bluuebunny/crossref_metadata_2025 huggingface dataset:
Inorganic nitrogen assimilation in the non‐N2‐fixing cyanobacterium Phormidium laminosum. I. Cellular levels of glutamine synthetase and NADPH‐dependent glutamate dehydrogenase
Authors: Martínez‐Bilbao Mercedes , Alaña Aitor , Arizmendi Jesús María , Serra Juan Luís
Published: May 2006

Cell‐free extracts of nitrate‐grown as well as of ammonium‐grown cells of the filamentous non‐nitrogen‐fixing cyanobacterium Phormidium laminosum (strain OH‐1‐p.Cl1) showed detectable levels of both glutamine synthetase (GS, EC 6.3.1.2) and NADPH‐dependent glutamate dehydrogenase (GDH, EC 1.4.1.4) activities. The GS level of nitrate‐grown cells was higher than that of ammonium‐grown cells, whereas the GDH level was higher in ammonium‐grown cells and depended on the external ammonium concentration. When nitrate‐grown cells were transferred to an ammonium‐containing medium, a decrease of GS and an increase of GDH specific activities occurred, even in the presence of nitrate. Conversely, when ammonia‐grown cells were transferred to a nitrate‐containing medium, an increase of GS and a decrease of GDH‐specific activities took place. Both these effects were inhibited by chloramphenicol and were probably mediated by de novo protein synthesis. When either cell type was transferred to a medium without nitrogen source, the specific activities of both enzymes increased. When nitrate‐grown cells were transferred to nitrate medium with L‐methionine‐DL‐sulphoximine (MSX) added, the specific activity of GDH also increased. Here we present some evidence that, under certain conditions of nitrogen availability, GDH would play a minor role in ammonium assimilation.
Inorganic nitrogen assimilation in the non‐N2‐fixing cyanobacterium Phormidium laminosum. II. Effect of the nitrogen source on the nitrite reductase levels
Authors: Arizmendi Jesús María , Fresnedo Olatz , Martinez‐Bilbao Mercedes , Alaña Aitor , Serra Juan Luís
Published: May 2006

The effect of different inorganic nitrogen sources on the cellular levels of nitrite reductase (NiR. EC 1.7.7.1) activity has been studied in the filamentous non‐N2‐fixing cyanobacterium Phormidium laminosum (strain OH‐1‐p.Cl,). Nitrate‐grown cells gave the highest NiR in cell‐free extracts [ca 165 nmol of nitrite reduced (mg protein)‐1 min‐], whereas no activity could be detected in extracts from ammonium‐grown cells. The in vivo effect of ammonium on NiR was similar to that exerted by chloramphenicol, suggesting that de novo synthesis of protein was probably repressed by this ion. When ammonium was removed from the culture medium, a rapid increase of de novo synthetized NiR occurred, and the appearance of the enzyme was slightly stimulated by the presence in the medium of either nitrate or nitrite. However, remarkably high levels of NiR [around 1.2 μmol of nitrite reduced (mg protein) −1min−1] could be routinely measured in nitrogen‐deficient cells, indicating that the enzyme was ammonium‐repressible rather than nitrate‐ or nitrite‐inducible.
Plant responses to H2S and SO2 fumigation. II. Differences in metabolism of H2S and SO2 in spinach
Authors: Maas Frank M. , de Kok Luit J. , Strik‐Timmer Willy , Kuiper Pieter J. C.
Published: May 2006

Fumigation of spinach (Spinacia oleracea L. cvs Estivato and Monosa) with H2S or SO, for 1 to 6 days resulted in accumulation of sulfhydryl (SH) compounds in the shoots of both H2S‐ and SO2‐exposed plants. The sulfate concentration in shoots of SO2‐exposed plants increased linearly with time. SH accumulation showed saturation kinetics as a function of time as well as H2S concentration, ascribed to the internal H2S concentration in the plant and the availability of substrates for glutathione synthesis, respectively. SH compounds accumulated more at lower exposure temperatures, whereas sulfate accumulation was more pronounced at higher temperatures. These results are discussed in relation to the possible foliar uptake of H2S and SO2, the temperature dependence of uptake and the water solubility of these gases. The possibility of SO2‐induced H2S emission rather than sulfate accumulation as a source for SH accumulation is also discussed. Cessation of fumigation resulted in a decrease in SH compounds and sulfate content that could be accounted for by sulfur metabolism and growth, respectively.
Possible mechanisms of light‐induced chlorophyll degradation in senescing leaves of Hydrilla verticillata
Authors: Kar R. K. , Choudhuri M. A.
Published: May 2006

Light treatment markedly accelerated the chlorophyll loss in senescing leaves of Hydrilla verticillata [(L.f.) Royle] as compared to dark treatment, whereas such acceleration could not be observed in senescing spinach (Spinacia oleracea L.) leaves. The light‐induced cholorophyll loss in Hydrilla was retarded slightly by chloramphenicol and markedly by cycloheximide. Catalase (EC 1.11.1.6) activity did not change appreciably in Hydrilla leaves either in light or in darkness, while in spinach it declined markedly in the dark, and light retarded such decline. Peroxidase activity in Hydrilla showed faster increase in light than in darkness, while in spinach it increased only in light during senescence. The activity of phenol(pyrogallol)‐specific peroxidase increased markedly in light, and that of ascorbate‐specific peroxidase decreased slightly both in light and darkness during senescence of Hydrilla leaves. This rise in phenolspecific peroxidase activity was prevented by cycloheximide treatment. Pretreatment of Hydrilla leaves with monophenol (2,4‐dichlorophenol) and o‐diphenol (hydroquinone) accelerated and retarded, respectively, the light‐induced cholorophyll loss. Pretreatment of Hydrilla leaves with H2O2 augmented the chlorophyll loss more markedly in light than in darkness. The endogenous level of H2O2 increased more in light than in dark during senescence of Hydrilla leaves. Treatment of Hydrilla leaves with 3‐(3.4‐dichlorophenyl)‐l,l‐dimethylurea. a photosystem II inhibitor, prevented both light‐induced rise in H2O: level and chlorophyll loss, but it was without effect in the dark. Retardation of light‐induced chlorophyll loss occurred during senescence of Hydrilla leaves when light was given in different photoperiods in a 24‐h daily cycle for 6 days instead of as continuous irradiance. There was a negative correlation between the length of the photoperiod and the extent of cholorophyll loss.
Changes in the mineral composition of soybean xylem sap during monocarpic senescence and alterations by depodding
Authors: Noodén L. D. , Mauk C. S.
Published: May 2006

Evidence from earlier studies with explants (stem cutting with a leaf and a pod) indicates that a decline in the supply of mineral nutrients from the roots may prepare the leaves for induction of monocarpic senescence in soybean [Glycine max (L.) Merrill cv. Anoka). In order to assess the changes in mineral flux from the root system, xylem sap was collected from a decapitated plant under 100 kPa pressure over 50 min. The sap volume yield declines after flowering starts, but increases during pod extension and then decreases again during podfill. The concentrations of K, Ca, Mg, P, S, Zn, Fe, Mn, Cu, Mo and Si rise and then fall during reproductive development, but the exact timing differs among the elements. In contrast, B, Al and Na concentrations show a slow rise initially with a large increase in late pod development. Depodding, which prevents the early death of the plant, inhibits the changes of some elements (K, Mg) but not others (Ca. Mg, P, S, Zn. Fe. Mn, B, Cu, Al), and it does not prevent the decrease in sap volume delivered. Inasmuch as the mineral concentration of xylem sap quantitatively reflects upward mineral flux, the supply of most minerals to the shoot declines, and this decrease seems to be an important factor in the preparatory phase of monocarpic senescence. The different minerals show different patterns of change, which indicate differences in the transport mechanisms and their regulation.
Synthesis of glutamate by mitochondria – An anaplerotic function for glutamate dehydrogenase
Authors: Yamaya Tomoyuki , Oaks Ann
Published: May 2006

The photorespiratory nitrogen cycle was initially thought to be a closed cyclic process. If this were true the loss of glutamate, glutamine, serine or glycine to other processes, such as protein synthesis or export from the leaves, would not be possible in a stoichiometric sense. However, recent studies with [15N]‐labeled amino acids show that there are alternative sources of nitrogen for photorespiration, indicating that the nitrogen cycle is not a closed cyclic system. In addition recent work with 15NH4Cl and [15N]‐glycine and a metabolically competent mitochondria system has shown that glutamate is synthesized in the mitochondria. Hence the glutamate dehydrogenase (GDH, EC 1.4.1.2) in mitochondria could also be active in the reassimilation of NH4. We would like to propose that one function of mitochondrial GDH is to synthesize glutamate from some of the NH4 released by photorespiration and that this glutamate represents a reserve for use in biosynthetic reactions.
Nitrogen fixation and nitrate reduction in the root nodules of legumes
Authors: Becana Manuel , Sprent Janet I.
Published: May 2006

Published data on, and hypotheses regarding the effect of NO−3on functioning of legume root nodules are reviewed. It is concluded that a short‐term reversible effect of NO−3may act via an increased resistance to O2diffusion in nodules; this is coupled to decreased bacteroid respiration. For longer exposures to NO−3nodule activity is irreversibly lost, but how this relates to carbohydrate deprivation or NO‐2accumulation is unclear. Complicating factors include denitrification reactions and the interaction of NO−2with leghaemoglobin.
Association of polyamines to different parts of various plant species
Authors: Felix Hansruedi , Harr Jost
Published: May 2006

The variation in polyamine content in different plant species and in different parts within a plant can be considerable. To get general information about levels of polyamines in plants and about the association of polyamines to different types of tissue, 30 plants from 13 plant families were examined for their polyamine content before and after germination using high pressure liquid chromatography (HPLC) analysis. A marked increase in polyamine content occurs in the cotyledons or endosperms in the seeds on germination, i.e. in the nutrient storing and exporting part of the plant. In the radicle, hypocotyl or coleoptile, i.e. growing parts of the plant, an increase in polyamine content is rarely observed. Additionally, polyamine levels can be very low [below 1 nmol (g fresh weight)‐1] in different parts of various species. Obviously, levels in the pmol (g fresh weight)‐1 range satisfy the needs of many growing plant parts. The high levels of polyamines found especially in cotyledons cannot be explained by their postulated association with increased cell division rates.
Lipid composition of plasma membranes from barley leaves and roots, spinach leaves and cauliflower inflorescences
Authors: Rochester C. P. , Kjellbom P. , Larsson C.
Published: May 2006

Highly purified plasma membranes (PM) were obtained from barley (Hordeum vulgare L. cv. Kristina) leaves and roots, spinach (Spinacia oleracea L. cv. Viking II) leaves, and cauliflower (Brassica oleracea) inflorescences by partitioning in an aqueous polymer two‐phase system. The sterol and polar lipid composition of the PM, including the fatty acid composition of the glycerolipids, was determined. Dominating lipids were free sterols, glucocerebroside, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), although large variations in content were observed between the PM of the different species and organs. Thus, the spinach leaf PM contained only 7% (mol %) free sterol compared to over 30% free sterol in the other PM analysed, with the barley root PM as the other extreme (57% free sterol). On the other hand, sterol derivatives were more abundant in the spinach leaf PM, containing 13% acylated sterol glycosides. Cerebroside constituted 16% of the lipids in the barley leaf PM but only 3% in cauliflower. The phospholipids PC and PE ranged from 25 and 24%, respectively, in the spinach leaf PM to 8 and 7%, respectively, in the barley root PM. As a result of the large variations in sterol and phospholipid content, the ratio of free sterol to phospholipid varied from 2.2 in the barley root PM to only 0.1 in the spinach leaf PM. Sitosterol, campesterol and stigmasterol were the completely dominating sterols in the barley and cauliflower PM, whereas the unique sterol composition of spinach was dominated by spinasterol. Palmitic (16:0), linoleic (18:2) and linolenic (18:3) acid were the major glycerolipid fatty acids. The fatty acid composition of the barley root PM was the most saturated (44% 16:0, 13% 18:3), whereas that of the cauliflower PM was the most unsaturated (21% 16:0,42% 18:3). Thus, very large variations were observed in both total lipid and fatty acid composition of the PM investigated, which represent both mono— and dicotyledons, as well as both photosynthetic and non‐photosynthetic tissue. The consequences of this large diversity in composition of the lipid bilayer for the function of integral PM proteins are discussed.
Carbohydrate partitioning, photosynthesis and growth in Lemna gibba G3.I. Effects of nitrogen Limitation
Authors: Thorsteinsson Björon , Tillberg Jan‐Eric , Tillberg Elisabeth
Published: May 2006

The growth rate of Lemna giba L. G3 was varied by limiting the supply of nitrogen (N) under otherwise constant condition. Two experimental approaches were used. 1) A series of suboptimally growing cultures were supplid daily with exponentially increasing doses on N. 2) Optimally growing cultures were transferred to a N‐fre medium and cultivated in it for 10 days. Lveles of starch, sucrose, glucose, fructose, and systems. At RGR ranging from optimal to 50% of optimal caused decreased levels of soluble sugars, but increased lvels of starch.Starch accumulation showed a strong negative correlation with the CO2 assimilation rate, indicating increased triose phosphate/inorganic phosphate (TP/Pi) ratio in the chloroplast causing end product inhibition of photosyntheisis. The data indicat the quantitative rlationship betwen the photosynthetic activity and the carbon utilization rate influnces the activity of the sucrose synthesis pathway and thus the rate of the triose hosphate/Pi exchange at the chloroplast membrane, which in turn regulates the activity of starch synthesis and the Calvin cycle.
Carbohydrate partitioning, photosynthesis and growth in Lemna gibba G3. II. Effects of phosphorus limitation
Authors: Thorsteinsson Björn , Tillberg Jan‐Eric
Published: May 2006

The relationship between CO2 assimilation rate, growth and partitioning of carbon among starch, sucrose, glucose and fructose were studied in phosphorus (Pi)‐limited Lemna gibba L. G3. Two experimental models were used: 1) Cultures were grown at various stable, suboptimal rates regulated by the supply of Pi; 2) cultures growing at optimal rates were transferred to Pi‐free medium. The response to a Pi deficiency can be divided into two phases. Phase I is characterized by hyperactivity of the sucrose synthesis pathway, leading to high levels of glucose and fructose. Phase II is characterized by starch accumulation associated with a decrease in the cytoplasmic pools of soluble sugars owing to inhibition of carbon export from the chloroplast. A strong negative correlation was found between the CO2 assimilation rate and starch levels. No significant correlation was found between assimilation and ATP levels and decrease in relative growth rate did not significantly affect the adenylate energy charge (EC). The regulatory aspects of the partitioning of carbon among soluble sugars and starch as well as the negative correlation between carbohydrate levels and CO2 assimilation at Pi‐limited growth are discussed.
Rhizobium strain effects on pea: The relation between nitrogen accumulation, phosphoenolpyruvate carboxylase activity in nodules and asparagine in root bleeding sap
Authors: Rosendahl Lis , Jakobsen Iver
Published: May 2006

Pisum sativum L. cv. Bodil was infected with various strains of Rhizobium leguminosarum (R501, 128c53, B155, 18a or 1044). The Rhizobium genotype influenced the activity of the plant enzyme phosphoenoipyruvate (PEP) carboxylase (EC 4.1.1.31), and the assimilation of fixed N in the root nodules. The specific activity of nodule PEP carboxylase was lowest in the symbioses, which accumulated the least total N (R501 and 128c53). The root bleeding sap of the less effective symbioses contained a lower proportion of asparagine and a higher proportion of glutamine than the more effective symbioses (B155,18a and 1044). The N yield of the symbioses was related neither to the net respiratory CO2 evolution of the root system nor to the nitrogenase linked nodule respiration. The lower yielding symbioses accumulated a larger proportion of the fixed N in the nodules due to a higher proportion of total dry weight contained in the nodule tissue. However, the concentration of soluble protein in the nodules of the lower‐yielding symbioses was lower than that recorded for the higher yileding symbioses. The effect of the Rhizobium strains on N yield was maintained at maturity, and reflected in seed yields.
ABA‐induced proline accumulation in barley leaf segments: Dependence on protein synthesis
Authors: Pesci Pierantonio
Published: May 2006

The kinetics of proline accumulation in barley (Hordeum vulgare L. cv. Georgie) leaf segments showed a lag phase of ca 3 h when the increase was induced by abscisic acid (ABA), but not when the accumulation of the imino acid was promoted by isobutyric acid (IBA). Cycloheximide (CHI) supplied together with ABA, either from the beginning of the treatment or some time before the end of the lag phase, completely abolished ABA‐induced proline accumulation, whereas no block was observed when the inhibitor was supplied after the lag phase. Cordycepin (COR) exibited a similar effect. The IBA‐induced increase in proline was not influenced by CHI for at least 5 h.

When segments were pretreated with ABA for a period longer than the lag phase in the absence of salts in the external medium, there was no significant increase in proline. If KCI was added to the incubation medium after such a pretreatment, however, proline increased even after removal of the hormone from the external medium. This increase in proline occurred without any lag phase, and was only partially inbibited by CHI and rapidly and totally blocked by fusicoccin (FC). These results suggest that some protein, characterized by a fast turnover and possibly conferring the sensitivity to KCI, is synthesized during the early hours (lag phase) of the ABA treatment.

The synthesis of this protein(s) does not seem to be involved in the increase in proline induced by IBA and is thus a peculiar aspect of that mediated by ABA.
Entropy budgets of soybean and bur oak leaves at night
Authors: Aoki I.
Published: May 2006

From energy budgets of soybean [Glycine max (L.) Merr. cv. Chippewa] and bur oak (Quercus macrocarpa) leaves at night, entropy fluxes into or out of leaves are calculated. The absorbed entropy balances with the emitted entropy; this is not the case for leaves during the day and for an animal at night. On the assumption that the entropy in leaves is at steady state, entropy production in leaves becomes small and almost zero. Since entropy production is a measure of activity in organisms, the activity in leaves is small at night; this is in contrast to leaves during the day. Thus, a large portion of the activity in leaves is “on” in the daytime and “off” at night. Most of the activity in leaves may be triggered by solar radiation.
Mobilisation of reserves and the earliest synthesis of sterols and latex triterpenes during germination and early seedling growth of Euphorbia lathyris
Authors: Groeneveld Henri W. , Elings Jopie C. , Koops Andries J.
Published: May 2006

Seedlings of Euphorbia lathyris L. were grown in the dark at 25°C. Levels of amino acids, sugars and soluble phosphate in the endosperm increased upon germination after 4 days of imbibition, while the amounts of mineral reserves Mg2+ and K+ started decreasing. Ca2+ was not translocated from the endosperm to the seedling. Maximum values for amino acids were found on day 7, and the highest amounts of sugars were present on day 10. The endosperm was completely depleted by day 12.

Before germination (days 1–3) a low level of sterol synthesis in the embryo was detected with labeled sucrose and serine and to a lesser extent with labeled pyruvate. The label of [2‐14C]‐mevalonate proceeded exclusively to squalene. Laticifers started the synthesis of their triterpenes upon germination (day 4), using sucrose as a main substrate. A concurrent increase of sterol synthesis outside the laticifers was traced with labeled serine. Radioactive triterpenes, 4 α‐methylsterols and sterols were detected in growing seedlings after [14C]‐mevalonate uptake, but most of its label accumulated in squalene. The use of labeled mevalonate in sterol synthesis in growing seedlings is discussed.
Plant growth regulator activities of stereochemical isomers of triadimenol
Authors: Köller Wolfram
Published: May 2006

Etiolated seedlings of wheat (Triticum aestivum L. cv. Jubilar) were treated with individual isomers of triadimenol in order to determine the biochemical basis for plant growth retardation. The Is, 2R isomer showed the highest activity as a plant growth retardant, followed by the 1R, 2s form. The inhibition of growth was not relieved by exogenous gibberellic acid suggesting a mode of action different from inhibition of gibberelln synthesis. Labelling of sterols with radioactive acetate and methionine demonstrated a strong inhibition of sterol synthesis, most likely at the step of C‐14 demethylation of obtusifoliol. The extent of growth inhibition was accompanied with the potency of individual isomers to inhibit sterol synthesis. The inhibition of gibberellin synthesis appears of less importance for growth retardation.
Isolectin composition of individual clones of Urtica dioica: Evidence for phenotypic differences
Authors: Van Damme Els J. M. , Peumans Willy J.
Published: May 2006

Analysis of the isolectin composition of 102 individual nettle (Urtica dioica L.) clones by ion‐exchange chromatography revealed the occurrence of at least 11 different isolectins, which all had the same molecular structure and exhibited identical carbohydrate‐binding specificity and agglutination properties. All 11 isolectins, however, did not occur simultaneously; 34 combinations of either 1, 2, 3, 4 or 5 isolectins were found. Since the occurrence of multiple molecular forms of the nettle agglutinin cannot be explained by the (partial) autotetraploid character of stinging nettle it is postulated to rely on the expression of a family of closely related lectin genes.
Control by phytochrome of the synthesis of protein related to senescence in chloroplasts of barley (Hordeum vulgare)
Authors: Cuello Juan , Quiles María J. , Sabater Bartolomé
Published: May 2006

Protein synthesis has been measured in chloroplast isolated from detached leaves of barley (Hordeum vulgare L. cv. Hassan). The effects of hormone and light treatments of the leaves on chloroplast protein synthesis have been compared with effects on other senescence symptoms. Interruption of the dark with red light retards senescence and increases chloroplast protein synthesis. The effect of red light was reversed by far‐red light. Red light did not act additively with kinetin, and it competed with ethylene and abscisic acid, accelerators of senescence, which decreased protein synthesis. In contrast to the interruption of the dark with red light, continuous light decreased chloroplast protein synthesis. It may be concluded effects on chloroplast protein synthesis. The retardation of senescence by continuous light is not necessarily related to Pu Instead, energy provided by photosynthesis may be an important factor.
Phytochrome effects on K+ fluxes in guard cells of Commelina communis
Authors: Roth‐Bejerano Nurit , Nejidat Ali
Published: May 2006

The effect of phytochrome on K+ transport in guard cells of Commelina communis L. was studied following stomatal movement and using the K+−channel blockers tetraethylammonium (TEA), Cs+ and quinidine. TEA and quinidine prevented stomatal opening and closure in red light, but not when it was supplemented with far‐red. This indicates that channels that can be blocked by TEA and quinidine are regulated by phytochrome. Evidence for a phytochrome effect on K+ leakage through other membranal compartments was also found. These phytochrome effects are modified by temperature. Elevated temperature decreases the involvement of channels and increases K+ transport through other membrane compartments, while low temperature causes channel opening and diminishes K+ leakage. The interaction between phytochrome effects and those of temperature is discussed.
Seed dormancy in Acer: Is there a common mechanism for all Acer species and what part is played in it by abscisic acid?
Authors: Pinfield N.J. , Stutchbury P.A. , Bazaid S.M.
Published: May 2006

Seeds of Acer pseudoplatanus L. are usually considered to show only testa‐imposed dormancy, but a transient embryo dormancy has also been identified at the time of fruit dispersal. Even embryos that did not show full dormancy at this stage possessed low germinative vigour. Removal of embryo dormancy and the development of increased germination potential did not require the low temperatures necessary for the removal of testa‐imposed dormancy in this species. Germination rates of embryos from freshly harvested or briefly stored fruits were accelerated by removal of cotyledonary tissue, the most rapid responses occurring in isolated embryonic axes following complete removal of both cotyledons. Longer storage reduced this effect because of the increases in germinative vigour of whole embryos. Abscisic acid (ABA) reinforced embryo dormancy in embryos from freshly harvested or briefly stored fruits and also reduced germination rates in similarly derived isolated embryonic axes. This response to ABA also became progressively less marked as the storage period was extended. Loss of embryo dormancy was correlated with a reduction in endogenous abscisic acid levels in both whole embryos and cotyledons, suggesting that endogenous ABA contributes to the regulation of embryo dormancy in these seeds. There are no indications, however, that endogenous ABA is directly implicated in the low temperature processes associated with the removal of testa‐imposed dormancy. The relevance of embryo dormancy in the intact seed of A. pseudoplatanus is discussed.
Effects of interpolated dark periods during the first long day of floral induction on the cell cycle in the shoot apex of Silene coelirosa
Authors: Ormrod J. C. , Francis D.
Published: May 2006

Seeds of Silene coeli‐rosa L. were germinated and grown at 20°C in short days of 8 h light from fluorescent and tungsten (F + T) bulbs and 16 h darkness for 28 days (day 0). At 1700 h of day 0, the plants were exposed to 16 h light from T (LD) followed by 8 h F + T, or the same treatment interrupted at 1700 h of day 0 by 20 or 60 min darkness. Plants were exposed to tritiated (methyl‐[3H])‐thymidine for 2 h (1645–1845 h) and sampled every 2 h for 24 h. The cell cycle (percentage labelled mitoses method), and changes in cell number were measured in the shoot apical meristems. The cell cycle in the LD, 20 and 60 min dark‐interrupted LD (diLD) treatments was 10, 11 and 13 h, respectively. Mean cell generation times were ca 3–5 h longer, suggesting that the shorter cell cycles were transient. The proportions of cells with 2C or 4C amounts of nuclear DNA, indicated that imposition of darkness resulted in a progressive lengthening of G1 from about 3 h in the LD to 7 h in the 60 min diLD treatment. Conversely, G2 shortened from about 4 h in the LD to 3 h in the 60 min diLD treatment. Measurements of labelling index indicated that S‐phase was about 1.5 to 2 h in each treatment. The data are discussed in relation to the known inhibitory effect of the diLD treatments on flowering.
Glyphosate‐increased levels of indole‐3‐acetic acid in yellow nutsedge leaves correlate with gentisic acid levels
Authors: Cañal María Jesús , Tamés Ricardo Sánchez , Fernández Belén
Published: May 2006

The effects of glyphosate [N‐(phosphonomethyl)glycine] on endogenous in‐dole‐3‐acetic acid (IAA) level, IAA oxidase activity, and possible interactions with alterations in phenolic metabolism have been examined in yellow nutsedge (Cyperus esculentus L.) plants. IAA was quantified by flame ionization detector gas‐chroma‐tography, phenols were quantified by high‐performance liquid chromatography and the auxin protection and the IAA oxidase activities were determined spectrophoto‐metrically and/or polarographically. A significant increase in IAA content was recorded after glyphosate treatment. No IAA oxidase activity was detected in control and treated tissues. Auxin protection activity and gentisic acid were present in all extracts assayed, and their concentrations increased as the rate of glyphosate application increased. Addition of gentisic acid to an extract of control plants increased the auxin protection detected. These findings indicate that the high levels of free IAA in yellow nutsedge leaves after glyphosate application are due to the inhibition of the IAA oxidase activity by increased levels of the IAA‐protecting phenol gentisic acid.
The role of calcium ions in gravity singal perception and transduction
Authors: Poovaiah B. W. , McFadden J. J. , Reddy A.S.N.
Published: May 2006

Ca2+ is implicated as a messenger in coupling various environmental stimuli, such as gravity and light, to response. In recent years, it has become evident that Ca2+ plays a central role in all three phases of gravitropism – perception, transduction and response. The root cap, which is known to contain high amounts of Ca2+ and calmoduin, is the primary site of gravity preeception. The possible role of phosphoinositide turnovr and Ca2+ and Ca2+ calmodulin‐dependent enzymes such as Ca2+– ATPase and protein kinases in gravitropsim is discussed. A model is proposed to describe the role of Ca2+ in both normal and light‐dependnt gravity response in roots.
Effect of lectins on auxin‐induced elongation and wall loosening in oat coleoptile and azuki bean epicotyl segments
Authors: Hoson Takayuki , Masuda Yoshio
Published: May 2006

Auxin‐induced elongation of coleoptile segments of oat (Avena sativa L. cv. Victory) was suppressed by agglutinin from Canavalia ensiformis DC. (concanavalin A), Triticum vulgaris Vill. germ, Dolichos biflorus L., Glycine max Merr. and Limulus polyphemus L. at 0.5 mg ml−1, while that of epicotyl segments of azuki bean (Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by agglutinin from Canavalia ensiformis DC., Tetragonolobus purpureus Moench and Ulex europaeus L. I when segments were incubated at pH 6.0. These lectins suppressed elongation without any prominent lag period. This suppression of elongation by the lectins was not apparent at pH 4.0. When a ligand for lectins, for instance methyl‐α‐D‐mannopyranoside, was added simultaneously with the lectin, elongation of segments was completely or partly restored. The lectins that suppressed elongation were bound to the cell walls of the segments and inhibited the auxin‐induced cell wall loosening (decrease in the minimum stress‐relaxation time of the cell wall). Thus, the lectins may, at least partly, suppress elongation by inhibiting cell wall loosening. Our results demonstrate that the wall components containing α‐D‐mannose (α‐D‐glucose), N‐acetyl‐D‐glucosamine, N‐acetyl‐D‐galactosamine or D‐glucuronic acid play an important role in wall loosening of oat coleoptiles, while the wall components containing α‐D‐mannose (α‐D‐glucose) or L‐fucose are important for that of azuki epicotyls.
NAD(P)H oxidase and peroxidase activities in purified plasma membranes from cauliflower inflorescences
Authors: Askerlund Per , Larsson Christer , Widell Susanne , Møller Ian M.
Published: May 2006

An NAD(P)H oxidase activity stimulated by phenolic compounds has been investigated in purified plasma membranes (pm) and in an intracellular membrane (icm) fraction depleted in plasma membranes, both obtained from a microsomal fraction from cauliflower inflorescences (Brassica oleracea L.). The phenolic compounds salicylhydroxamic acid (SHAM), ferulic acid, coniferyl alcohol, n‐propyl gallate, naringenin, kaempferol and caffeic acid all strongly stimulated the activity. Peroxidase (EC 1.11.1.7), or a peroxidase‐like enzyme, was responsible for the NAD(P)H oxidase activity, which proceeded through a free‐radical chain reaction and was inhibited by catalase (EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1) and KCN. Most of the total activity was soluble; however, the membrane‐bound activity was highly enriched in the pm compared to the icm. The catalase activity was 6 times higher in the icm‐fraction than in the pm‐fraction, but this was not the reason for the much lower phenol‐stimulated NADH oxidase activity in the icm. Peroxidase activity measured with o‐dianisidine and H2O2 had about the same specific activities in the pm‐and icm‐fractions.

Neither the phenol‐stimulated NADH oxidase nor the peroxidase activity could be washed away from the pm even by 0.7 M NaCl, indicating that these activities are truly membrane‐bound. SHAM as well as the other phenolic compounds capable of stimulating the NADH oxidase reaction were potent inhibitors of blue light‐induced cytochrome b‐reduction in the pm fraction.
A comparison between 3,5‐diiodo‐4‐hydroxybenzoic acid and 2,3,5‐triiodobenzoic acid. I. Effects on growth and gravireaction of maize roots
Authors: Beffa Roland , Martin Hilary V. , Pilet Paul‐Emile
Published: May 2006

A comparison between the effects of DIHB and TIBA on growth and gravireaction of 15 mm primary maize (Zea mays L. cv. LG 11) roots is presented. Intact roots were pretreated in the dark for 1 h with buffered solutions (pH 5.0 or 6.0) containing DIHB (10, 50, 100 μM). The plantlets were then maintained either vertically or horizontally in the dark or the light, and growth and gravireaction were recorded using a macrophotographic technique. Pretreatment with DIHB slightly inhibited growth and delayed gravireaction. These effects were most marked with DIHB at 100 μM and were enhanced when DIHB was applied at pH 5.0. Similar effects were observed in roots pretreated with TIBA, but at a lower concentration (1 μM). The similarities between DIHB and TIBA as regards both chemical structure and the inhibition of gravireaction and growth, lead us to suggest that a major mode of action of DIHB, like TIBA, is the inhibition of indol‐3yl‐acetic acid transport.
A comparison between 3,5‐diiodo‐4‐hydroxybenzoic acid and 2,3,5‐triiodobenzoic acid. II. Effects on uptake and efflux of IAA in maize roots
Authors: Martin Hilary V. , Beffa Roland , Pilet Paul‐Emile
Published: May 2006

An explanation is sought for the inhibition of maize root growth and gravireaction brought about by treatment with 3,5‐diiodo‐4‐hydroxybenzoic acid (DIHB). The effects of DIHB and 2,3,5‐triiodobenzoic acid (TIBA) on the uptake and efflux of [3H]‐indol‐3yl‐acetic acid (IAA) were tested using segments prepared from the elongation zone (2 to 7 mm region) of maize (Zea mays L. cv. LG11) roots.

The uptake of [3H]‐IAA (21 nM) by root segments incubated in buffered solutions (pH 5.0) was measured over a 5‐min time‐course. No significant effect of DIHB at 100 μM was observed, whereas TIBA at 10 μM slightly stimulated the uptake of [3H]‐IAA. This experiment was repeated with the addition of non‐radioactive IAA (total IAA concentration 1.0 μM). Up to 3 min DIHB (100 μM) had no significant effect, but thereafter a slight stimulation of IAA net uptake was observed. Treatment with TIBA (10 μM) stimulated the accumulation of IAA in the segments.

The effects of DIHB (10, 50, 100 μM) and TIBA (10 and 50 μM) on the efflux of [3H]‐IAA from segments that had been pretreated in [3H]‐IAA (22 nM) were then tested. Treatment with DIHB or TIBA at pH 5.0 inhibited IAA efflux; the inhibition by TIBA was more marked than that produced by DIHB. This experiment was repeated using DIHB (10, 50, 100 μM) buffered at pH 6.0, and an inhibition of IAA efflux was again observed.

Both DIHB (10 μM) and TIBA (10 μM) inhibited the binding of [3H]‐NPA to a 5000–48000 g membrane fraction prepared from whole maize roots. The effects of the two substances were similar: 40% inhibition of specific binding by DIHB and 41% inhibition by TIBA. This indicates that DIHB, like TIBA, binds to the N‐1‐naphthyl‐phthalamic acid‐sensitive carrier for IAA efflux.

It is concluded that DIHB, like TIBA, inhibits IAA transport at the level of efflux. The similarity between DIHB and TIBA as regards chemical structure and their inhibitory effects on IAA efflux and NPA binding strongly suggest that they act on the same carrier for IAA efflux across the plasmalemma.
ATP‐dependent H+‐pumping of a low‐density fraction of pea stem microsomes
Authors: Vianello Angelo , Macrì Francesco , Antone Paolo Dell'
Published: May 2006

A low‐density fraction of pea (Pisum sativum L. cv. Alaska) stem microsomes, obtained from a discontinuous sucrose gradient, possessed an H+‐ATPase able to generate a proton gradient and an electrical potential. The proton pumping was insensitive to monovalent cations, to vanadate and oligomycin, required a permeant anion and was inhibited by nitrate, N, N'‐dicyclohexylcarbodiimide and diethylstilbestrol. The H+‐ATPase had a pH optimum around 6.0–6.5 and was saturable with respect to the substrate Tris‐ATP (Km≅ 0.4 mM). Ca2+ (0.05–1 mM) induced a dissipation of the ATP‐generated δpH without affecting ATPase activity. At physiological concentrations (1–5 mM), nitrate caused an initial slight increase of the ATP‐generated proton gradient followed by a complete dissipation after 2–3 min. The dissipating effect was not caused by inhibition of ATPase activity, since ATP prevented the nitrate‐induced collapse of δpH. On the other hand, ATPase activity, evaluated as release of Pi, was not inhibited by concentrations lower than 20 mM KNO3. These results indicate that nitrate entered the vesicles in response to an electrical potential and then could exit in symport with protons, while Ca2+ entered in exchange for protons (antiport).
Effects of Ca2+ and other divalent cations on uptake of Ni2+ by excised barley roots
Authors: Körner Lena E. , Møller Lan M. , Jensén Paul
Published: May 2006

Excised roots of 7‐day‐old, dark‐grown barley (Hordeum vulgare L. cvs Gunilla and Møyar) were used to characterize effects of Ca2+ and other divalent cations on uptake of Ni2+ (63Ni2+). The uptake of Ni2+ in the roots (free space uptake and influx) and the Ni2+ remaining in the roots after desorption for 15 min in 1.0 mM EDTA (mainly in‐flux) were both independent of the Ca2+ concentration in the pretreatment solution up to about 0.1 mM and then increased to a maximum at 1 mM Ca2+. Without pretreatment, the higher the Ca2+ concentration in the uptake solution, the less Ni2+ was taken up. Ni2+ influx in the roots was reduced less by Ca2+ than was loose binding of Ni2+ in the free space of the roots (the amount of Ni2+ removed by the desorption procedure). The ratio between Ni2+ influx and Ni2+ uptake had a maximum around 1 mM Ca2+ and was higher the lower the external Ni2+ concentration. With Mg2+ in the uptake solution, Ni2+ influx was more reduced than loose binding of Ni2+, in contrast to the results with Ca2+. Both Ca2+ and Mg2+ were non‐competitive inhibitors of Ni2+ influx. Mn2+ did not influence Ni2+ influx, whereas Zn2+ and Cu2+ inhibited Ni2+ influx strongly and competitively and Co2+ weakly and competitively. The heavy metals Cd2+ and Pb2+ appeared to inhibit Ni2+ influx non‐competitively.
The expression of photosynthetic traits during and following severe chilling stress of European and tropical maize genotypes
Authors: Stamp P.
Published: May 2006

Four genotypes of maize (Zea mays L.), one from North‐West Europe, two from tropical highlands and one from tropical lowlands were grown at 24°C until full expansion of the second leaf. Seedlings were then subjected to 2 days at 5°C, with or without a previous conditioning phase at 10°C for 4 days. After stress plants were allowed to recover at 24°C for 5 days. Previous conditioning protected the tropical lowland variety to some extent against losses in chlorophyll content and ribulose I,5‐bisphosphate carboxylase (EC 4.1.1.39) activity by severe chilling stress. Without conditioning heavy losses occurred during the recovery phase. In all other genotypes the values of these traits decreased more with than without conditioning. Phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity was little affected during stress, but declined considerably during the recovery phase, with the exception of the North‐West European genotype. Previous conditioning prevented or retarded losses of NADP+ malate dehydrogenase (EC 1.1.1.82) activity during the stress phase. However, at the end of the recovery phase losses were as high with as without conditioning, and activity was very low in one tropical highland genotype and in the tropical lowland genotype. In summary, the chilling stability of photosynthetic traits was better in the North‐West European genotype than in the tropical ones.
Nodulation and nitrogenase activity in nitrogen‐fixing woody plants stimulated by CO2enrichment of the atmosphere
Authors: Norby Richard J.
Published: May 2006

The responses of three species of nitrogen‐fixing trees to CO2enrichment of the atmosphere were investigated under nutrient‐poor conditions. Seedlings of the legume,Robinia pseudoacaciaL. and the actinorhizal species,Alnus glutinosa(L.) Gaertn. andElaeagnus angustifoliaL. were grown in an infertile forest soil in controlled‐environment chambers with atmospheric CO2concentrations of 350 μl−1(ambient) or 700 μl−1. InR. pseudoacaciaandA. glutinosa, total nitrogenase (N2reduction) activity per plant, assayed by the acetylene reduction method, was significantly higher in elevated CO2, because the plants were larger and had more nodule mass than did plants in ambient CO2. The specific nitrogenase activity of the nodules, however, was not consistently or significantly affected by CO2enrichment. Substantial increases in plant growth occurred with CO2enrichment despite probable nitrogen and phosphorus deficiencies. These results support the premises that nutrient limitations will not preclude growth responses of woody plants to elevated CO2and that stimulation of symbiotic activity by CO2enrichment of the atmosphere could increase nutrient availability in infertile habitats.
Seasonal patterns of reproductive and vegetative sink activity in early and late maturing peach (Prunus persica) cultivars
Authors: DeJong T. M. , Doyle J. F. , Day K. R.
Published: May 2006

Weekly measurements of fruit growth, fruit respiration and shoot extension growth were made in the field on early (June Lady) and late (O'Henry) maturing cultivars of peach (Prunus persica L. Batsch). The seasonal patterns of fruit growth and respiration for the two cultivars were very similar except that the early maturing cultivar bloomed a few days earlier than the late cultivar and had a shorter intermediate stage (Stage II) of fruit growth. Maximum rates of fruit respiration per unit weight at 20°C were similar for both cultivars during the first two stages of fruit growth but higher for the early cultivar during the final stage of fruit growth. Maximum fruit growth rates within any particular stage of fruit growth were similar for both cultivars, but the mean fruit weight of the late cultivar was greater at the end of Stage II, because of the extended length of this stage compared to the early cultivar. The final stage of most rapid fruit growth and respiration coincided with the period of most rapid shoot extension growth in the early maturing cultivar but occurred after this period in the late maturing cultivar. Genetic selection for early fruit maturity in peach has apparently had little effect on timing of shoot growth and this may result in increased competition between vegetative and reproductive sinks during peak periods of fruit growth in early maturing cultivars.
Regulation of monocarpic senescence of Brassica campestris by the developing pods
Authors: Biswas A. K. , Mandal S. K.
Published: May 2006

Senescence of Brassica campestris L. cv. B‐9 was studied with regard to seed maturation and source‐sink relationships. In normal control plants leaf senescence (as determined by the change in chlorophyll level) started and proceeded in a progressive manner from base to apex during the period of early pod setting. Complete yellowing of the leaves occurred well before the seed maturation and pod wall senescence. The pod wall always senesced before the attainment of final seed weight. In two different sets of acrocarpous plants containing 65 pods and 10 pods, respectively, leaf senescence was delayed during the pod filling period. It started non‐sequentially after complete yellowing and senescence of the pod wall. The degree of leaf senescence at the post‐pod filling stage was almost proportional to the number of pods present. When peduncles of the acrocarpous 10‐podded plants were removed after the pod filling stage of the plant, leaf senescence was delayed compared to plants whose pedicels were removed, although the senescence pattern of the upper three leaves was nonsequential in both cases. Defruiting at an early stage of development delayed leaf senescence, although the pattern of such senescence remained unaltered (i.e. nonsequential). Defoliation hastened the seed‐filling process and pod wall senescence. Plants containing fewer pods had higher average seed weight, although yield per plant was reduced.

These results suggest that the pod wall serves as a temporary as well as intermediary storage organ and that foliar senescence is not directly related to seed maturation. The possible cause of uncoupling between foliar senescence and seed development is discussed.
Reversal of triazole‐induced stomatal closure by gibberellic acid and cytokinins in Commelina benghalensis
Authors: Santakumari M. , Fletcher R. A.
Published: May 2006

Although not as effective as ABA, the triazoles S‐3307 and triadimefon induced partial closure of stomata in isolated epidermal strips of Commelina benghalensis L. Both in the light and dark the stomatal closure induced by triazoles was reversed by GA and cytokinins, with GA being more effective. In an in vivo system using excised shoots, increasing triazole concentrations resulted in a proportional increase in stomatal diffusive resistance. Light was ineffective in reversing the triazole‐induced stomatal closure both in vivo and in vitro, which indicates that the effects of triazoles are probably mediated through hormonal regulation rather than an effect on photochemical reactions.
Blue, red and blue plus red light control of chloroplast pigment and pigment‐proteins in corn mesophyll cells: Irradiance level‐quality interaction
Authors: Eskins Kenneth , McCarthy Susan A.
Published: May 2006

Corn (Zea mays L. cv. OP Golden Bantum) was grown under low irradiance blue, red or blue plus red light. Red was more effective than blue light for synthesis of Chl a, b and light‐harvesting proteins (LHC‐2) associated with photosystem 2(PS2). Blue light was slightly more effective for synthesis of light‐harvesting proteins (LHC‐1) associated with photosystem 1 (PS1), but below a fluence rate of 1 μmol m−2 s−1 the response to blue vs that to red depended on irradiance level. Blue light containing a small amount of red light was as effective as red light for Chl a and b synthesis, but no more effective than blue light for LHC‐2 synthesis. Adding small amounts of blue light to red repressed the effect of red light on LHC‐2 synthesis and produced irradiance response curves similar to those produced by blue alone for LHC‐2 synthesis. This repression by blue light depended on the ratio of red to blue and the level of the blue light.