bluuebunny/crossref_metadata_2025 huggingface dataset:
Chilling sensitivity in higher plants: the role of phosphatidylglycerol
Authors: BISHOP D. G.
Published: April 2006

Abstract A compilation of data on the level of high melting point fatly acids in the phosphalidylglycerol of leaves of higher plants suggests that the content of these acids is not directly related to the chilling sensitivity of the plant. Within a given plant family the level of high melting point fatty acids in phosphatidylglycerol appears to be relatively constant, although the individual species may differ widely in their susceptibility to low temperature. It seems possible that differences observed in the levels of high melting point fatty acids in the phosphatidylglycerols of chilling‐sensitive and chilling‐tolerant plants may be largely due to choice of experimental material.
Effect of nitrate‐nitrogen limitation on photosynthesis of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)
Authors: OSBORNE B. A. , GEIDER R. J.
Published: April 2006

Abstract Nitrate limited growth of the diatom Phaeodactylum tricornutum in chemostat cultures produced marked changes in biochemical composition and a six‐fold reduction in the specific growth rate. This was associated with a reduction in the carbon and chlorophyll a specific light saturated rates, with little effect on light limited photosynthesis. Variations in specific growth rate were quantitatively related to carbon specific net photosynthesis and maximum chlorophyll a specific light saturated rates were positively correlated with cell nitrogen contents. The correlation between nitrogen content and photosynthesis for P. tricornutum and the differential effect of nitrogen supply on the light response curve of photosynthesis is qualitatively and quantitatively similar to published results for terrestrial vascular plants. There was little change in the photon (quantum) yield of photosynthesis which was not significantly different from 0.125mol O2 mol photon‐1 the theoretical upper limit based on the Z scheme, even under severe nitrate deficiency. The capacity to maintain a high photon yield under nitrate limitation is discussed in relation to the nitrogen requirements of the stromal and membrane components of the photosynthetic apparatus.
Effects of sodium chloride on tobacco plants
Authors: FLOWERS T. J. , FLOWERS S. A. , GREENWAY H.
Published: April 2006

Abstract The effect of salinity on the growth and ion concentrations in a number of tobacco cultivars is described. Sodium chloride, at a concentration of 200 mol m−3, hardly affected the fresh weight, but significantly reduced the dry weight. The difference in the response of fresh and dry weights to salt was due to a change in succulence (water per unit leaf area); the latter increased with increasing leaf Na+ and Cl− concentration. Under saline conditions, increasing the external Na+: Ca− ratio by decreasing the Ca2+ concentration increased the accumulation of Na+ and Cl− into the leaf tissue.
Field water relations of a compass plant, Lactuca serriola L.
Authors: WERK K. S. , EHLERINGER J.
Published: April 2006

Abstract Field water relations of Lactuca serriola serriola and L. serriola integrifolia were examined. Leaf conductance to water vapour was high early in the morning and declined rapidly during the midday hours. Leaf water potentials decreased to their minima early in the morning and remained low all day. Afternoon recovery of leaf conductance occurred occasionally. Leaf conductance was shown to have a linear response to vapour concentration difference. No differences were seen between L. serriola serriola and L. serriola integrifolia. The pattern of diurnal gas‐exchange activity appeared to be complemented by the pattern of intercepted solar irradiance which results from the compass plant leaf orientation observed in L. serriola.
Growth response to step‐decrease in nutrient availability in small birch (Betula pendula Roth)
Authors: McDONALD A. J. S. , LOHAMMAR T. , ERICSSON A.
Published: April 2006

Abstract Changes in the uptake and allocation of carbon and nitrogen, after a step‐decrease in nutrient availability, were investigated in small birch (Betula pendula Roth). By demonstrating stable nutrition, before and after the decrease in nutrient supply, it was possible to eliminate the effects of plant size and age. Immediately following the step‐decrease in nutrient availability, net nitrogen uptake to leaves and the relative rate of increase in shoot area tended to zero. Although photosynthetic rate per shoot area decreased, carbon uptake remained in excess of that used in structural growth and respiration. More of the excess carbon was accumulated as starch in leaves than in roots. After a lag phase, the relative rates of increase in plant dry matter, starch amount, net nitrogen uptake to leaves and shoot area development equalled that of the reduced rate of nutrient supply. It is concluded that the reduction in plant relative growth rate was much more attributable to the reduced allocation of photosynthate to leaf area growth than to the reduction in photosynthesis per shoot area.
Water relations of compound leaves and phyllodes in Acacia koa var. latifolia
Authors: HANSEN D. H.
Published: April 2006

Abstract Moisture release characteristics and field measurements of physiological parameters (conductance and water potential) and environmental parameters (ambient temperature, water vapour saturation deficit and photosynthetic photon flux density) were measured for phyllodes and compound leaves of Acacia koa over a 2 month period at Hawaii Volcanoes National Park, Hawaii, to determine what differences in water relations might occur between leaf types. The phyllodes were found to contain more water at full turgor, use less water in turgor control and have stomatal conductances more closely associated with bulk leaf water status and environmental variables. These results suggest that the phyllodes are more drought adapted, whereas the compound leaves probably promote more rapid early growth during periods of high moisture availability.
Tissue water relations and leaf growth of tropical corn cultivars under water deficits
Authors: SOBRADO M. A.
Published: April 2006

Abstract This study reports on the effect of water deficit on the tissue water relations and leaf growth of six corn cultivars, growing in glasshouse conditions, in order to understand growth responses to drought of tropical corn. A mild water‐stress treatment was imposed slowly; plants reached a minimum pre‐dawn leaf water potential of about –1.5 MPa by day 12 after watering was withheld. Analysis of the water relation characteristics of growing leaves using the pressure–volume technique demonstrated that under water deficits all the cultivars changed their moisture‐release curves compared with irrigated plants. Osmotic potential at full turgor was lowered in water‐stressed plants of all the genotypes and the degree of such change was between 0.34 MPa and 0.58 MPa. Thus, turgor pressure was lost at a lower water potential in water‐stressed plants than in irrigated plants of all the varieties. Volumetric elastic moduli were also increased under water deficits and the increase ranged between 10% and 141% among the cultivars. In all the genotypes, the stress imposed led to a reduction of leaf area and dry matter accumulation. Leaf expansion was very sensitive to low turgor pressure and it ceased when turgor reached 0.2 MPa. Thus, varieties able to maintain a higher degree of turgor pressure (i.e. by osmotic adjustment) under water deficits may be able to prolong leaf growth.
Turgor and osmotic relations of the desert shrub Larrea tridentata
Authors: MEINZER F. C. , RUNDEL P. W. , SHARIFI M. R. , NILSEN E. T.
Published: April 2006

Abstract Leaf water relations characteristics of creosote bush, Larrea tridentata, were studied in view of previous reports that its leaves commonly experience zero or negative turgor under dry conditions. Leaf turgor loss point () was determined by a pressure‐volume method for samples subjected to a hydration procedure and for untreated samples. Hydration caused to increase by as much as 3 M Pa. Hydration of samples also caused changes in other leaf water relations characteristics such as symplastic solute content, tissue elasticity and symplasmic water fraction, but total leaf solute content was unchanged. Comparison of our field plant water potential data with values of obtained by the two methods resulted in predictions of turgor loss during part or all of a diurnal cycle based on hydrated samples, and turgor maintenance (at least 0.3 MPa) based on untreated samples. Pooled data for obtained from both partially hydrated and untreated samples showed that L. tridentata maintains fairly constant levels of turgor over a wide range of leaf water potential. Dilution of cell contents by apoplastic water introduced significant errors in psychrometric determinations of osmotic potential in both frozen and thawed leaf tissue and expressed cell sap. Use of these values of osmotic potential resulted in predictions of zero turgor at all plant water potentials measured in the field.
Chilling injury: a plea for uniform terminology
Authors: RAISON J. K. , LYONS J. M.
Published: April 2006

Abstract This article proposes definitions for the terms now commonly applied to studies of both the molecular and cellular aspects of chilling injury. They are proposed with the intent of increasing the precision and clarity of communications on the subject and arc based on the present understanding and current hypotheses regarding the molecular events underlying the development of the visible symptoms of chilling injury.
Determination of free space, growth, solute concentrations and parameters of water relations of suspension‐cultured tobacco cells
Authors: DRACUP M. , GIBBS J. , STUIVER C. E. E. , GREENWAY H. , FLOWERS T. J.
Published: April 2006

Abstract Methods were developed for measuring water content of the free space of suspension‐cultured tobacco cells using 3H‐ or 14C‐sorbitol. Sorbitol was not taken up by cells in significant quantities over the 3 min taken to label free space. Free space accounted for 50–60% of the water content of cell pellets irrespective of whether 3H‐ or 14‐C‐sorbitol was used. 14C‐inulin labelled 13.5% less of the water in cell pellets than 3H‐sorbitol, probably due to inadequate penetration by inulin into the free space in the cell wall matrix and within clumps of cells. Measurement of free space is necessary for measuring growth on a fresh or dry weight basis, solute concentrations and parameters of water relations of cells. Techniques for making these measurements on tobacco cells were also developed in this study.

Solutes were measured after extraction from cells by expressing sap or by boiling cells in ethanol. Similar solute concentrations were found using both methods of extraction. By expressing sap from cells grown in culture medium with an osmotic pressure of 0.24 MPa, the cells were found to have an internal osmotic pressure of 0.70 MPa. Glucose, fructose, sucrose, amino acids and K+ accounted for 60% of this osmotic pressure. Elastic moduli were estimated using the Boyle‐Van't Hoff relationship after suspending cells in solutions with different osmotic pressures and assessing their water content or internal osmotic pressure. For two different lines of tobacco cells, elastic modulus varied between 1 MPa and 5.4 MPa at turgor pressures of 0.15–0.52 MPa (line 1) and between 0.2 MPa and 4.2 MPa at turgor pressures of 0.04–0.26 MPa (line 2).
Comparison of lag times in plant physiology
Authors: RICH T. C. G. , SMITH H.
Published: April 2006

Abstract Comparison of lag (or latent) times is a useful tool in plant physiology for investigating potential mechanisms involved in a response. There are two main ways of deriving the lag time, but only one of these can be properly used for comparative purposes. The other method is biased by the faster responding plants and may not give a representative estimate for the lag time in the population. The fact that the two methods give different, non‐comparable results has been widely overlooked. We suggest more care should be taken for their correct use, and propose two terms which can be used to describe the different estimates of the lag time to avoid confusion.
A field portable gas‐exchange system for measuring carbon dioxide and water vapour exchange rates of leaves during fumigation with SO2
Authors: ATKINSON C. J. , WINNER W. E. , MOONEY H. A.
Published: April 2006

Abstract A field portable, steady‐state gas‐exchange system which measures both CO2 and water vapour exchange of single intact leaves during fumigations with SO2 is described.

Within the leaf cuvette temperature, light, humidity and both CO2 and SO2 concentrations are controlled to preset levels. Gas flow and concentrations are controlled by mass flow controllers. Photosynthetic uptake of CO2 can be determined either by differential depletion or null balance measurement. Water vapour exchange is measured differentially and transpiration and conductance to water vapour determined. Sulphur dioxide is measured directly within the cuvette exhaust gas line by UV‐pulse fluorescence.

The performance of this system under field conditions is described and the physiological measurements compared with those obtained with other systems.
Osmotic sensitivity in relation to salt sensitivity in germinating barley seeds
Authors: BLISS R. D. , PLATT‐ALOIA K. A. , THOMSON W. W.
Published: April 2006

Abstract Cultivars of barley (Hordeum vulgare L.) were tested for germination sensitivity to progressively higher concentrations of salt, mannitol, and betaine. The three solutes were equally inhibitory at equal osmotic potential, but there was a consistent difference in osmotic sensitivity between two cultivars, CM‐67 and Briggs (Briggs was the most sensitive). There was no difference between the two cultivars in salt or water uptake from salt solutions during imbibition. Brief presoaking in water did not improve salt resistance, indicating that a hydration‐dependent decrease in membrane permeability is not involved in salt tolerance. The calcium content of Briggs was higher than CM‐67. These results suggest that salt inhibits barley germination primarily by osmotic effects, and that salt influx during imbibition does not play a role in this inhibition. A hypothesis regarding salt effects on germination is discussed.
The inhibitory effect of NaCl on barley germination
Authors: BLISS R. D. , PLATT‐ALOIA K. A. , THOMSON W. W.
Published: April 2006

Abstract The possibility that the nature of the inhibitory effect of NaCl is different during imbibition compared to germination was investigated. Germination in both NaCl and betaine (a non‐toxic solute) improved with pre‐imbibition in water. Seeds imbibed in inhibitory concentrations of either solute could be induced to germinate by brief exposure to water. Electron micrographs of tissue from seeds imbibed in 0.5 kmol m−3 NaCl for 25 h showed cells identical to those in seeds imbibed in water for only 1 h, but seeds imbibed for 6 h in water exhibited many changes in ultrastructure. These results are consistent with the hypothesis that seed hydration must reach a critical value before germination can proceed, and that the inhibitory effect of NaCl is primarily osmotic in barley seeds that have not reached this hydration threshold. Although isotonic solutions of betaine and NaCl were equally inhibitory to germination, isotonic solutions of betaine and NaCl were not equally inhibitory to continued development in seeds which had been pre‐imbibed in water. Calcium ions improved both germination and plumule emergence of pre‐imbibed seeds in NaCl solutions, but calcium had little effect on pre‐imbibed seeds placed in betaine. Very high concentrations of NaCl or betaine inhibited germination, but did not kill dry seeds. Both solutes, on the other hand, were lethal at high concentrations to germinating seeds. NaCl killed germinating seeds more rapidly than betaine, but calcium reduced the rate of killing to nearly that of betaine. We conclude that hydrated seeds are sensitive to both osmotic and toxic effects of NaCl and that calcium mitigates the toxic effect of NaCl, but not the osmotic effect.
The penetration of light through soil
Authors: TESTER M. , MORRIS CHRISTINA
Published: April 2006

Abstract There has been little written on the penetration of light through soil. In this review, we attempt to collate most of the work that has been published on this topic in order to stimulate further research and to clarify the often‐confused literature.

Light penetration can be measured directly with, for example, a spectroradiometer, or indirectly by using germination of light‐sensitive seeds or the presence of growing algae as bioindicators. Although the penetration of light through soil is greatly affected by factors such as soil moisture content and particle size and colour, it generally appears that physiologically and ecologically significant amounts of light rarely penetrate more than 4–5 mm through the soil, and may often penetrate much less than this. Any penetration beyond 10 mm would generally not be significant, especially as most soils are covered with litter, algae or lichens, or are shaded from direct sunlight. However, for some light‐stimulated geo‐tropic responses of roots, which can be sensitive to very low fluences, the penetration of light to greater depths could well be significant. The role of light in soil in directing root growth is also discussed.
A comparison between the utilization of storage protein and exogenous nitrate during seedling establishment in Zea mays L.
Authors: WATT M. P. , CRESSWELL C. F.
Published: April 2006

Abstract During the first 5 d of germination in the presence of exogenous l5NO−3 and the inhibitor of nitrification N‐SERVE, the nitrogen reserves of the caryopses of Zea mays L. were found to account for 75% of the total nitrogen content of the developing seedlings. During this period, an increasing pool of 14NO−3 was detected in both the grain and the seedling. The accumulation of nitrate in the grain and the extent of hydrolysis of seed reserves were enhanced when nitrate was removed from the growing medium. The significance of a possible oxidative pathway from reduced nitrogen to nitrate is discussed.
The effect of freezing nights on photosynthesis, stomatal conductance, and internal CO2 concentration in seedlings of Engelmann spruce (Picea engelmannii Parry)
Authors: DELUCIA E. H.
Published: April 2006

Abstract The effect of freezing night temperatures on net photosynthesis, stomatal conductance, and internal CO2 concentration was investigated in unhardened seedlings of Engelmann spruce. Exposure to – 2.5°C in the dark for 10 h caused a slight and reversible reduction in gas‐exchange parameters on the following days. Substantial and irreversible inhibition of photosynthesis occurred after exposure to ‐4°C or –5°C. Despite a parallel decline in stomatal conductance and net photosynthesis, exposure to a hard freeze caused a decrease in the stomatal limitation to gas exchange. Hard‐freeze conditions (less than – 4°C) also caused a decrease in carboxylation efficiency and apparent quantum yield, indicating a freeze‐induced failure of the dark reactions and electron transport. There was no significant difference in the photosynthetic response to freezing temperatures in different elevational populations of spruce, although acclimatory adjustments were observed. Gas exchange in seedlings grown under cool conditions (14°C day/9°C night) was less affected and recovered more rapidly after exposure to a hard freeze than in seedlings grown under warm conditions (24°C day/19°C night).
Action potentials as multifunctional signals in plants: a unifying hypothesis to explain apparently disparate wound responses
Authors: DAVIES E.
Published: April 2006

AbstractI suggest that action potentials, which occur in most, if not all, plants, play a major role in intercellular and intracellular communication. Long‐distance communication is achieved through the transmitted changes in membrane potential, whereas local signalling is achieved through changes in the subcellular localization of ions (K+, Cl−, and Ca2+) and of water, and perhaps by membrane depolarization and current flow. These local changes in ion concentration can lead to modified activities of enzymes in the cell wall (e.g. pectinase), the plasma membrane (e.g. cellulose synthetase, callose synthetase), and the cytoplasm (e.g. protein kinase). In particular, the elevated concentration of cytoplasmic Ca2+is shown to have a major, yet complex, role, especially in the modulation of translation. I suggest further that, in addition to their role in wounding, action potentials may also be important signalling mechanisms for chilling injury, mechanical perturbation and invasion by pathogens, as well as for light and gravity.
Stomatal behaviour and leaf water potential of chilled and water‐stressed Solanum melongena, as influenced by growth history
Authors: EAMUS D.
Published: April 2006

Abstract Leaf diffusion resistance and leaf water potential of intact Solanum melongena plants were measured during a period of chilling at 6 °C. Two pretreatments, consisting of a period of water stress or a foliar spraying of abscisic acid (ABA), were imposed upon the plants prior to chilling. The control plants did not receive a pretreatment. In addition to intact plant studies, stomatal responses to water loss and exogenous abscisic acid were investigated using excised leaves, and the influence of the pretreatment observed. Chilled, control plants wilted slowly and maintained open stomata despite a decline in leaf water potential to –2.2 MPa after 2 d of chilling. In contrast plants that had been water stressed or had been sprayed with abscisic acid, prior to chilling, did not wilt and maintained a higher leaf water potential and a greater leaf diffusion resistance. In plants that had not received a pretreatment, abscisic acid caused stomatal closure at 35 °C, but at 6°C it did not influence stomatal aperture. The two pretreatments greatly increased stomatal sensitivity to both exogenous ABA and water stress, at both temperatures. Stomatal response to water loss from excised leaves was greatly reduced at 6°C. These results are discussed in relation to low temperature effects on stomata and the influence of preconditioning upon plant water relations.
14C sucrose efflux from the perimedulla of growing potato tubers
Authors: OPARKA K. J. , PRIOR D. A. M.
Published: April 2006

Abstract An experimental system has been developed for studying efflux of 14C assimilates in growing potato tubers. Small wells are cut into the phloem‐rich perimedulla and filled with trap solutions of varying composition which inhibit or promote assimilate efflux. One well on each tuber acts as the treatment while a second well acts as the control. Movement of 14C into wells occurred at comparable rates to that found in intact tissue, harvested from importing tubers in the form of microcores. Sucrose was the predominant translocated sugar in the stolon and was not hydrolysed in either the wells or the microcores following unloading. Efflux into wells containing agar traps was stimulated 40‐fold relative to buffer controls by the addition of 20 mol m−3 EGTA to the agar. This was interpreted as passive efflux to the apoplast due to increased membrane permeability in the pathway between the sieve elements and the collecting wells. The EGTA stimulation was reversed by addition of Ca2+. 14C efflux into buffered solutions was inhibited significantly by both DNP and PCMBS, suggesting the involvement of active and carrier‐mediated transport components. However, it was not possible to determine whether these compounds acted at the site of unloading only, or on the short‐distance transfer step between phloem and collecting wells. The rate of tracer efflux was not significantly different when 1 mol m−3 and 300 mol m−3 sucrose were applied to the wells, indicating insensitivity of solute movement to low apoplastic solute concentrations. However, raising the solute concentration to 800 mol m−3 caused a severe inhibition of tracer efflux. These results were duplicated with mannitol as the osmoticum. It is suggested that plasmolysis prevented further efflux by disruption of a predominantly symplastic transport pathway between the phloem and collecting wells.
Translatable mRNA changes in ethylene induced abscission zones of Phaseolus vulgaris (Red Kidney)
Authors: KELLY P. , TREWAVAS A. J. , LEWIS L. N. , DURBIN M. L. , SEXTON R.
Published: April 2006

Abstract The wheat germ translation system was programmed with soluble RNA extracted from foliar abscission zones of Phaseolus vulgaris, These extracts were taken at various times after the induction of abscission. A translation product with a molecular weight of 42 kilodalton (kD) was only present after this treatment, though three other species 32, 27 and 17 kD increased substantially. The isozyme of cellulase with a pi of 9.5 could not be conclusively identified amongst the products though the 32 kD protein is probably chitinase. Comparison of the abscission zone translatable RNA with that from adjacent petiole and stem tissues showed the 17 kD protein developed in all these location. The 42, 32 and 27 kD bands were found predominantly in the zone and petiole.
Hydraulic flow characteristics in the lignotuberous mallee Eucalyptus behriana F. Muell. in the field
Authors: KÜPPERS M. , NEALES T. F. , KÜPPERS B. I. L. , SWAN A. G. , MYERS B. A.
Published: April 2006

Abstract The lignotuberous mallee Eucalyptus behriana F. Muell, had much lower predawn leaf water potentials (not higher than – 1.2MPa) than other eucalypts (as high as – 0.2MPa), even after extended rain. This led to the expectation that the lignotuber of E. behriana might have specific hydraulic characteristics. Keeping the soil around partially defoliated mallces for several days underwater did not raise the water status above the maximum leaf water potential observed under natural conditions. Digging a plant out and placing its roots in water after removal of the soil rapidly increased the water status to a level consistant with other eucalypts. This indicated that the major impedance to water uptake was a component of the soil rather than in the roots or in the lignotuber.

Some of the individual mallces had only two major stems or branches. One stem or branch was kept covered throughout the experiments to prevent transpiration. The other stem was subjected to a variety of different conditions in order to modify water loss from it. The transpiring branch affected the water status of the non‐transpiring plant parts. Hydraulic resistances in the shoot and root/lignotuber were determined from differences in the leaf water potential of covered and uncovered branches, at high water flow rates through the plant. Resistances in branches, including the liquid phase component of the leaf, were significantly larger than in root or lignotuber.

The total plant hydraulic resistance of E. behriana was similar to that of other eucalypts, such as E. pauciflora Sieb. ex Spreng. or E. delegatensis R. T. Bak., even though its growth form was different and its natural leaf water potentials were much lower. An osmotic adjustment at the leaf level was observed in the mallee, keeping its bulk leaf turgor in the same range as compared to the other eucalypt species.
Changes in hydraulic conductance of citrus trees following a reduction in wetted soil volume
Authors: COHEN Y. , MORESHET S. , FUCHS M.
Published: April 2006

Abstract The effcct of the transition from fully to partially wetted soil voluine on transpiration rate and hydraulic conductance of mature citrus trees was examined in a 23‐year‐old, coninicrcial, sprinklerirrigated, Shanio u t i orange orchard. I rriga t i on frequency was determined by the rate of water loss from the soil, a s measured by neutron probes. The hydraulic conductance of tlic tree was coniputed from the rclationship between sap flow i n the trunk and leaf water potential. The diurnal valucs of leaf water potential and sap flow shifted towards lower levels as tlie water stored in the root zone was depleted. In the fully wetted soil volume the tree hydraulic conductance remained constant throughout the irrigation period, from June to Novcniber. However, partial wetting of the soil volume (40%) caused a reduction in the hydraulic conductance of the tree. Tlie decreased hydraulic conductance is attributed to tlie permanent interruption of water transport in part of tlie root system. Tlie rcsults of tlie experiment suggest that despite tlie increase of irrigation frequency, partial wetting intensifies water stress in tlie trees.
Nitrogen fixation by three species of leguminosae in the Canadian High Arctic Tundra
Authors: SCHULMAN H. M. , LEWIS M. C. , TIPPING E. M. , BORDELEAU L. M.
Published: April 2006

Abstract. Significant levels of nitrogenase activity (nitrogen fixation) were demonstrated in three species of Arctic legumes (Oxytropis maydelliana, O. arctobia and Astragalus alpinus) growing in high tundra at Sarcpa Lake, Melville Peninsula, N.W.T. Nitrogenase activity of intact plants was correlated with the number of nodules per plant, with field soil temperatures and limited by water shortage. Activity in freshly detached nodules showed a plateau of maximum activity between 10°C and 25°C and a near linear decline with temperature down to 0°C. Unusually, the segmented nodules of all three species are perennial in which growth and leghaemoglobin production resumes each spring from an overwintering apical meristem. Nodules are most numerous in the warmer soil stratum (2–10 cm. depth). Other studies indicate that the arctic rhizobia belong to a single cold‐adapted species which has co‐evolved with the legumes of tundra.
Silver ions inhibit the ethylene‐stimulated production of ripening‐related mRNAs in tomato
Authors: DAVIES K. M. , HOBSON G. E. , GRIERSON D.
Published: April 2006

Abstract. Silver ions effectively inhibited both the initiation and the continuation of tomato (Lyeopersicon esculentum Mill) ripening. Studies of protein synthesis in vivo showed that application of 2 mol m−3 silver thiosulphate to mature green fruit prevented the appearance of several novel proteins associated with ripening, including the softening enzyme polygalacturonase. However, total protein synthesis, as judged by the incorporation of [35S] methionine into proteins, continued unabated after silver treatment. Ripening was also arrested when silver was supplied after ripening had begun. The accumulation of several ripening‐related mRNAs, including that for polygalacturonase, was studied by translation in vitro and using cDNA clones as hybridization probes. Silver was shown to prevent the appearance of polygalaturonase mRNA when supplied to mature green fruit and to cause a rapid reduction in the concentration of mRNA for polygalacturonase and other ripening‐related proteins when supplied after ripening had begun. It is proposed that silver exerts its effects due to interaction with the ethylene perception mechanism. The results suggest that perception of ethylene is vital not only for the initiation of ripening but also for the continued expression of genes required for ripening.
The wilty tomato mutants flacca and sitiens are impaired in the oxidation of ABA‐aldehyde to ABA
Authors: TAYLOR I. B. , LINFORTH R. S. T. , AL‐NAIEB R. J. , BOWMAN W. R. , MARPLES B. A.
Published: April 2006

Abstract. Deuterium‐labelled ABA‐aldehyde was fed to various tomato genotypes. Normal and notabilis mutant plants incorporated substantial amounts of the label into ABA. In contrast, two ABA‐deficient mutants, flacca and sitiens, reduced ABA‐aldehyde to a mixture of cis‐ and trans‐ABA alcohol rather than oxidizing it to ABA. It was concluded that ABA‐aldehyde is the immediate precursor of ABA in higher plants. It appears that the flacca and sitiens lesions both act to block the last step of the ABA biosynthetic pathway. The mutant gene loci are likely to be involved in coding for different sub‐units of the same dehydrogenase enzyme.
Hormonal regulation of barley nuclease: investigation using a monoclonal antibody
Authors: BROWN P. H. , MECHAM R. P. , DAVID HO T.‐H.
Published: April 2006

Abstract. A monoclonal antibody prepared against barley (Hordeum vulgare L., cv. Himalaya) nuclease (EC 3.1.30.2) was characterized with solid‐state enzyme‐linked immunosorbent assays and immuno‐blotting. The antibody was specific for intracellular and secreted nuclease. Hormonal regulation of the synthesis and secretion of nuclease in isolated aleurone layers was investigated by immunoprecipitation of biosynthetically‐labelled nuclease using polyclonal antibodies and by immunoblot analyses using the monoclonal antibody, respectively. Gibberellic acid (GA3) induced the de novo synthesis and secretion of nuclease in a time‐and concentration‐dependent manner. Nuclease was detected in aleurone layers incubated in 1 mmol m−3 GA3, after 24 h. The maximum rates of nuclease synthesis and secretion occurred 36–48 h after hormone treatment. A minimum concentration of 10−6 mol m−3 GA3 was required for nuclease synthesis and secretion, whereas the maximum rate of nuclease secretion occurred at concentrations of 10−5 mol m−3 and higher. In the presence of abscisic acid, the synthesis and secretion of nuclease from GA3‐treated aleurone layers was almost completely inhibited. Based on these findings, the authors conclude that all nuclease within and secreted from aleurone layers treated with GA3 is the result of its de novo synthesis.
Analysing partitioning of recently fixed and of reserve carbon in reproductive Phaseolus vulgaris L. plants
Authors: GEIGER D. R. , SHIEH WEN‐JANG
Published: April 2006

Abstract. Partitioning of recently‐fixed carbon among plant organs and subsequent distribution of reserve carbon were studied by supplying whole shoots of bean plants (Phaseolus vulgaris L.) with 14C‐labelled CO2 of constant specific radioactivity throughout a photoperiod. The gain of tracer carbon in each part revealed net accumulation of recently‐fixed carbon from direct fixation, import or both. Growth rate coefficients describing the present pattern of plant growth were calculated from ratios of tracer carbon to total carbon present in plant organs and were used to project future plant form. The period 10–20 d after the start of flowering was marked by a major increase in partitioning of recently‐fixed carbon to reproductive growth. Growth rates for the plant and its parts during this period were projected on the basis of growth rate coefficients and were found to be similar to rates measured by gravimetric growth analysis. Changes in tracer carbon recovered in individual organs after chase periods of various lengths revealed net decreases for leaves and stems. About 9% of the carbon distributed to fruits came from reserves even in the absence of obvious stress. Respiratory loss during the chase period was determined from the progressive drop in recovery of the original tracer carbon. The methods are being applied to measure current net accumulation rates in studies of sink organ physiology, and to compare partitioning of recently‐fixed and of stored carbon in several plant species under defined growth conditions.
Molecular biology of phytochrome
Authors: COLBERT J. T.
Published: April 2006

Abstract.One approach to elucidating the mechanism of phytochrome action is to characterize thoroughly the phytochrome molecule. This approach has added to our understanding of phytochrome action by demonstrating that distinct phytochrome molecules predominate in etiolated and green plants, by allowing determination of the complete amino acid sequences ofAvena SativaL. (oat) andCucurbita pepoL. (zucchini) phytochrome, by indicating that phytochrome is unlikely to be a membrane spanning protein, and by providing evidence that phytochrome may be a protein kinase. Phytochrome has also proved useful as a model system in which to study the regulation of gene expression in plants. Expression of the phytochrome genes appears to be regulated at the transcriptional, post‐transcriptional, and post‐translational levels and thus affords an opportunity to investigate the carefully controlled regulation of a gene that has a central role in plant development.
Photocontrol of plastid gene expression
Authors: LINK G.
Published: April 2006

Abstract. Recent strategies in the analysis of plastid gene expression at both the RNA and protein level are presented and current knowledge in this rapidly expanding research area is summarized. The role of transcriptional and post‐transcriptional mechanisms in the expression of nuclear and organelle genes for plastid constituents is discussed, with emphasis on the control of these mechanisms by light. Available evidence points to species‐specific, tissue‐specific, and developmental stage‐specific differences in the extent to which photoregulation is involved at each level of plastid gene expression.
Molecular biology of wound‐inducible proteinase inhibitors in plants
Authors: RYAN C. A. , AN G.
Published: April 2006

Abstract. The techniques of molecular biology are being employed to investigate at the gene level the systemically mediated, wound‐induced accumulation of two defensive proteinase inhibitor proteins in plant leaves. These techniques have added a new dimension to biochemical and physiological studies already underway to understand the mechanism of induction by wounding. The acquisition of cDNAs from the RNAs coding for the two inhibitors facilitated studies of mRNA synthesis in leaves in response to wounding, and provided probes to obtain wound‐inducible proteinase inhibitor genes from tomato (Lycopersicon esculentum) and potato (Solarium tuberosum) genomes. Successful transformations of tobacco plants with fused genes, containing the 5′ and 3′ regions of the inhibitor genes with the open reading frame of the chloramphenicol acelyltransferase (cat) gene, have provided a wound‐inducible chloramphenicol acetyltransferase (CATase) activity with which to seek cis‐ and transacting elements that regulate wound‐inducibility to help to understand the interaction of cytoplasmic and nuclear components of the intracellular communication systems that activate the proteinase inhibitor genes in response to wounding by insect pests.
Genetic and molecular approaches to the study of the anaerobic response and tissue specific gene expression in maize
Authors: BAILEY‐SERRES J. , KLOECKENER‐GRUISSEM B. , FREELING M.
Published: April 2006

Abstract. Plant gene expression is regulated during development and in response to environmental stimuli. For example, the pattern of gene expression in roots changes dramatically when seedlings are placed under low oxygen conditions. Roots respond to anaerobiosis by increasing cytosolic‐glycolytic enzyme activity. Through the use of genetic and molecular techniques we have begun to characterize the differential expression of isozymes which show increased synthesis under anaerobic conditions and tissue specific expression during plant development.
The accumulation and storage of nitrogen by herbaceous plants
Authors: MILLARD P.
Published: April 2006

Abstract Accumulation of nitrogen (N) by plants in response to N supply outstripping demand is contrasted with storage of N, which implies that N in one tissue can be reused for the growth or maintenance of another. Storage can, therefore, occur in N‐deficient plants; accumulation can not. The consequence of accumulation and storage of N is considered, particularly in relation to the reproductive growth of annual plants, which can often use a great deal of stored N. Nitrate and proteins are the forms of N most often stored in vegetative tissues and, quantitatively, ribulose 1,5‐bisphosphate carboxylase/oxygenase is often the most important protein store. While storing nitrate will be less costly to the plant in terms of energy, protein stores offer several possible advantages. These advantages are (i) maximizing the potential for carbon assimilation, (ii) avoiding problems with the regulation of leaf turgor and (iii) allowing the reduction on nitrate to occur in the young, fully illuminated leaf.
Role of nitrate in regulating germination of Sinapis arvensis L. (wild mustard)
Authors: GOUDEY J. STEPHEN , SAINI H. S. , SPENCER M. S.
Published: April 2006

Abstract Depending on the applied concentration, nitrate can either stimulate or inhibit germination of dormant seeds of Sinapis arvensis L. (wild mustard). Seed NO−3 levels that corresponded to the maximal germination frequencies recorded, ranged from 0.3 to 4.4 nmol seed−1 for applied NO−3 concentrations between 2.5 and 20 mol m−3. Germination was significantly lower in seeds containing more than 5 nmol NO−3. Although the presence of NO−3 within the seed was required to promote germination, seed NO−3 levels were 5 to 15 times less than levels calculated from the volume of solution taken up by the seeds. Seed NO−3 levels also responded in a passive fashion to the external NO3− concentration when the seeds were incubated on filter paper or in soil. In a representative soil containing 26 mg NO−3‐N per kg dry weight and 8 to 16% water by weight, the amount of NO−3 taken up by the seeds reached inhibitory levels. Our results suggest that levels of inorganic nitrogen (NO−3, NH+4) in managed soils may play an important role in regulating germination of dormant S. arvensis seeds.
A two‐way gas transport system in Nelumbo nucifera
Authors: MEVI‐SCHUTZ J. , GROSSE W.
Published: April 2006

Abstract The aquatic vascular plant Nelumbo nucifera Gaertn. is able to improve its oxygen supply to the submerged and buried organs by a thermo‐osmotic gas transport. Investigations with tracer gas and oxygen measurements have shown that thermo‐osmotic gas transport exists in N. nucifera when there is a temperature difference between the lacunar air of the leaves and the surrounding atmosphere. The gas transport was increased by up to 935% when a temperature difference of 2.9 ± 1.0 K was detected. Lacunar pressure of up to 166 ± 44 Pa was measured in both young and old leaves. In contrast to the flow‐through ventilation system recently described for Nuphar lutea and Nymphoides peltata, a two‐way flow in separate air canals in the petioles of both young and old Nelumbo leaves may carry oxygen‐rich air down to the rhizome and excess air back to the atmosphere. Anatomical investigations have shown that, in Nelumbo, the two largest air canals of the petiole end directly under the mesh system of the centre plate. These large air canals are proposed to be predominant in the upward flow of air in sunlight. The other air canals of the petiole veer into the leaf blade well below the centre plate. The gas flow system through fresh leaves may carry as much as 10.3 ± 4.5 cm3 air per minute to the buried rhizome.
Day‐night changes of citric‐acid levels in crassulacean acid metabolism: phenomenon and ecophysiological significance
Authors: LÜTTGE U.
Published: April 2006

Abstract A reappraisal is offered of old and new observations of substantial day‐night changes of citric‐acid levels in crassulacean acid metabolism (CAM). In contrast to malic acid, the biochemical consequences and the ecophysiological significance of nocturnal accumulation of citric acid in CAM have not received due attention. Considerations show that citric‐acid accumulation does not provide a means for nocturnal storage of CO2. It may, however, serve carbon retention by internal recycling and sustain the water budget affording a vacuolar osmoticum. Since citric‐acid accumulation energetically is considerably more favourable than malic‐acid accumulation, this may have important ecophysiological implications. The questions raised by these reflections can and need to be tackled experimentally.
The effect of divalent cations on Na+ tolerance in Charophytes. I: Char a buckellii
Authors: HOFFMANN R , BISSON M. A.
Published: April 2006

Abstract The comparative Na+ tolerance of Chora buckellii cultured in freshwater (FW) or artificial Waldsea water (AWW, which contains about 110 mol m−3 each Na +, Mg2+, Cl− and SO2‐4 was tested with respect to the external Na+ to Ca2+ ratio (Na: Ca). Fifty per cent of FW cells subjected to 70 mol m−3 NaCl, which raised Na:Ca from 10: 1 to 700: 1 and the external osmotic pressure from 0.024 to 0.402 MPa, died within 6 d. Death was associated with the loss of Na/K selectivity, H+ ‐pump activity and turgor. Restoration of Na:Ca to 10:1 in high Na+ medium with CaCl2 ensured 100% survival and maintained H+‐pump activity and Na/K selectivity of FW cells. Turgor was regulated within 3 d with net uptake of Na +, K+ and Cl− in the vacuolc. Mg2+ was not as effective as Ca2+ in enhancing survival or maintaining H+ ‐pump activity and Na/K selectivity of FW cells in the presence of elevated Na+. However, turgor was regulated within 3 d by accumulation of Cl− and an unknown cation in the vacuole. All AWW cells subjected to an increase of 70 mol m −3 NaCl, which raised Na: Ca from 16:1 to 25: 1 and the external osmotic pressure from 0.915 to 1.22 MPa, survived and maintained H + ‐pump activity. Turgor was regulated within 6d by accumulating Na +, K+ and Cl− in the vacuole. All AWW cells subjected to 70molm−3 NaCl in a medium in which Na:Ca was equal to 700:1 survived and maintained H + ‐pump activity, but showed loss of Na/K selectivity. Turgor was regulated with an unknown osmoticum(a) within 6 d.
Site‐directed monoclonal antibodies against the amino terminus of 124‐kDa phytochrome from Avena sativa L.
Authors: PLUMPTON C. , PARTIS M. D. , THOMAS B. , HUSKISSON N. S. , BUTCHER G. W.
Published: April 2006

Abstract Two monoclonal antibodies (AFRC MAC 184 and 185) have been raised in rats against a synthetic octadecapeptide corresponding to the N‐terminus of Avena phytochrome. The peptide was conjugated to tuberculin purified protein derivative (PPD) for immunization and the cell lines screened by ELISA using the free peptide. Both antibodies bind to intact 124‐kDa phytochrome on Western blots and in a double antibody sandwich ELISA. In the ELISA, they have an approximately four‐fold higher affinity for Pr than Pfr. Conformational changes during photoconversion, therefore, involve the extreme N‐terminus of the phytochrome molecule.
Mediation of high‐temperature injury by roots and shoots during reproductive growth of wheat
Authors: KUROYANAGI T. , PAULSEN G. M.
Published: April 2006

Abstract Previous studies suggest that high temperature stress on wheat (Triticum aestivum L.) involves root processes and acceleration of monocarpic senescence. Physiological changes in wheat roots and shoots were investigated to elucidate their relationship to injury from elevated temperatures after anthesis. Plants were grown under uniform conditions until 10 d after anthesis, when shoot/root regimes of 25°C/25°C, 25°C/35°C, 35°C/25°C and 35°C/35°C were imposed. Growth and senescence of shoots and grain were influenced more by root temperatures than by shoot temperatures. High root temperatures increased activities of protease and RNasc enzymes, and loss of chlorophyll, protein and RNA from shoots, whereas low root temperatures had opposite effects. High root temperatures appeared to induce shoot senescence directly. High shoot temperatures probably disrupted root processes, including export of cytokinins, and induced high leaf protease activity, senescence and cessation of grain development. The authors concluded that responses of wheat to high temperatures, whether of roots or shoots, are manifested as acceleration of senescence and may be mediated by roots during grain development.