bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of maintenance respiration in plant growth
Authors: AMTHOR JEFFREY S. 
Published: April 2006

Abstract Plant growth is the balance of photosynthetic gains and respiratory losses, and it is therefore essential to consider respiration in analyses of plant productivity. The partitioning of dark respiratory losses into two functional components, a growth component and a maintenance component, has proved useful. The growth loss is that associated with synthesis of new biomass while the maintenance loss is that associated with maintenance of existing biomass.Experimental evidence indicates that the respiratory cost of maintenance in herbaceous plants is about equal to the cost of growth over a growing season, with daily maintenace expenditures less important in the small, rapidly growing plant but increasing in significance as plant size increases and the relative growth rate decreases. Because it is such a large fraction of the total carbon budget of a plant, any variations in maintenance requirements may result in significant alterations in productivity. In the present work the theoretical and empirical bases of maintenance respiration are described: magnitudes of maintenance expenditures are summarized; and applications to models of plant growth and productivity are discussed. It is concluded that the costs of maintenance should be included in analyses of plant growth.
Concurrent measurements of stem density, leaf and stem water potential, stomatal conductance and cavitation on a spaling of Thuja occidentalis L.
Authors: DIXON M. A. , GRACE J. , TYREE M. T. 
Published: April 2006

Abstract Concurrent estimates of stem density, leaf and stem water potential, stomatal conductance and ultrasonic acoustic emissions (cavitations) in an excised sapling of Thuja occidentalis L. were made. As the sapling dehydrated in air, the decline in leaf water potential to about ‐ 2.0 MPa was followed by apparent rehydration of the foliage while the stem showed no sign of rehydration. The rate of acoustic emissions peaked prior to the onset of rehydration which coincided with virtual stomatal closure. There was a significant decline in stem density until maximum foliage rehydration level was reached. From this point, leaf water potential, stem water potential and stem density continued a relatively slow decline while acoustic emission rate and stomatal conductance remained low.Removal of the bark and majority of foliage from the sapling resulted in increased cavitation and more rapid deelines in leaf and stem water potential and stem density.
Nutrient inflows into apple roots. I. 32P‐orthophosphate uptake from solution by M.9 rootstocks and Worcester Pearmain seedlings
Authors: BHAT K. K. S. 
Published: April 2006

Abstract. The rates of uptake of 32P‐labelled orthophosphate by whole root systems of young apple trees (M.9 rootslocks and Worcester Pearmain seedlings) were measured in solution culture. Using a solution depletion technique, the 32P‐phosphate uptake rates per unit length, surface area or fresh weight of roots were determined as a function of 32P‐phosphate concentration in solution at the root surface over the range 0.25–10 mmol m−3. The effect of P concentration within various plant parts on the relation between uptake rate and external P concentration was studied using plants differing in internal P levels.The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m−3. Fluxes, inflows and unit absorption rates increased approximately proportionately with solution concentration up to 10mmolm−3. Except perhaps in the case of the low‐P M.9 plant, there was no evidence of a diminishing returns type of relationship over the range of solution concentrations examined. The threshold P concentration in solution above which uptake rates cease to increase thus appears to be higher for apples than for other species.At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low‐P plants than for high‐P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P.
Effect of water stress on the enzymes of nitrogen metabolism in mung bean (Vigna radiata Wilczeck) nodules
Authors: KAUR AMARJIT , SHEORAN I. S. , SINGH RANDHIR 
Published: April 2006

Abstract. Water stress created by withholding irrigation in mung bean resulted in decreased leaf water potential and nodule moisture content. Decreased leaf water potential was associated with decreased activity of nitrogenase, glutamine synthetase (GS), asparagine synthetase (AS), aspartate amino transferase (AAT), xanthine dehydrogenase (XDH) and uricase. However, the activity of glutamate dehydrogenase increased three‐fold under severe stress. The activity of allantoinase and allantoicase was not affected by moderate stress but decreased under severe stress. The in vitro production of allantoic acid from allantoin and uric acid in the cytosol fraction decreased more than its production from xanthine and hypoxanthine. The production of NADH also decreased under stress.During recovery from severe stress, the activity of XDH and uricase further decreased, whilst that of allantoinase and allantoicase increased compared to the control. This corresponded with the higher content of ureides during recovery. The recovery in other enzymes was not complete although leaf water potential and nodule moisture content recovered fully within 24 h.
Diurnal cycles of leaf extension in unsalinized and salinized Beta vulgaris
Authors: WALDRON L. J. , TERRY N. , NEMSON J. A. 
Published: April 2006

Abstract. Continuous high resolution measurement of sugar beet leaf extension over 5 d in growth chambers showed average leaf extension rates (LER) in darkness to be from three to six times those in light for plants growing in non‐salinized media. The changes in LER in light‐dark transitions occurred within seconds, a response which was more rapid than stomatal opening or closing. When the growth medium was salinized to 100 mol m−3 NaCl, LER's were reduced by about 50% in darkness and 90% in light, markedly increasing the ratio of dark to light LER.A 2‐d episode of root‐zone salinity imposed midway through a 5‐d period of measurement decreased LER and produced higher leaf temperatures. LER and diurnal leaf temperature patterns reverted to their pre‐salinized levels when root‐zone salinity was removed. Thus, the effects of short episodes of high sodium chloride in the growth medium appear to be reversible, suggesting a water stress mechanism of growth reduction rather than toxicity effects of salt.
Estimation of Tissue Construction Cost from Heat of Combustion and Organic Nitrogen Content
Authors: WILLIAMS K. , PERCIVAL F. , MERINO J. , MOONEY H. A. 
Published: April 2006

Abstract. We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency (EB). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost.
Leaf Diffusive Conductance and Tap Root Cell Turgor Pressure of Sugarbeet
Authors: PALTA J. A. , WYN‐JONES R. G. , TOMOS A. DERI 
Published: April 2006

Abstract. The interrelationships of leaf diffusive conductance, tap root cell turgor pressure and the diameter of the tap root of sugarbeet were studied. The study was conducted on well‐watered plants growing in pots under artificial light in the glasshouse. In a typical experiment, on illumination (400 μmol m−2 s−1) leaf conductance increased from 0.6 to 7.4 mm s−1. Cell turgor pressure in the tap root decreased from 0.8 MPa to 0.45 MPa and the root diameter (9.0 cm) contracted by 145μm. Removal of light resulted in the reversal of each of the above parameters to their previous values. Quantitively similar results were obtained when sugar beet plants were uprooted and the response of each of the parameters was measured. The sequence of events however was different. On stimulation by light, changes in leaf diffusive conductance preceded the turgor and root diameter changes (which were simultaneous) by some 15–20min. In contrast, on uprooting the simultaneous changes in root turgor pressure and diameter preceded the changes in leaf conductance. The lag times between changes in diffusive conductance and turgor pressure in the root were between 20 and 30 min.Tap root turgor pressure and diameter correlated strongly and permitted the calculation of an apparent whole root volumetric elastic modules (55–63 MPa). The small changes in tissue volume relative to the transpiration rate suggest that the tap root is not a significant source of transpirational water during the day.
Water translocation inKalanchoë daigremontianaduring periods of drought
Authors: SCHÄFER C. , LÜTTGE U. 
Published: April 2006

Abstract.Kalanchoë daigremontianastrongly reduced daily water loss within 6 d of drought using CAM to restrict transpiration and net CO2uptake to the dark period.Water translocation from old to young leaves of the plant was an additional mechanism which reduced the negative effects of drought on the water relations of young leaves. Excision of old leaves after 7–9 d of drought resulted in a decrease in the water content of young leaves. This was observed despite a decrease in transpirational water loss from young leaves. Water content in young leaves increased slightly in plants with all their leaves in place.The dry weight of young leaves clearly increased during the experimental period when old leaves were present, but it remained relatively constant in plants without old leaves. Obviously, in addition to water, solutes were transported from old to young leaves of the plant via the phloem. Xylem tension was higher in young compared to old leaves; thus, water translocation could have occurred via xylem elements.Since transport of organic matter in the phloem is also linked to water flow, phloem transport additionally may contribute effectively to the balance of the water budget in young leaves.
Concentrations of CO2 and O2 in floodwater and in internodal lacunae of floating rice growing at 1–2 metre water depths
Authors: SETTER T. L. , KUPKANCHANAKUL T. , KUPKANCHANAKUL K. , BHEKASUT P. , WIENGWEERA A. , GREENWAY H. 
Published: April 2006

Abstract. Environment and plant measurements were made to determine what factors may limit growth of deepwater and floating rice plants during partial or complete submergence. Field surveys included measurements of temperature, pH, light, O2 and CO2 in floodwater in Thailand. In addition, measurements were made of O2 and CO2 concentrations inside internodal lacunae of deepwater and floating rice growing at 0.5–2.0 m water depths.The bulk of measurements were taken during periods when the changes in water level were less than 50 mm d−1. In the 0–0.02 m surface layer of floodwater at any location there were large changes in oxygen concentrations over diurnal cycles: there were decreases during the night down to 0.02–0.18 mol m−3 O2 at 0600 h and increases during the day to 0.13–0.28 mol m−3 O2 at 1500 h (0.28 mol m−3 being 120% of the O2 concentration of air saturated water at 30°C). During the day oxygen concentrations decreased with increasing water depth; concentrations just above the soil surface were occasionally zero. Most of this gradient disappeared during the night, and at dawn the 0.6 m surface layer of water had uniform low O2 concentrations.O2 concentrations were also measured during flash floods in Thailand. In contrast to the conditions with only small increases in water level, the O2 concentrations in the water during flash floods were more uniform with depth and changed little over a diurnal cycle, the O2 ranging between 0.14–0.19 mol m−3.In most locations floodwater contained 0.2–1.9 mol m−3 CO2 and 0.7–1.6 mol m−3 bicarbonate; however, in a location with acid sulphate soil CO2 was only 0.05–0.2 mol m−3, and bicarbonate concentrations were several fold lower. Concentrations of CO2 in floodwater increased with increasing water depth.O2 and CO2 concentrations inside internodal lacunae of rice were determined in the field when water depth were 1–2 m. Concentrations of O2 in internodes at the water surface were 16–20%, and decreased to 10% and 5% at 0.8 and 1.8 m water depth respectively. There was no diurnal cycle in O2 concentrations inside internodes. In contrast, CO2 concentrations in the lacunae increased with water depth and ranged from 1–3% in internodes at the water surface to 5–10% in internodes at 1.8 m water depth. There was evidence for a diurnal cycle in CO2 concentrations in the basal internode near the soil surface, CO2 increased during the day and decreased during the night.The above data are used to show that there is little or no relationship between gas concentrations in floodwater and internodal lacunae of rice plants. Results are discussed in relation to O2 supply to submerged portions of rice and metabolism of these tissues at low O2 concentrations.
The citrus leaf cuticle in relation to measurement of leaf water potential using thermocouple psychrometers*
Authors: OOSTERHUIS D. M. , PARKER M. L. , WULLSCHLEGER S. D. , KIM K. S. 
Published: April 2006

Abstract. Cuticular resistance to water vapour diffusion is an important aspect of thermocouple psychrometry and may introduce significant error in the measurement of leaf water potential (Ψ). The effect of the citrus (Citrus mitis Blanco) leaf cuticle on water vapour movement was studied using the times required for vapour pressure equilibration during thermocouple psychrometric measurement of Ψ. Cuticular abrasion with various carborundum powders was used to reduce the diffusive resistance of both the adaxial and abaxial leaf surfaces, and the extent of the disruption to the leaf was investigated with light and electron microscopy.Cuticular abrasion resulted in reduced equilibration times due to decreased cuticular resistance and greater water vapour movement between the leaf and the psychrometer chamber. Equilibration times were reduced from over 5 h in the unabraded control leaves to 1 h with cuticle abrasion. This was associated with the decrease in diffusive resistance with cuticular abrasion from over 55 s cm−1 to less than 8 s cm−1 for both the adaxial and abaxial leaf surfaces.Scanning electron micrographs of the abraded leaf tissue revealed considerable disruption of the stomatal ledge and of the guard cells, surface smoothing and displacement of waxes into the stomatal aperture, and damage to veins. Observations with the transmission electron microscope revealed frequent disruption of epidermal cell walls, and damage to both the cytoplasmic and vacuolar membranes.
A dynamic model for photosynthesis by an aquatic plant,Egeria densa
Authors: LAING W. A. , BROWSE J. 
Published: April 2006

AbstractThis paper describes a dynamic model for photosynthesis by an aquatic plant,Egeria densa.The model takes into account an HCO−3pump, high diffusion resistances and PEP carboxylase, and develops a set of differential equations to form the time‐dependent solutions for photosynthesis. The predicted changes in pH, [CO2]aqand total inorganic carbon are compared with experimental data and the model is found to describe the data.The model is then used to examine the effect of O2on photosynthesis under these conditions, and shows that the increase in internal CO2concentration due to the recycling of photorespiratory CO2directly stimulates gross CO2fixation and can more than compensate for the O2inhibition of gross photosynthesis. The importance of the HCO−3pump in O2inhibition is also examined.The CO2compensation point (where inorganic carbon influx and efflux are equal) is examined and the importance of the HCO−3pump and PEP carboxylase in reducing the compensation concentration is discussed.The model was developed in order to study the photosynthesis of an aquatic weed, which will be reported in a later paper.
NaCl effects on 4‐desmethylsterol composition of plasma‐membrane‐enriched preparations from citrus roots
Authors: DOUGLAS T. J. 
Published: April 2006

Abstract The free 4‐desmethylsterol composition of plasma‐membrane‐enriched preparations from white fibrous roots of Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. kharna Raf.) and Etrog citron (C. medica L.) seedlings grown in the presence of 0, 50, or 100 mol m−3 NaCl for 28 d was quantitated by gas chromatography (GC) on analytical capillary (SE‐54 fused silica) columns and the sterols were identified by combined gas chromatography‐mass spectrometry (GC‐MS).Only three 4‐desmethylsterols were positively identified by GC‐MS, viz. campesterol, stigmasterol and sitosterol. Cholesterol could not be positively identified in any of the membrane preparations. Campesterol levels were generally similar for all treatments and for all three genotypes, approximating 30% of the total free 4‐desmethylsterol content of the plasma membranes. At all levels of salinity (0, 50 or 100 mol m−3 NaCl) sitosterol levels decreased in the order Rangpur lime > Kharna khatta > Etrog citron and stigmasterol levels decreased in the reverse order. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron at each level of salinity and was reduced by salt treatment in all three genotypes.Salt‐induced reductions in the ratio of ‘more planar’ to ‘less planar’ sterols correlated inversely with the accumulation of Cl− in the leaves of the three genotypes suggesting a role for plasma membrane sterols in the Cl− exclusion mechanism. A model relating sterol structure, membrane sterol composition and membrane permeability to Cl− exclusion ability in citrus is presented.
Phospholipid, galactolipid and free sterol composition of fibrous roots from citrus genotypes differing in chloride exclusion ability
Authors: DOUGLAS T. J. , SYKES S. R. 
Published: April 2006

Abstract Fibrous roots of four citrus hybrids and parent rootstocks from which the hybrids were generated, all selected for their different Cl− exclusion abilities, were assayed for phospholipid, galactolipid and free 4‐desmethylsterol content. There was no correlation between a plant's ability to exclude Cl− and the level of either phospholipid, galactolipid, or total free sterol in the roots of control plants. However, an inverse correlation was established between the ratio of phospholipid to free sterol in control roots and total leaf Cl− levels of plants treated with 50 mol m−3 NaCl for 56 d.With the exception of a significant decrease in hybrid 80‐05‐05, galactolipid levels were unaffected by salt treatment. Phospholipid levels were significantly increased in two parent rootstocks viz. Trifoliate orange (Poncirus trifoliata (L.). Raf.) and Carrizo citrange (Citrus sinensis (L.) Osbeck ×P. trifoliata) and one hybrid (80‐02‐08) but were otherwise unchanged by salt treatment. Free sterol levels were significantly increased by salt treatment in all of the better Cl− excluders except Carrizo citrange i.e. in Rangpur lime (Citrus reticulata Blanco var. austera hybrid?), Cleopatra mandarin (Citrus reticulata Blanco) and all hybrids except 80–05–13. In all genotypes examined, salt‐treatment resulted in a significant decrease in the ratio of sitosterol to stigmasterol reflecting, primarily, an increase in the stigmasterol level. The two poorer Cl− excluders (Trifoliate orange and hybrid 80–05–13) both underwent a significant decrease in the ratio of ‘more planar’ to ‘less planar’ sterols.The inverse correlation between the phospholipid to free sterol ratio of control plants and leaf Cl− level of salt treated plants suggests that this ratio has the potential to be used as a biochemical marker of Cl− exclusion ability in citrus.
Stomatal mechanism as the basis of the evolution of CAM and C4 photosynthesis
Authors: COCKBURN W. 
Published: April 2006

Abstract. The similarities between the component reactions of the presently known variants of photosynthetic carbon metabolism (crassulacean acid metabolism, the acid metabolism of Tillandsia usneoides, aquatic acid metabolism, and C4 photosynthesis) when considered along with their widely scattered taxonomic distribution strongly suggest polyphyletic origins resulting from evolutionary modification of a common, universally distributed metabolic sequence. The synthesis and consumption of four‐carbon acids in the cation‐balancing reactions involved in the regulation of stomatal aperture appear to exhibit all of the characteristics likely to be displayed by such a metabolic progenitor.The present status of the proposal that the expression of aspects of stomatal metabolism in photosynthetic mesophyll cells represents the basis for the evolution of the variant of photosynthetic carbon metabolism is discussed. The prospects of experimental approaches which may yield information relevant to the proposal are also explored.
The uptake of inorganic carbon by freshwater plants
Authors: WALKER N. A. 
Published: April 2006

Abstract. The uptake of bicarbonate for photosynthetic assimilation by charophyte plants uses a chemiosmotic mechanism involving primary outward active transport of H+ in ‘acid zones’ of the membrane, and passive H+ re‐entry in spatially separate ‘alkaline’ zones. In the process large electric currents circulate in the medium, and large local pH changes occur; bicarbonate ions, diffusing inwards across the unstirred layer of medium, encounter a number of competing mechanisms for the transfer of the carbon across the membrane. These are:

transport of H2CO3 by diffusion
transport of CO2 by diffusion; or
co‐transport of HCO3 and H+.

The decision amongst these mechanisms is not yet possible. There are parallels between the charophytes and aquatic angiosperms that are indicated, and contrasts with the chlorophytes.