bluuebunny/crossref_metadata_2025 huggingface dataset:
Photosystem II in Symbiotic Algae
Authors: Smillie RM
Published: January 2006

Symbiotic brown algae (zooxanthellae), Gymnodinium microadriaticum (= Symbiodinium microadriaticum), were isolated from the coral polyp Pocillopora damicornis and from the mantle of the clam Hippopus hippopus collected from coral reefs near Lizard Island on the Great Barrier Reef. Passage of the coral and clam zooxanthellae through a Yeda Press at 2000 and 21 000 p.s.i., respectively, yielded preparations of chloroplast lamellae with the ratio of chlorophyll α to chlorophyll c ranging from 0.95 to 1.2. The chloroplast preparations photoreduced 2,6-dichlorophenolindophenol (DCPIP) at rates of 1.66 (coral zooxanthellae chloroplasts) and 1.96 (clam zooxanthellae chloroplasts) micromoles DCPIP reduced per minute per milligram total chlorophyll in white light. Rates were 30-50% lower in red light. The photoreduction was inhibited more than 99% by 2.5 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Comparisons made with maize chloroplasts indicated that the clam zooxanthellae chloroplasts required only slightly higher light intensities for maximum rates of photoreduction of DCPIP than the grana-containing maize mesophyll chloroplasts. The coral zooxanthellae chloroplasts required a still higher light intensity for near saturation of the photoreduction of DCPIP, but not as high as that required by maize bundle sheath chloroplasts.
Chloroplasts prepared from green algae isolated from the tissues of a tunicate of unknown species also photoreduced DCPIP but at low rates. Light saturation for the reaction was attained at around the same intensity as for the clam zooxanthellae chloroplasts.
Based on the photosynthetic rate of zooxanthellae isolated from the clam Tridacna maxima and the number of cells contained in the mantle, it was concluded that the photosynthetic potential of the mantle of T. maxima, on either a chlorophyll or area basis, was about the same as that of a leaf of a C3 plant.
Light-Induced pH Gradients in Isolated Spinach Chloroplasts
Authors: Chow WS , Hope AB
Published: January 2006

The fluorescence quenching of certain fluorescent, weakly ionizing amines has been used to estimate the pH difference (ΔpH) between the intrathylakoid spaces of chloroplasts and the external medium under various conditions. The amines N-(1-naphthyl)ethylenediamine and 9-aminoacridine gave consistent and similar estimates of ΔpH provided the concentration ranges 0.25 - 2 μM and 0.05 - 0.5 μM, respectively, were not exceeded. Values for ΔpH of up to 4 units were estimated for control chloroplasts. Only a small decrease in ΔpH was caused by FCCP and DCMU concentrations that decreased photophosphorylation rates to 10-20% of control.
The kinetics of the onset and decay of ΔpH, and of the uptake and release of protons by the chloroplasts, were followed after the sudden application or withdrawal of actinic light. These kinetics suggest a model for the ionic relations of stripped chloroplasts with internal buffering capacity, [α], and dissociation constant, Ka, as parameters. At pH8, [α] is about 80 mol m-3 and Ka is 0.07 mol m-3 (pKa = 4.15). The model is successful in predicting the relation between [H+]I (the internal proton concentration) and ΔH+o (the light-driven uptake of protons from the external medium), as well as the size of ΔH+o , but needs extending to deal with published experiments on the light-driven translocation of chloride ions.
High-Resolution Measurements of Transient Changes in the Growth Rate of Intact Lupin Seedlings
Authors: Marshall DC , Penny D
Published: January 2006

Measurements of the growth rate of intact lupin seedlings were made under steady-state conditions and as the environment was altered. Although the growth rate frequently changed smoothly with the new condition, there were several cases where periodicity or oscillations in the growth rate were observed. These cases included growth oscillations induced by: the solution in which the roots were immersed being changed back from a mannitol solution to water; the replacement of anaerobic conditions by air or oxygen; the tension being increased on the hypocotyl; and, under some condi- tions, the addition or removal of high CO2 concentrations. The observed periodicity is more complex than is accounted for by a simple relationship of the minimum yield stress increasing or decreasing with the growth rate, but more information is needed to develop a better model.
Photosynthesis and Transpiration in Dicotyledonous Plants. I. Expanding Leaves of Tobacco and Sunflower.
Authors: Rawson HM , Woodward RG
Published: January 2006

The aims of this paper were (1) to determine if irradiance and nutrition influence the timing of peak photosynthesis (Fmax) in expanding tobacco Ieaves and (2) to assess the relative importance of stomatal (rs) and mesophyll (rm) resistances to CO2 uptake as leaves expand.
Growth conditions affected rates of leaf expansion and final leaf areas (Amax) but not the time from leaf emergence to Amax (25 days). Patterns of photosynthesis with time were similar in all treatments-F rose rapidly to Fmax and then declined, and Fmax occurred on day 13 when the areas of leaves in different treatments were from 65-80 % Amax. We suggest that temperature may determine the timing of Fmax.
Changes in both rs and rm were associated with changes in F prior to Fmax. Although changes in rm were up to five times greater than in rs during this period, the relative reduction in the two resistances was similar. Absolute changes in rs and rm were similar immediately after Fmax, and during this period of 7 days F declined by almost 50%. Thereafter, relative changes were closely matched. Possible mechanisms for the control of the resistances by the plant are discussed. We discuss the hypothesis that Fmax was maintained for only a limited period in expanding tobacco leaves because of the lack of a sink for assimilate. Expanding sunflower leaves maintained Fmax for a much longer period and reasons are presented for this different behaviour.
Water use efficiency (ω) of tobacco leaves changed as they expanded and was greatest under good nutrition and poorest under low irradiance. Maximum ω for tobacco and sunflower was similar.
Physiological Investigations on Restrictions to Transport of Sucrose in Ears of Wheat
Authors: Jenner CF
Published: January 2006

Accumulation of sucrose in glumes and pales of detached ears of wheat cultured on solutions of sucrose is directly dependent on external concentration; compared with the external level, sugar builds up to higher levels inside these organs, and the uptake of sugar is not reduced much by metabolic inhibitors. In contrast, influx of sucrose into the grains is saturated at relatively low (external) levels of sucrose; the concentration within the grains is lower than in the supplying solution, and movement into the grains is very sensitive to the action of metabolic inhibitors.
Sucrose enters the cultured ear in the transpiration stream and its build-up in the structures enclosing the grain is due to the evaporation of water. Transport to the grain, on the other hand, is dependent upon translocation in the phloem. It is suggested that the passage of sucrose to the grain is restricted by processes involved in transfer from xylem to phloem, or by translocation within the sieve tubes, or both. It is postulated that similar limitations operate on the transport of sucrose derived from normal assimilation.
The detached-ear technique may be of value as a method of estimating the scale of limitations to grain growth conferred by the supply of assimilates to the grain.
Symbiotic Nitrogen Fixation by Coralloid Roots of the Cycad Macrozamia riedlei: Physiological Characteristics and Ecological Significance
Authors: Halliday J , Pate JS
Published: January 2006

'Coralloid' roots containing blue-green algae occur commonly on the upper root stocks of M. riedlei in natural habitat in Western Australia. Each coralloid mass persists for several seasons; replacement sets form at irregular intervals, especially after fire.
15N2 and acetylene reduction assays demonstrate that coralloid roots fix nitrogen at physiologically significant rates.
C2H2 reduction rates by coralloid roots are higher in winter than in summer. Performance is positively correlated with rainfall; soil temperature appears to be of lesser importance. Diurnal fluctuations in nitrogenase activity occur.
Calibration using 15N2 gives a molar ratio of C2H2 reduced : N2 fixed of 5.8 : 1. The seasonal average of C2H2 reduction of 14.8 nmol per g fresh wt coralloid root per min is then equivalent to 37.6 g N per kg fresh wt per year, a fixation rate potentially capable of doubling coralloid root nitrogen once in every 8 weeks, and whole plant nitrogen every 8-11 years.
Returns of fixed nitrogen in two natural populations of Macrozamia are estimated by compounding measurements of biomass of host and symbiotic organs with the seasonal average for coralloid fixation rate. The values obtained (18.8 and 18.6 kg N ha-1 year-1) indicate that Macrozamia contributes significantly to the nitrogen economy of its ecosystem.
Assimilate Movement in Lolium and Sorghum Leaves. I. Irradiance Effects on Photosynthesis, Export and the Distribution of Assimilates
Authors: Wardlaw IF
Published: January 2006

At low light levels (20 W m-2 PAR), little difference was detectable in net photosynthetic rates between leaves of the C3 grass Lolium temulentum and the C4 grass Sorghum sudanense. At low light, both species also had similar rates of export of photosynthate per unit leaf area, although the rate of export of 14C, following the assimilation of 14CO2 by the uppermost fully expanded leaf, was much greater in Sorghum. As light levels were increased to 96 W m-2 PAR or greater, net photosynthesis rose more in Sorghum than in Lolium and a greater proportion of the assimilate was exported from the Sorghum leaf, while Lolium with the thicker leaf showed a much greater capacity for storage of photosynthate. High and low light pretreatments, which altered the amount of both soluble and insoluble dry matter in the leaf, had little effect on the percentage rate of export of 14C following the uptake of 14CO2, which suggests that the bulk of the stored material may be effectively separated from the pathway of transfer from the chloroplast to the vascular system within the leaf. The pattern of distribution of 14C-labelled assimilates to other parts of the plant was only slightly affected by reduced light during the 4-h translocation period' however, a 3-day pretreatment at low light significantly reduced the proportion of the assimilates moving to the roots.
Gas Exchange of Mitchell Grass (Astrebla lappacea (Lindl.) Domin) in Relation to Irradiance, Carbon Dioxide Supply, Leaf Temperature and Temperature History
Authors: Doley D , Yates DJ
Published: January 2006

Relationships were established between photosynthesis in A. lappacea and photosynthetic quantum flux, ambient CO2 concentration and leaf temperature. There were no substantial differences between plants raised in a glasshouse and under three temperature regimes in growth cabinets in their responses to light level and CO2 concentration. Large variations in the rate of photosynthesis were observed in plants raised under any environmental regime, this being due in part to the effects of leaf age. It was concluded that the greatest rate of photosynthesis observed in a series of experiments represented the best approximation to the rate attainable in the absence of limitations imposed by factors extraneous to the experiment concerned. The temperature responses of net photosynthesis, dark respiration and transpiration were influenced by growth regime temperature; the leaf temperature at which photosynthesis was maximal increased with growth regime air temperature up to at least 33°C. Plants transferred from one temperature regime to another exhibited the behaviour characteristic of the new regime within one day and two nights of the transfer. Estimates of gas diffusive resistances indicated that both the stornatal and CO2 mesophyll (residual) resistances adapted to changed temperature conditions after about one thermoperiod. The temperatures at which these diffusive resistances were minimal varied in the same sense as the changes in growth regime temperature. The roles of these aspects of behaviour in the adaptation of A. lappacea to its environment are discussed.
Responses of Subterranean Clover Communities to Temperature. I. Dry Matter Production and Plant Morphogenesis
Authors: Fukai S , Silsbury JH
Published: January 2006

Subterranean clover communities were grown in temperature-controlled naturally lit glasshouses at 15, 20, 25 and 30�C. Dry matter yield, leaf area and the distribution of dry matter between plant parts were determined at about 14-day intervals for up to 130 days from planting. Leaf appearance, leaf death, leaf number and growth of laterals were observed for individual plants in the community over a similar time period. A logistic growth curve was found for each temperature and crop growth rate calculated from the equation fitted for each growth curve. The optimum temperature for growth was relatively high (20-25°C) when plants were young, but decreased during growth so that after 100 days total dry matter was inversely related to temperature over the range 15-30°C. Both the rate of leaf appearance and the rate of leaf death on the main stem were constant at each temperature during the experimental period and were directly related to temperature. The number of leaves per unit ground area was determined mainly by the rates of leaf appearance and leaf death on the main stem, since the contribution of laterals was small. The proportion of stem and petiole to total dry matter increased, and that of green leaf lamina decreased, with increase in total dry matter. Neither was markedly affected by temperature. An inverse relationship between specific leaf area and temperature resulted in a lower ratio of leaf area to total dry matter at 15°C compared with that at 20, 25 or 30°C.
On the Translocation of Sugar: Van Der Waals' Forces and Surface Flow
Authors: Richmond P , Wardlaw IF
Published: January 2006

Theoretical analysis of sucrose adsorption to structural protein surfaces in terms of the Lifshitz continuum theory of van der Waals' forces suggests that this may provide a mechanism for rapid sucrose equilibration within the sieve tube system. It is also suggested that mobility of hydrated sucrose at an interface would reduce the resistance to bulk flow of solution through the sieve tubes.
Effect of Nucleosides on Respiration of Sliced Carrot Root Tissue
Authors: Adams PB , Rowan KS
Published: January 2006

Optimal concentrations of nucleosides rapidly stimulate the rate of oxygen uptake of carrot slices by up to 50% and promote large increases in concentration of ADP. The effect supports the conclusion that respiration of freshly cut slices and the development of induced respiration are controlled primarily by the concentration of ADP rather than by the concentration of orthophosphate.
Physiology of Grain Yield in Wheat Growing on Stored Water
Authors: Passioura JB
Published: January 2006

The grain yield of wheat plants grown in the glasshouse on a fixed and limiting supply of water can be substantially increased by forcing the plants to use water slowly when young so that they have more water available while filling their grains. Water use was manipulated either (1) by providing the entire water supply at sowing and allowing the plant to develop only one root (instead of the usual 5-20) or (2) by metering the water to the plants at varying rates. With a water supply of 1800 � 50 g per plant (equivalent to 180mm transpiration from a canopy containing 100 plants m-2), the grain yield ranged from zero, for plants uncontrolled in water use, to 3.5 g per plant for plants left with at least 400 g water to use after anthesis. Plants which used less than 200 g water after anthesis had yields approximately proportional to the amount of water used, giving about 1 g grain per 80 g water (compared with 1 g dry matter per 200 g water for the whole plant). The high efficiency of water use for grain growth was apparent rather than real. It arose because the grain of severely stressed plants was filled largely (up to two-thirds) from reserves, rather than largely from current photosynthate.
Development of Freezing Tolerance in Leaves of C4 Grasses
Authors: Rowley JA
Published: January 2006

The rate of development of freezing tolerance in the leaves of 11 C4-photosynthetic pathway grasses growing outdoors at Palmerston North (40° 23′S., 175 37′E.) in field plots was measured during autumn and winter. The leaves of two species only, Paspalum dilatatum and Eragrostis curvula, increased markedly in freezing tolerance and survived frosts in mid-winter.
To simulate autumn and winter conditions, temperature and daylength were decreased gradually in a controlled-environment growth cabinet. Leaves of P. dilatatum grown in this cabinet showed similar changes in freezing tolerance to leaves grown outdoors in autumn and winter. The temperature at which leaves were severely damaged decreased from - 3.4°C to - 8.9°C. Expanding leaves responded to the current hardening temperature, but little increase in freezing tolerance occurred in leaves exposed to the hardening temperature once their growth was completed.
Quantitative Assessment of Symplastic Transport of Pre-Nectar Into the Trichomes of Abutilon Nectaries
Authors: Gunning BES , Hughes JE
Published: January 2006

The anatomy and ultrastructure of the stalk cell region of Abutilon megapotamicum var. variegatum floral nectary trichomes has been investigated and the observations related to estimates of the rate of secretion of nectar. Evidence was obtained that an apoplastic barrier exists in the anticlinal walls of the stalk cell, and is taken to indicate that a flow of pre-nectar, equivalent in volume to the nectar that is secreted from the apex of the trichome, passes through the stalk cell protoplast. In terms of volume of water, the plasma membrane of the stalk cell might have a large enough hydraulic conductivity to cope but, in terms of sugar transport, the required flux is 3-4 orders of magnitude greater than literature values for plant cell membranes. By contrast, the plasmodesmata in the distal periclinical wall of the stalk cell provide a low resistance pathway for a bulk flow of sugar solution. The desmotubules of the plasmodesmata are clearly connected to the endoplasmic reticulum of the adjacent cells. The cytoplasmic annulus between the desmotubule and the inner face of the plasma membrane is (in the majority of cases) parallel sided and non-constricted. The hydraulic conductivity of the cytoplasmic annulus route through the plasmodesmata is 1.4 × 10-5 m3 m-2 (of distal wall) s-1 bar-1; that of the hypothetical desmotubular route is about 2.3 × 10-6 in the same units. These conductivities are 4.5 and 45 times greater than corresponding values for root endodermal plasmodesmata reported in the literature. The results are discussed in relation to the physiology of nectar production in Abutilon.
Malate Accumulation in Leaf Slices of Mesembryanthemum crystallinum in Relation to Osmotic Gradients Between the Cells and the Medium
Authors: Winter K , Luttge U
Published: January 2006

Leaf slices of two sets of M. crystallinum plants were used in the present study. The first set were plants grown in 400 mM NaCl and showing diurnal oscillations of malate levels typical of crassulacean acid metabolism (CAM). The second set were plants grown in non-saline media and exhibiting no CAM-like diurnal malate fluctuations. Both sets of leaf slices accumulated malate during a 12-h light or dark period, depending on the osmotic pressure of the incubation medium. Highest malate accumulations were obtained when media were isotonic or slightly hypertonic. These osmotic characteristics are similar to those of leaf slices of the CAM plant Kalanchoe daigremontiana as reported elsewhere. However, discrepancies are observed in light and temperature dependence. Unlike in K. daigremontiana leaf slices and in intact leaves with CAM (i.e. also in intact leaves of M. crystallinum grown on highly saline media), in both sets of M. crystallinum leaf slices used here light stimulated malate accumulation. Compared to 15°C, 25°C had either no effect on malate accumulation or stimulated malate accumulation. After leaf slices had accumulated malate in the dark in isotonic or slightly hypertonic media, malate accumulation continued in the light when the osmolarity of the medium remained unchanged. When the osmotic pressure of the medium was lowered considerably, however, malate accumulation in the light was much reduced or else there was a loss of malate from the tissue. Mechanisms different from CAM may be partially involved in the changes of malate levels in these experiments. The significance of the experimental results for the interpretation of the balance between net carbon gain via C3 pathway and CAM in M. crystallinum is discussed.
Relation Between Acid Proteinase Activity and Redistribution of Nitrogen During Grain Development in Wheat
Authors: Dalling MJ , Boland G , Wilson JH
Published: January 2006

Accumulation of grain nitrogen was studied in the wheat cultivars Argentine IX and Insignia. The pattern of nitrogen removal from several tissues of each cultivar was compared with the pattern of acid proteinase activity. There was a highly significant relation between the rate of nitrogen loss from the tissues and the rate estimated from the enzyme activity measurements. This suggests an important role for acid proteinase enzymes in leaf senescence. Redistribution of nitrogen present in the plant at anthesis accounted for 78.5 and 80.6 % of the final grain nitrogen yield of Argentine IX and Insignia respectively.
Cruciferous Oilseed Proteins: the Protein Bodies of Sinapis alba Seed
Authors: Kirk JTO , Pyliotis NA
Published: January 2006

The solubility properties of the proteins of oil-free meal of white mustard seed (S. alba) in various aqueous extraction media are described. Electrophoresis on cellulose acetate of a salt extract of the seed meal at pH 7.0 shows the presence of two positively charged protein bands: a slow moving intense band (I) and a less intense band with higher mobility (II). On the basis of Sephadex G100 chromatography and sedimentation behaviour, these bands are deemed to be identical with the two major protein classes (12 S and 1.7 S, respectively) present in this and other Brassica-related species, as described by other workers.
Centrifugation after filtration of a seed meal homogenate yields a preparation that is completely soluble in salt solution, and can be shown by electron microscopy to consist entirely of protein body fragments. Only the 12 S protein can be detected in significant quantity in this preparation: this protein at least we may assume to be present in the aleurone (protein) grains observed in micrographs of the cotyledon cells.
In germinating seeds, disappearance of protein bodies is accompanied by a diminution in total salt-soluble protein and in the amounts of the 12 S and 1.7 S proteins, supporting their identification as storage proteins. The rate of utilization is the same in the light and in the dark. Proteolytic activity was detected in the ungerminated seed. The level of activity was more than sufficient to account for the subsequent observed rate of protein utilization. Proteolytic activity per seed increased by only 40-70% during 4 days germination.
Conversion of Pyruvate Under Natural and Artificial Anaerobiosis in Maize
Authors: Leblova S , Zima J , Perglerova E
Published: January 2006

Lactate is formed during the initial hours of seed swelling during natural anaerobiosis in maize. Ethanol is formed later, at a concentration greater by one order. With 7-day-old seedlings, first lactate and then ethanol are also formed after transfer of the plants to an atmosphere of nitrogen. Lactate and alcohol dehydrogenases are active in the germinating seed.
The molecular weight of maize alcohol dehydrogenase (EC 1.1.1.1) is 62 000 � 5000. Inhibition by chelating agents and 'sulphydryl poisons' indicates the probable presence of metal and -SH groups. The enzyme oxidizes ethanol at an optimum pH of 8.7 with a Km of 1.8 x 10-2 M and reduces acetaldehyde at an optimum pH of 6.7 with a Km of 1.0 x 10-3M. It is inhibited by succinate, malate, lactate and acetate, non-competitively with respect to the substrate. Acetoxime is a competitive inhibitor and butyrylamide, acetamide and cyclohexanone oxime are non-competitive inhibitors.
Interaction of Gibberellin With Photoinduction in the Initiation of the Dormant Phase in Vernalized Hordeum bulbosum L
Authors: Ofir M
Published: January 2006

Vernalized plants of H. bulbosum growing in short (8-h) photoperiods may be induced to form bulbs after exposure to a number of long (16-h) photoperiods. This response was enhanced significantly by application of gibberellic acid (GA3) just before, concurrently with, or at the end of the photoinductive treatment. Exogenous GA3 induced bulb formation even with subthreshold photoinductive treatment but failed to do so without it (i.e. in short days throughout). Thus, induction of bulb initiation under long days may involve both a gibberellin-like factor and one that is unlike gibberellin. Plants treated with GA3 before, or concurrently with, photoinductive treatments produced the bulb at a lower internode than those treated later or not at all. Gibberellin may affect bulb initiation by sensitizing a receptive internode. The non-gibberellin-like factor also produced under long days is required for expression of bulb formation.
Composition and Ultrastructure of Leaf Cuticles From Fruit Trees, Relative to Differential Foliar Absorption
Authors: Leece DR
Published: January 2006

Differential foliar absorption of chemicals by peach, apple and orange was related to cuticle thickness, weight, surface wax and embedded wax content and to surface wax wettability, ultrastructure and composition. Surface wax concentration, especially on abaxial leaf surfaces, correlated well with resistance to foliar absorption. The abaxial surface wax on peach leaves was built up in layers around and over the guard cells (which are preferred paths of spray entry into leaves) whereas apple and orange guard cells were relatively wax-free. Peach surface waxes were more difficult to wet than orange waxes and, although more polar than orange waxes, may be more resistant to water penetration as they were rich in hydrocarbons and triterpenoids.
Enhancement of foliar absorption may require improved partitioning of sprays through the surface waxes or the bypassing of the waxes via stomatal penetration.
Changes in Abscisic Acid Levels During Imbibition and Germination of Non-Dormant and Thermodormant Lettuce Seeds
Authors: Mcwha JA
Published: January 2006

Non-dormant lettuce seeds (Lactuca sativa L. cv. Great Lakes) have an optimum temperature for germination of about 25°C. When the seeds were imbibed for 20 h at this temperature their content of abscisic acid fell from 98.0 ng per g fresh weight to less than 6 ng per g original fresh weight. When seeds were imbibed at 10 and 32°C, they exhibited dormancy. An inverse relationship was found between the abscisic acid content of the seeds and their percentage germination.
Synthesis of Sorbitol in Apricot Leaves
Authors: Bieleski RL , Redgwell RJ
Published: January 2006

When 14CO2 was supplied as a 30-s pulse to photosynthesizing apricot leaves, the pattern of the various phosphate esters, organic acids and amino acids was consistent with the operation of the normal C3 photosynthetic pathway. Fructose 6-phosphate became labelled much more rapidly than glucose 6-phosphate and fructose was more rapidly labelled than glucose. Sorbitol was the major end-product of photosynthesis, becoming the predominant 14C-containing compound within 10 min of starting the 14CO2 pulse, and containing more than half the total radioactivity after 30 min. Sorbitol may be synthesized by way of fructose or fructose 6-phosphate rather than glucose or glucose 6-phosphate. Sorbitol phosphate was shown to be present in the tissue as 2% of the total hexose monophosphate, and to become labelled as rapidly as the hexose monophosphates. The pathway of sorbitol synthesis may therefore follow the sequence: fructose 6-phosphate → sorbitol phosphate → sorbitol.
Properties of Phosphoenolpyruvate Carboxykinase Operative in C4 Pathway Photosynthesis
Authors: Hatch MD , Mau S
Published: January 2006

A procedure is described for partially purifying phosphoenolpyruvate carboxykinase [ATP : oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.49] from leaves of Chloris gayana Kunth. In three steps the enzyme was purified about 60-fold with 22% recovery of activity. This procedure removes enzymes, particularly malate dehydrogenase, that preclude the use of a simple spectrophotometric assay for phosphoenolpyruvate carboxykinase. The activity of the enzyme in the direction of oxaloacetate decarboxylation was about 10 times that in the reverse direction. At the optimal pH of 8.0, ATP was the preferred nucleoside triphosphate but CTP, UTP, GTP and ITP were also active. A requirement for Mn2+ could not be replaced by Mg2+. The Michaelis constants for oxaloacetate and ATP were 0.035 mM and 0.024 nM, respectively. The photosynthetic intermediates fructose 1,6-bisphosphate, 3-phosphoglyceric acid and dihydroxyacetone phosphate significantly inhibited the enzyme at concentrations in the region of 1-5 mM. Unlike the phosphoenolpyruvate carboxykinase from other sources, the capacity of the leaf enzyme to catalyse the decarboxylation of oxaloacetate to pyruvate was negligible. The properties of the enzyme are discussed in relation to its proposed role in C4 pathway photosynthesis.
Plant Growth Regulating Activity of 3-Indolylthioalkanoic Acids
Authors: Harris RLN , Geissler AE
Published: January 2006

The plant growth-regulating activity of 3-indolylthioacetic acid and �-(3-indolylthio)propionic acid has been assessed using etiolated pea stem segment and curvature tests with indolylacetic, indolylpropionic and indolylbutyric acids as standards for comparison.
The sulphur-containing compounds are significantly less active in these tests than analogues containing methylene in place of sulphur and attempts to rationalize these differences in terms of physicochemical properties of the compounds are described. The effect of the 3-substituent in indoles on the size of the fractional positive charge on the ring nitrogen has been measured by n.m.r. spectroscopy.
Effect of the Plastoquinone Antagonist Dibromothymoquinone on Electron Transport Reactions in Chloroplast Preparations
Authors: Stewart A , Larkum AWD
Published: January 2006

The effects of dibromothymoquinone (DBMIB) on electron transport in types A, B, C and D spinach and pea chloroplast preparations have been studied. DBMIB (1 x 10-6M) strongly inhibited electron transport to methyl viologen in all the types of chloroplasts, while electron transport to ferricyanide was inhibited by 60%. Envelope-free (type C) chloroplast preparations with poor photosynthetic control were inhibited more strongly than intact (types A and B) chloroplast preparations at low (< 5 x 10-7M) concentrations of DBMIB. Type C preparations with good photosynthetic control were less strongly inhibited except in the presence of uncoupler or in the absence of ADP. Above 1 x 10-6M DBMIB, inhibition of electron transport to ferricyanide became progressively less and, with type A chloroplast preparations, a large stimulation compared to the control level occurred. Phenylenediamine stimulated high rates of electron transport to ferricyanide in the presence of low concentrations of DBMIB. At higher DBMIB concentrations, the stimulation was completely reversed and envelope-free chloroplasts again showed greater sensitivity to DBMIB compared to intact chloroplasts.
DBMIB appears to have a number of sites of interaction with the thylakoid membrane.
Chloroplast Polyribosomes and Synthesis of Fraction 1 Protein in the Developing Wheat Leaf
Authors: Brady CJ , Scott NS
Published: January 2006

In a study of the development of the second leaf of seedling wheat, the contents per lamina of fraction 1 protein and total soluble protein increased for 6 days after leaf emergence, and the contents of cytoplasmic and chloroplast rRNA for 5 days. Net synthesis of fraction 1 protein per unit of cyto-plasmic and chloroplast rRNA decreased with time. During the growth phase, incorporation of radioactive amino acids into fraction 1 protein was proportional to the amount of, rather than the rate of increase of, fraction 1 protein. After the maximum content of fraction 1 protein had been reached, incorporation into fraction 1 protein decreased both with time and relatively to other soluble proteins. The content of RNA and the proportion of rRNA found in cytoplasmic and chloroplast polyribosomes also fell. The rate of decrease in incorporation into fraction 1 protein exceeded the rate of decrease in chloroplast polyribosomes. We conclude that chloroplast polyribosomes are active in the turnover of fraction 1 protein large subunit during the growth phase, but are proportionately more active in making other proteins in older leaves.
The Role of the Peripheral Cell Layers in the Geotropic Curvature of Sunflower Hypocotyls: a New Model of Shoot Geotropism
Authors: Firn R , Digby J
Published: January 2006

The rate of elongation of sunflower (Helianthus annuus L.) hypocotyl sections was found to be dependent on the rate of growth of the outermost cell layers (peripheral cell layers) of that tissue. Hypocotyl sections from which those layers had teen peeled grew but did not show typical geotropic curvature. A model of geotropic curvature is proposed where the differential growth causing curvature is due to a differential rate of elongation between the upper and lower peripheral cell layers of a horizontal shoot. In the model it is speculated that the peripheral cell layers are the site of both geoperception and georesponse. The model does not involve a lateral movement of a growth regulator and experiments with longitudinally bisected hypocotyl sections provided evidence consistent with this model but inconsistent with the Cholodny-Went theory of geotropism.
Seedling Development in Peach, Prunus persica (L.) Batsch. I. Effects of Testas and Temperature
Authors: Zigas RP , Coombe BG
Published: January 2006

Testas inhibited the germination and stem elongation of peach seeds, and the inhibition was removed by 10 weeks of stratification (i.e. exposure to cold temperatures while imbibed). Intermediate lengths of stratification (4-8 weeks) promoted the production of morphological lesions on leaves. The lack of lesion promotion after 10 weeks of stratification was due to a loss of potency by the testas, not to an inability of embryos to respond. Stratification at 25°C had no effect on the properties of the testa. The large effects of the testa on the embryo following stratification at 3°C occurred only after the seed had been shifted from 3°C to 25°C conditions, and especially during the first 3 days after the shift. The lesion-stimulating properties of the testa were reduced by leaching. The active principle was distributed throughout the testas but was transferred to the embryo by diffusion at the radicle.
Sensitivity to Desiccation of Leaf Extension in Prairie Grass
Authors: Chu ACP , Mcpherson HG
Published: January 2006

The short-term response of leaf extension rates and leaf water potential (Ψ1) to controlled diurnal changes in the environment of a pasture species, prairie grass (Bromus catharticus) was followed over a soil drying cycle. Consistent relationships between rates of leaf extension and leaf water status were found only when measurements had been made under a common environment or when the effects of the environmental differences were allowed for by comparing the response of desiccated plants to that of well watered control plants under the same conditions. In the early stages of desiccation, leaf extension rates were extremely sensitive to reduction in Ψ1. Water potentials of only 2-3 bars below that of well watered control plants were sufficient to depress leaf extension rates by 50%. However, as desiccation became more severe, leaf extension rates became much less responsive to further reductions in Ψ1. We infer that it will be possible to resolve some of the apparent discrepancies among various reports on the sensitivity of leaf extension rates to desiccation when allowance can be made for the actions of other important influences, such as temperature in this experiment, and when Ψ1 at the site of measurement can be related unequivocally to Ψ1 at the region of elongation.
Aspects of Adaptation by Wheat and Barley to Soil Moisture Deficits
Authors: Rawson HM , Bagga AK , Bremner PM
Published: January 2006

Experiments were designed to examine whether drought imposed on plants between sowing and flowering endows them with adaptations which enable them to cope more effectively with drought occurring during grain growth. Specifically, the character sought was adaptation persistence.
In two experiments, one in a growth chamber, the other in a glasshouse, plants of two-rowed and six-rowed barleys, and of durum and aestivum wheats, were grown in canopies in 1-metre-deep pots filled with soil, so that the development of water stress might approximate that in the field. Various drying cycles were imposed during the vegetative phase, after which plants were rewatered and allowed to fill their grain during a further drying cycle.
During the initial drying cycles there were morphological changes, including changes in area per leaf, leaf area per plant, specific leaf weight and in the numbers of plant organs; the plants to which water was applied sparingly had better water-use efficiency than those with a plentiful supply. On rewatering, however, the previously droughted plants became prodigal in their water use and in the final drying cycle there was little evidence that the earlier responses improved the efficiency of water use either per unit dry matter gain or per unit grain produced. Thus any adaptations were not persistent. Indeed, in general, plants which were heavier at anthesis (i.e. those which had lost more water by this stage), used water most efficiently in grain production. This result is discussed in relation to current photosynthesis and the remobilization of reserves during grain-filling. 14C data indicated that barley plants exposed to drought during grain growth did not retranslocate more stored materials than those which were frequently watered during this stage.
Development of Photochemical Activity in Chloroplast Membranes. I. Studies With Mutants of Barley Grown Under a Single Environment
Authors: Smillie RM , Nielsen NC , Kenningsen KW , Wettstein DV
Published: January 2006

The development of photochemical competence in chloroplast thylakoid membranes was studied using a series of nuclear gene mutants of barley. The chloroplasts of each mutant reached a different developmental stage when grown under a single set of environmental conditions. Photochemical capacity as well as morphological and compositional features were compared for chloroplasts in the primary leaves of eight mutants and wild-type barley (Hordeum vulgare cv. Sval�fs Bonus) after growth of the plants for 7 days at 21°C and 1700 lux.
The results obtained indicated a sequence for the progressive acquisition of photochemical capability by the chloroplast membranes. The least developed of the mutant chloroplasts photoreduced ferricyanide but not 2,6-dichloroindophenol (DCIP). Immature chloroplast membrane systems from other slightly more developed mutants showed a low activity for DCIP photoreduction which was stimulated by diphenylcarbazide. In these mutants, however, the rate of photoreduction of ferricyanide was not stimulated by the uncoupler methylamine, proton pump activity was not detected and photosystem I activity was low. In the more developed of the mutant thylakoid systems, photoreductive activity was stimulated by methylamine and a proton gradient was generated in the light. The more developed the system, the greater was the stimulation obtained with methylamine. Other changes which were correlated with lamellar membrane development included a decrease in the light intensity required to saturate ferricyanide and DCIP photoreductive activities and an increase in the degree of inhibition of the photoreduction of ferricyanide by the photosystem II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). The activity changes were not correlated with either the amount of grana present or the ratio of chlorophyll a to b. Mutants showing low rates of DCMU-sensitive photoreduction of ferricyanide and DCIP were aberrant in protein composition of the chloroplast membranes.
Relationship Between the Capacity to Ripen and Ontogeny in Tomato Fruits
Authors: Mcglasson WB , Adato I
Published: January 2006

Tomato fruits were harvested at 10, 15, 20, 25 and 35 days after anthesis and held in humidified ethylene-free air streams at 20°C. The time from anthesis to ripening (first appearance of red colour) was about 42 days in attached control populations but the time to first colour in detached fruits ranged from 43 days in 35-day fruits to 68 days in 10-day fruits. The delayed ripening in fruits detached at 10 days was largely explained by the further slow development of these fruits. One to four locules began to swell about 10 days after harvest and swelling continued slowly for up to 42 days after harvest. The swollen locules usually turned red 8-10 days after swelling ceased. The undeveloped portion faded to a yellow-green colour and eventually became necrotic. The swollen locules usually contained more germinable seeds than the remainder of the fruit tissue. Although some localized swelling was seen in detached 15-day fruits, the entire fruits ripened normally.
Fruits of the same populations were treated with 2 g/l ethephon [(2-chloroethyl)phosphonic acid], both on the plant and following detachment. Ripening began earlier in detached fruits treated at all ages but the largest responses were found in fruits detached at 10,15 and 35 days. Ethephon advanced ripening in attached fruits only in those treated at 25 and 35 days after anthesis. Treatment with ethephon did not alter the appearance of detached 10-day fruits or the distribution of germinable seeds.
A similar pattern of development was seen in detached fruits of the mutants rin and nor. The swollen locules of 10-day rin and nor fruits developed the characteristic colour and appearance of mature mutant fruits (yellow in rin, yellow-orange in nor) while the undeveloped parts of the fruits faded to a yellow-green colour and eventually became necrotic as in fruits of the normal strain. It is proposed that developing tomato fruits undergo a transition period which is largely completed by about 15 days from anthesis. During this transition period changes prerequisite for the eventual expression of ripening take place.
Effects of Ethylene and Propylene on Post-Harvest Development and Ripening of Young Normal and Mutant Tomato Fruits
Authors: Adato I , Mcglasson WB
Published: January 2006

When tomato fruits of cv. Rtugers (normal), and of the rin and nor mutants were detached 10 days after anthesis (24% of the total growth period), they usually developed a characteristic swelling of one or more locules, which eventually developed a red, yellow or yellow-orange colour typical of the mature fruits of each strain. The remainder of the fruit tissues lost chlorophyll and eventually became necrotic. Ethylene treatment (25 �l/l) started 2 h after harvest advanced the onset of swelling in 10-day fruits of all strains. Treatment that was started 7 days after harvest had no effect on the onset of swelling in Rutgers and rin and had only a small effect on nor fruits.
When ethylene was applied before first visible swelling (FS), the undeveloped portions of the fruits rapidly became necrotic and this necrosis spread to the swollen locules before they coloured. From FS and onwards, ethylene increased the rate of swelling and advanced colouring of the swollen locules. In some treated rin fruits, the swollen locules became intensely pink or red.
Propylene treatment (500 �l/l) started 2 h after harvest also advanced the onset of swelling and red colour development in swollen locules in Rutgers fruits, as well as advancing the onset of the respiratory climacteric and the associated rise in ethylene production. Swelling in both control and propylene-treated fruits was not associated with any marked changes in respiration and ethylene production.
Flowering in Pisum: Does Gibberellic Acid Directly Influence the Flowering Process?
Authors: Reid JB , Dalton PJ , Murfet IC
Published: January 2006

Gibberellic acid is shown to cause a substantial delay in the flowering node, time of flower initiation and leaf requirement for flowering in the late pea cultivar line 24, grown under an 8-h photoperiod. In continuous light, gibberellic acid caused only a small delay in the flowering node and leaf require- ment. As the plants became older the effect of applied gibberellic acid decreased. This was not due to initiation having already occurred or to the gibberellic acid not penetrating the plant. It is suggested that gibberellic acid has a direct effect on the flowering process in line 24 plants grown under an 8-h photoperiod and that it may act by reducing the effect of age on the gene Sn.
Thermal Adaptation of Pennisetum: Leaf Structure and Composition
Authors: Pearson CJ , Bishop DG , Vesk M
Published: January 2006

Studies were made of the effects of growth temperatures and transition to colder temperature on chloroplast ultrastructure, chlorophyll accumulation, lipids and protein of two Pennisetum americanum cultivars and a P. americanum × P. purpureum biotype which differed in temperature sensitivity.
All genotypes had structure and chlorophyll distribution consistent with NADP-malic enzyme C4 systems and lipid phase transitions at temperatures similar to those of other 'chilling-sensitive' plants. All accumulated less starch at low temperature and there was mobilization of starch, aggregation of thylakoids in mesophyll chloroplasts and swelling of loculi on transition from 24/19 to 18/13°C. Intolerance of Pennisetum to low temperature was clearly not due to accumulation of starch, nor were genotypic differences in temperature sensitivity related to starch. The cold susceptibility of cv. Ingrid Pearl, in contrast with the tolerance of the intraspecific and interspecific hybrids, was associated with inability to accumulate chlorophyll in the mesophyll of some leaves; fluctuations in chlorophyll a/b ratios within 5 days of transition to lower temperature; and inability to accumulate higher concentrations of soluble proteins in apparently normal leaves grown at 18/13°C. Genotypic differences in temperature sensitivity did not appear related to the physical properties of membranes, which did not change within 5 days of transition to 18/13°C.