bluuebunny/crossref_metadata_2025_split huggingface dataset:
Salinity resistance and plant growth revisited
Authors: NEUMANN P. 
Published: November 2003

ABSTRACTThis article reconsiders a recent hypothesis concerning the physiology of growth inhibition by salinity and its relevance to the breeding of salt‐resistant crops (Munns 1993, Plant, Cell and Environment 16, pp. 15–24). The hypothesis states that the osmotic effects of salinity on water availability will strongly and equally inhibit the growth of related species and varieties. The genotypic diversity needed for breeding increased resistance to growth inhibition by salinity is only expected to appear after weeks or months. Higher rates of salt accumulation in more sensitive varieties then lead to accelerated leaf senescence. This further inhibits new growth, as compared with more resistant varieties. Accordingly, breeders aiming to increase crop growth under salinity should focus efforts on manipulating genes which can decrease rates of salt accumulation. However, the osmotic inhibition of growth by salinity appears to involve regulatory physiogical changes. Thus, some genotypic diversity might be expected. Clear evidence is presented for genotypic diversity in early growth responses to salt or PEG‐induced osmotic stress, in several species and varieties. The conclusion is that development of plants with increased resistance to inhibition of growth by the osmotic effects of external salinity (in addition to increased resistance to salt accumulation) is both feasible and desirable.
The apparent feedforward response of stomata to air vapour pressure deficit: information revealed by different experimental procedures with two rainforest trees
Authors: FRANKS P. J. , COWAN I. R. , FARQUHAR G. D. 
Published: November 2003

ABSTRACTA decrease in steady‐state leaf transpiration rate with increased vapour pressure difference between leaf and air, which is reversible and independent of leaf water status, is evidence for feedforward control of stomatal aperture (Cowan 1977). A recent survey of gas exchange data by Monteith (1995), covering 52 sets of measurements on 16 species, reported that evidence for feedforward control was rare and usually reliant on a single point. We conducted gas exchange experiments on an additional 13 species and observed an apparent feedforward response in only two. However, the response was not reversible and depended upon experimental procedure. In view of this we discuss the appropriate use of the term ‘feedforward’.
Growth and water use of the mangroves Rhizophora apiculata and R. stylosa in response to salinity and humidity under ambient and elevated concentrations of atmospheric CO2
Authors: BALL M. C. , COCHRANE M. J. , RAWSON H. M. 
Published: November 2003

ABSTRACTTwo mangrove species, Rhizophora apiculata and R. stylosa, were grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m−3 NaCl), humidity (43 and 86% relative humidity at 30°C) and atmospheric CO2 concentration (340 and 700 cm3 m−3). Under ambient [CO2], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO2] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt‐tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO2] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended on both the species and the growth conditions. In summary, elevated [CO2] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity × aridity gradients.
Sodium and potassium transport to the xylem are inherited independently in rice, and the mechanism of sodium: potassium selectivity differs between rice and wheat
Authors: GARCIA A. , RIZZO C.A. , UD‐DIN J. , BARTOS S.L. , SENADHIRA D. , FLOWERS T.J. , YEO A.R. 
Published: November 2003

ABSTRACTThe heritability of sodium and potassium transport to the xylem was measured by the regression of Fn+1, on Fn means in two segregating breeding populations of rice (Oryza sativa L.). The narrow‐sense heritabilities of shoot sodium concentration were 0.42 and 0.43 in the two populations, respectively, and the corresponding values for the heritability of shoot potassium concentration were 0.46 and 0.52. The sodium: potassium ratio was apparently heritable (0.36 and 0.40) because it was regressed positively on sodium concentration and negatively on potassium concentration. There was no significant relationship between the shoot sodium and potassium concentrations themselves. It is concluded that sodium and potassium uptake in rice are controlled by different genes which segregate independently. The magnitude of the transpirational bypass flow was estimated to be some 10 times greater in rice than in wheat (Triticum aestivum L.) and was found to be highly correlated with sodium uptake in rice but not in wheat. It is concluded that the bypass flow provides an additional pathway for sodium uptake in rice and that this accounts for the functional and genetic independence of sodium and potassium uptake in rice and consequently for the lesser prominence of potassium:sodium discrimination in rice than in wheat.
Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought
Authors: BALDOCCHI D. 
Published: November 2003

ABSTRACTForests in the south‐eastern United States experienced a prolonged dry spell and above‐normal temperatures during the 1995 growing season. During this episode, nearly continuous, eddy covariance measurements of carbon dioxide and water vapour fluxes were acquired over a temperate, hardwood forest. These data are used to examine how environmental factors and accumulating soil moisture deficits affected the diurnal pattern and magnitude of canopy‐scale carbon dioxide and water vapour fluxes. The field data are also used to test an integrative leaf‐to‐canopy scaling model (CANOAK), which uses micrometeorological and physiological theory, to calculate mass and energy fluxes. When soil moisture was ample in the spring, peak rates of net ecosystem CO2 exchange (NF) occurred around midday and exceeded 20 μmol m−2 s−1. Rates of NK were near optimal when air temperature ranged between 22 and 25°C. The accumulation of soil moisture deficits and a co‐occurrence of high temperatures caused peak rates of daytime carbon dioxide uptake to occur earlier in the morning. High air temperatures and soil moisture deficits were also correlated with a dramatic reduction in the magnitude of NE. On average, the magnitude of NE decreased from 20 to 7 μmol m−2 s−1 as air temperature increased from 24 to 30°C and the soil dried. The CANAOK model yielded accurate estimates of canopy‐scale carbon dioxide and water vapour fluxes when the forest had an ample supply of soil moisture. During the drought and heat spell, a cumulative drought index was needed to adjust the proportionality constant of the stomatal conductance model to yield accurate estimates of canopy CO2 exchange. The adoption of the drought index also enabled the CANOAK model to give improved estimates of evaporation until midday. On the other hand, the scheme failed to yield accurate estimates of evaporation during the afternoon.
Apparent responses of stomata to transpiration and humidity in a hybrid poplar canopy
Authors: MEINZER F. C. , HINCKLEY T. M. , CEULEMANS R. 
Published: November 2003

ABSTRACTIt has been proposed that the stomatal response to humidity relies on sensing of the transpiration rate itself rather than relative humidity or the saturation deficit per se. We used independent measurements of stomatal conductance (gs), transpiration (E), and leaf‐to‐air vapour pressure difference (V) in a hybrid poplar canopy to evaluate relationships between gs and E and between gs and V. Relationships between E, V and total vapour phase conductance or crown conductance (gc) were also assessed. Conductance measurements were made on exposed and partially shaded branches over a wide range of incident solar radiation. In exposed branches, gs appeared to decline linearly with increasing E and increasing V at both high and low irradiance. However, in a partially shaded branch, a bimodal relationship between gs and E was observed in which gs continued to decrease after E had reached a maximum value and begun to decrease. The relationship between gs and V for this branch was linear. Plots of gc against E always yielded bimodal or somewhat variable relationships, whereas plots of gc against V were invariably linear. It was not possible to derive a unique relationship between conductance and E or V because prevailing radiation partially determined the operating range for conductance. Normalization of data by radiation served to linearize responses observed within the same day or type of day, but even after normalization, data collected on partly cloudy days could not be used to predict stomatal behaviour on clear days and vice versa. An additional unidentified factor was thus also involved in determining operating ranges of conductance on days with different overall radiation regimes. We suggest that the simplest mechanism to account for the observed humidity responses is stomatal sensing of the epidermal or cuticular transpiration rate rather than the bulk leaf or stomatal transpiration rate.
Sink‐stimulated photosynthesis and sink‐dependent increase in nitrate uptake: nitrogen and carbon relations of the parasitic association Cuscuta reflexa–Ricinus communis
Authors: JESCHKE W. D. , HILPERT A. 
Published: November 2003

ABSTRACT Ricinus communis L. was grown under limiting N supply in quartz sand culture, fed with 0.2, 1 or 5 mol m−3 NO3−, or in liquid culture with 0.022, 0.05 or 0.5 mol m−3 NO3−. Some of the plants were infected with Cuscuta reflexa Roxb. As occurred for the host, dry matter production and growth of C. reflexa were severely depressed with decreasing N supply to the host. When parasitized by C. reflexa, the shoot and root dry weight of Ricinus was diminished at all levels of N nutrition, but the total dry weight of host plus parasite was almost the same as that of uninfected Ricinus. In contrast to the situation in Lupinus albus (Jeschke et al. 1994b), infection by Cuscuta resulted in increased tissue N levels in the host and the N content of the system Ricinus plus C. reflexa was the same or even somewhat larger than that of uninfected plants. This indicated a sink‐dependent stimulation of nitrate uptake. As a result of decreased root weights, nitrate uptake g−1 FW was stimulated by 80, 60 or only 40% at 0.2, 1 or 5 mol m−3 nitrate supply. Increased nitrate uptake was reflected, particularly at low N supply, in xylem transport; xylem sap nitrate concentrations were substantially elevated, while those of amino acids were decreased in parasitized plants. This indicated an inhibition of nitrate assimilation in roots of parasitized plants under limiting N supply. Besides these effects on N relations, C. reflexa induced a substantial sink‐dependent stimulation of net photosynthesis in host leaves and a concomitant increase in stomatal opening and transpiration. This stimulation depended on the relative sink size induced by Cuscuta, on nitrogen nutrition and on leaf age, indicating that delayed senescence of leaves contributes to the overall effects of Cuscuta on its host. The Cuscuta‐induced inhibition of nitrate assimilation in the roots and the increase in nitrate uptake suggest that nitrate reduction was shifted towards the leaves in the presence of C. reflexa. The stimulating effects of C. reflexa in the Ricinus‐Cuscuta association are compared with the strongly inhibitory effects occurring in the tripartite association L. albus–Rhizobium–Cuscuta reflexa.
Waterlogging and fire impacts on nitrogen availability and utilization in a subtropical wet heathland (wallum)
Authors: SCHMIDT S. , STEWART G.R. 
Published: November 2003

ABSTRACTProtein, amino acids and ammonium were the main forms of soluble soil nitrogen in the soil solution of a subtropical heathland (wallum). After fire, soil ammonium and nitrate increased 90‐ and 60‐fold, respectively. Despite this increase in nitrate availability after fire, wallum species exhibited uniformly low nitrate reductase activities and low leaf and xylem nitrate. During waterlogging soil amino acids increased, particularly γ‐aminobutyric acid (GABA) which accounted for over 50% of amino nitrogen. Non‐mycorrhizal wallum species were significantly (P < 0.05) 15N‐enriched (0.3–4.3‰) compared to species with mycorrhizal associations (ericoid‐type, ecto‐, va‐mycorrhizal) which were strongly depleted in 15N (‐6.3 to ‐1.8‰). Lignotubers and roots had δ15N signatures similar to that of the leaves of respective species. The exceptions were fine roots of ecto‐, ecto/va‐, and ericoid type mycorrhizal species which were enriched in 15N (0.1–2.4‰). The 515N signatures of δ15Ntotal soil N and δ15Nsoil NH4+ were in the range 3.7–4.5‰, whereas δ15Nsoil NO3− was significantly (P < 0.05) more enriched in 15N (9.2–9.8‰). It is proposed that there is discrimination against 15N during transfer of nitrogen from fungal to plant partner. Roots of selected species incorporated nitrogen sources in the order of preference: ammonium > glycine > nitrate. The exception were proteoid roots of Hakea (Proteaceae) which incorporated equal amounts of glycine and ammonium.
NaCl homoeostasis as a factor for the survival of the evergreen halophyte Armeria maritima (Mill.) Willd. under salt stress in winter
Authors: KÖHL K. I. 
Published: November 2003

ABSTRACTThe combination of NaCl and low temperature stress makes winter a critical time for evergreen halophytes at temperate latitudes. As part of a study of ecotypic differentiation of the evergreen Armeria maritima (Mill.) Willd., inland and salt‐marsh populations were compared with respect to their growth and survival, osmotic adjustment and NaCl concentrations (based on dry weight) under salt stress in pot experiments in winter. Increased leaf necrosis in all populations under salt stress indicated a higher NaCl sensitivity in winter than in summer. Plants from inland populations were more sensitive than salt‐marsh populations. Inland and salt‐marsh populations showed similar capacities for seasonal osmotic adjustment, high seasonal increase of praline concentration and long‐term betaine accumulation. Inland and salt‐marsh populations allocated Na and Cl preferentially to the shoot. In inland populations, Na and Cl accumulated to high concentrations in leaves, whereas the much lower NaCl concentration in salt‐marsh populations suggested that in these plants, Na uptake was regulated to match the growth‐dependent ion demand of the shoot. The prevention of NaCl accumulation in times of slow growth by a NaCl homoeostasis system seemed to be an important adaptation with respect to the survival of evergreen plants in salt marshes.
Seasonal water use characteristics of tall wheatgrass [Agropyron elongatum (Host) Beauv.] in a saline environment
Authors: BLEBY T. M. , AUCOTE M. , KENNETT‐SMITH A. K. , WALKER G. R. , SCHACHTMAN D. P. 
Published: November 2003

ABSTRACTIt is essential to characterize the water use of plants that have potential for the stabilization of rising saline ground‐water which could lead to increases in soil salinity. In this study, several techniques were used to determine the seasonal water use characteristics of the perennial grass Agropyron elongatum (tall wheatgrass) growing in a moderately saline, dryland environment with a fluctuating shallow groundwater table varying in electrical conductivity between 0 and 10 dS m−1. Soil conditions were examined in terms of water potential measurements, plant water sources were identified using a stable isotope of water (deuterium, 2H) and evapotranspiration was estimated using hydrological and ventilated chamber methods. Seasonal changes in soil water potential were caused by salt accumulation and soil moisture leading to changes in plant water availability, particularly in the surface soil region over summer and autumn. Evapotranspiration in A. elongatum was high over summer during the peak period of growth (4 mm d−1), with evidence of water use from groundwater and from specific regions of the soil profile. Evapotranspiration was low during the period that A. elongatum was partially senescent in autumn (< 0.5 mm d−1) and the lowest leaf water potential of ‐3 MPa that was measured occurred during this period of moderate water stress. Intermediate levels of water use (1.5 mm d−1) were measured during winter when the entire soil profile was available for water uptake. Based on physiological characteristics, including aspects of summer water use, root morphology and salt tolerance in A. elongatum, we conclude that this species is suitable for stabilizing the level of moderately saline groundwater in parts of southern Australia, which could reduce the potential for soil salinization.
Does transpiration control stomatal responses to water vapour pressure deficit?
Authors: BUNCE J. A. 
Published: November 2003

ABSTRACTThree types of observations were used to test the hypothesis that the response of stomatal conductance to a change in vapour pressure deficit is controlled by whole‐leaf transpiration rate or by feedback from leaf water potential. Varying the leaf water potential of a measured leaf by controlling the transpiration rate of other leaves on the plant did not affect the response of stomatal conductance to vapour pressure deficit in Glycine max. In three species, stomatal sensitivity to vapour pressure deficit was eliminated when measurements were made at near‐zero carbon dioxide concentrations, despite the much higher transpiration rates of leaves at low carbon dioxide. In Abutilon theophrasti, increasing vapour pressure deficit sometimes resulted in both decreased stomatal conductance and a lower transpiration rate even though the response of assimilation rate to the calculated substomatal carbon dioxide concentration indicated that there was no ‘patchy’ stomatal closure at high vapour pressure deficit in this case. These results are not consistent with stomatal closure at high vapour pressure deficit caused by increased whole‐leaf transpiration rate or by lower leaf water potential. The lack of response of conductance to vapour pressure deficit in carbon dioxide‐free air suggests that abscisic acid may mediate the response.
Chlorophyll a fluorescence, enzyme and antioxidant analyses provide evidence for the operation of alternative electron sinks during leaf senescence in a stay‐green mutant of Festuca pratensis
Authors: KINGSTON‐SMITH A. H. , THOMAS H. , FOYER C. H. 
Published: November 2003

ABSTRACTMutation of the sid gene in Festuca pratensis prevents chlorophyll degradation. The senescing leaves retain their chlorophyll complement and stay green. Nevertheless, CO2 assimilation and ribulose‐bisphosphate carboxylase/oxygenase content decline in both mutant and wild‐type plants. Photosynthesis and chlorophyll a fluorescence measurements were performed in air and at low oxygen to prevent photorespiration. The maximum extractable activity of ribulose 1,5 bisphosphate carboxylase was higher in the senescent mutant leaves than in those of the wild‐type control hut Mas much lower than that observed in the mature leaves of either genotype. The activation state of this enzyme was similar in mutant and wild‐type lines at equivalent stages of development. Analysis of chlorophyll a fluorescence quenching with varying irradianco showed similar characteristics for mature leaves of the two genotypes. Genotypic variations in photosystem II (I'SII) efficiency were observed only in the senescent leaves. Photochemical quenching and the quantum efficiency of PSII were greater in the senescent mutant leaves than in (he wild type at a given irradiance. The calculated electron flux through PSII was substantially higher in the mutant with a greater proportion of electrons directed to photorespiration.Maximum catalytic activities of ascorbate peroxidase decreased in senescent compared to mature leaves of both genotypes, while glutathione reductase and monodehydroascorbate reductase were unchanged in both cases. Superoxide dismutase activity was approximately doubled and dehydroascorbate reductase activity was three times higher in senescent leaves compared with the mature leaves of both genotypes. In no case was there a difference in enzyme activities between mutant and wild type at equivalent growth stages. The pool of reduced ascorbate was similar in the mature leaves of the two genotypes, whereas it was significantly higher in the senescent leaves of the mutant compared with the wild type. Conversely, the hydrogen peroxide content was significantly higher in the mature leaves of the wild type than in those of the mutant, but in senescent leaves similar values were obtained. In leaves subjected to chilling stress the reduced ascorbate pool was higher in both mature and senescent leaves of the mutant than in their wild‐type counterparts. Similarly, the hydrogen peroxide pool was significantly lower in both mature and senescent leaves of the mutant than in the wild type. We conclude that, in spite of deceased CO2 assimilation, the mutant is capable of high rates of electron Slow. The high ascorbate/hydrogen peroxide ratio observed in the mutant, particularly at low temperatures, suggests that the senescent leaves are not subject to enhanced oxidative stress.
Mutational analysis of chilling tolerance in plants
Authors: TOKUHISA J. G. , FELDMANN K. A. , LaBRIE S. T. , BROWSE J. 
Published: November 2003

ABSTRACTA mutational approach was taken to identify genes required for low‐temperature growth of the chilling‐tolerant plant Arabidopsis thaliana. The screen identified mutants that were specifically compromised in their ability to grow at 5°C but were indistinguishable from wild type when grown at 22°C. The populations screened were mutated either by ethyl methanesulphonate or by T‐DNA insertion. In both cases symptoms at 5°C included chlorosis, reduced growth, necrosis and death. This diversity of phenotypes demonstrates roles for chilling‐tolerance responses in such diverse processes as organdie biogenesis, cell metabolism and cell and organ development. Co‐segregation analysis on the first five mutants isolated from the T‐DNA lines indicated that in three of them, pfc1, pfc2 and sop1, the chilling phenotype is the result of T‐DNA insertion in a gene required for chilling tolerance rather than the creation of a temperature‐conditional mutation in an essential housekeeping gene. This identification of T‐DNA tagged alleles will facilitate cloning of the PFC1, PFC2 and SOP1 loci and allow for the biochemical and molecular genetic characterization of these chilling‐tolerance genes and the proteins that they encode.