bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acclimation of snow gum (Eucalyptus pauciflora) leaf respiration to seasonal and diurnal variations in temperature: the importance of changes in the capacity and temperature sensitivity of respiration
Authors: Atkin O. K. , Holly C. , Ball M. C. 
Published: March 2003

ABSTRACTWe investigated the relationship between daily and seasonal temperature variation and dark respiratory CO2 release by leaves of snow gum (Eucalyptus pauciflora Sieb. ex Spreng) that were grown in their natural habitat or under controlled‐environment conditions. The open grassland field site in SE Australia was characterized by large seasonal and diurnal changes in air temperature. On each measurement day, leaf respiration rates in darkness were measured in situ at 2–3 h intervals over a 24 h period, with measurements being conducted at the ambient leaf temperature. The rate of respiration at a set measuring temperature (i.e. apparent ‘respiratory capacity’) was greater in seedlings grown under low average daily temperatures (i.e. acclimation occurred), both in the field and under controlled‐environment conditions. The sensitivity of leaf respiration to diurnal changes in temperature (i.e. the Q10 of leaf respiration) exhibited little seasonal variation over much of the year. However, Q10 values were significantly greater on cold winter days (i.e. when daily average and minimum air temperatures were below 6° and –1 °C, respectively). These differences in Q10 values were not due to bias arizing from the contrasting daily temperature amplitudes in winter and summer, as the Q10 of leaf respiration was constant over a wide temperature range in short‐term experiments. Due to the higher Q10 values in winter, there was less difference between winter and summer leaf respiration rates measured at 5 °C than at 25 °C. The net result of these changes was that there was relatively little difference in total daily leaf respiratory CO2 release per unit leaf dry mass in winter and summer. Under controlled‐environment conditions, acclimation of respiration to growth temperature occurred in as little as 1–3 d. Acclimation was associated with a change in the concentration of soluble sugars under controlled conditions, but not in the field. Our data suggest that acclimation in the field may be associated with the onset of cold‐induced photo‐inhibition. We conclude that cold‐acclimation of dark respiration in snow gum leaves is characterized by changes in both the temperature sensitivity and apparent ‘capacity’ of the respiratory apparatus, and that such changes will have an important impact on the carbon economy of snow gum plants.
Carbohydrate metabolism in a heat‐girdled maize source leaf
Authors: Jeannette E. , Reyss A. , Grégory N. , Gantet P. , Prioul J.‐L. 
Published: March 2003

ABSTRACTHeat‐girdling in maize leaves was used for blocking assimilate export and producing alterations in carbohydrate metabolism. A rapid drop (< 24 h) in CO2 fixation and a large increase of sucrose and starch content were observed. Reduction in photosynthetic assimilation was not due to stomatal limitation since the girdled leaves remained turgid and their photosynthetic rate was not restored by 4% CO2. After 24 h, the girdled leaves became red through accumulation of anthocyanins and reduction of chlorophylls. A possible relationship between carbohydrate accumulation in girdled leaves and gene expression was examined through transcript levels of the ribulose‐1,5‐bisphosphate carboxylase oxygenase small‐subunit (rbcS), the leaf‐specific ADPglucose pyrophosphorylase small‐subunit (Agp‐l2), and Bz1, an anthocyanin pathway‐specific gene. The mRNA levels in girdled leaves were also compared with those in excised leaves placed on sucrose or sorbitol solutions. rbcS mRNA disappeared 8 h after the girdling treatment and after 1 day on sucrose. Agp‐l2 expression was reduced by two‐thirds with girdling or sucrose feeding while Bz1 expression was strikingly enhanced by both treatments. Thus, carbohydrate accumulation produced a short‐term feedback inhibition of photosynthesis and some long‐term modifications in gene expression.
Peroxidase isozyme patterns in the skin of maturing tomato fruit
Authors: Andrews J. , Malone M. , Thompson D. S. , Ho L. C. , Burton K. S. 
Published: March 2003

ABSTRACTThe cessation of tomato fruit growth is thought to be induced by an increase in the activity of enzymes which rigidify cell walls in the fruit skin. Peroxidase could catalyse such wall‐stiffening reactions, and marked rises in peroxidase activity were recently reported in skin cell walls towards fruit maturity. Peroxidase isoforms in the fruit are here analysed using native gel electrophoresis. New isoforms of apparent Mr 44, 48 and 53 kDa are shown to appear in cell walls of the fruit skin at around the time of cessation of growth. It is inferred that these isozymes are present in the cell wall in vivo. Fruit from a range of non‐ripening mutants were also examined. Some of these do not soften or ripen for many weeks after achieving their final size. The new isozymes were found in skin cell walls of mature fruit in each of these mutants, as in the wild‐type and commercial varieties. It is concluded that the late‐appearing isozymes are not associated with fruit ripening or softening, and are probably not ethylene‐induced. They may act to control fruit growth by cross‐linking wall polymers within the fruit skin, thus mechanically stiffening the walls and terminating growth.
Turgor regulation in the salt‐tolerant alga Chara longifolia
Authors: Stento N. A. , Ryba N. Gerber , Kiegle E. A. , Bisson M. A. 
Published: March 2003

ABSTRACT Chara longifolia is a salt‐tolerant Charophyte which regulates its turgor inresponse to osmotic stress. Membrane depolarization, in creased membrane conductance, and cessation of cytoplasmic streaming (due to increase in cytoplasmic Ca2+) precede regulation in response to hypotonic stress. Measurements of these three parameters are presented here with simultaneous turgor measurements. Variability in the occurrence, rate and extent of turgor regulation in individual cells was correlated with magnitude of the stress. Hypertonic stress showed the same slow time course as was found previously, requiring several days for complete regulation. Fifty μM nifedipine, a Ca2+ channel blocker, inhibited turgor regulation. In the presence of 5 μM nifedipine, turgor regulation was delayed. An increase in conductance preceded regulation, but membrane depolarization was less and no detectable change in cytoplasmic streaming was observed, requiring modifications to a previously presented model for turgor regulation. There was no significant difference in 45Ca2+ influx under control and stress conditions. However, the control flux was insensitive to nifedipine, whereas under stress the flux is inhibited 54% by nifedipine. We suggest that osmotic stress results in a rapid increase in a nifedipine‐sensitive Ca2+ entry mechanism, followed very quickly by a decrease in the control entry mechanism.
Ion channels and the transduction of light signals
Authors: Spalding E. P. 
Published: March 2003

ABSTRACTStudies of biological light‐sensing mechanisms are revealing important roles for ion channels. Photosensory transduction in plants is no exception. In this article, the evidence that ion channels perform such signal‐transducing functions in the complex array of mechanisms that bring about plant photomorphogenesis will be reviewed and discussed. The examples selected for discussion range from light‐gradient detection in unicellular algae to the photocontrol of stem growth in Arabidopsis. Also included is some discussion of the technical aspects of studies that combine electrophysiology and photobiology.
Turgor pressure, membrane tension and the control of exocytosis in higher plants
Authors: Fricke Wieland , Jarvis Michael C. , Brett Christopher T. 
Published: March 2003

ABSTRACTBoth turgor pressure and differences in membrane tension are capable of providing an energy input into exocytosis, the process of fusion of Golgi vesicles with the cell membrane in plants. It is shown that the contribution of turgor pressure is much larger than that of membrane tension, so that the exocytotic process is not likely on thermodynamic grounds to be reversible unless another source of energy is made available. However, recycling of membrane material as flattened, empty vesicles is energetically possible and is likely to be favoured when the magnitude of membrane tension in the cell membrane is low. Thus the outward flows of membrane and cell wall material are in principle linked to turgor, whereas membrane tension influences the inward flow of membrane material.
The onset of photosynthetic acclimation to elevated CO2 partial pressure in field‐grown Pinus radiata D. Don. after 4 years
Authors: Griffin K. L. , Tissue D. T. , Turnbull M. H. , Whitehead D. 
Published: March 2003

ABSTRACTThe effects of CO2 enrichment on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied in current year and 1‐year‐old needles of the same branch of field‐grown Pinus radiata D. Don trees. All measurements were made in the fourth year of growth in large, open‐top chambers continuously maintained at ambient (36 Pa) or elevated (65 Pa) CO2 partial pressures. Photosynthetic rates of the 1‐year‐old needles made at the growth CO2 partial pressure averaged 10·5 ± 0·5 μmol m−2 s−1 in the 36 Pa grown trees and 11·8 ± 0·4 μmol m−2 s−1 in the 65 Pa grown trees, and were not significantly different from each other. The photosynthetic capacity of 1‐year‐old needles was reduced by 25% from 23·0 ± 1·8 μmol m−2 s−1 in the 36 Pa CO2 grown trees to 17·3 ± 0·7 μmol m−2 s−1 in the 65 Pa grown trees. Growth in elevated CO2 also resulted in a 25% reduction in Vcmax (maximum carboxylation rate), a 23% reduction in Jmax (RuBP regeneration capacity mediated by maximum electron transport rate) and a 30% reduction in Rubisco activity and content. Total non‐structural carbohydrates (TNC) as a fraction of total dry mass increased from 12·8 ± 0·4% in 1‐year‐old needles from the 36 Pa grown trees to 14·2 ± 0·7% in 1‐year‐old needles from the 65 Pa grown trees and leaf nitrogen content decreased from 1·30 ± 0·02 to 1·09 ± 0·10 g m−2. The current‐year needles were not of sufficient size for gas exchange measurements, but none of the biochemical parameters measured (Rubisco, leaf chlorophyll, TNC and N), were effected by growth in elevated CO2. These results demonstrate that photosynthetic acclimation, which was not found in the first 2 years of this experiment, can develop over time in field‐grown trees and may be regulated by source‐sink balance, sugar feedback mechanisms and nitrogen allocation.
Ecophysiological consequences of differences in plant size: in situ carbon gain and water relations of the epiphytic bromeliad, Vriesea sanguinolenta
Authors: Schmidt Gerold , Zotz Gerhard 
Published: March 2003

ABSTRACTThis field study with the C3 bromeliad Vriesea sanguinolenta (Cogn. & Marchal 1874) was initiated to explore the importance of size‐related ecophysiological changes in vascular epiphytes in a natural tropical setting. In this species, a step change from atmospheric to tank‐forming life form occurs during early ontogeny, followed by a continuous size increase of individuals with water‐impounding tanks. Although our study focused on the water‐impounding phase, this growth pattern also allowed us to compare ecophysiological consequences of a step change in life form with those associated with size increments among plants of identical life form. The shift in life form was accompanied by relatively minor changes, for example in leaf morphology (decrease in leaf thickness and trichome density) and leaf physiology (decrease in photosynthetic capacity), while there were more substantial changes during the tank‐forming phase. A major trend was a decreasing dependence of larger plants on internally stored water due to a more efficient tank. We suggest that the resulting, more reliable water supply in larger plants may be the proximate cause for the observed size‐related differences in leaf anatomy (relative reduction of water storage tissue, and relative and absolute increase in chlorenchyma thickness), leaf morphology (increase in stomatal density, decrease in trichome density), and leaf physiology (increase in net rates of CO2 uptake, more conservative stomatal behaviour, higher residual transpiration). The results are compared with previous studies on heteroblasty in bromeliads, but are also discussed in the context of a gradual shift from a drought‐tolerance to a drought‐avoidance strategy.
Ion transport in roots: measurement of fluxes using ion‐selective microelectrodes to characterize transporter function
Authors: Newman I. A. 
Published: March 2003

ABSTRACTThe transport of mineral ions into and out of tissues and cells is central to the life of plants. Ion transport and the plasma membrane transporters themselves have been studied using a variety of techniques. In the last 15 years, measurement of specific ion fluxes has contributed to the characterization of transport systems. Progress in molecular genetics is allowing gene identification and controlled expression of transporter molecules. However the molecular expression of transporter gene products must be characterized at the functional level. The ion‐selective microelectrode technique to measure specific ion fluxes non‐invasively is ideally suited to this purpose. This technique, its theory, its links with others and its application and prospects in plant science, are discussed. Ions studied include hydrogen, potassium, sodium, ammonium, calcium, chloride and nitrate. Applications discussed include: solute ion uptake by roots; gravitropism and other processes in the root cap, meristematic and elongation zones; Nod factor effect on root hairs; osmotic and salt stresses; oscillations; the effects of light and temperature. Studies have included intact roots, leaf mesophyll and other tissues, protoplasts and bacterial biofilms. A multi‐ion capability of the technique will greatly assist functional genomics, particularly when coupled with imaging techniques, patch clamping and the use of suitable mutants.
The effect of nitrogen on growth and key thallus components in the two tripartite lichens, Nephroma arcticum and Peltigera aphthosa
Authors: Sundberg B. , Näsholm T. , Palmqvist K. 
Published: March 2003

ABSTRACTRelationships between growth, nitrogen and concentration of unique biont components were investigated for the tripartite lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Nitrogen availability was manipulated during 4 summer months by removing cephalodia and their associated N2 fixation activity, or by weekly irrigation with NH4NO3. Chlorophyll and ribulose 1·5‐biphosphate carboxylase/oxygenase (Rubisco), and chitin and ergosterol were used as photobiont and mycobiont markers, respectively. Nitrogen concentrations were similar in older and newer parts of the same thallus, varying between 2 and 5 g m−2, with P. aphthosa having higher concentrations than N. arcticum. Both chlorophyll (Chl a) and chitin were linearly correlated with thallus N, but N. arcticum invested more in fungal biomass and had lower Chl a concentrations in comparison with P. aphthosa at equal thallus N. During the 4 months, control and N‐fertilized thalli of N. arcticum increased in area by 0·2 m2 m−2 and P. aphthosa by 0·4 m2 m−2. Thallus expansion was significantly inhibited in samples without cephalodia, but there was no effect on lichen weight gain. Mean relative growth rate (RGR; mg g−1 d−1) was 3·8 for N. arcticum and 8·4 for P. aphthosa, when time (d) reflected the lichen wet periods. RGR was 2–3 times lower when based on the whole time, i.e. when including dry periods. The efficiency (e) of converting incident irradiance into lichen biomass was positively and linearly correlated with thallus Chl a concentration to the same extent in both species. The slower growth rates of N. arcticum, in comparison with P. aphthosa, could then be explained by their lower nitrogen and Chl a concentrations and a subsequently lower light energy conversion efficiency. Functional and dynamic aspects of resource allocation patterns of the two lichens are discussed in relation to the above findings.
Abscisic acid regulation of gene expression during water‐deficit stress in the era of the Arabidopsis genome
Authors: Bray E. A. 
Published: March 2003

AbstractChanges in gene expression may lead to cellular adaptation of water‐deficit stress, yet all of the induced mRNAs may not play this role. Changes in gene expression must be signalled by transduction mechanisms that first sense a water deficit. This first step triggers changes in gene expression that function to synthesize additional signals such as abscisic acid (ABA). The enzymes involved in ABA biosynthesis have been cloned and their regulation during water‐deficit stress is being characterized. Once ABA levels are increased, further signalling mechanisms are initiated to signal new gene expression patterns that are proposed to play a role in cellular adaptation to water‐deficit stress. As the genome of Arabidopsis is now completed, much more information can be exploited to characterize these responses.
A possible stress physiological role of abscisic acid conjugates in root‐to‐shoot signalling
Authors: Sauter A. , Dietz K.‐J. , Hartung W. 
Published: March 2003

AbstractAbscisic acid (ABA) conjugates, predominantly their glucose esters, have recently been shown to occur in the xylem sap of different plants. Under stress conditions, their concentration can rise substantially to levels that are higher than the concentration of free ABA. External ABA conjugates cannot penetrate apoplastic barriers in the root. They have to be hydrolysed by apoplastic enzymes in the root cortex. Liberated free ABA can then be redistributed to the root symplast and dragged directly across the endodermis to the stele. Endogenous ABA conjugates are formed in the cytosol of root cells, transported symplastically to the xylem parenchyma cells and released to the xylem vessels. The mechanism of release is unknown; it may include the action of ABC‐transporters. Because of its extremely hydrophilic properties, ABA‐GE is translocated in the xylem of the stem without any loss to the surrounding parenchyma. After arrival in the leaf apoplast, transporters for ABA‐GE in the plasmalemma have to be postulated to redistribute the conjugates to the mesophyll cells. Additionally, apoplastic esterases can cleave the conjugate and release free ABA to the target cells and tissues. The activity of these esterases is increased when barley plants are subjected to salt stress.
Effects of pubescence and waxes on the reflectance of leaves in the ultraviolet and photosynthetic wavebands: a comparison of a range of species
Authors: Holmes M. G. , Keiller D. R. 
Published: March 2003

AbstractTotal reflectance of ultraviolet and photosynthetically effective wavelengths was measured for a range of different leaf types. Two approaches were employed. Firstly, reflectance of monochromatic wavebands at 330 and 680 nm was measured for a total of 45 different species covering a wide range of genera. In the second, specific leaf types that displayed different degrees of reflectance were treated to remove hairs and waxes that contributed to their reflectance. Selected waxy and non‐waxy leaves were also studied in more detail over the spectral range 270–500 nm. It was found that both pubescence (presence of hairs) and glaucousness (presence of a thick epicuticular wax layer) had marked effects on total reflectance. Pubescent leaves tended to be more effective in reflecting longer wavelengths than ultraviolet radiation. The extent of this effect depended on hair type. Glaucous leaves demonstrated that surface waxes were very effective reflectors of both UV and longer wavelength radiation.
Soil insects alter fine root demography in peach (Prunus persica)
Authors: Wells C. E. , Glenn D. M. , Eissenstat D. M. 
Published: March 2003

AbstractMinirhizotrons were used to assess the effects of soil insect suppression on the demography of peach fine roots (<1 mm diameter) over two growing seasons. The experiment was conducted at the USDA–ARS Appalachian Fruit Research Station in Kearneysville, WV, USA using six 15‐year‐old peach trees. Clear butyrate minirhizotrons were installed beneath each tree in April 1996. Soil drench treatments were applied around individual minirhizotron tubes at monthly intervals and consisted of 1 L of water or 250 µL of a broad‐spectrum insecticide in 1 L of water. Roots were videotaped at 2‐ to 4‐week intervals during the 1996 and 1997 growing seasons. Insecticide application was associated with a significant increase in fine root longevity: the median lifespans of insecticide‐treated roots were 46–125 d longer than those of control roots. In addition, the development of brown pigmentation was significantly delayed in insecticide‐treated roots. Insecticide application did not appear to increase soil fertility, as accumulation of NO3–, NH4+, and PO42‐ on mixed bed ion‐exchange resin was similar in treated and untreated soil. These results suggest that interactions with below‐ground insects can significantly influence root longevity and may alter the rate at which roots undergo developmental changes in anatomy and physiology.
Carbon and nitrogen dynamics in acid detergent fibre lignins of beech (Fagus sylvatica L.) during the growth phase
Authors: Dyckmans J. , Flessa H. , Brinkmann K. , Mai C. , Polle A. 
Published: March 2003

AbstractTo study the incorporation of carbon and nitrogen in different plant fractions, 3‐year‐old‐beech (Fagus sylvatica L.) seedlings were exposed in microcosms to a dual‐labelling experiment employing 13C and 15N throughout one season. Leaves, stems, coarse and fine roots were harvested 6, 12 and 18 weeks after bud break (June to September) and used to isolate acid‐detergent fibre lignins (ADF lignin) for the determination of carbon and nitrogen and their isotope ratios. Lignin concentrations were also determined with the thioglycolic acid method. The highest lignin concentrations were found in fine roots. ADF lignins of all tissues analysed, especially those of leaves, also contained significant concentrations of nitrogen. This suggests that lignin‐bound proteins constitute an important cell wall fraction and shows that the ADF method is not suitable to determine genuine lignin. ADF lignin should be re‐named as ligno‐protein fraction. Whole‐leaf biomass was composed of 50 to 70% newly assimilated carbon and about 7% newly assimilated nitrogen; net changes in the isotope ratios were not observed during the experimental period. In the other tissues analysed, the fraction of new carbon and nitrogen was initially low and increased significantly during the time‐course of the experiment, whereas the total tissue concentrations of carbon remained almost unaffected and nitrogen declined. At the end of the experiment, the whole‐tissue biomass and ADF lignins of fine roots contained about 65 and 50% new carbon and about 50 and 40% new nitrogen, respectively. These results indicate that significant metabolic activity was related to the formation of structural biopolymers after leaf growth, especially below‐ground and that this activity also led to a substantial binding of nitrogen to structural compounds.