bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparisons of photosynthesis and photoinhibition in the CAM vine Hoya australis and several C3 vines growing on the coast of eastern Australia
Authors: ADAMS W. W. , TERASHIMA I. , BRUGNOLI E. , DEMMIG B.
Published: April 2006

Abstract. The CAM vine Hoya australis and three C3 vines, Smilax australis, Ipomoea pes‐caprae and Kennedta rubicunda, were studied at a site on the coast of northeastern New South Wales, Australia. The level of CAM activity (nocturnal acid accumulation) was comparable in H. australis growing in full sunlight and in deep shade. Acclimation to shade by H. australis was indicated by thinner leaves, increased chlorophyll content, decreased chlorophyll a/b ratios, lower dark respiration rates, and lower light compensation points. When growing in full sunlight H. australis exhibited reductions in photochemical efficiency, as indicated by reduced quantum yields and Fv/Fm fluorescence from PS II as well as low rates of photosynthesis at high light. Sun leaves of H. australis experienced a massive quenching of fluorescence from PS II during normal exposure to midday irradiance which was rapidly reversible under low irradiance conditions in the late afternoon. This quenching indicated a reduction in photochemical efficiency, part of which could be accounted for by an increase in non‐radiative energy dissipation, while part of it was due to one or more processes not yet identified. Changes in PS II fluorescence from shade H. australis exposed to full sunlight suggest a decrease in the rate constant for photochemistry indicative of damage to the reaction centre, as well as an increase in non‐radiative energy dissipation. The C3 vine S. australis was also shade tolerant, but exhibited little evidence of photoinhibition when growing in full sunlight. Ipomoea pescaprae and K. rubicunda, both of which were apparently shade intolerant (being found only in full sunlight), possessed high quantum yields and much higher photosynthetic capacities than either H. australis or S. australis. From this study, and several others, it appears that plants possessing CAM experience photoinhibition to a greater degree than do C3 species in full sunlight under natural conditions, which is probably exacerbated by some degree of CAM‐idling.
Effects of ethylene and some other environmental factors on different stages of germination in red root pigweed (Amaranthus retroflexusL.) seeds*
Authors: SCHONBECK M. W. , EGLEY G. H.
Published: April 2006

Abstract.Ethylene was found to promote two distinct processes during germination of redroot pigweed (Amarantus retroflexusL.) seeds: embryo expansion that splits the seed coat (incomplete germination), and radicle penetration through the more elastic endosperm (complete germination). The two events can be separated in time by subjecting seeds to low water potential or low CO2levels, which arrest germination of some seeds at the incomplete stage. Ethylene applications to incompletely germinated seeds promote complete germination, with a response threshold near 0.02 cm3m−3and saturation near 0.5 cm3m−3. Higher ethylene concentrations (0.5 to 50 cm3m−3) given during the first day of seed imbibition also increase the percentage of seeds which initiate embryo expansion and split the seed coat. Light and elevated CO2also promote radicle penetration of the endosperm in seeds incubated under water stress. The results support the view that the germination pause at the incomplete stage is an adaptation to environmental stresses that can be overcome with exogenous ethylene or certain other stimuli.
Effects of boundary layer conductance on substomatal pressures of carbon dioxide
Authors: BUNCE J. A.
Published: April 2006

Abstract. Gas exchange measurements were made on single leaves of three C3 and one C4 species at air speeds of 0.4 and 4.0 m s−1 to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m−2 s−1 at the lower air speed, and 1.2 to 1.5 mol m−2 s−1 at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C3 species, and about 3 Pa lower in the C4 species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C3 species. The commonly reported values of substomatal carbon dioxide pressure for C3 and C4 species were found to occur only when measurements were made at the higher air speed.
Light and chlorophyll gradients within Cucurbita cotyledons
Authors: KNAPP A. K. , VOGELMANN T. C. , McCLEAN T. M. , SMITH W. K.
Published: April 2006

Abstract. Measurement of light within 10–14‐d‐old green and etiolated Cucurbita pepo cotyledons were made with fibre‐optic microprobes to assess the influence of chlorophyll distribution and anatomical variations in mesophyll cell type (spongy versus palisade) on internal light pattern. More than 50% of the pigment in green cotyledons occurred in the upper (adaxial) 300 μm and this gradient strongly influenced the internal propagation of 680 nm light. When the upper (adaxial) surface was irradiated with 680 nm light, almost complete absorption occurred within the first 400 μm (palisade) of approximately 1200‐μm‐thick cotyledons. In contrast, when lower (abaxial) surfaces were irradiated with 680 nm light, penetration extended throughout the spongy mesophyll to about the 700 μm depth. Measurements of collimaled and scattered light gradients at 550, 680 and 750 nm indicated that collimaled light was rapidly scattered by mesophyll cells. In cotyledons irradiated on the upper surface, spongy mesophyll cells received only scattered light. Furthermore, comparisons of scattered light gradients obtained from cotyledons irradiated on upper and lower surfaces suggested that spongy mesophyll cells scatter light more effectively than palisade cells, probably due to the greater proportion of intercellular air spaces in spongy mesophyll tissue. These data also indicate that both the spectral quality and quantity of light incident on palisade versus spongy mesophyll cells differs, perhaps contributing to developmental and physiological differences between these two mesophyll cell types.
Effect of high external NaCl concentrations on ion transport within the shoot of Lupinus albus. I. Ions in xylem sap
Authors: MUNNS RANA
Published: April 2006

Abstract. Xylem sap was collected from individual leaves of intact transpiring lupin plants exposed to increasing concentrations of NaCl by applying pneumatic pressure to the roots. Concentrations of Na+ and Cl− in the xylem sap increased linearly with increases in the external NaCl concentration, averaging about 10% of the external concentration. Concentrations of K+ and NO3−, the other major inorganic ions in the sap, were constant at about 2.5 and 1.5 mol m−3, respectively. There was no preferential direction of Na + or Cl− to either young or old leaves: leaves of all ages received xylem sap having similar concentrations of Na+ and Cl−, and transpiration rates (per unit leaf area) were also similar for all leaves. Plants exposed to 120–160 mol m−3 NaCl rapidly developed injury of oldest leaves; when this occurred, the Na+ concentration in the leaflet midrib sap had increased to about 40 mol m−3 and the total solute concentration to 130 osmol m−3. This suggests that uptake of salts from the transpiration stream had fallen behind the rate of delivery to the leaf and that salts were building up in the apoplast.
A model for photosynthesis and photorespiration in C3 plants based on the biochemistry and stoichiometry of the pathways
Authors: FARAZDAGHI H. , EDWARDS G. E.
Published: April 2006

Abstract. A model is developed for photosynthesis and photorespiration in C3 plants, using an equation for the multisubslrate ordered reaction of ribulose 1,5‐bisphosphalc carboxylase‐oxygenase (Farazdaghi & Edwards, 1988). The model examines net CO2 fixation with O2 inhibition, and mutual inhibition when equilibrium exists between carboxylation and oxygenation (at the CO2 compensation point). It is based on the stoichiometry of energy requirements and O2, and CO2 exchange in the cycles, the quantum efficiency for RuBP generation, the maximum capacity for RuBP generation, the carboxylation efficiency with respect to [CO2], and the oxygenation efficiency with respect to [O2]. With increasing concentrations of CO2 above the CO2 compensation point, decreasing quantum flux density, or decreasing O2, simulations show that the rate of photorespiration progressively decreases. The two components of O2 inhibition of photosynthesis change disproportionately with increasing CO2 concentration. According to the model, the energy utilized during photosynthesis at the CO2 compensation point is about half that under atmospheric conditions.
Seasonal patterns of water relations and enzyme activity of the facultative CAM plant Portulacaria afra (L.) Jacq.
Authors: GURALNICK L. J. , TING I. P.
Published: April 2006

Abstract. Portulacaria afra (L.) Jacq. is a perennial facultative CAM species showing a seasonal shift from C3 to CAM photosynthesis. The shift to CAM during the summer occurs despite continued irrigation of the plants. The authors examined the hypothesis that the seasonal shift to CAM occurred because of low transient water potentials. They measured changes in whole leaf water, osmotic and pressure potentials over the course of the shift. They also studied changes in enzyme activity to ascertain if PEP carboxylase and PEP carboxykinase were induced during the seasonal shift to CAM. Water potentials were high, from ‐0.1 to ‐0.5 MPa, predawn and midday, when the C3 pathway of photosynthesis was utilized. Osmotic potentials were constant, from ‐0.7 to ‐ 0.8 MPa, indicating very little change in turgor. P. afra shifted to CAM indicated by large diurnal acid fluctuations (300 400 meq m−2) despite C3‐like predawn water potentials. Midday water potentials usually decreased 0.2‐0.7 MPa, while the osmotic potential remained unchanged or decreased slightly. Thus, a midday loss of turgor was associated with the use of the CAM pathway. The results support the hypothesis that the induction of CAM occurred due to low transient water potentials and may be partially mediated through the loss of turgor. The shift to CAM is only a partial induction with PEP carboxykinase showing high activity all year round while PEP carboxylase increases three‐to five‐fold over C3 levels. Relatively high levels of CAM enzyme activity enables the utilization of the CAM pathway in the winter and spring in response to high daytime temperatures and increased evaporative demand. These results would lead to an increase in water use efficiency during such periods when compared to other inducible CAM species.
Sensitivity of soybean leaf development to water deficits
Authors: RANDALL H. C. , SINCLAIR T. R.
Published: April 2006

Abstract. Drought effects on the final leaf area of individual leaves were hypothesized to depend on the leaf developmental stage at which drought occurred. To evaluate this hypothesis, final leaf area and cell number were measured for soybean (Glycine max (L.) Merr.) leaves that were at different stages of development when single or cyclical drought treatment was imposed. Leaf emergence rate from the meristem, as depicted by changes in the plastochron index, was not as sensitive as leaf expansion to cyclical droughts. For leaf expansion, small leaves, once they emerged from the meristem, suffered larger decreases in growth than leaves undergoing rapid leaf area expansion. Decreases in final leaf area as a result of a cyclical drought were correlated with decreases in final cell number. Decreases resulting from a single 8‐d drought were dependent on the age of the leaf at the time of drought, because small leaves were found to have proportionately larger decreases in final cell number and area than larger leaves. These results indicated that age‐dependent leaf responses to drought are based on the relative activity of cell division and expansion at the time stress was imposed.
Two forms of exopolygalacturonase increase as peach fruits ripen
Authors: DOWNS C. G. , BRADY C. J.
Published: April 2006

Abstract. Freestone peach cultivars are distinguished from clingstone cultivars by a more extensive softening of the mesocarp tissue, and by the separation of mesocarp and endocarp during ripening. Cultivars of both types have been reported to develop exopolygalacturonase activity during ripening, but the enzyme has not been characterized in any detail. During development of freestone peaches (Prunus persica L. var Coronet), two exopolygalacturonase enzymes were detected 42, 65 and 85 d after full bloom and in ripe fruit. During ripening one enzyme (exoPG 1) increased 36‐fold and the other (exoPG 2) 90‐fold but exoPG 2 accounted for a 73% of the total activity in ripe fruit. ExoPG 1 was purified 24‐fold and exoPG 2 540‐fold. ExoPG 2 is a slightly acidic glycoprotein. ExoPG 1 and exoPG 2 differ slightly in their pH optima and in their responses to calcium: each produces monogalacturonic acid as a reaction product. Similar enzymes were found in Flavorerest, a semi‐freestone peach.
Drought‐stress‐induced polypeptide accumulation in tomato leaves
Authors: BRAY E. A.
Published: April 2006

Abstract. Tomato (Lycopersicon esculentum Mill ev. Ailsa Craig) leaf polypeptides, radiolabelled with L‐[36S] methionine during drought stress, were separated by two‐dimensional polyacrylamide gel electrophoresis. Three sets of polypeptides were distinguished: those that decreased, increased or transiently increased in response to drought stress. Three sets of polypeptides also could be distinguished during recovery from drought stress: those that increased, decreased rapidly or decreased slowly and could still be detected after 6 h of recovery. The set of polypeptides that decreased during drought stress was the same set that increased during recovery and those that increased during stress, decreased during recovery. The leaf ABA concentration increased rapidly in response to drought stress and decreased rapidly during recovery from drought stress, returning to the nonstress level after 6 h of rehydration. There was a correlation between the accumulation of some of the drought‐induced polypeptides and the pattern of ABA accumulation during stress and recovery from stress.
Photosynthesis of Ulva fasciata. IV. pH, carbonic anhydrase and inorganic carbon conversions in the unstirred layer
Authors: BEER S. , ISRAEL A.
Published: April 2006

Abstract. The common marine macroalga Ulva was found to have a surface pH of about 10 during photosynthesis. Under such a condition, the equilibrium CO2 concentration within the unstirred layer would be below reported CO2 compensation points, and dehydration of HCO3 could not occur. Even at a compensation point approaching zero, uncatalysed rates of HCO3 to CO2 conversion within the unstirred layer volume could not support photosynthetic rates as measured under stirred conditions in the presence of a carbonic anhydrase inhibitor. Based on this, it is concluded that Ulva takes up HCO3. It is likely that HCO3 uptake leads to high internal CO2 levels which, in turn, suppress photorespiration and thus cause this plant's efficient gas exchange features. Carbonic anhydrase activity was measurable only in plant extracts. However, inhibitor studies suggest the presence of a surface enzyme. The possible functions of extracellular carbonic anhydrase in Ulva are assessed in terms of CO2 hydration during emergence and a possible HCO3, transport system.
Production of ethylene by gravistimulation: a potential problem with the interpretation of data from some experimental techniques
Authors: DE WIT F. L. , LIU J.‐H. , REID D. M.
Published: April 2006

Abstract. Gravistimulation was investigated as a potential and unwanted component in the interpretation of physiological investigations on plants. Using both seedlings and mature sunflower plants, two situations are described where gravistimulation contributes significantly to the outcome of an experiment not initially designed to include this parameter. The number of adventitious roots formed in derooted seedings decreased when the tops of the plants were allowed to bend over under their own weight, and the effect correlated positively with the rate of ethylene production by non‐vertical stems. In droughted mature plants, and increase in leaf and stem ethylene caused by water stress was supplemented by additional ethylene produced in the lower halves of stems. Drought had caused these stem tissues to wilt, become gravistimulated, and thus produce more ethylene. Other situations in which gravistimulated ethylene production and its physiological consequences are likely to be complicating factors in experiments are discussed. It is concluded that procedures that unnecessarily place experimental material in non‐vertical orientations should be avoided.
Oligosaccharides that induce proteinase inhibitor activity in tomato plants cause depolarization of tomato leaf cells
Authors: THAIN J. F. , DOHERTY H. M. , BOWLES D. J. , WILDON D. C.
Published: April 2006

Abstract. Two size ranges of oligosaccharide elicitors of pectic origin have been investigated for their effects on tomato plants. Both size ranges, with degrees of polymerization of 1–7 and 10–20 respectively, induced the accumulation of proteinase inhibitor (PI) activity in excised plants, and also induced changes in membrane potential of leaf mesophyll cells. The depolarizations were substantial, rapid, and reversible on removal of the elicitors. The effects are discussed in the context of early events in the signal transduction pathway linking oligosaccharides to changes in PI gene expression.
Thermal history regulates methylbutenol basal emission rate in Pinus ponderosa
Authors: GRAY DENNIS W. , GOLDSTEIN ALLEN H. , LERDAU MANUEL T.
Published: April 2006

Methylbutenol (MBO) is a 5‐carbon alcohol that is emitted by many pines in western North America, which may have important impacts on the tropospheric chemistry of this region. In this study, we document seasonal changes in basal MBO emission rates and test several models predicting these changes based on thermal history. These models represent extensions of the ISO G93 model that add a correction factor Cbasal, allowing MBO basal emission rates to change as a function of thermal history. These models also allow the calculation of a new emission parameter Estandard30, which represents the inherent capacity of a plant to produce MBO, independent of current or past environmental conditions. Most single‐component models exhibited large departures in early and late season, and predicted day‐to‐day changes in basal emission rate with temporal offsets of up to 3 d relative to measured basal emission rates. Adding a second variable describing thermal history at a longer time scale improved early and late season model performance while retaining the day‐to‐day performance of the parent single‐component model. Out of the models tested, the Tamb,Tmax7 model exhibited the best combination of day‐to‐day and seasonal predictions of basal MBO emission rates.
Spatial coordination of aluminium uptake, production of reactive oxygen species, callose production and wall rigidification in maize roots
Authors: JONES D. L. , BLANCAFLOR E. B. , KOCHIAN L. V. , GILROY S.
Published: April 2006

Aluminium (Al) toxicity associated with acid soils represents one of the biggest limitations to crop production worldwide. Although Al specifically inhibits the elongation of root cells, the exact mechanism by which this growth reduction occurs remains controversial. The aim of this study was to investigate the spatial and temporal dynamics of Al migration into roots of maize (Zea mays L.) and the production of the stress response compound callose. Using the Al‐specific fluorescent probe morin, we demonstrate the gradual penetration of Al into roots. Al readily accumulates in the root’s epidermal and outer cortical cell layers but does not readily penetrate into the inner cortex. After prolonged exposure times (12–24 h), Al had entered all areas of the root apex. The spatial and temporal accumulation of Al within the root is similarly matched by the production of the cell wall polymer callose, which is also highly localized to the epidermis and outer cortical region. Exposure to Al induced the rapid production of reactive oxygen species and induced a significant rigidification of the cell wall. Our results suggest that Al‐induced root inhibition in maize occurs by rigidification of the epidermal layers.
Involvement of gibberellins in the stem elongation of sun and shade ecotypes of Stellaria longipes that is induced by low light irradiance
Authors: KUREPIN LEONID V. , PHARIS RICHARD P. , REID DAVID M. , CHINNAPPA C. C.
Published: April 2006

Plants from two ecotypes of Stellaria longipes, alpine (an open, sunny habitat) and prairie (where adjacent plants provide a shaded habitat), were grown under normal and reduced levels of photosynthetically active radiation (PAR). Growth under low PAR is significantly promoted in both ecotypes. When quantified by the stable isotope dilution method, endogenous gibberellins (GAs) (GA1, GA8, GA20, GA19) were significantly elevated under low PAR in both ‘sun’ and ‘shade’ ecotypes, as was GA53 in the shade ecotype. Changes in endogenous GA1 levels were significantly correlated with stem growth during a 28 d growth cycle and with relative growth rate (RGR) for height under low PAR for both ecotypes. Interestingly, under low irradiance PAR, changes (both increases and decreases) in GA8, the 2β‐hydroxylated ‘inactive’ catabolite of GA1, closely parallel bidaily stem growth changes for both ecotypes. Because the significantly greater stem elongation of both ecotypes in response to low irradiance PAR is associated with significant increases in the endogenous levels of five GAs (GA53, GA19, GA1, GA8) in the early 13‐hydroxylation GA biosynthesis pathway (measured at days 7, 14 and 21), we conclude that the low irradiance PAR has very likely induced an overall increase in GA biosynthesis.
The effect of gibberellic acid on the response of leaf extension to low temperature
Authors: FARRELL A. D. , OUGHAM H. J. , TOMOS A. D.
Published: April 2006

The effect of cooling on leaf extension rate (LER) and on relative elemental growth rate (REGR) was measured in both gibberellic acid (GA)‐responsive dwarf barley and in the same barley variety treated with GA. Seedlings were maintained at 20 °C while their leaf extension zone (LEZ) temperature was reduced either in steps to −6 °C in short‐term cooling experiments, or to 10 °C for 48 h in long‐term cooling experiments. Short‐term cooling resulted in a biphasic response in LER, with a clear inflection point identified. Below this point, the activation energy for leaf extension becomes higher. The short‐term response of LER to cooling was altered by the application of GA, which resulted in a lower base temperature (Tb), inflection point temperature and activation energy for leaf extension. Both GA‐treated and untreated seedlings were less sensitive to cooling maintained for a prolonged period, with LER making a partial recover over the initial 5 h. Although long‐term cooling reduced maximum REGR, it resulted in a longer LEZ and an increase in the length of mature interstomatal cells in GA‐treated and untreated seedlings. These changes in overall physiology appear to enhance the ability of the leaves to continue expansion at suboptimal temperatures. In both GA‐treated and cold‐acclimated tissue, the occurrence of a longer LEZ was associated with a lower temperature sensitivity in LER.
Environmental and developmental effects on the biosynthesis of UV‐B screening pigments in Scots pine (Pinus sylvestris L.) needles
Authors: KAFFARNIK FLORIAN , SEIDLITZ HARALD K. , OBERMAIER JOSEF , SANDERMANN HEINRICH , HELLER WERNER
Published: April 2006

The major UV‐B screening pigments of the epidermal layer of Scots pine (Pinus sylvestris) needles are flavonol 3‐o‐glycosides (F3Gs) esterified with hydroxycinnamic acids at positions 3′′ and 6′′. Acylation is the last step in biosynthesis and is catalysed by position‐specific hydroxycinnamoyl transferases (3′′ and 6′′HCT). The UV‐B dependence of these enzyme activities was studied in primary needles of Scots pine seedlings grown under different UV‐B conditions in environmentally controlled sun simulators. 6′′HCT activity was induced upon UV‐B irradiation while 3′′HCT activity was not induced but showed high constitutive values. To investigate the biosynthesis of diacylated F3Gs during needle development under natural conditions, the HCT activities and metabolite contents were analysed in needles of field‐grown mature pine trees. Accumulation of diacylated compounds as well as of 6′′HCT activity occurred transiently in the first year of needle development only. In contrast, 3′′HCT activity exhibited broad maxima in two consecutive years during needle growth. The data suggest that acylated F3Gs are first formed as soluble compounds which are then translocated into the cell wall to be bound by their hydroxycinnamoyl residues.
Response of Chlorella to Scandium and Potassium at Various pH
Authors: HOROVITZ C. T. , WEGMANN K.
Published: April 2006

The response of Chlorella pyrenoidosa cells to moderate potassium deficiency and to the addition of various scandium amounts in the nutrient solution were studied at different pH. The effects on growth, chlorophyll content, oxygen consumption, and the 14CO2 incorporation in photosynthesizing cells were measured. Considerable metabolic changes inside the cells were registered under the given nutrient conditions. The separated 14C‐labelled compounds showed, at acid and neutral pH in complete nutrient solution, an increase in the relative content of sugar phosphates and a decrease in the relative content of sucrose, caused by increasing scandium concentrations. Moderate potassium deficiency caused a diminution of the relative content of sugar phosphates. The relative content of amino acids was increased by scandium added to complete nutrient solution, but it decreased under potassium deficiency.
The ATP Levels Obtained in Photophosphorylation, Glycolysis and Oxidative Phosphorylation in Scenedesmus Titrated with Desaspidin
Authors: OKKEH ASSAD , KYLIN ANDERS
Published: April 2006

The ATP levels in photophosphorylation, glycolysis and oxidative phosphorylation, in the unicellular green alga Scenedesmus obtusiusculus, were titrated with narrow concentration intervals of desaspidin in the presence of different concentrations of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), which allows the differentiation between non‐cyclic, pseudocyclic and true cyclic photophosphorylation. The data on photophosphorylative ATP levels were compared with earlier data on total binding of phosphate. In the true cyclic process, both parameters are equally sensitive towards desaspidin. Under pseudocyclic conditions and in non‐cyclic photophosphorylation, the level of ATP is more sensitive towards desaspidin than is total binding of phosphate. This suggests a structural difference between the cyclic and the two non‐cyclic (one of which is also pseudocyclic) sites. The non‐cyclic ATP level is more sensitive towards desaspidin than is pseudocyclic. This may be connected with the higher ATP level under pseudocyclic as compared to non‐cyclic conditions.
Volatilization of Mercury by Algae
Authors: BEN‐BASSAT D. , MAYER A. M.
Published: April 2006

The presence of Chlorella cells in a medium containing HgCl2 causes a rapid decrease of the mercury content in the algal suspension. The rate of decrease depends on the inoculum concentration. The presence of Hg in the medium induces a lag in the growth, whose length depends on the initial concentration of Hg and of the inoculum. Binding and/or uptake of mercury by the cells is not dependent on temperature. The mercury content per cell declines somewhat at the time at which the culture resumes growth at a rate similar to that of the controls without mercury.
Manganese Absorption and Transport in Rice
Authors: RAMANI SARADHA , KANNAN SESHADRI
Published: April 2006

The absorptive patterns of Mn2+ in excised rice roots, leaf tissues and intact plants, were studied. The rates of absorption of Mn2+ followed different patterns in the roots and the leaf tissues. The uptake from 0.1 and 5 mM MnSO4 was found to be sensitive to metabolic inhibitors. The time course of uptake from 0.1 mM and 5 mM MnSO4 followed a biphasic pattern which represented only the metabolic component of absorption. A secondary biphasic pattern of uptake at 5 mM MnSO4 (one at 20 min and another at 80 min) appears quite anomalous and is probably related to structural virations or cellular compartments. When absorption and transport of Mn2+ were measured in intact rice and wheat plants, it was found that Mn2+ was easily translocated to shoot from roots and the transport of Mn2+ was comparable to that of K+.
The Formation of Coremia in Ceratocystis piceae Induced by Hexanal
Authors: FRIES NILS
Published: April 2006

Hexanal, and to a lesser degree nonanal, added in gaseous form induce coremia formation in the blue stain fungus Ceratocystis piceae (Münch) Bakshi grown in axenic agar culture. The optimum initial concentration of hexanal in the gas phase proved to be c. 2 mg/1 (2 × 10−5M). Possible ecological implications are discussed.
Bolting Susceptibility of Sugar Beet (Beta vulgaris) in Relation to Contents of Sulfhydryls and Disulfides and to Protein Composition of Membranes
Authors: LEXANDER KERSTIN
Published: April 2006

The aim of the investigation was to correlate the sensitivity to low temperature that leads to bolting of sugar beet with a property of seedlings or seeds, analyzable without cold treatment. Populations or inbred lines were investigated, the bolting percentages of which had been determined in field trials. Sulfhydryls (—SH) and disulfide sulphur (‐S‐) were analyzed by amperometric titration with silver nitrate. Disulfides were broken with sulphite, and proteins were unfolded with urea.

Negative correlations were found between the bolting percentage and (‐SH + ‐S‐) per leaf fresh or dry weight unit and per leaf protein nitrogen, with urea at the titrations. Positive correlations were obtained between the bolting percentage and the ratio of (‐SH + ‐S‐) titratable in the absence of urea to that titratable in the presence of urea, when leaf homogenates or leaf or seed protein precipitates were examined. Centrifugation experiments showed that membrane proteins were responsible for the correlation. By polyacrylamide gel electrophoresis of the membrane proteins it was found that the proportion between some of these proteins was correlated with the bolting percentage.

From these results and such from analyses of beet plants during and after cold treatment a hypothesis was constructed: Low bolting susceptibility, i.e., low sensitivity to low temperature, is caused by a high proportion of a hydrophobic membrane protein, rich in ‐SH or ‐S‐. This protein interferes with the reactivity of the plants to gibberellins resulting from low temperatures or long days.
Biosynthesis of Abscisic Acid under Osmotic Stress: Studies Based on a Dual Labelling Technique
Authors: LOVEYS B. R. , BRIEN C. J. , KRIEDEMANN P. E.
Published: April 2006

Sterile liquid suspension cultures from grape pericarp tissue incorporate label from mevalonic acid into abscisic acid (ABA), some of which is subsequently released into the surrounding medium. The addition of mannitol to the culture medium caused plasmolysis of individual cells and increased ABA generation and release. Levels in the medium increased up to 30 fold over a period of 8 h in the presence of mannitol (720 milliosmol).

A dual labelling technique using 14C and 3H mevalonic acid was developed to distinguish between labelled compounds produced by turgid tissue and those specifically associated with the substantial increase in ABA synthesis following mannitol treatment.
Aminotransferase Activity in Relation to Floral Differentiation in Wheat Plants
Authors: SRIVASTAVA G. C. , SIROHI G. S.
Published: April 2006

The present investigation was carried out to study the transamination reaction in relation to floral differentiation in wheat (cv. NP 876) under three photoperiodic conditions. Three selected aminotransferases namely glutamic‐glyoxylate, glutamic‐pyruvate, and alanine‐glyoxylate were studied in the top young leaves at various growth and developmental stages. The activity of all the three systems increased progressively during the vegetative phase till the plants produced reproductive buds. When flower primordia started differentiating, there was a sharp decrease in the aminotransferase activity followed by an increase during anthesis period. Photoperiodic treatments clearly show that even when the vegetative period of the plant is shortened considerably by long day or extended by short day, the aminotransferase activity remains closely associated with different developmental processes.
Morphogenesis in Tissue Cultures of Different Organs of Nigella sativa
Authors: BANERJEE S. , GUPTA S.
Published: April 2006

Calli were isolated from root, stem and leaf segments of Nigella sativa (Fam. Ranunculaceae) on White's medium containing napthaleneacetic acid and coconut milk. From all the three types of calli, roots were differentiated. Shoot development occurred in stem and leaf calli only after the omission of first coconut milk and then of auxin from the basal medium and also in IAA (2.0 mg/ml) and coconut milk (15 % v/v) in the medium. Frequency of organ formation and the maintenance of this capacity depend upon the nature as well as the age of the callus tissue.
Quelques Modifications Physico‐chimiques et Physiologiques liées à la Sénescence des Feuilles
Authors: VIGNES DOMINIQUE , CALMÉS JEAN
Published: April 2006

During the senescence of the leaves of Parthenocissus tricuspidata Planchon, the high level of Ca2+ ions liberated from pectic membranes in the aqueous medium of the blade causes a decrease in photophosphorylation and chlorophyll regeneration, while carboxylation and diffusion resistances increase. After the hydrolysis of its carbohydrate and protein reserves, the leaf blade can no longer contribute to the nutrition of the plant and abscission is prepared.
Influence de la 6‐benzylaminopurine sur la différenciation plastidiale dans les cotylédons de concombre
Authors: FARINEAU NICOLE , ROUSSAUX JEAN
Published: April 2006

Treatment with 6‐benzylaminopurine (6‐BAP; 10−5 g/ml) accelerates the growth of detached cucumber cotyledons (Cucumis sativas L.), primarily through an increased water uptake by the tissues. A comparative study of pigment composition and ultrastructure in 6‐BAP treated and untreated cotyledons shows that cytokinin, in the presence of light, accelerates the transformation of etioplasts into chloroplasts. 6‐BAP also enhances the synthesis of membrane precursors as indicated by the formation of a dense prolamellar body and by the persistence of a pseudo‐cristalline structure in 6‐BAP treated material. Stimulation of biosynthetic activity by cytokinin leads simultaneously to an increase in the rate of the pigment synthesis and to an acceleration in the building of the lamellar system. Furthermore, chloroplasts of 6‐BAP treated cotyledons show abnormal features such as a striking increase in the number of thylacoids per granum and a poor development of the intergranal system.
Effects of Some Chemicals on the Oxygen Evolution and Oxygen Uptake in Isolated Wheat Chloroplasts Irradiated without the Addition of an Oxidant
Authors: EGNÉUS HANS
Published: April 2006

The oxygen exchange, obtained when isolated chloroplasts of Triticum aestivum, wheat, are irradiated without the addition of a Hill oxidant has been investigated using an oxygen electrode. Ascorbate, catalase, 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐p‐benzoquinone(DBMIB), diethyldithio‐carbamate (DEDT), dichlorophenylmethylurea (DCMU), and potassium cyanide were added to the Chloroplasts in order to investigate the oxygen exchange. At least two oxygen uptake reactions, one sensitive to catalase and one catalase‐insensitive, appeared upon irradiation. Hydrogen peroxide was the product of the oxygen uptake in the former process, and water was the reductant. The formation of hydrogen peroxide was probably associated with photosystem I. The other oxygen consuming reaction was found to be insensitive to both catalase and potassium cyanide. After the chloroplasts had been treated with DCMU, it was possible to show that the catalase‐insensitive oxygen uptake was localized in photosystem I, and that a cyclic electron transport system or some endogenous reductant (‐s) acted in the oxygen uptake.

Addition of ascorbate or DEDT to the chloroplasts led to an enhanced oxygen uptake in 710 nm light. This was probably due to the effect of these compounds on the superoxide radical ion formed in photosystem I. The stimulated oxygen uptake was only weakly affected by catalase, indicating that hydrogen peroxide was not a product of this oxygen uptake. Addition of DEDT and potassium cyanide inhibited (strongly respectively weakly) the oxygen uptake when photosystem II was functioning. The effect of these compounds was probably due to an inhibition of the electron transport at the plastocyanin.

DBMIB inhibited the oxygen uptake reactions and the cooperation between the two photosystems. The cooperation between the photosystems was also studied in DCMU‐treated chloroplasts. The reactions in photosystem II, measured as oxygen evolution, were more inhibited than the coupling between the photosystems.

The oxygen “gush” appearing upon irradiation in light of 650 nm was not affected by a DBMIB‐treatment, showing that the oxygen evolution was due to the reduction of plastoquinone. The reoxidation in the dark of the plastoquinone pool was stimulated by DBMIB and potassium cyanide indicating that an oxygen uptake could be associated with plastoquinone.

The sites of interaction of oxygen with the electron transport pathways in chloroplasts, and the different reductants for the oxygen consuming reactions are discussed.
Production of Pectinase and Cellulase by Cladosporium cucumerinum with Dissolved Carbohydrates and Isolated Cell Walls of Cucumber as Carbon Sources
Authors: SKARE N. H. , PAUS F. , RAA J.
Published: April 2006

The scab fungus Cladosporium cucumerinum can use pectins and polygalacturonic acid as sole sources of carbon. Cellulose and Ca‐polygalacturonate are not available carbon sources for the fungus. When growing on sucrose or pectin, pectinase is produced. In these cases the production of cellulase is insignificant. On a mixture of pectin and carboxymethylcellulose also cellulase is produced.

Both pectinase and cellulase are released into the culture filtrate when the fungus grows on cell walls without ionic proteins, whereas only cellulase is released when cell walls with ionic proteins are the carbon source. Pectinase produced by the pathogen can bind to isolated cell walls. The bound pectinase can be extracted with 1 M NaCl from cell walls without ionic proteins, but not from cell walls with ionic proteins.

A water‐extract or 1 M NaCl‐extract of cucumber hypocotyls with visible disease symptoms contains cellulase but no pectinase activity. Lack of pectinase activity in the 1 M NaCl‐extract may be due to inhibition by a component that could be extracted by NaCl from the cucumber cell walls.
Comparative Effects of Indoleacetic Acid and Gibberellic Acid on Growth of Decapitated Etiolated Epicotyls of Pisum sativum cv. Alaska
Authors: DAVIES ERIC , ÖZBAY ORHAN
Published: April 2006

Measurements were made of the growthof the sub‐apical region of decapitated, etiolated epicotyls of Pisum sativum L. cv. Alaska after treatments with indoleacetic acid (IAA), gibberellic acid (GA) and triiodobenzoic acid (TIBA). Growth was measured either at the end of a 2‐day period, at short intervals during growth, or was monitored continuously for 2–3 h using a position‐sensing transducer.

In experiments measuring growth after 2 days, high levels (0.1–10 μg/plnat) of IAA caused expansion, whereas similar levels of GA caused elongation. When both hormones were applied together, the effects of IAA were dominant and expansion ensued, even when GA was present at 100 times the amount of IAA. Very low amounts of IAA (0.5–5 ng/plant), however, caused elongation. The elongation elicited by high GA or low IAa was inhibited to a similar extent by TIBA and this inhibition of elongation was associated with an increased expansion at the extreme tip. When application of the hormones was delayed, GA‐induced elongation was reduced considerably, IAA‐induced elongation was lessened somewhat and IAA‐induced expansion was partially converted into elongation.

In experiments measuring elongation at short intervals, high levels of IAA caused rapid elongation followed after 3 to 6 h by expnasion. Both GA and low levels of IAA extended the duration of elongation with little apparent effect on the rate of growth. In fast‐growth experiments, low, intermediate and high levels of IAA doubled the rate of elongation with a lag period of about 20 min, whereas GA had at most a very slight stimulatory effect on the growth rate.

It is concluded that the main role of GA in this system is to maintain physiological levels of IAA in the growing zone and that the level of IAA present determines whether elongation or expansion will take place.
Regulation of Transpiration in Avena. Responses to Red and Blue Light Steps
Authors: BROGÅRDH TORGNY
Published: April 2006

The transpiration responses of primary Arena leaves to red and blue light steps were investigated. The response to a red light step was a so‐called slow response (with a rise time of about 8 min). The response to a blue light step consisted of both a slow, and a rapid response (with a rise time of about 2 min). CO2‐free air outside the leaf eliminated only the slow response, i.e. in CO2‐free ait the plant responded to blue light steps but not to red ones. A short exposure of red light prior to a blue light step enhanced the rapid response. The same enhancement of the rapid response could be achieved by means of a temporary pretreatment with CO2‐free air. The magnitude of the rapid response was dependent on the blue light irradiance and no threshold effects could be detected. — The experimental results are discussed by means of a model, based on stomatal regulation by, ion transport between the subsidiary cells and the guard cells. It is suggested that the slow transpiration response is due to CO2‐regulation of the stomatal aperture and that the rapid response reflect a CO2‐independent blue light sensitive process, which acts directly on the ion transport through the subsidiary and guard cell membranes.
Sulphate Uptake in Two Mutants of Chlorella vulgaris with High and Low Sulphur Amino Acid Content
Authors: PASSERA CALVINO , FERRARI GIOVANNI
Published: April 2006

Two mutants of Chlorella vulgaris characterized by higher and lower content of sulphur amino acids compared with the wild strain were assayed for the efficiency of the sulphate uptake mechanism. In both mutants uptake exhibited positive cooperation kinetics and was strongly stimulated by sulphate starvation. Stimulation was depressed by cysteine and to a higher extent by methionine. Mutations affected the uptake efficiency concordantly with the level of sulphur amino acids. Addition to the starved strains of sulphate or chromate reduced the induced transport to the lower values of the non‐starved strains. Addition of cycloheximide during the induction period prevented a further enhancement of transport without depressing the attained rate in the low sulphur mutant; it was followed by a rapid fall to the non‐induced rate in the high sulphur mutant.
Sources of Nitrogen Supporting Growth and Embryogenesis in Cultured Wild Carrot Tissue
Authors: WETHERELL D. F. , DOUGALL D. K.
Published: April 2006

This paper seeks to calarify conflicting reports on the nitrogen requirements for in vitro embryogenesis in Daucus carota.

Tissue derived from petiole explants of the wild strain of this species were tested with a variety of sources of cellular nitrogen under conditions otherwise favorable for in vitro embryogenesis. The use of very small, sieved and well‐washed inocula reduced the carry‐over of soluble materials with the inoculum. Embryo yield was quantified by direct counting of samples.

Nitrate at concentrations ranging from 5 to 95 mM KNO3 supportes only weak growth and very low embryogenesis under the exacting conditions of these experiments. As little as 0.1 mM NH4Cl added to a nitrate medium allows some embryogenesis and 10 mM NH4Cl is near optimal when KNO3 is in the range of 12 to 40 mM concentration. Glutamine, glutamic acid, urea and alanine can individually partially replace NH4Cl as a supplement to KNO3. Glutamine, alanine, and possibly glutamic acid can serve as sole sources of nitrogen supporting both good growth and embryogenesis. It was concluded that a reduced nitrogen source is required, at least as a supplement to nitrate, for rapid growth and for in vitro embryogenesis of cultured wild carrot tissue. The relationship of pH of the culture medium to growth and embryogenesis was explored and optima observed at approximately pH 5.4 for both processes.
The Effect of Metabolic Poisons on ATP Level and on Active Phosphate Uptake in Chlorella pyrenoidosa
Authors: JEANJEAN ROBERT
Published: April 2006

Influence of light and dark aerobic conditions and of various metabolic poisons [3‐(3,4‐dichlorophenyl)1,1‐dimethylurea (DCMU), 2,4‐dinitrophenol (2,4‐DNP), carbonyl cyanide‐m‐chlorophenylhydrazone (m‐CCCP), α,α′bis(hexafluoroacetonyl) acetone (1799), N,N′‐dicyclohexylcarbodiimide (DCCD), sodium azide, fatty acids] on the active phosphate uptake and on the ATP level has been investigated. Cells in the dark have the same level of ATP as in the light though the phosphate transport is decreased. Similar findings are observed with DCMU. Other poisons used inhibit phosphate uptake and decrease ATP level. However their effect is more drastic on phosphate transport than on the ATP level. There is no good correlation between the ATP level and phosphate transport.
Nitrate, Ammonium and Kinetin Effects on Growth and Enzyme Activities of Paul's Scarlet Rose Callus
Authors: CALDAS R. A. , CALDAS L. S.
Published: April 2006

Factorial experiments using the three variables nitrate, ammonium, and kinetin at six different concentrations each (nitrate 4.64 to 215 mM; ammonium 2.15 to 100 mM; and kinetin 0.1 to 4.64 mg/l) were set up to measure the effects of each of these factors, and their interactions, on the fresh weight, protein, and enzyme activities of callus of Paul's Scarlet Rose. Optimum fresh weight values were obtained with nitrate at 46.4 mM. Ammonium inhibited growth at concentrations above 2.15 mM, and kinetin had no significant effect. Significant interaction between nitrate and ammonium effects on growth was found. Kinetin did not interact significantly with either nitrate or ammonium to influence the fresh weight. The specific activity of glutamate dehydrogenase (NAD) in the aminating reaction increased with increasing ammonium concentrations to 21.5; at higher concentrations the activity remained high. Glutamine synthetase specific activity was constant over a large range of nitrate and ammonium concentrations, increasing only when nitrate went from 46.4 to 100 mM. Glutamine synthetase was sensitive to the nitrate: ammonium interaction. Specific activity decreased at progressively higher ammonium levels when nitrate concentration increased. No glutamate synthase activity was detected at optimal nitrate concentrations.