bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen Inhibition of Photosynthetic Oxygen Evolution in Marine Plants
Authors: Downton WJS , Bishop DG , Larkum AWD , Osmond CB
Published: January 2006

The effect of oxygen concentration on oxygen exchange in six species of the Chlorophyta, one of the Cyanophyta, one of the Rhodophyta, three of the Phaeophyta, zooxanthellae from Tridacna maxima (clam) and Pocillopora damicornis (coral), and a marine angiosperm was investigated with a polaro- graphic oxygen electrode. The rate of photosynthesis in air-saturated sea water ranged from 14 to 248 micromoles of oxygen evolved per hour per milligram of chlorophyll. Photosynthesis was inhibited by 15-85% in sea water adjusted to between 65 and 90% of oxygen saturation. A post- illumination burst of oxygen uptake was observed on darkening and the size of this burst was in- fluenced by oxygen concentration. Steady-state rates of oxygen uptake in the dark were enhanced at higher oxygen tensions. The likelihood that the dissolved oxygen content of sea water may regulate the productivity of reef communities is discussed.
Effect of Phosphorus Nutrition and Cytokinins on Flowering in the Tomato, Lycopersicon esculentum Mill
Authors: Menary RC , Staden JV
Published: January 2006

Ten days of phosphorus deficiency results in a decrease in the number of flowers that develop on the first truss of tomato plants. This effect on flower number is accompanied by a decrease in the cytokinin activity of the root exudate. The involvement of cytokinins in flower development is further implicated by the fact that application of kinetin to the growing medium increased the number of flowers produced by the seedlings. Preliminary identification of cytokinins in root exudate has revealed the presence of compounds that cochromatograph with zeatin and zeatin riboside on Sephadex LH20.
Variation of Stomatal Diffusive Resistance With Ambient Humidity in Sunflower (Helianthus annuus)
Authors: Aston MJ
Published: January 2006

Experiments with sunflower were set up to supply quantitative information on the relationship between transpiration diffusive resistance and evaporative demand as affected by changes in ambient humidity. The experiments were run on whole plants with the roots in nutrient solution to ensure an adequate supply of water. Particular attention was paid to relating calculated diffusive resistance values with measured diffusion values and visual observations of the stomata.
The transpiration diffusive resistance of the stomata was found to increase in a linear manner as the water vapour concentration difference between leaf and surrounding air increased. Changes in calculated diffusive resistance were paralleled by changes in the diffusion of nitrous oxide through the stomata. Visual observation showed that the stomata closed as resistance increased and vice versa. Stomata from both adaxial and abaxial surfaces of the leaf demonstrated increases in diffusive resistance with increasing evaporative demand but the response of the adaxial surface change was not always concurrent with that of the abaxial surface.
Leaf water content did not change as evaporative demand was changed, reflecting the observation that uptake of water through the roots equalled the amount lost by transpiration.
It was concluded that changes in diffusive resistance were directly related to the stomatal aperture and that the primary response was at the level of the stomatal apparatus. There was no evidence of stomatal control resulting from lowered tissue water content.
Anomalous results may be obtained in gas exchange experiments where a constant area of leaf is sealed into a cuvette. Tests indicate that errors arise where the leaf is held too firmly.
Male Sterility in Sorghum bicolor (L.) Moench Induced by Low Night Temperature. I. Timing of the Stage of Sensitivity
Authors: Brooking IR
Published: January 2006

Male sterility was induced in grain sorghum (CK 60 × Tx 415) by exposure of plants to five low- temperature nights (25°C day/ 10°C night). Sensitivity was greatest at the late archesporial cell- pollen mother cell development period, up to the leptotene stage of meiosis. Female fertility was unaffected. For a complete inflorescence, the period of sensitivity extended from flag leaf ligule emergence until the flag sheath had elongated to about 20 cm, a period of 6-7 days under 25°C day/ 20°C night conditions.
Pollen development proceeded in an apparently normal manner following low temperature treatment, but was arrested just prior to maturation at the vacuolate two-celled microspore stage. Sterile pollen at anthesis was devoid of starch and had low levels of free proline. Assays of anther proline levels proved to give a reliable index of pollen maturation.
Vine Response to Carbon Dioxide Enrichment During Heat Therapy
Authors: Kriedemann PE , Sward RJ , Downton WJS
Published: January 2006

Virus diseases which limit productivity in horticultural plants can be eliminated, or at least ameliorated, by propagating shoot tips from 'heat-treated' parent material. Grapevines (Vitis vinifera L.) undergoing heat therapy have to be grown at high temperature (37-40°C, day and night) for sustained periods (3-6 months) and the present paper reports how CO2 enrichment (1200-1300 ppm) can become an aid to their survival under these rigorous conditions.
Vine growth rate more than doubled due to elevated CO2, and dry matter distribution was altered in favour of greater root growth. Nevertheless, stomatal resistance was increased (twofold), so that the ratio of assimilation to transpiration was substantially improved. Photosynthetic capacity of individual leaves was enhanced (laboratory measurement at 35°C and 950 ppm CO2) whereas photorespiration appeared depressed-a favourable combination for growth at elevated temperature. These physiological responses are discussed in relation to changes in both nitrate reductase and ribulosebisphosphate carboxylase activities and are compared with the behaviour of Leea brunoniana Clarke, a naturally occurring relative of V. vinifera from northern Australia.
Pathways of CO2 Fixation in the Cam Plant Kalanchoe daigremontiana. III. Correlation With δ13C Value During Growth and Water Stress
Authors: Osmond CB , Bender MM , Burris RH
Published: January 2006

Seedlings of K. daigremontiana were grown in the same controlled-environment room under nine different day temperature and light regimes. In each treatment, irrigated plants maintained dawn water potentials of approximately -5 bar whereas droughted plants ranged to -22 bar. Irrigated plants showed a characteristic stomatal opening on illumination, closure during deacidification and partial stomatal opening following deacidification. Stomata of droughted plants remained closed throughout the light period. Irrigated and droughted plants showed comparable dark acid synthesis. Low light levels and low day temperature resulted in lower dark acid synthesis and more protracted deacidification in the light. The δ13C value (total carbon) of old as well as newly formed leaves of irrigated plants tended to become less negative throughout the experiment except in low-light, low-day-temperature treatments. This trend was accentuated in the δ13C value (total carbon) of whole shoots of droughted plants. These data are consistent with an increase, with age, in the proportion of CO2 assimilated in the dark during growth of irrigated plants, and with the greater dependence on dark CO2 assimilation during the slower growth of droughted plants. Differences in the δ13C value of soluble and insoluble carbon from irrigated and droughted plants assayed at dawn appear to be consistent with the established starch to acid relationships in crassulacean plants.
Regulation of Anthocyanin Synthesis in Apple Skin. I. Comparison of the Effects of Cycloheximide, Ultraviolet Light, Wounding and Maturity
Authors: Chalmers DJ , Faragher JD
Published: January 2006

Cycloheximide applied to apple skin discs inhibited anthocyanin synthesis even at very low concentrations (0.01 �g ml-1) but stimulated accumulation in whole apple skin at concentrations between 0.05 and 30 �g ml-1. When cycloheximide was applied as a drop to whole fruit, anthocyanin synthesis was inhibited in the zone of application. A region of enhanced synthesis surrounded the inhibited area when the concentration was 1 �g ml-1 or higher. Inhibition appears to be the primary effect, while stimulation is a secondary effect of the application of cycloheximide.
Similarly, exposure to u.v. light for 5-60 min promoted anthocyanin accumulation. Wounding of fruit tissue, as a specific treatment or while preparing skin discs, increased the level of anthocyanin in the skin and replaced the stimulating effect on anthocyanin formation of applied u.v. light or cycloheximide. The effects of wounding and cycloheximide decreased with increasing fruit maturity.
The data suggested that wounding, u.v. light, maturity and cycloheximide act through a common effector, perhaps ethylene.
Regulation of Anthocyanin Synthesis in Apple Skin. III. Involvement of Phenylalanine Ammonia-lyase
Authors: Faragher JD , Chalmers DJ
Published: January 2006

The relationship between L-phenylalanine ammonia-lyase (PAL) activity and anthocyanin synthesis in apple skin was investigated. Enzyme activity was induced by exposure to white light. After a lag phase of less than 10 h, PAL activity increased to a maximum at 30 h and then declined. Anthocyanin accumuIation, after a lag phase of 20 h, continued at a constant rate for a further 100 h.
The increased rate of anthocyanin accumulation which resulted from u.v. light and cycloheximide treatment of whole fruit was preceded by comparable increases in the level of PAL activity. Wounding, which stimulated anthocyanin synthesis in skin discs, caused a far greater increase in PAL activity. In wounded tissue (skin discs) neither u.v. light or cycloheximide treatment caused any increase in anthocyanin accumulation or PAL activity. Cycloheximide inhibited anthocyanin formation in skin discs and, to a lesser extent, reduced PAL activity. When cycloheximide was applied as a single drop to a whole fruit, it inhibited anthocyanin formation but increased PAL activity in the skin to which it was applied. In a surrounding ring of skin, both anthocyanin level and PAL activity were increased.
Without light, anthocyanin synthesis did not occur and there was virtually no PAL activity in whole fruit skin. However, in skin discs held in the dark, PAL activity developed to the same level as in illuminated discs, but no anthocyanin accumulated.
The results indicate that, although the level of PAL activity may control the rate of anthocyanin synthesis in whole fruit, it is not the only critical enzyme regulating anthocyanin synthesis in apple skin. The mechanisms by which treatments may stimulate PAL activity and anthocyanin synthesis and the possible involvement of ethylene are discussed.
Interactions Between Growth, Phosphate Content and Nitrogen Fixation in Mycorrhizal and Non-Mycorrhizal Medicago sativa
Authors: Smith SE , Daft MJ
Published: January 2006

Nodulated Medicago sativa cv. Europe plants, both non-mycorrhizal and mycorrhizal (inoculated with Glomus mosseae), were grown in sand or soil with a range of phosphate levels. The following parameters were measured: intensity of mycorrhizal infection, intensity of nodulation, growth, phosphate content, nitrogenase activity (acetylene reduction) and nitrogen content.
Both nodulation and mycorrhizal infection had occurred within 2 weeks of inoculation with the appropriate endophytes. Major increases in dry weight of mycorrhizal plants were not apparent until approximately 10 weeks from inoculation. However, mycorrhizal plants showed more extensive nodulation, coupled with higher rates of nitrogenase activity from 2 weeks onwards, and at the final (12-week) harvest had higher values of % N. Phosphate content of mycorrhizal plants (�g P/g dry wt) was also greater than non-mycorrhizal plants at 7 weeks. By 10 or 12 weeks, when significant mycorrhizal enhancement of growth was apparent, the total nitrogen and total phosphorus per mycorrhizal plant were also higher, but nitrogenase activity and phosphate content measured on a dry weight basis showed no significant differences between mycorrhizal and non-mycorrhizal plants. It is clear that mycorrhizal enhancement of phosphate uptake and nitrogen fixation precedes any effect on growth and the results indicate the importance of the time factor in the development of this tripartite symbiosis between legume, Rhizobium and mycorrhizal fungus.
The Source of Carbon for Proline Synthesis in Osmotically Stressed Artichoke Tuber Slices
Authors: Wrench P , Wright L , Brady CJ , Hinde RW
Published: January 2006

When thin slices of tubers of Helianthus tuberosus L. are plasmolysed in mannitol solutions, the initially large pool of free arginine decreases within 24 h and then, during the next 72 h, a several- fold increase in the concentration of free proline occurs.
Radioactivity from DL-ornithine, L-arginine and L-glutamate was shown to label proline in plasmolysed discs of tubers. The percentage conversion to proline of each of the precursors was 20 to 50 times greater in discs plasmolysed for 24 h than in freshly plasmolysed discs. By comparing the transfer of radioactivity from L-[U-14C]arginine and L-[5-3H]arginine to proline, metabolism of arginine directly to proline without passage through a glutamate pool was established. It is concluded from this and other evidence that pathways from arginine and glutamate to proline operate independently. Calculations based on the specific activity of precursors, the pool sizes of free arginine and glutamate, and the transfer rates of radioactivity to proline indicate that arginine is quantitatively the more important precursor for proline synthesis in this tissue.
Agronomic and Physiological Responses of Soybean and Sorghum Crops to Water Deficits II. Crop Evaporation, Soil Water Depletion and Root Distribution
Authors: Burch GJ , Smith RCG , Mason WK
Published: January 2006

The effects of soil water depletion on crop evaporation and root absorption of water were studied in soybean and sorghum crops. Sorghum did not deplete the maximum soil water store by more than 100 mm, whereas rainfed crops of soybeans, cvv. Ruse and Bragg, depleted the soil water store by 130 and 170 mm, respectively. This was sufficient to reduce soybean yields by 35% and hasten maturity in both cultivars when compared with irrigated crops. The post-flowering efficiency of water use by rainfed crops of soybeans was about one-third that of sorghum.
The root distribution of Ruse and its pattern of soil water extraction indicated that during bean- fill it was unable to exploit water from much below 80 cm depth, but this effect was offset by its reaching maturity before yield was severely affected by water stress. As Ruse approached maturity, its root densities decreased in soil layers below 10 cm depth, whereas Bragg, which matured 2 weeks later than Ruse, maintained a deep root system and continued to deplete water down to 120 cm. The contrast in root distribution between soybean cultivars also influenced the level of soil water depletion at which crop evaporation fell below the potential rate. Soil and root resistances to water absorption were used to interpret the effects of root density and soil water depletion on water uptake.
The regional implications of the results were examined using a water balance model to analyse historical rainfall records. It was concluded that similar soil moisture conditions could be expected about 1 year in 5, indicating that these results have a ready application for irrigation scheduling in this area.
Compositional Changes During Grape Berry Development in Relation to Abscisic Acid and Salinity
Authors: Downton WJS , Loveys BR
Published: January 2006

Changes in the chemical composition of developing Cabernet Sauvignon berries from salt-treated and low-salt vines were followed. Although salinity advanced the timing of veraison, the sequence of changes in the salt-affected berries remained the same as in berries from control plants, viz. concentrations of abscisic acid and reducing sugar increased before proline, arginine, potassium and chloride increased, and before acidity declined. The contribution of these substances to osmotic changes within developing grape berries is discussed.
Osmotically Induced Changes in the Pressure-Flow Relationship of Maize Root Systems
Authors: Nulsen RA , Thurtell GW
Published: January 2006

An hypothesis is proposed that the observed non-linearity of flow v. applied pressure is due, not to a change in root resistance, but to an accumulation of osmotica outside the stele which changes the potential gradient driving water flow.
Sap exudation rate from the detopped root system of well watered maize (Zea mays L.) plants that were sealed in a pressure chamber was a linear function of the applied air pressure when the applied pressure was greater than the numerical value of the osmotic potential of the solutions used to irrigate the plants. At applied pressures less than the numerical value of the solution osmotic potential, exudation rate was a curvilinear function of applied pressure. The exudation rate decreased at all pressures when the osmotic potential of the solution used to irrigate was decreased through the values 0, - 70, - 190 and - 380 kPa. The osmotic potential of the exudate remained between - 60 and - 70 kPa when both - 70 and - 380 kPa solutions were used.
Effect of Relative Size and Distance of Competing Sinks on the Distribution of Photosynthetic Assimilates in Wheat
Authors: Cook MG , Evans LT
Published: January 2006

The objective of these experiments was to examine to what extent the size of a storage organ influences its ability to compete for a limited supply of assimilate. The experimental system consisted of wheat plants reduced to one main source of current photosynthate, usually the flag leaf of the main stem, and two main competing sinks, the ears of the first two tillers. The size of the two sinks was varied by the differential removal of grains 9 days after anthesis to give competing sinks comparable in every way except in the number of grains. 14C was assimilated by the flag leaf 2 days after grain removal, and its distribution determined after a further 2 days.
When the relative size of the two sinks was varied, the grains in the larger sink received more than their pro rata share of 14C-labelled assimilate from the flag leaf, the bias in favour of the larger sink increasing with increase in its relative size. Grain growth in the smaller sink depended to a greater extent on local sources of assimilate, from ear photosynthesis and stem reserves. The more completely ear photosynthesis was inhibited by DCMU the less was the advantage of the larger sink in securing flag leaf assimilates but, even under the most severe competition, there was a significant bias in favour of the larger sink. Reserve carbohydrates in the stem could not be completely eliminated although they were greatly reduced by early defoliation and inhibition of photosynthesis. Their presence precluded an unambiguous conclusion as to the role of sink size in the competition for assimilates from a common source. Relative distance of the competing sinks from the source was varied by using one of the three uppermost leaves on one tiller as the source of labelled assimilate. Proximity to source conferred a marked advantage, and greater sink size was particularly important in securing assimilates from distant sources.
Cotyledonary Storage Proteins in Pisum sativum. III. Patterns of Accumulation During Development
Authors: Millerd A , Thomson JA , Schroeder HE
Published: January 2006

An antiserum raised against proteins from isolated protein bodies of mature pea seeds recognized seven antigenically distinct protein families in cotyledon extracts analysed by crossed immunoelectrophoresis. This antiserum has been used to follow the sequence of appearance and pattern of accumulation of these proteins in peas grown under controlled environmental conditions. One antigen present in mature cotyledons was shown to be a haemagglutinin, one corresponded to legumin, and four distinct, non-crossreacting antigenic species were related to the vicilin series of proteins. Both the number of components detected and the order of their appearance during development were similar in three genotypes examined, but the quantitative representation of legumin relative to other components was genotype-specific. Quantitative differences were observed in the polypeptide composition of the vicilin components responsible for separate antigenic specificities, but qualitative differences were not excluded. During development, similar conspicuous quantitative changes in polypeptide composition, accompanied by a change in mean electrophoretic mobility, occurred amongst the molecules carrying the predominant antigenic determinant related to vicilin (peak 4); again, qualitative differences might also distinguish these components. The antigen responsible for peak 6 contained two major polypeptides distinct from the components of the legumin and vicilin fractions.
Peak 6 represented the first fully immunocompetent species to appear during development, but later became quantitatively less significant as the other antigenic species accumuIated. Legumin and the antigen forming peak 6 were first detected immunologically in an apparently incomplete form. These putative precursors disappeared during subsequent development, so that only the corresponding stable precipitin peaks were seen in the immunoelectrophoretic profiles of extracts from mature cotyledons.
Salt Stress and Comparative Physiology in the Gramineae. II. Glycinebetaine and Proline Accumulation in Two Salt- and Water-Stressed Barley Cultivars
Authors: Wyn Jones RG , Storey R
Published: January 2006

Under low-salt conditions, the glycinebetaine levels in the shoot exceeded the proline levels in two barley cultivars, California Mariout and Arimar. Stress induced by both polytheylene glycol (PEG) and NaCl caused an accumulation of both compounds. However, a gradual incremental increase in stress led to higher glycinebetaine than proline levels, whereas salt and osmotic shock led to proline levels far in excess of the glycinebetaine levels. Both stress regimes caused a greater proportional increase in proline than in glycinebetaine.
Preliminary data suggest that proline may be used as an internal assay for water stress in barley leaves. Comparison of the physiological responses of the barley cultivars to NaCl and PEG stress suggested that the suppression of growth by salt treatment was not due directly to the low external water potential but arose either from the ions, Na+ and Cl-, interfering with metabolic processes or from a number of possible but unsubstantiated interactions leading to a reduction in turgor potential and thus in the rate of cell expansion.
Root Absorption of Water and Physiological Responses to Water Deficits by Festuca arundinacea Schreb. And Trifolium repens L
Authors: Burch GJ , Johns GG
Published: January 2006

A study of water uptake by white clover (Trifoliurn repens) and tall fescue (Festuca arundinacea cv. Demeter) examined their comparative physiological responses to water deficits and the pattern of water absorptioil by their root systems. Fescue had more deep roots than clover and extracted more water from deep soil layers, finally resulting in a drier soil profile. Poor control of leaf transpiration in clover resulted in low leaf water potentials and increased leaf senescence; in fescue, better stomatal control and higher leaf water potentials prolonged its period of active growth.
The relationships between soil water content, transpiration rate and pattern of water absorption by both root systems were compared using an existing theory of water uptake. Two parameters for integrating soil water potential and soil conductance down the soil profile gave more consistent relationships with the transpiration rates of fescue than with those of clover. These two parameters may be less able to account for the pattern of soil water absorption by a clover root system and a possible explanation for this effect is discussed. Relative canopy conductance ratios gave similar relationships with the relative transpiration ratios for fescue and clover. Therefore, leaf senescence in clover was apparently important for balancing its rates of transpiration and water uptake. In contrast, fescue was able to rely upon its more extensive root system, effective stomatal control and ability to roll leaves to regulate its water balance.
Cotyledonary Storage Proteins in Pisum sativum. IV. Effects of Sulfur, Phosphorus, Potassium and Magnesium Deficiencies
Authors: Randall PJ , Thomson JA , Schroeder HE
Published: January 2006

The quantitative and qualitative effects of deficiency of S, P, K or Mg on the cotyledonary proteins of pea seeds have been studied using chemical, immunological and electrophoretic techniques.
Deficiency of S, P or K causes characteristic and consistent changes in the proportions of certain proteins both outside and inside protein bodies of mature seeds. Amongst the storage proteins in the protein bodies, S deficiency results in a relative decrease in legumin and in vicilin peak 3, accompanied by a relative increase in the predominant vicilin, peak 4. A quantitatively major cotyledonary protein of unknown function, located outside protein bodies and consisting of 22- kdalton polypeptides, is decreased by S deficiency. Deficiencies of P or K cause an increase in the quantitatively minor vicilin peak 3 and also a marked relative increase in legumin. Mg deficiency has little effect on the proportions of the storage proteins.
The degree of nutrient deficiency is reflected in seed and plant yields. Total N and trichloroacetic acid (TCA)-insoluble N and the contents of some other mineral elements in the seed are given. A 10-fold increase in sulfur supply above the optimum for yield did not increase N or S in the TCA- insoluble fraction.
Abscisic Acid Synthesis and Metabolism in Wheat Ears
Authors: King RW
Published: January 2006

During development of wheat grains their content of abscisic acid (ABA) increased, and this was also shown to occur in the grain of ears detached and grown in culture. Over a 10-day period of growth of ears in culture, their content of ABA increased from 0.31 to 2.56 ng/grain. Loss of ABA from the grain occurred on cessation of grain growth and drying of the grain. With loss of ABA, there was an associated but lesser accumulation of phaseic acid and dihydrophaseic acid, two known metabolites of ABA. Studies with [14C]abscisic acid indicated that premature drying of grain led to some conversion of ABA to compounds chromatographically similar to phaseic and dihydrophaseic acid, but the major products were more polar. Apparently, synthesis of ABA occurred in the developing grain (or at least in the ear) in association with a slow rate of degradation but, at maturity and drying of the grain, there was enhanced degradation of ABA. The physiological importance of these compounds in grain development and dormancy is discussed.
Vertical Wilting and Photosynthesis, Transpiration, and Water Use Efficiency of Sunflower Leaves
Authors: Rawson HM
Published: January 2006

Plants of two sunflower cultivars were exposed to a number of soil drying cycles and the gas exchange of young, fully expanded leaves at different nodes was measured continuously from when the leaves were turgid until when they were severely and vertically wilted. Peak rates of net photosynthesis increased with the height of leaf insertion but, regardless of node position, leaves at vertical wilting always had rates of net photosynthesis which were close to 50% of peak rates. Although the leaf water potential at which vertical wilting occurred ranged between - 1.3 and -2.2 MPa and varied even for a particular leaf position, there was a similar relationship between the rate of reduction in photosynthesis and the reduction in leaf water potential. No evidence was found for a threshold leaf water potential at which stomatal closure occurs.
Water use efficiency improved when leaves changed from a horizontal to a vertical orientation, apparently through changes in leaf temperature but. by the stage of wilting, water use efficiency had already markedly improved over efficiencies of turgid leaves. Much of this improvement stemmed from changes in leaf conductances. No clear differences between cultivars were evident in any parameter measured.
The likely effects that wilting will have on water use efficiency in the field and strategies for optimising water use on a diurnal basis are discussed.
Heat Injury in Leaves of Alpine, Temperate and Tropical Plants
Authors: Smillie RM , Nott R
Published: January 2006

Temperatures producing heat injury in leaves of 30 species were measured by following heat-induced changes in fluorescence of the leaf chlorophyll. Except for six alpine plants and four cereals, mainly leafy vegetables and leaves of young fruit trees were used. Dark-adapted leaves were heated at a rate of one Celsius degree per minute. Chlorophyll fluoroscence began to increase between 30 and 40°C and reached a peak around 50°C. The peak of fluorescence was reached at 47.1°C in an alpine plant Plantago glacialis, at 51.2°C in lettuce (Lactuca sativa) and at 57.6°C in pawpaw (Carica papaya). Similarly, in the cereals, the peak of fluorescence was reached at lower temperatures in the temperate ones (49.5°C in barley and 48.9°C in oats) than in the two from warm climates (55.2°C in maize and 53.5°C in sorghum). This difference in heat sensitivity between plants from the three groups did not hold for all plants surveyed and there was some overlapping between individual plants in different groups. However, the mean temperature, for the inital rise in fluorescence as well as for the peak of fluorescence, occurred at a lower temperature in the alpine group of plants and at a higher temperature in the tropical group of plants compared with the temperate group.
The results demonstrate a relationship between heat resistance and temperature of the environment in which the plants evolved, and illustrate the potential use of the chlorophyll fluorescence method for in vivo measurements of heat sensitivity in green plants.
Application of Phytohormones to Pea Roots After Removal of the Apex: Effect on Lateral Root Production
Authors: Goodwin PB , Morris SC
Published: January 2006

Removal of 2 mm of the primary root tip of Pisum sativum caused a complete halt to primary root elongation, but did not alter the total number of laterals formed. The auxins indole-3-acetic acid and 1-naphthaleneacetic acid, when applied to the stump in a lanolin emulsion, increased the number of lateral roots. High levels of abscisic acid and low levels of the cytokinins N6-benzylaminopurine and N6-(γ, γ-dimethylallylamino)purine, and of the gibberellins GA3 and GA7, resulted in decreased lateral root production. Kinetin was without effect. There appears to be an inverse relationship between auxins and cytokinins in root/shoot growth coordination. Auxins, which are produced in the shoot tip, inhibit lateral bud growth but promote lateral root initiation. Cytokinins, which are produced in the root tip, inhibit lateral root initiation, but promote lateral stem growth.
Frost Injury in Wheat: Ice Formation and Injury in Leaves
Authors: Marcellos H , Burke MJ
Published: January 2006

Freezing of water in leaves of a number of wheat cultivars was studied using pulsed nuclear magnetic resonance (n.m.r.) spectroscopy; these data were coordinated with measurements of the temperature dependance of freezing injury, and used to analyse the freezing process and its effects. The freezing temperature which resulted in 50% loss of cell electrolytes on thawing. T50, varied from -7 to -12.1°C in the material studied. Hardening treatments decreased T50 by 1.8° in the least hardy cultivar, Kite, and 3.3° in the most hardy cultivar, Cheyenne. Despite the contrast in hardiness level, freezing curves determined by n.m.r. were similar, the fraction of water remaining unfrozen, LT/L0, at temperature T having the relationship LT/L0 = ΔTm/T + b, where LT, L0 are the amounts of liquid water per unit dry weight at T and 0�C, respectively, ΔTm is the melting point depression and b the liquid water that does not freeze.
The freezing curves were similar because ΔTm varied little among hardy and less hardy samples. At their T50, the least hardy sample of Kite had lost 77.2% of its freezable water to extracellular ice at - 7°C, whereas the corresponding value for the hardy Cheyenne was 86.8% at its T50 of - 12.1°C. Greater hardiness in samples was closely associated with an ability to withstand greater amounts of freeze-induced dehydration, and not with alterations in °Tm.
Invertase From Leaves of Phaseolus vulgaris Plants Grown on Nutrient Solutions Containing NaCl
Authors: Hawker JS
Published: January 2006

Two invertases occur in leaves of P. vulgaris with pH optima near 5.0 and 7.5. They have been separated and partially purified by chromatography on DEAE-cellulose. Tris-HCl buffer at 10 mM inhibited the former enzyme by only 7% but the latter enzyme by 90%. A comparison of the enzymes from leaves of plants grown on 0, 20 and 50 mM NaCl in nutrient solution showed that the amount of the pH 5.0 enzyme was significantly lower in the NaCl treatments, whereas the amount of the pH 7.5 enzyme was not shown to be significantly affected by the salt treatment. The Km values for sucrose were about 7.5 and 27 mM for the partially purified pH 5.0 and pH 7.5 enzymes respectively, and they were not altered by NaCl treatment of the plants. A previous report of NaCl causing increasing Km values for sucrose at pH 5.0 in less pure extracts [Hawker and Walker (1978) Aust. J. Plant Physiol. 5, 73-80] was presumably an artefact, possibly caused by interference by the pH 7.5 enzyme or by other unknown reactions.
Drought Effects on Transpiration and Leaf Water Status of Cowpea in Controlled Environments
Authors: Hall AE , Schulze E
Published: January 2006

The factors responsible for the extreme drought avoidance of cowpeas [Vigna unguiculata (L.) Walp.] previously observed in several field environments were investigated. Drought avoidance is defined as the extent to which high plant water potentials are maintained in the presence of environmental drought. Cowpeas were grown in controlled environments and subjected to either frequent irrigation or progressive drought. Plants in the drought treatment were grown for up to 2 months on 2-2.5 litres per plant of available water supplied 5 days after emergence. Transpiration of whole plants was determined by pot weighing, and leaf water status was determined with a pressure chamber.
Well watered cowpeas avoided drought by two mechanisms: by avoiding water loss, because at constant air temperature transpiration increased only slightly with increases in vapour pressure deficit from 20 to 40 mbar; and due to an efficient water transport system which resulted in only small decreases in pressure chamber values with increases in transpiration at high rates of transpiration. Non-irrigated cowpeas avoided drought by maintaining low transpiration rates due to reduced leaf area and reduced transpiration per unit leaf area compared with irrigated plants.
Plant Peptidoglucans Affecting the Phenotypic Expression of Rhizobial Nitrogenase
Authors: Storey R , Reporter M
Published: January 2006

Dialysable substances capable of influencing rhizobial nitrogenase activity in vitro were obtained from Glycine max root cells during transfilter coculture with Rhizobium japonicum. These substances from the liquid plant-conditioned medium were chromatographed on Sephadex G-25, DEAE- cellulose and carboxymethylcellulose and on a concanavalin A-Sepharose column. The separated active column fractions initiated the phenotypic expression of nitrogenase activity (C2H2 reduction, H2 production) in different Rhizobium strains. Hydrolysis of these column fractions showed them to contain a small peptide and a glucan. Analysis of active fractions also showed the presence of bound copper. It was concluded that the plant fractions involved in stimulating rhizobial nitrogenase activity were peptidoglucans; at least one active fraction may also be a copper metallothionein.
Isolation, Culture and Plant Regeneration From Protoplasts of Nicotiana debneyi
Authors: Scowcroft WR , Larkin PJ
Published: January 2006

Mesophyll protoplasts of two genetically distinct genotypes of N. debneyi were cultured with sustained division following a plating efficiency in excess of 50%. Fully fertile mature plants were regenerated from callus cultures derived from protoplasts. Shoots were induced in medium containing 1 mg/l 6-benzylaminopurine and 0.5 mg/I indole acetic acid. The repeatably high efficiency of protoplast culture was used to evaluate the quantitative effects of two drugs, kanamycin and trimethoprim, which effectively inhibited colony formation at concentrations of 100 and 50 �g/ml, respectively. An enhancer of DNA uptake, poly-L-ornithine, had virtually no effect on sustained protoplast division at a concentration of 7.5 �g/ml or less.
Electrogenic Events in Chloroplasts and Their Relation to the Electrochromic Shift (P518)
Authors: Hope AB , Morland A
Published: January 2006

The absorbance change at 518 nm (ΔA518) was measured in response to single-turnover actinic laser flashes under varied conditions. This response is usually attributed to an electrochromic effect on endogenous pigments. Particularly in carefully prepared pea chloroplasts, a slowly rising portion of ΔA518 was consistently observed. The substances DBMIB, DCMU and ADP all removed the slow component in different ways. It is argued that this part of the P518 response is due to the electrogenic effect of protons released from the oxidation of plastoquinone. On this basis, it is suggested that P518 responds approximately equally to protons released during the oxidation of water and of plastoquinone, but with different time courses. ADP seems to switch the path of protons from plastoquinone to a route in which they do not induce a transthylakoid field.
Field evidence for the optimality hypothesis of gas exchange in plants
Authors: Hari Pertti , Mäkelä Annikki , Berninger Frank , Pohja Toivo
Published: January 2006

The ‘optimality hypothesis’ of gas exchange in plants has been
studied since the 1970s, but testing it in the field has proven difficult. A
recent reformulation of the hypothesis with detailing assumptions on leaf
structure makes it possible to solve the optimisation problem explicitly, such
that the predictions of gas exchange are readily testable against field data.
This form of the model was tested against field measurements of
photosynthesis, transpiration and stomatal conductance in Scots pine
(Pinus sylvestris) shoots during three clear summer
days. Model parameters were estimated independently from photosynthesis
measurements on preceding days. The measurements were carried out at a new
field measurement station with a very low level of noise. The predictions of
photosynthesis, transpiration andstomatal conductance explained
84–98% of the variance in the data.
Comparison of Stomatal Action of Orange, Soybean and Wheat Under Field Conditions
Authors: Meyer WS , Green GC
Published: January 2006

Diurnal trends in leaf diffusive conductance, Cs, leaf water potential ΨL and rates of evapotranspiration E*T were monitored on orchard-grown orange trees and field-grown crops of soybeans and wheat. Changes in these measurements were observed on soybeans and wheat as the soil water deficit increased. Maximum values of Cs of well watered plants differed between the three species (soybeans > wheat >> orange) probably as a result of different stomatal sizes and densities. Diurnal trends in Cs were common for all species, with maximum values occurring during midmorning followed by slightly lower midday values. The reduction in Cs around midday became much more pronounced as the soil water deficit increased. Slight increases in Cs values of soybeans and wheat were recorded during late afternoon. This pattern of stomatal aperture change can reasonably be explained in terms of responses to both radiant energy and plant water status. The pattern also seems to comply with the premise that stomates interact to optimize the rate of assimilation while minimizing the rate of transpiration in a given environment.
Stomatal action appeared to have little effect on daily ET in soybeans under well watered conditions; ET was closely related to incoming radiant energy. The low midday values of Cs apparently caused a midday plateau in the rate of CT in wheat while even lower daytime Cs values for orange seemed to cause a low and fairly constant rate of ET which was relatively insensitive to changes in incoming radiant energy.
The value of ΨL attained during mid morning at which Cs initially began to decline was fairly constant for soybeans (-0.9 to -1.1 MPa) as the predawn ΨL decreased from -0.1 to -0.8 MPa. A similar decline in predawn ΨL for wheat caused a change in the value of ΨL at which initial decreases in Cs were observed from - 1.3 MPa to -2.4 MPa. Thus there appeared to be little adjustment of stomatal action in soybeans but considerable adjustment in wheat.
Fruit Set in Lupinus angustifolius Cv. Unicrop. I. Phenology and Growth During Flowering and Early Fruiting
Authors: Farrington P , Pate JS
Published: January 2006

Interaction of vegetative and reproductive development was examined in Lupinus angustifolius L. cv. Unicrop, a grain legume in which only small proportions of flowers normally form fruit. Outgrowth of lateral shoots below an inflorescence coincided with shedding of flowers from upper positions on that inflorescence. Removal of laterals during early flowering of the inflorescence increased fruit number three- to fourfold, as did application to developing laterals of the growth retardants maleic hydrazide, AMO-1618, 'UNI-P-293', and 'Disugran'. Already-formed fruits appeared to restrict the number of fruit formed higher up an inflorescence, but their effect was small compared with that of lateral shoots. Shading of inflorescences due to overgrowth of surrounding laterals did not appear to affect fruit number of the inflorescence. Expanding laterals and secondary thickening of the main stem were major sinks for assimilates, while flowering inflorescences acquired only very small proportions (less than 3 %) of the shoot's current increment of dry matter. Studies of floral development showed that flower buds, open (white) flowers, and fruits were rarely shed, but that the 'corolla mauve' and 'corolla senescing' stages of late floral development were particularly vulnerable to abscission-promoting influences. This vulnerable period was marked by declining dry weight of the flower. It was not possible to determine whether the restrictive influence of lateral shoots on fruit number was of a hormonal character or due to the reduced supply of nutrients to developing flowers.
Fruit Set in Lupinus angustifolius Cv. Unicrop. II. Assimilate Flow During Flowering and Early Fruiting
Authors: Pate JS , Farrington P
Published: January 2006

Assimilate distribution in Lupinus angustifolius was studied during 7 weeks after emergence of the main inflorescence by feeding [14C]urea to a single leaf or group of leaves on a plant and measuring 14C in plant parts 24 h after feeding. Nine times of feeding were involved, each with 14C treatments encompassing leaves of the main stem and first-order laterals. The inflorescence was a minor sink for assimilates compared with root, main stem and developing lateral shoots. During the first 4 weeks the inflorescence relied on main stem leaves, especially the upper leaves, but in the fifth week leaves of upper laterals became principal sources of assimilates. The transition occurred after four to six basal fruits had set, and just as upper flowers were commencing to abscise. Estimates were made of transfer of photosynthetically fixed carbon from the uppermost main stem leaf to the inflorescence, using data on carbon dioxide exchange and changes in carbon content of this leaf and its translocatory commitment to the inflorescence as determined by 14C feeding. Assimilate flow from leaves to flowers was confined largely to organs of the same or adjacent orthostichies (2/5 phyllotaxis), but these affinities became less definite during fruiting. Import of 14C by reproductive units was related to phenology, position on an inflorescence, and accumulation of dry matter. All flowers attracted assimilates strongly at the bud stage but lost sink strength progressively after opening. Upper flowers destined to abscise failed to import assimilates or to bleed from phloem for several days before being shed. Lower flowers which set fruits showed a rapid resurgence of sink strength once their corollas had senesced and the young fruits had commenced to elongate.
Metabolic Aspects of Chilling Resistance: Alanine Accumulation and Glutamate Depletion in Relation to Chilling Sensitivity in Passionfruit Species
Authors: Patterson BD , Pearson JA , Payne LA , Ferguson IB
Published: January 2006

Changes in the level of different amino acids were measured when the leaves of a number of chilling- resistant and chilling-sensitive Passiflora species were kept at 0°C. An alpine species of Cardamine was used as a reference plant because it is well adapted to temperatures near 0°C. After 48 h at 0°C, alanine levels had increased several-fold in the chilling-sensitive group, while the level of glutamate had decreased several-fold. In the chilling-resistant group there was little change in the level of alanine observable after 48 h, but there was a substantial fall in the level of glutamate. These changes did not occur at higher temperatures. The changes in the levels of other amino acids were small. In leaves of Cardamine, neither alanine nor glutamate levels changed by more than 50%.
Levels of alanine rose about threefold in both chilling-resistant and sensitive species over the first 10 h of chilling. However, while levels continued to rise in the chilling-sensitive species, they had returned to near normal levels by 46 h in the resistant species. The reduction in glutamate was similar for both species; however it occurred more rapidly in the chilling-sensitive species.
It is concluded that chilling-resistance in Passiflora is associated with the ability to prevent a sustained accumulation of alanine at 0°C. It is not specifically associated with the ability to maintain levels of glutamate at 0°C.
Relation Between CO2 Evolution and in situ Reduction of Nitrate in Wheat Leaves
Authors: Naik MS , Nicholas DJD
Published: January 2006

In wheat leaf discs the evolution of 14CO2 from exogenously supplied 14C-labelled citric acid cycle intermediates was stimulated during the in situ anaerobic reduction of nitrate in the dark. Under these conditions, however, [1,4-14C]succinate was not metabolized. Similarly, when leaves were allowed to assimilate 14CO2 in the dark, thus producing endogenously labelled organic acids, the subsequent evolution of 14CO2 from discs prepared from these leaves was strongly dependent on nitrate reduction. A 1 : 1 stoichiometry between nitrite production and CO2 evolution was recorded during this in situ reduction of nitrate. The in situ reduction of nitrate was inhibited by malonate and D-malate and this effect was reversed by fumarate, probably by generating L-malate within the mitochondria. Mitochondrial NAD-malic enzyme (decarboxylating) (EC 1.1.1.38) was similarly inhibited competitively by malonate and D-malate, but not by succinate.
These results indicate that the citric acid cycle dehydrogenases which generate CO2 supply NADH for nitrate reduction in wheat leaves. It is likely that, under anaerobic conditions, nitrate acts as an alternative oxidant to O2 for the NADH generated by the citric acid cycle dehydrogenases resulting in simultaneous evolution of CO2. This ensures that the citric acid cycle operates at the required rate for nitrate assimilation.