bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acclimation processes in the light harvesting complex of the red alga Porphyridium purpureum (Bory) Drew et Ross, according to irradiance and nutrient availability
Authors: ALGARRA P. , RUDIGER W. 
Published: April 2006

ABSTRACTThe time‐course of acclimation (0‐5h) of the red alga Porphyridium purpureum with respect to total proteins, phycoerythrin (PE) and phycobilisomes (PBS) has been studied at different N availability and different light regimes. After a high N input, acclimation takes place in two phases. The first one, which is photoindependent is characterized by simultaneous increase of proteins and PE. At low N input, this first phase is not detected. In the second phase the PE content increases only under low light together with an increase of the PBS size, followed probably by an increase in the number of PBS. The effectiveness of the energy transfer increases under these conditions. A rapid decrease in the PBS size correlated with a decrease of the energy transfer is observed at high irradiance. Free PE plays an important role in the organization‐disorganization of the PBS at low N concentration (inverse correlation between free PE and PE attached to PBS). Free PE is not accumulated in the cell after a high N input at high irradiance. Independently of photoacclimation, two species of PBS appear with different PE content and different capacities to aggregate with other compounds. A clear correlation appears between the level of coupling of the PBS and the fluorescence ‘in vivo’ of the whole cells. The comparison between dissociated and undissociated PBS as well as between PBS obtained after the different acclimation processes allows the determination of the presence of two linker polypeptides probably associated with B‐PE (37 and 32–5 kDa) and two associated with PC and APC (27 and 25 kDa). That suggests that acclimation of PBS requires a parallel stoichiometric response of biliproteins and the linker polypeptides involved in the efficiency of the energy transfer.
Root growth as a function of ammonium and nitrate in the root zone
Authors: BLOOM A. J. , JACKSON L. E. , SMART D. R. 
Published: April 2006

ABSTRACTWe examined the effect of soil NH4+ and NO3− content upon the root systems of field‐grown tomatoes, and the influence of constant, low concentrations of NH4+ or NO3− upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH4+ or NO3−; they increased to a maximum in zones having 2μg‐N NO3− g−1 soil and 6 μg‐N NO3= g−1 soil, but decreased in zones having higher NH4+ or NO3− levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH4+ or NO3−, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO3−. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH4+ and NO3−.
Modulation of photosynthesis and respiration in guard and mesophyll cell protoplasts by oxygen concentration
Authors: MAWSON B. T. 
Published: April 2006

ABSTRACTStomatal movement is an energetic oxygen‐requiring process. In the present study, the effect of oxygen concentration on mitochondrial respiratory activity and red‐light‐dependent photosynthetic oxygen evolution by Vicia faba and Brassica napus guard cell protoplasts was examined. Comparative measurements were made with mesophyll cell protoplasts isolated from the same species. At air saturated levels of dissolved oxygen in the protoplast suspension media, respiration rates by mesophyll protoplasts ranged from 6 to 10μmoles O2 mg−1 chl h−1, while guard cell protoplasts respired at rates of 200–300 μmoles O2 mg chl−1 h−1, depending on the species. Lowering the oxygen concentration below 50–60 mmol m−3 resulted in a decrease in guard cell respiration rates, while rates by mesophyll cell protoplasts were reduced only at much lower concentrations of dissolved oxygen. Rates of photosynthesis in mesophyll cell protoplasts isolated from both species showed only a minor reduction in activity at low oxygen concentrations. In contrast, photosynthesis by guard cell protoplasts isolated from V. faba and B. napus decreased concomitantly with respiration. Oligomycin, an inhibitor of oxidative phos‐phorylation, reduced photosynthesis in mesophyll cell protoplasts by 27–46% and in guard cell protoplasts by 51–58%. The reduction in both guard cell photosynthesis and respiration following exposure to low oxygen concentrations suggest close metabolic coupling between the two activities, possibly mediated by the availability of substrate for respiration associated with photosynthetic electron transport activity and subsequent export of redox equivalents.
The effects of external NaCl on thylakoid stacking in lettuce plants
Authors: CARTER D. R. , CHEESEMAN J. M. 
Published: April 2006

ABSTRACTThe average degree of thylakoid stacking was determined for loose‐leaf lettuce plants which were grown in complete nutrient solutions containing either 10 or 100mol m−3NaCl. Digitonin fractionation and differential centrifugation were used to assay the level of thylakoid stacking. Based on a comparison between 10mol m−3NaCl‐grown and 100mol m−3NaCl‐grown lettuce plants of equal ages, digitonin assays indicated that significantly less stacking occurred in 100mol m−3NaCl‐grown plants. Isolated thylakoid membranes from 100mol m−3NaCl‐grown plants were also characterized by a greater capacity to absorb divalent cations and by a higher chlorophylla/bratio. Since plants from both growth salinities were capable of a marked increase in thylakoid stacking upon a transition from high to low irradiance, the observed differences in thylakoid stacking were not attributed to a salinity‐related impairment of stacking mechanisms. Instead, the salinity‐induced differences in thylakoid stacking appear to represent a process of controlled adjustment.
Photoinhibition of isolated mesophyll cells from cold‐hardened and non‐hardened winter rye
Authors: LAPOINTE L. , HUNER N. P. A. 
Published: April 2006

ABSTRACTCold‐hardened rye leaves have been shown to be more resistant to low temperature photoinhibition than non‐hardened rye leaves. Isolated mesophyll cells from winter rye (Secale cereale L. cv. Musketeer) were exposed to photoinhibitory light conditions to estimate the importance of leaf morphology and leaf optical properties in the resistance of cold‐hardened rye leaves to photoinhibition. Cold‐hardened rye cells showed more resistance to photoinhibition than non‐hardened rye cells when monitored with chlorophyll a variable to maximal fluorescence ratio (Fv/Fm). Thus, leaf morphology does not contribute to the resistance of cold‐hardened rye leaves to low temperature photoinhibition. However, cold‐hardened and non‐hardened rye cells showed a similar extent of photoinhibition when photsynthetic CO2 fixation rates were measured. They also showed the same capacity to recover from photoinhibition. During both photoinhibition and recovery, Fv/Fm and light limited CO2 fixation rates showed different kinetics. We propose that inactivation and subsequent reactivation during recovery of some light activated Calvin cycle enzymes explain the greater extent of photoinhibition of light limited CO2 fixation and its faster recovery compared to Fv/Fm kinetics during photoinhibition.
Extraction of water from Eucalyptus trees for analysis of deuterium and oxygen‐18: laboratory and field techniques
Authors: THORBURN P. J. , WALKER G. R. , BRUNEL J.‐P. 
Published: April 2006

ABSTRACTThis study investigated a methodology for sampling and extracting water from Eucalyptus spp. for analysis of stable isotopes of water. Firstly, water of known isotopic composition was extracted from stems of seedlings of Eucalyptus spp. by azeotropic distillation using three solvents (hexane, toluene and kerosene) in laboratory and glasshouse experiments. Kerosene and toluene gave the most accurate extractions, with a small negative bias (∼‐2‰ for δ2H and ∼‐0.4‰ for δ18O) due to incomplete extraction. This bias was not evident in further experiments, using kerosene, where water was extracted from stems and roots that had been pre‐treated in a manner that more closely reflected field conditions. Secondly, variation in δ2H in trees was investigated in the field to determine an accurate and convenient place for sampling. There was no significant difference in δ2H between water extracted from trunk sapwood and whole twigs, even twigs close to leaves, in samples taken from four Eucalyptus spp. at two field sites. The results mean that the most convenient part of the tree can be sampled. Also, there was little difference in δ2H between sapwood and heart‐wood samples, although small increases (∼ 2‰) in δ2H were observed in bark of trunks and twigs. Tree roots (15–25 mm diameter) had similar δ2H values to the surrounding soil in many cases, especially surface (<0.2 m depth) roots, rather than having δ2H values similar to twigs of the trees. These roots were absorbing water from surrounding soil, but not contributing significant quantities of water to the tree canopy. Thus, the δ2H of root water is not a good indicator of the isotopic composition of water in the upper parts of Eucalyptus trees.
Limitation of transpiration by hydraulic conductance and xylem cavitation in Betula occidentalis
Authors: SPERRY J. S. , POCKMAN W. T. 
Published: April 2006

ABSTRACTThe extent to which stomatal conductance (gs) was capable of responding to reduced hydraulic conductance (k)and preventing cavitation‐inducing xylem pressures was evaluated in the small riparian tree, Betula occidentalis Hook. We decreased k by inducing xylem cavitation in shoots using an air‐injection technique. From 1 to 18 d after shoot injection we measured midday transpiration rate (E), gs, and xylem pressure (Ψp‐xylem) on individual leaves of the crown. We then harvested the shoot and made direct measurements of k from the trunk (2–3 cm diameter) to the distal tip of the petioles of the same leaves measured for E and gs. The k measurement was expressed per unit leaf area (kl, leaf‐specific conductance). Leaves measured within 2 d of shoot injection showed reduced gs and E relative to non‐injected controls, and both parameters were strongly correlated with kl At this time, there was no difference in leaf Ψp‐xylem between injected shoots and controls, and leaf Ψp‐xylem was not significantly different from the highest cavitation‐inducing pressure (Ψp‐cav) in the branch xylem (‐1.43 ± 0.029 MPa, n=8). Leaves measured 7–18 d after shoots were injected exhibited a partial return of gs and E values to the control range. This was associated with a decrease in leaf Ψp‐xylem below Ψp‐cav and loss of foliage. The results suggest the stomata were incapable of long‐term regulation of E below control values and that reversion to higher E caused dieback via cavitation.
The effects of enhanced ozone and enhanced carbon dioxide concentrations on biomass, pigments and antioxidative enzymes in spruce needles (Picea abies L.)
Authors: POLLE A. , PFIRRMANN T. , CHAKRABARTI S. , RENNENBERG H. 
Published: April 2006

ABSTRACTDuring one growing period, 5‐year‐old spruce trees (Picea abies L., Karst.) were exposed in environmental chambers to elevated concentrations of carbon dioxide (750 cm3 m−3) and ozone (008 cm3 m−3) as single variables or in combination. Control concentrations of the gases were 350cm3 m−3CO2 and 0.02 cm3 m −3 ozone. To investigate whether an elevated CO2 concentration can prevent adverse ozone effects by reducing oxidative stress, the activities of the protective enzymes superoxide dismutase, catalase and peroxidase were determined. Furthermore, shoot biomass, pigment and protein contents of two needle age classes were investigated. Ozone caused pigment reduction and visible injury in the previous year's needles and growth reduction in the current year's shoots. In the presence of elevated concentrations of ozone and CO2, growth reduction in the current year's shoots was prevented, but emergence of visible damage in the previous year's needles was only delayed and pigment reduction was still found. Elevated concentrations of ozone or CO2 as single variables caused a significant reduction in the activities of superoxide dismutase and catalase in the current year's needles. Minimum activities of superoxide dismutase and catalase and decreased peroxidase activities were found in both needle age classes from spruce trees grown at enhanced concentrations of both CO2 and ozone. These results suggest a reduced tolerance to oxidative stress in spruce trees under conditions of elevated concentrations of both CO2 and ozone.
Effects of water velocity on photosynthesis and dark respiration in submerged stream macrophytes
Authors: MADSEN T. V. , ENEVOLDSEN H. O. , JØRGENSEN T. B. 
Published: April 2006

ABSTRACTThe effects of flow velocities on dark respiration and net photosynthesis of eight submerged stream macrophytes were examined in a laboratory oxygen chamber. The shoots/leaves were exposed to saturating free‐CO2 concentrations and were attached basally so that they could move in the flowing water. Net photosynthesis declined by 34–61% as flow velocity increased from 1 to 8.6cm s−1, while dark respiration increased 2.4‐fold over the same range. The increase in dark respiration could only account for between 19 and 67% of the decrease in net photosynthesis. The relationship between flow velocity (U) and net photosynthesis (P) was described by: P=b×Ua. The exponent, a, varied from ‐0.20 to –0.48 and showed a negative correlation to the surface: volume (SA: V) ratio of the plants, i.e. species with high SA: V ratio were more sensitive to flow. In contrast, net photosynthesis of plants firmly attached to a supporting frame was not significantly affected by increasing flow velocity. This result indicates that the physical stress imposed on the plants by agitation or stretching in the flowing water is a key factor for the observed response.
Sodium relations in Chenopodiaceae: a comparative approach
Authors: REIMANN C. , BRECKLE S.‐W. 
Published: April 2006

ABSTRACTSodium relations of 15 species of Chenopodiaceae were studied in seedlings grown on quartz sand at 10 mol m−3 of sodium and potassium. Uptake of sodium and potassium into whole plants and shoots was followed over 2 weeks. High alkali ion uptake rates were found in all species. The apparent selectivity of alkali ion uptake showed a continuous variation between species, from nearly perfect sodium exclusion to negligible cation selection. K/Na ratios above 6 were found in the shoots of eight species. For most of these plants above ground sodium concentrations were highest in the hypocotyls. However, in Chenopodium hybridum (shoot K/Na = 10) and C. urbicum (shoot K/Na = 17) above ground sodium concentrations were lowest in hypocotyls and highest in leaves, as in those species accumulating larger amounts of sodium. These differences are discussed with respect to the underlying mechanisms of ion regulation.
Plastid‐localized 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate synthase (DS‐Mn): the early‐pathway target of sequential feedback inhibition in higher plants
Authors: DOONG R. L. , GANSON R. J. , JENSEN R. A. 
Published: April 2006

ABSTRACTA plastid‐localized isozytne of 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate (DAHP) synthase, denoted DS‐Mn, has been identified in a number of higher‐plant species. Parallel characterizations were made of DS‐Mn from Spinacia oleracea leaf tissue, Solanum tuberosum tubers, and Nicotiana silvestris suspension culture as sources of enzyme from plant materials which vary in phytogeny, developmental and tissue state, and physiological state. A highly conserved property of DS‐Mn is a transition between inactive and active states, mediated by DTT as a hysteretic activator. A procedure for isolation of DS‐Mn in the labile, inactive state is given. The process of activation appears to exhibit a higher pH optimum than the catalytic optimum. DTT‐containing preparations are very stable. The enzyme characteristically exhibits stimulation by Mn++ in the range of 45–50%, relatively high affinity for erythrose‐4‐phosphate (E4P), dramatic substrate inhibition above about 0.5mol m−3 E4P, sigmoid substrate saturation curves for both E4P and phosphoenolpyruvate, and inhibition by L‐arogenate (competitive against E4P and non‐competitive against PEP). DS‐Mn has a relatively high temperature optimum in the range of 45–50°C. Enzyme activity was lost when bound metal was stripped away by EDTA treatment. Reconstitution of the native‐enzyme level of activity was obtained with Ca++, and additional stimulation was achieved with Mn++. DS‐Mn control by L‐arogenate in the chloroplast is proposed as one key circuit in an overall pattern of allosteric control for the entire pathway of aromatic amino acid biosynthesis. This pattern is called sequential feedback inhibition. The potential for modulation of this control system by environmental cues induced by light‐dark transitions is discussed.
Stomatal control by both [ABA] in the xylem sap and leaf water status: a test of a model for draughted or ABA‐fed field‐grown maize
Authors: TARDIEU F. , ZHANG J. , GOWING D. J. G. 
Published: April 2006

ABSTRACTA model of maize stomatal behaviour has been developed, in which stomatal conductance is linked to the concentration of abscisic acid ([ABA]) in the xylem sap, with a sensitivity dependent upon the leaf water potential (Ψ1). It was tested against two alternative hypotheses, namely that stomatal sensitivity to xylem [ABA] would be linked to the leaf‐to‐air vapour pressure difference (VPD), or to the flux of ABA into the leaf. Stomatal conductance (gs) was studied: (1) in field‐grown plants whose xylem [ABA] and Ψ1 depended on soil water status and evaporative demand; (2) in field‐grown plants fed with ABA solutions such that xylem [ABA] was artificially raised, thereby decreasing gs and increasing Ψ1 and leaf‐to‐air VPD; and (3) in ABA‐fed detached leaves exposed to varying evaporative demands, but with a constant and high Ψ1. The same relationships between gs, xylem [ABA] and Ψ1, showing lower stomatal sensitivity to [ABA] at high Ψ1, applied whether variations in xylem [ABA] were due to natural increase or to feeding, and whether variations in Ψ1, were due to changes in evaporative demand or to the increased Ψ1 observed in ABA‐fed plants. Conversely, neither the leaf‐to‐air VPD nor the ABA flux into the leaf accounted for the observed changes in stomatal sensitivity to xylem [ABA]. The model, using parameters calculated from previous field data and the detached‐leaf data, was tested against the observations of both ABA‐fed and droughted plants in the field. It accounted with reasonable accuracy for changes in gs (r2 ranging from 0.77 to 0.81). These results support the view that modelling of stomatal behaviour requires consideration of both chemical and hydraulic aspects of root‐to‐shoot communication.
Stomatal and environmental control of transpiration in a lowland tropical forest tree
Authors: MEINZER F. C. , GOLDSTEIN G. , HOLBROOK N. M. , JACKSON P. , CAVELIER J. 
Published: April 2006

ABSTRACTStomatal control of crown transpiration was studied in Anacardium excelsum, a large‐leaved, emergent canopy species common in the moist forests of Central and northern South America. A construction crane equipped with a gondola was used to gain access to the uppermost level in the crown of a 35‐m‐tall individual. Stomatal conductance at the single leaf scale, and transpiration and total vapour phase conductance (stomatal and boundary layer) at the branch scale were measured simultaneously using the independent techniques of porometry and stem heat balance, respectively. This permitted the sensitivity of transpiration to a marginal change in stomatal conductance to be evaluated using a dimensionless coupling coefficient (1‐ω) ranging from zero to 1, with 1 representing maximal stomatal control of transpiration. Average stomatal conductance varied from 0.09 mol m−2 s−1 during the dry season to 0.3 mol m−2 s−1 during the wet season. Since boundary layer conductance was relatively low (0.4 mol m−2 s−1), 1‐ω ranged from 0.46 during the dry season to only 0.25 during the wet season. A pronounced stomatal response to humidity was observed, which strongly limited transpiration as evaporative demand increased. The stomatal response to humidity was apparent only when the leaf surface was used as the reference point for measurement of external vapour pressure. Average transpiration was predicted to be nearly the same during the dry and wet seasons despite a 1 kPa difference in the prevailing leaf‐to‐air vapour pressure difference. The patterns of stomatal behaviour and transpiration observed were consistent with recent proposals that stomatal responses to humidity are based on sensing the transpiration rate itself.
Stress perception and response in a facultative halophyte: the regulation of salinity‐induced genes in Mesembryanthemum crystallinum
Authors: VERNON D. M. , OSTREM J. A. , BOHNERT H. J. 
Published: April 2006

ABSTRACTThe facultative halophyte Mesembryanthemum crystallinum (ice plant) shifts from C3 to CAM photosynthesis in response to water stress. The switch to CAM can also be induced by high salinity, presumably because osmotic stress causes water loss from leaf and stem tissues. A number of mRNAs (Ppc1, Imt1, B5 and Gpd1) that encode proteins involved in different biochemical pathways accumulate in M. crystallinum leaf tissues when plants are salt‐stressed. We hypothesized that environmental challenges that result in water stress invoke a common mechanism that triggers the coordinated induction of mRNAs involved in different aspects of the ice plant's adaptive stress response. Nuclear run‐on experiments indicated that Ppc1, Imt1, B5 and Gpd1 are all transcriptional I y activated in salt‐stressed leaf tissue. However, a comparison of Ppc1, Imt1, and B5 transcript levels after exposure of plants to growth regulators (6‐benzylamino purine and abscisic acid) and to different environmental stress treatments that affect plant water status (drought, low temperature and salinity) indicated that, despite the coordinated transcriptional activation of these genes during salt stress, their repsonses to other stimuli that also upset water balance are not the same. Our results are consistent with a model involving multiple control mechanisms governing stress perception and molecular response in the ice plant.
Influence of electrolytes on growth, phototropism, nutation and surface potential in etiolated cucumber seedlings
Authors: SPALDING E. P. , COSGROVE D. J. 
Published: April 2006

ABSTRACTA variety of electrolytes (10–30 mol m−3) increased the relative growth rate of etiolated cucumber (Cucumis sativus L. cv. Burpee's Pickler) hypocotyls by 20–50% relative to water‐only controls. The nonelectrolyte mannitol inhibited growth by 10%. All salts tested were effective, regardless of chemical composition or valence. Measurements of cell‐sap osmolality ruled out an osmotic mechanism for the growth stimulation by electrolytes. This, and the nonspecificity of the response, indicate that an electrical property of the solutions was responsible for their growth‐stimulating activity. Measurements of surface electrical potential supported this reasoning. Treatment with electrolytes also enhanced nutation and altered the pattern of phototropic curvature development. A novel analytical method for quantitating these effects on growth was developed. The evidence indicates that electrolytes influence an electrophysiological parameter that is involved in the control of cell expansion and the coordination of growth underlying tropisms and nutations.