bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of CO2 concentration and irradiance on the stomatal behaviour of maize, barley and sunflower plants in the field
Authors: LOUWERSE W. 
Published: April 2006

Abstract Maize, barley and sunflower plants were grown in the field, well supplied with water and nutrients. During growth, net CO2 exchange and transpiration of the crops at varying ambient CO2 concentrations and irradiance were determined by infra‐red gas analysis. In maize the net photosynthetic rate (Pn) was linearly related to the irradiance (I) and independent of the ambient CO2 concentration (Ca). The transpiration rate (ET) was also linearly related to I but decreased strongly with increasing Ca. In sunflower and barley Pn increased and ET decreased with increasing Ca. A mean stomatal conductance and intercellular CO2 concentration (Ci) were calculated. In all three species the internal CO2 concentration was independent of the irradiance. In maize it was also independent of Ca, but in sunflower and barley Ci was proportional to Ca with a ratio of 0.6.It is concluded that differences in stomatal behaviour are only partly species‐specific and depend mainly on growing conditions. The importance of stomatal regulation for crop growth under conditions of water shortage and CO2 depletion is discussed.
Changes in starch and glucose levels in the epidermis of Commelina communis in relation to stomatal movements
Authors: DONKIN MARIA E. , MARTIN E. S. 
Published: April 2006

Abstract Starch levels in Commelina communis epidermis, were shown to be higher in the dark than in the light, from plants kept under an imposed photoperiodic regime. These changes were also inversely correlated with diffusive conductance (1/diffusive resistance, 1 /R) of the leaves used. Even after advancing the photoperiod by 7 h the changes in starch levels continued for at least 1 d and were still inversely correlated with 1/R.Corresponding changes in glucose levels were measured in the same tissue and were found to correlate with 1/R at the end of the dark period and mid photoperiod, but not at the beginning of the dark period. These changes are discussed in relation to possible mechanisms of stomatal opening and closing.
Accumulation of carbon compounds in the epidermis of five species with either different photosynthetic systems or stomatal structure
Authors: THORPE NICOLETTE 
Published: April 2006

Abstract Measurements were made of the rate and pattern of 14CO2 fixation by the attached and detached epidermis and accompanying leaf tissue of Commelina cyanea (C3), Zea mays (C4), Kalanchoë daigremontiana (CAM), Allium cepa (C3) and Paphiopedilum venustum (C3). Guard cell plastids of the last two species contain no starch and chlorophyll, respectively. The fine structure of guard cells of these species was also examined.The epidermis of all species when detached from the leaf fixed CO2 by PEP carboxylation but at rates related to those of the underlying mesophyll. When attached to the leaf during 14CO2 feeding a much higher rate of accumulation of radioactivity in substances other than malate and aspartate was found. The results indicated that although concentrations of various metabolites in the two tissues varied greatly, there was fairly ready transport from mesophyll to epidermis. Of recently formed compounds, amino acids appeared to be most readily transported in Commelina and sugars in Zea and Kalanchoë. Epidermal cells appeared to be highly permeable, there being rapid and extensive loss of most labelled products from epidermis placed on CaSO4 solution.
Stomatal response to environment and a possible interrelation between stomatal effects on transpiration and CO2 assimilation
Authors: HALL A. E. , SCHULZE E.‐D. 
Published: April 2006

Abstract It had been hypothesized that if daily CO2 assimilation is to be maximized at a given level of daily transpiration, stomatal apertures should change during the day so that the gain ratio (∂A/∂g)/(∂E/∂g) remains constant. These partial differentials describe the sensitivity of assimilation rate (A) and transpiration rate (E) to changes in stomatal conductance (g). Experiments were conducted to determine whether stomata respond to environment in a manner which results in constant gain ratios.Gas–exchange measurements were made of the stomatal and photosynthetic responses of Vigna unguiculata L. Walp. in controlled environments. Leaf conductance to water vapour responded to step changes in temperature and humidity so that for different steady‐state conditions the gain ratio remained constant on all but one day. Depletion of water in the root zone resulted in day‐to‐day increases in gain ratio which were correlated with decreases in maximum leaf conductance to water vapour. The significance of the results for plant adaptation and stomatal mechanisms, and methods for measuring the gain ratio, are discussed.
Unidirectional sodium fluxes in red beet storage tissue (Beta vulgaris L. cv. Platronde Egyptische): effects of the phytohormones indol‐3yl‐acetic acid and abscisic acid
Authors: FRANÇOIS G. , BOGEMANS J. , NEIRINCKX L. 
Published: April 2006

Abstract. The influence of indol‐3yl‐acetic acid (IAA) and abscisic acid (ABA) on the capacities of the cytoplasm and vacuole and their effects on unidirectional sodium fluxes across the plasmalemma and the tonoplast of aged red beet storage tissue was investigated. After loading the tissue in a labelled NaCl solution the efflux of radio‐activity was measured in unlabelled NaCl. By means of compartmental analysis the capacities and fluxes were determined and compared with those obtained after loading and elution in the presence of IAA or ABA.It was established that both IAA and ABA affect sodium transport across the principal cell membranes. Both hormones inhibited the efflux across the plasma‐lemma, possibly by affecting a Na+ for H+ exchanging system. Efflux across the tonoplast was stimulated by IAA and influx across the same membrane was enhanced by ABA. It was suggested that IAA stimulated a proton pump at this level while the influence of ABA remained difficult to explain.
Photosynthetic efficiency of Betula pendula acclimated to different quantum flux densities
Authors: ÖQUIST G. , BRUNES L. , HÄLLGREN J‐E. 
Published: April 2006

Abstract. Seedlings of Betula pendula were grown in a controlled environment chamber at quantum flux densities of 50, 250 and 600 μmol m−2 s−1. The relationship between the flux densities of absorbed CC2 and quanta was determined for shoots of whole seedlings. Rates of both light‐saturated and in situ (measured under the growing conditions) net photosynthesis were determined and the pholosynthetic quantum yields under light‐limiting conditions were calculated. Anatomical leaf characteristics, chlorophyll contents and sizes and densities of the photosynthetic units (chlorophyll/P700) were determined. Chloroplasts were isolated and their rates of 2,6‐dichlorophenol indophenol photoreduction were measured together with their pool sizes of the electron transport carriers plastoquinone and cylochrome ƒ.Although acclimated to different quantum flux densities, the three birch populations showed the same quantum yield of net photosynthesis. This was approximately 0.028 in normal air (21.2 kPa oxygen) and about 0.040 when photorespiration was largely inhibited in 2.0 kPa oxygen. In addition, the in situ net photosynthesis rates were limited by the absorbed quantum flux density for low, intermediate and high light grown seedlings. It was concluded that birch acclimated to the three light regimes at different levels of organization (metabolic and anatomical). Thus, the quanta which were absorbed in situ could be transferred into chemical equivalents at an optimal and constant efficiency. The use of different reference bases for expressing rates of net photosynthesis are also discussed.
Uptake of SO2 in shoots of Scots pine: field measurements of net flux of sulphur in relation to stomatal conductance
Authors: HÄLLGREN J‐E. , LINDER S. , RICHTER A. , TROENG E. , GRANAT L. 
Published: April 2006

Abstract. Net fluxes of gaseous sulphur compounds, water vapour and carbon dioxide to current‐ and one‐year‐old shoots of Scots pine were simultaneously measured in the field. The shoots were fumigated in temperature‐controlled assimilation chambers with sulphur dioxide at concentrations ranging from 40 to 250 μg m−3 (15–95 ppb). The hypothesis that stomatal opening regulates the uptake of sulphur dioxide was tested. The following conclusions were reached concerning the dry deposition of sulphur dioxide to a dry coniferous shoot.There was a marked diurnal variation in the uptake rate of sulphur dioxide. The net deposition velocity of sulphur was about three times higher during the day than during the night during July‐October. Stomatal opening was not the primary factor controlling the dry deposition rate of sulphur dioxide. The net dry deposition rate was significantly smaller than the calculated rate based on stomatal conductances for water vapour.Part of this deviation could be explained by re‐emission of reduced sulphur compound(s) from the needles. The re‐emission of sulphur was a light‐dependent process and might be of great significance for the sulphur balance calculations.A variable deposition velocity should be used in atmospheric transport models to account for the diurnal and seasonal variation in the surface resistance of a dry canopy.
Thoughts on the possible role of phytochrome destruction in phytochrome controlled responses
Authors: BLAAUW‐JANSEN G. 
Published: April 2006

Abstract. Fluence‐response curves for low‐energy phytochrome responses show two steps at red light exposures c. two orders of magnitude apart. This Feature of the fluence‐response relationship can be interpreted as the consequence of the following processes:

Induction of a photoresponse by a very low level of Pfr.
Activation of a Pfr‐destroying enzyme above a threshold level of [Pfr].
Dependency of the rate of Pfr destruction on [Pfr] once the threshold level is reached.

In this way, adaptation of the phytochrome control system to a broad range of light doses could be realized.
Changes in the proportion of endogenous osmotic solutes accumulated by Chlorella emersonii in the light and dark
Authors: SETTER T. L. , GREENWAY H. 
Published: April 2006

Abstract. The type of endogenous osmotic solute accumulated by Chlorella emersonii grown at high external osmotic pressure (πext) depended on the light/dark conditions: proline accumulated to high concentrations in cells in the light, while sucrose accumulated to high concentrations in the dark. These findings were made during the alternating light dark cycles used to obtain synchronized cultures, i.e. cultures containing cells at only one stage of development at any one time. Similar decreases in proline and increases in sucrose in the dark were found for cells previously grown in continuous light to obtain non‐synchronized cultures, i.e. cultures containing cells at all stages of development.In cultures synchronized at 200 mol m −3 NaCl (πext= 1.01 MPa), recently divided ‘daughter cells’ at the beginning of the light periods contained 60 mol m−3 proline and 100mol m−3 sucrose, while mature cells towards the end of light periods contained 130 mol m proline and 20 mol m−3 sucrose. The changes in proline and sucrose which occurred in synchronized cultures were due mainly to light/dark conditions and to a much lesser extent to different stages of cell development. The proportion of proline to sucrose in daughter cells collected from non‐synchronized cultures in continuous light was not different from the proportion in heterogeneous populations of cells.Results are discussed in relation to the accumulations of two, rather than one, endogenous osmotic solute and to growth reductions of C. emersonii exposed to high external osmotic pressures.
A method for measuring radial differences in water content of intact tree stems by attenuation of gamma radiation
Authors: EDWARDS W. R. N. , JARVIS P. G. 
Published: April 2006

Abstract. A technique is described for the nondestructive measurement of water content variations in the stems of trees.The density of intact tree stems in the forest was estimated using attenuation of gamma radiation. Water content was calculated after subsequent derivation of the volume fraction of solid matrix.A radial sequence of such measurements was obtained by measuring a sequence of chords, and assuming homogeneity within concentric tori. Analysis of the source of errors showed that the system was a close approximation of an ideal, rigid‐geometry, mono‐energetic source/detector system, with basic precision dependent on the quantity of gamma radiation measured. Correlation coefficients between the gamma‐attenuation technique and subsequent gravimetric estimates of water content for two field experiments reported here were 0.882 and 0.938.The technique was shown to be capable of describing the radial and diurnal variation in water content at two heights in the stem of a 20‐year‐old tree of Pinus contorta.
Stomatal response to vapour pressure deficit and the effect of plant water stress
Authors: JOHNSON JON D. , FERRELL WILLIAM K. 
Published: April 2006

Abstract The dynamic response of stomata to changes in atmospheric humidity was investigated in Fragaria × ananassa Duch., Picea engelmannii Parry, and Pseudotsuga menziesii (Mirb.) Franco; and the effect of water stress on this response was determined in Pseudotsuga menziesii.The plants were rotated through three regimes of ambient temperature and vapour pressure deficit: 35°C–3. 5kPa, 35°C–0. 5 kPa, and 20°C–1. 5kPa. Branch and leaflet conductance were measured with a steady‐state porometer, first at ambient vapour pressure deficit and then at one of four treatment conditions achieved by increasing or decreasing vapour pressure within the porometer cuvette. All three species showed similar stomatal response: enhanced conductance at low vapour pressure deficit and depressed conductance at high vapour pressure deficit. Engelmann spruce was more sensitive than Douglas fir and strawberry.Plant water status significantly altered stomatal response to vapour pressure deficit. The relationship of conductance of xylem water potential was linear under ambient conditions but became curvilinear when conductance was measured above and below ambient vapour pressure deficit. Between −0. 5 MPa and −2. 0 MPa xylem water potential, the stomata were sensitive to vapour pressure deficit, but below − 2. 0 MPa, the sensitivity decreased.
Leaf area index, canopy structure and photosynthesis of red clover (Trifolium pratense L.)
Authors: JOGGI D. , HOFER U. , NÖSBERGER J. 
Published: April 2006

Abstract. The influence of leaf age, total leaf area and its dispersion in space on canopy photosynthesis were studied using microswards of red clover (Trifolium pratense L.) which were established in the greenhouse. Two varieties, Renova (flowering) and Molstad (non‐flowering), were sown in separate plastic boxes at densities of 225, 400 and 625 plants per m2.Vertical distribution of photosynthetically active radiation (PAR), leaf area, leaf age and 14CO2‐fixation were determined periodically. Net photosynthesis and dark respiration of canopies were measured. Maximum photosynthetic capacity of individual leaves was measured on plants taken from the intact canopy or from plants where shading of the growing leaves had been prevented.Net photosynthetic rate of canopies increased linearly with leaf area index (LAI) up to an LAI of 3.5 and then declined at higher LAI, independent of variety and sowing density. Below the optimum LAI, net photosynthesis depended mainly on interception of PAR. Decrease in canopy photosynthesis above the optimum LAI was due to a higher proportion of old leaves with decreased photosynthetic capacity, and not to an increase in respiring plant parts. It is concluded that LAI and position of leaf age categories in the canopy are more important than vertical distribution of leaf area in determining canopy photosynthesis of red clover.
Transmembrane hyperpolarization and increase of K+ uptake in maize roots treated with permeant weak acids
Authors: MARRÈ M. T. , ROMANI G. , MARRÈ E. 
Published: April 2006

Abstract. Treatment with weak acids (butyrate, isobutyrate, trimethylacetate, DMO) at a concentration of I mol m−3 in apical maize root segments induced a rapid, marked hyperpolarization (ca. 30 mV) of the transmembrane electrical potential, stable for at least 30 min. With butyrate, this effect increased with the increase of butyrate concentration in the medium, reaching a value of ca. 75 mV at a concentration of 5 mol m−3.Both the butyrate uptake and the hyperpolarization were roughly proportional to the pH‐regulated, undissociated/dissociated acid ratio in the medium. The butyrate‐induced hyperpolarization was reduced progressively, but was still present when K+ concentration in the medium was raised from 1 to 10 mol m−3.The hyperpolarization was accompanied by a significant increase of K+ uptake, and was almost completely suppressed by the presence of the protonophore carbonylcyanid‐p‐trichlorometoxy‐phenylhydrazone (CCCP) and strongly reduced by erytrosin B, an inhibitor of some animal ATPases and of a K+‐activated, DCCD‐ and vanadate‐sensitive Mg2+‐ATPase from plant microsomes. The hyperpolarization effect of butyrate was additive to that of fusicoccin at low, but not at high (5 mol m−3), concentrations of the weak acid. These results suggest that the intracellular pH regulates the activity of the electrogenic proton pump at the plasmalemma.
Turgor‐regulated translocation
Authors: LANG ALEXANDER 
Published: April 2006

Abstract.The role played by potassium in plants is examined, in particular its connection with phloem translocation. The possibility emerges that trans‐location may be a turgor‐regulated process in which potassium plays a central role.A simple mechanistic hypothesis is proposed and the evidence for it is discussed. The hypothesis is strongly supported by both the direct and the circumstantial evidence.An important conclusion is the need to reassess the importance of the translocation process in the control of assimilate partitioning. Hitherto, as implied by Münch's hypothesis, control has been assumed to be exerted by source and/or sink activity with the translocation pathway playing a more passive secondary role. If the present proposal is correct the translocation process emerges instead as a dominant factor in the control of assimilate partitioning.
The relationship between stomatal conductance, transpiration rate and tracheid structure in Pinus radiata clones grown at different water vapour saturation deficits
Authors: WHITEHEAD D. , SHERIFF D. W. , GREER D. H. 
Published: April 2006

Abstract. Stomatal conductance and needle water potential of P. radiata clones were measured after 2, 5 and 8 months on plants grown in controlled environment rooms with markedly different water vapour saturation deficits (D). Conductance was significantly lower at high D, but water potential differences between treatments were not significant. When trees were moved between treatments most of the changes in conductances occurred within 2 h, with residual changes after 24 h. Water potentials were not different 24 h after the trees were moved. The effects were completely reversible.Transpiration rates of individual trees were highest in the high D treatment and lowest in the low D treatment. They were not linearly related to D because of decreasing conductance with increasing D.Height growth, diameter growth and foliage areas were not significantly different between treatments. Tracheid lumen diameters tended to be larger in trees grown at higher D although treatment differences were not significant.There were significant clonal differences in shoot conductance and tracheid dimensions.
High and low temperature tolerances and their relationships to distribution of agaves
Authors: NOBEL PARK S. , SMITH STANLEY D. 
Published: April 2006

Abstract. The potential influence of tissue tolerances to extreme temperatures on distributional limits was investigated for 15 taxa (14 species) of leaf‐succulent agaves from the south‐western United States and northern Mexico. As a group, the agaves exhibited a moderate low temperature tolerance of – 11°C (based on a 50% inhibition in the number of mesophyll cells taking up a stain, neutral red). However, nearly all of the species were able to tolerate extremely high tissue temperatures of over 60°C. Nocturnal acid accumulation by these crassulacean acid metabolism plants was about 6°C more sensitive to temperature extremes than was cellular membrane integrity.High and low temperature acclimation in response to changing day/night air temperatures was observed in all 15 taxa, with high temperature acclimation averaging two‐fold greater than low temperature acclimation (3.8°C versus 2.0°C per 10°C change in ambient temperature). Species occupying the coldest habitats exhibited the greatest low temperature tolerances and acclimation; several such species, such as Agave utahensis and A. schottii, had small rosette sizes which resulted in higher minimum leaf temperatures. Species from the hottest habitats had among the greatest high temperature tolerances and acclimation; the two species from open desert scrub habitats, A. deserti and A. lecheguilla, had the lowest leaf shortwave absorptances observed, which would result in lower maximum leaf temperatures. Thus morphology and tissue tolerances to stressful temperatures reflect the temperature extremes of a plant's native habitat, although low temperature tolerance appears to limit the distribution of agaves more than high temperature tolerance.
Contribution of osmotic adjustment to the dehydration tolerance of water‐stressed pigeon pea (Cajanus cajan (L.) millsp.) leaves
Authors: FLOWER D. J. , LUDLOW M. M. 
Published: April 2006

Abstract Water‐stressed pigeonpea leaves have high levels of osmotic adjustment at low leaf water potentials. The possible contribution of this adjustment of dehydration tolerance of leaves was examined in plants grown in a controlled environment. Osmotic adjustment was varied by withholding water from plants growing in differing amounts of soil, which resulted in different rates of decline of leaf water potential.The level of osmotic adjustment was inversely related to leaf water potential in all treatments. In addition, at any particular water potential, plants that had experienced a rapid development of stress exhibited less osmotic adjustment than plants that experienced a slower development of stress. Leaves with different levels of osmotic adjustment died at water potentials between –3.4 and –6.3 MPa, but all leaves died at a similar relative water content (32%). Consequently, leaves died when relative water content reached a lethal value, rather than when a lethal leaf water potential was reached. Osmotic adjustment delayed the time and lowered the leaf water potential when the lethal relative water content occurred, because it helped maintain higher relative water contents at low leaf water potentials. The consequences of osmotic adjustment for leaf survival in water‐stressed pigeonpea are discussed.
Possible significance of changes in the light requirement of Cirsium palustre seeds after dispersal in ash coppice
Authors: PONS T. L. 
Published: April 2006

Abstract. It is demonstrated that after the feelling of ash coppice Cirsium palustre becomes established from seed that was produced during the previous coppice cycle and has lain underground for several years. These seeds are light‐requiring and it is probable that their germination is triggered by exposure to light during coppicing in winter.It is assumed that the seeds become light‐requiring because phytochrome in the far‐red absorbing form high. This facilitates their incorporation in the seed bank in summer. However, the disappearance of Pfr is inhibited at low temperatures; this means that the seeds can store the light stimulus in winter and will not germinate until they experience higher temperatures in spring. The significance of the inhibition of seed germination under a leaf canopy is that it enhances the seeds chance of being incorporated in the soil seed bank.