bluuebunny/crossref_metadata_2025 huggingface dataset:
Requirement for the action of endogenous ethylene during germination of non‐dormant seeds of Amaranthus caudatus
Authors: Kepczynski Jan , Karssen Cees M.
Published: April 2006

The role of endogenous ethylene during germination of non‐dormant seeds of Amaranthus caudatus L. was investigated. The seeds readily germinated in water and darkness at 24°C. Application of ethylene or of its precursor I‐aminocyclopropane‐I‐carboxylic acid (ACC) slightly increased the rate of germination. Both compounds effectively antagonized osmotic inhibition by polyethyleneglycol. Application of aminoethoxyvinylglycine (AVG) reduced ethylene production by 90% but did not inhibit germination. However, germination was inhibited by 2,5‐norbornadiene, a competitive inhibitor of ethylene action. This inhibition was counteracted by ethylene, ethephon or ACC and enforced by AVG. It is concluded that the action of endogenous ethylene is an indispensable factor during germination of non‐dormant seeds of A. caudatus. Ethylene action is required from the start of imbibition on. In water, low levels of endogenous ethylene are sufficient for this action. PEG increased the ethylene requirement considerably.
Changes in cytokinins during initiation and development of potato tubers
Authors: Jameson Paula E. , McWha James A. , Haslemore Roger M.
Published: April 2006

Cytokinin‐like activity was assayed in stolons and tubers of Solanum tuberosum L. ssp. andigena (Juz. et Buk.) Hawkes cv. 165 grown in pots under controlled environment conditions. The plants were allowed to tuberise without the application of environmental or other external stimuli. The soluble sugar and starch contents of stolon tips and tubers were measured. Starch accumulation was a precise indicator of tuber initiation. Cytokinin‐like activity began to increase in tubers with a diameter greater than 7.5 mm and, as assessed on a per tuber basis, was greatest in the largest size‐category analysed. However, expressed as a function of fresh and dry weight, activity was greatest in tubers of 15–20 mm in diameter. Increases in cytokinin‐like activity occurred subsequent to tuber formation, indicating that the tuberisation stimulus is unlikely to be cytokinin‐like in nature.
Effects of low concentrations of O3, leaf age and water stress on leaf diffusive conductance and water use efficiency in soybean
Authors: Reich Peter B. , Schoettle Anna W. , Amundson Robert G.
Published: April 2006

Ozone, leaf age and water stress each affected leaf conductance in soybean [Glycine max (L.) Merr. Hodgson], but there were no interactions among these factors. Exposure to increased concentrations of O3 (0.01, 0.05, 0.09. and 0.13 μl l−1) resulted in linear declines in abaxial and adaxial conductances in leaves of all ages. There were no differences in relative response to O3 between the two leaf surfaces. For well‐watered plants, water use efficiency also decreased with exposure to increased O3 concentrations (water‐stressed plants were not tested). Abaxial conductance increased as leaves aged from 4 to 10 days and then declined with further aging. Adaxial conductance decreased with all increases in leaf age beyond 4 days, and the ratio of abaxial/adaxial conductance increased continuously throughout the leaf lifespan. During water‐stress cycles (water withheld for 2–3 days) leaves of water‐stressed plants had lower conductances than those from well‐watered plants, and there was no difference in relative response between abaxial and adaxial stomata.
Influence of light intensity during growth on photosynthesis and activity of several key photosynthetic enzymes in a C4 plant (Zea mays)
Authors: Usuda Hideaki , Ku Maurice S. B. , Edwards Gerald E.
Published: April 2006

Maize (Zea mays L. Hybrid Sweet Corn, Royal Crest), a C4 plant, was grown under different light regimes, after which the rate of photosynthesis and activities of several photosynthetic enzymes (per unit leaf chlorophyll) were measured at different light intensities. Plants were grown outdoors under direct sunlight or 23% of direct sunlight, and in growth chambers at photosynthetic photon flux densities of about 20% and 8% of direct sunlight. The plants grown under direct sunlight had a higher light compensation point than plants grown under lower light. At a light intensity about 25% of direct sunlight, plants from all growth regimes had a similar rate of photosynthesis. Under saturating levels of light the plants grown under direct sunlight had a substantially higher rate of photosynthesis than plants grown under the lower light regimes. The higher photosynthetic capacity in the plants grown under direct sunlight was accompanied by an increased activity of several photosynthetic enzymes and in the amount of the soluble protein in the leaf. Among five photosynthetic enzymes examined, RuBP carboxylase (EC 4.1.1.39) and pyruvate, Pi dikinase (EC 2.7.9.1) were generally just sufficient to account for rates of photosynthesis under saturating light; thus, these may be rate limiting enzymes in C4 photosynthesis. Pyruvate, Pi dikinase and NADP‐malate dehydrogenase (EC 1.1.1.82) were the only enzymes examined which were light activated and increased in activity with increasing light intensity. In the low light grown plants the activity of pyruvate, Pi dikinase closely paralleled the photosynthetic rate measured under different light levels. With the plants grown under direct sunlight, as light intensity was increased the activation of pyruvate, Pi dikinase and NADP+‐malate dehydrogenase proceeded more rapidly than photosynthesis.
Chloroplasts in the epidermis of Sarracenia (the American pitcher plant) and their possible role in carnivory ‐ An immunocytochemical approach
Authors: Joel Daniel M. , Gepstein Shimon
Published: April 2006

A photosynthetic apparatus is present in the epidermis of the bottom zone of the pitcher of Sarracenia purpurea L. ssp. purpurea. This has been demonstrated using conventional light and electron microscopy, as well as fluorescent and immunohistochemical techniques. Red intrinsic fluorescence by these chloroplasts indicates photochemical activity. Antibodies against the coupling factor of chloroplast ATPase and against the subunits of ribulose‐bis‐phosphate‐carboxylase were bound to the epidermal chloroplasts. This has been visualized using a ferritin‐isothiocyanate labeled second antibody. These results unequivocally prove the existence of the two main proteins which are associated with the photophosphorylation (membrane protein) and carbon dioxide fixation (stromal protein). The possible implication of this system to interrelationships between the carnivorous plant and aquatic insects inhabiting its leaves is discussed.
Senescence of attached leaves: Regulation by developing pods
Authors: Grover Anil , Koundal K. R. , Sinha S. K.
Published: April 2006

Analysis of total nitrogen, chlorophyll content, ribulose‐1,5‐bisphosphate carboxylase/oxygenase activity and net photosynthesis rate was carried out on the leaves that support the developing pods in pigeon pea [Cajanus cajan (L.) Millsp. cv. Prabhat] at several stages during pod filling. A continuous loss in all the above‐mentioned parameters was observed during the course of pod development. When no pods were allowed to develop by continuous flower removal treatment, there was a considerable delay in loss of all these metabolic parameters. Excision of pods after their mid‐development resulted not only in no further loss, but also in a significant recovery both of total nitrogen and of other investigated characteristics.
Intracellular adenylate pools and protein degradation during zoosporangial differentiation in Allomyces arbuscula
Authors: Ojha Mukti , Turian Gilbert
Published: April 2006

In Allomyces arbuscula Butl., strain Bali, the ratio of protein to dry weight remained constant in exponentially growing but decreased in differentiating cultures. The adenylate pools (ATP, ADP, AMP) and energy charge which integrates them, increased during zoospore germination and stabilized around 0.9 during differentiation. The level of ATP increased early during the induction of zoosporangia for up to 1 h and then declined. The ADP and AMP remained low for most of the time except for a transient increase in ADP (first 30 min induction). The energy charge was low in spores. The rate of turnover of proteins during growth and differentiation was more or less similar for up to 1.5 h after transfer. Subsequently very little turnover of proteins occurred in the growing plants. In differentiating plants, the rate of degradation was maintained and by the end of the 4 h experimental period 30% of the vegetative proteins were degraded. The intracellular ammonium showed a peak between 30 to 60 min of induction and was higher in the differentiating mycelia than in actively growing plants, while the glutamate pool remained around 1 μmol (mg protein)−1 in both types of plants. The physiological role of these protein degradation products is discussed.
The role of hormones in regulating the germination of polymorphic seeds and early seedling growth of Atriplex triangularis under saline conditions
Authors: Khan M. Ajmal , Ungar Irwin A.
Published: April 2006

Germination of the polymorphic seeds and seedling growth of Atriplex triangularis under various salinity, gibberellic acid and kinetin treatments were determined. Gibberellic acid (GA3; 2.9 mM) promoted germination and growth at high NaCl concentrations (345 mM). Kinetin (4.7 μM) stimulated germination at all salinities and seed sizes tested. GA3 and kinetin generally increased seedling growth at all concentrations of salinity studied. Higher concentrations of kinetin were found to be inhibitory.
IAA level and dry matter accumulation at different positions within a wheat ear
Authors: Bangerth Fritz , Aufhammer Walter , Baum Ottheinrich
Published: April 2006

Dry matter accumulation and IAA level of grains in various positions within the wheat (Triticum aestivum L. cvs Solo and Kolibri) ear were investigated during the grain filling period. Main shoot ears were partitioned into basal, central and apical regions and further into proximal and distal grains. Results from a two‐year experiment with two wheat cultivars of different grain size are presented. The IAA level increased rapidly from about 8 until 20 to 30 days after anthesis, and then decreased dependent upon year and cultivar. The differences in IAA levels, both among spikelets in different regions of the ear (i.e. basal, central and apical) and also among florets within a spikelet (i.e. proximal and distal), were positively correlated with the differences in dry matter accumulation. Although the correlations held true within cultivars in a particular year, differences in dry matter between cvs Solo and Kolibri or differences from year to year were not well correlated with the corresponding changes in IAA levels. Possible interactions between dry matter accumulation and IAA levels are briefly discussed.
A relationship between carbon dioxide, photosynthetic efficiency and shade tolerance
Authors: Teskey Robert O. , Shrestha Rajesh B.
Published: April 2006

Net photosynthesis and transpiration of seedlings from shade tolerant, moderately tolerant and intolerant tree species were measured in ambient carbon dioxide (CO2) concentrations ranging from 312 to 734 ppm. The species used, Fagus grandifolia Ehrh. (tolerant), Quercus alba L., Q. rubra L., Liriodendron tulipifera L. (moderately tolerant), Liquidambar styraciflua L. and Pinus taeda L. (intolerant), are found co‐occurring in the mixed pine‐hardwood forests of the Piedmont region of the southeastern United States. When seedlings were grown in shaded conditions, photosynthetic CO2 efficiency was significantly different in all species with the highest efficiency in the most shade tolerant species, Fagus grandifolia, and progressively lower efficiencies in moderately tolerant and intolerant species. Photosynthetic CO2 efficiency was defined as the rate of increase in net photosynthesis with increase in ambient CO2 concentration. When plants which had grown in a high light environment were tested, the moderately tolerant and intolerant deciduous species had the highest photosynthetic CO2 efficiencies but this capacity was reduced when these species grew in low light. The lowest CO2 efficiency and apparent quantum yield occurred in Pinus taeda in all cases. Water use efficiency was higher for all species in enriched CO2 environments but transpiration rate and leaf conductance were not affected by CO2 concentration. High photosynthetic CO2 efficiency may be advantageous for maintaining a positive carbon balance in the low light environment under a forest canopy.
Growth responses of Vigna radiata seeds to laser irradiation in the UV‐A region
Authors: Govil Sudha Rani , Agrawal D. C. , Rai K. P. , Thakur S. N.
Published: April 2006

We have investigated the effect of pulsed nitrogen laser radiation (337.1 nm) on morphological characteristics and biochemical contents in seedlings from treated greengram (Vigna radiata L.) seeds, which were germinated and grown in Petri dishes for a week. The shoot and root lengths, and fresh and dry weights of the seedlings were maximum with the 30 min exposure, while protein was maximum with 20 min, RNA and DNA contents with 5 min exposure time. Chlorophyll content was not affected by the irradiation.
Influence of phytohormones and other effectors on proton extrusion by isolated protoplasts from rape leaves
Authors: Schubert S. , Matzke H.
Published: April 2006

The roles of phytohormones and fusicoccin in H+ extrusion by isolated protoplasts from rape leaves (Brassica napus L. cv. Belinda) were investigated and compared to results obtained with leaf segments of the same plants. Net H+ release by protoplasts, which was at least partly due to ATPase activity, was enhanced by 10 μM indole‐3‐acetic acid and reduced by 20 μM abscisic acid, whereas fusicoccin (10 μM), brassinosteroid (3 μM), kinetin (20 μM) and gibberellic acid (10 μM) had no effect. Hormone effects and H+ release were not detectable with leaf segments from the same plants. However, using field‐grown plants, indole‐3‐acetic acid and especially fusicoccin stimulated the acidification of the external medium by leaf segments. Hormonecontrolled H+ release by leaf cells is interpreted as the first step in acid‐triggered and turgor‐regulated cell growth.
Ferredoxin‐sulfite reductase and ferredoxin‐nitrite reductase activities in leaves of Pisum sativum: Changes during ontogeny and in vitro regulation by sulfide
Authors: von Arb Christoph , Brunold Christian
Published: April 2006

Since ferredoxin‐dependent sulfite reductase (EC 1.8.7.1) and nitrite reductase (EC 1.7.7.1) can both catalyze the reduction of SO2‐3 and NO−2, physiological and biochemical evidence is needed for properly classifying the two enzyme activities. They were therefore compared during ontogeny of pea leaves and in the effect of their products, sulfide and ammonium, on their catalytic activity. In the crude extract of the young second leaf of pea plants, Pisum sativum L. cv. Vatters Frühbusch, no ferredoxin‐nitrite reductase activity could be detected, but ferredoxin‐sulfite reductase and ATP‐sulfurylase (EC 2.7.7.4), measured for comparison, were at 24 and 14%, respectively, of their maximal activity per leaf. After 11 and 12 days, respectively, ATP‐sulfurylase and ferredoxin‐sulfite reductase were no longer detectable, whereas ferredoxin‐nitrite reductase was still at more than 30% of its maximal activity per leaf. Ferredoxin‐sulfite reductase was inhibited by 50% with 18 μM and 100% with 30 μM sulfide produced by this enzyme during its assay. Sulfide at 100 μM added to the assay mixture completely inhibited ferredoxin‐sulfite reductase activity in the crude extract, the 30000 g pellet and its supernatant. The same addition reduced ferredoxinnitrite reductase activity by 20% in the crude extract and by 100% in the 30000 g pellet. NH+4 at 100 μM did not affect ferredoxin‐sulfite reductase or ferredoxin‐nitrite reductase activity.

The inhibition by sulfide and the changes in activity during ontogeny similar to ATP‐sulfurylase (which catalyzes the first step of assimilatory sulfate reduction) represent biochemical and physiological evidence for the correct classification of ferredoxin‐sulfite reductase. The complete inhibition of ferredoxin‐nitrite reductase activity in the 30000 g pellet by S2‐ indicates that this activity was due to a ferredoxin‐sulfite reductase.
Ethephon and auxin induce mycorrhiza‐like changes in the morphology of root organ cultures of Mugo pine
Authors: Rupp Larry A. , Mudge Kenneth W.
Published: April 2006

The effects of ethylene and auxin on the morphology and anatomy of root organ cultures of Pinus mugo Turra var. mugo were investigated to test the hypothesis that changes in root morphology associated with formation of ectomycorrhizae may be related to ethylene produced by ectomycorrhizal fungi or by host plant roots in response to fungus‐produced auxin. Morphological changes characteristic of mycorrhizal infection include dichotomous branching of lateral roots, inhibition of root hair formation and enlargement of cortical cells. Lateral roots on non‐mycorrhizal root organ cultures, grown in a defined medium, underwent dichtotomous branching while root hair formation was inhibited in response to the ethylene released by 50 and 100 μM ethephon (2‐chloroethylphosphonic acid), but no effect on cortical cell dimensions was observed. The auxin, naphthaleneacetic acid (1 and 10 μM) also stimulated dichotomous branching and inhibited root hair formation, but to a lesser extent and with a greater lag time than ethephon. Auxin‐stimulated ethylene production by root organ cultures was demonstrated. This appeared to be responsible, at least in part, for the auxin‐induced dichotomous branching since the ethylene action inhibitor, silver thiosulfate (0.1 mM) inhibited the response to auxin by 35%.
Relative effectiveness and interaction of ultraviolet‐B, red and blue light in anthocyanin synthesis of apple fruit
Authors: Arakawa Osamu , Hori Yutaka , Ogata Ryosuke
Published: April 2006

The effect of light on anthocyanin production in apple (Malus pumila Mill. cv. Jonathan) skin disks was investigated, with prolonged irradiation from different light sources. High fluence rates of white light provided from a xenon lamp were unable to produce large amounts of anthocyanin, and anthocyanin production became saturated at about 30 W m−2. When UV‐B light, provided by a fluorescent lamp which had an emission peak at 312 nm, was combined with the white light, anthocyanin production was synergistically stimulated and increased up to the highest fluence rates of white light tested (44 W m−2). This UV‐B light was more effective than red and blue light provided from fluorescent lamps, but anthocyanin production became saturated at about 1.7 W m−2. However, simultaneous irradiation with red and UV‐B light had a synergistic effect. UV‐B light was also effective in increasing anthocyanin production in whole fruit. Therefore this synergism seemed to have an important role in the development of the desirable red skin color under field light conditions. The results of aminoethoxyvinylglycine treatment suggested that ethylene was not involved in the stimulative effect of UV‐B light.
Chlorate‐resistant rose cells: influx, efflux and reduction of [36Cl]‐chlorate
Authors: Murphy Terence M. , Wrona Anne F. , Wycoff Keith
Published: April 2006

Clones of Rosa damascena Mill. cv. Gloire de Guillan, selected for growth in solid medium containing 56 mM NaClO3, were studied to determine the reason for their resistance to this toxic salt. The cells grew on medium containing nitrate as the only nitrogen source, and they synthesized nitrate reductase (EC 1.6.6.2) in the presence of nitrate. The cells were resistant in the presence of nitrate. However, their resistance was greatly increased by the presence of glutamate in the medium. The cells took up [36Cl]‐ClO3‐ and reduced it to ClO2−, but the fraction of ClO3− that they reduced under our experimental conditions was less than that reduced by wild type. The slower production of ClO2− apparently accounted for the resistance of the cells to ClO3−. We suggest several possible reasons for the low rate of reduction of ClO3−.
Effect of different light qualities on the ultrastructure, thylakoid membrane composition and assimilation metabolism of Chlorella fusca
Authors: Wilhelm Christian , Krámer Petra , Wild Aloysius
Published: April 2006

Chlorella fusca (Shihira et Krauss) strain C‐1.1.10 was grown under three different light qualities (red, white or blue light) in homocontinuous cultures. Under electron microscopy, blue light cultures showed enlarged cells, thinner cell walls and lower starch content than red light cells. Under blue light, the degree of stacking of the thylakoid membranes was significantly lower than under white or red light conditions. Changing the light from blue to red the ratio of exposed to appressed membranes was doubled. Compared to red light cells, blue light cells exhibited higher photosynthetic rates per chlorophyll molecule and contained less chlorophyll per dry weight. Blue light stimulated the content of soluble protein as well as that of soluble carbohydrates. The dry weight productivity per unit time was enhanced under blue light conditions. The thylakoid protein complexes which are generally assumed to be localized in the exposed membranes were found in higher concentrations under blue light than under red light. In blue light, both the Photosystem II/Photosystem I ratio and the ratio of light‐harvesting chlorophyll protein to P‐700 chlorophyll a‐protein were lower than in red light. Blue light cells contained twice the concentration of cytochrome f, which correlates well with their higher photosynthetic capacity. When altering the light quality, the degree of change in the reaction center complexes was much lower than expected given the corresponding degree of change in the ratio of exposed to appressed membranes. These results are discussed in light of the question as to whether the variation in the stoichiometry of the laterally distributed complexes can be explained by changes in the degree of stacking alone.
Cytometric aspects of the leaves of the halophyte Suaeda maritima
Authors: Hajibagheri M. A. , Flowers T. J. , Hall J. L.
Published: April 2006

An analysis of the frequency of occurrence of chloroplasts, mitochondria and microbodies in leaf cells of the halophyte Sueda maritima (L.) Dum, showed a remarkable increase (almost a doubling) in the number of mitochondria per cell section when plants were grown in saline (340 mol m−3 NaCl) as opposed to non‐saline conditions. Chloroplast and microbody volume per cell increased under saline conditions, but number per cell was insensitive to salt. Chloroplasts contained a greater number of starch grains in plants grown under saline as compared to non‐saline conditions and, under both conditions, were closely associated with the cell wall adjacent to the intercellular spaces. The implications for growth, photosynthesis and respiration are discussed.
Interaction of light quality and benzimidazole on pigment contents and on photochemical activity of chloroplasts isolated from detached senescing wheat (Triticum aestivum) leaves
Authors: Sayeed Shabbir A. , Behera B. K. , Mohanty Prasanna
Published: April 2006

The possibilities of an interaction between light and the growth regulator benzimidazole in retarding senescence‐induced changes in activity of chloroplasts isolated from detached wheat (Triticum aestivum L. cv. Kalyansona) leaves have been investigated. The effect of benzimidazole on the rate of degradation of chlorophylls in light depended on the quality of light used. Far‐red irradiation given to detached leaves in the presence of benzimidazole retarded the pigment loss more significantly than did white or red light of similar intensity. Senescence‐induced loss in chloroplast photochemical activity was higher than the loss of chlorophylls. Loss of photosystem I activity was greater than photosystem II activity. Benzimidazole maintained the gramicidin‐mediated enhancement in whole chain electron transport uniformly throughout the incubation period irrespective of the light quality. There was no effect of light and benzimidazole in retarding the loss in photochemical activity, although the same preserved the chlorophyll contents as well as characteristics of the chloroplast absorption spectrum.
DNA changes involving repeated sequences in senescing soybean (Glycine max) cotyledon nuclei
Authors: Chang Dau‐Yin , Miksche Jerome P. , Dhillon Sukhraj S.
Published: April 2006

Age‐related DNA changes in soybean (Glycine max L. cv. Ransom) cotyledon nuclei were investigated by Feulgen cytophotometry and cloned DNA probes. The amount of nuclear DNA in 17‐day‐old senescing cotyledons was 23% lower than that of 5‐day‐old young cotyledons. In order to understand the nature of senescence‐related DNA loss, fragments of repetitive DNA from young cotyledons were cloned into Escherichia coli HB101 cells by DNA recombination. The cloned DNA probed changes in specific repeated nucleotide sequences in senescing cotyledons. The colony hybridization between cloned DNA and [32P]‐labeled total DNA from 5‐ and 17‐day cotyledons indicated loss of specific repeated sequences. The selected sequences of repeated DNA further showed a loss in their copy numbers. The study suggested that some repetitive DNA sequences were degraded selectively in the genome of senescing cotyledons.
Effect of CO2 and phosphate deprivation on the control of nitrate, nitrite and ammonium metabolism in Chlorella
Authors: Di Martino Rigano Vittoria , Martello Anna , Di Martino Catello , Rigano Carmelo
Published: April 2006

Chlorella vulgaris Beijerinck, strain 211/12, uses nitrate, nitrite and ammonium at pH 8.2 but not at pH 6.4 when kept under conditions of CO2‐deprivation, as observed in cell suspensions aerated with CO2‐free air during a 20–30. h period Most of the nitrate absorbed at pH 8.2, however, was not assimilated but was released into the external medium as nitrite and ammonium. Cells of Chlorella previously grown in phosphate‐limited continuous cultures were unable to absorb nitrate, nitrite or ammonium under conditions of phosphate starvation at either pH 6.4 or 8.2 in cell suspensions flushed with air containing 5% CO2, However, in cell suspensions flushed with CO2‐free air, the capacity of the alga to absorb and reduce nitrate and to excrete nitrite and ammonium at pH 8.2 was restored.

It is hypothesized that in Chlorella the metabolism of nitrate, nitrite and ammonium is influenced by the availability of other nutrients and controlled by the cell's carbon status at the level of ion entry into the cell. With respect to nitrate this carbon‐dependent control is distinct and works independently of that triggered by the cell's nitrogen status.
Effect of K+ and H+ stress and role of Ca2+ in the regulation of intracellular K+ concentration in mung bean roots
Authors: Torimitsu Keiichi , Hayashi Makoto , Ohta Eiji , Sakata Makotu
Published: April 2006

The effects of external K+, H+ and Ca2+ concentrations on the intracellular K+ concentration, [K+]i, and the K+‐ATPase activity in 2‐day‐old mung bean roots [Vigna mungo (L.) Hepper] were investigated. [K+]i, in mung bean roots was markedly decreased by external K+ or H+ stress and did not recover the initial value even after the stress was removed. This decrease in [K+]i, gradually disappeared with the addition of (Ca2+. Ca2+ may offset the harmful effects of ion stress. Ca2+ seems to have two effects on K+ transport; control of K+ permeability and activation of K+ uptake, although K+‐ATPase activity was inhibited by Ca2+ concentrations higher than 10–4 M. We suggest that Ca2+ activates K+ uptake indirectly through the acidification of the cytoplasm.
Photokinetic and photophysical parameters of the blue light induced phototransformation of phytochrome in the presence of flavin
Authors: Appenroth Klaus‐J. , Hermann Gudrun , Augsten Helmut , Müller Eberhard
Published: April 2006

Flavin mononucleotide (FMN) transfers its excitation energy to phytochrome Pr with a rate constant <8.7 × 1011 I mol‐1 s‐1. This reaction is not specific for Pr. the transfer to the phytochrome Pfr proceeds with ?5.8 × 1011 1 mol‐1 s‐1. These rate constants are lower limits because the complex‐formation constants are unknown. Assuming a horsier energy transfer a greater complex‐formation constant, as well as a greater orientation factor or a smaller distance in the complex FMN‐Pfr than in FMN‐Pr would be the possible reason for the difference between the rate constants.

It is shown that the “flavin effect” can only be of physiological relevance if the local phytochrome concentration does not reach the millimolar range at the same place Under these conditions the reaction Pr Pfr proceeds more effectively, but the reaction Pr Pfr less effectively than in the absence of the donor FMN. which gives rise to a shift of the equilibrium in favour of Pfr.
Pigment and quinone content of two photosynthetic barley mutants
Authors: Grumbach K. H.
Published: April 2006

The pigment and quinone content of wild‐type barley (Hordeum vulgareL., cv. Svalöfs Bonus) and of two photosynthetic mutants was assayed. Wild type plants and the photosystem Hacking mutantviridis zb63contained chlorophyll a and b. whereaschlorina‐f2contained only chlorophyll a The inability of the mutant chlorina‐f2 to convert chlorophyll a into chlorophyll a appears to he the primary effect of the mutation. In both mutants, the carotenoid composition was virtually identical to that of the wild type. As compared to the wild type.chlorina‐f2contained less lutein and neoxanthin. The mutantviridis‐zb63contained less β‐carotene but more antheraxanthin and xeaxanthin than the wild type. The quinone content and composition of the wild type and the photosynthetic mutants was similar, and both mutants biosynthesized plastid quinones and chromanols starting from [14C]‐labeled tyrosine. The data indicate that carotenoid and quinone biosynthesis are not altered in the two mutants as compared to the wild type.
The effect of Cd2+ on the biosynthesis of chlorophyll in leaves of barley
Authors: Stobart Allan K. , Griffiths W. Trevor , Ameen‐Bukhari Ibraheem , Sherwood Robert P.
Published: April 2006

The effect of cadmium on the biosynthesis of chlorophyll has been investigated in the leaves of dark‐grown seedlings of barley (Hordeum vulture L. cv. Proctor). Cd2+ inhibited the production of chlorophyll by affecting 1) the synthesis of 5‐aminolacvulinic acid and 2) the protoehlorophyllide reductase ternary complex with its substrates. Cd2+ had no effect on the constituent enzymes that catalyse the synthesis of free protoehlorophyllide from 5‐aminolaevulinic acid. The results obtained are consistent with Cd2+ inhibiting the formation of chlorophyll by reacting with essential thiol groups in both the protochlorophyllide reductase protein and the enzyme(s) involved in the light dependent synthesis of 5‐aminolaevulinic acid.
Scanning electron microscopic evidence for a budding mode of chloroplast multiplication in higher plants
Authors: Kulandaivelu G. , Gnanam A.
Published: April 2006

Scanning electron microscopic observations of leaf sections of certain plants show two distinct types of chloroplast multiplication. In the normal mode, chloroplast division is achieved by binary fission. In Bryophyllum pinnatum Kurz. the chloroplast multiplication occurs by a process similar to the budding of yeast. The advantages of using scanning electron microscopy to follow closely the different stages of chloroplast division are demonstrated.
The place of brassinolide in the sequential response to plant growth regulators in elongating tissue
Authors: Sasse Jenneth M.
Published: April 2006

In the sequential response to plant growth regulators in young elongating tissue from peas and wheat the peak of sensitivity to 24‐epi‐brussinolide (1 μM) occurs after those of gibberellin and cytokinin and begins before that of auxin in isolated wheat (Triticum vulgare L. ev. Egret) coleoptiles aged from 21‐96 h. In dwarf pea (Pisum sativum L. cv. Greenfeast) segments, the peak of sensitivity also lies between those of gibberellin and auxin, and it also occurs before sensitivity to auxin in sections from first leaves of wheat. All the leaf sections and all but the most mature coleoptiles and pea segments were sensitive to fusicocein (1 μM).
Light period of Crassulacean Acid Metabolism: Control of carbon transfer from malic acid to carbohydrates by CO2 concentration
Authors: Fischer A. , Kluge M.
Published: April 2006

In the CAM plants, Kalanchoë tubiflora (Harvey) Hasset, Sedum morganianum E. Walth and Sedum rubrotinctum R. T. Clausen, the effects of CO2 concentrations on the light‐dependent 14C transfer from the nocturnally synthetized [14C]‐malic acid to starch have been studied. CO2 concentrations up to 5 × 103 μ1 1–1 did not inhibit this carbon transfer. Higher CO2 concentrations, however, were increasingly inhibitory. At 104 μl 1–1 CO2, the carbon transfer was practically prevented.

The malic acid consumption in the light showed the same response to CO2 concentrations as the [l4C]‐transfer. Photosynthesis itself was not inhibited by the CO2 concentrations applied. It is assumed that, during phase III of CAM, light controls the internal CO2 concentration via photosynthesis; and that the internal CO2 concentration then controls the rate of malate decarboxylation.
Inhibition of photosynthesis by freezing temperatures and high light Levels in cold‐acclimated seedlings of Scots pine (Pinus sylvestris). ‐ I. Effects on the light‐limited and light‐saturated rates of CO2assimilation
Authors: Strand Martin , Öquist Gunnar
Published: April 2006

Shoots of cold‐acclimated seedlings ofPinus sylvestrisL. were subjected to low temperatures either in darkness or at a photon flux density of 1300 umol m−2s−1. CO2and water vapour exchange of the seedlings were measured at 12°C before and after treatment. Quantum yield at 12°C decreased both with decreasing temperatures below 0°C during, exposure to high light, and with increasing duration of light exposure. Quantum yield was also inhibited after treatment in darkness when needles were exposed to temperatures below their freezing point. Exposure of the pine shoots to a temperature of ‐7 to ‐8°C for 3 h in high light or darkness decreased quantum yield after thawing by ca 50 and 20%, respectively. Furthermore, light or dark exposure of the pine shoots at ‐7°C for 3 h decreased both the initial slope of the response of CO2assimilation rate to intercellular partial pressure of CO2, and the CO2assimilation rate at high partial pressures of CO2. It is concluded that excess light both at low temperatures, and freezing temperatures, cause inhibitions at the metabolic level, although the mechanisms may be different.
Quantitative relationships between osmotic potential amd epicotyl growth in Vigna radiata as affected by osmotic stress and cotyledon excision
Authors: Zhao Yu Ju , Kamisaka Seiichiro , Masuda Yoshio
Published: April 2006

The correlation between osmotic potential and epicotyl growth in intact and decotyiized mung bean seedlings (Vigna radiata (L.) Wilczek) grown under osmotic stress was studied. The following results were obtained: 1) Epicotyl elongation in intact seedlings grown in vermiculite containing 0.2 M mannitol was not substantially affected, but was strongly inhibited in decotylized ones. 2) Osmotic potential in the epicotyl was. decreased by osmotic stress due to 0.2 M mannitol, and was increased by cotyledon excision. 3) Epicotyl elongation was well correlated with net osmotic concentration, which is. the difference in osmotic concentration between the vacuolar sap of epicotyl cells and the 0.2 M mannitol added to the vermiculite. The net osmotic concentration was also correlated with cell elongation, but not with cell division in the epicotyl. 4) The concentrations of soluble sugars, free amino acids and potassium ions in the epicotyl increased in response to osmotic stress. Cotyledon excision decreased the concentrations of soluble sugars and free amino acids, while it had no effect on potassium ion concentration.

Based on these results, a role of osmoregulation in regulating epicotyl growth of mung bean is discussed in relation to osmotic stress and cotyledon excision.
Catabolism of indole‐3‐acetic acid to indole‐3‐methanol in a crude enzyme extract and in protoplasts from Scots pine (Pinus sylvestris)
Authors: Sundberg Björn , Sandberg Göran , Jensen Einar
Published: April 2006

The catabolism of radiolabelled indole‐3‐acetic acid was investigated in a crude enzyme extract and a protoplast‐rich fraction from Scots pine (Pinus sylvestris L.). Analysis by ion‐pair reverse‐phase and normal‐phase high performance liquid chromatography indicated that [14C]‐indole‐3‐methanol was a major catabolite of [2‐14C]‐indole‐3‐acetic acid in the crude enzyme system. This was confirmed by combined gas chromatograpby‐mass spectrometry which demonstrated the conversion of [2, 4, 5, 6, 7‐2H5]‐indole‐3‐acetic acid to [2H]‐indole‐3‐methanol. In addition to indole‐3‐methanol, the enzyme system converted indole‐3‐acetic acid to a number of other catabolites. Feeds with [1‐14C]‐ and [2‐14C]‐mdole‐3‐acetic acid suggest that, with the exception of two minor components, these catabolites result from decarboxylation. The effects of 2, 4‐dichlorophenol, phenol and hydrogen peroxide upon the reaction rate and product formation in the crude enzyme system were also investigated. Phenols favoured the formation of indole‐3‐methanol and enhanced the reaction rate. In contrast to the enzyme extract [14C]‐indole‐3‐methanol was only a minor product when P. sylvestris protoplasts were incubated with [2‐14C]‐indole‐3‐acetic acid.
Light‐induced, dark‐reversible colour shifts in petals of Phlox
Authors: Bjön Gunvor S. , Braune Wolfram , Björn Lars Olof
Published: April 2006

Flowers of some Phlox (Phlox x paniculata L.) varieties undergo daily colour shifts, being blue in the early morning, turning red during the day, and returning to blue in the evening. The colour shift, which occurs only in the upper (adaxial) petal surfaces, is due to the daily changes in ambient light. In the laboratory, colour shifts could be induced by 2.5 h of ultraviolet, visible or far‐red light and recorded by reflectance spectrophotometry.

There are indications that irradiations with different kinds of light cause qualitatively different colour shifts, and that thus more than one photoreceptor pigment and more than one primary light reaction may be involved. The presence of phytochrome was demonstrated in petals of white Phlox flowers by in vivo transmission spectrophotometry. It is therefore possible that colour shifts in coloured Phlox flowers are mediated by phytochrome. Possibly the movement of ions (e.g. hydrogen ions) into or out of the vacuole (where the visible pigments are located) is affected by light absorption in a pigment in the tonoplast.
Light‐triggered action potentials in the liverwort Conocephalum conicum
Authors: Trebacz K. , Zawadzki T.
Published: April 2006

The response to light of a liverwort, Conocephalum conicum L., measured as a change in the resting potential, consists of two stages. The first stage is a slight depolarization dependent on light intensity. This plays the role of a generator potential (GP) which induces the second stage ‐ an action potential of the all‐or‐none character. Action potentials induced by light and by electrical stimuli have the same properties, i.e. identical time course, propagation velocity, and refractory periods. A summation occurs of sub threshold light stimuli and of light and electrical stimuli. The presence of 5⋅10‐−6M DCMU cancelled the light response and blocked ‐ by inhibition of the electron transport chain ‐ the mechanism leading to GP generation. However, this effect did not produce any change in the response to electrical stimuli.
Endogenous nitrate loss as an assay for nitrate reduction in vivo
Authors: Soares M. Inês M. , Lips S. Herman , Cresswell Cristopher F.
Published: April 2006

An in vivo assay method for nitrate reduction is proposed, based on the use of endogenous nitrate rather than on the accumulation of nitrite. Loss of endogenous nitrate and accumulation of nitrite were studied in barley (Hordeum vulgare L. cv. Gars Clipper ex Napier) leaves. Leaf sections were incubated in the dark in a gaseous environment of air or N2. Nitrate disappeared under both conditions, the highest loss being observed in tissue under anaerobiosis. Nitrite accumulated only in leaf sections under anaerobiosis, but the amount of nitrite accumulated was much lower than the amount of nitrate lost. A comparative study of the capacity of barley leaf sections to use endogenous nitrate and accumulate nitrite showed that both activities were dependent on temperature in a manner characteristic of enzymatic reactions. Disappearance of endogenous nitrate increased with increasing levels of nitrate in the tissue.
Further support for the involvement of phytoehrome in stomatal movement
Authors: Roth‐Bejerano Nurit , Nejidat All , Itai Chanan
Published: April 2006

The involvement of phytochrome in stomatal movement in Commelina communis L. is indicated by the following observations: 1) Short irradiation with red or blue light causes opening, of isolated stomata and swelling of guard cell protoplasts. This is reversed by subsequent far red irradiation. 2) In a similar way, stomatal response to prolonged irradiation with red or blue light is decreased by concomitant far red irradiation. 3) Pretreatment with filipin, which interferes with phytochrome binding to membranes, decreases stomatal opening in red and blue light. The stomatal responses to blue and red light are modified by DCMU, N2, CO2‐enriched atmosphere, and CO2‐free air, which are known to affect, among other processes, chlorophyll fluorescence. Increased chlorophyll fluorescence by DCMU, N2 and CO2‐enriched atmosphere enhanced stomatal opening in blue light and inhibited it in red light. CO2‐free air, which decreases chlorophyll fluorescence, had the opposite effect.
Isolation of mutants of fast‐growing soybean strains that are effective on commercial soybean cultivars
Authors: Buenlia‐Claveria Ana M. , Ruiz‐Sainz Jose E.
Published: April 2006

Fast‐growing rhizobia that nodulate soybeans (Glycine max L. cvs Peking and Malayan) have been isolated. Initial inoculation of commercial cultivars of soybean with these strains results in the formation of a few pink nodules. Isoiates from these nodules form fully effective symbiosis with the soybean cultivar from which they were isolated. These results demonstrate that is is possible to isolate effective mutants of fast‐growing soybean strains by allowing the plants to select for effective mutants. These mutants are potentially valuable because, if their symbiotic properties can be improved, they could possibly be used as commercial soybean inoculants.
The stimulating effects of NaCl on root growth of Rhodes grass (Chloris gayana)
Authors: Waisel Y.
Published: April 2006

Rhodes grass (Chloris gayana Kunth. cv. common) is a halophytic forage grass. Like most halophyles, its growth is positively affected by low levels of salinity but is inhibited by high salinity. However, such a definition is not clear and not unmistakable: NaCl concentrations which inhibit the growth of the whole plant stimulate the growth of single roots when applied to them individually.
Effect of drought and prolonged refrigeration on senescence in cut carnation (Dianthus caryophyllus)
Authors: Paulin A. , Kerhardy F. , Maestri B.
Published: April 2006

Severe water stress (40 and 50 h without water at 23°C) and long periods of refrigeration (4 and 5 weeks at 0°C) caused the peak of ethylene production by cut carnation flowers to appear soon after the return to normal conditions. Water stress caused a decrease in ψosm, but this increased back to the initial value on return to normal conditions. Accelerated wilting and massive ion leakage, probably a result of the Joss of membrane integrity, was associated with this premature burst of ethylene. Large amounts of acetaldehyde and ethanol accumulated during prolonged refrigeration (3, 4 or 5 weeks at 0°C). This accumulation of toxic metabolites may explain why the refrigeration of cut flowers for long periods causes a rapid wilting on return to normal conditions.
Autolysis of cell walls in pea epicotyls during growth. Enzymatic activities involved
Authors: Labrador Emilia , Nicolas Gregorio
Published: April 2006

Pisum sativum L. (cv. Lincoln) epicotyl cell walls show autohydrolysis and release into the incubation medium up to 120 μg of sugar per mg of cell wall dry weight in 30 h. Cell walls from younger epicotyls with high growth capacity showed higher auto‐lytic capacity than older epicotyls. This suggests that both processes, growth and au‐tolysis, are related. The proteins responsible for autolysis were extracted from the wall fraction with high saline solution (3M LiCl) and enzymatic activities associated with the proteins were studied. The highest activity corresponded to α‐galactosidase; lower activities were found for β‐galactosidase, a‐arabinosidase and exoglucanase. Changes in enzymatic activities and changes in the proportion of sugars released in autolysis by cell walls during the growth of epicotyls support the notion that α‐galac‐tosidase is one of the enzymes involved in the process of autolysis, and that the liberation of arabinose and galactose in this process occurs as arabinogalactan.
Sugar transport in leaf discs ofPhaseolus coccinius
Authors: Daie J.
Published: April 2006

Kinetic profiles for sucrose, glucose and 3‐OMG glucose were determined in leaf discs ofPhaseolus cocciniusL. (cv. Scarlet). All three sugars exhibited identical uptake kinetics. At sugar concentrations below 25 mM, transport was due to an active, carrier‐mediated transport system. A linear component was the dominant mode of uptake at sugar concentrations above 25 mM. Sucrose and glucose carriers were specific for these sugars, since no uptake inhibition was observed from competing sugars. Sucrose was not hydrolyzed by leaf tissue because the label in asymetrically labeled sucrose was not randomized. Furthermore, no label was present in hexose fractions when tissue was incubated with [84C]‐sucrose. Therefore, [14C]‐sucrose uptake did not reflect hexose uptake.

Both saturable and linear components of uptake contribute significantly to total uptake rates. The former, however, is more important when apoplastic sugar concentrations are low. The molecular nature of the linear component is not well understood but accounts for most of the uptake at high sugar concentrations.
Uptake of amino acids and peptides by developing barley embryos
Authors: Sopanen Tuomas , Sinervo Tuija , Ahokas Hannu
Published: April 2006

Developing embryos of barley (Hordeum vulgare L. cv. Bomi) detached 21–27 days after anthesis took up 1 mM [14C]‐glutamine at pH 5 and 30°C at a rate of about 20 nmol embryo−l h−1 (5 μol g−1h−1). The uptake was inhibited by about 50% by di‐nitrophenol and by about 80% by 300 mM unlabelled glutamine or alanine. The bulk of the uptake appeared, therefore, to be due to carrier‐mediated active transport. The pH optimum of the uptake was 4.5. Leucine, proline, lysine, arginine and as‐paragine were taken up at approximately similar rates as glutamine, and they also inhibited the uptake of glutamine. This, suggests that the uptake of glutamine was at least partly due to an unspecific carrier(s) also shared by other amino acids. The embryos also took up the dipepti.de glycykarcosine; the rate was about 6 nmol embryo−1h−1 (1.5 μol g−1h−1) (2 mM glycylsarcosine, pH 4.5, 30°C). The uptake was inhibited by about 70% by dinitrophenol or by 300 mM glycylglycine. This indicates that the bulk of the uptake was due to carrier‐mediated active transport. The pH optimum of the uptake was about 4.5.

The rates of glutamine and glycylsarcosine uptake increased during the early and middle stages of embryo development (until day 28 after anthesis), but decreased towards the end of the maturation of the grain. These changes, as well as the relatively high activities, suggest that carrier‐mediated active uptake of amino acids, and possibly also that of peptides, plays a role in the nutrition of the developing embryo.