bluuebunny/crossref_metadata_2025 huggingface dataset:
Present and potential uses of the natural abundance of stable isotopes in plant science, with illustrations from the marine environment
Authors: RAVEN J. A.
Published: April 2006

The use of stable isotope natural abundance measurements in plant ecophysiological research is discussed in the context of studies of 13C/12C ratios in marine plants, with emphasis on the uniqueness of the information given by natural abundance measurements and of the importance of complementary data obtained by other techniques in making full use of the natural abundance data. (1) Inorganic C acquisition and assimilation in marine plants can involve diffusive entry of CO2, or the occurrence of a CO2‐concentrating mechanism frequently involving active HCO3− influx. For diffusive CO2 entry, the δ13C measurements can give unique information on the fractional limitation of photosynthesis by CO2 transport which, with photosynthetic rate measurements, can be used to compute transport conductances. For active HCO3−, influx, the δ13C values uniquely permit computation of the ratio of the bidirection fluxes (influx/efflux) which, with photon yield data, can be used to given information on the mechanism of the efflux. The analyses are absolutely dependent on external (non‐δ13C) data distinguishing between diffusive CO2 entry and the occurrence of a CO2 concentrating mechanism. (2) δ13C measurements on marine photolithotrophs and on members of other trophic levels collected from the sea can give unique data on food webs, with measurements of δ values for other isotopes and compositional data adding precision to the interpretations. (3) Measurements of in situδ13C values for extant marine photolithotrophs, compared with δ13C values for ancient atmospheric CO2, can give unique information on the mechanism of atmospheric CO2 draw‐down at the start of glacials; other information permits more concrete conclusions to be drawn.
The measurement of stable isotope natural abundance variations
Authors: PRESTON T.
Published: April 2006

Precise stable isotope natural abundance analysis of the elements of organic matter, yields a wealth of information for the biologist. Robust sample preparation methodology and analytical instrumentation is necessary to achieve precise results. Basic principles of isotope ratio mass spectrometry (IRMS) are detailed, with particular regard to sample size, gas production and transfer into the IRMS ion source. Gas preparation methods developed to give quantitative yields of pure simple gases from organic and inorganic materials include vacuum line combustion, ampoule combustion and automated elemental analysers used off and on‐line. The new technique of GC‐C‐IRMS, where individual volatile organic compounds are separated by GC, combusted and analysed on‐line by IRMS, is also described. The conventional dual batch inlet developed by geochemists for the most precise analysis of stable isotopes, is contrasted with continuous flow‐IRMS analysis. The needs of the biological scientist for rapid throughput of small samples are discussed in this context. It is argued that the development of new instrumental approaches will permit many new applications of stable isotope methodology in the biological sciences.
Physical and chemical basis of carbon isotope fractionation in plants
Authors: O'LEARY M. H. , MADHAVAN S. , PANETH P.
Published: April 2006

Naturally‐occurring variations in the abundances of the stable isotopes of carbon and other elements can be used to understand the dynamics of natural processes in chemistry, biochemistry, biology, medicine, ecology and other fields. The use of carbon‐13 isotopic abundances as an indicator of photosynthetic function in plants has become common. The purpose of this article is to describe the physical and chemical processes that contribute to the abundances of carbon‐13 in plant materials, and to provide a framework for understanding how those processes control the isotopic contents of natural materials.
Stable sulphur isotopes in plants: a review
Authors: TRUST B. A. , FRY B.
Published: April 2006

The determination of the natural abundances of stable isotopes has become a useful method by which to study the transformations of elements in biological and ecological studies as well as to investigate the mechanisms of chemical reactions. Unlike carbon and nitrogen isotopes, however, stable sulphur isotopes are used infrequently, and their potential as tracers in biochemical and physiological studies are only beginning to be realized. This review provides an overview of research involving stable sulphur isotopes in studies of plant metabolism and pollution. Topics discussed include the mechanisms and accompanying isotopic fractionations involved during the uptake and assimilation of inorganic sulphur compounds by plants, the utility of plants as bioindicators of environmental sulphur pollution, and the emission of isotopically light H2S by plants in response to high concentations of sulphur. Future advances in the field are proposed.
Differential uptake of summer precipitation among co‐occurring trees and shrubs in a pinyon‐juniper woodland
Authors: FLANAGAN L. B. , EHLERINGER J. R. , MARSHALL J. D.
Published: April 2006

Measurements of the ratio of deuterium to hydrogen (D/H) in stem xylem water were used to determine the relative uptake of summer precipitation by four co‐occurring plant species in southern Utah. The species compared included two trees, Juniperus osteosperma and Pinus edulis, and two shrubs, Artemisia tridentata and Chrysothamnus nauseousus. There were significant differences among species in the relative use of summer precipitation. Chrysothamnus nauseosus had stem water D/H ratios in May through August 1990 that were not significantly different from that of groundwater. In contrast, the other three species had stem water D/H ratios that were intermediate between the groundwater value and summer precipitation values, indicating that a mixture of both precipitation and groundwater was being used by these species. The two tree species generally had higher D/H values than did A. tridentata indicating a higher average uptake of summer precipitation, although the roots of J. osteosperma and P. edulis may not be as responsive to small precipitation events as A. tridentata. There was a strong negative correlation between stem water D/H ratios and predawn water potential, which suggests a relationship between plant rooting pattern and water source use. In addition, water‐use efficiency during photosynthetic gas exchange, calculated from leaf carbon isotope composition, differed among species and was strongly correlated with differences in the relative uptake of summer precipitation.
Vascular anatomy of fabaceous nodules of determinate growth
Authors: WALSH K. B. , ATKINS R. S. , LOW C. S.
Published: April 2006

The vascular anatomy of nodules of 12 genera of tropical pasture and grain legumes of three tribes of theFabaceaeis described. Tracheary strands branch dichotomously and repeatedly from a root connection and generally terminate within sealed pockets of endodermis. Anastomosis of vascular strands at the nodule tip to form a complete xylem circuit was seen in three genera (Vigna, GlycineandLablab). The functional significance of vascular structure is discussed in terms of pathways of solute movement between the infected cells and the root, and the permeability of the nodule cortex to gases.
Quantitative determination of changes induced by NaCl in vacuoles and cellular size of Lycopersicon esculentum root cells
Authors: SÁNCHEZ‐AGUAYO I. , GONZÁLEZ‐UTOR A. L.
Published: April 2006

Changes induced by NaCl in the sizes of both cells and vacuolar compartments of tomato seedling roots were determined using morphometric and stereological analysis. Parameters evaluated showed that cellular volume was smaller in roots grown under saline conditions than in control roots. This reduction was greater when NaCl concentration was increased. Similar behaviour can be observed in the vacuolar compartment where high concentrations of NaCl produce a reduction in vacuolar volume although the number of vacuoles per cell does not change under saline conditions.
The dissipation of excess excitation energy in British plant species
Authors: JOHNSON G. N. , YOUNG A. J. , SCHOLES J. D. , HORTON P.
Published: April 2006

The reversible dissipation of excitation energy in higher plants is believed to protect against light‐induced damage to the photosynthetic apparatus. This dissipation is measured as the non‐photochemical quenching of chlorophyll fluorescence. A method is described whereby the saturated capacity for rapidly reversible non‐photochemical quenching can be compared between plant species. This method was applied to 22 common British plant species whose habitat was quantified using an index that describes shade tolerance. An association was found between occurrence in open habitats and a high capacity for non‐photochemical quenching. It was found that, whilst this capacity was species dependent, it did not depend upon the conditions under which the plant was grown. The possible role of zeaxanthin as a determinant of quenching capacity was examined by measuring the contents of xanthophyll cycle carotenoids for each species. Comparing species, no correlation was seen between the saturated level of non‐photochemical quenching and zeaxanthin content expressed relative to either total carotenoid or to chlorophyll. When zeaxanthin was expressed relative to the amount of xanthophyll cycle intermediates (zeaxanthin, antheraxanthin and violaxanthin), a weak correlation was seen.
Relationships between carotenoid composition and growth habit in British plant species
Authors: JOHNSON G. N. , SCHOLES J. D. , HORTON P. , YOUNG A. J.
Published: April 2006

The pigment composition of leaves from a number of different plant species collected from field sites in the region of Sheffield, UK, have been compared using high‐performance liquid chromatography. Expression of pigment content per unit leaf area was dominated by variation in the total leaf chlorophyll. Neither chlorophyll per unit area nor the chlorophyll a/b ratio were found to be correlated with the habitat from which the plants originated. When the amounts of different carotenoids were expressed relative to the total carotenoid pool, it was found that whilst neither total carotene (α‐ +β‐carotene) nor neoxanthin correlated with ability to grow in shade, the leaf content of both lutein and the total xanthophyll cycle carotenoids (zeaxanthin, anther‐axanthin and violaxanthin) did, with lutein content being high in shade species and xanthophyll cycle intermediates low. There was a strong negative correlation between the relative amounts of each of these groups of carotenoids. The ratio of lutein to xanthophyll cycle carotenoids was strongly correlated to an index of shade tolerance.
Impaired phytochrome‐mediated shade‐avoidance responses in the aurea mutant of tomato
Authors: CASAL J. J. , KENDRICK R. E.
Published: April 2006

Internode extension‐growth responses to neighbouring plants and to red to far‐red ratios (R:FR) were investigated in wild‐type (WT) and aurea (au)‐mutant seedlings of tomato grown under natural radiation. The genomic location of the au mutant is not known, but one of its consequences is the reduced phytochrome level. In WT seedlings, internode growth was promoted by the presence of non‐shading neighbours reflecting far‐red light (FR), the shade of a tall canopy, FR provided as a supplement during the photoperiod, and FR pulses either provided at the end of the day or delayed into the dark period. Supplementary FR during the photoperiod also promoted growth in herbicide‐treated partially bleached WT seedlings. The au mutant showed higher background extension‐growth rates, but only responded to the most severe treatments: deep shade light and very low R:FR at the end of the day, i.e. au‐mutant seedlings were less sensitive than WT seedlings to R:FR signals. Wild‐type seedlings were transferred from the glasshouse to a growth room and exposed to white light with two levels of phytochrome‐absorbable radiation but similar phytochrome photoequilibria and radiation for photosynthesis. The plants exposed to the lowest level showed a transient increase of internode extension growth rate and a simultaneous reduction of response to FR pulses, i.e. reproduced some of the features of au‐mutant seedlings. Phytochrome itself could set the degree of response to Pfr during neighbour detection.
The spatial distribution of chloroplast water in Acer platanoides sun and shade leaves
Authors: McCAIN D. C. , CROXDALE J. , MARKLEY J. L.
Published: April 2006

We evaluated a new, two‐dimensional (2‐D) nuclear magnetic resonance (NMR) imaging technique as a method for measuring the distribution of chloroplasts in leaves. NMR images that showed the distribution of chloroplast water and of total water as a function of depth into Acer platanoides sun and shade leaves were compared with the distribution of chlorophyll in the same leaf types (as measured by fluorescence microscopy), with the cellular structure (by scanning electron microscopy), and with published information. Results showed that the volume fraction of chloroplast water was much larger in shade than in sun leaves, and that it averaged about one‐third larger in the palisade than in the spongy parenchyma region of both leaf types. Chlorophyll fluorescence was more intense in shade than in sun leaves. In sun leaves, fluorescence was maximal in the palisade region near the junction with the spongy parenchyma, while in shade leaves, fluorescence was maximal in the upper part of the spongy layer. We concluded that 2‐D NMR imaging reliably indicates the location of chloroplast water.
Determination of foliar uptake of chemicals: influence of leaf surface microflora
Authors: SCHREIBER L. , SCHÖNHERR J.
Published: April 2006

Analysing uptake and desorption kinetics of methylglucose in needles of Picea abies (L.) Karst., the effect of NaN3 on methylglucose uptake, and the correlation between different degrees of colonization of needle surfaces with epiphytes and equilibrium uptake of methylglucose, showed that methylglucose was taken up only by epiphytes but not by the needles themselves. Thus, amounts of methylglucose taken up are a measure of the amounts of epiphytic microorganisms. Uptake of methylglucose into epiphytes was very rapid and equilibrium was obtained within 2h. Amounts taken up could completely be desorbed again from epiphytes within 2‐6 h. It is pointed out that the possible influence of leaf surface microorganisms must be considered in studies of foliar uptake of chemicals, in order to avoid erroneous conclusions.
Gravity sensing in oat coleoptiles: scatter in growth orientation under different g‐conditions
Authors: JOHNSSON A. , CHAPMAN D. K. , BROWN A. , JOHNSON‐GLEBE C. , KARLSSON C. , HEATHCOTE D. G.
Published: April 2006

Dark‐grown oat seedlings depart from the expected vertical orientation, suggesting that the coleoptile is less responsive to the lateral component of a gravitational stimulus than would be expected. This phenomenon was studied by investigating the gravitropic curvatures of oat (Avena sativa L. cv. Seger) coleoptiles at 10g and over a range of longitudinally applied centripetal accelerations up to 19·4g. In most experiments, the plants were grown and observed at a particular g‐level throughout the experiment. Time‐lapse video recordings permitted studies of the scatter, measured as the variability of the plants' angle from the vertical (or root mean square value, RMS). The coleoptiles' heights at the end of the experiments were not significantly altered under the centrifugation. Scatter increased with plant age and decreased with increasing g. It decreased in an almost linear fashion as a function of the logarithm of the g‐acceleration. In a series of experiments, the g‐level was changed from 10g to a higher test g‐acceleration. The scatter was then reduced within half an hour after the g‐transition. It is pointed out that the experiments confirm that the scatter is g‐related but that it was not predicted quantitatively by present theories of the oat coleoptile's gravitropic response kinematics.
Cold‐induced purpling of Pinus contorta seedlings depends on previous daylength treatment
Authors: CAMM E. L. , McCALLUM J. , LEAF E. , KOUPAI‐ABYAZANI M. R.
Published: April 2006

The characteristic cold‐induced foliar accumulation of anthocyanin (‘purpling’) seen in many species of pine seedlings in the autumn can be contingent upon photoperiod received months previously. In nursery‐grown seedlings of Pinus contorta Dougl. var. latifolia Engelm., a 4‐week exposure during August of 10‐h days followed by return to ambient photoperiod diminished the frequency of purpling following the November onset of cold weather (21% compared to 71% of the untreated controls). Anthocyanin accumulation (primarily cyanidin 3‐glucoside) was controlled differently than general phenolic metabolism, and involved the integration of two temporally separated environmental signals.
Plants as competing populations of redundant organs
Authors: SACHS T. , NOVOPLANSKY A. , COHEN D.
Published: April 2006

At any given time, a vascular or land plant may be a colony of functional sectors, each consisting of a shoot and its associated roots. In most plants, however, the activity of the cambium can change the relative vascular contacts of neighbouring shoots. Vascular tissues can even differentiate along new orientations, forming contacts that change the sectorial structure of the plant. Such reoriented differentiation is induced by the same auxin from developing leaves as are other types of vascular differentiation. The occurrence of vascular reorientation is determined by two criteria: the presence of an auxin flow that exceeds the transport capacity of the tissues that follow the previous, established orientation and the availability of nearby channels that are not fully occupied, not‘protected’ by their own flow of auxin. These controls of vascular orientation suggest that neighbouring shoots (and neighbouring roots) compete with one another, by means of signals indicating their state and their environment, for vascular contacts with the rest of the plant. Such internal competition between genetically equivalent shoots is an adaptation to heterogeneous environments: it is the shoots in the best conditions available to the plant that receive the support of a greater part of the root system. The potential for changes of vascular contacts points to open problems and to neglected aspects of the role of the cambium in plant organization.
The boundary layer and the apparent responses of stomatal conductance to wind speed and to the mole fractions of CO2 and water vapour in the air
Authors: APHALO P. J. , JARVIS P. G.
Published: April 2006

The experiments and simulations reported in this paper show that, for stomata sensitive to both CO2 and water vapour concentrations, responses of stomatal conductance (gws) to boundary layer thickness have two components, one resulting from changes in intercellular CO2 concentration (χci) and another from changes in leaf surface water vapour saturation deficit (Dws). The experiments and simulations also show that the boundary layer conductance (gwb) can significantly alter the apparent response of gws to ambient air CO2 mole fraction (χca) and water vapour mole fraction (χwa). Because of the feedback loop involved the responses of gws for χca and χwa each include responses to both χci and Dws. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χci and Dws—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response of gws for a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses of gws to χci and Dws, the apparent responses of gws to Dwa and χca depend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with different methods.
Interactive effects of high temperature and elevated carbon dioxide concentration on cowpea [Vigna unguiculata(L.) Walp.]
Authors: AHMED F. E. , HALL A. E. , MADORE M. A.
Published: April 2006

Limitations in carbohydrate supplies have been implicated as a factor responsible for reproductive failure under heat stress. Heat stress affects two stages of reproductive development in cowpea [Vigna unguiculata(L.) Walp.], and genotypes are available with tolerance and sensitivity to heat during these different stages. The objectives of this study were to determine the responses of these cowpea lines to ambient and elevated [CO2], under heat stress and optimal temperature, and test whether differences in carbohydrate supplies due to genotypes, CO2enrichment and heat stress are associated with differences in sensitivity to heat during reproductive development. Plants were grown in reach‐in growth chambers and subjected to day/night temperatures of either 33/20 or 33/30°C, and [CO2] levels of either 350 or 700 μmol mol‐1. Under intermediate night temperature (33/20°C), all lines set substantial numbers of pods. Under high night temperature (33/30°C) with either ambient or elevated [CO2], one heat‐sensitive line produced no flowers and the other set no pods, whereas the heat‐tolerant line abundantly set pods. High night temperature reduced the overall carbohydrate content of the plants, especially peduncle sugars, and caused decreases in photosynthetic rates. The high pod set of the heat‐tolerant line, under high night temperature, was associated with higher levels of sugars in peduncles compared with the heat‐sensitive lines. The heat‐tolerant line accumulated substantial shoot biomass, exhibited less accumulation of starch in leaves, and possibly had less down‐regulation of photosynthesis in response to CO2enrichment and heat stress than the heat‐sensitive lines. Elevated [CO2] resulted in higher overall carbohydrate levels in heat‐sensitive lines (starch in leaves, stems and peduncles), but it did not increase their heat tolerance with respect to flower production or pod set. Heat‐induced damage to floral buds and anthers in the sensitive lines was associated with low sugars levels in peduncles, indicating that heat had greater effects on assimilate demand than on leaf assimilate supply. The heat‐tolerant line was the most responsive genotype to elevated [CO2] with respect to pod production under either high or intermediate temperatures.
Nitrogen and phosphorus dynamics of a tallgrass prairie ecosystem exposed to elevated carbon dioxide
Authors: OWENSBY C. E. , COYNE P. I. , AUEN L. M.
Published: April 2006

A tallgrass prairie ecosystem was exposed to ambient and twice‐ambient CO2 concentrations in open‐top chambers and compared to unchambered ambient CO2 during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii (C4), A. scoparius (C4), Sorghastrum nutans (C4) and Poa pratensis (C3). Nitrogen and phosphorus concentrations in A. gerardii, P. pratensis and dicotyledonous herbs above ground biomass were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, N and P concentrations in peak biomass were estimated by an early August harvest. N and P concentrations in root production as a function of treatment were estimated using root ingrowth bags that remained in place throughout the growing season. Total N and P in above‐ and belowground biomass were calculated as products of concentration and peak biomass by species groups. N concentration in A. gerardii and dicotyledonous herb aboveground biomass was lower and total N higher in elevated CO2 plots than in ambient CO2 plots. N concentration in P. pratensis aboveground biomass was lower in elevated CO2 plots than in ambient, but total N did not differ among treatments in 2 out of 3 years. In 1990, N concentration in root ingrowth bag biomass was lower and total N greater in elevated CO2 than in ambient CO2 plots. Root ingrowth bag biomass N concentration did not differ among treatments in 1991, but total N was greater in elevated CO2 plots than in ambient CO2 plots. P concentration was lower under elevated CO2 compared to ambient in 1989, but did not differ substantially among treatments in 1990 or 1991. In all years, total P in aboveground A. gerardii and root ingrowth bag biomass was greater under elevated CO2 than ambient. P concentration and total P in P. pratensis was similar among treatments.
Abaxial and adaxial stomata from Pima cotton (Gossypium barbadense L.) differ in their pigment content and sensitivity to light quality
Authors: LU Z. , QUIÑONES M. A. , ZEIGER E.
Published: April 2006

Sensitivity to light quality and pigment composition were analysed and compared in abaxial and adaxial stomata of Gossypium barbadense L. (Pima cotton). In most plants, abaxial (lower) stomatal conductances are higher than adaxial (upper) ones, and stomatal opening is more sensitive to blue light than to red. In greenhouse‐grown Pima cotton, abaxial stomatal conductances were two to three times higher than adaxial ones. In contrast, adaxial stomatal conductances were 1·5 to two times higher than abaxial ones in leaves from growth chamber‐grown plants. To establish whether light quality was a factor in the regulation of the relationship between abaxial and adaxial stomatal conductances, growth‐chamber‐grown plants were exposed to solar radiation outdoors and to increased red light in the growth chamber. In both cases, the ratios of adaxial to abaxial stomatal conductance reverted to those typical of greenhouse plants. We investigated the hypothesis that adaxial stomata are more sensitive to blue light and abaxial stomata are more sensitive to red light. Measurements of stomatal apertures in mechanically isolated epidermal peels from growth chamber and greenhouse plants showed that adaxial stomata opened more under blue light than under red light, while abaxial stomata had the opposite response. Using HPLC, we quantified the chlorophylls and carotenoids extracted from isolated adaxial and abaxial guard cells. All pigments analysed were more abundant in the adaxial than in the abaxial guard cells. Antheraxanthin and β‐carotene contents were 2·3 times higher in adaxial than in abaxial guard cells, comparing with ad/ab ratios of 1·5–1·9 for the other pigments. We conclude that adaxial and abaxial stomata from Pima cotton have a differential sensitivity to light quality and their distinct responses are correlated with different pigment content.
Long‐term effects of elevated CO2 and nutrients on photosynthesis and rubisco in loblolly pine seedlings
Authors: TISSUE D. T. , THOMAS R. B. , STRAIN B. R.
Published: April 2006

The effects of long‐term CO2 enhancement and varying nutrient availability on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied on loblolly pine (Pinus taeda L.) seedlings grown in two atmospheric CO2 partial pressures (35 and 65 Pa) and three nutrient treatments (low N, low P, and high N and P). Measurements taken in late autumn (November) after 2 years of CO2 enrichment and nutrient addition showed that photosynthetic rates were higher for plants grown at elevated CO2 only when they received supplemental N. Total rubisco activity and rubisco content decreased at elevated CO2, but there was an increase in activation state. At elevated CO2, proportionately less N was found in rubisco and more N was found in the light reaction components. These results demonstrate acclimation of photosynthetic processes to elevated CO2 through reallocation of N. Loblolly pine grown in nutrient conditions similar to native soils (low N availability) had lower needle N and chlorophyll content, lower total rubisco activity and content, and lower photosynthetic rates than plants grown at high N and P. This suggests that the magnitude of the photosynthetic response to a future, high‐CO2 environment will be dependent on soil fertility in the system.
Natural CO2 springs in Italy: a resource for examining long‐term response of vegetation to rising atmospheric CO2 concentrations
Authors: MIGLIETTA F. , RASCHI A. , BETTARINI I. , RESTI R. , SELVI F.
Published: April 2006

It is estimated that more than 100 geothermal CO2 springs exist in central‐western Italy. Eight springs were selected in which the atmospheric CO2 concentrations were consistently observed to be above the current atmospheric average of 354μmol mol‐1. CO2 concentration measurements at some of the springs are reported. The springs are described, and their major topographic and vegetational features are reported. Preliminary observations made on natural vegetation growing around the gas vents are then illustrated. An azonal pattern of vegetation distribution occurs around every CO2 spring regardless of soil type and phytoclimatic areas. This is composed of pioneer populations of a Northern Eurasiatic species (Agrostis canina L.) which is often associated with Scirpus lacustris L. The potential of these sites for studying the long‐term response of vegetation to rising atmospheric CO2 concentrations is discussed.
Drought‐induced leaf shedding in walnut: evidence for vulnerability segmentation
Authors: TYREE M. T. , COCHARD H. , CRUIZIAT P. , SINCLAIR B. , AMEGLIO T.
Published: April 2006

Trees of Juglans regia L. shed leaves when subjected to drought. Before shedding (when leaves are yellow), the petioles have lost 87% of their maximum hydraulic conductivity, but stems have lost only 14% of their conductivity. This is caused by the higher vulnerability of petioles than stems to water‐stress induced cavitation. These data are discussed in the context of the plant segmentation hypothesis.
Stabilizing microtubules with taxol increases microfilament stability during freezing of rye root tips
Authors: CHU B. , KERR G. P. , CARTER J. V.
Published: April 2006

We have used double fluorescence labelling to investigate the effect of freezing on microtubules and microfilaments in root‐tip cells of rye (Secale cereale L. cv Rymin). Freezing to ‐5°C (which does not kill these cells) caused partial depolymerization of both, but microfilaments were more resistant than microtubules. When microtubules were stabilized against freeze‐induced depolymerization by pre‐treating seedlings with taxol, microfilaments exhibited enhanced stability as well. Almost all the frozen cells containing taxol‐stabilized microtubules also contained microfilaments. When seedlings were treated with the microtubule‐destabilizing drug APM prior to freezing, microfilaments became more susceptible to freeze‐induced depolymerization than in controls. These data suggest a physical interaction between microtubules and microfilaments in these cells.
Gamete orientation and induction of gametogenesis by pheromones in algae and plants
Authors: MAIER I.
Published: April 2006

This review attempts to give a concise overview of the widespread occurrence and the significance, structure and function of pheromones in the chemical communication between individuals of the same species during sexual reproduction in algae and plants. Also included is information on the Oomyctes and the chytridiomyceteAllomyces.The terminology in respect of pheromone function and pheromone‐induced reactions is discussed.
Root demography in kiwifruit (Actinidia deliciosa)
Authors: REID J. B. , SORENSEN I. , PETRIE R. A.
Published: April 2006

A rhizotron was used to study fine‐root demography in mature vines of kiwifruit (Actinidia deliciosa). The vines were grown in a deep, well drained, silt loam and received normal orchard management. Roots were measured from 10 to 160cm depth at biweekly intervals for 2 years. After an initial phase of rapid colonisation of the repacked soil behind the rhizotron windows, the total length of visible roots per vine remained quite steady. This apparent stability of the total belied fast and sustained localized turnover of the fine roots at all soil depths. Fifty‐one per cent of the roots survived ≤28d, 69% died at an age ≤56d and only 8% survived >252d. For each year, the cumulative length of roots grown was equivalent to about 2·75 times the maximum net length of roots visible. These may be the largest annual rates of root turnover yet reported. This has important ramifications for the carbon balance, mineral nutrition and water relations of the plant.
Blue light controls solar tracking by flowers of an alpine plant
Authors: STANTON M. L. , GALEN C.
Published: April 2006

In at least18plant families, leaves or flowers can maintain a specific orientation with respect to diurnal movements of the sun. Previous work on heliotropic leaves has demonstrated that blue light (400–500nm) provides the cue for their tracking response. Floral heliotropism occurs in several families of arctic and alpine plants, but the spectral sensitivity of the response has not been studied previously. Moreover, no studies on the spectral sensitivity of any heliotropism have been conducted on wild plants growing in their natural habitat. Working under field conditions, we used coloured acrylic filters to determine whether heliotropism by flowers of the snow buttercup (Ranunculus adoneus) is responsive to broad‐band blue or red light. Flowers were able to orient towards the sun under boxes made entirely of blue‐transmitting filters and in red‐transmitting boxes having a single blue side that faced the sun. In these treatments, solar tracking ability was not significantly different from that observed in adjacent control flowers. In contrast, the precision of solar orientation was significantly reduced in red‐transmitting boxes and red boxes with a single blue side oriented away from the sun. In the early morning, flowers covered by red‐transmitting boxes failed to orient in the direction of sunrise, suggesting that this floral response, unlike that seen in some heliotropic leaves, lacks a residual‘memory’ for previous solar movements.
Functional aspects of secondary carotenoids in Haematococcus lacustris (Girod) Rostafinski (Volvocales). V. Influences on photomovement
Authors: HAGEN C. , BRAUNE W. , VOGEL K. , HÄDER D.‐P.
Published: April 2006

Secondary carotenoids are suspected to modulate photomovement in Haematococcus lacustris [Girod] Rostafinski (Volvocales). To investigate the influence of these extrachloroplastic ketocarotenoids on phototactic and photophobic responses in the flagellate stage of the green alga, flagellate suspensions differing in the content of secondary carotenoids were grown from green and red aplanospores. Photo‐orientation of these flagellates induced by unilateral irradiation was investigated using a computer‐aided system for microscopic image analysis. Results were hypothetically summarized as follows:

(1) Diminution of precision of the positive phototaxis was found in red flagellates. This might be due to cellular shading of the blue‐light‐sensitive photoreceptor by secondary carotenoids.

(2) Red flagellates exhibited an increase in the photophobic response. This finding is discussed in relation to an adaptive increase of the photoreceptor sensitivity, thought to be a result of the higher optical density of the corresponding cell suspension in the blue wavelength region.
Applications of a thermal imaging technique in the study of the ascent of sap in woody species
Authors: ANFODILLO T. , SIGALOTTI G. B. , TOMASI M. , SEMENZATO P. , VALENTINI R.
Published: April 2006

We present applications of infrared thermograph to the direct observation of water transport in stems of woody species. Presently, the method gives only qualitative information on the path of sap movement along the stem, and therefore, does not replace any of the common quantitative methods of sap flow measurement. Nevertheless, the thermal imaging technique provides a novel approach to the study of the ascent of sap and could have a role in supporting more quantitative methods. Thermography permits visualization of the thermal variations of a fairly large area of the stem in real time, and hence, is well suited for spatial analysis of sap movement. Three experiments were carried out during the summers of 1991 and 1992, with the following objectives: to define the sap flow distribution in the active annual rings; to identify grain anomalies in the sap wood; and to study the consequences of induced embolism on the path of sap flow. Altogether, we tested more than 10 woody species (broad‐leaves and conifers) either in natural conditions or in the nursery. We found considerable differences in the spatial distribution of sap flow not only between species and individuals but also within a single tree. Grain anomalies or embolized zones in the xylem, which are easily demonstrated, often further modify the path of sap flow. The irregularity of sapwood dimensions and of sap flow among tree rings requires careful evaluation of the positioning of the probes when using methods for quantitative measurements.
Cellular differentiation in root caps of Zea mays that do not secrete mucilage
Authors: MOORE R. , MILLER I.
Published: April 2006

We quantified the structural changes accompanying cellular differentiation in root caps of Zea mays cv. Ageotropic to determine the developmental basis for the nongraviresponsiveness of their primary roots. Cells of the calyptrogen and columella of primary roots of the ageotropic mutant have structures indistinguishable from those of caps of primary roots of Z. mays cv. Kys the graviresponsive, wild‐type parent of Z. mays cv. Ageotropic. However, the relative volumes of dictyosomes, dictyosome‐derived vesicles and starch in the outermost peripheral cells of wild‐type roots were significantly lower than were those in peripheral cells of mutant roots. This corresponds to a dramatic accumulation of starch and mucilage‐filled vesicles in peripheral cells of mutant roots. Cellular differentiation in root caps of graviresponsive seminal roots of the Ageotropic mutant resembled that of primary and seminal roots of the wild‐type cultivar, and differed significantly from that of primary roots of the mutant. We conclude that the mutation that blocks secretion of mucilage from peripheral cells of Ageotropic roots: (1) expresses itself late in cellular differentiation in root caps; (2) is expressed only in primary (but not seminal) roots of the Ageotropic mutant; and (3) is consistent with malfunctioning dictyosomes and dictyosome‐derived vesicles being the cellular basis for agravitropism of primary roots of this mutant.
Physiological processes limiting plant growth in saline soils: some dogmas and hypotheses
Authors: MUNNS R.
Published: April 2006

Recent progress in improving the salt tolerance of cultivated plants has been slow. Physiologists have been unable to define single genes or even specific metabolic processes that molecular biologists could target, or pinpoint the part of the plant in which such genes for salt tolerance might be expressed. While the physiological might be expressed. While the physiological processes are undoubtedly complex, faster progress on unraveling mechanisms of salt tolerance might be made if there were more effort to test hypotheses rather than to accumulate data, and to integrate cellular and whole plant responses. This article argues that salts taken up by the plant do not directly control plant growth by affecting turgor, photosynthesis or the activity of any one enzyme. Rather, the build‐up of salt in old leaves hasten their death, and the loss of these leaves affects the supply of assimilates or hormones to the growing regions and thereby affects growth.
Feedback limitation of photosynthesis of Phaseolus vulgaris L grown in elevated CO2
Authors: SOCIAS F. X. , MEDRANO H. , SHARKEY T. D.
Published: April 2006

The capacity for photosynthesis is often affected when plants are grown in air with elevated CO2 partial pressure. We grew Phaseolus vulgaris L. in 35 and 65 Pa CO2 and measured photosynthetic parameters. When assayed at the growth CO2 level, photosynthesis was equal in the two CO2 treatments. The maximum rate of ribulose‐1,5‐bisphosphate (RuBP) consumption was lower in plants grown at 65 Pa, but the CO2 partial pressure at which the maximum occurred was higher in the high‐CO2‐grown plants, indicating acclimation to high CO2. The acclimation of RuBP consumption to CO2 involved a reduction of the activity of RuBP carboxylase which resulted from reduced carbamylation, not a loss of protein. The rate of RuBP consumption declined with CO2 when the CO2 partial pressure was above 50Pa in plants grown under both CO2 levels. This was caused by feedback inhibition as judged by a lack of response to removing O2 from the air stream. The rate of photosynthesis at high CO2 was lower in the high‐CO2‐grown plants and this was correlated with reduced activity of sucrose‐phosphate synthase. This is only the second report of O2‐insensitive photosynthesis under growth conditions for plants grown in high CO2.
Effects of atmospheric CO2 enrichment on early growth of Vivia faba, a plant with large cotyledons
Authors: RADOGLOU K. M. , JARVIS P. G.
Published: April 2006

Seedlings of Vicia faba L. were grown in open‐top growth chambers at present (P=350μmol−1) and at elevated (E=700μmol mol−1) atmospheric CO2 concentration. The effects of CO2 enrichment on the first phase of growth after germination were examined over 45 d. There were no positive effects of CO2 enrichment on growth of the seedlings during this early phase. No differences were observed in leaf area or in total dry weight. No differences were found in morphology or anatomy of the leaves. The numbers of stomatal and epidermal cells, thickness of leaf, of epidermis and of mesophyll cell‐layers were unaffected by CO2 enrichment. Also, no differences were observed in leaf concentrations of chlorophyll, reducing carbohydrates or starch. These results contrast markedly with results from similar experiments on poplar hybrids and Phaseolus vulgaris obtained in the same growth facility. It seems that the intitial growth is under internal control such that the atmospheric CO2 concentration has no effects. The lack of response in this case may be attributed to the presence and longevity of the large cotyledons which provided available substrate for growth.
Intensity of hydrostimulation for the induction of root hydrotropism and its sensing by the root cap
Authors: TAKAHASHI H. , SCOTT T. K.
Published: April 2006

Roots of Pisum sativum L. and Zea mays L. were exposed to different moisture gradients established by placing both wet cheesecloth (hydrostimulant) and saturated aqueous solutions of various salts in a closed chamber. Atmospheric conditions with different relative humidity (RH) in a range between 98 and 86% RH were obtained at root level, 2 to 3mm from the water‐saturated hydrostimulant. Roots of Silver Queen corn placed vertically with the tips down curved sideways toward the hydrostimulant in response to approximately 94% RH but did not respond positively to RH higher than approximately 95%. The positive hydrotropic response increased linearly as RH was lowered from 95 to 90%. A maximum response was observed at RH between 90 and 86%. However, RH required for the induction of hydrotropism as well as the responsiveness differed among plant species used; gravitropically sensitive roots appeared to require a somewhat greater moisture gradient for the induction of hydrotropism. Decapped roots of corn failed to curve hydrotropically, suggesting the root cap as a major site of hydrosensing.
Wall‐to‐membrane linkers in onion epidermis: some hypotheses
Authors: PONT‐LEZICA R. F. , McNALLY J. G. , PICKARD B. G.
Published: April 2006

Wall‐to‐wall linkage may help maintain cell integrity and polarity, and focus mechanical stress from wall to mech‐anotransductive ion channels within the plasm a lemma. When cells of onion bulb scale epidermis shrink during plasmolysis with CaCl2, the plasmalemma remains attached to the cell wall by Hechtian strands which we hypothesize might possibly be drawn out from linkages fulfilling the above functions. We show that at least many of the attachment loci are independent of the plasmodesmata. A priori, wall glycoproteins seem good candidates for the wall‐to‐membrane linkers; therefore, we investigated the distribution in wall and plasmalemma of antigen recognized by antibody to hydroxyproline‐rich glycoprotein (HRGP). Using fluorescent secondary antibodies, we showed that polyclonal antibodies prepared against wall HRGP from soybean bind to the onion walls (following mild depectination), but also bind to the plasmalemma after the wall is enzymatically digested. The distribution of the antibodies is punctate. On the plasmalemma, the points tend to be scattered more or less uniformly, but can cluster at termini of large streaming strands (which rarely form in wall‐constrained cells.) These streaming strands can be seen to exert tension on the membrane. We hypothesize that (1) the antigen on the surface of the protoplast may correspond to the antigen in the walls, (2) such antigen may be responsible for adhesion of membrane to wall at the linkage sites visualized by CaCl2 plasmolysis, and (3) the linkage sites may be transmembrane proteins to which cytoskeleton can attach at the inner surface.
Nodule growth and activity may be regulated by a feedback mechanism involving phloem nitrogen*
Authors: PARSONS R. , STANFORTH A. , RAVEN J. A. , SPRENT J. I.
Published: April 2006

We present a mechanism of regulation of growth and activity of legume root nodules which is consistent with published experimental observations. The concentration of reduced nitrogen compounds, probably amino acids, flowing into the nodules from the phloem, is sensed by the nodules; growth and activity of the nodules is adjusted accordingly. In many legumes this response may involve changes in the oxygen diffusion resistance of the nodule cortex. A straightforward feedback mechanism in which nodule activity is lowered when reduced N in the phloem is high and increased when it is low is envisaged. Almost all import into nodules is via the phloem sap originating in the lower leaves. As a plant develops, these mature leaves no longer utilize nitrogen delivered in the xylem and so export it in the phloem. In plants with an adequate nitrogen supply (from nodules or combined nitrogen in soil), a high concentration of nitrogen containing compounds in the phloem from the lower leaves may inhibit nodule growth as well as activity. This suggestion is an alternative to the hypotheses of carbohydrate deprivation or nitrate inhibition which are commonly used to explain the effects of combined nitrogen on nodule growth and activity.
Plant growth modelling without integrating mechanisms
Authors: CHEESEMAN J. M.
Published: April 2006

The integration of root and shoot activity for resource acquisition and allocation is a central problem both in experimental physiology and in mathematical growth modelling. A key feature in all proposed solutions is the mechanism by which roots and shoot communicate their resource status, their needs or their demands. In experimental studies, chemical messengers (hormones or nutrients) have been central. In mathematical models, partitioning or productivity functions of one form or another have been incorporated to fill a similar role. In this paper, the central hypothesis is that growth and resource allocation can be based solely on local, internal, non‐structural resource concentrations and local kinetic rules, without the need for additional mechanisms to integrate activities at the organis‐mal level. The specific objective was to develop a formal model using the classical two‐compartment, two‐resource framework which did not include direct intercompartmental coordinating or communicating mechanisms or resource partitioning functions. The formalization effort was successful based on two criteria. First, the ‘plants’ grow at steady and balanced rates when ‘growth conditions’ are constant; and second, challenged with experimental manipulations such as pruning or limitations in resource acquisition, their growth responses mimic those of real plants. Analysis of the results indicates that the complex integrated growth patterns of the modelled plants are emergent properties – having no direct or indirect mechanistic basis – of the simple system. They imply that similar ‘mechanism‐less’ integration is possible in real plants as an emergent property of strictly local, cellular‐level activities.