bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of light intensity on the activity of starch synthesizing enzymes and starch synthesis in developing wheat grains
Authors: Mengel Konrad , Judel Günther‐Klaus
Published: April 2006

The activities of starch synthesizing enzymes were investigated in wheat grains (Triticum aestivum L. cv. Kolibri) throughout the grain development period. Starch phosphorylase (E.C. 2.4.1.1.) activity was especially high during the early period of grain development, while starch synthase I (ADP glucose α‐glucan 4‐α‐glucosyl‐transferase, E.C. 2.4.1.21) had a maximum activity during the later stage of grain filling. The synthetic potential of starch phosphorylase measured in vitro was about 16 times higher than the quantity of starch actually produced. It is therefore suggested that starch phosphorylase is of substantial importance in grain starch synthesis, particularly in the early period of grain growth. The synthetic potential of starch synthase I measured in vitro made up 25 to 50% of the starch production and the synthetic potential of starch synthase II (UDP glucose α‐glucan 4α‐glucosyl‐transferase. E.C. 2.4.1.11) only about 5%.

Reducing light intensity (shading) during the grain filling period depressed grain growth and starch production by about 20%. Starch phosphorylase was not significantly affected by the reduced light intensity if enzyme activity is calculated on unit grain weight and not as activity per grain. Starch synthase I activity, however, was depressed by shading during the later stage of grain development. The depressed starch production found under low light conditions, however, cannot only be explained by an affected starch synthase I activity, but probably was also related to other still unknown factors limiting grain growth under low light conditions. The poor starch production in the shaded plants was not due to an insufficient supply of assimilates.
Factors affecting the inhibitory effect of indolylacetic acid on root formation in pea cuttings
Authors: Eliasson Lennart
Published: April 2006

Indol‐3yl‐acetic acid (IAA) present in the rooting solution for 1–4 days appreciably decreased the number of roots subsequently formed in pea stem cuttings. Removal of the lowest 10 mm of the cutting base after IAA treatment abolished the inhibitory effect of IAA almost completely. The number of roots formed from the remaining part of the base internode after excision of the basal centimeter of the internode 4 days after the cuttings were taken was similar to that of the control. It is concluded that the first root primordia, which develop near the cut surface, have an inhibitory influence on development of further roots. The inhibitory effect of IAA may be explained as a strengthening of this dominance phenomenon.

Addition of charcoal to the rooting solution delayed the appearance of roots but increased the number of roots developed during a standard rooting period. Adsorption of stimulatory and inhibitory compounds at the surface of the cutting base is believed to be the reason for these results as no evidence of accumulation of inhibitory compounds in the solution was obtained. Charcoal reversed the inhibitory effect of IAA if added after the IAA treatment. This reversal was almost complete if the IAA treatment lasted for one day only but decreased drastically if the IAA treatment was extended over 4 days.
Cytokinin activity in Lupinus albus
Authors: Davey J. E. , Van Staden J.
Published: April 2006

The distribution and metabolism of {8‐14C}zeatin incorporated into the transpiration stream of fruiting white lupin plants (Lupinus albus L.) has been studied. The distribution pattern of 14C in the different aerial organs suggests that the amount of cytokinin being incorporated into any one organ may have been a function of its transpiration rate. Once in these organs, particularly the leaves, zeatin was rapidly metabolised and or utilised. This resulted in the formation of a number of labelled compounds that did not give a response with the soybean callus bioassay. Substances co‐eluting with zeatin glucoside and ribosylzeatin appeared to be the principal biologically active metabolites. From the present evidence it can be concluded that the leaf and side shoots received a major proportion of the applied labelled cytokinin. However, the presence of a small amount of radioactivity co‐eluting with zeatin and ribosylzeatin in the fruits indicates that the high levels of cytokinins normally associated with these organs need not necessarily all have been synthesised in situ.
Cytokinin activity in Lupinus albus
Authors: Van Staden J. , Davey J. E.
Published: April 2006

The fate of {8‐14C}zeatin injected into the mature leaves and oldest fruits of fruiting white lupin plants (Lupinus albus L.) was studied. Applied zeatin was metabolised rapidly by both organs. Within 24 h radio‐ and cytokinin‐like activity that co‐eluted with zeatin glucoside and ribosylzeatin could be detected within them. While no evidence could be found for the export of labelled cytokinins from the fruits there were some indications that zeatin glucoside may have been exported from the mature leaves.
The ultrastructure of Anabaena azollae in Azolla pinnata
Authors: Neumüller Magnus , Bergman Birgitta
Published: April 2006

The water fern Azolla pinnata R. Br. was collected in Northwestern India and its structure was examined using scanning and transmission electron microscopy. Emphasis was given to the symbiotic cyanobacterium. Anabaena azollae, and to its relationship to the hairs of the leaf cavities. The cyanobacterial filaments are loosely arranged and often adhere to the protruding hairs and the folded cell walls of the cavities. The vegetative cells show a typical bilayered cell wall. Thylakoids are few and evenly dispersed in mature vegetative cells and appear to lack phycobilisomes. Clusters of polyglucoside granules are distinguished between the thylakoids. Thylakoid membranes are often seen forming whirls and lattices. Polyhedral bodies (carboxysomes) appear particularly frequently in younger cells and in the proximity of polyphosphate bodies. Presence of structured granules, often positioned at both sides of the cross‐wall of neighbouring vegetative cells, suggest a positive nitrogen balance. A high frequency of heterocysts is noted, while spores are not observed.

The outer cell wall of the unbranched, mostly two‐celled, hairs shows frequent invaginations. The cytoplasma of the mature hair contains numerous organelles, and is penetrated by an electron transparent network with blebs and vesieles appearing. The exchange of metabolites between the symbiotic partners is discussed in relation to the structures noted.
In vitro control of de novo flower differentiation from tobacco thin cell layers cultured on a liquid medium
Authors: Cousson A. , Thanh Van K. Tran
Published: April 2006

Thin cell layers of tobacco (three to six layers of epidermal and subepidermal cells) were allowed to float on the surface of a liquid medium. Whereas the control on an identical medium solidified by agar gave 100% of explant‐forming flowers, no flowers formed in the absence of agar (100% of the explants formed buds). In order to initiate flower formation, various modifications of the liquid medium were tried: different ratios of indolyl‐3‐butyric acid (IBA) to kinetin (Kin) from 1 to 100, a range of pH from 4.0 to 7.0, and glass beads of different diameters (in an attempt to change the physico‐chemical characteristics of the culture substrate itself). On a liquid medium with glass beads, four types of morphogenesis (flowers, buds, a mixed programme of flowers and buds, and a non‐morphogenetic programme –i.e. the explants remained unchanged) were separately induced by changing one of the three factors: pH, IBA and Kin in equimolar concentrations, and diameter of the glass beads. Changing only the IBA/Kin ratio failed to provoke flower differentiation. pH of the medium was found to change after autoclaving and the effect of glass beads on morphogenesis was partly related to modification of pH.
Nitrogen metabolism of Plantago lanceolata as dependent on the supply of mineral nutrients
Authors: Stulen Ineke , Lanting Lineke , Lambers Hans , Posthumus Freek , van de Dijk Siebren J. , Hofstra Rinie
Published: April 2006

Various aspects of nitrogen metabolism of Plantago lanceolata L., a grassland species from a relatively nutrient poor habitat, were investigated under high nutrient conditions or low nutrient conditions. In addition the responses after switching the plants from high nutrient conditions to low nutrient conditions and vice versa were studied. The activities of nitrate reductase (NR), glutamate dehydrogenase (GDH) and glutamine synthetase (GS) were determined. In the roots they were correlated with the level of the nutrient supply. Not only NR but also GDH and GS increased upon a switch from low nutrients to high nutrients and decreased upon a switch from high nutrients to low nutrients. Reduced nitrogen content of both roots and shoots was also correlated with the nutrient supply and changed rapidly after a switch. The flexibility of the nitrogen metabolism of Plantago lanceolata is discussed in relation to its ecological habitat.
Analysis of plating technique for viability and drug‐sensitivity determinations using Rosa cells
Authors: Strauss André , King Patrick J.
Published: April 2006

Rosa Paul's Scarlet’cell suspension cultures were used as a test system for working out a method of viability and drug‐sensitivity determination based on plating efficiency. High plating efficiencies (80–95%) were obtained on a simple synthetic medium when aggregates of a mean size of c. 100 cells/unit from exponential phase cultures were plated at a density of 1500 units/plate in the middle layer (5 ml) of three layers of the agar‐solidified medium (total = 30 ml). This 3‐layer plating technique produces homogeneous colony growth and simplifies the microscopical evaluation of plating efficiencies. The reduction of plating efficiencies seen when the smaller aggregates of stationary phase cultures were plated was mainly due to low cell density and could be overcome by enriching the medium with various supplements. Reconstitution experiments using mixtures of inactivated and non‐inactivated aggregates demonstrated that plating efficiency can be taken as a goodmeasure of viability. The described plating technique was found to be more sensitive and reliable compared to two other methods for determining p‐fluorophenylalanine‐sensitivity of Rosa cells.
Water relations of cotton plants under nitrogen deficiency
Authors: Radin John W.
Published: April 2006

Nitrogen deficiency in cotton plants (Gossypium hirsutum L.) increased the threshold water potentials for both stomatal closure and leaf senescence (defined as loss of chlorophyll and protein) during drought. These studies attempted to answer two questions: (1) What is the basis for the N/water interaction on senescence? (2) Is there a direct relationship between stomatal closure and senescence?

Young and old leaves from N‐deficient and N‐sufficient plants maintained their relative sensitivities to water stress when excised leaf discs were floated on solutions of polyethylene glycol in dim light. In this leaf disc system, both leaf aging and N deficiency increased the threshold water potential for senescence. Leaf aging and N deficiency also decreased the concentration of exogenous abscisic acid necessary to initiate senescence in discs. A role for cytokinins in controlling senescence could not be clearly shown.

In young leaves of both N‐deficient and N‐sufficient plants, stomata closed at water potentials much higher than those causing senescence. During leaf aging, the water potentials causing senescence increased more than those causing stomatal closure. The two processes thus occurred at about the same potentials in the oldest leaves. These data argue against a general cause‐and‐effect relationship between stomatal closure and senescence. Rather, each process apparently responded independently to absicsic acid accumulated during drought.
Release of membrane proteins in relation to heat injury of spinach chloroplasts
Authors: Volger Henning , Santarius Kurt A.
Published: April 2006

Thylakoids isolated from spinach leaves (Spinacia oleracea L. cvs. Monatol and Montako) were exposed to supraoptimal temperatures that inactivated their photochemical reactions. Membrane injury was accompanied by release of a small amount of membrane proteins. When sucrose was present during high‐temperature treatment, thylakoids were partially protected and release of membrane proteins was less pronounced than in the absence of sugar. From thylakoids, which were isolated from heat‐damaged spinach leaves, less protein was released when heated again after the isolation procedure, indicating that protein release also takes place during heat inactivation in vivo. Sodium dodecyl sulfate gel electropherograms of thylakoids demonstrated that heat inactivation of the lamellae was not accompanied by significant changes in the pattern of the proteins, which remained in the membranes. The same was found when thylakoids were solubilized with Triton X‐100 before and after heat damage. It is suggested that the protein release that occurs during heat treatment is a consequence of irreversible alterations in the membrane structure; these changes may be responsible for thermal damage of chloroplast membranes.
Factors influencing the frequency of callus formation among cultured rice (Oryza sativa) anthers
Authors: Chaleff R. S. , Stolarz A.
Published: April 2006

The effect of various experimental parameters upon the frequency of callus formation from cultured anthers of Oryza sativa has been investigated. Although certain medium components were found to be critical to callus formation, the concentration of these components had little effect upon the frequency of callus formation. The degree to which the callus formation frequency was influenced by cold pretreatment of the flowers was variable. Even though plants were grown under uniform conditions and flowers containing pollen in the microspore stage of development were selected for dissection, the frequency of callus formation varied nonrandomly between flowers. In experiments with populations of flowers in a physiological and developmental state favorable to callus formation 35% of plated anthers produced callus and at least 60% of these calluses gave rise to green plants.
Comparative analysis of the effects of fusicoccin (FC) and of its derivative dideacetylfusicoccin (DAF) on maize leaves and roots
Authors: Radice Marco , Scacchi Alessandro , Pesci Piero , Beffagna Nicoletta , Marrè Maria Teresa
Published: April 2006

In maize (Zea mays L. cv. DEKALB XL 640) leaf discs or root segments fusicoccin (FC) is by about 5‐10 times more active than its derivative dideacetylfusicoccin (DAF) in stimulating proton extrusion and the hyperpolarization of the transmembrane electrical potential (PD). Also the uptake by leaf discs in liquid medium and the affinity for a receptor present in cell free membrane preparations are by 3–5 times greater for FC than for DAF, while a much greater difference (by about two orders) in activity between the two substances is observed for their effects on leaf transpiration.

FC reaches in the leaf tissue a concentration much higher than that of DAF. This is interpreted as due to the higher activity of FC in inducing stomata opening, thus accelerating the transpiratory water flow. The long distance translocation of both FC and DAF mainly depends on mass flow. Thus the initial stimulus on transpiration would induces an increase in concentration of the active substance in the reactive tissue, in a kind of autocatalytic cycle, resulting in the amplification of the difference in activity at cell level between the two toxins.

The data on the promotion of H+ extrusion and the hyperpolarization of PD confirm the correlation and thus the possible cause‐effect relationship between FC (or its less active derivative DAF) binding to a receptor at the membrane, and the functions studied. The relationships between the “pathological” (transpiration and wilting) and the “physiological” (electrogenic proton secretion) effects of FC and DAF are also in agreement with the view that all of the known effects of FC and of its active derivatives can be explained as consequences of the activation of electrogenic proton extrusion.
The use of population parameters in the analysis of germination of lettuce seed
Authors: Berrie Alex. M. M. , Taylor Graham C. D.
Published: April 2006

Probit analysis was used to determine the parameters of the germinating population of lettuce seed. Seeds were induced to germinate under different conditions and it was shown that with light induced germination the germinating populations were the same. However, when gibberellic acid (GA3) was the inductive agent then the germinating populations were not the same being concentration dependent. – This type of analysis offers a rigorous comparison of different inductive treatments.
Photosynthesis as related to xylem water potential and carbon dioxide concentration in Sitka spruce
Authors: Beadle C. L. , Neilson R. E. , Jarvis P. G. , Talbot H.
Published: April 2006

Current‐year shoots of Sitka spruce (Picea sitchensis (Bong.) Carr.) were removed from the forest canopy. After steady‐state rates of net photosynthesis were obtained in a leaf chamber, the shoots were excised in air and removed at different times to establish a relationship between net photosynthesis and xylem water potential. The experiment was repeated at five ambient carbon dioxide concentrations.

Net photosynthesis remained constant over a wide range of xylem water potential and increased linearly with ambient carbon dioxide concentration between 20 and 300 cm3 m−3. At low water potential net photosynthesis declined at each ambient carbon dioxide concentration and there was little difference in the potential (±0.05 MPa) at which zero photosynthesis was observed.

There was a small increase in the CO2 compensation concentration at low xylem water potentials, but calculated mesophyll conductance still declined at low water potential after correction for this change in compensation concentration. Mesophyll conductance reached zero within the same range of water potential as net photosynthesis. The results suggested that the non‐stomatal contribution to the decline of photosynthesis was approximately 30% until almost complete stomatal closure occurred.
Carbon dioxide exchange in lichens: Partition of total CO2 resistances at different thallus water contents into transport and carboxylation components
Authors: Green T. G. A. , Snelgar W. P.
Published: April 2006

The total resistances to CO2 uptake by Sticta latifrons Rich, and Pseudocyphellaria amphisticta Kremp. were separated into transport and carboxylation components by calculation after transformation of net photosynthesis rate against CO2 concentration curves into a linear form. The use of this technique circumvented the problem of measuring the internal CO2 concentration of the lichen thalli. Both species exhibited an increase in transport resistance at high thallus water contents and an increase in both transport and carboxylation resistances at low water contents. At low and intermediate water contents internal transport resistances were larger than carboxylation resistances when measured at limiting CO2 concentrations. However, at ambient CO2 concentrations carboxylation processes were the dominant factors limiting photosynthesis at all, except the high, water contents.
Carbon dioxide exchange in lichens: Estimation of internal thallus CO2 transport resistances
Authors: Snelgar W. P. , Green T. G. A. , Beltz C. K.
Published: April 2006

The gaseous exchange pathways of Sticla latifrons Rich. and Pseudocyphellaria amphisticta Kremp. were examined using both light and scanning electron microscopes. The size and frequency of the pores in the gas exchange structures (cyphellae and pseudocyphellae) and in the medulla were measured and from these CO2 diffusion resistances were calculated. Pseudocyphellae were found to be smaller and more widely spaced than cyphellae, consequently the resistance of the pseudocyphellae, was much greater than that of the cyphellae. Medulla resistances were low in both lichens and are probably unimportant, even at high water contents. No evidence of hyphal swelling was found. Gas exchange structure resistances were more than five fold greater than medulla resistances. It is suggested that this arrangement of resistances may simultaneously encourage refixation of respired CO2 and maintain a non desiccating environment for the lichen algae. The internal transport resistances calculated in this work approximate experimentally obtained values.
Relationship between tracheary element differentiation and the cell cycle in single cells isolated from the mesophyll of Zinnia elegans
Authors: Fukuda Hiroo , Komamine Atsushi
Published: April 2006

A relationship between tracheary element differentiation and the cell cycle was studied in single cells isolated from the mesophyll of Zinnia elegans L. cv. Canary bird. Almost all nuclei of isolated mesophyll cells were at the 2 C level of DNA, indicating that almost all cells were initially in the G1 phase and that somatic polyploidy was absent. Cultured cells underwent partially synchronous DNA replication at 42 h and mitosis at 54 h of culture, and the first cell cycle time was approximately 58 h.

The occurrence and timing of DNA replication and mitosis during cytodifferentiation to tracheary elements were investigated using microspectrophotometry, microfluorometry, tritiated thymidine autoradiography, and serial observation. More than 55% of the nuclei of the immature tracheary elements were at the 2 C level of DNA and were not labeled by continuous feeding with tritiated thymidine, providing clear evidence that these cells differentiated without interventing DNA replication. Some tracheary elements (approximately 30%) were formed after one round of the cell cycle, and others (less than 5%) were formed after passing through the S phase, but without intervening mitosis. All types of tracheary elements appeared simultaneously after 58 h of culture, and their patterns of increase in number were similar. From the results, we propose a hypothesis concerning the relationship between cytodifferentiation and the cell cycle.
Separation of metabolic and non‐metabolic steps of Rb+ uptake in spring wheat roots with different K+ status
Authors: Jensén Paul
Published: April 2006

Uptake of Rb+ from a complete nutrient solution with 2.0 mM Rb+ was studied in roots of spring wheat seedlings (Triticum aestivum L. cv. Svenno) with different K+ levels. The relationship between Rb+ uptake and concentration of K+ in the roots indicated a negative feedback mechanism operating through allosteric control. The Rb+ uptake process in root cells was divided into two steps: (1) binding of the ion in the free space, and (ii) transmembrane transport into the cytoplasm. Metabolic and non‐metabolic components of uptake were separated by addition of the metabolic inhibitor 2,4‐dinitrophenol (DNP) to the nutrient solution. It is suggested that metabolic Rb+ uptake requires energy in two uptake steps (for binding to the carrier entity in the free space and for transmembrane transport) or in one step only (for transmembrane transport), dependent on the K+ status of the roots. The change from metabolic to non‐metabolic binding in the free space is accomplished by changing the conformational state of the carrier (slow/fast transitions). There may be a hysteretic effect on metabolic Rb+ uptake through a slow transition between carrier states. This is superimposed on the negative cooperativity, strengthening further cooperativity at intermediate K+ levels in the roots. Non‐metabolic Rb+ uptake probably consists of two components, a carrier‐mediated (facilitated diffusion) and a parallel diffusive component.
Nutrition and growth of birch and grey alder seedlings in low conductivity solutions and at varied relative rates of nutrient addition
Authors: Ingestad Torsten
Published: April 2006

Birch (Betula verrucosa Ehrh.) and grey alder (Alnus incana Moench) seedlings were grown with varied relative addition rates of all nutrients, up to optimum for vegetative growth. The root medium was basically distilled water to which the nutrients, contained in stock solutions in fixed proportions, were added every second hour and in exponentially increased amounts for consumption during the subsequent period. The nutrient weight proportions previously found to be required in birch (100 N:65 K:13 P) were used in all treatments. However, the nutrient proportions required in grey alder were found to be somewhat different (100 N:50 K:18 P). The use of the required proportions in the additions was important for maintenance of maximum growth, efficient nutrient utilization, and low concentrations in the root medium. Luxury consumption and inefficiency occurred at high concentrations. The results show that the nutrient requirements are sufficiently defined, for different relative growth rates, by the nutrient proportions and the relative addition rate.

No clear relationships were found between conductivity or concentration in the root medium and the addition rate, net uptake rate, nutrient status, or relative growth rate. The results are in good agreement with data from low concentration and depletion experiments reported in the literature, showing that non‐limited uptake rates occur down to very low concentrations. Thus, there is strong evidence that concentration has been incorrectly used when applied as the treatment variable for plant nutrition in plant science and cultivation practice. The dominant factors in sub‐optimum and optimum nutrition are the amounts of nutrients available per unit of time, the growth rate, and the nutrient proportions. At low concentration levels, physical factors such as stirring and flow rate of nutrient solution and boundary layer effects are decisive for the rates with which the nutrients become available to the roots. Therefore, at low levels, concentration alone cannot be used as the factor determining nutrient uptake rate. At high levels, concentration is effective as a supra‐optimum factor and increased internal percentage contents cause decreased uptake efficiency, thus counter‐acting the concentration effect.

Nitrogen effects dominated the stress indications when the internal nitrogen percentage content decreased from optimum to the level of the treatments in the beginning of the experiments. Leaf deficiency symptoms disappeared and the root/shoot ratio change ceased when nitrogen status stabilized. Strong linear regressions were found between any two of the variables: relative addition rate of nutrients, relative growth rate, and nutrient status.
Fusicoccin structure‐activity relationships: Stimulation of growth by cell enlargement and promotion of seed germination
Authors: Ballio A. , De Michelis M. I. , Lado P. , Randazzo G.
Published: April 2006

The activity of a number of fusicoccin derivatives and analogues has been assayed on growth by cell enlargement and on proton extrusion in pea (Pisum sativum L, cv. Alaska) internode segments, on growth by cell enlargement in isolated squash (Cucurbita maxima Dechesne in Lam. variety Mantovana) cotyledons, and on germination of light‐requiring lettuce (Lactuca sativa L. cv. Grand Rapids) and of abscisic acid‐inhibited radish (Raphanus sativus L. variety Tondo Rosso Quarantino) seeds. A similar pattern of activity in the different tests was found for most fusicoccin derivatives and analogues. As with fusicoccin, the activity of its derivatives and analogues on growth of pea internodes is paralleled by the activity on the capability of the tissue to acidify the incubation medium.

The obtained data are in full agreement with the view that the activity of fusicoccin on different physiological processes depends on its primary activation of a single system, involved in proton extrusion.
Sulphate induced accumulation of glutathione and frost‐tolerance of spinach leaf tissue
Authors: de Kok Luit J. , de Kan Peter J. L. , Tánczos Otto G. , Kuiper Pieter J. C.
Published: April 2006

Water‐extractable sulfhydryl content of spinach leaf discs increased up to four‐fold when they were incubated with sulphate (10–100 mM) for 20 h in light or darkness. The accumulated sulfhydryl compound was reduced glutathione. An increased glutathione content did not result in a higher frost‐tolerance of the spinach leaf discs. Both freezing temperature and time of exposure to freezing, determined as the point at which 50% of the cells were killed, remained unchanged after incubation with sulphate. These observations suggest that a sulfhydryl compound as glutathione does not play a direct role in protection of plants against freezing injury.
Inhibition of the conversion of glycine to serine in spinach leaf mitochondria
Authors: Gardeström Per , Bergman Anders , Ericson Ingemar
Published: April 2006

Isonicotinyl hydrazide, glycine hydroxamate, aminoacetonitrile and KCN inhibited the conversion of glycine to serine in spinach (Spinacea oleracea L. cv. Viking II) mitochondria. The site of inhibition for the different inhibitors was studied. Isonicotinyl hydrazide and glycine hydroxamate both inhibited the partial reactions glycine‐bicarbonate exchange and serine hydroxymethyltransferase. The inhibition was competitive for the exchange reaction and noncompetitive for serine hydroxymethyltransferase. Aminoacetonitrile at low concentration (1 mM) inhibited the glycine‐bicarbonate exchange specifically, whereas serine hydroxymethyltransferase was inhibited only at higher concentrations. Aminoacetonitrile was a competitive inhibitor for both reactions. The serine hydroxymethyltransferase was inhibited by KCN whereas the glycine‐bicarbonate exchange was only partially inhibited. The KCN‐inhibition of serine hydroxymethyltransferase was competitive.
Brassinolide, a growth‐promoting steroidal lactone
Authors: Yopp John H. , Mandava N. Bhushan , Sasse J. M.
Published: April 2006

Brassinolide (BR), a naturally‐occurring‐steroidal lactone from rape (Brassica napus L.) pollen, was compared with auxin for activity in a number of bioassay systems. Responses similar to IAA were elicited by BR in bioassays based upon bean hypocotyl hook opening, elongation of maize mesocotyl, pea epicotyl and azuki bean epicotyl sections, and fresh weight increase in Jerusalem artichoke (2,4‐D used) and pea epicotyl sections. The azuki bean and dwarf pea epicotyl bioassays were much more responsive to BR than IAA (at 10 μM). Responses approximately two‐fold greater in magnitude were elicited by IAA in the maize mesocotyl, bean hypocotyl hook and Jerusalem artichoke bioassays. Little or no response was elicited by BR (0.01 to μM) in the cress root or decapitated pea‐lateral bud bioassays. A powerful synergism between BR and IAA was observed in the azuki bean, pea epicotyl and bean hypocotyl hook bioassays. Although, as previously reported, other steroidal substances are active in some of the bioassay systems tested, none compared with BR in magnitude and diversity of elicited responses.
Evolution of ethylene by sulphur dust addition
Authors: Recalde‐Manrique Luís , Díaz‐Miguel Manuel
Published: April 2006

Kidney‐bean plants (Phaseolus vulgaris L. cv. Contender) were dusted with sulphur 25 days after germination. The amount of ethylene evolution was measured in shoots (with attached leaves) and roots from plants in several stages of development. The growth of shoots and roots was also measured, and the flowering time observed. The ethylene evolution was associated with precise morphogenic stages. The amounts of ethylene produced from sulphur treated plants, compared with that evolved from control plants, showed two stages of stimulation in shoots, one preceding full bloom and one preceding fruit‐set. Inhibition of ethylene evolution due to sulphur dust occurred in roots before initiation of floral primordia and before full bloom. The treatment with sulphur dust seemed to increase the number of leaves per plant, but only in the vegetative stage. Likewise, the earliness of flowering was enhanced. The effects of elemental sulphur dust treatments on ethylene evolution may be attributed to a slow oxidation of elemental sulphur in air producing SO2; this SO2 greatly enhances ethylene evolution from leaf tissues.
Membrane and ion transport properties in cereals under acidic and alkaline stress
Authors: Zsoldos Ferenc , Erdei László
Published: April 2006

The effects of pH on the growth and the K+ (86Rb) uptake and K+ content of excised rice (Oryza sativa L. cv. Dunghan Shali) and wheat (Triticum aestivum L. cv. GK Szeged) roots were investigated. Rice roots responded to H+ stress with an increased K+(86Rb) influx and a decreased K+ content, suggesting an increased exchange between the cytoplasmic K+ pool and the external medium. Under the same experimental conditions wheat did not show any anomalous K+(86Rb) influx. Growth of both rice and wheat was relatively insensitive to pH between 4 to 10.
Membrane and ion transport properties in cereals under acidic and alkaline stress
Authors: Bérczi Alajos , Erdei Lárszló , Zsoldos Ferenc
Published: April 2006

An electron spin resonance study of fatty acid spin labels incorporated into plasmalemma from rice (Oryza sativa L. cv. Dunghan Shali) and wheat (Triticum aestivum L. cv. GK Szeged) roots is presented. Plasmalemma‐rich microsomal fractions of rice and wheat roots were prepared by centrifugation and final pellets were resuspended in buffer solution with pH values from 3 to 8 in the presence and absence of Ca2+. The effects of pH and Ca2+ on the hyperfine splitting extremum 2A11 were measured and compared to earlier influx experiments on the same roots. The possible contribution of passive ion transport to the permeability properties of these roots is discussed.
Tissue culture of Alhagi camelorum – a legume of high regenerative capacity
Authors: Bharal Shashi , Rashid A.
Published: April 2006

Alhagi camelorum cultures provide a system with a high propensity for plantlet regeneration from root, hypocotyl, stem, and leaf explants. Excluding leaf explants, all explants regenerate to form shoot‐buds on a simple basal medium suggesting a differential morphogenic potential of different parts of the same plant. All parts of the plant including leaves, form shoot‐buds on cytokinin‐containing media which markedly promote shoot‐bud differentiation, alone or in combination with indoleacetic acid or naphthaleneacetic acid. Rooting occurs on media containing indoleacetic acid and naphthaleneacetic acid. 2, 4‐Dichlorophenoxyacetic acid is inhibitory for differentiation and induces callusing. Callus induced on benzylaminopurine and 2,4‐dichlorophenoxyacetic acid differentiates to form shoot‐buds on transfer to cytokinin‐containing medium. Upon transfer to basal medium shoots produce roots. Plants have been transferred to soil.
Acetylene reduction and respiration of bacteroids isolated from French‐beans receiving nitrate
Authors: Trinchant Jean‐Charles , Rigaud Jean
Published: April 2006

The competition between combined nitrogen and nitrogen fixation in legumes was studied after a 24 h exposure of nodulated French‐beans to nitrate. Acetylene reduction by bacteroids was significantly inhibited and even nitrogenase extracted from nitrate‐treated plant nodules showed reduced activity. Sensitivity to nitrate was directly related to nodule age and also increased with increasing oxygen tensions in the bacteroid incubations with or without a gas phase; it was particularly marked when glucose was used in place of succinate as energy‐yielding substrate. Bacteroid respiration was also depressed by nitrate‐treatment of the plants, leading to diminished acetylene reduction and this effect increased with increasing oxygen concentrations. Added oxyleghemoglobin partly restored oxygen consumption and acetylene reduction by bacteroid suspensions.
The effect of phytochrome and white light of high and low intensity on the uptake and distribution of 14C‐labelled kinetin in radish seedlings (Raphanus sativus)
Authors: Buschmann C. , Grumbach K.
Published: April 2006

The influence of light intensity and phytochrome on the uptake of 14C‐kinetin (6‐furfurylamino‐[8‐ 14C]‐purine) by the plant and the translocation of the phytochrome between the roots, the hypocotyl and the cotyledons were investigated with radish seedlings (Raphanus sativus L. cv. Saxa Treib) grown in the dark or under white light of high (20,000 lux, 90 W m−2) or low intensity (2,000 lux, 14 W m−2). The highest uptake of labelled kinetin was found in plants grown in continuous darkness. The total uptake of kinetin was decreased by strong light and to a finally higher extent by weak light. Under white light most of the kinetin accumulated in the root, whereas in the dark an enhanced translocation of the phytohormone into the cotyledons was observed. In etiolated radish seedlings, light acting on phytochrome (daily 5 min red or far red light pulses) decreased the translocation of 14C‐kinetin into the cotyledons. Under far red light a pronounced uptake of the phytohormone into the roots was found. The data are discussed with regard to the interaction of light and phytohormones on plant development.
Release and refixation of ammonia during photorespiration
Authors: Bergman Anders , Gardeström Per , Ericson Ingemar
Published: April 2006

Photorespiratory ammonia metabolism in isolated spinach (Spinacia oleracea L. cv. Viking II) mitochondria was measured using a selective ammonia electrode. The mitochondria showed high rates of ammonia production in the presence of glycine. The isolated mitochondria contained less than 0.02% of the glutamine synthetase activity present in the original homogenate and no significant reassimilation of the released ammonia could be observed with added glutamate or α‐ketogluterate. Exogenous added glutamine synthetase did reassimilate the released ammonia. In a recombinated system, with a chlorophyll to mitochondrial protein ratio equal to the ratio in vivo, chloroplasts could very effectively reassimilate the ammonia released in the mitochondria during oxidation of glycine.
Inhibition of auxin‐induced cell elongation by galactose
Authors: Yamamoto R. , Sakurai N. , Masuda Y.
Published: April 2006

Galactose at concentrations higher than 3 mM inhibited specifically auxin‐induced elongation of oat, wheat and rice coleoptile segments but not of pea and mung bean stem segments. Glucose, arabinose, rhamnose, xylose, mannose and glucosamine did not inhibit auxin‐induced elongation of coleoptile segments. Galactose inhibited auxin‐induced but not hydrogen ion‐induced growth.
Changes in potassium fluxes in cells of carrot storage tissue related to turgor pressure
Authors: Enoch Sarai , Glinka Zvi
Published: April 2006

The effect of increasing external osmotic pressure on potassium fluxes in aged and fresh‐cut discs of Daucus carota L. storage tissue was investigated. An increase of the external osmotic pressure by 5 bars of mannitol solution increased the rate of K+ net uptake of aged discs to 180% of their control rate. At 3°C and in 0.1 mM azide, in which a net efflux of potassium was observed, the mannitol treatment caused a reduction in the net efflux. In fresh‐cut discs, in which the capability of net influx was rather low and a substantial net release of potassium was noted, the increase in the external osmotic pressure by mannitol caused a 70% inhibition in the net efflux. This effect was also observed at 3°C.

Measurements of separate fluxes confirmed the assumption that the mannitol treatment brought about two distinct effects on K+ fluxes: (a) raised the metabolically‐dependent influx and (b) lowered the membrane permeability‐dependent efflux. When a permeating solute (ethylene glycol) was used instead of mannitol, no effect on K+ flux was detectable. Reasons are given for relating the observed changes in K+ fluxes to the reduction in turgor pressure of the cells.
Differences in the nature of thermodormancy and far‐red dormancy in lettuce seeds
Authors: Blaauw‐Jansen G.
Published: April 2006

Lettuce seeds cv. Noran germinate at 23°C in light as well as in darkness. However dormancy can be induced either by a long exposure (24 h) to far‐red radiation or by an exposure of 48–72 h to a temperature of 37°C. The difference in response of these two types of dormant seeds to conditions inducing germination indicate that in both types Pfr is inactivated, but that a dark process required for immediate action of Pfr does not proceed at 37°C as it does during far‐red radiation.
Adventitious rooting in hypocotyls of sunflower (Helianthus annuus) seedlings
Authors: Fabijan Dorothy , Taylor John S. , Reid David M.
Published: April 2006

The effect of brief application (usually for 3 h) of various growth regulators and their antagonists on the production of adventitious root primordia in sunflower hypocotyls over a 3 day period, was investigated. Gibberellic acid inhibited, while an inhibitor of gibberellin biosynthesis promoted rooting. Low concentrations of cytokinins increased, but higher levels inhibited primordia formation. Auxin was able to stimulate or inhibit root production, depending upon the quantity applied, and triiodobenzoic acid applied to the top of the hypocotyls lowered the rate of root formation.

From experiments in which benzyladenine, silver nitrate and benzyl isothiocyanate were supplied to the hypocotyl for various 3 h periods after root removal, we concluded that some of the important events necessary for adventitious root production occur during the first few hours after excision of the original root system. We also suggest that the hypocotyl cells on the first day go through a phase during which primordia production is blocked by endogenous ethylene and on the second day enter a phase during which endogenous ethylene promotes rooting.
Coniferyl alcohol, sinapyl alcohol and scopoletin in tobacco callus tissue during growth of a subculture
Authors: Andersen Roger A. , Kemp Thomas R. , Vaughn Thomas H.
Published: April 2006

Coniferyl and sinapyl alcohols were isolated, identified and quantitatively determined as unbound (or weakly bound) phenylpropanoids in neutral hot‐water extracts of Nicotiana tabacum L. callus tissue. This is the first identification of these alcohols in cultured tobacco callus. Scopoletin was also detected in these extracts, and it was the most abundant of these three phenylpropanoids with concentrations that ranged from 50–119 μg/g dry wt. Coniferyl alcohol (17–34 μg/g dry wt.) and sinapyl alcohol (23–35 μg/g dry wt.) were present in nearly equimolar concentration ratios and at levels which were about half those determined for unbound (or weakly bound) scopoletin. The amount of scopoletin extracted increased about 10 times when 1 M HCl‐50% methanol ‐ 0.3% ascorbic acid was used as the extractant. This indicated that most scopoletin moieties were strongly bound, perhaps by acid‐hydrolyzable linkage. Coniferyl alcohol and sinapyl alcohol were not found in the acid extracts, presumably because they were acid‐labile. In general, the concentration of each endogenous unbound (or weakly bound) phenylpropanoid appeared to remain relatively constant throughout the growth phase of the subculture. The only exceptions to this were the relatively higher concentrations of scopoletin and coniferyl alcohol present during the initial 0–2 weeks of subculture.
Nitrate assimilation and nitrogen circulation in Austrian pine
Authors: Martin Francis , Chemardin Michel , Gadal Pierre
Published: April 2006

Nitrate uptake, reduction and translocation were examined in 5‐week‐old Austrian pines (Pinus nigra Arnold var. nigricans Host.) during exposure to 5 mM NaNO3. The rate of nitrate uptake was linear during the 7 h light period. 15N‐NO3− was detected in all parts of the pine except in the needles. By the 7th hour, 43% of the absorbed nitrate had been reduced, and this increased to 64% by the 24th hour. The major part of the total reduction occurred in the roots at this growth stage. Accumulation of 15N in reduced soluble and insoluble fractions was more prevalent in roots than in shoots. In the needles, the translocated nitrogen was mainly incorporated into the insoluble fraction. It is likely that most of the nitrogen from nitrate was transported from the roots to the aerial organs as organic nitrogen; however part of the upward nitrogen flux took place as nitrate ions.

An experiment in which an exposure for 24 h to 5 mM Na15NO3 was followed by 13 days exposure to Na14NO3 (pulse chase experiment) revealed a half time of about 1 day for depletion of root nitrate. A large part of this depletion was due to the loss of 15N‐NO3− to the nutrient solution. The remaining pool of 15N‐nitrate was partitioned between a metabolically inactive and an active pool. During the chase period, the simultaneous decrease of 15N‐incorporation in the soluble N fraction and increase in the insoluble N fraction in different pine parts, particularly in the needles, suggested that protein synthesis occurred mostly in young tissues of the shoot and was the major sink of the newly absorbed 15N‐NO3.
Temperature dependence of the barley root plasma membrane‐bound Ca2+‐ and Mg2+‐dependent ATPase
Authors: Caldwell Charles R. , Haug Alfred
Published: April 2006

Arrhenius plots of the maximal velocities for the Ca2+‐and Mg2+‐dependent ATPase activities found in a plasma membrane‐rich microsome fraction isolated from the roots of barley (Hordeum vulgare L. cv. Conquest) were nonlinear. Arrhenius plot analyses using a relation which produced curvilinear Arrhenius plots accurately fit the data and allowed the calculation of the activation enthalpies and molar heat capacities of activation. The temperature dependence of the computed Km values for the Ca2+‐ and Mg2+‐dependent ATPase activities was complex, with the highest enzyme‐substrate affinities being obtained near the barley seedling growth temperature (16°C). Using electron paramagnetic resonance spectroscopy with amphiphilic cationic and anionic spin probes, it was possible to demonstrate that temperature changes and increasing Ca2+ concentrations could alter the mobility of the membrane lipid polar head groups. Inhibition of the ATPase activities by high levels of Ca2+ may result from a Ca2+‐induced reduction in the lipid polar head group mobility. The possible role of lipid polar head group‐protein interactions in the complex temperature dependence of the barley root ATPase kinetic constants is discussed.
Effect of ABA, fusicoccin and thiourea on germination and K+ and glucose uptake in chick‐pea seeds at different temperatures
Authors: Aldasoro Juan José , Matilla Angel , Nicolás Gregorio
Published: April 2006

Germination and growth of seeds of Cicer arietinum L. are retarded or inhibited either by temperatures above 30°C or by the presence of abscisic acid (ABA). Both treatments affect the uptake of K+ and glucose. ABA may affect the properties of the cell membrane or the kinetics of the enzymes bound to it. Fusicoccin (FC) and thiourea (TU) are to a greater or lesser extent able to counteract the inhibition produced by ABA and high temperatures. Both FC and TU increase the uptake of K+ by the embryonic axis. FC seems to act directly on H+ extrusion, but the mode of action of TU appears to be different. The results seem to indicate the importance of the activation of the ion transport process for the growth of the embryonic axis during early germination, and suggest a control of the growth of the embryo by part of the cotyledons. Physiological inhibitors such as ABA might be implied in the control mechanism.