bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolation and characterization of variant wheat cultivars for ABA sensitivity
Authors: BLUM A. , SINMENA B. 
Published: April 2006

ABSTRACTGenetic variants for abscisic acid (ABA) sensitivity are important for investigating the role of ABA sensitivity in conditioning plant response to environmental stress, and especially to those soil conditions that may elicit a root‐mediated hormonal signal. This study was performed in order to isolate variation in ABA sensitivity among wheat (Triticum aestivum and T. durum) cultivars, as characterized by two plant responses: (i) shoot growth reduction in response to 5×10−2mol m−3 ABA (racemic) in the root medium of hydroponically grown plants, and (ii) changes in transpiration and gas exchange in a bioassay of detached leaves (leaflaminac) infused with 10−4mol m−3 ABA.Very significant (P≤0.01) and repeatable differences were found among 36 wheat cultivars and 19 landraces in the growth rate in ABA‐containing nutrient solutions, expressed as a percentage of the growth rate in control nutrient solutions (ABA/control ratio). In duplicate experiments, the ABA/control ratio ranged between 60 and 83% for the least sensitive cultivars (V2151‐3, Bethlehem, K1056 and Sunstar) and between 9 and 19% for the most sensitive cultivars (Sundor, Comet, Barkaec and V5). In the transpiration bioassay, performed with seven selected cultivars, it was found that the reductions in transpiration of ABA‐infused leaves corresponded very well with the reductions in growth in response to ABA in the root media. Measurement of gas exchange in the detached leaves of two cultivars differing in ABA sensitivity (Bethlehem and Sundor) showed that variable ABA sensitivity was expressed very well in the stomatal conductance, carbon exchange rate (CER) and photosynthetic capacity (CER/Ci ratio) of the leaf. These results therefore allowed us to isolate wheat variants for ABA sensitivity and to conclude that, while ABA sensitivity is expressed in the growth of plants challenged by ABA in the root medium, the control of sensitivity resides, at least partly, in the leaf.
15N natural abundance of vascular rainforest epiphytes: implications for nitrogen source and acquisition
Authors: STEWART G. R. , SCHMIDT S. , HANDLEY L.L. , TURNBULL M. H. , ERSKINE P. D. , JOLY C. A. 
Published: April 2006

ABSTRACTThe foliar natural abundance of 15N was analysed to compare the potential nitrogen sources of vascular rainforest epiphytes and associated soil‐rooted trees. Leaves of epiphytes collected from six rainforest communities in Brazil, Australia and the Solomon Islands were depleted in 15N relative to the trees at each site. Epiphyte δ15N was as low as ‐6.4%o, while trees were generally enriched in 15N (0.7 to 3.5%o). These results indicate either that epiphytes use nitrogen sources depleted in 15N or that discrimination against 15N is an intrinsic function of epiphyte physiology. At three sites, epiphytes could be grouped into those having both low δ15N and low leaf‐nitrogen content and those possessing both high δ15N and high leaf‐nitrogen content. The second group had δ15N values in the range sometimes attributable to N2 fixation (‐2 to 0%o). There was no correlation between growth form and δ15N. It is concluded that epiphytes may utilize 15N‐depleted nitrogen from atmospheric deposition and N2 fixation.
ABA xylem concentrations determine maximum daily leaf conductance of field‐grown Vitis vinifera L. plants
Authors: CORREIA M. J. , PEREIRA J. S. , CHAVES M. M. , RODRIGUES M. L. , PACHECO C. A. 
Published: April 2006

ABSTRACTDifferences in maximum leaf conductance in grapevine plants growing in soils with contrasting water availabilities during mid‐summer in Portugal could be accounted for by differences in the concentration of ABA in xylem sap. This conclusion is reinforced by the observation that the relationship between leaf conductance and endogenous ABA concentration can be mimicked by the application of exogenous ABA to leaves detached from irrigated plants. During the day, leaf conductance decreased after a morning peak, even when the leaves remained in a constant environment at a moderate temperature and leaf‐to‐air vapour pressure difference. This decline in leaf conductance was not a consequence of an increase in the xylem ABA concentration or the rate of delivery of this compound by the transpiratory stream. The afternoon depression in leaf conductance was associated with an apparent limitation in stomatal opening potential, which persisted even when detached leaves were fed with water and rehydrated. The reason for this inhibition has still to be identified.
Water in the stems of sessile oak (Quercus petraea) assessed by computer tomography with concurrent measurements of sap velocity and ultrasound emission
Authors: RASCHI A. , TOGNETTI R. , RIDDER H. ‐W. , BÉRES C. 
Published: April 2006

ABSTRACTConcurrent measurements of heat pulse velocity and ultrasound acoustic emission were performed on the trunks of adult Quercus petraea plants under different water stress conditions. On the trunk section of the plants the wood density was measured non‐destructively using a mobile computer tomograph which measures the attenuation of a collimated beam of radiation which traverses the trunk. By scanning the trunk in different directions, it is possible to map wood density in the section. As wood density is strictly correlated with water content, this method allows evaluation of the water content in the trunk section and the water conditions in the different parts of the section. The computer‐tomograph technique is non‐invasive and is not influenced by climatic fluctuations. A close agreement was found between wood density and heat pulse velocity; the relationship between these two parameters and ultrasound acoustic emission is discussed. Trunks of sessile oak appear well suited as water storage reservoirs playing an important role in tree survival during extended periods of low soil water availability, especially in the context of global climatic change. Here the computer‐tomograph methodology is described and suggestions arc made for further research development.
Temporal variability and scaling behaviour in the fine‐root system of kiwifruit (Actinidia deliciosa)
Authors: REID J. B. , BOWDEN M. 
Published: April 2006

ABSTRACTWe show that temporal variability in root populations can depend upon the scale of measurement (particularly the sampled soil volume). The presence of roots in a range of volumes of soil was studied using perspex tubes installed horizontally into the soil around three mature kiwifruit vines. Roots intercepting lines scored on the tubes were counted using a periscope. For small volumes of soil (c. 2–4 cm3) the root counts varied with time in a very irregular manner, and as the interval between measurements increased the autocorrelation between the measurements decayed rapidly. At about half of the locations monitored there was no significant autocorrelation between measurements 27 d apart. Linear interpolation in these time series was unreliable, and where the correlation dimension could be resolved it was usually non‐integer (suggesting chaotic behaviour). The time series measured at different locations were poorly correlated, indicating weak coordination. As the observed soil volume increased, the coordination between locations improved, the autocorrelation function increased, and linear interpolation errors decreased (although these remained substantial). Clearly there are considerable fundamental constraints on our ability to predict the root behaviour of kiwifruit vines at scales that are appropriate for mechanistic models of nutrient and water uptake. We discuss the need for a new conceptual model of the fine‐root systems of kiwifruit and similar species.
A field study of the effects of elevated CO2 on carbon assimilation, stomatal conductance and leaf and branch growth of Pinus taeda trees
Authors: TESKEY R. O. 
Published: April 2006

ABSTRACTA study was conducted in 21‐year‐old loblolly pine (Pinus taeda L.) trees growing in plantation in north central Georgia, USA. The experiment used branch chambers to impose treatments of ambient, ambient +165 and ambient + 330 μmol mol−1 CO2. After one growing season there was no indication of acclimation to elevated CO2. In August and September, carbon assimilation, measured by two different methods, was twice as high at ambient +330 μmol mol−1 CO2 than at ambient. Dark respiration was suppressed by 6% at ambient +165 and by 14% at ambient + 330 μmol mol−1 CO2. This suppression was immediate, and not an effect of exposure to elevated CO2 during growth, since respiration was reduced by the same amount in all treatments when measured at a high CO2 concentration. Elevated CO2 increased the growth of foliage and woody tissue. It also increased instantaneous transpiration efficiency, but it had no effect on stomatal conductance. Since the soil at the study site had low to moderate fertility, these results suggest that the growth potential of forests on many sites may be enhanced by global increases in atmospheric CO2, concentration.
Predominant localization of mitochondria enriched with glycine‐decarboxylating enzymes in bundle sheath cells of Alternanthera tenella, a C3–C4 intermediate species
Authors: DEVI M. T. , RAJAGOPALAN A. V. , RAGHAVENDRA A. S. 
Published: April 2006

ABSTRACTMesophyll protoplasts and bundle sheath cells were prepared by enzymatic digestion of leaves of Alternanthera tenella, a C3‐C4 intermediate species. The intercellular distribution of selected photosynthetic, photorespiratory and respiratory (mitochondrial) enzymes in these meso‐phyll and bundle sheath cells was studied. The activity levels of photosynthetic enzymes such as PEP carboxylase (EC 4.1.1.31) or NAD‐malic enzyme (EC 1.1.1.39) and photorespiratory enzymes such as glycolate oxidase (EC 1.1.3.1) or NADH‐hydroxypyruvate reductase (EC 1.1.1.29) were similar in the two cell types. The activity levels of mitochondrial TCA cycle enzymes such as citrate synthase (EC 4.1.3.7) or fumarase (EC 4.2.1.2) were 2‐ to 3‐fold higher in bundle sheath cells. On the other hand, the activity levels of mitochondrial photorespiratory enzymes, namely glycine decarboxylase (EC 2.1.2.10) and serine hydroxymethyltransferase (EC 2.1.2.1), were 6‐9‐fold higher in bundle sheath cells than in mesophyll protoplasts. Such preferential localization of mitochondria enriched with the glycine‐decarboxylating system in the inner bundle sheath cells would result in efficient refixa‐tion of CO2 from not only photorespiration but also dark respiration before its exit from the leaf. We propose that predominant localization of mitochondria specialized in glycine decarboxylation in bundle sheath cells may form the basis of reduced photorespiration in this C3‐C4 intermediate species.
Changes in chromatin structure associated with germination of maize and their relation with desiccation tolerance
Authors: LEPRINCE O. , COLSON P. , HOUSSIER C. , DELTOUR R. 
Published: April 2006

ABSTRACTMorphological and physicochemical measurements of chromatin condensation were made on germinating maize (Zea mays L.) radicles to determine whether the loss of genetic activities that occurs during the loss of desiccation tolerance is linked to irreversible changes in chromatin condensation. Chromatin samples were compared at different stages of germination (0, 24 and 72 h after imbibition), before (control) and after 24 h of desiccation. Morphological changes in chromatin structure and condensation were characterized by a qualitative and quantitative electron microscope study of chromatin which was allowed to spread in 0.2 mol m−3 EDTA and then laid on coated microscope grids. The experiments showed similar levels of chromatin condensation in quiescent embryos and 24‐h‐old radicles (desiccation‐tolerant material). After 72 h of imbibition, when radicle emergence and desiccation intolerance had ceased, the chromatin underwent a major decondensation towards various lower order folded structures. Regardless of the desiccation tolerance stage, an in vivo drying treatment of 24‐ and 72‐h‐old radicles before chromatin extraction did not induce significant changes in the extent of condensation compared to their respective controls. Similar conclusions were drawn from measurements of several spectroscopy properties (absorbance ratios: A260/A240, A260/A400; thermal denaturation, and linear electric dichroism) of chromatin fragments that were obtained after nuclease digestion and then dissolved in 0‐2 mol m−3 EDTA. In quiescent and 24‐h‐old material, chromatin fragments were poorly soluble but highly stable during thermal denaturation. Chromatin fragments were 3‐5‐fold more soluble and less thermally stable in 72‐h‐old material than in 24‐h‐old material. In vivo desiccation had no significant effects on these properties compared to the respective controls. Collectively these data suggest that desiccation did not induce irreversible changes in the condensation properties of chromatin. The likelihood that the decondensation process occurring during germination is linked to the loss of desiccation tolerance is discussed.
Quantification of ozone influx and apoplastic ascorbate content in needles of Norway spruce trees (Picea abies L., Karst) at high altitude
Authors: POLLE A. , WIESER G. , HAVRANEK W. M. 
Published: April 2006

ABSTRACTThe objective of the present study was to investigate whether peak concentrations of ozone can deplete the apoplastic ascorbate pool of needles from Norway spruce trees (Picea abies L. Karst.) and, thereby, contribute to damage to forest trees. Twigs of forest trees grown at high altitude (1950m above sea level; Mt Patscherkofel, Austria) were enclosed in situ in chambers and fumigated for 5‐5 or 17 h with ozone concentrations ranging from 60 to 798 nmol mol−1. Adjacent branches were fumigated with filtered air. Ozone influx into the foliage ranging from 1‐7 to 17nmolm−2s−1 had little effect on whole‐needle ascorbate or glutathione contents. However, apoplastic ascorbate decreased by about 30% when the needles were exposed to environmentally relevant ozone concentrations and increased about 3‐fold at higher ozone concentrations. This response suggests the induction of ascorbate as a protective system and may also be important under field conditions. Needles of spruce trees from high altitude that were exposed to chronically increased ozone concentrations contained significantly higher apoplastic ascorbate concentrations than needles from spruce trees from lower altitudes with lower mean atmospheric ozone concentrations. The results show that peak concentrations of ozone do not act in spruce via a depletion of the apoplastic ascorbate pool.
Interpretation of seasonal changes of xylem embolism and plant hydraulic resistance in Fagus sylvatica
Authors: MAGNANI F. , BORGHETTI M. 
Published: April 2006

ABSTRACTThe annual course of xylem embolism in twigs of adult beech trees was monitored, and compared to concurrent changes of tree water status and hydraulic resistances. Xylem embolism was quantified in 1‐year‐old apical twigs by the hydraulic conductivity as a percentage of the maximum measured after removal of air emboli. Tree and root hydraulic resistances were estimated from water potential differences and sap flux measurements. The considerable degree of twig embolism found in winter (up to 90% loss of hydraulic conductivity) may be attributed to the effect of freeze‐thaw cycles in the xylem. A partial recovery from winter embolism occurred in spring, probably because of the production of new functional xylem. Xylem embolism fluctuated around 50% throughout the summer, without significant changes. Almost complete refilling of apical twigs was observed early in autumn. A significant negative correlation was found between xylem embolism and precipitation; thus, an active role of rainfall in embolism reversion is hypothesized. Tree and root hydraulic resistances were found to change throughout the growing period. A marked decrease of hydraulic resistance preceded the refilling of apical twigs in the autumn. Most of the decrease in total tree resistance was estimated to be located in the root compartment.
Lack of C4 photosynthetic metabolism in ears of C3 cereals
Authors: BORT J. , BROWN R. H. , ARAUS J. L. 
Published: April 2006

ABSTRACTThere is continuing controversy over whether a degree of C4 photosynthetic metabolism exists in ears of C3 cereals. In this context, CO2 exchange and the initial products of photosynthesis were examined in flag leaf blades and various ear parts of two durum wheat (Triticum durum Desf.) and two six‐rowed barley (Hordeum vulgare L.) cultivars. Three weeks after anthesis, the CO2 compensation concentration at 210 mmol mol−1 O2 in durum wheat and barley ear parts was similar to or greater than that in flag leaves. The O2 dependence of the CO2 compensation concentration in durum wheat ear parts, as well as in the flag leaf blade, was linear, as expected for C3 photosynthesis. In a complementary experiment, intact and attached ears and flag leaf blades of barley and durum wheat were radio‐labelled with 14CO2 during a 10s pulse, and the initial products of fixation were studied in various parts of the ears (awns, glumes, inner bracts and grains) and in the flag leaf blade. All tissues assimilated CO2 mainly by the Calvin (C3) cycle, with little fixation of 14CO2 into the C4 acids malate and aspartate (about 10% or less). These collective data support the conclusion that in the ear parts of these C3 cereals C4 photosynthetic metabolism is nil.
The different effects of PEG 6000 and NaCI on leaf development are associated with differential inhibition of root water transport
Authors: CHAZEN O. , HARTUNG W. , NEUMANN P. M. 
Published: April 2006

ABSTRACTThe inhibitory effects of PEG on whole‐plant growth can exceed the effects of other osmolytes such as NaCI, and this has been ascribed to toxic contaminants, or to reduced oxygen availability in PEG solutions. We investigated another possibility, namely that PEG has an additional inhibitory effect on root water transport which in turn affects leaf development. The effects on first‐leaf growth of applications of PEG 6000 or isoosmotic NaCI to the roots were determined using hydroponically grown maize (Zea mays L.) seedlings. Leaf growth rates were inhibited within minutes of PEG application to the roots and remained inhibited for days. The inhibitory effects on growth of NaCI, and also of KCl and mannitol, were much smaller. The comparative effects of NaCI and PEG on root water transport were determined by assaying pressurized flow through excised roots. PEG induced a 7‐fold greater inhibition of flow through live roots than NaCI. Killing of the roots by heat treatment, to reduce cell membrane resistances to solute penetration, nearly doubled the flow rate for roots in NaCI, but not for roots in PEG. We suggest that the greater viscosity of PEG solutions, as compared with NaCI, may be a primary factor contributing to the additional inhibition of water flow through live and killed roots. PEG did not have additional effects on leaf turgor but had a 3 times greater inhibitory effect than NaCI on the irreversible extensibility of the leaves and induced 16 times more leaf accumulation of the growth inhibitory stress hormone abscisic acid (ABA). We conclude that greater inhibition of root water transport by PEG 6000, as compared with NaCI, leads to additional reductions in extensibility, additional ABA accumulation, and a greater inhibition of leaf growth.
Foliar maintenance respiration of subalpine and boreal trees and shrubs in relation to nitrogen content
Authors: RYAN M. G. 
Published: April 2006

ABSTRACTA nitrogen‐based model of maintenance respiration (Rm) would link Rm with nitrogen‐based photosynthesis models and enable simpler estimation of dark respiration flux from forest canopies. To test whether an N‐based model of Rm would apply generally to foliage of boreal and subalpine woody plants, I measured Rm (CO2 efflux at night from fully expanded foliage) for foliage of seven species of trees and shrubs in the northern boreal forest (near Thompson, Manitoba, Canada) and seven species in the subalpine montane forest (near Fraser, Colorado, USA). At 10°C, average Rm for boreal foliage ranged from 0.94 to 6.8μmol kg−1 s−1 (0.18–0.58 μmol m−2 s−1) and for subalpine foliage it ranged from 0.99 to 7.6 μmol kg−1 s−1 (0.28–0.64μmol m−2 s−1). CO2 efflux at 10°C for the samples was only weakly correlated with sample weight (r = 0.11) and leaf area (r = 0.58). However, CO2 efflux per unit foliage weight was highly correlated with foliage N concentration [r = 0.83, CO2 flux at 10°C (mol kg−1 s−1) = 2.62 × foliage N (mol kg−1)J, and slopes were statistically similar for the boreal and subalpine sites (P=0.28). CO2 efflux per unit of foliar N was 1.8 times that reported for a variety of crop and wildland species growing in warmer climates.
Evaluation of the role of damage to photosystem II in the inhibition of CO2 assimilation in pea leaves on exposure to UV‐B radiation
Authors: NOGUÉS S. , BAKER N. R. 
Published: April 2006

ABSTRACTMature pea (Pisum sativum L., cv. Meteor) leaves were exposed to two levels of UV‐B radiation, with and without supplementary UV‐C radiation, during 15 h photoperiods. Simultaneous measurements of CO2 assimilation and modulated chlorophyll fluorescence parameters demonstrated that irradiation with UV‐B resulted in decreases in CO2 assimilation that are not accompanied by decreases in the maximum quantum efficiency of photosystem II (PSII) primary photochemistry. Increased exposure to UV‐B resulted in a further loss of CO2 assimilation and decreases in the maximum quantum efficiency of PSII primary photochemistry, which were accompanied by a loss of the capacity of thylakoids isolated from the leaves to bind atrazine, thus demonstrating that photodamage to PSII reaction centres had occurred. Addition of UV‐C to the UV‐B treatments increased markedly the rate of inhibition of photosynthesis, but the relationships between CO2 assimilation and PSII characteristics remained the same, indicating that UV‐B and UV‐C inhibit leaf photosynthesis by a similar mechanism. It is concluded that PSII is not the primary target site involved in the onset of the inhibition of photosynthesis in pea leaves induced by irradiation with UV‐B.
Diurnal water relations of expanding and full‐sized cotton fruits and subtending leaves
Authors: VAN IERSEL M. W. , OOSTERHUIS D. M. 
Published: April 2006

ABSTRACTWater relations of cotton (Gossypium hirsutum L.) fruits have received less attention than those of leaves, although crop water status has an important influence on fruit physiology. This study was conducted to describe diurnal changes in the water relations of cotton fruits and subtending leaves. Young, expanding fruits and full‐sized fruits were compared because of previously reported changes in xylem maturity with ontogeny. Diurnal changes in relative water content were greater in leaves than in the capsule walls of fruits. The capsule walls of young fruits had a higher relative water content than subtending leaves, and water content was lower in full‐sized (87%) than in expanding (92%) fruits. Water potentials of subtending leaves were always approximately 0‐3 MPa lower than those of capsule walls. Water potential gradients favoured passive water flow from young fruits to branches, but water potentials of branches and the capsule walls of full‐sized fruits were similar (−0.7 MPa). Water potential gradients were consistent throughout the day. These results indicate that xylem transport to young fruits is unlikely, but may occur in older fruits.