bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory for growth of plants derived from the nitrogen productivity concept
Authors: Ågren Göran I.
Published: April 2006

A theory is developed on the assumption that growth of plants is determined by the current amount of nitrogen in the plants. The nitrogen‐growth relation is formalized in the nitrogen productivity concept (amount of biomass produced per amount of nitrogen in the biomass and per unit of time), which is essentially a constant for a given species under fixed environmental conditions. A number of results follow for increases in whole plant biomass: (A) The relative growth rate is a linear function of the internal nitrogen concentration. (B) The maximal relative growth rate uniquely determines the scaling of the time axis. (C) Exponential growth is consistent only with stable internal nitrogen concentration. Dose‐response curves expressed in reduced variables (the ratio between a variable and the same variable for a plant growing under optimal conditions) are universal, so that all species and all environmental conditions yield the same curve. This is confirmed by experimental data. The shape (linear, exponential, etc.) of the nitrogen uptake curve is the only parameter differentiating these universal curves. The Mitscherlich curve or variations of it can be fitted very closely to the derived dose‐response curves, except under exponential growth. A conclusion drawn from the analysis is that the results of nutrition experiments cannot be properly interpreted unless the variation with time of the amount of nitrogen in the plant is known. The theory can be extended to more complex situations, for example, time‐varying environmental conditions.
The localization of serine hydroxymethyltransferase in leaves of C3 and C4 species
Authors: Gardeström Per , Edwards Gerald E. , Henricson Dag , Ericson Ingemar
Published: April 2006

The intracellular distribution of serine hydroxymethyltransferase (EC 2.1.2.1) was studied in young wheat (Triticum aestivum L. cv. Starke II) leaves by fractionation of protoplasts and further purification of peroxisomes and chloroplasts. Essentially all of the activity in wheat leaves was located in the mitochondria. Within the mitochondria the enzyme was mainly in the matrix as shown by centrifugation of sonicated wheat mitochondria. In the C4 plants, Zea mays (L. cv. Earliking), Panicum miliaceum and Panicum maximum (cv. Australia) belonging to different C4 types, serine hydroxymethyltransferase was almost exclusively found in bundle sheath cells. The location of this enzyme in leaves is consistent with its role relative to glycine decarboxylation during photorespiration.
Optical properties of Lactuca and Taraxacum seed and fruit coats: Their role as light filters
Authors: Widell Karl‐Olof , Vogelmann Thomas C.
Published: April 2006

The optical properties of seed and fruit coats were examined from several varieties of light‐sensitive achenes. Taraxacum vulgare L. and Lactuca sativa L. cv. Grand Rapids achenes with dark fruit coats and L. sativa cvs Huvudsallat and Issallat with white fruit coats were examined. Transmission spectra varied among the different achenes: white fruit coats of Lactuca acted as neutral density filters between 450 and 780 nm, whereas Taraxacum transmitted 2–36% in this region. The ribbed fruit coat structure greatly affected transmission so that at different locations in the same coat, transmission varied between 20 to 80% at 660 and 730 nm. Fruit coats of Grand Rapids lettuce and Taraxacum transmitted more far‐red than red light with T660/T730 ratios of 0.8 and 0.4, respectively. The relationship between the optical properties of fruit coats and light‐stimulated germination is discussed.
Initial stages in the course of adventitious bud formation on embryos of Picea abies
Authors: von Arnold Sara , Eriksson Tage
Published: April 2006

Adventitious buds on embryos of Picea abies (L.) Karst. developed after a pulse treatment with 250 μM benzyladenine (BA) of pH 5.5 for 2 h. Light and temperature regimes were not critical during the initial stages. Adventitious buds developed faster after a pulse treatment and the variation among different experiments was lower compared to when the embryos were cultured on media supplemented with BA. Various stages of the differentiation of adventitious buds were identified: stage 1 ‐ appearance of meristematic centres (approximately the first two weeks); stage 2 ‐ development of adventitious bud primordia (approximately the third week); stage 3 ‐ adventitious bud development (from approximately the 4th to the 8th week). This system may be used for further studies on bud differentiation.
Photosensitivity of seedlings differing in their potential to synthesize anthocyanin
Authors: Drumm‐Herrel Helga , Mohr Hans
Published: April 2006

In the present report the suggestion (Paech, K. 1950. Biochemie und Physiologie der sekundären Pflanzenstoffe. ‐ Springer, Berlin, pp. 201–203) was tested that the photosynthetic apparatus requires light protection during the early phase of its development and that this is the reason (in a teleonomic sense) for the transient formation of large amounts of juvenile anthocyanin in outer tissue layers of seedlings and young leaves of deciduous trees and shrubs. Seedlings of two species (Sinapis alba L. and Sesamum indicum L.) which differ in their potential to produce anthocyanin were compared under identical light conditions. The results obtained are compatible with the idea that juvenile anthocyanins are involved in photoprotection. However, the experimental results also indicate that full photostability of the plastid is attained ‐ irrespective of the presence or absence of anthocyanin ‐ once a certain amount of chlorophyll has been accumulated. Thus, photosensitivity of a seedling under natural light conditions is restricted to an early phase of development prior to intense greening.
L‐Asparaginase activity in Leptosphaeria michotii. Isolation and properties of two forms of the enzyme
Authors: Jerebzoff‐Quintin Simonne , Jerebzoff Stéphan
Published: April 2006

The properties of L‐asparaginase (EC 3.5.1.1) in Leptosphaeria michotii (West) Sacc., which has previously been shown to have an activity rhythm, were analyzed. Two forms of L‐asparaginase were isolated from acetic acid and ammonium sulfate fractionations followed by DEAE‐Sephacel chromatography. The activity of L‐asparaginase changed rhythmically with the same period as that of crude extracts, but the rhythms of the two enzyme forms were out of phase. The two asparaginase forms differed in their isoelectric points and the substrate concentrations for attaining half‐maximal velocity; non‐Michaelis‐Menten kinetics for hydrolysis of L‐asparagine were observed. Analyses of asparaginase form II by polyacrylamide gel electrophoresis showed that four proteins, irrespective of the phase of the activity rhythm at which the enzyme was extracted, could be detected: asparaginase oligomer (Mr 130 000 to 140 000), its dimer, an aggregate (Mr 500 000 to 600 000) having a low asparaginase activity, and a protein (Mr 60 000) without asparaginase activity; the same proteins were found in asparaginase form I. These results indicate that L. michotii asparaginase could be implicated in a protein complex.
Diurnal changes in sucrose phosphate synthase activity in leaves
Authors: Huber S. C. , Kerr P. S. , Rufty T. W.
Published: April 2006

Studies were conducted to identify and compare diurnal changes in sucrose phosphate synthase (EC 2.4.1.14) activity in leaves of different species, and the effect of nitrogen nutrition on the rhythm in soybean [Glycine max (L). Merr] leaves. In recently expanded corn (Zea mays L.) leaves, a single peak of enzyme activity was observed at the beginning of the photoperiod. A similar pattern was observed in older corn leaves, but activities (leaf fresh weight basis) were lower. In recently expanded pea (Pisum sativum L.) and soybean leaves, two peaks of sucrose phosphate synthase activity were observed over a 24‐h light:dark period, one at the beginning and one at the end of the photoperiod. A similar pattern was observed in older soybean leaves, but activities were generally lower and the amplitude of the changes was reduced. In a separate experiment, soybean plants were grown in the greenhouse with either 2 or 10 mM nitrate. The high‐N plants had higher rates of photosynthesis and translocation, and greater activities of sucrose phosphate synthase in leaf extracts, compared to low‐N plants. Over both experiments with soybeans, changes in sucrose phosphate synthase activity during the photoperiod were closely aligned with changes in translocation rate.
Organic free radical levels in seeds and pollen: The effects of hydration and aging
Authors: Priestley David A. , Werner Brenda G. , Leopold A. Carl , McBride Murray B.
Published: April 2006

In view of their possible role in oxidative deterioration of seeds and pollen, organic free radicals were measured by electron spin resonance in embryonic axes and cotyledons of soybean [Glycine max (L.) Merr], embryo and endosperm fractions of corn [Zea mays L.] and pollen of cattail [Typha latifolia L.]. A pronounced decline in the radical signal ensued when hydration increased above about 7% (wet weight basis) in both the seed materials and in pollen. Moderate hydration of the soybean axis followed by drying led to a small decrease in organic free radicals compared to untreated material, especially if the desiccation step was performed under nitrogen. In a comparison of soybeans of various ages under normal storage, organic free radical levels in the axis showed little or no increase with age. In marked contrast, over 5 days of accelerated aging at 40°C and near‐saturating humidity, organic radical levels approximately doubled in the axis. This pronounced increase in free radical content was not associated with a decrease in the proportion of polyunsaturated fatty acids. The data suggest that hydration of seed and pollen causes a release of free radicals from the trapped state.
Polyribosome metabolism, growth and water status in the growing tissues of osmotically stressed plant seedlings
Authors: Mason H. S. , Matsuda K.
Published: April 2006

Relationships between growth of osmotically stressed intact seedlings and polyribosome levels and water status of growing tissues were examined. Sudden exposure of barley (Hordeum vulgare L. cv. Arivat) roots to a solution of −0.8 MPa polyethylene glycol caused leaf growth to stop almost immedately, but growth resumed at a much lower rate after 0.5–1 h. In the growing region of leaves, the polyribosome: total ribosome ratio of free (non‐membrane‐bound) ribosomes was significantly reduced after 15 min stress, but a decrease in the large polyribosome:total polyribosome ratio occurred only after 1–2 h. Membrane‐bound and free polyribosome levels both decreased to 70% of unstressed control values after 4 h stress. Recovery of total polyribosomes occurred within 1 h after relief of 4 h stress, but required 3 h after relief of 24 h stress. Stress detectably reduced the water potential and osmotic potential of growing tissue within 0.5–1.0 h, and osmotic adjustment continued for up to 10 h. Recovery of water status was incomplete after 1 h relief of a 4 h stress. In contrast, expanded blade tissues of stressed plants underwent minor changes in water status and slow decreases in polyribosomes levels. These results confirm that growing tissues of barley leaves are selectively responsive to stress, and suggest that changes in growth, water status and polyribosome levels may be initiated by the same signal. Measurements of seedling growth, polyribosome levels and water status of growing tissues of barley and wheat (Triticum aestivum L. cv. Zaragoza) leaves, etiolated pea (Pisum sativum L. cv. Alaska) epicotyl and etiolated squash (Cucurbita pepo L. cv. Elite) hypocotyl stressed with polyethylene glycol solutions of −0.3 to −0.8 MPa for 12 h or more showed that polyribosome levels were highly correlated with seedling growth rate as well as with tissue water and osmotic potentials, while turgor remained unchanged. These results suggest that long‐term growth of osmotically stressed plants may be limited by a reduced capacity for protein synthesis in growing tissues and is not dictated by turgor loss.
Changes in enzyme activities involved in formation and interconversion of UDP‐sugars during the cell cycle in a synchronous culture of Catharanthus roseus
Authors: Amino Shin‐ichi , Takeuchi Yuichi , Komamine Atsushi
Published: April 2006

Changes in the activities of enzymes involved in UDP‐sugar formation [UDP‐glucose pyrophosphorylase (EC 2.7.7.9), sucrose synthase (EC 2.4.1.13) and UDP‐glucuronic acid pyrophosphorylase (EC 2.7.7.44)], and interconversion [UDP‐glucuse 4‐epimerase (EC 5.1.3.2), UDP‐glucose dehydrogenase (EC 1.1.1.22), UDP‐glucuronic acid decarboxylase (EC 4.1.1.35) and UDP‐xylose 4‐epimerase (EC 5.1.3.5)] were investigated during the cell cycle in a synchronous culture of Catharanthus roseus (L.) G. Don. The specific activities of UDP‐glucose pyrophosphorylase and UDP‐glucose 4‐epimerase increased in the G2 phase before the first cell division, and those of sucrose synthase, UDP‐glucose dehydrogenase and UDP‐glucuronic acid pyrophosphorylase increased in the G1 phase after the first cell division. However, during the cell cycle, UDP‐glucuronic acid decarboxylase and UDP‐xylose 4‐epimerase did not change significantly in their specific activities. Changes in enzyme activities are discussed in relation to those reported previously for cell wall composition (S. Amino et al. 1984. Physiologia Plantarum 60: 326–332).
Photoperiod and light quality effects on rate of dark respiration and on photosynthetic capacity in developing seedlings of Chenopodium rubrum
Authors: Tsala G. , Frosch S. , Bonzon M. , Bergfeld R. , Kossmann I. , Greppin H. , Wagner E.
Published: April 2006

Development and acclimation of energy transduction were studied in seedlings of Chenopodium rubrum L. ecotype selection 184 (50° 10′ N; 105° 35′ W) in response to photomorphogenic and photoperiodic treatments. Dark respiration and photosynthetic capacity [nmol O2 (pair of cotyledons)−1 h−1] were measured with an oxygen electrode. Changes in chloroplast ultrastructure were analyzed concomitantly. After germination, seedlings were grown at constant temperature either in darkness or in continuous light (white, red, far‐red and blue) or were subjected to diurnal cycles of light/dark or changes in light quality. Dark respiration was low in far‐red light treated seedlings. In red light treated seedlings dark respiration was high and the mean value did not depend on fluence rate or photoperiod. Blue light stimulated transitorily and modulated dark respiration in photoperiodic cycles. Photosynthetic capacity was reduced by far‐red light and increased by red light. In response to blue light photosynthetic capacity increased, with indications of a requirement for continuous energy input. Phytochrome and a separate blue light receptor seemed to be involved. In continuous red light a clear cut circadian rhythm of dark respiration was observed. Blue light had a specific effect on chloroplast structure.
Anatomy of chlorenchyma cells in maize lines developed at different latitudes and grown at sub‐ and supraoptimal temperatures
Authors: Stamp P. , Thiraporn R. , Geisler G.
Published: April 2006

Three inbred lines of maize (Zea mays L.) from cool temperate regions and three from warm regions were grown at 14, 22, 30 and 38°C up to the same physiological age, the full expansion of the third leaf. The laminae of the second leaf were studied for anatomical traits of the chlorenchyma. The genotypic variation was considerable for all properties. Nevertheless, general temperature response curves existed for many properties with few deviations of single lines. The cross‐sectional area of mesophyll cells and cross‐sectional area and number of chloroplasts declined from 14 to 22°C, increased up to 30°C and declined again up to 38°C. The ratio of shortest to longest diameter of chloroplasts was low in mesophyll cells at intermediate temperatures, and maximum in bundle sheath cells at 30°C. Temperature response curves for other properties of the bundle sheath cells were predominantly genotype specific. Chloroplasts in bundle sheath cells were sometimes smaller than those of mesophyll cells, dependent on temperature and genotype. Values of lines from cool temperate and warm regions were mostly overlapping, but the cross‐sectional area of mesophyll cells was larger in the latter than in the former lines at low temperature. The results are discussed in relation to the expression of photosynthetic properties.
Controlling plant growth via the gibberellin biosynthesis system – II. Biochemical and physiological alterations in apple seedlings
Authors: Wang S. Y. , Byun J. K. , Steffens G. L.
Published: April 2006

Some physiological and biochemical changes in apple seedlings (Malus domestica Borkh cv. ‘York Imperial’) caused by an inhibitor of gibberellin biosynthesis, paclobutrazol [(2RS, 3RS)‐1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1,2,4‐triazol‐1‐yl) pentan‐3‐ol], were determined. Paclobutrazol shifted assimilate partitioning from leaves to roots, increased carbohydrates in all parts of apple seedlings, increased chlorophyll content on a leaf area basis, increased soluble protein in leaves, increased mineral element concentration in leaf tissue and increased root respiration. Foliar application of gibberellic acid (GA3) counteracted the effects induced by paclobutrazol.
Effect of potassium status on K+ (Rb)+ uptake and transport in sunflower roots
Authors: Diaz de la Guardia Manuel , Fournier José M. , Benlloch Manuel
Published: April 2006

Young sunflower plants (Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K+ levels (0.25 and 2.5 mM) were used to study the effect of K+ content in the root on uptake and transport of K+ to the exuding stream of decapitated plants. Roots of plants grown in low K+ gave higher exudation flux, higher K+ concentration in exudate and higher K+ flux than high K+ roots. After 6 h of uptake the K+ flux in low K+ roots was about three times that in high K+ roots. When the roots were kept in a nutrient solution in which Rb+ replaced K+, low K+ roots exuded much more Rb+ than K+ after the first 2 h, whereas high K+ roots exuded about similar amounts of K+ and Rb+. In intact plants grown at three different K+ levels (0.1, 1.0 and 10.0 mM), there was an inverse relationship between the K+ level in the nutrient solution and the Rb+ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes.
Mechanism for Cd2+ inhibition of (K++ Mg2+)ATPase activity and K+ (86Rb+) uptake join roots of sugar beet (Beta vulgaris)
Authors: Lindberg Sylvia , Wingstrand Göran
Published: April 2006

Steady state kinetics were used to examine the influence of Cd2+ both on K+ stimulation of a membrane‐bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K+(86Rb+) uptake in intact or excised beet roots. The in vitro effect of Cd2+ was studied both on a 12000–25000 g root fraction of the (Na++K++Mg2+)ATPase and on the ATPase when further purified by an aqueous polymer two‐phase system. The observed data can be summarized as follows: 1) Cd2+ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd2+ at concentrations <100 μM inhibits the specific K+ activation at both high and low affinity sites for K+. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K+ <5 mM, the inhibition by Cd2+ with respect to K+ is uncompetitive. In the presence of MgATP and K+ >10 μM, the inhibition by Cd2+ is competitive. 3) At the low concentrations of K+, Cd2+ also inhibits the 2,4‐dinitrophenol(DNP)‐sensitive (metabolic) K+(86Rb+) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP‐insensitive (non metabolic) K+(86Rb+) uptake is little influenced by Cd2+. As Cd2+ inhibits the metabolic uptake of K+(86Rb+) and the K+ activation of the ATPase in the same way at low concentrations of K+, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K+ is low, the presence of Cd2+ could be disadvantageous.
Calmodulin is not involved in the regulation of exogenous NADH oxidation by plant mitochondria
Authors: Schwitzguébel Jean‐Paul , Nguyen Tan Duc , Siegenthaler Paul‐André
Published: April 2006

The oxidation of exogenous NADH by mitochondria from potato (Solanum tuberosum L., cv. Bintje) tubers, measured with different electron acceptors, oxygen, cytochrome c, duroquinone and ubiquinone 1, was greatly enhanced under high salt conditions compared to low salt conditions, confirming the stimulatory effect of electrostatic screeening of negative membrane charges by cations. In addition to this nonspecific stimulation, the oxidation of exogenous NADH showed a specific dependence on Ca2+. Results presented here suggest that calmodulin was not directly involved in the regulation of exogenous NADH oxidation by potato mitochondria: (1) Calmodulin antagonists were found to inhibit electron flow at several sites in a nonspecific manner. (2) Using a phenothiazine‐Affi Gel column, it was not possible to demonstrate the presence of calmodulin in Triton X‐100 solubilized mitochondria. (3) Fractions eluted from a calmodulin‐Sepharose column with EGTA [ethyleneglycolbis (β‐aminoethylether)‐N, N, N′, N′‐tetraacetic acid] did not display any activity related to mitochondrial electron transport, suggesting that NADH dehydrogenase had no specific affinity for calmodulin. The possible indirect involvement of calmodulin in the regulation of exogenous NADH oxidation by Ca2+ is discussed.
Effects of saponin extracts from Solanum elaeagnifotium fruits on ion uptake by clover seedlings
Authors: Agüero Marta S. , Boland Ricardo L.
Published: April 2006

Solanum elaeagnifolium Cav. fruits contain high concentrations of steroidal saponins. Treatment of 3‐day‐old clover seedlings with aqueous fruit extracts modified Ca2+ uptake without significantly altering K+ and H2PO4− uptake. The extracts increased Ca2+ uptake in the concentration range of 0.2 to 20 mM Ca2+. Uptake curves could be represented by two phases. In the lower phase (0.2‐1.0 mM Ca2+), this change could be related to an increase in Vmax. Pretreatment of seedlings with saponin extracts significantly reduced ATP‐dependent Ca2+ uptake and Ca2+‐dependent ATPase activity in a fraction isolated from root homogenates by centrifugation at 1500 g for 15 min. Saponins purified from S. eleagnifolium extracts by thin‐layer chromatography modified in vitro the Ca2+‐ATPase activity of this fraction, indicating that the steroid may act directly on Ca2+ transport across membranes.
l‐Tryptophan metabolism in wound‐activated and Agrobacterium tumefaciens‐transformed potato tuber cells
Authors: Rausch Thomas , Minocha Subhash C. , Hilgenberg Willy , Kahl Günter
Published: April 2006

The in vivo metabolism of L‐tryptophan in wound‐activated and Agrobacterium tumefaciens, strain C 58, transformed tissues of white potato tubers (Solanum tuberosum L. cv. Saskia) was investigated. The following metabolites of L‐tryptophan were identified in both tissues by co‐chromatography with authentic standards in several thinlayer chromotography (TLC) and high pressure liquid chromatographic (HPLC) systems: indole‐3‐acetic acid (IAA), indole‐3‐acetaldehyde, indole‐3‐ethanol, indole‐3‐acetamide and tryptamine. Labelled indole‐3‐acetaldoxime was only found in transformed tissue. Crown gall tissue generally incorporated [14C]‐L‐tryptophan into precursors of IAA at a distinctly higher rate than did wound tissue. Tryptamine and indole‐3‐ethanol accumulated about ten‐fold more label in crown gall cells than in cells from wounded tissue. The incorporation of radioactivity into indole‐3‐acetamide as determined by 2 consecutive TLC systems followed by HPLC analysis was rather low, though consistently observed in both tissues. An indole‐3‐acetamide hydrolyzing enzyme, the putative product of gene 2 on the T‐DNA, could be extracted from the transformed tissue only. The indole‐3‐ethanol level was 4.3 nmol (g dry weight)−1 and 41 nmol (g dry weight)−1 for wounded tissue and primary crown gall tissue, respectively, as determined by HPLC with a [14C]‐labelled internal standard. The experiments are critically discussed in relation to recent reports on a T‐DNA encoded enzyme of IAA biosynthesis in crown gall tumors.
Respiration of crop species under CO2 enrichment
Authors: Gifford Roger M. , Lambers Hans , Morison James I. L.
Published: April 2006

Respiratory characteristics of wheat (Triticum aestivum L. cvs Gabo and WW15), mung bean (Vigna radiata L. Wilczek cv. Celera) and sunflower (Helianthus annuus L. cv. Sunfola) were studied in plants grown under a normal CO2 concentration and in air containing an additional 340 (or 250) μl l−1 CO2. Such an increase in global atmospheric CO2 concentration has been forecast for about the middle of the next century. The aim was to measure the effect of high CO2 on respiration and its components. Polarographic and, with wheat, CO2 exchange techniques were used. The capacity of the alternative pathway of respiration in roots was determined polarographically in the presence of 0.1 mM KCN. The actual rate of alternative pathway respiration was assessed by reduction in oxygen consumption caused by 10 mM salicylhydroxamic acid.

Each species responded differently. In wheat, growth in high atmospheric CO2 was associated with up to 45% reduction in respiration by both roots and whole plants. Use of respiratory inhibitors in polarographic measurements on wheat roots implicated reduction in the degree of engagement of the alternative pathway as a major contributor to this reduced respiratory activity of high‐CO2 plants. No change was found in the total sugar content per unit wheat root dry weight as a result of high CO2. In none of the species was there an increase in the absolute, or relative, contribution by the alternative pathway to total respiration of the root systems. Thus the improved photosynthetic assimilate supply of plants grown in high CO2 did not lead to increased diversion of carbon through the non‐phosphorylating alternative pathway of respiration in the root. On the contrary, in wheat grown in high CO2 the reduced loss of carbon through that route must have contributed to their larger dry weight.
The kinetics and thermal stability of phosphogluco‐isomerase isozymes of ryegrasses (Lolium spp.)
Authors: Jones Thomas W. A.
Published: April 2006

The Michaelis constants (Km) and activation energies (Ea) for allozymes of cytosolic phosphogluco‐isomerase (PGI‐2; EC 5.3.1.9) from ryegrasses (Lolium perenne L., Lolium multiflorum Lam. and interspecific hybrids) have been investigated. Differences were found between the allelic isozymes, but intra‐allelic variations were at least as large. The thermal stability of the isozymes also varied, with the most commonly occurring form (the b‐allozyme) having the highest stability at 50°C. Some possible explanations for these findings are discussed and the implications for plant breeders outlined.
Metabolic significance of indoleacetylaspartic acid in developing cotton leaves
Authors: Elkinawy Mahasen
Published: April 2006

The formation of indoleacetylaspartic acid (IAAsp) and its metabolic significance were studied in the developing cotyledons and primary two leaves of cotton (Gossypium barbadense L. cv. Giza 68, long staple). Levels of indoleacetic acid (IAA), IAAsp, bound IAA and degradation of tryptophan (Trp)‐carboxyl‐[14C] by enzyme extracts were estimated from leaf emergence to full expansion. The patterns were also followed in the two cotyledons before and after germination. The results suggest synthesis of IAAsp in response to either active Trp‐conversion or hydrolysis of bound IAA. Ester IAA accumulating during leaf expansion, or other bound forms of IAA initially stored in the cotyledons may be the substances hydrolysed. IAAsp appears to be accumulated during phases of low demand and to be exhausted during phases of high demand on IAA. Synthesis and hydrolysis of the conjugate may, therefore, influence the steady state concentration of the hormone during leaf development.
Nitrogen acquisition in four co‐existing species from an upland acidic grassland
Authors: Atkinson Christopher J.
Published: April 2006

The concentration of both nitrate and ammonium nitrogen was measured in soil taken from an upland acidic (pH 4.5) grassland habitat, containing four co‐existing species, Deschampsia flexuosa (L.) Trin., Festuca ovina L., Juncus squarrosus L. and Nardus stricta L. Both nitrate and ammonium nitrogen were found to be present in the soil, in similarly small quantities. The effect of both sources of nitrogen on relative growth rate was studied, and an attempt was made to determine whether nitrate or ammonium nitrogen is the immediate source of nitrogen for these plants using assays of nitrate reductase (EC 1.6.6.2) and ammonium uptake. All four species showed larger growth rates on the same concentration of ammonium nitrogen compared to nitrate nitrogen. All species showed low activities of leaf nitrate reductase, even in plants grown on 18 mol nitrate m−3. Ammonium uptake activity appeared to be higher in species which showed the lowest nitrate reductase activity and least response to increasing nitrate concentration in the growth medium.
Conversion of sucrose to starch in the developing Pennisetum typhoides grain
Authors: Bhullar Sukhdev S. , Singh Rangil , Sital Jagjit S. , Bhatia Iqbal S.
Published: April 2006

Developing grains of pearl millet (Pennisetum typhoides Burm. S & H cv. PIB 155) were sampled and analyzed for starch and its free‐sugar precursors. The activities of invertase, sucrose‐ADP (UDP) glucosyl transferase and of α‐amylase and β‐amylase in relation to the rate of starch accumulation in the developing grain were assayed. By culturing detached ears, the incorporation of 14C from free sugar precursors to starch was studied. The starch content gradually increased until grain maturity. The rate of starch accumulation was maximum around 12 days after anthesis. Around this period, the activities of sucrose‐ADP(UDP) glucosyl transferase and α‐amylase, β‐amylase were also at a peak. Invertase activity was high during the early period of grain development but gradually declined as the grains matured. In the most actively metabolising milky grains, incorporation of 14C from [14C]‐sugars to starch was maximum in the mid mid‐milky grains. Addition of 20 mM K+ to the culture solution did not affect the incorporation of 14C from supplied sucrose to the free sugar pool and to the starch of the grain, but Mg2+ supply at 20 mM concentration lowered 14C incorporation from exogenous sucrose to grain free sugars, although the utilization of the latter for starch synthesis was enhanced.
ATP involvement in plant tissue responses to low temperature
Authors: Sobczyk Elzbieta Anna , Marszalek Anna , Kacperska Alina
Published: April 2006

The effects of chilling and freezing temperature on membrane permeability and ATP content were studied in the leaves of cucumber (Cucumis sativus L.) and winter rape (Brassica napus L. var. oleifera L.) leaves, grown at different temperatures. In the winter rape leaves, the endogenous ATP content was modified by application of dinitrophenol (DNP) solutions of different concentrations. The low temperature‐induced changes in membrane permeability (as monitored by the conductivity method) were found to be associated with ATP decrease, both in the chilling‐sensitive and chilling‐resistant (subjected to freezing) plants. In tissues showing reversible injuries, changes in ATP content preceded those in membrane permeability and the adenylate energy charge was affected slightly. In tissues showing irreversible membrane damage, the ATP content was always below 0.4 μmol (g dry weight)−1 and the adenylate energy charge was near 0.5. DNP treatment increased freezing sensitivity of winter rape leaves. In the cold‐hardened winter rape leaves, however, freezing and thawing did not significantly affect ATP content or the energy charge, although the specimen showed a rather large increase in membrane permeability. In these leaves ATP content recovered about 20 h after a freezing and thawing treatment. It is proposed that a decrease in ATP supply might be the primary reason for the membrane leakiness at low temperature, both in chilling‐sensitive and chilling‐resistant (subjected to freezing) plants. The conclusion is, however, not true for the cold‐acclimated, frostadapted cells.
The role of cell wall synthesis in sustained auxin‐induced growth
Authors: Brummell D. A. , Hall J. L.
Published: April 2006

The dependence of auxin‐induced growth on continued cell wall synthesis was investigated in stem segments of etiolated pea (Pisum sativum L. cv. Alaska) seedlings using the cell wall synthesis inhibitors monensin and 2,6‐dichlorobenzonitrile (DCB). Monensin (5 μM) potently inhibited indole‐3‐acetic acid (IAA)‐induced growth, particularly during the second hour of treatment, whereas growth in fusicoccin (FC) was inhibited much less effectively. Incorporation of [14C]‐glucose into both matrix and cellulose fractions of the wall showed a sharp increase beginning after about 60 min, this rise being promoted by both IAA and FC. Monensin inhibited this rise in incorporation of label and completely removed the promotion of this by IAA, although some promotion by FC remained. Monensin inhibited incorporation into cellulose in a manner similar to that into matrix, but the use of the apparently specific cellulose synthesis inhibitor DCB showed that cellulose synthesis could be strongly inhibited without effect on growth, at least in the short term. The results support the view that sustained auxin‐induced growth depends upon the incorporation of new matrix cell wall components into the wall.
Effect of tunicamycin on in vitro ripening of tomato pericarp tissue
Authors: Handa Avtar K. , Singh Narendra K. , Biggs M. Scott
Published: April 2006

Ripening of pericarp tissue from mature green, early breaker and late breaker stages of tomato (Lycopersicon esculentum Mill. cv. Dombito) fruit development was inhibitied by tunicamycin. Ripening was evaluated by lycopene accumulation, chlorophyll degradation, rate of ethylene production and cell wall‐bound polygalacturonase (EC 3.2.1.15) activity. Maximum inhibition of these ripening parameters occurred at a treatment of 240 μM tunicamycin for 2 h except for cell wall‐bound polygalacturonase activity, which was greatly inhibited by concentrations of 12 μ tunicamycin or higher. Tunicamycin treatment at 120 μM for 2 h inhibited the incorporation of [3H]‐mannose into macromolecules (about 70%) and pronase‐sensitive material (about 65%) and the incorporation of [3H]‐leucine into proteins (about 20%). Our results indicate that protein glycosylation plays an important role in the ripening of tomato pericarp tissue.
Changes in the levels of prenylquinones and tocopherols in Calendula officinalis during vegetation
Authors: Janiszowska Wirginia , Rygier Jolanta
Published: April 2006

For the first time changes in the levels of 5‐ and 6‐phytyltoluquinones and of 7‐ and 8‐methyltocols were investigated during the whole vegetation period of a higher plant Calendula officinalis L. cv. Radio. Besides, the changes in γ‐ and α‐tocopherols, γ‐and α‐tocopherolquinones, plastoquinone, ubiquinone and vitamin K1 were also studied. The concentrations of 5‐ and 6‐phytyltoluquinones increased rapidly in imbibed seeds, and equally rapidly decreased in one‐week‐old seedlings; whereas 7‐methyltocol decreased from germination and dropped to zero in the 3rd week. In contrast, plastoquinone, ubiquinone, 8‐methyltocol, α‐tocopherolquinone, α‐ and γ‐tocopherols increased continuously from the seeds to the flowering stage. During senescence their levels, except that of ubiquinone, decreased. The investigated compounds occurred not only in seeds and shoots but also in flowers. In the roots only ubiquinone and small amounts of α‐tocopherol were found. An increase in temperature from 20 to 29°C enhanced the level of α‐ and γ‐tocopherols 10 times in the shoots, and the level of δ‐tocopherol 7 times.
Autoinhibition of ethylene production in tobacco leaf discs: Enhancement of 1‐aminocyclopropane‐1‐carboxylic acid conjugation
Authors: Philosoph‐Hadas Sonia , Meir Shimon , Aharoni Nehemia
Published: April 2006

Ethylene biosynthesis in leaf discs of tobacco (Nicotiana tabacum L. cv. Xanthi), as measured by the conversion of L‐[3,4‐14C]‐methionine to 14C2H4, was markedly inhibited by exogenous ethylene. This inhibition was accompanied by a decrease in total (free + conjugated) content of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), most of which appeared in its conjugated inactive form. The autoinhibitory effect of ethylene was reversible and could be relieved by Ag+. The Ag+‐treated leaf discs, with or without ethylene, contained only free ACC at an increased level. The results suggest that in tobacco leaves, the autoinhibition of ethylene production resulted from reduction in the availability of free ACC, through both suppression of ACC formation and increased ACC conjugation.
Effect of silver ions and ethylene on auxin metabolism and auxininduced ethylene production in tobacco leaf discs
Authors: Aharoni Nehemia
Published: April 2006

The antagonistic effects of ethylene and Ag+ on the metabolism of [1‐14C]indole‐3‐acetic acid (IAA) and on the rates of ethylene production were studied in tobacco leaf discs (Nicotiana rustica var. Brasilia). During the first 10 h of incubation, Ag+‐pretreated leaf discs contained more free [14C]IAA than untreated ones due to decreased oxidative decarboxylation, and the discs also produced more ethylene. Exogenously supplied ethylene nullified these effects of Ag+. However, the most pronounced effect of Ag+ in increasing ethylene production, as well as the strongest antagonistic effect of exogenous ethylene, were found between 24 and 48 h of incubation. During this time span no effect on the level of free IAA and on its decarboxylation could be observed. It is suggested that ethylene exerted its autoinhibitory effect by a feedback control on the IAA‐induced ethylene biosynthesis. Possible mechanisms for the autoinhibitory effect of ethylene are discussed.
The light‐dependent regulation of gene expression during plastid development in higher plants
Authors: Harpster Mark , Apel Klaus
Published: April 2006

In recent years there has been a considerable increase in our understanding of the manner by which light affects gene expression during chloroplast development. In most systems that have been studied, light acts through sensitive photoreceptor molecules and quantitatively increases or represses the level of expression of specific nuclear‐and plastid‐encoded genes. Although the mechanisms are obscure, a picture is beginning to emerge in which the coordination of nuclear and plastid gene expression is controlled by regulatory mechanisms originating within their respective subcellular compartments. This review summarizes some of our current knowledge concerning the nature of light‐regulated gene expression in higher plants and provides a prospectus for future research in this area.
Effects of root restriction on growth correlations, water relations and senescence of alder seedlings
Authors: Tschaplinski Timothy James , Blake Terence John
Published: April 2006

Root restriction may be of importance for productivity in both forestry and agriculture. To study the physiological effects of root restriction in European alder (Alnus glutinosa Gaertn.), seedlings were grown in aerated liquid culture under one of four root volumes to induce the following levels of root restriction: 1.5, 6,16 and 500 ml. Root restriction for 96 days reduced shoot elongation, plant dry weight, leaf area and chlorophyll levels and increased leaf area/root dry weight ratio and correlative bud inhibition in seedlings. The initial reduction in root/shoot ratios of severely restricted seedlings was followed by a reduction in leaf water potential, the development of internal water deficits in the upper shoots, a reduction in stomatal opening and transpiration rates and, eventually, stomatal closure. Severe prolonged root restriction (1.5 ml root volume) resulted in a decline in seedling vigour and ultimately, senescence as determined by increased electrical impedance ratios, followed by visible leaf senescence and later, by whole plant senescence. Of the severely restricted seedlings, 40% were dead after 96 days of restriction. The results suggest that imbalanced root/shoot ratios caused the development of internal water stress and the consequent reduction in stomatal aperture, culminating in leaf and whole plant senescence.
The role of phosphorus in nitrogen fixation by young pea plants (Pisum sativum)
Authors: Jakobsen Iver
Published: April 2006

The influence of P on N2fixation and dry matter production of young pea (Pisum sativumL. cv. Bodil) plants grown in a soil‐sand mixture was investigated in growth cabinet experiments. Nodule dry weight, specific C2H2reduction and P concentration in shoots responded to P addition before any growth response could be observed. The P concentration in nodules responded only slightly to P addition. A supply of P to P‐deficient plants increased both the nodule dry weight, specific C2H2reduction and P concentration in shoots relatively faster than it increased shoot dry weight and P concentration in nodules. Combined N applied to plants when N2fixation had commenced, increased shoot dry weight only at the highest P levels. This indicates that the smaller plant growth at the low P levels did not result from N deficiency. The reduced nodulation and N2fixation in P‐deficient plants seem to be caused by impaired shoot metabolism and not by a direct effect of P deficiency of the nodules.
Changes in intracellular UDP‐sugar levels during the cell cycle in a synchronous culture of Catharanthus roseus
Authors: Amino Shin‐ichi , Takeuchi Yuichi , Komamine Atsushi
Published: April 2006

UDP‐sugar contents were measured using high performance liquid chromatography and gas chromatography during the cell cycle in a synchronous culture of Catharanthus roseus (L.) G. Don. UDP‐glucose, UDP‐galactose, UDP‐glucuronic acid, UDP‐xylose and UDP‐arabinose could be determined, and 75–90% of the UDP‐sugars were UDP‐glucose. The contents of UDP‐glucose and UDP‐galactose increased in the late G2‐M and the late S‐M phases, respectively, whereas UDP‐glucoronic acid and UDP‐arabinose increased in amount in the G1 phase. These changes in the levels of UDP‐sugars during the cell cycle generally correlated well with the changes in cell wall constituents and in the activities of the enzyme involved in synthesis and interconversion of UDP‐sugars reported by S. Amino et al. (Physiol. Plant. 1985. 64: 111–117).
Changes in synthetic activity of cell walls during the cell cycle in a synchronous culture of Catharanthus roseus
Authors: Amino Shin‐ichi , Takeuchi Yuichi , Komamine Atsushi
Published: April 2006

The incorporation rates of [14C] glucose into various fractions of the cell walls and into the sugar constituent of each fraction were investigated in a synchronous culture of Catharanthus roseus (L.) G. Don in order to elucidate the synthetic aspects of the cell walls during the cell cycle. Changes in the incorporation of radioactivity were closely correlated with changes in the amount of each cell wall fraction as well as with those in sugar composition as reported previously (S. Amino et al. Physiol. Plant. 60: 326–332, 1984). The specific activity of galactose was higher than that of other sugars throughout the cell cycle, and a temporary increase in the incorporation of radioactivity into all cell wall fractions except cellulose was observed just before the increase in cell numbers. The synthetic activities may play key roles in the regulation of cell wall polysaccharide dynamics during the cell cycle.
Homeostasis in cucumber plants during low temperature stress
Authors: Szaniawski Ryszard K.
Published: April 2006

Shoots, roots and whole plants of Cucumis sativus L. cv. Inspektowy Warszawski were subjected to different temperatures. The magnitude and direction of alterations of growth depended on the organ that was submitted to stress conditions. Changes in soluble protein level in leaves and in roots were inversely correlated with changes of total organic nitrogen level in both organs. In spite of differentiated temperature conditions between plant organs, the allometric coefficients and the ratio between maintenance respiration in shoot and in roots remained constant. Such constancy may be treated as an indicator of homeostasis of the whole‐plant system. The results point to the importance of both shoot and roots in the response of the plant to temperature stress.
Cysteine‐induced H2S emission, ATP depletion, and membrane electrical responses in oat coleoptiles
Authors: Kinraide Thomas B. , Staley Thomas E.
Published: April 2006

Incubation of oat (Avena sativa L. cv. Victory) coleoptile segments in 4 mM L‐cysteine reduced the tissue ATP level to 42 nmol (g fresh weight)−1 (35% of normal) over a 2 h period. Emissions of H2S accompanied this depletion in ATP suggesting an H2S production by desulfhydration of cysteine similar to that reported in other plants. Additions of exogenous H2S to the sections also caused ATP depletion. Aminooxyacetate, an inhibitor of cysteine desulfhydrase (EC 4.4.1.1), eliminated the cysteine‐induced H2S emission and the ATP depletion. Prolonged exposure to cysteine depressed the electrical polarity of the cell membrane from – 116 mV to –85 mV. That and other electrical responses appear to reflect a reduced capacity for ATP‐dependent H+ extrusion. These effects should be taken into account whenever cysteine is used in physiological experiments.
Characterization of membrane‐bound MgATPases, purified by aqueous two‐phase partitioning, from young sugar beet roots
Authors: Wingstrand Göran
Published: April 2006

Membrane‐bound MgATPase activity from roots of young sugar beet (Beta vulgaris L. cv. Monohill) was investigated in a membrane fraction purified by partition in an aqueous polymer two‐phase system. After two steps of “washing” with fresh bottom phase (rich in dextran), the polyethylene glycol rich top phase (U3) was practically free of mitochondrial membranes (cytochrome oxidase), and the remaining MgATPase activity showed high substrate specificity for ATP. An optimum for the MgATPase activity was found at pH 7. The activation by Na+ or K+ was strongest on the acid side without any observable shift in pH optimum. Oligomycin had no effect, but vanadate strongly inhibited the U3 MgATPase and the K+ activation was lost. The complex activation pattern achieved by varying the Na+/K+ ratio at constant total concentration was interpreted as a synergistic (Na++ K+)‐activation. The U3 fraction MgATP‐ase activity showed a 4‐fold increase in the presence of 0.01% Triton X‐100 implying that the MgATPase activity is located in vesicles of which 75% or more are sealed with the ATP binding site on the inside. Comparison with the properties of plasma membrane. ATPases from other plants indicated that the U3 fraction MgATPase was mainly of plasma membrane origin.
An effect of Na+ on K+ uptake in intact seedlings of Zea mays
Authors: Cheeseman John M.
Published: April 2006

Models for the regulation of K+ uptake in higher plant roots have become more complex as studies have moved from the level of excised low‐salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.

The uptake of K+ by low‐salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na+ concentration over a wide range. However, independence of Na+ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na+ in the uptake medium enhanced K+ uptake. In the presence of Na+, K+ uptake rates were similar in whole plants with high root K+ contents to rates in excised or intact, low‐salt roots.