bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogenase Activity and Associated Carbon Budgets in Seedlings of Acacia mangium Measured With a Flow-Through System of the Acetylene Reduction Assay
Authors: Sun JS , Simpson RJ , Sands R
Published: January 2006

Following introduction of acetylene into the flow-through gas system, nitrogenase activity of young seedlings of Acacia mangiurn Willd. increased during the initial gas mixing period but declined thereafter. Nitrogenase-linked respiration also declined rapidly for 3-4 min and slowly thereafter following introduction of acetylene. Seedlings of 12-42 weeks showed a decline in nitrogenase-linked respiration of 15-40%. Nitrogenase activity and nodulated root respiration declined further when the oxygen concentration in the gas flowing past the nodules was reduced. These concomitant declines in nodulated root respiration and nitrogenase activity were used to explore the relation between nodulated root respiration and nitrogenase activity, and to provide an estimate of the carbon cost of nitrogenase activity, and the growth and maintenance respiration of nodulated roots. The carbon cost of nitrogenase activity was 2-8 μmol CO2 μmol-1 C2H2 reduced for young seedlings (12-20 weeks) and was lower (1.3) for older seedlings (30-42 weeks). Nitrogenase activity was 1.2 μmol C2H4 g-1 nod. dw min-1 for plants at 12 weeks, but was 0.3 μmol C2H4 g-1 nod. dw min-1 for plants at 42 weeks after transplanting. The proportion of nitrogenase-linked respiration in nodulated root respiration also declined rapidly with plant age, being 70% at 12 weeks and only 6% at 42 weeks after transplanting.
Genetic Variation in the Effects of Root Impedance on Growth and Transpiration Rates of Wheat and Barley
Authors: Masle J
Published: January 2006

Genotypes of wheat and barley, including modern and landrace lines, were compared in their response to soil resistance to root penetration during the early vegetative phase (up to 5 leaf stage). All genotypes exhibited reduced growth and transpiration rates at high soil resistance, but there was large variation in the magnitude and time course of these effects and in the mechanisms underlying the growth reduction (changes in net assimilation rate, carbon partitioning within the plant, relative effects of leaf primordia development, versus growth of expanding leaves). Similar wide ranges of responses were observed among landrace and modern wheats. In both wheat and barley, the genotypes with lower sensitivity to soil resistance, in terms of relative growth rate, were those with the slowest net assimilation rate and root growth rate at low soil resistance, and those for which carbon allocation to the impeded roots, relative to the shoot, was significantly increased, to the extent that root relative growth rate even became greater (in terms of mass, not of length) than on loose soil. For a number of genotypes, growth was slowed down throughout the experiment whereas for others it was reduced only during the first few days following germination. In contrast, transpiration rate was at all stages lower at high than at low soil resistance. This indicates that the effects of soil resistance to root penetration on stomatal conductance involve different controls - or different sensitivities to a common signal - from those operating on cell division and expansion.
Carbon Isotope Discrimination and Gas Exchange in Coffea arabica During Adjustment to Different Soil Moisture Regimes
Authors: Meinzer FC , Saliendra NZ , Crisosto C
Published: January 2006

Although carbon isotope discrimination (Δ) has been reported to decline in plants growing under reduced soil moisture, there is little information available concerning the dynamics of adjustments in Δ and gas exchange following a change in soil water availability. In this study Δ, photosynthetic gas exchange, and growth were monitored in container-grown coffee (Coffea arabica L.) plants for 120 days under three soil moisture regimes. At the end of 120 d, total leaf area of plants irrigated twice weekly was one half that of plants irrigated twice daily, although their assimilation rates on a unit leaf area basis were nearly equal throughout the experiment. This suggested that maintenance of nearly constant photosynthetic characteristics on a unit leaf area basis through maintenance of a smaller total leaf area may constitute a major mode of adjustment to reduced soil moisture availability in coffee. Intrinsic water-use efficiency (WUE) predicted from foliar Δ values was highest in plants irrigated weekly, intermediate in plants irrigated twice weekly and lowest in plants irrigated twice daily. When instantaneous WUE was estimated from independent measurements of total transpiration per plant and assimilation on a unit leaf area basis, the reverse ranking was obtained. The lack of correspondence between intrinsic and instantaneous WUE was attributed to adjustments in canopy morphology and leaf size in the plants grown under reduced water supply which enhanced transpiration relative to assimilation. Values of Δ predicted from the ratio of intercellular to ambient CO2 partial pressure determined during gas exchange measurements were not always consistent with measured foliar Δ. This may have resulted from a patchy distribution of stomatal apertures in plants irrigated weekly and from a lag period between adjustment in gas exchange and subsequent alteration in Δ of expanding leaves. The importance of considering temporal and spatial scales, and previous growth and environmental histories in comparing current single leaf gas exchange behaviour with foliar Δ values is discussed.
Effects of Anoxia on Uptake and Loss of Solutes in Roots of Wheat
Authors: Greenway H , Waters I , Newsome J
Published: January 2006

This paper reports on leakage of K+, Cl-, free amino acids and soluble sugars from roots of 4-5-day-old intact wheat seedlings, exposed to anoxia. Leakages were slower from hypoxically than from aerobically pretreated roots. For the first 24 h of anoxia, leakage of K+ and free amino acids was similar, while sugar leakage was slow. Subsequently, leakage of all three solutes usually increased with time. Net losses of K+ and Cl-, after 48 or 72 h exposure of intact seedlings to anoxia, were faster, and/or occurred earlier: (i) in expanding than in expanded root tissues; (ii) at 25� than at 15�C. Re-aeration showed that expanded root tissues retained their capacity to take up K+ and accumulate Cl-, for at least 12 h after the root tips had lost their ability to elongate.
Roots which had lost their elongation potential after 20 h of anoxia, as diagnosed by microscopic observation, still had high solute concentrations in the 1-5 mm and 10-20 mm segments from the root tip, but the 0-1 mm apices had lost 70-90% of their K+, free amino acids and soluble sugars. In contrast, solute concentrations were still high in 0-1 mm tips which had not yet lost their elongation potential. Thus, either irreversible injury of the apices is caused by sudden loss of membrane integrity, or there is another cause of death leading to rapid leakage.
Short-Term Measurements of Carbon Isotope Discrimination in Several C4 Species
Authors: Henderson SA , Caemmerer SV , Farquhar GD
Published: January 2006

Carbon isotope discrimination (Δ) and leaf gas-exchange were measured simultaneously for a number of C4 species. Linear relationships were found between A and the ratio of intercellular to ambient partial pressures of CO2, pI/pa. These data were used to estimate the fraction of CO2 released by C4-acid decarboxylation in the bundle sheath, which subsequently leaks out to the mesophyll. We define this fraction as the leakiness of the system and it is also a measure of the extent to which phosphoenolpyruvate (PEP) carboxylations exceed ribulose 1,5-bisphosphate (RuBP) carboxylations. For Sorghum bicolor and Amaranthus edulis, leakiness was estimated at 0.2 and was constant over a wide range of irradiances (between 480 and 1600 μmol quanta m-2 s-1), intercellular CO2 pressures (between 30 and 350 μbar) and leaf temperatures (from 21�C to 34�C). At irradiances less than 240 μmol quanta m-2 s-1, leakiness appeared to increase. For a number of dicotyledonous and monocotyledonous species, of the various C4-decarboxylation types, leakiness was also estimated at 0.2. Contrary to expectation, amongst the 11 species examined, those with suberised lamellae did not show lower values of leakiness than those without suberised lamellae. For one NAD-ME and one PCK monocot, the estimates of leakiness were significantly higher at 0.30 and 0.25, respectively. Long-term discrimination (assessed from carbon isotope composition of leaf dry matter) did not correlate well with these short- term measures of discrimination. We suggest that this may be due to differences between species in fractionations occurring after photosynthesis.
Construction of an Overlapping YAC Library of the Arabidopsis thaliana Genome
Authors: Schmidt R , Cnops G , Bancroft I , Dean C
Published: January 2006

As part of an international effort to construct an overlapping yeast artificial chromosome (YAC) library of the Arabidopsis thaliana genome, we have been identifying and linking YAC clones that cover the top halves of chromosomes 4 and 5. All the available RFLP markers mapping to these regions were hybridised to filters carrying different YAC libraries. The YAC colonies were arrayed such that an entire library was contained on one small filter, greatly simplifying the screening procedure. The collaborative effort has currently resulted in 30% of the genome being represented in mapped YAC clones. Probes derived from the ends of the YAC inserts, using either inverse polymerase chain reaction (PCR) or left-end rescue, are now being used to walk out to link the YAC clones hybridising to adjacent RFLP markers.
Suppressors of an Arabinose-Sensitive Mutant of Arabidopsis thaliana
Authors: Cobbett CS , Medd JM , Dolezal O
Published: January 2006

Studies of an arabinose-sensitive mutant, ara1-1, of Arabidopsis thaliana, which has reduced arabinose kinase activity, are reviewed. Further studies describe the isolation of suppressor mutations of the arabinose-sensitive phenotype. Neither the ability to metabolise arabinose nor arabinose kinase activity is restored in these suppressed mutants, demonstrating that they are not true revertants. In contrast, in a number of suppressor mutants the ability to metabolise arabinose is further reduced and, in one case, arabinose kinase activity is also further reduced. This observation and genetic studies which show the suppressor mutations are closely linked to the original ara1-1 mutation indicate that both these mutations lie in the same gene. A likely explanation for these observations is that the suppressor mutations block the transport of arabinose into the cell. This suggests a direct or indirect role for the ARA1 gene product in arabinose transport. Further mapping studies of the ARA1 locus are described.
A Model of Nutrient Response in Eucalyptus grandis Seedlings
Authors: Sands PJ , Cromer RN , Kirschbaum MUF
Published: January 2006

Rate of growth in tree seedlings is dependent (amongst other factors) on the rate at which nutrients are absorbed by roots. Rate of nutrient addition to Eucalyptus grandis seedlings influences rate of growth through three main physiological mechanisms: the effects of plant nutrient concentration on biomass partitioning, specific leaf area, and assimilation. A simple dynamic model is presented to describe growth of E. grandis seedlings in response to different relative addition rates of nitrogen and phosphorus as reflected in plant nutrient status. The model takes account of effects of nutrient concentrations on partitioning, specific leaf area and light saturated assimilation rate.
Model simulations demonstrate the influence relative nutrient addition rate has on key processes that influence relative growth rate, and that the relative importance of each of these is dependent on plant nutrient status. If plants are deficient in nitrogen, changes in growth consequent upon improved nutrient status are mediated primarily through effects on assimilate partitioning and light saturated assimilation rate. If plants have high nitrogen status, changes in growth consequent upon improved nutrient status are mediated primarily through effects on specific leaf area. If plants are deficient in phosphorus, changes in growth consequent upon improved nutrient status are mediated through effects on assimilation. If plants have high phosphorus status, changes in growth consequent upon improved nutrient status are mediated through effects on both assimilation and specific leaf area.
Effect of Four Nitrogen Compounds on Nodulation and Nitrogen Fixation in Faba Bean, White Lupin and Medic Plants
Authors: Guo RQ , Silsbury JH , Graham RD
Published: January 2006

A pot experiment with sand as a rooting medium was conducted to investigate the effect of four different nitrogen sources (urea, nitrate, ammonium, nitrate + ammonium) at two concentrations (5 and 10 mM nitrogen) on nodulation and nitrogen fixation in faba bean (Vicia faba L. cv. Fiord), white lupin (Lupinus albus L.) and medic (Medicago rugosa Desr. cv. Paraponto). Results showed that all nitrogen forms were able to suppress nodule formation, nodule growth and nitrogenase activity, measured by acetylene reduction (AR) in all species studied, and the higher concentration had a stronger depressive effect than the lower level. Medic was inhibited most in terms of number of active nodules and AR activity per plant. Among the nitrogen forms, the suppression by NH4Cl was the most severe on nodulation causing the lowest nodule number and nodule weight, and on AR activity in all crops, while urea at 5 mM level seemed to be the least inhibitory. The depressive effect on AR was mainly due to the depressive effect on nodule formation and nodule growth, rather than to a direct influence on nodule specific activity.
Effect of Growth Form, Salinity, Nutrient and Sulfide on Photosynthesis, Carbon Isotope Discrimination and Growth of Red Mangrove (Rhizophora mangle L.)
Authors: Lin GH , Sternberg LDSL
Published: January 2006

The red mangrove (Rhizophora mangle L.), a dominant mangrove species in Florida, frequently occurs in two distinct growth forms, scrub and tall trees. These two growth forms show significant differences in physiology in the field, with lower CO2 assimilation rate, stomatal conductance, and carbon isotope discrimination or higher transpiration efficiency for the scrub form. To elucidate the possible factors responsible for these physiological differences, we studied the physiological and growth responses of scrub and tall red mangrove seedlings grown hydroponically in the greenhouse under 12 different growth conditions combining three salinities (100, 250, 500 mM NaCl), two nutrient levels (10, 100% strength of full nutrient solution), and two sulfide concentrations (0, 2.0 mM Na2S). The two growth forms showed similar physiological and growth responses to these treatments, suggesting no genetic control of physiological and growth differences between the growth forms of this species. High salinity, low nutrient level, and high sulfide concentration all significantly decreased CO2 assimilation, stomatal conductance, and plant growth, but only salinity significantly decreased intercellular CO2 concentration and leaf carbon isotope discrimination, suggesting that the lower carbon isotope discrimination, or higher transpiration efficiency, observed for scrub mangroves in the field is caused only by high salinity during the dry season. Hypersalinity thus seems to be one of the stressful environmental conditions common to all scrub red mangrove forests studied in southern Florida.
Water Relations in Cowpea and Pearl Millet Under Soil Water Deficits. III. Extent of Predawn Equilibrium in Leaf Water Potential
Authors: Petrie CL , Hall AE
Published: January 2006

Pearl millet [Penniseturn americanum (L.) Leeke] consistently develops lower predawn leaf water potentials than cowpea [Vigna unguiculata (L.) Walp.] when plants are subjected to progressive soil drying, even when they are grown as intercrops in the same pot. Lack of equilibrium in water potential during the predawn, within the plants and between plants and soil, was studied as a possible explanation for this difference. Experiments were conducted in a glasshouse in pots containing an artificial rooting medium which had a high water-holding capacity and was easy to separate from roots. Leaf and root predawn xylem water potentials were measured with a pressure chamber. In cowpea, leaf water potential (ΨL) values during the dry treatment were similar to values of root water potential (ΨR), indicating an approximate equilibrium within the plants. In millet, measurements were made on plants grown in both large and small pots. With large pots, ΨL and ΨR values in millet were similar, but with small pots, predawn ΨL was lower than ΨR. When the surfaces of these small pots were covered with evaporation barriers, however, no significant differences developed between ΨL and ΨR at predawn during soil drying, indicating an approximate equilibrium within millet. During the early stages of the dry treatment, leaf surface conductances measured at predawn indicated that significant water flux occurred at night from the leaves of both cowpea and millet. Leaf surface conductances declined to negligible levels as the dry treatment progressed, however, and night-time fluxes of water from leaves cannot explain the significant difference in predawn ΨL that developed between cowpea and millet. In order to determine whether the lower predawn ΨL in millet was due to a resistance to water uptake at the root surface, an osmoticum (- 0.5 MPa mannitol solution) was applied to pots of cowpea and millet intercrops after substantial differences in predawn ΨL had developed, and ΨL was measured. Measurements taken 9 h later indicated that predawn ΨL had recovered in millet, and the values of ΨL in millet and cowpea after mannitol treatment were similar to the osmotic potential of the mannitol solution. These results suggest that the lower predawn ΨL in millet than in cowpea under drought is due to the development of a substantial soil resistance to water movement to the root surfaces of millet.
Roles of Carbon Gain and Allocation in Growth at Different Nitrogen Nutrition in Eucalyptus camaldulensis and Eucalyptus globulus Seedlings
Authors: Sheriff DW
Published: January 2006

Potted Eucalyptus camaldulensis and E. globulus seedlings were grown in sand with added mineral nutrients. Mineral nitrogen was added, either (1) only a small initial quantity (N1) or (2) regularly (N2). Other nutrients were supplied regularly to both treatments. Biomass increment and nutrient concentrations of organs and gas exchange of leaves were measured. Growth, foliage area, and foliar N concentration changed little in N1 seedlings, all increased exponentially in N2 seedlings. Partitioning of dry matter and nitrogen was unaffected by ontogeny or treatment in E. globulus, but changed with time in E. camaldulensis. Within a treatment biomass increase was similar for both species, but foliar biomass and area, total foliar N, and response of carbon assimilation to foliar N were greater in E. globulus. Effects of these on carbon assimilation were partly offset by higher foliar N concentrations in E. camaldulensis. Comparative growth rates of the species were not related to leaf area.
Carbon assimilation and diffusive conductance were linearly related with different relationships for the two treatments. Intercellular partial pressures of CO2 were constant at c. 300 and 220 μPa Pa-1 in N1 and N2 treatments of both species. This indicates a controlling mechanism that maintained intercellular CO2 constant, but was affected by treatment. Instantaneous potential assimilatory transpiration efficiency [(rate of carbon assimilation)/(rate of transpiration)] and instantaneous potential assimilatory nitrogen use efficiency [(rate of carbon assimilation)/(N content)] of leaves (at saturating light) were similar in the two species and showed treatment effects apparently not caused by foliar N concentration. These efficiencies were generally high compared to values published for woody plants.
A simple model illustrates the importance in predicting growth of accurately knowing: foliage mass, partitioning of biomass to foliage, and rates of carbon assimilation. Effects of small differences in carbon assimilation on biomass increment are shown to be potentially large because they can cause accumulation of large differences in foliar mass.
Evidence for the Involvement of Glycollate Synthesis in the Stimulation of Glycerate Uptake by Light in Isolated Chloroplasts
Authors: Yu JW , Woo KC
Published: January 2006

The glycerate/glycollate (Glc) translocator in chloroplasts of C3 plants mediates the initial export of glycollate from and the final import of glycerate into the chloroplasts during photorespiration. Glycerate uptake into oat (Avena sativa L.) chloroplasts was stimulated by light. Studies with a single-layer (SL) and a stable double-layer (SDL) silicone oil system indicated that this light stimulatory effect was caused, at least in part, by glycollate synthesised during the pre-illumination period. Firstly, preincubation with glycerate and glycollate increased [14C]glycerate uptake to an extent similar to the stimulation by light. Secondly, [14C]glycerate uptake was not inhibitied by 3-(3',4'-dichloropheny1)-1, 1-dimethylurea and carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone when it was measured in a short time (2 s) in the SDL system. Thirdly, inhibition of ribulose 1,5-bisphosphate oxygenation (and so glycollate synthesis) by KCN abolished the observed stimulation of [14C]glycerate uptake in the light.
Thidiazuron Induces High-Frequency Shoot Regeneration in Intact Seedlings of Pea (Pisum sativum), Chickpea (Cicer arietinum) and Lentil (Lens culinaris)
Authors: Malik KA , Saxena PK
Published: January 2006

Axenic seedling cultures of chickpea (Cicer arietinum L.), lentil (Lens culinaris Medik.) and garden pea (Pisum sativum L.) were established by culturing mature seeds on Murashige and Skoog medium (MS) supplemented with thidiazuron (TDZ). Of various cytokinins or compounds with cytokinin-like activity (Kinetin, TDZ, Zeatin) tested for inducing shoot formation in pea seeds cultures, TDZ was found to be most effective. Pea seedlings exhibited a unique pattern of shoot formation which was accomplished in two distinct phases. Multiple shoots developed within a week, from the nodal and basal regions of the primary epicotyl in a medium that contained 5-50 μM TDZ. When these seedlings were exposed for a prolonged time period (3-4 weeks), to the same medium, numerous shoot buds emerged de novo from the base and/or from the upper part of multiple shoots. These shoots had no apparent vascular connection with parent tissues. The inductive capability of TDZ was then tested in several other genotypes of Pisum sativum and two other large-seeded grain legumes, Cicer arietinum, and Lens culinaris. In Cicer arietinum, and Lens culinaris, multiple shoots developed after 1 week of seed culture on media that contained 1-50 μM TDZ. However, de novo differentiation of shoot buds occurred in cultures exposed to TDZ for 4-6 weeks, only from nodal and subjacent areas. Secondary shoot formation occurred frequently in all of the species tested. Developing shoots were able to form roots and eventually whole plants on a modified MS medium containing 2.5 μM NAA. No genotypic difference for morphogenesis was observed.
Immunocytochemical Localisation of Nodule-Specific Sucrose Synthase in Soybean Nodules
Authors: Zammit A , Copeland L
Published: January 2006

The distribution of the nodule-specific form of sucrose synthase (nodulin-100) in soybean nodules has been studied by immunocytochemical methods. Ultrathin sections were labelled with immunogold, and semi-thin sections with immunogold followed by staining with silver. The enzyme was located in the host cytosol, and was present to a much greater extent in uninfected inner cortical cells and interstitial cells than in infected cells. This adds further evidence that conversion of sucrose to dicarboxylic acids takes place to a greater extent in uninfected inner cortical cells and interstitial cells, than in infected cells.
The Effect of Chloramphenicol on Photoinhibition of Photosynthesis and Its Recovery in Intact Kiwifruit (Actinidia deliciosa) Leaves
Authors: Greer DH , Laing WA , Woolley DJ
Published: January 2006

Photoinhibition of photosynthesis in kiwifruit [Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson] leaves in high light and its subsequent recovery in low light was assessed in the presence of chloramphenicol (CAP), an inhibitor of chloroplast-encoded protein synthesis. Rooted cuttings were grown in a controlled environment at a photosynthetic irradiance of 700 μmol m-2 s-1 and a day/night temperature of 25/20�C. Time-courses of photoinhibition and recovery treatments were followed by measuring CO2 exchange and chlorophyll fluorescence at 77K and 692 nm.
CAP both exacerbated photoinhibition and blocked recovery for at least 150 min, especially at high temperatures. The close conformation of these two effects affirm that photoinhibition and recovery occur concomitantly. There was no apparent effect of CAP on the xanthophyll cycle, either during photoinhibition or recovery, indicating that zeaxanthin-mediated non-radiative energy (thermal) dissipation was unaffected by CAP. Because the CAP-induced increase in photoinhibition was not matched by an increase in the ratio of zeaxanthin to violaxanthin and antheraxanthin, the capacity of this photoprotective mechanism was apparently saturated.
The primary effect of CAP on chlorophyll fluorescence was to affect Fm, the maximum fluorescence. There was only a minor effect on the initial fluorescence, Fo, during the photoinhibition and recovery treatments. The calculation of the rate constants for non-radiative dissipation (kD) and photochemistry (kp) from the fluorescence measurements indicated that an increase in kD occurred during high-light exposures and this was stimulated by CAP. However, since zeaxanthin was not mediating this, an alternative quencher in kiwifruit leaves, perhaps damaged PSII centres, is proposed. This would be consistent with an increased inactivation of PSII, as indicated by the changes in kp.
Physiological Adaptation to High Ion Concentrations or Water Deficit by Callus Cultures of Highbush Blueberry, Vaccinium corymbosum
Authors: Muralitharan MS , Chandler SF , Steveninck RFMV
Published: January 2006

Callus cultures of highbush blueberry were selected for 10 passages on medium supplemented with 50 rnol m-3 NaCl, 50 rnol m-3 KCl, 25 mol m-3 Na2SO4, 25 mol m-3 K2SO4 or 100 mol m-3 mannitol. On all salts, growth of selected callus was greater (200-250%) than that of non-selected callus, and selected callus grew optimally on the type of salt on which it was selected. Conventional (whole plant analysis) and electron probe X-ray microanalysis showed that selected callus accumulated more ions (approximately 1.5-3.0-fold) than non-selected callus on all salts, and there was a positive correlation between vacuolar ion concentration and fresh weight.
Growth of NaCl-selected callus but not non-selected callus was greatly enhanced (2.25-fold) in the presence of 100 mol m-3 mannitol, while growth of a mannitol-selected callus line was also enhanced.
In callus grown on NaCl or mannitol, slight increases in levels of glycinebetaine, choline and proline were measured. Sucrose, glucose, fructose, sorbitol and malate concentrations significantly increased in callus grown on NaCl or mannitol, and selected callus produced 4-fold more sugars than non-selected callus. The total increases in concentrations of all measured sugars were 210 μmol gFW-1 in NaCl-selected callus grown on 50 mol m-3 NaCl, and 296 μmol gFW-1 in mannitol selected callus grown on 100 rnol m-3 mannitol.
The results of this study indicate that adaptation of blueberry callus cultures for optimal growth on salt-containing media is probably due to adaptation to water stress, not tolerance to specific ions. Osmotic adjustment, achieved by ion uptake and production of sugars, appears to be the physiological mechanism of adaptation.
Perturbed Leaf Development in Sorghum bicolor Exposed to Salinity: a Marker of Transition Towards Adaptation
Authors: Seligmann H , Amzallag GN , Lerner HR
Published: January 2006

Pretreatment for 3 weeks with NaCl, within the range 35-150 mol m-3, of 8 day old Sorghum bicolor cv. 610, results in adaptation of the plants to high salinity; plants become tolerant to 300 mol m-3 NaCl, which is lethal for unadapted plants. During the adaptation period one or more developmentally perturbed leaves (DPL) may occur. DPL formation is positively correlated with the mean relative growth rate (RGR) of the plant following exposure to 300 mol m-3 NaCl, which reflects the degree of adaptation to high salinity. Treatments with exogenous phytohormones affect both DPL formation as well as the adaptation response. When plants 14 days old or more are exposed to salinity, neither adaptation nor DPL formation occurs, demonstrating the existence of a developmental window during which these phenomena may take place. These data suggest that DPL does not result from salt damage to the plant, but rather that it should be considered as a marker of the adaptation process.
Osmotic Adjustment in Water Stressed Grapevine Leaves in Relation to Carbon Assimilation
Authors: Rodrigues ML , Chaves MM , Wendler R , David MM , Quick WP , Leegood RC , Stitt M , Pereira JS
Published: January 2006

The response of grapevine plants to severe water deficit (predawn leaf water potential of - 1.13 MPa), imposed at a rate of about 0.16 MPa day-1 was studied in terms of leaf water relations characteristics, stomatal behaviour and gas exchange. Carbohydrate status of leaves was also analysed in order to assess the contribution of soluble sugars as osmotic solutes during drought. Pressure/volume analysis showed an active osmotic adjustment in water-stressed leaves, which decreased osmotic potential at full turgor by 0.45 MPa and the apoplastic water fraction showed a reduction of 19% as compared to the well- watered plants. Cell wall elasticity was not significantly affected by water stress, and turgor loss point in stressed leaves was reached at lower water potential and relative water content values than in the well-watered controls. Photosynthesis was markedly reduced in water-stressed plants. However, well-watered and water-stressed leaves had similar concentrations of glucose and fructose. The concentrations of sucrose and starch decreased in water-stressed leaves. This accounted for a marked decrease in the ratio of leaf dry weight to area in droughted plants. The changes in concentrations of soluble carbohydrates could not account for the difference in osmotic potential between water-stressed and well-watered leaves.
Mechanisms of Sugar Uptake Into Endosperm and Aleurone Protoplasts Isolated From Developing Wheat Grains
Authors: Niemietz C , Jenner CF
Published: January 2006

Grain-filling in cereals depends upon imported assimilates, and in wheat all assimilates entering the grain pass through the endosperm cavity which is part of the apoplast separating the maternal from the filial generation. The outermost layer of the endosperm, the aleurone layer is in contact with the contents of the endosperm cavity. Entry into the endosperm necessitates passage through the plasmalemma. Putative mechanisms involved in the transport of carbohydrate into the endosperm have been evaluated by characterising the mechanism(s) transporting sugars into protoplasts prepared from cells isolated from the aleurone layer and the starchy endosperm separately.
Protoplasts obtained from both types of cells absorbed sucrose, glucose and fructose by diffusion. Only in the case of sucrose uptake by aleurone protoplasts was there evidence for a saturable carrier mechanism. Based on calculated rates of uptake by the protoplasts it can be estimated that transport by diffusion is sufficiently fast to support observed rates of starch synthesis, and that carrier mediated transport of sucrose can account for only a small fraction of the total import.
Regulation by Gibberellins of the Orientation of Cortical Microtubules in Plant Cells
Authors: Shibaoka H
Published: January 2006

Gibberellins control the direction of expansion of plant cells. They change the orientation of cellulose microfibrils by changing the orientation of cortical microtubules and, hence, the direction of cell expansion. When gibberellins change the orientation of cortical microtubules, they also change their stability. If the way in which gibberellins change the orientation of microtubules is identical to the way in which they change microtubule stability, then studies on the mechanism that regulates this stability should give us some clues to the mechanism that regulates the orientation of microtubules. With this possibility in mind, we undertook a series of studies on the stability of cortical microtubules. These revealed that the association of cortical microtubules with the plasma membrane is an important part of the mechanism for their stabilisation. Gibberellins seem to change the stability of microtubules by affecting their association with the plasma membrane. To study the way in which the gibberellins affect this association, it is necessary to clarify the molecular architecture of the structure that links cortical microtubules with the plasma membrane.
p34cdc2 Related Proteins in Control of Cell Cycle Progression, the Switch Between Division and Differentiation in Tissue Development, and Stimulation of Division by Auxin and Cytokinin
Authors: John PCL , Zhang K , Dong C , Diederich L , Wightman F
Published: January 2006

Progress through the plant cell cycle involves changes of phosphorylation state and catalytic activity in p34cdc2 -like protein. The plant protein has protein kinase activity, binds p13suc1, copurifies with cyclin B-like protein and its catalytic activation at mitosis is shown, by a metaphase arresting mutant, to be tightly coupled to cyclin accumulation and breakdown. These properties correlate with findings in other laboratories that some plant cdc2 genes can complement the yeast cdc2 gene. Activation of p34cdc2 at mitosis is proposed to trigger preprophase band breakdown since these two events continue in cells inhibited with okadaic acid although completion of chromosome condensation and spindle formation, which normally precede breakdown, do not occur and are therefore not triggers. In plant development the level of this key division protein relative to other proteins declines in cells entering division to less than one-tenth of that in dividing cells and resumption of division follows restoration of the level in all tissues that have been tested, including cotyledon, stem pith and root. Hormonal induction of division revealed tissue-specific differences in effects of individual hormones on p34cdc2-like protein accumulation and its catalytic activation. In tobacco pith, auxin could induce synthesis of p34cdc2-like protein but cytokinin was necessary for its activation and for cell cycle activity. Within the cell cycle, hormone-dependent control points were identified at late G1 and at mitotic initiation by measurement of nuclear DNA content and the timing of activation of p34cdc2 and cell division, in Nicotiana suspension culture cells restimulated with hormone. Auxin was required at both control points, but cytokinin was required only at mitotic initiation. A direct effect of auxin on cdc2 gene expression is indicated by an increase of cdc2 mRNA levels within 10 min of exposing root tissue to 3-indolylacetic acid (IAA).
Modulation of Plant Gene Expression by Cytokinins
Authors: Chen CM , Jin G , Andersen BR , Ertl JR
Published: January 2006

Cytokinins play important roles in plant growth and development. They regulate the synthesis or degradation of proteins and nucleic acids. Specific mRNAs and proteins are up- and down-regulated by the hormones. Regulation of plant gene expression by cytokinins is at the levels of transcription and post-transcription. Expression of a single gene can be modulated by the interaction of two hormones since the levels of cytokinin-enhanced nitrate reductase transcript are reduced by abscisic acid. Relatively high-affinity cytokinin-binding proteins have been isolated, but the physiological role of the binding proteins remains unknown. Examination of X-ray crystal structures of cytokinin molecules indicates that correct stereochemical conformation is required for a biologically active cytokinin. Using available genetic, immunological, biochemical and recombinant DNA techniques, some questions regarding the mechanisms of cytokinin action may be answered in the near future.
The Physiology of Flower Induction — Paradigms Lost and Paradigms Regained
Authors: Evans LT
Published: January 2006

Three aspects of the physiology of flowering - namely photoperiodic time measurement, the florigen hypothesis, and models for floral differentiation - are examined in relation to T.S. Kuhn's concept of paradigms.
AC Impedance Measurements on Chara corallina. III. Characterisation of the Plasma Membrane Coat Using a New Presentation of Impedance Spectra
Authors: Chilcott TC , Coster HGL
Published: January 2006

It has been shown that the measurement of electrical impedence can provide a non-invasive approach to detect the presence of the plasma membrane coat (PMC). Further, the measurements provide an estimate of the geometrical properties of plasmalemmasomes (charasomes) which are similar to estimates determined from electron micrographs. Impedance measurements were made in the range of 1-104 Hz. A transfer (network) function with either four or five time constants was fitted to the spectra. We present transfer functions as spectra in which peaks are observed at the reciprocal of these time constants. We call the reciprocal time constants frequency constants.
Our analysis suggests that two peaks in the frequency range of 1-102 Hz arise from the series combination of the plasmalemma and tonoplast and a peak at very high frequencies (>>104 Hz) arises from the static cytoplasm.
The remaining two peaks in the frequency range of 102-103 Hz we attribute to the presence of the PMC. The peak at the higher frequency we ascribe to the PMC along smooth sections of plasmalemma and that at the lower frequency we ascribe to the PMC in plasmalemmasomes (charasomes). We found that this peak was not present in spectra obtained from cells without plasmalemmasomes.
Our model for the ultrastructure of the PMC and plasmalemmasomes is in good agreement with electron micrographs of these regions. Additionally, our measurements give a physiological range for the electrical properties of the PMC. Conductance and capacitance ranges are 13.6-52 S m-2 and 6.7-17 mF m-2 respectively.
Effect of Uv Radiation on Endogenous Inhibitors of Growth in the Hypocotyl of Phaseolus vulgaris
Authors: Kato-Noguchi H , Sumitomo M
Published: January 2006

In order to correlate the role of endogenous inhibitors of growth of bean plants with the inhibition of such growth by UV radiation, a search for specific growth inhibitors was undertaken using the neutral and acidic fractions of acetone extracts from the hypocotyls of UV-irradiated bean seedlings (Phaseolus vulgaris L. cv. Morocco). Tho neutral and two acidic inhibitors were isolated and they were named N-1 and N-2 (neutral inhibitors) and A-1 and A-2 (acidic inhibitors), respectively, on the basis of the order of their elution from a silica-gel column. Variations in the activity of the inhibitors in hypocotyls of two cultivars (cvv. Morocco and Kentucky 101) after the onset of UV radiation were determined by use of a bean bioassay, and results were compared with those of UV-induced inhibition of growth. The growth of hypocotyls of the two cultivars decreased rapidly. However, the more noticeable change was a marked decrease in the growth of the hypocotyls of cv. Morocco. On the other side, the difference in the activity of N-1 between the two cultivars was particularly great, and the changes with time in levels of N-1 in hypocotyls of each cultivar matched the time course of the UV-induced inhibition of growth of hypocotyls of the same cultivar. No such correlation was found with N-2, A-1 and A-2. These results suggest that the activity of N-1 may serve to distinguish the growth habit of the two cultivars to UV radiation.
Carbohydrate Storage and Mobilisation by the Culm of Wheat Between Heading and Grain Maturity: the Relation to Sucrose Synthase and Sucrose-Phosphate Synthase
Authors: Wardlaw IF , Willenbrink J
Published: January 2006

Wheat plants grown under non-stress conditions at a dayhight temperature of 18/13�C under glasshouse conditions from head emergence to maturity showed a maximum accumulation of water-soluble, non-structural carbohydrates 20-25 days after anthesis. This storage was largely as fructans with the timing and amount of storage and mobilisation varying between cultivars, although the maximum concentration (fructose equivalents per unit stem fresh weight) was similar in all cultivars. The main storage in the culm was located in the lower part of the peduncle enclosed by the flag leaf sheath, in the penultimate internode and for one cultivar also in the flag leaf sheath. 14CO2 pulse-chase studies showed that there was a considerable delay in the incorporation of flag leaf assimilates into stem fructans, a delay probably associated with transfer and metabolic processes in the stem itself.
At anthesis, when soluble carbohydrates were rapidly accumulating in the culm, the level of activity of sucrose synthase (SS) in the penultimate internode was much greater than that of sucrose phosphate synthase (SPS). The activity of SS declined rapidly as active storage ceased. This pattern was the reverse of that found in the leaf where SPS, rather than SS, was initially high and declined towards maturity. These changes are discussed in relation to the possible role of sucrose synthesising enzymes, particularly SS, in the accumulation and mobilisation of stem reserves in wheat.
Leaf Hairs of Olive (Olea europaea) Prevent Stomatal Closure by Ultraviolet-B Radiation
Authors: Grammatikopoulos G , Karabourniotis G , Kyparissis A , Petropoulou Y , Manetas Y
Published: January 2006

In olive (Olea europaea L.), hair removal had no effect on the photosynthetic rate and the apparent leaf resistance to water vapour diffusion in leaves illuminated with white light (900 μmol m-2 s-1 photosynthetically active radiation) devoid of ultraviolet-B radiation. In addition, intact and dehaired leaves showed no significant differences in absorptance in the visible spectral region, while leaf temper- ature was independent of hair removal. These results indicate that leaf hairs of O. europaea may play only a marginal role in leaf energy balance and transpiration. When the white light was supplemented with ultraviolet-B radiation (5.89 W m-2), however, there was a considerable decrease in the photo- synthetic rate, and a simultaneous increase in leaf resistance to water vapour in dehaired leaves. Photochemical efficiency of photosystem II, evaluated from chlorophyll fluorescence emitted from the illuminated side, was reduced in all cases, but the reduction in dehaired, ultraviolet-B treated leaves was more pronounced and irreversible, indicating that the reduction of the photosynthetic rate may result from both stomatal limitation and electron flow inhibition. Photosynthetic capacity of dehaired leaves, measured at 5% CO2, however, was not influenced by ultraviolet-B radiation. We suggest, therefore, that ultraviolet-B radiation reduces photosynthetic rates by closing the stomata, while the observed reduction in photosystem II photochemical efficiency may concern only a superficial chloroplast population, contributing negligibly to whole leaf photosynthesis. Under the conditions of our experi- ments, the protective function of the indumentum against ultraviolet-B radiation predominates over the water conservation function.
Sensitivity of Wheat Phasic Development to Major Environmental Factors: a Re-Examination of Some Assumptions Made by Physiologists and Modellers
Authors: Slafer GA , Rawson HM
Published: January 2006

In this review we assess the universality of several assumptions that are commonly made about development in wheat. The assumptions tested are that:
(1) wheat is most sensitive to the environmental variables of temperature and photoperiod during the vegetative period;
(2) any responses to vernalisation and photoperiod are complete by the time that the apex has become reproductive and the stems begin to elongate;
(3) cultivars differ little in their responses to temperature aside from any responses to vernalisation;
(4) cultivar differences in 'intrinsic earliness' or 'basic development rate' are unaffected by temperature;
(5) photoperiod and vernalisation responses are quantitative and that these responses are well understood and can be generalised.
We show that, in terms of development, all wheats are responsive to temperature throughout their life cycles though to differing degrees, most are responsive to photoperiod at least until heading and, contrary to expectations, with potentially increasing sensitivity once the flowering process is triggered, and many are responsive to a memory of vernalising temperatures to well beyond the double ridge stage. In all these responses we show that there is considerable genotypic variation and that it is usually difficult to guess the responses of one genotype to the main environmental variables from the responses of another. This is partially because overall sensitivity to each of the main variables can differ, and the responses can be interactive, but also because the primary responses and interactions can differ between developmental phases. This can result in a high level of complexity of response whenever any variable is changed. The level of complexity is a negative feature when it comes to modelling and forecasting responses across widely differing environments but a highly positive feature when considering the enormous genotypic variation available for selection.
Base Temperatures for Growth Processes of Lychee, a Recurrently Flushing Tree, Are Similar but Optima Differ
Authors: Batten DJ , Lahav E
Published: January 2006

Potted plants of cultivars 'Haak Yip' (Hei Ye), 'Tai So' (Da Zao) and 'Bengal' were grown in temperature-controlled glasshouse rooms at 10, 15, 20, 25, 30 or 35�C to determine cardinal temperatures for various growth processes. At other times plants of cvv. 'Brewster' (Chen Zi), 'Kwai May Pink' and 'Wai Chee' (Huai Zhi) were grown at various constant temperatures and cvv. 'Tai So' and 'Wai Chee' were grown at 27/21�C and 18/12�C (12 h day/12 h night). A modified Richards' function accurately described leaflet elongation with time. Functions fitted to derived parameters of maximum relative elongation rate and duration allowed the accurate determination of minimum and optimum cardinal temperatures for leaflet elongation. The maximum temperature for leaf elongation was well in excess of 35�C. Other processes studied included shoot elongation, increase in leaf area per plant, dry matter (DM) production, new shoot DM, DM partitioning between roots, shoots and leaves, flush periodicity, leaf morphology and total non-structural carbohydrate (TNSC) status. The minimum temperatures were similar for different processes whereas the optimum temperatures determined were different. These are compared, along with data from published studies on other physiological processes of lychee. Leaflet elongation occurred at a significantly higher optimum temperature than DM accumulation, a difference which could not be attributed to effects of temperature on partitioning, and is probably facilitated by the recurrent flushing mode of growth of lychee. There were few differences between the cultivars. 'Haak Yip' growth appeared to be more tolerant of high temperatures than 'Tai So' or 'Bengal' and 'Bengal' had higher leaf concentrations of TNSC at moderate to high temperatures. A model relating shoot periodicity to temperature (heat units) is suggested which could help in studying the relationship between flushing and flower initiation.