bluuebunny/crossref_metadata_2025 huggingface dataset:
Apparent Total CO2 Equilibrium Point in Marine Algae during Photosynthesis in Sea Water
Authors: Tolbert NE , Garey W
Published: January 2006

A constant CO2 equilibrium level was reached with marine algae in a closed container in sunlight in sea water. With an air atomosphere, values of 5 mg CO2 per litre were maintained by Boodlea composita and by Halimeda cylindracea, and 2 mg per litre by Enteromorpha sp. These equilibrium values were increased in an atmosphere of 100% oxygen. These values may be comparable with compensation point analyses for land plants and are indicative of photorespiration in marine algae.
Influence of Oxygen Concentration on Photosynthesis in Marine Plants
Authors: Black CC , Burris JE , Everson RG
Published: January 2006

Photosynthesis was studied in various atmospheres of oxygen with marine plants grown on the Great Barrier Reef near Lizard Island, Australia. Inhibition of photosynthesis in a 100 % oxygen atmosphere ranged from 12 to 83 % in specific marine plants when compared to a nitrogen or helium atmosphere. The rates of photosynthesis in these marine plants were in general similar to those of terrestrial plants which fix CO2 via the reductive pentose phosphate cycle. We conclude that photo-respiration is present in specific marine plants at levels similar to those found in terrestrial plants with the reductive pentose phosphate cycle.
Malate Dehydrogenase and Other Enzymes
Authors: Ting IP
Published: January 2006

The activity and some properties of NADH malate dehydrogenase in extracts of marine plants was investigated. Activity was detected in 24 species examined and average rates [in µmol min-1 (mg chlorophyll)-1] in the major groups were: Cyanophyta, 47; Chlorophyta, 74; Phaeophyta, 35; Rhodophyta, 69; and Anthophyta, 150. The zooxanthellae of clams and coral also showed substantial NADH malate dehydrogenase activity [4-63 µmol min-1 (mg chlorophyll)-1]. Some kinetic properties of the enzyme from Halimeda cylindracea were studied and the inhibition of enzyme activity by NaCl and sea water was examined. The activity of NADP malate dehydrogenase (decarboxylating) was measured in several organisms [0.15 - 5.0 µmol min-1 (mg chlorophyll)-1] and the presence of low activity phosphoenolpyruvate carboxylase was qualitatively established. These observations are discussed in relation to pathways of CO*2 metabolism in marine plants.
Glycollate Oxidase and Glycollate Dehydrogenase in Marine Algae and Plants
Authors: Tolbert NE
Published: January 2006

Glycollate : dichlorophenolindophenol reductase, or glycollate dehydrogenase, was present in 15 green marine algae and one blue-green alga collected around Lizard Island, Australia. No enzyme activity was found in red or brown algae or zooxanthellae. Glycollate dehydrogenase was also found in the marine grasses Cymodocea and Thalassia, and this is the first report of it in higher plants. However, glycollate oxidase was present in the particulate fraction from Halophila, another marine monocotyldonous plant. On Lizard Island, the C3 plants, the C4 salt plants Distichlis and Salsola, and a crassulacean acid metabolism plant, Sesuvium all contained glycollate oxidase.
Anomalous Water Relations in Copper-Deficient Wheat Plants
Authors: Graham RD
Published: January 2006

Leaf water potential, diffusive resistance, relative water content, weekly water use, yields and head bending were measured on wheat plants subjected to four copper levels (0, 0.4, 0.8 or 4.0 mg Cu per pot) and two water levels (6 or 12% soil water content). Severe copper deficiency (Cu 0) resulted in no grain yield, wilting, increased leaf diffusive resistance and, at the same time, increased leaf water potential relative to plants receiving 4.0 mg Cu (Cu 4.0). Water supply effects were observed but there was no interaction between copper and water treatments. Mild copper deficiency (Cu 0.4, Cu 0.8) resulted in small yield decreases, relative to Cu 4.0, and increased head bending towards maturity. It is concluded that wilting, characteristic of copper-deficient plants, is due to structural weakness (decreased lignification) and not to the water status of the plants; also, increased leaf diffusive resistance is due to a specific effect of copper deficiency on guard cells and not to decreased leaf water potential.
The Action Potential in Chara corallina: Effect of Temperature
Authors: Beilby MJ , Coster HGJ
Published: January 2006

An investigation has been made of the effect of temperature on excitation in cells of C. corallina. It was found that the duration both of the action potential and of the transient current during excitation under voltage clamp increased with decreasing temperature, from ~1 s at 40°C to ~30 s at 3.5°C. The form of the transient response, however, was independent of temperature. While the peak potential during an action potential was largely independent of temperature, the peak transient current during a voltage clamp increased with increasing temperature up to ~30°C. Beyond this temperature, the peak current decreased again with increasing temperature.
The activation enthalphy (ΔH*) calculated from Arrhenius plots of the duration of the action potential or of the transient current under voltage clamp varied continuously with temperature, having the values of ~7 kJ/mol for T > 20°C and ~350 kJ/mol for T < 7°C.
The peak of the transient conductance changes (during voltage clamp at -45 mV) increased progressively with increasing temperatures; for T < 7°C there was almost no transient change in conductance. °H* for peak transient conductance change was ~7 kJ/mol for T > 20°C and ~145 kJ/mol for T < 7°C.
At low temperatures (<7°C), ΔH* for the excitation channels was similar to that for the dehydration of K+, Na+ or Cl- ions. At high temperatures (>35°C), ΔH* for both the passive and excitation channels was about the same as that for diffusion in a free solution. This suggests a progressive change in the degree of dehydration required for ion permeation in the channels.
In the light of the known frequency dependence of the membrane capacitance of this species (at low frequencies), considerations are also given to the implications of the similarity in their temperature dependence, of the duration of the action potential and the duration of the transient currents during voltage clamps.
On the Significance of Increased Protein Synthesis in Ripening Banana Fruits
Authors: Brady CJ , O'connell PBH
Published: January 2006

Banana fruit slices exposed to ethylene at a concentration of 5 �l per litre for 12 h ripened within 6 days. Slices treated with ethylene for only 6 h ripened at the same time as slices not treated with ethylene. Twenty four hours after the initiation of either a 6- or 12-h ethylene treatment, protein synthesis in pulp tissue showed similar increases. It is concluded that the increase in protein synthesis is a response to ethylene treatment rather than to ripening. Isotope dilution experiments show that radioactive valine added to pulp slices is diluted by endogenous valine before incorporation into protein. From the incorporation studies it is deduced that the ethylene-provoked increase in protein synthesis is responsible, within 24 h, for synthesis equivalent to a substantial proportion of the protein in pulp cells. Double-labelling experiments establish that the increased synthesis in response to ethylene treatment involves replacement of a large range of soluble proteins, and is not limited to the synthesis of a few specific proteins.
The Basis of Osmotic Pressure Maintenance During Expansion Growth in Helianthus annuus Hypocotyls
Authors: Mcneil DL
Published: January 2006

In etiolated sunflower (H. annuus) hypocotyls, the intracellular osmotic pressure was maintained in spite of the dilution caused by growth. The principal osmotic substances present were hexoses (44 � 6 mol m-3 glucose and 40 � 5 mol m-3 fructose) and organic potassium salts (30 mol m-3). ,
Potassium fluxes in vivo (intact rooted seedlings) and in vitro (1 cm, peeled, cut sections in an aerated bathing solution) were similar, indicating that the sectioning had not affected cell fluxes. The uptake of 3-O-methyl glucose by cut sections from a bathing medium was lower than the uptake estimated using intact tissue (in vitro influx was 5 % of the net accumulation rate of intact tissue). This suggested that some pathway of hexose uptake other than from the extracellular spaces occurred in vivo.
To explain this difference in reducing sugar accumulation rates the following pathway is suggested:
(1) Transport of sucrose from the cotyledons via the phloem;
(2) Direct unloading of the sucrose into the symplast;
(3) Transport of the sucrose into the vacuole down a sucrose concentration gradient maintained by hydrolysis of sucrose to glucose and fructose; (4) Low hexose efflux from the vacuole (5 % of in vivo influx), preventing loss from the vacuole.
Ultrastructural Localization of Ions. II. X-Ray Analytical Verification of Silver Precipitation Products and Distribution of Chloride in Mesophyll Cells of Barley Seedlings
Authors: Steveninck RFMV , Ballment B , Peters PD , Hall TA
Published: January 2006

The ultrastructural localization of Cl- by means of a silver precipitation technique has been verified by means of X-ray analytical electron microscopy (EMMA-4 electron microscope plus KEVEX energy dispersive analyser). It was shown that the localization method was specific for Cl- in the case of electron-dense deposits in chloroplasts, plasmodesmata and plasmalemma of barley mesophyll cells.
It was pointed out that the use of nitric acid rinses in order to remove non-specific deposits of silver phosphates and carbonates has pitfalls and that the precipitation technique should always be used in conjunction with X-ray microprobe analysis.
Ultrastructural Localization of Ions. Iii. Distribution of Chloride in Mesophyll Cells of Mangrove (Aegiceras Corniculatum Blanco).
Authors: Steveninck RFMV , Armstrong WD , Peters PD , Hall TA
Published: January 2006

Ultrastructural localization of Cl- by means of a silver ion precipitation technique combined with X-ray energy spectroscopy (EMMA-4 electron microscope plus KEVEX energy dispersive analyser) showed the presence of two types of vacuoles in mesophyll cells of mangrove (A. corniculatum Blanco). Type A vacuoles contained large amounts of osmiophilic organic solute and little or no Cl-, while type B vacuoles were shown to be free of osmiophilic organic solute but to contain significant quantities of Cl-.
X-ray spectroscopy of electron-opaque deposits in chloroplasts showed the presence of AgCl deposits and deposits of silver in approximately equal proportions. Fine granular deposits in plastoglobuli were also shown to consist of silver. Deposits in the cytoplasmic phase and in the plasmodesmata, however, always consisted of AgCl.
The significance of the two types of vacuoles is discussed in relation to the symplastic or apoplastic transport of Cl- from conducting tissue to the salt glands.
Assimilate Movement in Lolium and Sorghum Leaves. II. Irradiance Effects on the Products of Photosynthesis
Authors: Wardlaw IF , Marshall C
Published: January 2006

The rate of export and longitudinal movement of 14C-labelled assimilates in the phloem was found to be greater in Sorghum sudanense than in Lolium temulentum. Sucrose was the predominant metabolite translocated from the leaf in both species in both low and high light conditions. The effect of irradiance on the rate of formation and nature of the products of photosynthesis was examined using 14CO2 pulse-chase techniques and the differences in the primary metabolites closely followed those expected for a C3 and a C4 species. Reduction in irradiance reduced the rate of incorporation of 14C into sucrose, especially in Sorghum, and led to the accumulation of amino acids in both species. Although species differences in export of 14C-labelled assimilate were not apparently related to the rate of 14C incorporation into sucrose, this could account for the delay in export of 14C-labelled assimilates associated with reduced irradiance. There was a rapid initial labelling of starch and the proportion of *14C incorporated as starch was enhanced at high irradiance, particularly in Sorghum. Overall, the results support the view that there is a greater partitioning of assimilate into storage (starch) at high irradiance relative to assimilate moving into the phloem and that irradiance (in the range 20-96 W m-2) did not directly influence vein loading.
Nitrogen Compounds Transported in the Xylem of Sugar Cane
Authors: Waldron JC
Published: January 2006

Microcapillary tubes were inserted directly into xylem vessels of leaves and stalks of sugar cane (Saccharum spp.) to determine the form in which nitrogen is translocated from the roots towards the leaves. On a low nitrogen regime, the xylem fluid of both sugar cane and related species and genera contained nitrogen dominantly in the amino form. Nitrate was also present and increased markedly in some varieties when the supply of nitrate fertilizer to the roots was increased.
The amino N and nitrate N levels tended to be lowest in the xylem fluid of those leaves most active in photosynthesis.
Strophiolar Water Conduction in Seeds of the Trifolieae Induced by Action on the Testa at Non-Strophiolar Sites
Authors: Ballard LAT
Published: January 2006

When impermeable legume seeds are made permeable to water by mechanical treatments that make strophioles conductive, it is not known whether the strophioles themselves must be acted on directly. To investigate this question the testas of individual seeds from the genera Medicago, Stylosanthes and Trifolium were either broken through completely by cutting, filing or piercing, or stressed by squeezing or striking, at sites remote from the strophioles. As determined by serial photography, 30-90 % of the previously impermeable seeds became conductive at the strophiole.
These results indicate that the strophiole can become conductive without being acted on directly. They also suggest that the strophiole and general testa should be regarded as an integrated system in which both water-repellency and mechanical properties of the testa are important in the control of water absorption.
Stress Metabolism. IX. The Significance of End-Product Inhibition of Proline Biosynthesis and of Compartmentation in Relation to Stress-Induced Proline Accumulation
Authors: Boggess SF , Aspinall D , Paleg LG
Published: January 2006

The rapid and extensive accumulation of proline during water stress in barley (cv. Prior) and tobacco (cv. White Burley) indicates that feedback inhibition of proline synthesis under these circumstances is unlikely. The incorporation into proline of radioactivity from administered L-[14C]glutamic acid was inhibited by the presence of proline in turgid but not in stressed tissues, suggesting that feedback inhibition of proline synthesis occurs in turgid but not in stressed tissues. An alternative explanation of the data, that the radioactivity in the L-glutamate pool of turgid tissue was diluted by non-labelled glutamate derived from the oxidation of the added proline, was not supported. Although rapid oxidation of added proline occurred, this did not appear to enter, to any significant extent, the glutamate pool concerned with proline synthesis.
Neither aqueous nor non-aqueous isolation techniques demonstrated any specific enrichment with proline of specific cell fractions during stress. Moreover, in plants which had accumulated radioactivity in free proline during stress from administered L-[14C]glutamate, radioactivity accumul- ated in the proline incorporated in protein to an extent which suggested that the whole proline pool was equally available for protein synthesis. This does not favour the hypothesis that proline is accumulated exclusively in specific cellular organelles during stress.
Effects of Fusicoccin and Kinetin in Isolated Cotyledons of Fenugreek (Trigonella foenum-graecum L.)
Authors: Rijven AHGC
Published: January 2006

Isolated cotyledons of fenugreek (T. foenum-graecum L.) were incubated in darkness and the effects of fusicoccin and kinetin on fresh weight increase and nucleic acid content of the cotyledons, and pH changes of the medium were measured.
Both fusicoccin and kinetin stimulated fresh weight increase; KCl doubled the effect of fusicoccin but increased that of kinetin by only 20%; other salts (LiCl, NaCI, NH4Cl) could not replace KCI. The fresh weight increase in the presence of fusicoccin and kinetin together exceeded that in the presence of either alone, over a range of fusicoccin concentrations. Nucleic acid content was increased only marginally by fusicoccin, but substantially by kinetin. In contrast, the pH of the medium was lowered significantly by fusicoccin but not (or marginally) by kinetin. With fusicoccin in the solution, the fresh weight increase was less and later inhibited by cycloheximide than with kinetin in the solution; in the absence of KCI, fusicoccin-induced fresh weight increase was especially insensitive to cycloheximide. The fresh weight increase was not inhibited at all by ethylene or by 2,4-dichlorophenoxyacetic acid with fusicoccin in the solution, but it was significantly inhibited with kinetin in the solution.
Dormancy and Impotency of Cocklebur Seeds. V. Growth and Ethylene Production of Axial Segments in Response to Oxygen
Authors: Esashi Y , Watanabe K , Ohhara Y , Katoh H
Published: January 2006

Growth responses to exogenous CO2 or ethylene and the production of CO2 or ethylene in embryonic axes excised from dormant or non-dormant seeds of cocklebur (Xanthium pensylvanicum Wallr.) were examined in relation to oxygen tension. There were two ethylene-producing systems in the axes, one anaerobic and one aerobic. The former was active in dormant seeds and the latter was active in non-dormant seeds. The axes from non-dormant but impotent small seeds, incapable of germinating under ordinary conditions, showed higher activities for both systems. However, there was no qualitative difference in the oxygen response as to CO2 output between the dormant and non-dormant axes, but CO2 output under aerobic conditions was greater with non-dormant seeds.
Regardless of dormancy status, growth stimulation of axes by CO2 occurred when it was applied during the beginning of incubation and in atmospheres with oxygen concentrations insufficient to permit normal axial growth. Nevertheless, the stimulation of ethylene production by CO2 was parallel with the increase of oxygen tension, suggesting that the CO2-stimulated ethylene production could not be the result of CO2-stimulated axial growth.
The growth response was most sensitive to ethylene after the CO2-sensitive period and before an oxygen-requiring period. Similarly to the action of CO2, the most striking effect of ethylene on the growth of non-dormant axes was obtained in oxygen-deficient atmospheres. However, the synergistic interaction between CO*2 and ethylene occurred only in aerobic conditions. Unlike the non-dormant axes, the dormant ones, whose aerobic ethylene productivity was very small, responded to ethylene with increased growth in proportion to increasing oxygen tension.
Dormancy and Impotency of Cocklebur Seeds. VI. Growth and Ethylene Production of Cotyledon Segments in Response to Oxygen
Authors: Esashi Y , Kotaki K , Ishidoya O
Published: January 2006

Cotyledon tissue excised from dormant or non-dormant large cocklebur (Xanthium pensylvanicum Wallr.) seeds were examined for growth responses to CO2 or ethylene and for ethylene production under different oxygen tensions. Regardless of the dormancy status, cotyledons responded to CO2 and ethylene in a very similar manner to axes: the maximum growth response to CO2 and ethylene was obtained in quasi-anaerobioses in the case of the non-dormant cotyledons, but in increased oxygen tensions in the case of the dormant ones. A cooperative action of CO2 and ethylene was prominent in the presence of oxygen in suitable amounts. CO2 began to exert an effect first after water imbibition, then ethylene and lastly oxygen was needed to allow normal cotyledon growth.
As the ethylene-producing system of cotyledons, active in quasi-anaerobioses, differed from that of axes in requirement for oxygen, the enhancement of ethylene production by exogenous CO2 was greater under reduced rather than increased oxygen tensions. Finally, the possible mechanism of cocklebur seed germination in subterranean habitats was discussed from the likely involvement of these three gaseous factors in axial and cotyledonary growth.
The Role of Ethylene in Abscission of Cling Peach Fruit
Authors: Jerie PH
Published: January 2006

Ethylene production was measured in fruit of a number of cling peach cultivars within 1 h of picking. During the period when ethylene production on the tree was rising exponentially, fruit from cultivars with low preharvest drop produced ethylene at much lower rates than fruit from high-drop cultivars. Also, the ethylene peak tended to occur earlier relative to flesh colouring in high-drop cultivars. The level of endogenous ethylene controlled the rate of abscission, which was retarded by holding the fruit in an atmosphere of 15% CO*2. Abscission was accelerated by injection of (2-chloroethyl)- phosphonic acid, but the cultivars Golden Queen and Phillips, and an unnamed cultivar, differed from each other in their sensitivity.
Changes in the Concentrations of Abscisic Acid in Fruits of Normal and Nr, rin and nor Mutant Tomatoes During Growth, Maturation and Senescence
Authors: Mcglasson WB , Adato I
Published: January 2006

The concentrations of free and base-hydrolysable (bound) abscisic acid (ABA) were measured in fruits of cv. Rutgers (normal) and of the mutants Nr, rin and nor during growth, maturation and senescence. Measurements were made also of postharvest changes in free ABA in immature Rutgers fruits.
Free ABA began to accumulate rapidly in the pericarp of developing fruits of Rutgers, Nr and rin during the period of most rapid growth but accumulation in nor was delayed and slower. Peak concentrations in Rutgers, Nr and rin were similar but the maximum level in nor was about 50% lower. Peak concentrations of free ABA coincided with the completion of growth in Rutgers and rin but peak levels in Nr and nor were not reached until several days later. Colouring in all strains occurred at approximately the same time as the accumulation of peak concentrations of free ABA. Changes in bound ABA paralleled those in free ABA in pericarp tissue of all strains but the levels were about one-seventh of those of free ABA. Free and bound ABA were measured in seeds and associated mucilaginous tissue only in 50% developed and fully grown fruits. In the younger fruits of Rutgers, Nr and rin, this fraction contained a higher concentration of free ABA than the pericarp tissue. In fully grown fruits, the level of ABA in the seeds and associated tissue was much less than in this fraction of younger fruits and less than half that in the pericarp tissue. Free ABA in seeds and associated tissues remained low in nor fruits of both ages. The ratios of bound and free ABA in seeds and associated tissues in all strains were generally similar to those found in pericarp tissue. In Rutgers fruits, free ABA increased after harvest.
It is suggested that ABA is produced in both pericarp and seeds plus associated mucilaginous tissue. Accumulation of ABA does not seem to be a result of increased ethylene production but conversely may be involved in the increased ethylene evolution which accompanies ripening in normal strains. Since the pattern of changes in ABA and the accumulation of peak concentrations in pericarp tissue was not consistently related to growth but was closely related to the onset of symptoms of ripening or senescence, ABA may be a regulator of ripening in the tomato.
Photosynthesis in Gomphrena celosioides and Its Classification Amongst C4-pathway Plants
Authors: Repo E , Hatch MD
Published: January 2006

Monocotyledonous C4 species classified as NADP-ME-type transfer malate from mesophyll to bundle sheath cells where this acid is decarboxylated via NADP malic enzyme (EC 1.1.1.40) to yield pyruvate and CO2. The dicotyledon G. celosioides is most appropriately classified in thls group on the basis of high leaf activities of NADP malic enzyme and NADP malate dehydrogenase (EC 1.1.1.82). However, this species contains high aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2) activities and centripetally located bundle sheath chloroplasts, features more typical of other groups of C4 species that cycle aspartate and alanine between mesophyll and bundle sheath cells. During the present study, we found that these aminotransferases and NADP malate dehydrogenase were predominantly located in mesophyll cells, that malate was the major C4 acid labelled when leaves were exposed to 14CO2, and that label was initially lost most rapidly from the C-4 of malate during a chase in 12CO2. These results are consistent with the major route of photosynthetic metabolism being the same as that operative in other NADP-ME-type species, although this may be supplemented by a minor route utilizing aspartate. In contrast to monocotyledonous NADP-ME-type C4 species, isolated bundle sheath cells from G. celosioides were capable of rapid photoreduction of NADP as judged by products formed during assimilation of 14CO2 and their capacity for light-dependent oxygen evolution. This was related to a relatively high frequency of single unstacked granum in the chloroplasts of these cells.
Accumulation of Sorbitol and Glucose by Leaf Slices of Rosaceae
Authors: Bieleski RL
Published: January 2006

Pear (Pyrus domestica Medik.) leaf slices, which form sorbitol photosynthetically, took up sorbitol from solution by an active transport mechanism. Uptake was linear with time, was sensitive to metabolic inhibitors and cold, occurred against a concentration gradient, and was not reversed by washing the tissue. Glucose uptake was similar to sorbitol uptake, but showed consistent differences in response to tissue aging, sugar concentration, light, and to competing sugars and sugar analogues. There was little competition between sorbitol and glucose, suggesting that the two may be taken up by separate mechanisms. The relationship of uptake to concentration could be interpreted as biphasic with constants resembling those for sugar uptake in other tissues: for sorbitol, (a) Km 3 × 10-3M and Vmax 1000 nmol per g fresh wt per h, (b) Km 1 × 10-1 M, Vmax 19 500; and for glucose, (a) Km 1 × 10-3 M and Vmax 600, (b) Km 0.6 × 10-1 M and Vmax 10 500. The ability of various species to accumulate sorbitol was compared. Species which normally contain sorbitol accumulated it as readily as glucose, while other species accumulated it much less rapidly. In pear leaf tissue, sorbitol was poorly metabolized while glucose was largely converted to sorbitol. In rose (Rosa sp., cultivated) leaf tissue (which does not contain sorbitol), sorbitol and glucose were both extensively metabolized to sucrose and other compounds. In pear, sorbitol may be segregated into a non-metabolic pool, thus serving as a specific storage compound in place of sucrose as in other plants.
Stomatal Development in Etiolated Vicia faba: Relationship Between Structure and Function
Authors: Lurie S
Published: January 2006

In V. faba plants grown in the dark, the following pattern of stomatal development was observed: (1) stomatal differentiation occurs simultaneously on all areas of the young leaf; (2) at a certain point (about 10 days of growth in the dark) differentiation ceases but maturation of stomata continues; (3) there is no difference in the pattern or time of development of stomata on the outermost or innermost leaf of the leaf group; (4) plastids of mature dark-grown stomata contain starch but plastids of immature stomata do not.
When plants of different ages are brought from the dark into the light, stomata of older plants achieve physiological competence in a shorter time than do stomata of younger plants.
Growth Pattern, Carbon Dioxide Exchange and Dry Weight Distribution in Wheat Growing Under Differing Photosynthetic Environments
Authors: Gifford RM
Published: January 2006

Wheat (cv. WW15) was grown as a crop stand in different CO2 concentrations (ambient, ambient plus 200 � 20 vpm CO2, ambient minus 150 � 20 vpm CO2) from germination to maturity in naturally lit growth cabinets under winter or summer light conditions, at 21°C by day and 16°C at night. Ambient CO2 concentration during the daylight hours averaged 280-300 vpm.
CO2 level had little effect on phenology of the mainshoot; most of the growth response was through tillering. From data on flag leaves in the winter light experiment, there was no indication of any positive or negative feedback on growth acting through maximum leaf net photosynthesis rate. Leaf area index was increased by CO2 at low light and the related self-shading acted as a negative feedback partially countering the effect due to an enhanced rate of CO2 uptake per unit leaf area. Dark respiratory CO2 loss represented a greater proportion of CO2 uptake in the light for the CO2-depleted crop than for the control crop. But the reciprocal effect was not evident for the enriched crop. Contrary to classical ideas on growth responses to variation of colimiting factors, the growth response to CO2 enrichment was relatively greater under the low radiation than the high radiation regime. The grain was the tissue most flexible in its responsiveness to changes in assimilation under the conditions of the summer experiment. For this crop, for which the grain yield of the control was very high (0.97 kgm-2), response of yield to CO2 enrichment corresponded to 0.25% per vpm.
Regulation of Anthocyanin Synthesis in Apple Skin. II. Involvement of Ethylene
Authors: Chalmers DJ , Faragher JD
Published: January 2006

Ethylene production by immature apple fruit was stimulated by cycloheximide application, u.v. irradiation and wounding. After fruit were treated with 1 and 10 �g ml-1 cycloheximide, the rate of ethylene production increased to 2 and 10 times the control level, respectively. In skin discs cut from whole fruit (wounded tissue), the rate of ethylene production was stimulated to at least 40 times that in whole fruit. This wound-stimulated ethylene production was partially inhibited by an initial application of cycloheximide. Ultraviolet irradiation of whole fruit stimulated the rate of ethylene production to more than 25 times the control rate after 15 min irradiation. In skin discs, u.v. irradiation caused only a 50-100% increase in ethylene production rate. The effects of certain treatments on ethylene were quantitatively comparable with the effects of the same treatments on anthocyanin formation in whole fruit. Ethylene at 30 �l 1-1 stimulated anthocyanin in skin of immature apples by 16%. Possible mechanisms by which ethylene may stimulate anthocyanin synthesis are discussed.
A Carbohydrate-Binding Arabinogalactan-Protein From Liquid Suspension Cultures of Endosperm From Lolium multiflorum
Authors: Anderson RL , Clarke AE , Jermyn MA , Knox RB , Stone BA
Published: January 2006

Water-soluble arabinogalactan-proteins have been isolated from tissue-cultured rye grass endosperm cells and their culture medium by precipitation with the β-glucosyl Yariv artificial antigen. The intracellular and extracellular polymers are similar in composition and molecular size (apparent mol. wt 2.2 — 2.8 × 105). The protein portion represents up to 7% of the molecule and is rich in hydroxyproline, alanine and serine. The carbohydrate portion (84%) consists solely of arabinose (36%) and galactose (64%) and methylation analysis shows it to be a branched 1,3 : 1,6-galactan substituted by arabinofuranosyl residues. The carbohydrate compositions and methylation analyses for polymers precipitated by the β-glucosyl Yariv antigen from lima beans, cashew, tomato, silver beet and asparagus and an arabinogalactan-peptide from wheat endosperm are compared. As a group, they show homologies both in their peptide and polysaccharide portions. A histochemical method, based on precipitation with the β-glucosyl Yariv antigen, showed the binding polymers to be localized in discrete irregular vesicles in the tissue-cultured rye grass endosperm cells. Native rye grass endosperm cells show staining between starch granules, and staining is also seen in the aleurone cells of barley, wheat and rye grass.
Inhibition of Flowering in Lolium temulentum L. By Water Stress: a Role for Abscisic Acid
Authors: King RW , Evans LT
Published: January 2006

A brief, 8-h water stress during the induction of flowering in L. temulentum reduces the flowering response, the more so the greater the stress. Water stress also affected leaf photosynthetic rate, relative water content of leaves and leaf elongation.
Water stress was most inhibitory to flowering when applied during the period of high-intensity light at the beginning of the one long day. The abscisic acid (ABA) content of leaves increased up to 30-fold during the imposition of water stress and fell rapidly after stress was relieved, regardless of when the stress was imposed. The greater the stress, the higher was the level of ABA in leaves and the greater was the inhibition of flowering. The ABA content of apices also rose in response to water stress, in some cases during the stress treatment but usually 8-22 h later. Flowering was inhibited when apical ABA contents were high at the end of the long day.
Although water stress may influence the flowering of plants in several ways, these experiments suggest that water stress during the long day induction of L. temulentum inhibits flowering by raising the content of ABA at the shoot apex during floral evocation.
Leaf Elongation Rate in Panicum maximum var. trichoglume Following Removal of Water Stress
Authors: Ludlow MM , Ng TT
Published: January 2006

Different levels of stress were induced in P. maximum var. trichoglume by withholding water for various periods. Leaf elongation rate was measured during dark stress periods and after rewatering in both the light and the dark. Following rewatering, elongation rates of previously stressed plants exceeded those of controls for periods up to 33 h, during which time elongation rate was more related to previous levels of water stress than to current leaf water potential. In addition, there was a transient burst of elongation when plants were rewatered in the light. It is suggested that the stimulated rates result from expansion of cells which have accumulated during the stress because cell division is less sensitive to water stress than is cell expansion. Despite the stimulated rates of elongation after rewatering, the recovery was incomplete such that the final lengths of stressed leaves were less than those of unstressed plants.
Effects of Heat on the Physiology of Seedlings of Eucalyptus obliqua
Authors: Moore GM , Rowan KS , Blake TJ
Published: January 2006

Seedlings of E. obliqua L'Herit. were heated in air at different temperatures for various times. Mortality was assessed using a wide-range a.c. bridge, and the internal temperatures of the upper and lower stems and leaves were monitored. The extent of killing depended on both the temperature and the duration of heat. No killing occurred at 40°C and total killing occurred at 100°C; at intermediate temperatures, the extent of killing was a function of duration of treatment. The temperature inside the lower stem declined for 20 min after applying heat, followed by a gradual increase in parallel with the increase in temperature of the soil. This effect was attributed to the movement of water from the roots and soil into the lower stem, and could explain the capacity of seedlings of E. obliqua to survive a temperature of 80°C, which is higher than reported for other species.
Altitudinal Variation in the Photosynthetic Characteristics of Snow Gum, Eucalyptus pauciflora Sieb. Ex Spreng. II. Effects of Growth Temperature Under Controlled Conditions
Authors: Slatyer RO , Ferrar PJ
Published: January 2006

The photosynthetic responses of three altitudinal populations of snow gum, E. pauciflora Sieb. ex Spreng., were examined on material grown at a range of day/night temperatures from 8/4 to 33/28°C.
The pattern of the photosynthetic responses to growth temperature was generally similar for all populations but the material from the lowest-elevation, warmest, site showed the highest temperature optimum and significantly higher rates of net photosynthesis at the highest growth temperature. In a corresponding way, the material from the highest-elevation, coldest, site showed the lowest temperature optimum, and significantly higher rates of net photosynthesis at the lowest growth temperature. This pattern, also reflected in the responses of rI, the intracellular resistance, and rI, the gas-phase resistance, supported the view that E. pauciflora shows continuous variation in physiological responses through its altitudinal range.
The peak values of net photosynthesis were high for all populations, but were greatest, 81 ng cm-2 s-1, in the lowest elevation material and decreased to 72 ng cm-2 s-1 in the highest-elevation material. Corresponding values of rI ranged from 2.5 - 3.0 s cm-1, and for rI from 2.4 - 3.3 s cm-1. These levels compare favourably with levels reported for other woody species.
Altitudinal Variation in the Photosynthetic Characteristics of Snow Gum, Eucalyptus pauciflora Sieb. Ex Spreng. III. Temperature Response of Material Grown in Contrasting Thermal Environments
Authors: Slatyer RO
Published: January 2006

Photosynthetic temperature response curves were measured on seedlings of E. pauciflora grown from seed collected at high (1770 m) and low (915 m) elevation sites, in the Snowy Mountains. The material was grown in contrasting day/night temperature regimes (33/28 and 15/10°C) in the Canberra phytotron.
The material from the high elevation site showed a temperature optimum at about 20°C when grown at 15/10°C and at about 25°C when grown at 33/28°C. By comparison, the temperature optimum for the low elevation material was near 25° when grown at 15/10°C and shifted to about 30° when grown at 33/28°C. The general form of the temperature response curves was similar for both sets of material, although net photosynthesis of the higher elevation material dropped off more rapidly at temperatures above and below the optimum. When grown at 15/10�C, peak Ievels of net photosynthesis were higher in the high elevation material (66 ng cm-2 s-1 v. 54 ng cm-2 s-1). When grown at 33/28°C, peak levels were higher in the low elevation material (78 ng cm-2 s-1 v. 60 ng cm-2 s-1).
Similar response patterns were observed in intracellular resistance, ri, and gas phase resistance, ri, although there was relatively more change in ri, and relatively less change in ri, with respect to growth temperature and material, than in net photosynthesis. The most conservative parameter that was measured was the CO2 compensation point, Γ. Although it showed a strong dependence on measurement temperature, Γ was not significantly influenced by growth temperature or site location at the levels of probability used.
Regulation of K+ Influx in Barley Roots: Evidence for Direct Control by Internal K+
Authors: Glass ADM
Published: January 2006

Values for plasmalemma influx of K+ into excised barley roots, from solutions containing 0.05 mM KCl plus 0.5 mM CaSO4, were reduced by 50-60% following a 6-h pretreatment period in 50 mM KCl plus 0.05 mM CaSO4 solution. This reduction of influx, associated with increased internal K+ concentration, was independent of DNA, RNA and protein synthesis during the pretreatment period as indicated by its insensitivity to the presence of 5-fluorodeoxyuridine, actinomycin D, cycloheximide, p-fluorophenylalanine or anisomycin in the pretreatment solutions.
Roots of plantlets grown from gamma-irradiated barley seeds, which were incapable of under-going cell division and capable of only limited protein synthesis, were nevertheless able to reduce K+ influx values in response to increased internal K+ concentration.
The measurement of K+ influx from 0.05 mM KCl solutions following pretreatment periods as short as 15 min in 50 mM KCl gave no evidence of any lag period in the development of reduced influx associated with increased internal K+ status. The above experiments are discussed in terms of a model for the regulation of K+ influx which ascribes a direct 'allosteric' role to internal K+ in controlling influx.
Seedling Development in Peach, Prunus persica (L.) Batsch. II. Effects of Plant Growth Regulators and Their Possible Role
Authors: Zigas RP , Coombe BG
Published: January 2006

Treatment of peach embryos from partially stratified seeds with abscisic acid (ABA) inhibited germination and promoted the production of leaf lesions, responses which are typical of testa presence. A period of water stress during germination also promoted lesion production.
Neither testas nor ABA stimulated lesions on seedlings from 25°C-stratified seed, but mixtures of ABA and GA*3 were synergistic in promoting lesions; at the same time ABA and GA3 had opposite effects on germination and stem elongation, and mixtures had intermediate effects. Evidence was obtained for effects attributable to a balance between GA and ABA. Other inhibitors and promotors had no effect on lesions. The results from excision and substitution experiments permit an explanation of the effects of stratification in terms of three events: (a) a decrease in inhibitor activity in the testa; (b) an increase in gibberellin activity in the epicotyl; and (c) diffusion of inhibitor to the epicotyl via the radicle when the seed is returned to warm conditions.
Growth and Physiological Responses of Soybean Under Various Thermoperiods
Authors: Warrington IJ , Peet M , Patterson DT , Bunce J , Haslemore RM , Hellmers H
Published: January 2006

Diurnal changes in net photosynthesis, dark respiration, specific leaf weight, leaf water potential, stomatal conductance, starch and soluble sugar concentrations, and the activities of malate dehydro- genase and glycollate oxidase were measured in soybeans grown in 23/23,26/20 and 29/17°C thermo- periods, to determine their relationship to thermoperiodic effects on plant growth. Soybean height and main stem leaf number were significantly higher under the constant daylnight (23/23°C) temperature regime. Leaf, stem and root dry weights, and specific leaf weight were all highest where the day/night temperature differential was greatest (29/17°C). Differences in net photosynthesis, dark respiration, starch and soluble sugar concentration, and malate dehydrogenase activity were small between the thermoperiod treatments. However, glycollate oxidase activity was higher under the constant-temperature conditions. Starch concentration, specific leaf weight, and glycollate oxidase activity all increased throughout the photoperiod and subsequently decreased through the dark period. Net photosynthesis declined throughout the photoperiod and both dark respiration and malate dehydrogenase activity peaked at the beginning of the dark period. Each of these diurnal responses was similar under each thermoperiod. Leaf water potential and stomatal conductance did not differ between thermoperiods.
The Role of Photosynthesis in Flowering of the Long-Day Plant Sinapis alba
Authors: Bodson M , King RW , Evans LT , Bernier G
Published: January 2006

Flowering can be induced in the long-day plant Sinapis alba in 8-h photoperiods provided that the irradiance is close to that at which leaf photosynthesis is light-saturated (e.g. 96 J m-2 s-1). Three such 8-h cycles result in 10% flowering and six are required for full flowering, whereas only one long-day cycle of 16-20 h duration at a much lower irradiance (25 J m-2 s-1) is required for full flowering. High irradiance during the single long day promotes flowering when given for the first 8 h of a 16-h photoperiod, but is inhibitory over the last 8 h. Photosynthetic CO2 uptake is crucial for this response to high irradiance, as both its inhibitory and promotive effects on flowering are reversed by the removal of atmospheric CO2 during the period of high irradiance.
Compared with plants kept in short days (8-h photoperiod), export of 14C-labelled assimilates from the leaf during a 24-h period was only 50-60% greater in plants exposed to a long day (20-h photoperiod), because plants in short days compensated to a degree for their shorter photosynthetic period by mobilizing leaf reserves during darkness. However, flowering can occur with no evident enhancement of supply of assimilate to the shoot apex, for example following dis- placement of the short day or on removal of atmospheric CO2 during the last 12 h of exposure to a 20-h long day. Also, the flowering response to radiant flux density during the second half of a long day shows an optimum between 15 and 70 J m-2 s-1, with reduced flowering both above and below this irradiance. Thus, although there is no absolute requirement for long days to induce flowering in S. alba, light reactions cther than photosynthesis probably contribute to photoperiodic induction in this species.
Effects of Irradiance and Solar Radiation on Dry Matter Growth and Net CO2 Exchange of Trifolium subterraneum L. Swards at a Constant Temperature
Authors: Fukai S , Silsbury JH
Published: January 2006

Small swards of subterranean clover were grown at 20°C at different times of the year and at the same time under shades of different light transmission. Dry matter production and net CO2 exchange rates at different levels of irradiance were measured during growth. Crop growth rates and net CO2 exchange rates are examined in relation to plant attributes and to the daily solar radiation.
Dry matter growth curves varied according to the daily solar radiation. Increase in crop growth rate with increase in daily solar radiation was taken to be linear for swards with similar dry weight and was more rapid for closed canopies than for those not showing full light interception. Once a closed canopy was attained, further increase in total dry matter resulted in decreased crop growth rate due, apparently, to increased loss of dry weight through increased respiration rate.
The shape of the CO2 exchange/irradiance curve was linear up to 100 W m-2 (PAR) and curvilinear above that value. The rate of net CO2 exchange at 50 W m-2 (PAR) decreased with increase in shoot dry matter above 100 g m-2 due, apparently, to an increased rate of dark CO2 efflux: the rate was not affected by daily solar radiation during growth. The net CO2 exchange rate at 250 W m-2 (PAR) increased with increase in LAI up to 3 after which it became almost constant, varying only with the variation in daily solar radiation during growth. The rate of dark CO2 efflux was strongly affected by the amount of dry matter present and to a smaller extent by the crop growth rate or the daily solar radiation.
Growth and Phosphate Absorption in Lettuce and Cabbage Plants in Dilute Solution Culture
Authors: Temple-Smith MG , Menary RC
Published: January 2006

Growth and phosphate absorption of lettuce and cabbage plants were compared at seven solution phosphate concentrations in the range 0.06-8.0 �M. Phosphate levels were maintained constant throughout the 35-day growth period by the use of large volume (450 litres per 24 plants) continuous- flow solution culture units.
Both lettuce and cabbage achieved maximum relative growth rates of approximately 14 g dry matter per 100 g dry matter per day. For cabbage this rate of growth was achieved at a solution phosphate concentration of 0.5 �M. However, to attain the same rate of growth, lettuce required a solution phosphate level at least fourfold greater (between 2.0 and 4.0 �M) . These phosphate concentrations are many times lower than those previously reported for maximum yield of these species.
The ability of cabbage to achieve maximum dry matter yield at lower solution phosphate concentrations than that required by lettuce appears to be due to a combination of its greater rate of phosphate absorption per unit of root at low phosphate concentrations, its higher proportion of total plant phosphorus and dry matter contained in the shoot, and its higher phosphate utilization quotient at maximum yield.