bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of oxidative metabolism in watermelon plants subjected to cold stress
Authors: Rivero Rosa M. , Ruiz Juan M. , García Pablo C. , López-Lefebre Luis R. , Sánchez Esteban , Romero Luis
Published: January 2006

The objective of the present work was to determine the effect of thermal
stress on oxidative metabolism in Citrullus lanatus [Thomb.] Mansf.
cv. Dulce maravilla. Plants were grown for 30 d at two temperatures (10 and
35˚C), at which time we measured the leaf concentration of antioxidant
compounds (ascorbate, dehydroascorbate, reduced glutathione, oxidized
glutathione) and enzymatic activities [superoxide dismutase (SOD),
catalase, guaiacol peroxidase, ascorbate peroxidase, dehydroascorbate
reductase and glutathione reductase], as well as total hydrogen peroxide
(H2O2) concentration and shoot dry
weight. Our results indicate that chilling stress occurred in watermelon
plants at 10˚C, while 35˚C is the optimal temperature for this
plant. Low temperature stress caused: (i) decreased shoot weight; (ii)
accumulation of H2O2; (iii)
increased SOD activity; and (iv) decreased enzyme activities associated with
detoxifying H2O2. The novelty of
this study centres on the fact that so few cold-sensitive species have been
examined to date — additional cold-sensitive species need to be studied
to determine if there are shared characteristics in terms of how they respond
to cold stress. Most studies have examined single antioxidant responses,
whereas we conducted a comprehensive examination of many antioxidant
responses.
The Effects of Enhanced UV-B Radiation on the Mediterranean Evergreen Sclerophyll Nerium oleander Depend on the Extent of Summer Precipitation
Authors: Drilias Periklis , Karabourniotis George , Levizou Efi , Nikolopoulos Dimosthenis , Petropoulou Yiola , Manetas Yiannis
Published: January 2006

Seedlings of Nerium oleander L. were grown in the field
under ambient or ambient plus supplemental UV-B radiation (simulating a
15% ozone depletion over Patras), and received natural precipitation or
additional irrigation during the summer dry period. Two experiments, in 1994
and 1995, were performed. Natural precipitation during summer in 1994 was near
the mean for the area but summer 1995 was exceptionally wet. During 1994,
supplemental UV-B radiation reduced by ca 25% the
above-ground biomass under natural summer precipitation but had no effect on
the plants receiving additional irrigation. During the wet 1995, UV-B
radiation caused a 5%, non-significant reduction in biomass under
natural summer precipitation, and a 16%, non-significant increase under
ample water availability. No effects of UV-B radiation were observed on PSII
photochemical efficiency (assessed from in vivo Chl
fluorescence), photosynthetic pigments, UV-B absorbing compounds, leaf
relative water content, leaf specific mass or leaf thickness. However, cuticle
thickness and cuticle mass (on a unit area basis) were increased by
supplemental UV-B radiation, on both leaf surfaces, independent of water
availability. We conclude that UV-B radiation effects on growth depend on the
extent of summer precipitation. The increase in cuticle thickness may
counteract UV-B radiation damage, through attenuation of UV-B radiation
and/or reduction of cuticular transpiration during the dry summer.
Temperature stress and oxygen inhibition of nitrogen fixation in a Nostoc cyanobacterium
Authors: Smith Geoffrey D. , Chazal Nola M. de , Tozer Greg , Clerk Lucy H.
Published: January 2006

The effect of elevated temperature and oxygen concentration on nitrogen
fixation was investigated in a Nostoc species previously
isolated in Java, Indonesia. This organism grows well under nitrogen-fixing
conditions at 25°C and also adapts to grow at 40°C. Cells grown at
these temperatures responded differently to thermal stress at 48°C; cells
grown at 25°C and stressed without oxygen at 48°C were subsequently
much more sensitive to oxygen than cells grown at 40°C. This indicates an
adaptation of the cells to growth at the higher temperature. In the presence
of an adequate supply of CO2, oxygenic photosynthesis in
the vegetative cells was not impaired by the thermal stress, nor was whole
cell respiration. The addition of H2 substantially
overcame the oxygen-inhibition for adapted cells but not for those grown at
25°C. Possible causes of the thermal inactivation of nitrogen fixation are
discussed.
Long Distance Transport of Potassium in Intact Peanut Seedlings: Effects of Sodium and Ouabain
Authors: Jagat Singh , Dieckert JW
Published: January 2006

Of the potassium originally present in peanut seeds, 66.3 % was transported to the shoot and 15.8 % to the root of the growing seedling after 8 days of growth, while the remaining 18 % could still be located in the cotyledons. At an external potassium level of 6 mM, long distance transport of potassium to the shoot by the intact peanut seedling was not affected by the sodium present in the culture solution. Ouabain at levels ranging from 0 to 30 mM also had no effect.
Biophysical Characterization of Mesophyll and Bundle Sheath Chloroplasts Isolated From the Leaves of Eleusine coracana, an Aspartate-Type C4 Plant. II. Photosynthetic Electron Transfer and Energy Conservation Reactions
Authors: Rathnam CKM , Das VSR
Published: January 2006

Mesophyll and bundle sheath chloroplasts isolated from the leaves of E. coracana, an aspartate-type C4 plant, have been utilized to study various photochemical activities in an effort to understand their high rates of photosysnthetic CO2 fixation. Bundle sheath chloroplasts were relatively more active in the overall process of photosynthetic electron transfer from water to NADP. Though photosystem II (PS II) and the associated non-cyclic photophosphorylation activities were of the same magnitude in both types of chloroplast, PS I and the associated cyclic photophosphorylation activities were three to four times more active in bundle sheath chloroplasts than in mesophyll chloroplasts. The influence of different illuminance on the electron and energy transfer reactions has been studied. At all the light levels tested, cyclic photophosphorylation activity was higher than non-cyclic in bundle sheath chloroplasts, while sigmoid kinetics were observed with mesophyll chloroplasts. Acid-base phosphorylation activities of the two types of chloroplast were similar. Heat treatment of the chloroplasts resulted in a selective inhibition of PS II in both types. Total leaf chlorophyll was approximately equally destributed between mesophyll and bundle sheath chloroplasts, which were found to have chlorophyll a-chlorophyll b ratios of 4.50 and 3.50 respectively. A working hypothesis for the energy requirements in the mesophyll and bundle sheath cells for the maintenance of various biochemical processes is proposed. It is also concluded that a greater part of the total leaf photochemical potential is associated with bundle sheath chloroplasts of E. coracana.
Effect of Water Deficit on Carbon Dioxide Exchange and Leaf Elongation Rate of Panicum maximum Var. trichoglume
Authors: Ludlow MM , Ng TT
Published: January 2006

The responses of carbon dioxide exchange and leaf elongation of potted P. maximum var. trichoglume plants to water deficits were investigated in controlled environments and outdoors during drying cycles down to -92 bars leaf water potential, The sensitivities of net photosynthesis and leaf elongation to water deficits were similar. The leaf water potentials at which net photosynthesis and elongation ceased (c. -12 bars), and stomatal resistance increased substantially (- 6 bars), were relatively unaffected by nitrogen supply, environmental conditions during growth, and whether plants had previously experienced stress. However, these factors influenced the rate of net photosynthesis, at high leaf water potentials by affecting stomatal resistance and at moderate water potentials by affecting both stomatal and intracellular resistances. Stomata1 resistance was more sensitive than intracellular resistance to water deficits. Dark respiration rate decreased with leaf water potential, and was higher in plants receiving additional nitrogen. At moderate leaf water potentials
(-7 to -9 bars), net photosynthesis of this C4 grass exhibited light saturation and rates similar to C3 plants.
We suggest that the difference in behaviour of controlled-environment-grown and field-grown plants to water deficits observed with some species is unlikely to be due to differences in the aerial environment, but may result from differences in the rate at which stress develops. The ecological significance and evolution of the C4 syndrome are discussed briefly.
Auxin Transport Inhibitors. II. 2-(1-Pyrenol)Benzoic Acid, a Potent Inhibitor of Polar Auxin Transport
Authors: Katekar GF , Geissler AE
Published: January 2006

2-(1-Pyrenoyl)benzoic acid is shown to be a highly active inhibitor of auxin transport by its ability to prevent the polar transport of indoleacetic acid in bean petioles. It is comparable in activity to other known auxin transport inhibitors, and also affects apical dominance and the geotropic and phototropic responses.
Development of Photochemical Activity in Chloroplast Membranes. II. Studies With a Mutant of Barley Grown Under Different Environments
Authors: Smillie RM , Nielsen NC , Henningsen KW , Wettstein DV
Published: January 2006

Chloroplast development in the barley mutant xantha-b12, a nuclear gene mutant derived from Hordeum vulgare L. cv. Sval�fs Bonus, was profoundly influenced by the temperature and light intensity to which the plants were subjected during growth. Low temperatures and high light intensities retarded chloroplast development. By growing this mutant under different combinations of temperature and light intensity, seedlings were produced containing chloroplasts at different developmental stages. Measurements of photochemical activities of the isolated chloroplasts indicated a sequence for development of photochemical competence in chloroplast membranes very similar to that adduced from a study of several different barley mutants grown under a single environment. A photoreductive capacity is initially acquired but energy conservation sites only become fully functional at an advanced stage of membrane development.
Analysis of the Effects of Virus Infection on the Photosynthetic Properties of Peach Leaves
Authors: Smith PR , Neales TF
Published: January 2006

Infection of peach leaves with the viruses causing 'peach rosette and decline disease' reduced their net photosynthetic rate (PN) over a range of light intensities. The Pmax value, derived from the asymptotic value of the light-response curve of young leaves was significantly reduced by 13%. The reduction of PN was partially attributable to increases in both the gas-phase (r1) and residual (rm) resistances. Virus infection, however, had no effect on the PN values of older leaves, as leaf senescence effects predominated over any effects of infection. The 'dark' respiration rate of young leaves was increased by virus infection by c. 50 %, but not significantly so.
The constants of the polynomial regressions, relating PN to the environmental variables of ambient CO2 concentration and irradiance, were used as indices of the leaf photosynthetic characteristics. The photochemical efficiency of young infected leaves was 28 % less than that of healthy controls, but infection had no effect on older leaves. The mean total leaf conductance to CO2 transfer was also reduced by 30 % (not significantly) in infected leaves. The CO2 and light compensation points were unaffected.
It is concluded that the (previously reported) large, inhibiting effects of virus infection on the growth of young peach trees are not attributable to these comparatively less severe effects on leaf photosynthesis but rather to effects on leaf growth.
Reversible Leaflet Movements in Relation to Drought Adaptation of Cowpeas, Vigna unguiculata (L.) Walp
Authors: Schakel KA , Hall AE
Published: January 2006

Two aspects of the heliotropic responses of leaflets of V. unguiculata cv. California Blackeye No. 5 were studied: the environmental conditions responsible for the responses, and the significance of the leaflet orientation responses for adaptation.
In the field under drought conditions, leaflets were observed to sun-track (diaheliotropism) in the morning and sun-avoid (paraheliotropism) by becoming more vertical in the afternoon. Overnight irrigation of droughted plants in the field resulted in leaflet movements on the day after irrigation similar to those of the well watered plants. Leaflets of well watered plants were diaheliotropic during the morning and evening, and essentially horizontal during the late morning and afternoon.
Controlled-environment studies confirmed field observations of drought effects on leaflet movement and showed that leaflet orientation responses are reversible within 3 h after irrigating droughted plants. Temperature variations similar to those experienced in the field had only small effects on leaflet orientation.
Vertical leaflet movement affected canopy architecture and significantly reduced percentage cover at midday. Manually moving the vertical leaflets of droughted plants caused substantial changes in leaflet temperatures, indicating that leaflet movement could substantially reduce heat load, water use, and water deficits in cowpeas.
Cytokinin Ribosides as Inhibitors of Ribonuclease Activity on Ribosomes From Fenugreek (Trigonella foenum-graecum L.)
Authors: Rijven AHGC
Published: January 2006

Ribonuclease activity on washed ribosomes, isolated from dark-incubated fenugreek cotyledons, depended on the presence of MgCl2 or spermine. Under appropriate conditions, the digestion of poly(C) was inhibited by 48% at 8 x 10-7 M 6-isopentenyladenosine, that of poly(U) was less sensitive to this riboside whilst no inhibition was observed with poly(A) as substrate. The digestion of poly(C) was inhibited by both 6-isopentenyladenine and by triacanthine (3-isopentenyladenine). Digestion of natural RNAs was also inhibited by 6-isopentenyladenosine but less so by other cytokinin ribosides and by 7-methylguanosine; it was not inhibited by unmodified nucleosides.
Isolation and Properties of Functional Mesophyll Protoplasts and Chloroplasts From Zea mays
Authors: Day DA , Jenkins CLD , Hatch MD
Published: January 2006

A procedure is described for the preparation of metabolically active mesophyll protoplasts from maize, and of functional, intact chloroplasts from these protoplasts. Intact protoplasts show no oxygen evolution with 3-phosphoglycerate or with oxalacetate plus pyruvate as substrates, even when these substances are provided at high concentrations. On the other hand, protoplast extracts and chloroplasts display rates of oxygen evolution of 2-3 �mol min-1 (mg Chl)-1 with the same substances. Pyruvate stimulates oxalacetate-dependent oxygen evolution substantially, indicating good coupling between non-cyclic electron flow and phosphorylation. Low PI concentrations stimulate 3-phosphoglycerate-dependent oxygen evolution; high PI concentrations, and pyridoxal phosphate, inhibit this activity, suggesting a common carrier for 3-phosphoglycerate and PI.
Presowing Hydration-Dehydration Treatments in Relation to Seed Germination and Early Seedling Growth of Wheat and Ryegrass
Authors: Lush WM , Groves RH , Kaye PE
Published: January 2006

Seeds of wheat (Triticum aestivum cv. Egret) and annual ryegrass (Lolium rigidum cv. Wimmera) were given a single hydration-dehydration cycle by adding a known amount of water and later air-drying them. Embryos enlarged during this initial hydration, and short periods at high water contents were equivalent to longer periods at lower water contents. After hydration to 145% of seed dry weight (wheat) or to 155% (ryegrass) followed by dehydration back to the original seed weights the speed of germination of both species was approximately doubled because the lag phase of germination was shortened. The proportion of ryegrass seeds that were dark-dormant was reduced if seeds were pretreated in light. Pretreatment did not increase germination synchrony, alter threshold temperatures for germination or enhance seedling growth rates. The viability of pretreated seed declined rapidly at - 15°C and at 50°C. The effect of pretreatment, i.e. early germination, is attributed mainly to embryo enlargement. More rapid imbibition of pretreated seeds may contribute in a minor way to differences in germination time.
Uptake and Metabolism of Hydroxyproline in Endosperm Cells of Lolium multiflorum (Ryegrass)
Authors: Pollard PC , Way PW , Fincher GB
Published: January 2006

Hydroxyproline is rapidly removed from the medium by suspension-cultured endosperm cells of ryegrass (Lolium multiflorum) in a process which exhibits Michaelis-Menten kinetics and is dependent on temperature and metabolic energy. Following uptake by the cells, hydroxyproline is rapidly converted to proline by a route which appears to be more direct than the pathways of hydroxyproline metabolism in mammalian and bacterial systems and which results in substantial conservation of the pyrrolidine ring. Four hours after providing the cells with 5.5 nM [3H]hydroxyproline, approximately 50% of the radioactivity is recovered as intracellular imino acids, intracellular protein and extracellular peptide material. The radioactivity is associated predominantly with proline and hydroxyproline residues.
In common with other plant and animal systems, hydroxyproline is not incorporated directly into protein. However, radioactivity originating in extracellular hydroxyproline is detected eventually in peptide linkage, where it appears first as peptidyl proline. In the extracellular fraction which contains arabinogalactan-protein, peptidyl proline is hydroxylated to form peptidyl hydroxyproline and, after 4 h, approximately 18% of the original 3H label is found in this fraction.
Accuracy and Usefulness of Psychrometer and Pressure Chamber for Evaluating Water Potentials of Pinus radiata Needles
Authors: Millar BD
Published: January 2006

Pressure chamber evaluations of xylem sap pressure potential (P) and thermocouple psychrometric evaluations of average water potential (Ψl) in needles from both transpiring and non-transpiring pine trees (Pinus radiata D. Don) were compared in order to determine the relative accuracy and usefulness of these methods for assessing Ψl. Markedly different but linear P v. Ψl relationships were obtained for pine needles of different age and also for the case where resin exudation masked the xylem and led to a 'resin error'. Evidence suggests that these differences are mainly due to injection and resin errors in pressure chamber determinations totalling as much as 1 MPa (a 10 bar). The psychrometric method appears to be the much more accurate. Radial water potential gradients across leaves did not result in differences between evaluations of P and Ψl, at least in P. radiata. The need for multiple 'calibrations' of the pressure chamber and the fundamental uncertainty about the constancy of such calibrations on the one hand and the slowness of the excised-needle psychrometer on the other can restrict the usefulness of these methods.
Studies on the Phloem Sealing Mechanism in Ricinus Fruit Stalks
Authors: Kallarackal J , Milburn JA
Published: January 2006

Fruit stalks of R. communis were made to exude phloem sap by repeated slicing at intervals of a few minutes. Samples 1 mm thick from the fruit stalks were fixed for electron microscopy. Samples were also fixed and processed for electron microscopy from previously intact (non-exuding) fruit stalks. Examination of the sieve tubes from these two different samples showed predominantly open sieve-plate pores in the exuding fruit stalk. The sieve plates of the non-exuding fruit stalk showed occlusion of the sieve-plate pores by P-protein. The starch grains from the broken plastids also had characteristic distributions. The implications of these observations are discussed in relation to comprehending the mechanism by which sieve-plate pores become choked, and so sealing the sieve-tube system as a result of injury.
The Influence of Zinc Supply to Seedlings of Pinus radiata D. Don on the Internal Transport of Recently Absorbed Zinc
Authors: Mcgrath JF , Robson AD
Published: January 2006

The movement of a 48 h pulse of 65Zn supplied to P. radiata seedlings growing in solutions containing varying concentrations of zinc was examined by taking a series of harvests following the application of the pulse. The movement of recently absorbed 65Zn through the stem and into the foliage was slower in plants with a low supply of zinc resulting in a greater accumulation of 65Zn in stems of these plants than in those with a high supply of zinc. Transferring plants from a low supply to a high supply of zinc decreased the quantity of 65Zn in the stem to the levels found in plants grown with a continuously high supply of zinc. Seedlings with a low external supply of zinc distributed more of the recently absorbed 65Zn to their lower needles than to their upper needles, probably as a consequence of the slower movement of zinc through plants with a low zinc supply.
The movement of zinc through seedlings of P. radiata was slow even in plants with an adequate supply of zinc. Two weeks after the pulse of 65Zn was applied, 65Zn was still moving from the stem into the foliage.
The Electrical Properties of Plant Cell Membranes. V. The Effects of Net Longitudinal Currents induced with External Current Electrodes upon the Cable Properties of Charophytes
Authors: Smith JR
Published: January 2006

Analytical solutions describing the electrical 'cable' properties of cylindrical, radially symmetric, cells with two concentric membranes are derived for experimental configurations whereby current is injected through the membranes via external electrodes located at different longitudinal positions, i.e. when a net longitudinal current is present. The spatial behaviour of the membrane voltages and longitudinal currents are calculated, using values that should be appropriate for Chara and Nitella. It is shown that the area-specific values of the conductances of the plasmalemma and tonoplast derived from such measurements can be significantly in error if the appropriate cable properties are not considered. It is also demonstrated how suitable location of the external current electrodes can significantly reduce any errors produced by the cable properties and concomitantly reduce the magnitude of the associated longitudinal variation in membrane voltage (thus substantially reducing the distortion produced by any non-linearities in the membrane I- V characteristics). In most configurations, location of the current electrodes two-thirds of the distance along the length of each cell section bathed in electrolyte will generally be close to optimum. It is also shown that measurement of the change in membrane voltage (in response to an injected current) approximately half-way along the section bathed in electrolyte will usually ensure that the measured conductance varies approximately linearly with that of the membrane.
Effects of Nitrate and Ammonium on Nitrogenase (C2H2 Reduction) Activity of Swards of Subterranean Clover, Trifolium subterraneum L
Authors: Silsbury JH , Catchpoole DW , Wallace W
Published: January 2006

Small swards of subterranean clover plants were grown under controlled conditions without mineral nitrogen and allowed to establish an effective nitrogen fixation system. Nutrient solutions containing nitrate from 0 to 16 mM or of ammonium from 0 to 5 mM were then applied and changes in nitrogenase activity (NA) estimated by acetylene reduction assay (AR) and the rate of hydrogen evolution (HE) for periods of up to 35 days. In two experiments a split-root system was used to enable mineral nitrogen to be applied to only one-half of a nodulated root system whilst the NA of both halves was monitored. NA by subterranean clover was very sensitive to exogenous mineral nitrogen, concentrations as low as 0.5 mM NO3- suppressing activity significantly, and 3-5 mM stopping it almost completely within 7 days. The degree of inhibition induced by concentrations between 0.5 and 3 mM NO3- was less at a photon irradiance of 1000 compared with 300 �mol quanta s-1 m-2 . Under some conditions NA continued at a reduced but steady rate in the presence of nitrate. NH4+ also markedly depressed NA but a concentration greater than 5 mM was needed to effect the same response. After NO3- was applied to an active symbiosis, nitrate reductase activity increased as NA decreased. Our results do not support the hypothesis of a direct effect of NO3- on nitrogenase due to the accumulation of toxic NO2-. Although our results allow that assimilate might be diverted from the nodules after the application of NO3- thus reducing N2-fixation, an alternative hypothesis is proposed: that nitrogenase and nitrate reductase work in a complementary manner in supplying reduced nitrogen to whole plants, and NO3- depresses N2-fixation through a regulatory system involving the level of soluble nitrogen in the plant.
We conclude that nitrogen fixation by subterranean clover in the field may be depressed below its potential due to the presence of soil mineral nitrogen.
CO2-enhanced C2H4 Production in Tissues of Imbibed Cocklebur Seeds
Authors: Esashi Y , Ooshima Y , Abe M , Kurota A , Satoh S
Published: January 2006

Both endogenous C2H4 production and the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to C2H4 in the axial tissues of upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds were enhanced by CO2, and this enhancement was accompanied by increased axial growth. However, in the seed-coat (endosperm layer), which had no growth potential, the endogenous C2H4 production was preferentially promoted by CO2. CO2 increased the content of ACC in both tissues. The maximal ACC-C2H4 conversion in the axial tissue occurred at CO2 concentrations that varied from 1 to 10%, depending upon the O2 tension of the ambient atmosphere. Similar to the inhibition of seed respiration by NaN3, the ACC-C2H4 conversion was more strongly inhibited by KCN or NaN3 in the presence of CO2 than in its absence. This suggests an increased involvement of the cytochrome path in cocklebur seed respiration in the presence of CO2. This suggestion was supported by data showing that CO2 elevated the ATP level in the axial tissues. Little CO2-enhancement of the ACC-C2H2 conversion occurred when the ATP level of seeds had been reduced by KCN pretreatment and maintained low in a hypoxia during a subsequent incubation period. These results suggested that CO2 enhances C2H4 production of imbibed cocklebur seeds in two different ways: through both increases of ACC supply and of ACC-C2H2 conversion, probably resulting from the CO2-induced increase in the cytochrome path flux or in the resultant ATP level.
Effects of a Brief Episode of Elevated Temperature on Grain Filling in Wheat Ears Cultured on Solutions of Sucrose
Authors: Bhullar SS , Jenner CF
Published: January 2006

The hypothesis that reduced grain weight resulting from elevated temperature is the result of a reduction in the supply of assimilates to the grain or lessened availability of sucrose within the endosperm for grain filling has been investigated. Detached ears of wheat were cultured on solutions of sucrose varying in concentration from a level which supports normal rates of grain filling to one above and one below that level. Contrary to expectation, at the low concentration of sucrose the rate of grain filling in detached ears increased more at elevated temperature than it did in ears supplied with higher concentrations of sucrose, or compared with ears developing on intact plants. In other experiments ears were detached and, after a brief exposure to elevated temperature, were cultured on solutions of sucrose. The residual effects of warming, expressed as slower grain filling and lower mature grain weight, were less pronounced at low than at higher concentrations of sucrose. This result also is not in accordance with the hypothesis.
Thylakoid Membrane Organisation in Sun/Shade Acclimation
Authors: Anderson JM , Chow WS , Goodchild DJ
Published: January 2006

The photosynthetic apparatus of plants responds to changing light quantity and quality with coordinated changes in both the light-harvesting antennae of the photosystems and the amounts of electron transport components and ATP synthase. These compositional modulations are accompanied by changes in thylakoid membrane organisation and photosynthetic capacity. It is now clear that there is a dynamic continuum of organisation and function of the photosynthetic apparatus from the appressed granal and non-appressed stroma thylakoids within a chloroplast, to different chloroplasts within a leaf, to leaves within and between species. While it is very unlikely that there is a unique solution to photosynthesis in the sun or shade, substantial changes in composition, and hence thylakoid membrane organisation and function, are elicited as part of sun/shade responses.
Photoinhibition at Chilling Temperatures
Authors: Smillie RM , Hetherington SE , He J , Nott R
Published: January 2006

Relative susceptibilities of chilled leaves to photoinhibition were determined for 15 species of crop annuals showing a wide range of chilling tolerance. Leaf tissue at 7°C was exposed to a moderate photon irradiance of 300 �mol m-2 s-1 and photoinhibition was measured by the decrease in chlorophyll fluorescence (Fv/Fm) measured at 77K. All chilling-resistant plants surveyed (barley, broad bean, oat, pea and wheat) were photoinhibited at chilling temperatures. The chilling-sensitive plants (bean, cucumber, lablab, maize, pearl millet, pigeon pea, sesame, sorghum and tomato) were more susceptible, the mean of values for susceptibility to photoinhibition being twice that of the chilling-resistant plants. Rice, however, showed a tolerance to photoinhibition at 7°C comparable to that of some of the chilling- resistant plants. Indica rices were more susceptible than japonica rices. Photoinhibition increased with decreasing temperature and with increasing photon irradiance in both the chilling-resistant and sensitive plants. In pea and cucumber, photoinhibition at 7°C was correlated linearly with the decrease in photosystem II activity assayed in chloroplast thylakoids isolated from similarly treated tissue.
Relative tolerances of leaves of the same 15 species to chilling injury in the dark were also measured. No linear correlation was found between susceptibility of chilled leaves to photoinhibition and susceptibility to dark chilling injury. The pattern of differences between species for photoinhibition at 7°C was largely preserved when photoinhibitory treatments were given at a non-chilling temperature (21°C) by increasing the photon irradiance to 900 �mol m-2 s-1. We conclude that, while the chilling-sensitive plants were generally more susceptible than the chilling-resistant ones to photoinhibition at low temperatures, this arose from a greater sensitivity to the irradiance rather than from the chilling sensitivity.
Photoinhibition associated with low temperatures was also demonstrated in the tropical fruit species, banana, pawpaw and Monstera. Low values of Fv/Fm recorded in leaves exposed to full sunlight during the winter month of July (range 0.39-0.56 compared with 0.70-0.79 in January) indicated that photoinhibition could adversely affect some tropical perennial fruit species cultivated in semitropical or warm temperate areas experiencing recurrent cool to cold winters.
Sucrose Accumulation in Red Beet Vacuoles by UDP Glucose-Dependent Group Translocation — Fact or Artefact?
Authors: Niemietz C , Hawker JS
Published: January 2006

Beetroot vacuoles obtained by slicing or enzymic techniques incorporated UDP[14C] glucose predominantly into an ethanol insoluble product. No labelled sucrose was detected. Chromatographic separations and kinetic experiments suggested the results were due to glucan synthase II (EC 2.4.1.34). Evidence is presented that this enzyme can account for many of the features previously attributed to the proposed UDPglucose-dependent group translocation mechanism for sucrose transport into red beet vacuoles. The possible interference by glucan synthase II in experiments published previously is discussed.
An Analysis of the Temperature Dependence of Photosynthesis Considering the Kinetics of RuP2 Carboxylase and the Pool of RuP2 in Intact Leaves
Authors: Oja VM , Rasulov BH , Laisk AH
Published: January 2006

Sunflower and cotton plants were grown in growth boxes at 460 �mol m-2 s-1. The mesophyll conductance in N2, the assimilatory charge (post-illumination CO2 uptake) and the CO2 capacity (the solubility of CO2 + HCO3- + CO32-) were measured at different temperatures. The mesophyll conductance had its maximum at 29-30°C in sunflower leaves and rapidly declined at higher and lower temperatures. In cotton, the maximum occurred at a somewhat higher temperature. The assimilatory charge changed in parallel with the mesophyll conductance. When the assimilatory charge was measured after a short exposure to CO2-free N2, it remained constant at lower temperatures and declined only at superoptimal temperatures. As the assimilatory charge reflects the RuP2 pool in the leaf, the temperature dependence of the mesophyll conductance at a constant assimilatory charge reveals the actual activation energy of the CO2 binding reaction of carboxylase (together with the CO2 transport conductance in the liquid phase of mesophyll cells) which was 29 kJ mol-� for both species.
At superoptimal temperatures, the primary cause for the reversible decrease of photosynthesis was a decrease in the assimilatory charge (RuP2 pool). The decrease cannot be caused by an inadequate rate of RuP2 resynthesis but is, presumably, the result of either too rapid drainage of triosephosphates to the cytosol from chloroplasts or de-energisation of thylakoids at high temperatures.
Variation in Salt Secretory Activity of Microhairs in Grasses
Authors: Amarasinghe V , Watson L
Published: January 2006

Salt secretory activity of leaf microhairs in 18 grass species was examined by quantitative ion chromatography of washings, and directly by scanning electron microscopy and qualitative energy dispersive X-ray microanalysis of microhair secretions. The sample represented the subfamilies Chloridoideae, Arundinoideae, Panicoideae and Bambusoideae, including microhairs of the 'chloridoid', 'panicoid' and 'Enneapogon' morphological types, and exemplified forms with and without 'partitioning membranes'. Salt secretion by microhairs was detected only in certain Chloridoideae, all having 'chloridoid type' microhairs with basal cell partitioning membranes. Salt secretion was not detected with any of the microhairs lacking basal cell partitioning membranes; and 'chloridoid type' microhairs of Sporobolus elongatus and Eleusine indica were not seen to secrete salt, despite their possession of partitioning membranes.
Effect of Water Stress on Stomatal Conductance and Leaf Water Relations of Leaves Along Current-Year Branches of Peach
Authors: Steinberg SL , Mcfarland MJ , Miller JC
Published: January 2006

A gradation, that reflects the maturity of the leaves, exists in the leaf water, osmotic and turgor potential and stomatal conductance of leaves along current and 1-year-old branches of peach.
Predawn leaf water potentials of immature folded leaves were approximately 0.24 MPa lower than mature leaves under both well-watered and dry conditions. During the daytime the leaf water potential of immature leaves reflected the water potential produced by water flux for transpiration. In well- watered trees, mature and immature unfolded leaves had a solute potential at least 0.5 MPa lower than immature folded leaves, resulting in a turgor potential that was approximately 0.8 MPa higher. The turgor requirement for growth appeared to be much less than that maintained in mature leaves.
As water stress developed and leaf water potentials decreased, the osmotic potential of immature folded leaves declined to the level found in mature leaves, thus maintaining turgor. In contrast, mature leaves showed little evidence of turgor maintenance. Stomatal conductance was lower in immature leaves than in fully mature leaves. With the onset of water stress, conductance of mature leaves declined to a level near that of immature leaves. Loss of turgor in mature leaves may be a major factor in early stomatal closure.
It was concluded that osmotic adjustment played a role in maintenance of a leaf water status favorable for some growth in water-stressed immature peach leaves.
Water Relations of the Banana. II. Physicochemical Aspects of the Latex and Other Tissue Fluids.
Authors: Baker DA , Kallarackal J , Milburn JS
Published: January 2006

The water potential and various physical and chemical aspects of latex and other tissue fluids of banana plants were investigated. Fluids including guttation fluid, phloem sap, nectar and expressed leaf sap, were compared with exuding latex to understand their relationships. The relationships between the refractive index and solute potential of the latex from both glasshouse-grown and plantation-grown plants were compared and found to be significantly different.
Latex was analysed for the major chemical constituents contributing to the solute potential. K+, Mg2+, Na+ and Ca2+ and Cl-, SO2-4 and PO2-4 were assayed. Of these, K+, Mg2+, Cl- and NO-3 were the major contributors to the solute potential. During exudation the concentration of the above ions declined. However they only partially explain the measured changes in refractive differences; the cause of this is discussed.
The sources of error in determining the water potential of the banana from the solute potential of the latex are discussed. The use of refractometer as a tool for field determination of banana water potential is also substantiated.
Rapid Leaf Growth in Wheat and Its Links With Flowering
Authors: Rawson HM
Published: January 2006

Recent papers have proposed that rapid leaf growth in pasture grasses in spring is linked with the switch from vegetative to floral development. The paper examines this possible link in wheat using various photoperiodic treatments and isolines with different vernalisation requirements to induce floral initiation at several plant ages. The findings were as follows.
(1) Induction of floral initiation by 3 long days at any plant age resulted in accelerated leaf expansion and relative growth rate of the whole plant. The effects were on shoots alone.
(2) At equivalent plant age, when a winter isoline had no signs of double ridges, and so was apparently vegetative, and a spring isoline was clearly floral, whole-plant relative leaf expansion rates were not significantly different between isolines though tillering was much less in the spring line.
(3) Photoperiodic treatments which were not sufficient to induce floral development irreversibly resulted in ephemeral increases in leaf expansion rate. These increases were followed by compensatory reductions.
These data suggest that rapid leaf expansion and floral development are not linked, although both can be initiated by extended photoperiods rich in far-red radiation. The relevance of these findings to the selection of wheat genotypes with rapid early growth is discussed.
Effects of Exposure of Wheat Ears to High Temperature on Dry Matter Accumulation and Carbohydrate Metabolism in the Grain of Two Cultivars. II. Carry-Over Effects
Authors: Jenner CF
Published: January 2006

Yield of wheat exposed in the field during the grain-filling stage to brief episodes of high (but sub- lethal) temperature is reduced as a consequence of lower single grain weight due mainly to diminished accumulation of starch. To simulate these effects, ears of wheat were enclosed in a transparent box midway through the grain filling stage and heated (35�C day/25�C night) above ambient conditions (21�C day/16�C night) for periods of up to 7 days. Afterwards the ears were returned to ambient conditions. Two cultivars known to differ in their tolerance of high temperature were compared.
Final single grain dry weight of the more tolerant cultivar (Kalyansona) was not significantly affected by exposure to heat, but it was reduced in cv. Sun 9E by approximately 15.5% after 7 days of exposure. Rate of grain filling in the cool conditions following previous exposure to high temperature was also substantially slower in both cultivars than it was in ears that had not been heated.
Following transfer from hot to cool conditions, the amounts of fructose and the concentration of UDP-glucose returned to control levels. On the other hand, quantities of sucrose in the grain of ears that had been heated rose higher than in ears that had been kept continuously in cooler conditions. Thus any effects of high temperature at the sucrose synthase step appeared to be readily reversible, and both cultivars responded similarly.
Cultivar-dependent responses were observed however in effects on the concentrations of hexose phosphates and ADP-glucose. After only one hot day the concentration of G-6-P, F-6-P and G-1-P returned to control levels following transfer to the cooler environment. After 2 or more days the concentrations of these metabolites did not recover in cv. Sun 9E but recovery was observed in cv. Kalyansona after 2 or 4 days' exposure, but not after 7 hot days. Last, concentrations of ADP-glucose in the cultivar of which starch deposition was reduced most at high temperature (Sun 9E) rose more after transfer from high to low temperature than was the case in the more tolerant cultivar (Kalyansona), and ADP-glucose concentrations fell more in the latter than in the former cultivar as a consequence of 7 days at high temperature.
It is suggested that more than one action of temperature could be involved in the cultivar-dependent responses to high temperature: effects on starch synthase activity as well as on the metabolism and possibly transport of hexose phosphates are possibilities in accordance with the information available.
Correlation Between the Development of Photorespiration and the Change in Activities of NH3 Assimilation Enzymes in Greening Oat Leaves
Authors: Yu JW , Woo KC
Published: January 2006

The development of photosynthetic capacity and photorespiration during chloroplast development in 7-day-old etiolated oat (Avena sativa L.) primary leaves was investigated together with changes in the activity of possible NH3-assimilating enzymes. The development of photosynthetic CO2 fixation and photorespiration capacity, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glutamine synthetase (GS) activities comparable to green leaves were completed within 48 h of continuous illumination. Chlorophyll synthesis and glutamate synthase (GOGAT) activity continued to increase beyond this time. Within this 48-h period, the activities of Rubisco, GS and GOGAT increased 2.3, 2 and 3 times repectively. Throughout the greening treatment, the GS and GOGAT activities were always high enough to sustain the expected rate of photorespiratory NH3 production. In contrast, glutamate dehydrogenase activity decreased during greening, and its measured rate was not high enough for photorespirtory NH3 assimilation. These results support the idea that the GS/GOGAT pathway is the major, if not the only, route for photorespiratory NH3 assimilation in the light in leaves of higher plants.
Cell-Specific Expression of Rubisco Small Subunit and Rubisco Activase Genes in C3 and C4 Species of Atriplex
Authors: Hudson GS , Dengler RE , Hattersley PW , Dengler G
Published: January 2006

In situ hybridisation techniques have been used to determine the distribution of mRNAs for ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco: EC 4.1.1.39) and Rubisco activase in leaves of Atriplex patula L. (C3) and A. rosea L. (C4). In A. patula, mRNA for Rubisco small subunit (encoded by the rbcS gene family) was found to accumulate in the mesophyll and bundle sheath, while in A. rosea it accumulated in the bundle sheath only, as shown previously for the C4 monocot Zea mays L. The spatial distribution of rca transcripts for Rubisco activase paralleled that for the rbcS transcripts in both C3 and C4 Atriplex species, providing evidence that Rubisco activase is required in cells only where Rubisco is present.
Proteolytic Inactivation of Glutamine Synthetase in Extracts From Wheat Leaves: Effects of pH, Inorganic Ions and Metabolites
Authors: Frohlich V , Fischer A , Ochs G , Wild A , Feller U
Published: January 2006

Glutamine synthetase in extracts from young wheat (Triticum aestivum L.) leaves was quite stable at pH 7.0-9.0, whereas it was remarkably more labile below and above this range. Added extract from senescing wheat leaves accelerated the inactivation over the whole investigated pH range (6.0-10.5) and was most effective around pH 8.5-9.0. At pH 7.5, glutamine synthetase inactivation by endogenous or other supplied endopeptidases was delayed in the presence of magnesium sulfate, magnesium chloride and L-lysine, while potassium chloride stabilised only slightly. No major effect was caused by the addition of sucrose, L-alanine, L-serine or glycine. These results, and the fact that the stabilities of various enzymes are affected differently by the same solutes, suggest stabilising interactions with the substrate protein (glutamine synthetase) rather than effects on the inactivating endopeptidases. From immunoblots, it became evident that the inactivation of glutamine synthetase was paralleled by the degradation of the intact subunit. A smaller fragment was detected on immunoblots during the catabolism of this enzyme. Stabilising solutes retarded the loss of the intact subunit and the formation of the fragment. Solute concentrations must be considered as factors regulating the catabolism of a particular protein by given proteolytic activities.
Growth Strategies of Eucalyptus camaldulensis Dehnh. At Three Sites in Northern Australia
Authors: Gibson A , Bachelard EP , Hubick KT
Published: January 2006

The morphology and physiology of trees of Eucalyptus camaldulensis growing in the field at two monsoonal and one semi-arid location were compared. In the wet season, shoot growth at the monsoonal locations was similar and larger than that at the semi-arid location. In the dry season, new shoot growth at the more humid monsoonal location (Petford) was similar to growth in the wet season while at the less humid (Katherine) and the semi-arid (Tennant Creek) locations, shoot growth was foreshortened and the leaves had larger dry weights per unit area.
In the summer wet season, leaves on both the north and south sides of the trees were maintained at or below (by up to 5�C) air temperatures throughout the day except for north facing leaves at Petford which were consistently above (by up to 3�C) air temperatures. Midday gas exchange in the dry season at both monsoonal localities was restricted to trees at the water's edge, whereas most trees, including those at drier sites, at the semi-arid location exhibited significant rates of gas exchange.
The results, which are discussed in relation to environmental variables (vapour pressure deficits, wind speeds) to which the trees are exposed, and to previous results obtained in the glasshouse, indicate that the differences in shoot growth and physiology are adaptations to the environment in which the trees have evolved.