bluuebunny/crossref_metadata_2025 huggingface dataset:
Blue light‐regulation of cell division in Adiantum protonemata: an approach with pulse stimulation
Authors: IINO M. , NAKAGAWA Y. , WADA M.
Published: April 2006

Abstract Cell division of the single‐celled Adiantum protonemata produced by red‐light (RL) incubation of germinated spores is induced by transfer to darkness and is stimulated by blue light (BL). It is known that the cellular process leading to this cell division includes one cell cycle and the BL response results from shortening of the Gl phase. The authors studied this BL regulation of cell cycle by giving a pulse of BL after RL termination and measuring changes in the proportion of divided cells. To minimize phytochrome responses arising from BL irradiation, the plants were kept in continuous far‐red light instead of total darkness after the RL incubation. The response to a pulse (10–100 s) approached saturation with increasing rluences in a manner that reciprocity is valid. The sensitivity to BL, investigated by measuring the response to a saturating pulse, showed an increase in the first several hours after RL termination, followed by a sustained sensitivity for 20 h. Time courses of the pulse‐induced responses showed a lag of about 12 h, which was considerably shorter than in the non‐stimulated control; the lag was approximately independent of the strength of BL stimulation or the timing of BL application after RL termination, and the major difference occurred in the slope. It is concluded that the sensitivity to BL is retained during the time span in which the dark‐dependent Gl phase progresses, and that the BL response is initiated independently of the reactions involved in the dark‐dependent Gl phase. A minimal reaction model of Gl phase is suggested to unify the results.
Stomatal and non‐stomatal limitations to carbon assimilation: an evaluation of the path‐dependent method
Authors: ASSMANN S. M.
Published: April 2006

Abstract Environmental stresses can decrease photosynthesis by a direct effect on photosynthetic capacity of the mesophyll or by a CO2 limitation resulting from stomatal closure. In the present study, a ‘path‐dependent method’ (Jones, 1985) for the partitioning of a stress‐related decline in assimilation rate between non‐stomatal and stomatal factors was evaluated, using light quality as a ‘stress’. Kinetic data on assimilation rate and conductance of Phragmipedium longifolium following a change in light quality from 95 μmol m−2s−1 white light to 95 μmol m−2s−1 red light failed to generate a smooth response curve for conductance. Partitioning of limitations on assimilation by a path‐dependent method that utilizes the actual trajectories of conductance and assimilation was therefore not feasible. A simplified path‐dependent method (Jones, 1985) which assumes that either mesophyll cells or guard cells respond first to a stress was applied to steady‐state measurements of assimilation and conductance under red and white illumination. Either 5% or 23% of the observed reduction in assimilation rate under white light was attributable to stomatal factors, depending on whether the ‘stomatal first’ or the ‘mesophyll first’ path was assumed. In the absence of additional information indicating the appropriate choice of path, arbitrary choice may therefore lead to widely divergent estimates, and potentially erroneous conclusions. An alternative approach to the evaluation of the importance to carbon assimilation of stomatal and non‐stomatal factors is suggested.
Movement of lucifer yellow in leaves of Coleus blumei Benth
Authors: FISHER D. G.
Published: April 2006

Abstract Individual spongy mesophyll cells in green areas of variegated Coleus blumei leaves were injected with the symplast‐mobile dye lucifer yellow and its movement to other cell types was followed with fluorescence microscopy. In 13 trials, the dye remained in the injected cell twice, moved only to other mesophyll cells five times, and moved up to and along minor veins six times. Where extensive movement of the dye occurred, the tissue was fixed with 4% glutaraldehyde, dehydrated, embedded in plastic, sectioned at 3 μm, and examined again with fluorescence microscopy. The dye was found in abaxial bundle‐sheath cells for up to 200 μm or more distant from the site of injection near the minor vein, but no convincing evidence was found for its presence in the vascular tissue itself. It thus appears that superficial whole‐mount views of lucifer yellow movement along leaf minor veins cannot be taken as certain evidence for symplastic transport of the dye into and along the vascular tissues.
Control of hypocotyl phototropism by phytochrome in a dicotyledonous seedling (Sesamum indicum L.)
Authors: WOITZIK F. , MOHR H.
Published: April 2006

Abstract The phototropic response in stems of higher plants is brought about by blue/UV light. The problem studied here is to what extent long‐wavelength light, which is absorbed by phytochrome, affects the phototropic response. A refined measurement of phototropism — a curvature index — was applied to the hypocotyl of the sesame seedling (Sesamum indicum L.). The time course of the phototropic response was followed in continuous unilateral weak blue light (B, 460 nm, 8 mW m−2). Long term red light (R) pretreatments, operating through phytochrome, strongly increase the rate and extent of the phototropic response once it is elicited by unilateral B, while the pretreatments decrease the sensitivity towards B. If a R pulse is given immediately prior to the onset of unilateral B, the rate of the response is strongly reduced compared to the time course of curvature observed when the pretreatment was terminated with a long wavelength far‐red light (FR) pulse.

R and FR were then applied simultaneously with unilateral B to manipulate the status of the phytochrome system during actual curvature. It was found that a low Pfr/P ratio (established by FR) stimulates the phototropic response far above the control (B alone), while a high Pfr/P ratio (established by R) reduces the response below the control. During bending a positive effect of phytochrome on the rate and extent of the phototropic response, which is saturated at a low level of Pfr, appears to be counteracted by an inhibitory effect which dominates at higher levels of Pfr, such as established by omnilateral R. However, if R is applied unilaterally from the same direction as B, R increases the rate of curvature. Apparently the sesame seedling is capable of detecting the direction of R relative to the direction of B. While a mechanistic explanation of these effects cannot be advanced at present, it is clear that the seedling is capable of super‐imposing information about the actual light conditions during bending on a ‘memory’ of the light conditions prior to the onset of bending. Thus, the previous as well as the actual light conditions determine its phototropic responsiveness.
Regulation of glycerol and starch metabolism in Chlamydomonas pulsatilla in response to changes in salinity
Authors: HELLEBUST J. A. , LIN YI‐HUNG
Published: April 2006

Abstract. Chlamydomonas pulsatilla rapidly adjusts its level of osmoregulatory solute, glycerol, when exposed to increased (upshock) or decreased (downshock) salinities. Rates of degradation, or loss, of glycerol are similar in light and dark, while rates of net synthesis proceed about 20% faster in the light than in the dark. Synthesis of glycerol in the dark is correlated with degradation of starch, and starch appears also to be utilized for glycerol synthesis in response to extensive salinity upshocks in the light, where photosynthesis is strongly inhibited. Under conditions of moderate upshocks in the light, photosynthesis is not affected, and net increases in both glycerol and starch were observed. Glycerol turnover takes place both under iso‐osmotic conditions, and during period of adjustments to osmotic downshocks, where there is a rapid net decrease in the glycerol pool. Half times for glycerol turnover were estimated from rates of incorporation of photoassimilated 14C into glycerol and glycerol pool sizes to be 20 and 74 min for cells incubated at 50 and 100% artificial seawater, respectively.
Photoperiod control of the initial phase of frost hardiness development in Pinus radiata
Authors: GREER D. H. , STANLEY C. J. , WARRINGTON I. J.
Published: April 2006

Abstract. The development of frost hardiness in Pinus radiata was investigated to establish whether there is quantitative relationship between photoperiod and the hardening process. Three controlled environment experiments were carried out. In the first, seedlings were exposed to a photoperiod that shortened from 13 h at a rate of 3 min d−1 to 9.5 h. At intervals, the photoperiod was either held constant or lengthened. In the second experiment, seedlings were exposed to one of five constant photoperiods between 9 and 12 h for up to 90 d. In the third, seedlings were exposed to photoperiods shortening at rates of 1 or 5 min d−1. Frost hardiness was also measured during the natural photoperiod‐controlled stage of hardening in outdoor‐grown seedlings. Frost hardiness developed at a constant rate in response to a shortening photoperiod once it had declined to about 12 h. This rate was consistent with the hardening rate that occurred in outdoor‐grown seedlings. Hardening stopped when the photoperiod became constant, indicating a tight coupling between changes in photoperiod and hardiness development. When the photoperiod was held constant, the extent of frost hardiness was directly dependent on the photoperiod but the rate of hardening was apparently independent of the length of photoperiod. However, the rate of hardening was dependent on the rate at which the photoperiod shortened, increasing linearly with increases in the rate of change in photoperiod between 0 and 3 min d−1. These results suggest shortening photoperiods control the first stage of the hardening process by regulating the rate of hardening. Frost hardening was inherently unstable once the maximum hardiness was reached since spontaneous dehardening occurred in spite of the controlled conditions. Dehardening also occurred when the photoperiod was lengthened suggesting that the cue for dehardening to commence was the shift from shortening to lengthening photoperiods.
Water balance of N2‐fixing root nodules: Can phloem and xylem transport explain it?
Authors: RAVEN J. A. , SPRENT J. I. , McINROY S. G. , HAY G. T.
Published: April 2006

Abstract Analysis of nodule inputs via the phloem and outputs via the xylem leads to the conclusion that water fluxes along those conduits alone would give a xylem sap osmolality in excess of that of sieve tubes and would thus plasmolyse the latter unless N2 fixation involved a very high respiratory consumption of organic C entering in the phloem, or there is significant water influx from soil through the nodule surface. Whether N2 fixation by attached nodules not in contact with an external water supply is energetically inefficient (and hence also, at a whole plant level, inefficient in terms of water‐use) is as yet untested. However, the hypothesis which we prefer involves the shortfall in water entry via the phloem being made up the parenchymatic water flux from the root to the nodule.
Greening and growth of suspension‐cultured cells of Chenopodium rubrum under conditions of heterotrophic and autotrophic nutrition
Authors: ZIEGLER P. , SCHEIBE R.
Published: April 2006

Abstract Dark‐grown cell suspension cultures of Chenopodium rubrum lacking chlorophyll greened strongly upon transfer to illumination and fresh medium. This greening took place both in the presence of sucrose as a carbon source and in a mineral salt medium under an atmosphere enriched in CO2. The synthesis of chlorophyll was in each case closely accompanied by the development of high levels of enzymes typical of photosynthesis. Greening in sugar‐containing medium resulted in a rapid acquisition of characteristic features of photomixotrophic cultures, which have the ability to survive for a prolonged period in a minimal photoautotrophic environment in the light long after the initially present sucrose has been depleted from the medium. Greening under autotrophic conditions represented a direct transition from starvation conditions resulting from prolonged heterotrophic batch growth to successful photoautotrophy. Thus, light triggered the build‐up of a competent photosynthetic apparatus irrespective of the nutritional necessity for autotrophy. Illumination and greening did not influence catabolic enzyme activities beyond that increase of metabolic activity which is required for the production of photosynthetic machinery.
Salinity resistance in Zea mays: fluxes of potassium, sodium and chloride, cytoplasmic concentrations and microsomal membrane lipids
Authors: HAJIBAGHERI M. A. , YEO A. R. , FLOWERS T. J. , COLLINS J. C.
Published: April 2006

Abstract Cytoplasmic concentrations, fluxes of K+, Na+ and Cl and microsomal membrane lipids were investigated in a salt‐sensitive and salt‐resistant variety of Zea mays. The salt resistance of Protador relative to LGH (salt‐sensitive) appears to be related to higher K+ fluxes and cytoplasmic concentrations, and lower Na+ and Cl fluxes and cytoplasmic concentrations, when grown in NaCl. There were no apparent differences in the simple chemical composition of root microsomal membrane lipids between the two varicties, neither were these affected by salt.
Adaptations by macroalgae to low carbon availability. I. A buffer system in Ascophyllum nodosum, associated with photosynthesis
Authors: AXELSSON L. , CARLBERG S. , RYBERG H.
Published: April 2006

Abstract The exchange of CO2, H+ and O2 between seawater and the intertidal brown macroalga Ascophyllum nodosum (L.) Le Jolis were measured in a flowthrough system. While the algae were kept in darkness, seawater with artificially increased alkalinity and pH at 9.85, was alternated with ‘normal’ seawater at pH 8.0. A proton buffering system, with capacity to release and reabsorb about 20 μmol protons per gram alga (fresh weight) was revealed. As the algae were returned to the ‘normal’ seawater, the kinetics of proton reabsorbtion indicated that a proton uptake was gradually induced. This proton uptake, which was not connected to ion exchange in the cell wall, reached its maximum after 12 h. If subjected to high alkalinity seawater in the light, A. Nodosum for a certain period of time was capable of carrying out O, evolution in excess of the import of inorganic carbon. This ‘photosynthetic buffering capacity’ amounted to about 17 μmol O; per gram alga. Besides depending on a buffer of photorcducible substances, this ‘photosynthetic buffering capacity’ appeared to be functionally connected with the proton buffer. The time course for the discharge of the ‘photosynthetic buffer system’ and for the reabsorbtion of protons into the proton buffer (about 6h for 90× of the capacity at a temperature of 6°C) suggests that the ‘photosynthetic buffer system’ has a functional importance in the adaptation of A. nodosum to intertidal regions. The function of the buffer system is discussed in relation to the crassulacean acid metabolism (CAM)‐like characteristics recently shown for the intertidal brown algal family Fucaceae.
Growth and nitrate uptake properties of plants grown at different relative rates of nitrogen supply. II. Activity and affinity of the nitrate uptake system inPisumandLemnain relation to nitrogen availability and nitrogen demand
Authors: OSCARSON P. , INGEMARSSON B. , LARSSON C.‐M.
Published: April 2006

AbstractNet nitrate uptake rates were measured and the kinetics calculated in non‐nodulatedPisum sativumL. cv. Marma andLemna gibbaL. adapted to constant relative rates of nitrate‐N additions (RA), ranging from 0.03 to 0.27 d−1forPisumand from 0.05 to 0.40 d−1forLemna, Vmaxof net nitrate uptake (measured in the range 10 to 100 mmol m−3nitrate, i.e. ‘system I’) increased with RAin the growth limiting range but decreased when RAexceeded the relative growth rate (RGR), Kmwas not significantly related to changes in RA. On the basis of previous13N‐flux experiments, it is concluded that the differences in Vmaxat growth limiting RAare attributable to differences in influx rates. Linear relationships between Vmaxand tissue nitrogen concentrations were obtained in the growth limiting range for both species, and extrapolated intercepts relate well with the previously defined minimal nitrogen concentrations for plant growth (Oscarson, Ingemarsson & Larsson, 1989). Analysis of Vmaxfor net nitrate uptake on intact plant basis in relation to nitrogen demand during stable, nitrogen limited, growth shows an increased overcapacity at lower RAvalues in both species, which is largely explained by the increased relative root size at low RA. A balancing nitrate concentration, defined as the steady state concentration needed to sustain the relative rate of increase in plant nitrogen (RN), predicted by RA, was calculated for both species. In the growth limiting range, this value ranges from 3.5 mmol m−3(RA0.03 d−1) to 44 mmol m−3(RA0.21 d−1) forPisumand from 0.2 mmol m−3(RA0.05 d−1) to 5.4 mmol m−3(RA0.03 d−1) forLemna.It is suggested that this value can be used as a unifying measure of the affinity for nitrate, integrating the performance of the nitrate uptake system with nitrate flux and long term growth and demand for nitrogen.
Epinasty promoted by salinity or ethylene is an indicator of salt‐sensitivity in tomatoes
Authors: JONES R. A. , EL‐BELTAGY A. S.
Published: April 2006

Abstract Six genotypes of tomato (Lycopersicon esculentum Mill.) that differ in their salt‐tolerance, were exposed to 200 mol m−3 NaCl for 4 weeks. Seedlings exhibited a marked decline in shoot dry weight accumulation and increased petiolar epinasty after exposure to salinity stress. Ranking accessions on the basis of their relative growth reduction in response to salinity, provided good agreement with the level of epinasty promoted during the salinity treatment. In the absence of salt‐stress, leaf epinasty promoted by exogenous ethylene treatment was found to be a positive indicator of the genotypes incipient salt‐sensitivity. Endogenous ethylene levels in untreated plants were negatively correlated with ethephon‐induced epinasty. Genotypes with normally high endogenous C2H4 levels were less responsive to ethephon treatment and also exhibited greater salt‐tolerance than genotypes with low endogenous C2H4 levels. These observations are consistent with the suggestion that a main feature of adaptation in the genotypes examined may involve modulation of their cellular sensitivity to C2H4. The results indicate that leaf epinasty, whether salt‐ or ethylene‐induced, is a sensitive indicator of salt‐sensitivity. Ethylene‐induced epinasty may, therefore, provide a simple basis upon which to identify and select salt‐tolerant plants.
The effect of air pollutants on physiological processes in plants
Authors: DARRALL N. M.
Published: April 2006

Abstract. Important physiological processes, photosynthesis, respiration, carbon allocation and stomatal function are known to be affected by air pollutants. A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride. Some of this variation is clearly due to genetic factors, but much is in response to differences in environmental conditions both prior to and during fumigation. Exposure of plants to mixtures of pollutants generally reduced the threshold at which effects were first detected and increased the level of inhibitory responses. In the majority of studies on stomatal responses to air pollutants, opening occurs at low concentrations, below the threshold for effects on photosynthesis, and closure occurs at injurious concentrations; this latter response often following the inhibition of photosynthesis. Effects on carbon allocation have been reported in response to air pollutants. Changes usually favour leaf development over root growth, which can compensate for a decline in net assimilation rate up to a certain point but may limit water uptake from soils with low moisture content. Future research into physiological effects of air pollutants should incorporate an integrated approach in which both key physiological parameters and growth parameters are measured together with estimates of the effective dose of pollutant. In this way, the underlying mechanisms to changes in growth and development will be more fully understood.
Fruit photosynthesis
Authors: BLANKE M. M. , LENZ F.
Published: April 2006

Abstract. In addition to photosynthesis as in the leaf, fruit possess a system which refixes CO2 from the mitochondrial respiration of predominantly imported carbon. This pathway produces malate by the action of phosphoenolpyruvate carboxylase, PEPC, (E.C. 4.1.1.31) and appears to be regulated primarily by the cytosolic concentration of HCO3/CO2 and malate. Malate is stored in the vacuole as malic acid, constituting a major carbon pool and a potential substrate for respiration. The PEPC in apple fruit proves to be an efficient form of the enzyme with low Michaelis constants, i.e. Km = 0.09 mol m‐3 PEP and 0.2 mol m–3 HCO3, and large Ki= 110 mol m‐3 HCO3. In fleshy fruit, chlorophyll and chloroplasts are unevenly distributed; they resemble the C3 sun‐type and arc concentrated in the perivascular tissue, with smaller chloroplasts, fewer grana per chloroplast and a larger degree of vacuolation than commonly found in a leaf of the same species. Fruit photosynthesis often compensates for respiratory CO2 loss in the light. However, due to respiration in the dark, CO2 loss is in excess of photosynthetic gain in the light, such that a continual loss of CO2 was observed in the diurnal cycle and which is maintained throughout fruit development. The rate of CO2 exchange decreases on a fresh weight or surface basis, but increases with fruit ontogeny on a per fruit basis, causing accumulation of several percent CO2 in the internal cavity. Stomata are present in the outer epidermis of those fruits examined, but with a 10‐to 100‐fold lesser frequency than in the abaxial epidermis of leaf of the same species. The number of Stomata is set at anthesis and remained constant, while the stomatal frequency decreases as the fruit surface expands. Stomata are as sensitive as in leaves in the early stages of fruit development, but often are transformed into lenticels during fruit ontogeny, thereby decreasing the permeability of the outer epidermis. The discrepancy between the CO2‐concentrating mechanism provided by PEPC analogous to C4/CAM Photosynthesis and the kinetics of fruit PEPC, characteristic of C3/non‐autotrophic tissue, suggests the definition of a new type of ‘fruit photosynthesis’ rather than its categorization within an existing type.
Abscisic acid produced in dehydrating roots may enable the plant to measure the water status of the soil
Authors: ZHANG J. , DAVIES W. J.
Published: April 2006

Abstract. Maize plants were grown in 1‐m‐long tubes of John Innes No. 2 potting compost. From the start of the experimental period, half of the plants were unwatered. Stomatal conductance of these plants was restricted 6 d after last watering and continued to decline thereafter. This was despite the fact that as a result of solute accumulation, unwatered plants showed consistently higher leaf turgors than well‐watered plants. Leaf water potentials of unwatered plants were not significantly lower than those of plants that were watered well. Main seminal and nodal roots showed solute regulation in drying soil and continued to grow even in the driest soil, and plants growing in drying soil showed consistently higher root dry weights than did well‐watered plants, water potentials and turgors of the tips of fine roots in the upper part of the column decreased as the soil dried. Soil drying below a water content of around 0–25 g cm−3 (a bulk soil water potential of between ‐0.2 and ‐0.3 MPa) resulted in a substantial increase in the ABA content of roots. As soil columns dried progressively from the top, ABA content increased in roots deeper and deeper in the soil. These responses suggest that ABA produced by dehydrating roots and which was subsequently transported to the shoots provided a sensitive indication of the degree of soil drying.
Differential desiccation sensitivity of corn and Pennisetum pollen linked to their sucrose contents
Authors: HOEKSTRA F. A. , CROWE L. M. , CROWE J. H.
Published: April 2006

Abstract. Two pollen species from the Gramineae family were investigated as to their differential sensitivity to desiccation. Germination in vivo ceased to occur after previous drying to 7–8% moisture content in Zea mays and 3% in Pennisetum typhoides. The reduced vitality coincided with extensive membrane damage, as evidenced by the considerable leakage of fluorescein and K+ from the prehumidified grains into liquid media. Further experiments were undertaken to investigate the basis for this interspecific difference: (1) phospholipid analyses revealed little difference in composition and content both before and after drying; (2) free fatty acid contents increased in both species upon drying but levels were generally low; and (3) sucrose was the sole soluble carbohydrate found in both species. Fresh maize pollen contained 5% sucrose, as compared to 14% in Pennisetum pollen. During slow drying (8h) this level went up to 12% and 17%, respectively. Drying corn pollen in the cold (2°C), or at high rate, limited sucrose levels and affected the resistance to drying. The authors conclude that survival of dehydration is correlated with the presence of sucrose. Finally, they tested the ability of sucrose to preserve dry liposomes prepared from phospholipids purified from the two species. When liposomes were dried in the presence of sucrose, fusion and leakage could largely be prevented at mass ratio's of sugar to lipid of > 4. Trehalose was also effective but myo‐inositol was not. No species differences were observed. The authors suggest that the presence of sucrose is a key factor in preserving membranes in dry pollen.
A carbon balance model of the sorghum‐Striga hermonthicahost‐parasite association
Authors: GRAVES J. D. , PRESS M. C. , STEWART G. R.
Published: April 2006

Abstract.Growth and gas exchange measurements are used to formulate a carbon balance model to describe the sorghum‐Striga hermonthicahost‐Parasite association.S. hermonthicareduces the growth and radically alters the architecture of infected sorghum plants. Grain and stem weight are reduced, whilst leaf and root biomass are maintained. Losses in host productivity result from two processes: export of carbon to the parasite and Parasite‐induced reductions in host photosynthesis. The latter occurs before the emergence of the Parasite above ground and accounts for 80% of the Predicted loss in production over the lifecycle of the association.S. hermonthicais dependent on carbon exported from the host, since the plant has low rates of photosynthesis coupled with high rates of respiration. Host‐derived carbon accounts for approximately one‐third of the total parasite carbon requirement.
Temperature sensing by plants: a review and hypothesis
Authors: MINORSKY P. V.
Published: April 2006

Abstract. The different effects which fast versus slow cooling have on such fundamental plant processes as ion transport, protoplasmic streaming, phloem translocation, growth, cell motility, water absorption and membrane potential are reviewed. When plant cells are rapidly cooled to non‐injurious temperatures, many of the physiological ramifications of rapid‐cooling stimulation are only transiently observed. It is proposed that these transient rapid‐cooling‐induced responses, sometimes elicited by temperature drops of only a few degrees centigrade, are manifestations of temperature sensing. The hypothesis is advanced that graded potentials, produced in response to rapidly falling temperature, are associated with graded increases in cytosolic free calcium. These transient increases in cytosolic free calcium give rise to many of the physiological effects elicited by rapid cooling. Other effects, however, such as those associated with alterations in membrane composition, gene expression and post‐translational modifications of proteins, may persist longer. The questions of the possible physiological advantage of temperature sensing, and its implications for the study of chilling injury, are discussed.
Electrophysiological evidence for a role for calcium in temperature sensing by roots of cucumber seedlings
Authors: MINORSKY P. V. , SPANSWICK R. M.
Published: April 2006

Abstract. Rapid‐cooling pulses to non‐stressful temperatures cause strong, transient depolarizations in cortical cells of cucumber roots. The amplitudes of these electrical responses are graded according to the rate and amplitude of the cooling pulse. Such graded potentials are typical of sensory processes and indicate that plants possess the ability to sense temperature change. La3+, a blocker of Ca2+ channels, and ethylene glycol bis‐(β‐aminoethyl ether) N,N,N′,N′‐acetic acid (EGTA), a Ca2+ chelator, inhibit the electrical responses elicited by rapid‐cooling pulses. High external [Ca2+] enhances them. These results indicate the involvement of a plasma membrane‐associated Ca2+ channel in the process of temperature sensing by plants. Calmodulin antagonists prolong the repolarization phase of the electrical responses, suggesting a role for calmodulin in the recovery from stimulation.
Osmotic stress, endogenous abscisic acid and the control of leaf morphology in Hippuris vulgaris L.
Authors: GOLIBER T. E. , FELDMAN L. J.
Published: April 2006

Abstract. Previous reports indicate that heterophyllous aquatic plants can be induced to form aerial‐type leaves on submerged shoots when they are grown in exogenous abscisic acid (ABA). This study reports on the relationship between osmotic stress (e.g. the situation encountered by a shoot tip when it grows above the water surface), endogenous ABA (as measured by gas chromatography‐electron capture detector) and leaf morphology in the heterophyllous aquatic plant, Hippuris vulgaris. Free ABA could not be detected in submerged shoots of H. vulgaris but in aerial shoots ABA occurred at ca. 40ng (g fr wt)−1. When submerged shoots were osmotically stressed ABA appeared at levels of 26 to 40ng (g fr wt)−1. These and other data support two main conclusions: (1) Osmotically stressing a submerged shoot causes the appearance of delectable levels of ABA. (2) The rise of ABA in osmotically stressed submerged shoots in turn induces a change in leaf morphology from the submerged to the aerial form. This corroborates the hypothesis that, in the natural environment, ABA levels rise in response to the osmotic stress encountered when a submerged shoot grows up through the water/air interface and that the increased ABA leads to the production of aerial‐type leaves.
Germination of cocklebur seed and growth of their axial and cotyledonary tissues in response to C2H4, CO2 and/or O2 under water stress
Authors: ESASHI Y. , ABE Y. , ASHINO H. , ISHIZAWA K. , SAITOH K.
Published: April 2006

Abstract. Germination modes of lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.) under different water stresses, prepared with mannitol solution, were examined in relation to gaseous factors. As the concentration of mannitol increased, germination was increasingly inhibited at a mode which was drawn by two straight lines having different slopes and meeting at an angle. One is a sharp line occurring at the lower concentrations of mannitol; the other is a gentle line occurring at higher concentrations of mannitol. The former reflected the growth response of axial tissues to mild water stress, whereas the latter reflected the growth response of cotyledonary tissues to severe water stress. The germination potential of cocklebur seeds increased with increasing temperature. Thus, the seeds were more resistant to water stress at higher than al lower temperatures. This increased germination potential under water stress resulted from the greater growth potential of axial tissues, but not cotyledonary tissues, at higher temperature. Increased O2 levels improved both the reduced axial and cotyledonary growth under water stress. Carbon dioxide predominantly enhanced axial growth under water stress, whereas C2H4 exclusively enhanced cotyledonary growth. Thus, these gases were effective in potentiating germination under water stress. When combined with each other, these gases caused more pronounced growth of the axial and cotyledonary tissues, leading to germination under more severe water stresses. Maximal axial and cotyledonary growth under water stress occurred in the simultaneous presence of CO2, C2H4 and O2, which allowed the germination at higher mannitol concentrations above 0.6 kmol m−3 From these results, it was suggested that cocklebur seeds would override water stress by depending upon both the Corresponding axial growth and the C2H4‐responding cotyledonary growth.
The influence of transpiration on the equilibration of leaf water with atmospheric water vapour
Authors: WALKER C. D. , LEANEY F. W. , DIGHTON J. C. , ALLISON G. B.
Published: April 2006

Abstract. The authors examine the isotopic composition of leaf water, at natural abundance levels, as influenced by transpiration rate. The isotopic composition of water of wheat leaves (Triticum aestivum L. var. Aroona) was followed while their transpiration rate adjusted to ‘steady‐state’ environmental conditions. Leaf diffusive resistance was modified by short‐term salt treatment and by plant culture in either nutrient solution, free‐draining sand, or vermiculite. Resultant changes in 18O and 2H in leaf water are described and fitted to the model of Leaney et al. (1985). The treatments with lower transpiration rates were found to have a greater fraction of their leaf water equilibrated with water vapour in the atmosphere. Comparable results were obtained with both 18O and 2H, with some differences being interpreted in terms of turbulence in the vapour diffusion path. The fraction of the leaf water equilibrated with the atmosphere varied between leaves of different ages. However, this may have been due to their different positions in the canopy.
Foliar stage in wheat correlates better to photothermal time than to thermal time
Authors: MASLE J. , DOUSSINAULT G. , FARQUHAR G. D. , SUN B.
Published: April 2006

Abstract. Analysis is made of leaf numbers observed in the field for several wheat genotypes over a wide range of sowing dates. Within any treatment, leaf number was a linear function of thermal time from seedling emergence (°C.d, the mean daily temperatures summed above a base temperature of 0°C) but the slope of the relation depended on sowing date. Leaf appearance rate doubled from October to February sowings, for which it was maximum, and usually decreased for later sowings. However, when expressed on the basis of photothermal time (°C.dl, temperatures accumulated during the light time period only), much of the sowing date effect was removed, except for the latest spring sowings. For these late sowings, leaf appearance rate was usually slower than expected. The authors conclude that both temperature and photoperiod are determinants of leaf appearance rate, and suggest that the slow rate for late sowings may be caused by a non‐linear response to the higher temperatures experienced by the plant during that part of the year. The genotypic differences indicate that it may also be associated with a lack of vernalization. The use of photothermal time rather than thermal time significantly improves prediction of leaf number. However, it still provides only an empirical description of the dependence of leaf number on time and climate.
Effects of nitrogen deficiency on leaf photosynthetic response of tall fescue to water deficit
Authors: GHASHGHAIE J. , SAUGIER B.
Published: April 2006

Abstract. The objective of the present work was to study the effect of nitrogen deficiency on drought sensitivity of tall fescue plants. The authors compared photosynthetic and stomatal behaviour of plants grown at either high (8 mol m−3) or low (0.5 mol m−3) nitrogen levels during a drought cycle followed by rehydration. Other processes investigated were stomatal and non‐stomatal inhibition of leaf photosynthesis, water use efficiency and leaf rolling. Plants were grown in pots in controlled conditions on expanded clay. A Wescor in situ hygrometer placed on the leaf base outside the assimilation chamber permitted, simultaneously to leaf gas exchange measurements, monitoring of leaf water potential. Drought was imposed by withholding water from the pot. CO2 uptake and stomatal conductance decreased and leaves started to roll at a lower leaf water potential in the high‐N than in the low‐N grown plants. Stomatal inhibition of leaf photosynthesis seemed larger in the low‐N than in the high‐N plants. Water‐use efficiency increased more in the high‐N than in the low‐N grown plants during the drought. The decrease of photosynthesis was largely reversible after rehydration in low‐N but not in high‐N leaves. The authors suggest that low‐N plants avoid water deficit rather than tolerate it.
Identification of cytokinins in primary crown gall tumours of tomato
Authors: NANDI S. K. , PALNI L. M. S. , LETHAM D. S. , WONG O. C.
Published: April 2006

Abstract. Identification of the cytokinin complex of primary crown gall tumours of tomato (Lycopersicon esculentum L.) by combined gas chromatography‐mass spectrometry has been described. Several cytokinins have been identified which included zeatin, dihydrozeatin, isopentenyladenine, and their respective riboside and nucleotide derivatives. In addition, 6‐benzylaminopurine, its riboside and the corresponding nucleotide have also been identified as major endogenous compounds in this tissue. This would appear to be the first report on the identification of cytokinins from a primary crown gall tumour tissue using unequivocal methods.
Oxygen diffusion and dark respiration in aquatic macrophytes
Authors: SORRELL B. K. , DROMGOOLE F. I.
Published: April 2006

Abstract.The supply of oxygen to respiring shoot tissue was investigated for three submerged macrophytes (Potamogeton crispusL.,Egeria densaPlanch, andMyriophyllum triphyllumOrchard). For all species, the response of oxygen uptake rates to the external O2concentration was a rectangular hyperbola over the range 0–5.0 × 10−3m3m−3. However, the response pattern for material with water‐infiltrated lacunar airspaces was non‐hyperbolic over this range. The change in response was interpreted as an increased substrate (O2) limitation, resulting from lower radial diffusion rates within the infiltrated material. Neither the uninfiltrated nor the infiltrated responses obeyed the linear and logarithmic formulae of the type observed for submerged macrophytes by earlier authors. These results suggest that the responses observed are affected by factors such as water velocity, internal restrictions to diffusion and the range of oxygen tensions investigated. Therefore, it is unlikely that one response formula can adequately account for the effects of oxygen concentration on submerged macrophyte oxygen uptake. The lacunar airspaces also represent a possible oxygen source for dark respiration. The consumption of oxygen from the airspaces was investigated by displacing the gas from the lacunae and measuring the subsequent increase in the rate of oxygen assimilation from the external liquid. Approximately 30% of the oxygen consumed byE. densaandP. crispus, and more than 40% of that consumed byM. triphyllum, was derived from the lacunar system. This O2supply is a consequence of the higher oxygen concentration in the lacunae than in the external medium, due to the low solubility of oxygen in water. Storage of photosynthetically‐produced oxygen in the lacunae could not be identified during a light/dark transient, due to rate changes caused by the effects of light on the respiratory metabolism. However, O2partial pressure gradients artificially set up between the lacunae and water equilibrated within an hour, suggesting that excess oxygen would be lost to the water within this time.
Effect of competition and leaf age on visible and infrared reflectance in pine foliage
Authors: CARTER G. A. , PALIWAL K. , PATHRE U. , GREEN T. H. , MITCHELL R. J. , GJERSTAD D. H.
Published: April 2006

Abstract. The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3‐month‐old and 15‐month‐old leaves of loblolly pine (Pinus taeda L.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from ‐2.2 to ‐0.9 MPa (r2= 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r2= 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r2= 0.55), and with increasing Mg in old leaves (470 nm, r2= 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affected by competition.
Relative growth rates of leaves from soybean grown under drought‐stressed and irrigated field conditions
Authors: RANDALL H. C. , SINCLAIR T. R.
Published: April 2006

Abstract. The relative growth rates and leaf area were graphed against leaf area, normalized with respect to final leaf area, to assess the applicability of the Lockhart cell wall expansion equation to soybean, Glycine max (L.) Merr., leaf development under field conditions. For leaves that had completed more than 20% of their growth, relative growth rates decreased linearly with an increase in the normalized leaf area, indicating that these leaves were undergoing strictly expansive growth. Drought stress significantly decreased the relative growth rate of these larger leaves. Small leaves which had completed less than 20% of their growth, were found to have highly variable relative growth rates. The large variability in relative growth rates indicated that the Lockhart cell wall expansion equation was inadequate to evaluate the growth of these young leaves. Drought stress had virtually no influence on the relative growth rates observed in the small leaves.
The pattern of secondary root formation in curving roots of Arabidopsis thaliana (L.) Heynh.
Authors: FORTIN M.‐C. , PIERCE F. J. , POFF K. L.
Published: April 2006

Abstract. A gravitational stimulus was used to induce the curvature of the main root of Arabidopsis thaliana. The number of secondary roots increased on the convex side and decreased on the concave side of any curved main root axes in comparison with straight roots used as the control. The same phenomenon was observed with the curved main roots of plants grown on a clinostat and of mutant plants exhibiting random root orientation. The data suggest that the pattern of lateral root formation is associated with curvature but is independent of the environmental stimuli used to induce curvature.
The kinetics of P‐700+reduction in leaves: a novelin situprobe of thylakoid functioning
Authors: HARBINSON J. , HEDLEY C. L.
Published: April 2006

Abstract.The half time (t1/2) of the reduction of P‐700+in the millisecond time frame is known to be limited by the reaction between plastoquinol and the cytochrome cytb6f complex. This is considered to be the rate limiting reaction of thylakoid electron transport and measurements of it provide a means of analysing how thylakoid election transport is regulatedin vivo.The half time for the reduction of photochemically oxidized P‐700 has been measuredin vivousing absorbance changes around 820 nm. The results showed that t1/2is independent of irradiance and decreases as photosynthetic induction progresses. Even with a constant t1/2the quantum efficiency of PSI declined as irradiance increased. The significance of the concept of photosynthetic control of electron transport is discussed in the light of these observations.
Relationships between nitrogen uptake and carbon assimilation in whole plants of tall fescue
Authors: GASTAL F , SAUGIER B.
Published: April 2006

Abstract. The present study investigates the relationships between nitrogen uptake, transpiration, and carbon assimilation. Plants growing on nutrient solution were enclosed for 10–16 d in a growth chamber, where temperature, photon flux density, vapour saturation deficit and CO2 concentration were controlled. One of these factors was modified every 4 to 5 d. Shoot photosynthesis and root and shoot respiration were recorded every half‐hour. Nitrogen uptake from the root medium and plant transpiration were measured daily. In most cases, an increase in photon flux density led to increases in transpiration, net daily carbon assimilation, and nitrogen uptake. By modifying transpiration rate without changing photosynthesis (varying vapour saturation deficit), or by modifying transpiration and carbon assimilation in opposite ways (varying CO2 air concentration), it was shown that nitrogen uptake does not follow transpiration, but is linked to the carbon uptake of the plant. When light was increased from low to intermediate levels, the N uptake/C assimilation ratio remained constant. At higher photon flux density, this ratio declined markedly. It is proposed that in the first case, growth is limited by carbohydrate availability, thus any increase in carbon assimilation leads to a proportional increase in nitrogen uptake, in contrast to the second situation where carbohydrates may accumulate in the plant without further nitrogen requirement.
Growth responses of Rumex species in relation to submergence and ethylene
Authors: VOESENEK L. A. C. J. , BLOM C. W. P. M.
Published: April 2006

Abstract. Submergence stimulates growth of the petioles of Rumex palustris and Rumex crispus under field, greenhouse and laboratory conditions. Growth of Rumex acetosa petioles was hardly influenced by submergence. These growth responses under flooded conditions can be partially mimicked by exposing non‐submerged Rumex plants to ethylene‐air mixtures. Submergence of intact plants in a solution of AgNO3 inhibited the elongation of all petioles of R. palustris and the youngest petiole of R. crispus and stimulated growth of the youngest petiole of R. acetosa, The ethylene‐air mixture experiments, the effect of AgNO3 and observed increase of the endogenous ethylene concentration during submergence suggest that ethylene plays a regulatory role in the growth responses of these Rumex species under submerged conditions. The three Rumex species showed a gradient in elongation responses to submergence, which correlates with the field distribution of the three species in a flooding gradient.