bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of parasitization by Cuscuta reflexa: RNase activity in the haustorial region of Cuscuta and infected host tissues
Authors: Gupta Anjali , Singh Madhav
Published: April 2006

In a study of host‐parasite interrelationship and the mechanism of parasitization, ribonuclease activity was determined in Cuscuta reflexa Roxb, and in infected and control host plants of Lantana camara L. In the haustoria‐bearing region of Cuscuta, the concave half of the vine bearing the haustorial site, always showed significantly higher RNase activity than the convex half, irrespective of the differing enzyme activity of the parasite tissue growing on different hosts —Brassica campestris L., Helianthus animus L., Lantana camara L., Medicago saliva L. and Solatium nigrum L. The uninfected host branch of L. camara showed the maximum specific RNase activity in the apical region which decreased toward the base, while the infected host branch showed minimum specific RNase activity in the apical region, gradually increasing towards the infected region.
Growth and the efficiency of root respiration of Pisum sativum as dependent on the source of nitrogen
Authors: de Visser Ries , Lambers Hans
Published: April 2006

Growth and efficiency of root respiration were investigated in Pisum sativum L. cv. Alaska and cv. Rondo. Plants were grown in culture solutions, either in symbiosis with Rhizobium leguminosanm, or with an abundant supply of nitrate or ammonium and completely lacking nodules. In comparison with plants utilizing nitrate or ammonium, Ni‐fixing plants showed lower rates of dry matter and nitrogen accumulation, as well as lower rates of total and cytochrome‐mediated root respiration. Rates of shoot dry matter accumulation and root respiration in plants utilizing ammonium were lower than in plants utilizing nitrate. The efficiency of root respiration was high in N2‐fixing plants, as indicated by a low activity of the SHAM‐sensitive, alternative, non‐phosphorylating pathway. In nitrate and ammonium grown plants of cv. Alaska, the efficiency of root respiration was about the same, and in both cases lower than in N2‐fixing plants. The efficiency of root respiration in non‐symbiotically grown pea plants was generally higher than in many non‐legumes. Comparison of the ATP costs of synthesis of root dry matter for different N‐sources was complicated by large differences in relative growth rate of the root and in shoot to root ratio between N‐treatments. A quantitative correction of the ATP production during synthesis of root dry matter for differences in shoot to root ratio and root maintenance respiration has been made. It is concluded that ATP costs of root dry matter production are highest in the case of N2‐fixing plants. In plants utilizing ammonium, ATP costs of synthesis of root dry matter were slightly lower than in plants utilizing nitrate. The physiological significance of the alternative pathway in root metabolism is discussed in relation to the assimilation of different sources of nitrogen.
A possible structural role for carotenoids and carotenoid precursors in etioplasts
Authors: Dahlin Clas , Ryberg Hans , Axelsson Lennart
Published: April 2006

Seedlings of wheat (Triticum aestivum L.) were grown in darkness in different concentrations of the herbicide SAN‐9789, an inhibitor of carotenoid synthesis. The ultrastructural appearance of etioplasts, containing different amounts of carotenoids, was compared to the contents of carotenoids and carotenoid precursors (phytoene and phytofluene). A correlation was found between the presence of carotenoids and the presence of partitions between prothylakoids. As the plants were grown in darkness, this correlation is interpreted as the result of a structural role of the carotenoids. The presence of the herbicide SAN‐9789 resulted in an increase in size and a change from osmiophilic to non‐osmiophilic plastoglobuli. This change in plastoglobuli was neither correlated to the increase in phytoene or phytofluene, nor to the decrease in carotenoids.
Relationship between C2H2 reduction, H2 evolution and 15N2 fixation in root nodules of pea (Pisum sativum)
Authors: Skøt Leif
Published: April 2006

The quantitative relationship between C2H2 reduction, H2 evolution and 15N2 fixation was investigated in excised root nodules from pea plants (Pisum sativum L. cv. Bodil) grown under controlled conditions. The C2H2/N2 conversion factor varied from 3.31 to 5.12 between the 32nd and the 67th day after planting. After correction for H2 evolution in air, the factor (C2H2‐H2)/N2 decreased to values near the theoretical value 3, or in one case to a value significantly (P < 0.05) below 3. The proportion of the total electron flow through nitrogenase, which is not wasted in H2 production but used for N2 reduction, is often stated as the relative efficiency (1‐H2/C2H2). This factor varied significantly (P < 0.05) during the growth period. The actual allocation of electrons to H2 and N2, expressed as the H2/N2 ratio, was independent of plant age, however. This discrepancy and the observation that the (C2H2‐H2)/N2 conversion factor tended to be lower than 3, suggests that the C2H2reduction assay underestimates the total electron flow through nitrogenase.
Cultivar and Rhizobium strain effects on the symbiotic performance of pea (Pisum sativum)
Authors: Skøt Leif
Published: April 2006

The symbiotic performance of four pea (Pisum sativum L.) cultivars in combination with each of four strains of Rhizobium leguminosarum was studied in growth chamber experiments in order to estimate the effects of cultivars, strains and cultivar × strain interaction on the variation in dry weight, N content and dry weight/N ratio. At harvest 63 days after planting, cultivars accounted for 75% of the variation in dry weight, while the Rhizobium strains accounted for 63% of the variation in N‐content and 70% of the variation in dry weight/N ratio. Cultivar × strain interactions were statistically significant, but of minor quantitative importance, accounting for 5–15% of the total variation. Rhizobium strains also influenced the partitioning of N between reproductive and vegetative plant parts and between root and shoot biomass.
Bioelectrical reactions of Nitellopsis obtusa induced by indole‐3‐acetic acid
Authors: Vorobiev Lev N. , Manusadžianas Levas
Published: April 2006

The complex of bioelectrical paramenters (membrane potential, membrane resistance and capacitance) of internodal cells of Nitellopsis obtusa was measured over a wide range of IAA concentration (10−10 to 10−4M) with two intracellular microelectrodes. Primary effects of IAA at a concentration as low as 10−10M were observed. The optimum range of IAA action was from 10−9 to 10−6M. The type of IAA‐induced electroresponse depended on the initial level of membrane potential, which characterized the energetic state of the plasmalemma. In the energized state (ca −200 mV) N. obtusa cells appeared to have 3 typical reactions: hyperpolarization (membrane potential less than K+‐equilibrium potential), depolarization (membrane potential higher than K+‐potential) and absence of response at K+‐electrochemical equilibrium. Membrane capacitance was found constant at 0.74 ± 0.05 μF cm−2, but membrane resistance increased up to 50% independently of the sign of the electrogenic reaction. Increase of membrance capacitance and decrease of the membrane resistance was a feature of the de‐energized state (ca −135 mV) and may be explained by lower viscosity of membrane lipids, which interacted with IAA. The complex of parameter, including cytoplasmic steaming taken as an indicator of energy supply, is discussed as indicating slow IAA penetration combined with a primary action of IAA on the plasmalemma receptor sites.
The transport of substances out of developing fruits in relation to the induction of apical senescence in Pisum sativum line G2
Authors: Gianfagna Thomas J. , Davies Peter J.
Published: April 2006

Apical sencscence in G2 peas occurs only in long days in the presence of fruit. The effect of fruits could be caused by the export of a senescence hormone from the fruits to the shoot tip. Export of radiolabeled material from developing fruits of G2 peas grown in long days was therefore examined following injection of the pods with [14C]‐sucrose, [14C]‐acetate, or [14C]‐mevalonate or after allowing the pods to photosynthesize in 14CO2 for 48 h. In all cases a small amount (<1%) of radioactivity was exported, primarily to the younger fruits on the same side of the plant and the to the shoot apex. After feeding 14CO2 to the fruit, the radiolabeled material partitioned into acidic ethyl acctate and possessed a carboxyl group. While this radioactivity had chromatographic properties similar to abscisic acid (ABA) in a number of solvent systems, it was not identical to either ABA, phascic acid or dihydrophaseic acid. The nature of the labeled material found in the apex was different in short days, in which senescence does not occur, or when the leaves were the source of the radioactive compounds. The labeled material in the apex was similar after feeding 14CO2, [14C]‐acctatc, or [14C]‐sucrose, but different if the fruits were injected with[14C]‐mevalonate.Identification of the chemical nature of the labeled material in the apex was not possible due to the small amount present. Parallel purification of an extract from treated fruits led to the identification of N‐benzoylaspartate and N‐phenylacetyl‐aspartate. The radiolabeled substance from the apex was run with these two chemically synthesized compounds on several gas chromatogtaphic columns, and was also recrystallized together several times. The label and the pure material did not have identical retention times; neither did they co‐purify so that, while similar, the material exported to the apex is not the above compounds.
Binding of phytochrome to plasma membranes in vitro
Authors: Sundqvist Christer , Widell Susanne
Published: April 2006

Plasma membranes were prepared from dark grown shoots of oat (Avena sativa, L. cv. Sol II) by means of an aqueous polymer two‐phase partition method. Phytochrome was prepared from the same material by brushite chromatography and immunoaffinity chromatography. The purified plasma membranes and the phytochrome were mixed and pelleted by centrifugation at 72 000 g. The pellet was washed and repelleted once, and the phytochrome found in the resulting pellet was regarded as specifically bound to the plasma membrane. This binding was increased in the presenee of Mg2+ and after red irradiation. The affinity constant was 3.4 ± 106M‐1 as extrapolated from a Scatchard plot. An increased binding in the presence of 1 M sodium chloride indicates that the binding is of a hydrophobic nature. A tryptic treatment increased the binding which could be interpreted as the removal of steric hindrance from the membranes and as the non‐existence of a trypsin‐degradable receptor protein.
5‐Oxo‐prolinase activity in tobacco suspension cultures: Regulation by sulfate nutrition
Authors: Rennenberg Heinz , Polle Andrea , Grundel Ina
Published: April 2006

In heterotrophic and photoheterotrophic tobacco (Nicotiana tabacum L., var. Samsun) suspensions cultured with growth‐limiting amounts of sulfate, 5‐oxo‐prolinase activity declines at the same time as the growth rate of the cells decreases. However, 5‐oxo‐prolinase activity is reduced to a greater extent than growth. As a result, the specific activity of 5‐oxo‐prolinase also declines when sulfur is scarce. The decrease in both growth and 5‐oxo‐prolinase activity can be prevented by adding sulfate to the suspensions during exponential growth. Addition of sulfate after the exponential growth phase restored neither growth nor 5‐oxo‐prolinase activity. These observations show that 5‐oxo‐prolinase activity in tobacco cells is regulated by the sulfate supply in the medium. Such a regulation is an essential prerequisite, but not a proof, for a role of 5‐oxo‐prolinase as the rate‐limiting factor in glutathione degradation.

During exponential growth the average specific activity of 5‐oxo‐prolinase in heterotrophic tobacco cells is twice as high as in photoheterotrophic cells. This difference is consistent with the idea that green cells are equipped for glutathione synthesis and export, and chloroplast‐free cells for uptake and degradation of this peptide.
Patterns of ammonium absorption and acetylene reduction during soybean developmental growth
Authors: Marcus‐Wyuer Lynn , Rains D.W.
Published: April 2006

Nodulated and unnodulated soybean plants (Glycine max (L.) Merr. cv. Amsoy 71) were grown in nutrient solution either lacking or containing N. Nodulated plants, dependent on N2 fixation, exhibited a generalized N‐stress and were less vigorous than unnodulated plants dependent on inorganic N assimilation.

Starting at preflowering throughout mid pod‐filling, NH4+ absorption, expressed on the basis of root dry weight, was determined for intact nodulated and unnodulated plants in short‐term kinetic experiments. Depletion of NH4+ was measured from the liquid phase of a mist chamber. Maximum NH4+ absorption occurred for both nodulated and unnodulated plants during vegetative growth. A pattern of progressive decrease in NH4+ absorption was similar in nodulated and unnodulated plants, however. NH4+ absorption was consistently greater in unnodulated plants. Simultaneous measurements of C2H2 reduction from the gas phase of the mist chamber revealed and 41‐day‐old plants, corresponding to late flowering and early pod‐filling.
Reversal of osmotic stress effects by gibberellic acid in Brassica campestris. Recovery of hypocotyl growth, protein and RNA levels in the presence of GA
Authors: Banyal Santosh , Rai Vinay K.
Published: April 2006

Inhibition of hypocotyl growth by water stress and the antagonistic effect of gibberellic acid was studied in Brassica campestris L. cv. Varuna. Water stress alone inhibited increases in length and fresh weight of the hypocotyl. Increasing levels of GA applied simultaneously reversed the effect of water stress. Growth was related directly to water status and inversely to water saturation deficit. However, in severely stressed seedlings GA increased the length of hypocotyls, while fresh weight showed either no change or was even reduced. Thus a distinct ‘uncoupling’ between increases in length and water status was observed. GA appears to act partially by increasing the water status of the seedlings and partially by sustaining protein and RNA levels.
Energy charge and emergence of the coleoptile and radicle at varying oxygen levels in Echinochloa crus‐galli
Authors: Rumpho Mary E. , Pradet Alain , Khalik Abdul , Kennedy Robert A.
Published: April 2006

Energy charge, [(ATP + 1/2 ADP)/(ATP + ADP + AMP)], was measured in Echinochloa crus‐galli (L.) Beauv. var. oryzicola seeds germinated in an aerobic or anaerobic environment. Within 24 h after the seeds were imbibed, total nucleotides increased and energy charge values went from 0.6 to at least 0.8 in both air and N2. Upon transfer from air to N2, the energy charge initially decreased, but subsequently (within 24 h) increased to at least 0.8. Total nucleotides also increased after an initial decline when transferred from air to N2. Emergence of the coleoptile and radicle were also examined at oxygen levels ranging from 21% to less than 0.005%. At all O2 levels, the time for 50% emergence of coleoptiles was less than for radice emergence. This was most evident when the O2 concentration was 1% or less. These data indicate that one of the adaptations that allows E. crus‐galli var. oryzicola to germinate and grow under anaerobic conditions is its ability to maintain a high level of energy. In its natural environment, this would permit coleoptile growth and penetration of the shoot into a more aerobic zone.
The physiological basis of seed dormancy in Avena fatua VI. Respiration and the stimulation of germination by ethanol
Authors: Adkins Stephen W. , Simpson Graham M. , Naylor James M.
Published: April 2006

Ethanol induced germination in several partly after‐ripened dormant lines of Avena fatua L. The dose‐response curves for the stimulation of germination and for oxygen uptake were similar, indicating that ethanol may stimulate germination by promoting oxygen uptake. A time‐sequence study showed that ethanol stimulated oxygen uptake by as much as 70% prior to the first visible signs of germination. A similar methanol treatment failed to induce germination or significantly elevate oxygen uptake, indicating that the promotive effects of ethanol are not common to all alcohols. The stimulation of both germination and oxygen uptake by ethanol was not inhibited significantly by salicylhydroxamic acid, an inhibitor of alternative respiration. Thus, stimulation of germination and oxygen uptake by ethanol does not require the operation of the alternative pathway of respiration. Similarly, the stimulation of germination and oxygen uptake by ethanol were not inhibited by sodium azide, an inhibitor of cytochrome‐mediated respiration. However, both germination and oxygen uptake were prevented when salicylhydroxamic acid and sodium azide were administered together. Thus, stimulation of these events by ethanol requires only the operation of one or other of these pathways of respiration; a specific requirement for the operation of the alternative pathway of respiration does not exist. The function of ethanol as a promoter of respiration is discussed with reference to dormancy and involvement of the Krebs cycle.
K+ and Na+ influxes in Nitella modified by pH and electric current
Authors: Williams E. J. , Dale N. , Trites L. F. , Fensom D. S.
Published: April 2006

K+ and Na+ influxes into Nitella translucens Agardh in buffered artificial pond water have been measured in the pH range 5.7 to 8.1 with and without sub‐threshold electric current. For pH levels below 7 the results confirm previous observations that neither ion is a major carrier of membrance current. At pH levels greater than 7 the effect of applied current is generally to depress cation influx. It is argued that this is evidence in favour of OH− being the principal charge carrier under these conditions. Observations of the effects of OH− gradients on K+ influx tend to support this hypothesis.
Effect of water stress on the lipid and fatty acid composition of cotton (Gossypium hirsutum) chloroplasts
Authors: Ferrari‐Iliou Roselyne , Thi Anh Thu Pham , da Silva Jorge Vieira
Published: April 2006

In order to investigate the effects of water stress on the photosynthetic compartment, analysis of chloroplast polar lipids and their fatty acid composition was made. Cotton (Gossypium hirsutum L. cv. Reba) plants were submitted to water stress by witholding irrigation. Chloroplasts were purified on a Percoll gradient and three fractions were collected: intact, apparently intact and broken chloroplasts. The percentage of broken chloroplasts increased with a decrease in leaf water potential, indicating a greater weakness of the membrane. Galactolipid content (expressed as mg lipid per mg chlorophyll), particularly digalactosyldiglyceride, decreased with decreasing water potential. Phospholipid content decreased in the broken chloroplast fraction. The fatty acid composition of chloroplasts was also affected. The perecentage of linolenic acid (18:3), the major fatty acid of thylakoids, decreased, whereas that of linoleic acid(18:2) and oliec acid (18:1) increased. An accumulation of fatty acids having less than 16 carbon atoms was also observed. These changes in the lipid and fatty acid composition of cotton chloroplasts under water stress might affect the properties of the thylakoid membrane and thereby the photosynthetic activity and the compartmentation of the leaf cells.
The role of proteolytic enzymes in protein degradation during senescence of rice leaves
Authors: Cheng Shu Hua , Kao Ching Huei
Published: April 2006

The role of proteolytic enzymes in protein degradation of detached and intact leaves of rice seedling (Oryza sativa L. cv. Taiching Native 1) during senescence and of mature leaves during reproductive development was investigated. The amount of soluble protein decreased by about 50% in 2, 4, and 15 days for detached, intact and mature leaves, respectively. Three proteolytic enzyme activities were monitored with pH optima of 4.5 for hemoglobin‐digesting proteinase, 5.5 for carboxypeptidase and 8.0 for aminopeptidase. No azocoll‐digesting proteinase activity could be detected in rice leaves. Dialysis did not alter the activities of any of the three proteolytic enzymes. Acid proteinase activity and aminopeptidase activity were highly unstable during storage of the enzyme extracts at 4°C. Proteolysis was stimulated by inclusion of meroaptoethanal either in the extraction medium or the assay medium.

Acid proteinase, carboxypeptidase and aminopeptidase were all present in detached, intact and mature leaves throughout senescence. There seems to be a direct correlation between protein degradation and increases of acid proteinase and carboxypeptidase activity in seedling leaves (detached and intact) during senescence. In senescing (detached and intact) leaves of seedlings the acid proteinase activity developed first, while that of carboxypeptidase developed later. Acid proteinase and carboxypeptidase may play major roles in protein degradation of leaves from seedlings during senscence. During reproductive development, protein degradation was associated with decreases in the activities of acid proteinase, carboxypeptidase and aminopeptidase in mature leaves suggesting that the enzymes were less important for protein degradation in this system. Hence, the role of protelytic enzymes in protein degradation during senescence of rice leaves appears to depend largely on the leaf system used.
Slow reversible bleaching and fluorescence quenching caused by carotenoid absorption in chromatophores and cells of Chromatium vinosum
Authors: Goedheer J. C.
Published: April 2006

Light absorbed by carotenoids in Chromatium can result in photobleaching of bacteriocholorophyll and quenching of B 890 fluorescence, whereas light of the same intensity absorbed by bacteriochlorophyll has no such effect. Photobleching and fluorescence quenching are partly and slowly reversible in the dark. They are prevented by removal of oxygen or by addition of various reductants and decreased by addition of NaN3− histidine or tryptophane. This suggests the participants of singlet excited oxygen in the measured phenomena. As change in temperature between 30° and –30°C and addition of gramicidin S, which changes the permeability of the membranes, does not affect photobleaching or fluorescence quenching markedly, enzymatic or structural properties do not seem to be involved. The results suggest that light absorbed by carotenoids is partly transferred to bacteriochlorophyll and partly used to excite carotenoids to triplet states. The latter process will counteract the function that carotenoids have in protecting chromatophore components against photobleaching.
Dormancy breaking and frost resistance induction in apple embryos as related to changes in reserve and polar lipids
Authors: Nguyen X. V. , Côme D. , Lewak St. , Mazliak P.
Published: April 2006

Apples (Pyrus malus L. cv. Golden Delicious) were kept at 0°C (temperature favourable for removal of embryo dormancy), and at 12 or 35°C (conditions inducing freezing resistance). At different intervals seeds were sampled, and germinability and survival to rapid freezing (‐7°C for 30 min) in embryos were determined. Lipids from embryos of the same samples were extracted and separated into triacylglycerol, diacylglycerol and polar lipid fractions. Certain fatty acids were then quantified in all fractions. Low temperature (0°C) of fruit storage promoted temporary accumulation of only tri‐ and diacylglycerols, whereas 12 and 35°C treatments resulted in an increase solely of polar lipid content. These relations were confirmed in experiments with transfer of fruits from one temperature of storage to another. Changes in the levels of certain fatty acids followed the pattern of total lipids of the three main classes. Together with earlier data, the results suggest that the changes in reserve lipids are related to the dormancy status of the embryo, whereas the changes in polar lipids reflect the resistance to rapid freezing.
Effect of benzyladenine on development of derooted watermelon seedlings
Authors: Longo Giovanna P. , Fantelli Raffaella , Longo Claudio P. , Rossi Gianfranca , Azzolini Irma , Pirovano Gilberto
Published: April 2006

We have examined the effects of benzyladenine (BA) on derooted watermelon (Citrullus vulgaris Schrad., cv. Fairfax) seedlings with special attention to the cotyledons. The growth regulator was supplied either as a droplet of solution between the cotyledons (application from above) or through the hypocotyl stump (application from below). Application of BA from above stimulates several developmental parameters of cotyledons [growth, lipid breakdown, chlorophyll and carotenoid accumulation, hydroxypyruvate reductase (EC 1.1.1.81.) activity]. The stimulation is much smaller with application from below. Also the distribution of labelled BA changes according to the method of application. The bulk of the label remains in the cotyledons when BA is supplied from above and in the hypocotyl when it is supplied from below. The absolute amount of radioactivity found in the cotyledons after 24 h of treatment is approximately the same in both cases. This seems to indicate that the different effects of the two treatments depend on concentration ratios of BA (or metabolic derivates) between hypocotyl and cotyledons rather than on absolute growth regulator levels.
Effects of carbon dioxide in anther cultures
Authors: Johansson Lars , Eriksson Tage
Published: April 2006

In anther cultures of Anemone canadensis L., Anemone dichotoma L., Anemone hupehensis Lemoine, Clematis viticella L. and Papaver setigerum DC. a positive relationship between incubation in 2% CO2 and the production of microspore‐derived embryos was observed. In anther cultures of Nicotiana tabacum L., Anemone hupehensis and Clematis viticella a combination of cold treatment (7°C) and incubation in 2% CO2 increased embryo production. In Anemone canadensis cold treatment increased the number of proembryos, whereas incubation in 2% CO2 had no effect. In Anemone hupehensis 5% CO2 increased embryo production by more than 2%. In Anemone dichotoma and Papaver setigerum 2% CO2 was the more efficient level. CO2 had no significant effect on pH in the culture medium in anther cultures of Anemone canadensis.
CO2enrichment of soybeans. Effects of leaf/pod ratio
Authors: Peet Mary M.
Published: April 2006

The effect of varying leaf number on response of soybean (Glycine max(L.) Merr. cv. Fiskeby V) to CO2enrichment was studied. Plants were trimmed at pod set to 15 pods and 1 or 3 leaves (15:1 and 5:1 pod/leaf ratio) and placed in 350 or 1000 μl/l CO2growth chambers. Photosynthetic rates and dry weights were measured 6 times in all plants at each CO2concentration over a period of 39 days. Measured at treatment CO2concentration, photosynthetic rates deelined rapidly in enriched plants, but remained higher than those of non‐enriched plants. When all plants were measured at the same CO2concentration, for most sampling dates, neither growth, CO2concentration or pod/leaf ratio significantly affected rates of photosynthesis per unit area of comparable leaves. CO2enrichment significantly increased total weights and pod weights in 15:1 but not 5:1 pod/leaf ratio plants. Plants with a 5:1 pod/leaf ratio had significantly higher total and pod weights than 15:1 ratio plants. Both the photosynthesis and dry weight data suggest that plants in the 5:1 ratio enriched treatment were sink‐limited, but plants in all other treatments were source limited.
Effects of temperature and gibberellin on the activity of endogenous cytokinin‐like substances in leaves of Begonia x cheimantha
Authors: Zieslin Naftaly , Kopperud Cor. , Heide Ola M. , Moe Roar
Published: April 2006

Changes in activity of endogenous cytokinin‐like substances were examined in intact plants and excised leaves of Begonia x chemantha Everett cv. Prinsesse Astrid (Christimas Begonia) by means of the tobacco callus bioassay. Cytokinin activity in the leaves of intact plants was higher in plants grown at 18°C than in those grown at 21° or 24°C. In excised leaves, an increase in cytokinin activity was observed during the first 4 days following leaf detachment. However, after the seventh day cylokinin activity decreased again. This decrease was more profound in leaves exposed to 24°C than in those exposed to 18°C.

Treatment of detached leaves with gibberellic acid (2.8 mM) caused an increase in measurable cytokinin activity. This increase was more profound in the zones of activity which correspond with zeatin glucosides on paper and Sephadex LH‐20 chromatography. Additional zones of activity appeared after Sephadex chromatography. These were of a more slow moving nature with elution volumes corresponding to Nb‐(Δ2‐isopentenyl)adenine and its derivaties. Water‐treated control leaves had higher activity in the regions corresponding to zeatin and zeatin riboside.
Physiological responses of Opuntia ficus‐indica to growth temperature
Authors: Nobel Park S. , Hartsock Terry L.
Published: April 2006

The influences of various day/night air temperatures on net CO2 uptake and nocturnal acid accumulation were determined for Opuntia ficus‐indica, complementing previous studies on the water relations and responses to photosynthetically active radiation (PAR) for this widely cultivated cactus. As for other Crassulacean acid metabolism (CAM) plants, net nocturnal CO2 uptake had a relatively low optimal temperature, ranging from 11°C for plants grown at day/night air temperatures of 10°C/0°C to 23°C at 45°C/35°C. Stomatal opening, which occurred essentially only at night and was measured by changes in water vapor conductance, progressively decreased as the measurement temperature was raised. The CO2 residual conductance, which describes chlorenchyma properties, had a temperature optimum a few degrees higher than the optimum for net CO2 uptake at all growth temperatures. Nocturnal CO2 uptake and acid accumulation summed over the whole night were maximal for growth temperatures near 25°C/15°C, CO2 uptake decreasing more rapidly than acid accumulation as the growth temperature was raised. At day/night air temperatures that led to substantial nocturnal acid accumulation (25°C/15°C.). 90% saturation of acid accumulation required a higher total daily PAR than at non‐optimal growth temperatures (10°C/0°C and 35°C/25°C). Also, the optimal temperature of net CO2 uptake shifted downward when the plants were under drought conditions at all three growth temperatures tested, possibly reflecting an increased fractional importance of respiration at the higher temperatures during drought. Thus, water status, ambient PAR, and growth temperatures must all be considered when predicting the temperature response of gas exchange for O. ficus‐indica and presumably for other CAM plants.
The effects of podolactone‐type inhibitors on fusicoccin‐induced growth and proton efflux
Authors: Sasse Jenneth M. , Cerana Raffaella , Colombo Roberta
Published: April 2006

Podolactones A and E and lycoritidinol inhibit growth induced by fusicoccin in dwarf pea (Pisum sativum L.) hooks and tips; however the inhibition is reduced at the highest fusicoccin concentrations. In short term experiments (3 h) on pea stem tissues, growth and proton efflux induced by fusicoccin are only partially inhibited by podolactone A and lycoricidinol. Auxin‐induced growth and proton efflux are completely suppressed by 10 μM lycoricidinol. The inhibitors do not affect ATP levels.
Lipid peroxidation in and photo‐damage to a light‐sensitive chlorescence pea mutant
Authors: Merzlyak Mark N. , Plakunova Ol'ga V. , Gostimsky Sergei A. , Rumyantseva Vera B. , Novak Karel
Published: April 2006

Leaves of 10‐ to 12‐day‐old chlorescence lethal Pisum sativum L. mutant are similar to control plants with respect to the content of chlorophylls, carotenoids, fatty acids and α‐tocopherol. Subsequent development of the mutant under high irradiation resulted in th destruction of the photosynthetic pigments, polyunsaturated fatty acids, α‐tocopherol, and also in the accumulation of liposoluble fluorescent products. No increase in the level of malondialdehyde was observed. In chloroplasts isolated from mutant plants the contents of chlorophyll a and β‐carotene were decreased to a greater extent than the more oxidized pigments (xanthophylls and chlorophyll b). The data obtained are discussed with special reference to the role of lipid peroxidation in the injury of plant cells under the action of visible light and to the antioxidative mechanisms stabilizing photosynthetic membranes.
Photosynthesis and nitrogen utilization in exponentially growing nitrogen‐limited cultures ofLemna gibba
Authors: Ingemarsson Björn , Johansson Lena , Larsson Carl‐Magnus
Published: April 2006

The photosynthetic performance and nitrogen utilization ofLemna gibbaL. G3 adapted to limited nitrogen supply was studied. The plants were adapted to two levels of nitrogen limitation where the nitrogen addition rates were calculated to sustain relative growth rates (RGR) of 0.15 day−1and 0.25 day−1, respectively. The photosynthetic performance of these cultures was compared to nitrogen‐sufficient cultures with an average RGR of 0.32 day−1. Plants transferred from nitrogen‐sufficient conditions attained RGR values corresponding to the nitrogen addition rates after 6 to 10 days. Light‐saturated net photosynthesis declined during adaptation according to the drop in growth rate, and a concomitant decrease in the respiration rate was recorded. The efficiency of net photosynthesis on a dry weight basis increased with increased nitrogen supply, whereas it was the same in all cultures when expressed on a chlorophyll basis. The light compensation point was unaffected by the nitrogen regime. Limited nitrogen supply resulted in an increased proportion of dry matter in the roots, which led to decreased leaf area ratios. The net assimilation rates also decreased, but not to the same extent as the leaf area ratios. Growth‐limiting amounts of nitrogen were added to the cultures once daily, and the net influx of N was higher than the requirement for N, also in adapted cultures with a steady growth rate. This resulted in transient, periodic fluctuations in the NO3−, NH4+and amino acid pools. Also the rates of NO3−reduction and NH4+assimilation fluctuated as did the amino acid assimilation which paralleled NH4+assimilation. The role of flux rates over the plasmalemma and tonoplast for control of nitrogen assimilation rates are discussed.
Adventitious shoot formation in cultures of immature female strobili of Larix decidua
Authors: Bonga J. M.
Published: April 2006

Discs taken from female strobili of 25‐year‐old Larix decidua Mill, trees produced adventitious shoots in vitro if strobili collected between about one week before and about one week after meiosis were used. Adventitious shoots arose mainly from the cut and abaxial surfaces of the bracts. Some arose from the cut surface of the ovuliferous scales. After separation and subculture of the shoots, more shoots were formed, mostly from callus. The shoots often had a clearly defined apical bud. Their needles elongated, but their stems generally failed to do so. Roots were not formed.
Light control of extractable nitrate reductase activity in higher plants
Authors: Duke Stanley H. , Duke Stephen O.
Published: April 2006

Light regulation of extractable nitrate reductase (NR) activity of higher plants is complicated by: 1) involvement of several photoreceptors, 2) differences in the relative importance of the several photoreceptors among species and among developmental stages of the same species, 3) two types of effects – alteration of activity of existing NR and influences on de novo synthesis of NR, and 4) differing forms of NR within the same species. The interrelationships of all of these factors are not clear. It may be that each system will have to be understood separately before a general model can be developed. Immunochemical quantification of NR from systems exposed to varied light regimes may enhance our understanding of this area. Currently few general conclusions can be made; however, we think that the following statements are true or are usually true: (1) Phytochrome influences extractable NR activity by the low irradiance response and high irradiance response in etiolated tissues. (2) In de‐etiolated tissues phytochrome can influence NR activity decay at the end of a light period by the low irradiance response. (3) The phytochrome equilibrium or the absolute level of Pfr influences extractable NR activity in green tissues under white light. (4) Blue light influences extractable NR activity through phytochrome and another, unknown, blue light‐absorbing pigment. Flavins may be involved in vitro in reactivation of inactivated NR. (5) Photosynthesis does not directly influence the induction of the forms of NR that require substrate and light for induction. (6) In some tissues there appears to be a close link between nitrite‐reducing and nitrate‐reducing capabilities. (7) Much circumstantial evidence from kinetic and protein‐synthesis‐inhibitor studies and the only available immunochemical data indicate that light induces de novo synthesis of NR, resulting in increased extractable activity.
Light‐induced linear dichroism in photoreversibly photochromic sensor pigments. – VI. Relation between the two pigments of the mycochrome system in Alternaria cichorii
Authors: Kumagai Tadashi , Björn Lars Olof
Published: April 2006

Conidiation in Alternaria cichorii Nattras is reversibly stimulated by near ultraviolet radiation (NUV, ca 313 nm) and inhibited by blue light (ca 450 nm) and seems to be a mycochrome‐mediated process. After induction with plane‐polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. From this the conclusions are drawn that (a) both the blue‐absorbing component (presumably a flavo‐protein) and the PNUV of the mycochrome system are membrane‐bound and that (b) the transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53° with the transition moment associated with NUV absorption in PNUV.
Total nitrogen and free amino acids in Morus alba stems from autumn through spring
Authors: Suzuki Takeo
Published: April 2006

During leaf senescence and abscission, total nitrogen in leaves of mulberry (Morus alba L. ev. Shin‐ichinose) declined substantially whereas total nitrogen in buds, bark and stem wood increased markedly, suggesting translocation of nitrogen from senescent leaves in the autumn. After leaf abscission the winter buds and stems remained almost unchanged with respect to fresh and dry weight and total nitrogen until bud break in spring. In burst buds these parameters then increased drastically during the new growth while they decreased markedly in stems. Free arginine in the stem bark accumulated in parallel with the accumulation of total nitrogen in buds and stems in the autumn. Accumulation of proline in the wood, bark and buds also started in October but continued even after leaf‐fall, increasing until mid‐January (wood), mid‐February (bark) and the new growth (buds). Prior to and in the early stage of bud break, proline in bark and wood decreased significantly and arginine in stem bark decreased slightly. Simultaneously, proline and arginine in the dormancy‐releasing buds and asparagine, aspartic acid and glutamic acid in the buds and stems increased appreciably, suggesting that this increase in free amino acids was mainly derived from free amino acids (proline and arginine) stored in stems. The resulting marked decrease in total nitrogen and the drastic increase in asparagine in the stems and sprouting buds/new shoots were primarily due to a breakdown of protein stored in stems.
Morphometric study of Lemna gibba in relation to the use of compartmental analysis and the flux‐ratio equation in higher plant cells
Authors: Gaudinet A. , Ripoll C. , Thellier M. , Kramer D.
Published: April 2006

Morphometric characteristics of Lemna gibba L. cells have been estimated. The mean relative volumes of the wall, of the cytoplasm and of the vacuoles were 0.03, 0.32 and 0.65, respectively. The distribution of the individual values has been studied: for instance 29% of the cells had a mean relative volume of the vacuoles close to 0.73, 39% to 0.68, 19% to 0.61 and 13% to 0.51. The mean value and distribution of the surface areas of the tonoplast and plasmalemma were also determined. This allows us to discuss the active or passive character of the transport of various substances at the plasmalemma and at the tonoplast, according to the usual flux‐ratio approach. The feasibility of such an approach in ordinary (non‐giant) living cells is discussed with regard to the degree of reliability of the measurements which can be performed with such cells.
Effects of auxin on wall polysaccharide composition and enzyme activity during extension‐growth of Pellia (Bryophyta)
Authors: Thomas Robert J. , Behringer Fredrich J. , Lombard Craig S. , Sparkowski Jason J.
Published: April 2006

Auxin‐induced changes in cell wall polysaccharide composition and enzyme activity of seta segments from the liverwort Pellia epiphylla (L.) Corda were studied using colorimetric, gas chromatographic, radioactive tracer, and viscometric techniques. Extension‐growth of segments doubled in the presence of aqueous 10 μM indole‐3‐acctic acid (IAA) ± 50 mM glucose. IAA‐enhanced growth was accompanied by (1) enhanced synthesis of all wall polysaccharides but cellulose, (2) increase in the relative glucose content of neutral wall sugars, and (3) change in the activity of wall‐bound glycosidase relative to controls, but no change in the activity of cellulase. Galactose and mannose (50 mM) suppressed auxin enhancement of both growth and wall synthesis. These findings suggest that auxin‐mediated extension‐growth of Pellia setae is dependent upon the maintenance of non‐cellulosic cell‐wall synthesis.
Changes in the activity of enzymes involved in purine “salvage” and nucleic acid degradation during the growth of Catharanthus roseus cells in suspension culture
Authors: Hirose Fumiko , Ashihara Hiroshi
Published: April 2006

Changes during growth in the activity of several enzymes involved in purine “salvage”, adenine phosphoribosyltransferase (EC 2.4.2.7), guanine phosphoribosyl‐transferase (EC 2.4.2.8), hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) and adenosine kinase (EC 2.7.1.20), the enzymes which catalyze the conversion of nucleoside monophosphate to triphosphate, nucleoside monophosphate kinase (EC 2.7.4.4) and nucleoside diphosphate kinase (EC 2.7.4.6), and several degradation enzymes, deoxyribonucleae(s), ribonuclease(s). phosphatase(s), nucleosidase (EC 3.2.2.1), 3′‐nucleotidase (EC 3.1.3.6) and 5′‐nucleotidase (EC 3.1.3.5) were examined in cells of Catharanthus roseus (L.) G. Don cultured in suspension. In addition, the incorporation of [8‐14C] adenine, [8‐14C] adenine, [8‐14C]hypoxanthine. [8‐14C] adenosine and [8‐14C]inosine into nucleotides and nucleic acids was also determined using intact cells.

The activities of all purine “salvage” enzymes examined and those of nucleoside monophosphate and diphosphate kinases increased rapidly during the lag phase and decreased during the following cell division and cell expansion phases. The rate of incorporation of adenine, guanine, hypoxanthine, and adenosine into nucleotides and nucleic acids was higher in the lag phase cells than during the following three phases. The highest rate of [8‐14C]inosine incorporation was observed in the stationary phase cells. The activity of all degradation enzymes examined decreased when the stationary phase cells were transferred to a new medium.

These results indicated that the increased activity of purine “salvage” enzymes observed in the lag phase cells may contribute to an active purine “salvage” which is required to initiate a subsequent cell division.
Abscisic acid induced decay of strawberry transpiration
Authors: Kubik M. , Plonka A.
Published: April 2006

The effect of 0–7.5 × 10−3μmol abscisic acid (ABA) on the transpiration of strawberry (Fragaria grandiflora Duch. ev. Red gauntlet), both under illumination and in darkness, was investigated with the use of an infrared gas analyser. Mathematical analysis of the results suggests that the decrease in transpiration after darkening can be described by a series of first‐order processes with continuous distribution of rate constants k. Application of ABA makes the rate constant distribution narrower, so that one single rate constant occurs at the highest doses. ABA accelerates the decrease of transpiration more in darkness than under illumination. This suggests that the process of efflux of osmotically active particles from guard cells is influenced more than influx. For ABA doses greater than 7.5 × 104μmol, the transpiration decreases in two stages, of which only the first one seems to be affected by ABA: but above this dose further acceleration of decay of transpiration after darkening is not observed. The observations may indicate that above this critical dose of ABA the rate determining step consists in guard cell wall relaxation rather than in efflux of osmotica.
Dormancy in red rice. IV. Response of unimbibed and imbibing seeds to nitrogen dioxide
Authors: Cohn Marc Alan , Castle Laurence
Published: April 2006

Nitrogen dioxide at 4 to 8 ml 1−1 breaks dormancy of dehulled, unimbibed seeds of red rice (Oryza sativa L.) with minimum exposure times to the gas of 20 min or less. The response is independent of incubation medium pH following treatment. Germination is complete within 2 days but proceeds 4 to 6 h more slowly than non‐dormant controls. The magnitude of response at a constant NO2 dose is dependent upon initial seed moisture. There was less than 40% germination at 9.6% initial moisture while germination was 95% at 12% initial moisture. NO2 treatment also breaks dormancy of imbibing, dehulled seeds, but the response is dependent upon the pH of the medium. Dormancy is broken at pHs close to the pKa of nitrous acid. Intact, unimbibed or imbibing seeds respond to NO2 treatment only if partially dry‐afterripened prior to exposure.
Stem hypoxia and root respiration of flooded maple and birch seedlings
Authors: Tripepi R. R. , Mitchell C. A.
Published: April 2006

Some researchers have attributed flood tolerance of woody plants to air entering the shoot through stems, leaves, or lenticels and diffusing to the roots to sustain aerobie respiration. The purpose of this study was to determine if internal aeration of roots by lower stems, changes in gross morphology of lower stems, or both, contribute to flood tolerance of certain tree species. Greenhouse‐grown seedlings of red maple (Acer rubrum L.) and river birch (Betula nigra L.) tolerated at least 30 days of flooding, where as sugar maple (Acer saccharum Marsh) and European white birch (also called silver birch, Betula pendula Roth) were intolerant. Flood treatment induced lentieel intumescences and adventitious root formation on red maple stems, but only adventitious roots formed on river birch stems. Stem morphology of sugar maple and European birch was unchanged by flooding. Flood stress decreased oxygen consumption capacity of excised roots from both tolerant and intolerant species. Exclusion of oxygen from the lower stems of flooded red maple and river birch prevented lenticel intumescence and adventitious root formation, but flood tolerance and root respiration capacity were unchanged. Neither internal aeration nor changes in stem morphology appear to account for flood tolerance of red maple and river birch.