order for all substrates. UDP was a strong inhibitor of the synthesis reaction. MgCl2 stimulated this reaction and partially reversed UDP inhibition. Molecular weight determined by gel filtration was 380 and 370 kdalton for the leaf and germ enzymes respectively. Both enzymes presented forms of higher molecular weight estimated to around 800 and 1000 kdalton. Neither sucrose synthase from leaves nor from germ were affected by fructose 6‐P, fructose 1,6—P2, glucose 1—P, glucose 6—P, fructose 2,6—P2 and cAMP.
Sugar and starch changes in pea cotyledons during germination
Authors: Monerri C. , Garcia‐Luis A. , Guardiola J. L.
Published: April 2006

Changes in starch and sugar contents in the cotyledons during germination have been compared in a smooth (cv. Alaska) and a wrinkled (cv. Progress) cultivar of the garden pea (Pisum sativum L.). In both cultivars there was an initial accumulation of sucrose due to the hydrolysis of sucrosyl oligosaccharides, but galactose did not accumulate in the cotyledons. Starch mobilization in the Progress pea was linear with time and started before the rise in α‐amylase (EC 3.2.1.1) activity in the cotyledons; sucrose was synthesized in the cotyledons, and their excision from the axis resulted in an additional accumulation of this sugar. In the Alaska pea, the onset of starch hydrolysis coincided with the rise in α‐amylase activity; no accumulation of sucrose was found in excised cotyledons, whilst the sucrose content decreased continuously in attached cotyledons.

The same sugars were found in the cotyledons of both cultivars, suggesting a common pathway for starch breakdown. Maltose, maltotriose and linear malto‐dextrins were not present and only trace amounts of glucose were detected, suggesting a degradation of starch by phosphorylase after an initial attack by α‐amylase. α‐Amylase activity in the cotyledons was higher in the presence of the axis, but was influenced by the water content of the cotyledons. Transient changes in α‐amylase activity correlated well with changes in the rate of starch hydrolysis, but after 2–3 days starch mobilization was reduced in excised cotyledons probably due to the resynthesis of starch.
ATPase activity of sunflower root membranes as affected by flooding
Authors: Mukherjee Habanta , Drakeford David , Reid David M.
Published: April 2006

Flooding of excised roots or roots of intact aeroponically grown sunflower (Helianthus annuus L. cv. Russian) caused a reduction in the activity of ATPases of microsomal membrane vesicles within 1 day. With increasing flooding of up to 3 days, the enzyme activity in the roots declined. During the same period, enzyme activity gradually increased in the non‐flooded aeroponically grown roots. Continuous aeration during flooding either maintained the activity of the enzyme to the level of the controls or enhanced it. The ATPase did not require MgSO4 and had a much higher activity at pH 6.7 than at pH 8.5. The activity of the ATPases was markedly inhibited by sodium orthovanadate. There was 8 to 44% stimulation of the activity of the ATPases due to KCl in the absence as well as presence of MgSO4. These data indicate that a substantial proportion of the ATPases, and thus the interface vesicles, could be of plasma membrane origin.
Tissue specificity of acid action in rapid elongation responses of lupin hypocotyls
Authors: Pearce David , Penny David
Published: April 2006

We have tested the acid‐responsiveness of hollow cylinders, peeled segments, and cores of stelar tissue of hypocotyls of light‐grown lupin seedlings (Lupinus angustifolius L. cv. New Zealand Bitter Blue), to determine how differential responsiveness of individual tissues to acid might govern the response of the intact hypocotyl. Hollow cylinders of cortex with the outer cell layers intact were less responsive to acid than was the cortex alone, which elongated strongly at pH 5. The stelar tissues were acid‐responsive (pH 5), but only if the cell layer surrounding the stele (the starch sheath) was disrupted. We conclude that all tissues were acid‐responsive, with the cortex alone most responsive, and the outer cell layers least responsive. We suggest that acid‐induced elongation of intact segments may be controlled by the response of the outer cell layers.