bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calcium transport between tissues and its distribution in the plant
Authors: CLARKSON DAVID T. 
Published: April 2006

Abstract. The low cytosol concentration of free Ca2+ makes the symplast of roots an ineffective pathway for the supply of the calcium needed for healthy growth in the aerial parts of plants. Ca2+ moves rapidly across the cortical apoplast by diffusion and mass flow but is probably diverted across the plasmamembranes of endodermal cells by Casparian bands. A proposal is made to account for the movement of calcium across the endodermis and it is estimated that Ca‐fluxes are likely to be appreciably greater than in the regulation of cell Ca level by cortical cells.Ca transport in the xylem occurs by mass flow of free Ca2+, and some organically complexed Ca, and by chromatographic movement along Ca‐exchange sites in the xylem walls. Delivery of Ca to transpiring leaves and to weakly transpiring meristematic zones is discussed in relation to the two modes of Ca movement in the xylem. Competition between sinks is intensified when [Ca2+] in xylem is low and transpiration is great.Tropic growth responses involve pumping of vacuolar calcium into the apoplast followed by its migration along gradients of electrical potential which develop in the apoplast after geo‐stimulation. An attempt is made to estimate plasmalemma efflux during this process.Redistribution from mature tissues to meristems in the pholem is likely to be small, if it occurs at all, since sieve tubes cannot have more than micro‐molar concentrations of free‐Ca2+ in them.
Calcium in plant senescence and fruit ripening
Authors: FERGUSON I. B. 
Published: April 2006

Abstract. Calcium has long been associated with regulation of the ripening process of fruit and post‐harvest storage life. Specifically, maintenance of relatively high calcium concentrations in fruit tissue results in a slower rate of ripening, as seen in lower respiration rates, reduced ethylene production, and slower softening of fruit flesh. There are also some specific fruit disorders such as bitter pit, which can be prevented if sufficient calcium is present. Senescence of other plant tissues such as leaves and flowers has also been shown to be retarded by the application of calcium.Work leading to the above information is reviewed and discussed in the context of what is currently known of cellular regulation of calcium in plants. The major sites for the action of calcium in senescence and ripening are suggested to be in membrane structure and function, and in cell wall structure. Although high external concentrations of calcium are an advantage in reducing the rate of senescence or ripening, it is emphasized that normal cell function requires the maintenance of low concentrations of free calcium in the cell cytosol. It is suggested that one possible feature of senescence is a breakdown in such cellular regulation.
Effects of weak acids on proline accumulation in barley leaves: a comparison between abscisic acid and isobutyric acid
Authors: PESCI P. , BEFFAGNA N. 
Published: April 2006

Abstract. When isobutyric acid (IBA) or abscisic acid (ABA) are supplied to leaf sections a similar rapid and marked decrease in the intracellular pH is observed. This acidification is accompanied by an increase in proline level which is about the same for both 3 mol m−3 IBA and 1 mol m−3 ABA treatments.Fusicoccin (FC), known to act at the proton pump level, almost completely suppresses the ABA‐induced acidification of the cell sap, whereas it only partially counteracts the acidifying effect of IBA, in particular during short periods of treatment. This effect of FC is paralleled by a similar inhibition of the induced proline accumulation: in fact, FC completely suppresses the ABA‐induced increase in proline during short treatment periods, whereas it is only effective in inhibiting the IBA‐induced proline accumulation after long treatment periods.These data seem to suggest that the ABA‐ and IBA‐induced changes in proline level might be mediated by changes in the intracellular pH.
Determination of free space, growth, solute concentrations and parameters of water relations of suspension‐cultured tobacco cells
Authors: DRACUP M. , GIBBS J. , STUIVER C. E. E. , GREENWAY H. , FLOWERS T. J. 
Published: April 2006

Abstract Methods were developed for measuring water content of the free space of suspension‐cultured tobacco cells using 3H‐ or 14C‐sorbitol. Sorbitol was not taken up by cells in significant quantities over the 3 min taken to label free space. Free space accounted for 50–60% of the water content of cell pellets irrespective of whether 3H‐ or 14‐C‐sorbitol was used. 14C‐inulin labelled 13.5% less of the water in cell pellets than 3H‐sorbitol, probably due to inadequate penetration by inulin into the free space in the cell wall matrix and within clumps of cells. Measurement of free space is necessary for measuring growth on a fresh or dry weight basis, solute concentrations and parameters of water relations of cells. Techniques for making these measurements on tobacco cells were also developed in this study.Solutes were measured after extraction from cells by expressing sap or by boiling cells in ethanol. Similar solute concentrations were found using both methods of extraction. By expressing sap from cells grown in culture medium with an osmotic pressure of 0.24 MPa, the cells were found to have an internal osmotic pressure of 0.70 MPa. Glucose, fructose, sucrose, amino acids and K+ accounted for 60% of this osmotic pressure. Elastic moduli were estimated using the Boyle‐Van't Hoff relationship after suspending cells in solutions with different osmotic pressures and assessing their water content or internal osmotic pressure. For two different lines of tobacco cells, elastic modulus varied between 1 MPa and 5.4 MPa at turgor pressures of 0.15–0.52 MPa (line 1) and between 0.2 MPa and 4.2 MPa at turgor pressures of 0.04–0.26 MPa (line 2).
A field portable gas‐exchange system for measuring carbon dioxide and water vapour exchange rates of leaves during fumigation with SO2
Authors: ATKINSON C. J. , WINNER W. E. , MOONEY H. A. 
Published: April 2006

Abstract A field portable, steady‐state gas‐exchange system which measures both CO2 and water vapour exchange of single intact leaves during fumigations with SO2 is described.Within the leaf cuvette temperature, light, humidity and both CO2 and SO2 concentrations are controlled to preset levels. Gas flow and concentrations are controlled by mass flow controllers. Photosynthetic uptake of CO2 can be determined either by differential depletion or null balance measurement. Water vapour exchange is measured differentially and transpiration and conductance to water vapour determined. Sulphur dioxide is measured directly within the cuvette exhaust gas line by UV‐pulse fluorescence.The performance of this system under field conditions is described and the physiological measurements compared with those obtained with other systems.
The penetration of light through soil
Authors: TESTER M. , MORRIS CHRISTINA 
Published: April 2006

Abstract There has been little written on the penetration of light through soil. In this review, we attempt to collate most of the work that has been published on this topic in order to stimulate further research and to clarify the often‐confused literature.Light penetration can be measured directly with, for example, a spectroradiometer, or indirectly by using germination of light‐sensitive seeds or the presence of growing algae as bioindicators. Although the penetration of light through soil is greatly affected by factors such as soil moisture content and particle size and colour, it generally appears that physiologically and ecologically significant amounts of light rarely penetrate more than 4–5 mm through the soil, and may often penetrate much less than this. Any penetration beyond 10 mm would generally not be significant, especially as most soils are covered with litter, algae or lichens, or are shaded from direct sunlight. However, for some light‐stimulated geo‐tropic responses of roots, which can be sensitive to very low fluences, the penetration of light to greater depths could well be significant. The role of light in soil in directing root growth is also discussed.
Hydraulic flow characteristics in the lignotuberous mallee Eucalyptus behriana F. Muell. in the field
Authors: KÜPPERS M. , NEALES T. F. , KÜPPERS B. I. L. , SWAN A. G. , MYERS B. A. 
Published: April 2006

Abstract The lignotuberous mallee Eucalyptus behriana F. Muell, had much lower predawn leaf water potentials (not higher than – 1.2MPa) than other eucalypts (as high as – 0.2MPa), even after extended rain. This led to the expectation that the lignotuber of E. behriana might have specific hydraulic characteristics. Keeping the soil around partially defoliated mallces for several days underwater did not raise the water status above the maximum leaf water potential observed under natural conditions. Digging a plant out and placing its roots in water after removal of the soil rapidly increased the water status to a level consistant with other eucalypts. This indicated that the major impedance to water uptake was a component of the soil rather than in the roots or in the lignotuber.Some of the individual mallces had only two major stems or branches. One stem or branch was kept covered throughout the experiments to prevent transpiration. The other stem was subjected to a variety of different conditions in order to modify water loss from it. The transpiring branch affected the water status of the non‐transpiring plant parts. Hydraulic resistances in the shoot and root/lignotuber were determined from differences in the leaf water potential of covered and uncovered branches, at high water flow rates through the plant. Resistances in branches, including the liquid phase component of the leaf, were significantly larger than in root or lignotuber.The total plant hydraulic resistance of E. behriana was similar to that of other eucalypts, such as E. pauciflora Sieb. ex Spreng. or E. delegatensis R. T. Bak., even though its growth form was different and its natural leaf water potentials were much lower. An osmotic adjustment at the leaf level was observed in the mallee, keeping its bulk leaf turgor in the same range as compared to the other eucalypt species.
Control of hypocotyl phototropism by phytochrome in a dicotyledonous seedling (Sesamum indicum L.)
Authors: WOITZIK F. , MOHR H. 
Published: April 2006

Abstract The phototropic response in stems of higher plants is brought about by blue/UV light. The problem studied here is to what extent long‐wavelength light, which is absorbed by phytochrome, affects the phototropic response. A refined measurement of phototropism — a curvature index — was applied to the hypocotyl of the sesame seedling (Sesamum indicum L.). The time course of the phototropic response was followed in continuous unilateral weak blue light (B, 460 nm, 8 mW m−2). Long term red light (R) pretreatments, operating through phytochrome, strongly increase the rate and extent of the phototropic response once it is elicited by unilateral B, while the pretreatments decrease the sensitivity towards B. If a R pulse is given immediately prior to the onset of unilateral B, the rate of the response is strongly reduced compared to the time course of curvature observed when the pretreatment was terminated with a long wavelength far‐red light (FR) pulse.R and FR were then applied simultaneously with unilateral B to manipulate the status of the phytochrome system during actual curvature. It was found that a low Pfr/P ratio (established by FR) stimulates the phototropic response far above the control (B alone), while a high Pfr/P ratio (established by R) reduces the response below the control. During bending a positive effect of phytochrome on the rate and extent of the phototropic response, which is saturated at a low level of Pfr, appears to be counteracted by an inhibitory effect which dominates at higher levels of Pfr, such as established by omnilateral R. However, if R is applied unilaterally from the same direction as B, R increases the rate of curvature. Apparently the sesame seedling is capable of detecting the direction of R relative to the direction of B. While a mechanistic explanation of these effects cannot be advanced at present, it is clear that the seedling is capable of super‐imposing information about the actual light conditions during bending on a ‘memory’ of the light conditions prior to the onset of bending. Thus, the previous as well as the actual light conditions determine its phototropic responsiveness.
Short‐ and long‐term effects of a change in the spatial distribution of nitrate in the root zone on N uptake, growth and root development of young lettuce plants
Authors: BURNS I. G. 
Published: April 2006

Abstract. The effects of a change in the distribution of nitrate within the root zone on N uptake and growth were studied using young lettuce plants after reducing the proportion of their root systems supplied with nitrate from 100 to ca 10% in split‐root experiments in the glasshouse. The main effects of the localized nitrate supply were concentrated in a 2‐week period immediately after the treatment was imposed, when a temporary reduction in nitrate uptake caused the gradual development of N deficiency and a decline in plant growth rate. The plants adapted to the change in nitrate distribution, initially by increasing unit absorption rates (uptake rates per unit weight of root) and more gradually by increasing production of new roots in the high‐nitrate zone. As a result, relative N uptake rates and relative growth rates were restored to the same levels as for control plants (given a spatially uniform N supply throughout) after ca 12d, even though only ca 12–15% of their roots were exposed to nitrate at this time. Thereafter, the plants continued to adapt by concentrating new root growth in the nitrate‐containing zone, ultimately allowing unit absorption rates to return to normal. There was no evidence of any significant N deficiency in the plants after the initial adaptive response was complete, even though the total‐N concentrations of the plants given the localized supply were consistently less than those given the uniform N treatment, and nitrate concentrations in the petiole sap were generally lower in leaves on one side of the plant (because of limited lateral movement of nitrate between xylem vessels during its transport to the shoot).The delay in the initiation of an adaptive response caused a significant check in growth, and the resulting relative weight differences were maintained throughout the subsequent life of the plant. Plants in all treatments matured on the same date, so yields for those grown with the localized supply were less than those of the control, and could not be recovered by delaying final harvest without unacceptable loss of quality. The pattern of the changes in N uptake and plant growth, and the effect on final yield, were similar to those exhibited by young lettuce plants subjected to a temporary interruption in nitrate supply, suggesting that the reduction in final yield for plants grown with the localized supply was largely the effect of the check in growth which occurred whilst the Plants were adapting to the change in nitrate distribution during the early part of the experiment. This implies that the rate of dry matter production of young lettuce plants can be altered by N treatment without affecting their rate of physiological development.
Modelling photosynthesis of cotton grown in elevated CO2
Authors: HARLEY P. C. , THOMAS R. B. , REYNOLDS J. F. , STRAIN B. R. 
Published: April 2006

ABSTRACTCotton plants were grown in CO2‐controlled growth chambers in atmospheres of either 35 or 65 Pa CO2. A widely accepted model of C3 leaf photosynthesis was parameterized for leaves from both CO2 treatments using non‐linear least squares regression techniques, but in order to achieve reasonable fits, it was necessary to include a phosphate limitation resulting from inadequate triose phosphate utilization. Despite the accumulation of large amounts of starch (>50 g m−2) in the high CO2 plants, the photosynthetic characteristics of leaves in both treatments were similar, although the maximum rate of Rubisco activity (Vcmax), estimated from A versus Ci response curves measured at 29°C, was ∼10% lower in leaves from plants grown in high CO2. The relationship between key model parameters and total leaf N was linear, the only difference between CO2 treatments being a slight reduction in the slope of the line relating Vcmax to leaf N in plants grown at high CO2. Stomatal conductance of leaves of plants grown and measured at 65 Pa CO2 was approximately 32% lower than that of plants grown and measured at 35 Pa. Because photosynthetic capacity of leaves grown in high CO2 was only slightly less than that of leaves grown in 35 Pa CO2, net photosynthesis measured at the growth CO2, light and temperature conditions was approximately 25% greater in leaves of plants grown in high CO2, despite the reduction in leaf conductance. Greater assimilation rate was one factor allowing plants grown in high CO2 to incorporate 30% more biomass during the first 36 d of growth.
Physiological adaptation of waxapple to waterlogging
Authors: LIN C. H. , LIN C. H. 
Published: April 2006

ABSTRACTWaxapple (Syzygium samarangense Men. et. Perry) plants receiving up to 40d of continuous flooding treatment showed no symptoms of physiological disorder, but the treatment resulted in early flowering. In this report, several physiological parameters of flooded plants are compared with those of nonflooded plants. Both control plants and 9‐d‐flooding‐treated plants exhibited aerenchyma formation in the cortex tissue beginning 5 cm from the root tip. After 7d flooding treatment, the oxygen consumption rate of the root section was only 20% of that of the controls. Following flooding treatment, the roots showed an increase in alcohol dehydrogenase activity as well as an increase in three isozymes. However, malate dehydrogenase activity was decreased, and no significant change of NADP‐malic enzyme activity was observed. There were no significant differences in levels of ethylene, 1‐aminocyclopropane‐1‐carboxylic acid and 1‐(malonylamino) cyclopropane‐1‐carboxylic acid in petiole and roots of flooded and non‐flooded plants during the stage examined. It is inferred that the presence of aerenchyma in the root cortex allows a higher level of internal gas exchange, and thus, makes waxapple surprisingly flood tolerant. However, reduced root oxygen consumption rate may have limited root respiration rate and vegetative growth.
High annual productivity of certain agaves and cacti under cultivation
Authors: NOBEL P. S. , GARCÍA‐MOYA E. , QUERO E. 
Published: April 2006

ABSTRACTTo help ascertain the maximal productivity of plants with Crassulacean acid metabolism, measurements were undertaken on four potentially highly productive CAM species at optimal leaf or stem area indices of 4 to 6. Shoot area and shoot biomass were based on regression equations for material harvested from adjacent plants at 3‐month intervals; in addition, the monitored platyopuntias were harvested to determine their dry weight at the end of the observation period. Agave mapisaga and A. salmiana near Mexico City had a productivity averaging 40Mg ha−1 year−1 and exhibited higher maximal rates of net CO2 uptake than previously reported for CAM plants (29–34 μmol m −2 s−1). When irrigated and fertilized daily, Opuntia amyclea and O. ficus‐indica in Saltillo, Coahuila, Mexico, had an average productivity of 46Mg ha−1 year−1. These are among the highest productivities ever reported for any plant species.
Water balance in the arborescent palm, Sabal palmetto. I. Stem structure, tissue water release properties and leaf epidermal conductance
Authors: HOLBROOK N. M. , SINCLAIR T. R. 
Published: April 2006

ABSTRACTThe functional importance of water storage in the arborescent palm, Sabal palmetto, was investigated by observing aboveground water content, pressure‐volume curve parameters of leaf and stem tissue and leaf epidermal conductance rates. The ratio of the amount of water stored within the stem to the leaf area (kg m−2) increased linearly with plant height. Pressure‐volume curves for leaf and stem parenchyma differed markedly; leaves lost turgor at 0.90 relative water content and –3.81 MPa, while the turgor loss point for stem parenchyma occurred at 0–64 relative water content and −0.96 MPa. Specific capacitance (change in relative water content per change in tissue water potential) of stem parenchyma tissue was 84 times higher than that of leaves, while the bulk modulus of elasticity was 346 times lower. Leaf epidermal conductance rates were extremely low (0.32–0.56 mmol m−2 s−1) suggesting that S. palmetto are able to strongly restrict foliar water loss rates. Structurally, stems of S. palmetto appear to be well suited to act as a water storage reservoir, and coupled with the ability to restrict water loss from leaf surfaces, may play an important role in tree survival during periods of low water availability.
Water storage in the wood and xylem cavitation in 1‐year‐old twigs of Populus deltoides Bartr.
Authors: LO GULLO M. A. , SALLEO S. 
Published: April 2006

ABSTRACTThe possible role of water expelled from cavitated xylem conduits in the rehydration of water‐stressed leaves has been studied in one‐year‐old twigs of populus deltoides Bartr. Twigs were dehydrated in air. At desired values of leaf water potential (Ψl) (between near full turgor and ‐1.62 MPa), twigs were placed in black plastic bags for 1–2h. Leaf water content was measured every 3–5 min before bagging and every 10 min in the dark. Hydraulic conductivity and xylem cavitation were measured both in the open and in the dark. Cavitation was monitored as ultrasound acoustic emissions (AE). A critical Ψl value of ‐0.96 MPa was found, at which AE increased significantly while the leaf water deficit decreased by gain of water. Since the twigs were no longer attached to roots, it was concluded that water expelled from cavitated xylem conduits was transported to the leaves, thus contributing to their rehydration. Xylem cavitation is discussed in terms of a ‘leaf water deficit buffer mechanism’, under not very severe water stress conditions.
Differentiation of freezing tolerance and vernalization responses in Cruciferae exposed to a low temperature
Authors: LAROCHE A. , GENG X.‐M. , SINGH J. 
Published: April 2006

ABSTRACTHigh levels of freezing tolerance were induced in leaves of different Cruciferae species including Brassica napus, Arabidopsis thaliana, Barbarea vulgaris, Thlaspi arvenses and Descurainia sophia by low‐temperature acclimation. Concomitantly, the amount of total RNA doubled in these three species. Analyses of methylation patterns and dosage of rRNA genes were carried out to determine whether or not alterations occur in this DNA during development of freezing tolerance. Hybridizations of Southern transfers with an rDNA probe revealed two additional EcoRI sites in purified DNA isolated from freezing‐tolerant leaves of winter B. napus cv Jet Neuf and D. sophia (both of which require low temperatures for vernalization), but not in isolates of A. thaliana or spring B. napus cv Topas. An increase of rDNA cistrons was also observed in both B. napus cv Jet Neuf and D. sophia but not in A. thaliana or B. napus cv Topas upon cold acclimation. These results suggest that low temperature induced amplification of rDNA and the differential methylation of EcoRI sites may possibly be related to the vernalization process but may not be related to the development of freezing tolerance. However, the higher activity of RNA polymerase (2.5 times more) observed upon cold acclimation may explain the concomitant increase in total RNA and may be related to the development of freezing tolerance in the Cruciferae.