bluuebunny/crossref_metadata_2025 huggingface dataset:
Systemin triggers an increase of cytoplasmic calcium in tomato mesophyll cells: Ca2+ mobilization from intra‐ and extracellular compartments
Authors: Moyen C. , Hammond‐Kosack * K. E. , Jones J. , Knight M. R. , Johannes E.
Published: March 2003

We show here that, within 1–2 min of application, systemin triggers a transient increase of cytoplasmic free calcium concentration ([Ca2+]c) in cells from Lycopersicon esculentum mesophyll. The systemin‐induced Ca2+ increase was slightly but not significantly reduced by L‐type Ca2+ channel blockers (nifedipine, verapamil and diltiazem) and the Ca2+ chelator [ethylene glycol tetraacetic acid (EGTA)], whereas inorganic Ca2+ channel blockers (LaCl3, CdCl2 and GdCl3) and compounds affecting the release of intracellular Ca2+ from the vacuole (ruthenium red, LiCl, neomycin) strongly reduced the systemin‐induced [Ca2+]c increase. By contrast, no inhibitory effect was seen with the potassium and chloride channel blockers tested. Unlike systemin, other inducers of proteinase inhibitor (PI) and of wound‐induced protein synthesis, such as jasmonic acid (JA) and bestatin, did not trigger an increase of cytoplasmic Ca2+. The systemin‐induced elevation of cytoplasmic Ca2+ which might be an early step in the systemin signalling pathway, appears to involve an influx of extracellular Ca2+ simultaneously through several types of Ca2+ permeable channels, and a release of Ca2+ from intracellular stores sensitive to blockers of inositol 1,4,5‐triphosphate (IP3)‐ and cyclic adenasine 5’‐diphosphoribose (cADPR)‐mediated Ca2+ release.
The regulation of isoprene emission responses to rapid leaf temperature fluctuations
Authors: Singsaas E. L. , Sharkey T. D.
Published: March 2003

Isoprene emission from leaves is temperature dependent and may protect leaves from damage at high temperatures. We measured the temperature of white oak (Quercus albaL.) leaves at the top of the canopy. The largest short‐term changes in leaf temperature were associated with changes in solar radiation. During these episodes, leaf temperature changed with a 1 min time constant, a measure of the rate of temperature change. We imposed rapid temperature fluctuations on leaves to study the effect of temperature change rate on isoprene emission. Leaf temperature changed with a 16 s time constant; isoprene responded more slowly with a 37 s time constant. This time constant was slow enough to cause a lag in isoprene emission when leaf temperature fluctuated rapidly but isoprene emission changed quickly enough to follow the large temperature changes observed in the oak canopy. This is consistent with the theory that isoprene functions to protect leaves from short periods of high temperature. Time constant analysis also revealed that there are two processes that cause isoprene emission to increase with leaf temperature. The fastest process likely reflects the influence of temperature on reaction kinetics, while the slower process may reflect the activation of an enzyme.
Metal localization in water hyacinth roots from an urban wetland
Authors: VESK P. A. , NOCKOLDS C. E. , ALLAWAY W. G.
Published: March 2003

PCA, principal components analysis MDS, multidimensional scaling STEM, scanning transmission electron microscopy  Metal localization within and around roots of water hyacinth (Eichhornia crassipes) growing in a wetland receiving urban run‐off was studied by energy dispersive X‐ray microanalysis of sections from freeze‐substituted roots. Sampling randomly from an order of magnitude gradient in metal concentrations (Cu and Pb) allowed us the opportunity to identify general patterns of metal localization. Iron was present at high levels at the root surface, and this may have been a root plaque as described for wetland plants with roots anchored in flooded soils. Iron levels decreased centripetally across the root and were higher in cell walls than within cells. Trace metals (Cu, Zn and Pb) were not localized at the root surface. In contrast with iron, trace metal levels increased centripetally across the root, tended to be higher inside cells and were highest within cells in the stele. Variability of localization was high for all metals analysed. Multivariate statistical analyses (principal components analysis and multidimensional scaling) were useful for identifying overall patterns in elemental distribution.
The role of photorespiration during drought stress: an analysis utilizing barley mutants with reduced activities of photorespiratory enzymes
Authors: WINGLER A. , QUICK W. P. , BUNGARD R. A. , BAILEY K. J. , LEA P. J. , LEEGOOD R. C.
Published: March 2003

C
i, intercellular CO2 concentration Fv/Fm, quantum efficiency of excitation capture by open photosystem II centres FBPase, fructose‐1,6‐bisphosphatase GAPDH, glyceraldehyde‐3‐phosphate dehydrogenase GDC, glycine decarboxylase GS‐2, chloroplastic glutamine synthetase HPR, hydroxypyruvate reductase PFD, photon flux density ΦCO2, quantum efficiency of CO2 assimilation ΦPSII, quantum efficiency of photosystem II electron transport ψ, water potential qN, non‐photochemical chlorophyll a fluorescence quenching qP, photochemical chlorophyll a fluorescence quenching RuBP, ribulose‐1,5‐bisphosphate Rubisco, ribulose‐1,5‐bisphosphate carboxylase‐oxygenase SBPase, sedoheptulose‐1,7‐bisphosphatase SGAT, serine : glyoxylate aminotransferase  The significance of photorespiration in drought‐stressed plants was studied by withholding water from wild‐type barley (Hordeum vulgare L.) and from heterozygous mutants with reduced activities of chloroplastic glutamine synthetase (GS‐2), glycine decarboxylase (GDC) or serine : glyoxylate aminotransferase (SGAT). Well‐watered plants of all four genotypes had identical rates of photosynthesis. Under moderate drought stress (leaf water potentials between –1 and –2 MPa), photosynthesis was lower in the mutants than in the wild type, indicating that photorespiration was increased under these conditions. Analysis of chlorophyll a fluorescence revealed that, in the GDC and SGAT mutants, the lower rates of photosynthesis coincided with a decreased quantum efficiency of photosystem II and increased non‐photochemical dissipation of excitation energy. Correspondingly, the de‐epoxidation state of xanthophyll‐cycle carotenoids was increased several‐fold in the drought‐stressed GDC and SGAT mutants compared with the wild type. Accumulation of glycine in the GDC mutant was further evidence for increased photorespiration in drought‐stressed barley. The effect of drought on the photorespiratory enzymes was determined by immunological detection of protein abundance. While the contents of GS‐2 and P‐ and H‐protein of the GDC complex remained unchanged as drought stress developed, the content of NADH‐dependent hydroxypyruvate reductase increased. Enzymes of the Benson–Calvin cycle, on the other hand, were either not affected (ribulose‐1,5‐bisphosphate carboxylase‐oxygenase and plastidic fructose‐1,6‐bisphosphatase) or declined (sedoheptulose‐ 1,7‐bisphosphatase and NADP‐dependent glyceraldehyde‐3‐phosphate dehydrogenase). These data demonstrate that photorespiration was enhanced during drought stress in barley and that the control exerted by photorespiratory enzymes on the rate of photosynthetic electron transport and CO2 fixation was increased.
Sky exposure, crown architecture, and low‐temperature photoinhibition in conifer seedlings at alpine treeline
Authors: GERMINO M. J. , SMITH W. K.
Published: March 2003

In the alpine‐treeline ecotone of the Snowy Range in Wyoming, USA, microsite sky exposure of Englemann spruce (Picea englemannii) and subalpine fir (Abies lasiocarpa) seedlings (< 5 years) was associated with the avoidance of low‐nocturnal temperatures and high insolation, factors which appeared to result in low‐temperature photoinhibition. In a field experiment, light‐saturated photosynthesis (Asat) in current‐year seedlings (newly germinated) of fir increased significantly (approximately seven‐fold) in response to increased long‐wave irradiance at night (warming), solar shading (approximately five‐fold), and the combination of the two treatments (approximately eight‐fold).Asatin current‐year spruce remained unchanged in response to all treatments, but was over four‐times higher than fir in control plots. These results indicated substantial low‐temperature photoinhibition, and were supported by similarAsattrends in natural seedlings. Increased needle inclination and clustering in more exposed microsites for both species implicates the possible role of structural adaptations for decreased sky exposure and warmer leaf temperatures at night.
Growth and energy status of arrowhead tubers, pondweed turions and rice seedlings under anoxic conditions
Authors: ISHIZAWA K. , MURAKAMI S. , KAWAKAMI Y. , KURAMOCHI H.
Published: March 2003

The responses of two aquatic plants, arrowhead (Sagittaria pygmaeaMiq.) and pondweed (Potamogeton distinctusA. Benn), to anoxia were compared with those of rice (Oryza sativaL.). Shoot elongation of arrowhead tubers was enhanced at around 1 kPa O2, whereas that of pondweed turions was slight in air and reached a maximum in the absence of O2. Anaerobic enhancement of alcohol dehydrogenase (ADH) activity took place in rice coleoptiles but not in arrowhead and pondweed shoots. Shoots of both arrowhead and pondweed maintained a more stable energy status than did the rice coleoptile under anaerobic conditions. Total adenylate nucleotide contents of arrowhead and pondweed shoots were constant under anaerobic conditions. Adenylate energy charge in both shoots remained at a high and stable level of more than 0·8 for at least 8 d. Three forms of ADH from arrowhead shoots were separated by starch gel electrophoresis, showing that the activity of each ADH form was different under aerobic and anaerobic conditions. The incorporation of35S‐labelled Cys and Met into soluble proteins in arrowhead shoots showed active protein biosynthesis and an involvement of a special set of polypeptides in the anaerobiosis.
Balancing carboxylation and regeneration of ribulose‐1,5‐ bisphosphate in leaf photosynthesis: temperature acclimation of an evergreen tree,Quercus myrsinaefolia
Authors: Hikosaka K. , Murakami A. , Hirose T.
Published: March 2003

Changes in the temperature dependence of the photosynthetic rate depending on growth temperature were investigated for a temperate evergreen tree,Quercus myrsinaefolia. Plants were grown at 250μmol quanta m–2s–1under two temperature conditions, 15 and 30 °C. The optimal temperature that maximizes the light‐saturated rate of photosynthesis at 350μL L–1CO2was found to be 20–25 and 30–35 °C for leaves grown at 15 and 30 °C, respectively. We focused on two processes, carboxylation and regeneration of ribulose‐1,5‐bisphosphate (RuBP), which potentially limit photosynthetic rates. Because the former process is known to limit photosynthesis at lower CO2concentrations while the latter limits it at higher CO2concentrations, we determined the temperature dependence of the photosynthetic rate at 200 and 1000μL L–1CO2under saturated light. It was revealed that the temperature dependence of both processes varied depending on the growth temperature. Using a biochemical model, we estimated the capacity of the two processes at various temperatures under ambient CO2concentration. It was suggested that, in leaves grown at low temperature (15 °C), the photosynthetic rate was limited solely by RuBP carboxylation under any temperature. On the other hand, it was suggested that, in leaves grown at high temperature (30 °C), the photosynthetic rate was limited by RuBP regeneration below 22 °C, but limited by RuBP carboxylation above 22 °C. We concluded that: (1) the changes in the temperature dependence of carboxylation and regeneration of RuBP and (2) the changes in the balance of these two processes altered the temperature dependence of the photosynthetic rate.
Effect of external oxygen demand on radial oxygen loss by Juncus roots in titanium citrate solutions
Authors: Sorrell B. K.
Published: March 2003

Radial oxygen loss (ROL) from the roots of two semiaquatic rushes, Juncus effusus L. and Juncus inflexus L., was studied in reducing titanium citrate buffer, using both closed incubations and a flow‐through, titrimetric system. In closed experiments, roots released oxygen at a constant rate over a wide range of external oxygen demands, with the ROL rate only depending on sink strength at low demands, and no oxygen release into oxidized solutions. In the titrimetric experiments, roots continued to release oxygen at constant rates when provided with a constant external oxygen demand. ROL was higher in J. effusus (9·5 ± 1 × 10−7 mol O2 h−1 root−1) than in J. inflexus (4·5 ± 0·5 × 10−7 mol O2 h−1 root−1). Light and dark changes around the shoots did not affect the ROL rate in J. inflexus, whereas in J. effusus ROL was ≈ 1·75 times higher in the light than in the dark, presumably due to changes in stomatal aperture. These results suggest that ROL is controlled by the external oxygen demand at low to moderate reducing intensities, but that structural limitations to oxygen diffusion rates prevent ROL from continuing to increase at higher external oxygen demands.
Accumulation of an apoplastic solute in the guard‐cell wall is sufficient to exert a significant effect on transpiration in Vicia faba leaflets
Authors: Ewert M. S. , Jr W. H. Outlaw , Zhang S. , Aghoram K. , Riddle K. A.
Published: March 2003

Accumulation of recently photosynthesized sucrose in the guard‐cell wall is the empirical foundation for a hypothesis that links the rates of photosynthesis, translocation, and transpiration (Plant Physiology 114, 109–118). Critical assumptions of this hypothesis were tested by use of Vicia faba, an apoplastic phloem loader. Following measurements of the leaflet‐apoplastic‐water volume (by P–V isotherm analysis) and the guard‐cell wall volume (by 3‐D analysis), intact leaflets were fed dilute solutions of mannitol, an impermeant non‐toxic osmolyte. Even at bulk‐leaflet mannitol concentrations that would have only a negligible osmotic effect on stomata, transpiration at constant temperature, water‐vapour pressure, air movement and irradiance was diminished up to 25%, compared with controls. This effect on transpiration, a manifestation of smaller stomatal aperture size, was explained by accumulation of mannitol, up to 350 mol m−3, in the estimated aqueous volume of the guard‐cell wall. The conclusion is that mannitol, a xenobiotic with structural similarity to sucrose, can move throughout the apoplast of a transpiring leaflet and accumulate in an osmotically significant concentration in the guard‐cell wall. These data therefore provide support for a new role for sucrose as a signal metabolite that integrates essential functions of the whole leaf. In addition, the results raise questions about the physiological or experimental accumulation of other guard‐cell‐targeted apoplastic solutes such as plant growth regulators, particularly abscisic acid, and ions.
Electrical resistance changes during exposure to low temperature measure chilling and freezing tolerance in olive tree (Olea europaea L.) plants
Authors: Mancuso S.
Published: March 2003

Electrical resistance changes in different organs of four olive tree (Olea europaea L.) varieties, characterized by different tolerance to chilling and freezing, were examined, during exposure to low temperature. Apparent critical temperatures (CT) and freezing temperatures (Tfr) were identified on the basis of the electrical resistance changes. Both temperatures were lower for the more chilling‐tolerant genotypes. From the apparent critical temperatures, the absolute critical temperature (CTabs) and the time delay of the chilling signal transduction process were calculated. In shoots, CTabs varied from 8·8 °C for Ascolana (chilling‐tolerant variety) to 13·6 °C for Coratina (chilling‐sensitive variety). The magnitude of the transduction time was very similar (about 2 min) for the three genotypes that are more sensitive to chilling, whereas it was significantly higher (about 3 min) for the most tolerant genotype. Different freezing temperatures were observed for different organs. It would appear from this experiment that the order of sensitivity is roots > leaves > shoots > vegetative buds. Accord was found between the absolute critical temperature of electrical resistance and the critical temperature of membrane potential. The occurrence of electrical resistance changes in the tissues of the olive trees exposed to low temperature suggests the use of this experimental procedure as a quick, easy and non‐destructive tool to screen plant tissues for chilling tolerance. The strong dependence of the electrical resistance on low temperature, and the critical temperature of around 10 °C, can yield interesting information about the lowest thermal limits for the continuation of normal physiological processes and therefore about the adaptability of plants to particular environments.
Relative humidity‐ and ABA‐induced variation in carbon and oxygen isotope ratios of cotton leaves
Authors: Barbour M. M. , Farquhar G. D.
Published: March 2003

Cotton (Gossypium hirsutum L. cv. CS50) plants were grown at two levels of relative humidity (RH) and sprayed daily with abscisic acid (ABA) at four concentrations. Plants grown at lower humidity had higher transpiration rates, lower leaf temperatures and lower stomatal conductance. Plant biomass was also reduced at low humidity. Within each humidity environment, increasing ABA concentration generally reduced stomatal conductance, evaporation rates, superficial leaf density and plant biomass, and increased leaf temperature and specific leaf area. As expected, decreased stomatal conductance resulted in decreased carbon isotope discrimination in leaf material (Δ13Cl). Plants grown at low humidity were more enriched in 18O than those grown at high RH, as theory predicts. Within each humidity environment, increasing ABA concentration increased oxygen isotope enrichment of leaf cellulose (Δ18Oc) and whole‐leaf tissue (Δ18Ol). Values of Δ13Cl and Δ18Ol predicted by theoretical models were close to those observed, accounting for 79% of the measured variation in Δ13Cl and 95% of the measured variation in Δ18Ol. Supporting theory, Δ13Cl and Δ18Ol in whole‐leaf tissue were negatively related.
The Arabidopsis thaliana ATP‐binding cassette proteins: an emerging superfamily
Authors: Davies T. G. E. , Coleman J. O. D.
Published: March 2003

Solute transport systems are one of the major ways in which organisms interact with their environment. Typically, transport is catalysed by integral membrane proteins, of which one of the largest groups is the ATP‐binding cassette (ABC) proteins. On the basis of sequence similarities, a large family of ABC proteins has been identified in Arabidopsis. A total of 60 open reading frames (ORFs) encoding ABC proteins were identified by BLAST homology searching of the nuclear genome. These 60 putative proteins include 89 ABC domains. Based on the assignment of transmembrane domains (TMDs), at least 49 of the 60 proteins identified are ABC transporters. Of these 49 proteins, 28 are full‐length ABC transporters (eight of which have been described previously), and 21 are uncharacterized half‐transporters. Three of the remaining proteins identified appear to be soluble, lacking identifiable TMDs, and most likely have non‐transport functions. The eight other ORFs have homology to the nucleotide‐binding and transmembrane components of multi‐subunit permeases. The majority of ABC proteins found in Arabidopsis can, on the basis of sequence homology, be assigned to subfamilies equivalent to those found in the yeast genome. This assignment of the Arabidopsis ABC proteins into easily recognizable subfamilies (with distinguishable subclusters) is an important first step in the elucidation of their functional role in higher plants.
Hydraulic architecture and water relations of Spartium junceum branches affected by a mycoplasm disease
Authors: Gullo M. A. Lo , Trifilò P. , Raimondo F.
Published: March 2003

Plant water relations, xylem anatomy and the hydraulic architecture of 1‐year‐old twigs of Spartium junceum, both healthy and affected by a phytoplasm disease, were studied. The disease causes twigs to be either shortened (witches broom disease, WBD) or flat (fasciate disease, FD). WBD twigs show a sevenfold increase in total leaf area, smaller and shorter xylem conduits, a higher stomatal conductance (gl) and a decline of minimum leaf water potentials (Ψl) below the turgor loss point. FD twigs had nearly twice the leaf area of the healthy controls as well as high gl values and Ψl values below the turgor loss point. Moreover, significant differences between healthy and affected twigs in stem stomatal conductance (gs) and in the total stem area were recorded. Affected twigs die back under drought stress, which is explained by a pronounced loss of hydraulic conductivity of the infected stems (40 and 60%) in FD and WBD as well as by the unfavourable ratio of weighted conduit radius (Σr4) to total surface area (At), so that the efficiency of the stem in supplying the whole transpiring area with water is strongly reduced.
Seasonal patterns of tissue water relations in three Mediterranean shrubs co‐occurring at a natural CO2 spring
Authors: Tognetti R. , Raschi A. , Jones M. B.
Published: March 2003

Seasonal changes in tissue water relations of Erica arborea L., Myrtus communis L. and Juniperus communis L., grown in a Mediterranean environment, were analysed under field conditions over a 12 month period by comparing plants grown in the proximity of a natural CO2 spring (about 700 μmol mol−1 atmospheric CO2 concentration, [CO2]) with plants in ambient conditions. Tissue water relations varied in response to changes in water availability, but the seasonal course of tissue water relations parameters was also related to ontogeny. Tissue water relations of these co‐occurring shrubs were not alike. Osmotic potentials and saturated mass/dry mass ratio were lowest during peak drought stress periods. Diurnal changes in osmotic potential at the point of turgor loss were least early in the season, maximal in mid‐season, and decreased again in autumn. Turgor potentials decreased as drought progressed and were highest in late fall and mid‐winter. Symplastic water fraction was highest in mid‐spring for E. arborea and M. communis and decreased during the summer, while the opposite was observed for J. communis. Common to all species, under elevated [CO2], was an increase of turgor pressure, particularly during the summer months. Other parameters showed species‐specific responses to long‐term elevated [CO2]. In particular, exposure to elevated [CO2] increased osmotic potentials in E. arborea under drought, while the opposite was the case for J. communis. Site differences in predawn to midday shifts were not strong in any of the species. Differences in tissue water relations suggest that the coexistence of these shrubs in the same environment with similar water availability are partially based on differential water relations strategies and water use patterns. Regardless of the mechanisms, growth of these shrubs in elevated [CO2] may be either less, similarly or more affected by drought stress than plants in ambient [CO2] depending on the species and season.
Stomatal conductance and photosynthesis vary linearly with plant hydraulic conductance in ponderosa pine
Authors: Hubbard R. M. , Ryan M. G. , Stiller V. , Sperry J. S.
Published: March 2003

Recent work has shown that stomatal conductance (gs) and assimilation (A) are responsive to changes in the hydraulic conductance of the soil to leaf pathway (KL), but no study has quantitatively described this relationship under controlled conditions where steady‐state flow is promoted. Under steady‐state conditions, the relationship betweengs, water potential (Ψ) andKLcan be assumed to follow the Ohm's law analogy for fluid flow. When boundary layer conductance is large relative togs, the Ohm's law analogy leads togs=KL(Ψsoil−Ψleaf)/D, whereDis the vapour pressure deficit. Consequently, if stomata regulate Ψleafand limitA, a reduction inKLwill causegsandAto decline. We evaluated the regulation of ΨleafandAin response to changes inKLin well‐watered ponderosa pine seedlings (Pinus ponderosa). To varyKL, we systematically reduced stem hydraulic conductivity (k) using an air injection technique to induce cavitation while simultaneously measuring Ψleafand canopy gas exchange in the laboratory under constant light andD. Short‐statured seedlings (< 1 m tall) and hour‐long equilibration times promoted steady‐state flow conditions. We found that Ψleafremained constant near − 1·5 MPa except at the extreme 99% reduction ofkwhen Ψleaffell to − 2·1 MPa. Transpiration,gs,AandKLall declined with decreasingk(P< 0·001). As a result of the near homeostasis in bulk Ψleaf,gsandAwere directly proportional toKL(R2> 0·90), indicating that changes inKLmay affect plant carbon gain.
Slow development of leaf photosynthesis in an evergreen broad‐leaved tree,Castanopsis sieboldii: relationships between leaf anatomical characteristics and photosynthetic rate
Authors: Miyazawa S.‐I. , Terashima I.
Published: March 2003

Changes in net photosynthetic rate on a leaf area basis and anatomical properties during leaf development were studied in an evergreen broad‐leaved tree,Castanopsis sieboldii andan annual herb,Phaseolus vulgaris. InC. sieboldii, surface area of mesophyll cells facing the intercellular air spaces on a leaf area basis (Smes) was already considerable at the time of full leaf area expansion (FLE). However, surface area of chloroplasts facing the intercellular air spaces on a leaf area basis (Sc), and chlorophyll and Rubisco contents on a leaf area basis increased to attain their maximal values 15–40 d after FLE. In contrast, inP. vulgaris, chloroplast number on a leaf area basis,ScandSmesat 10 d before FLE were two to three times greater than the steady‐state levels attained at around FLE. InC. sieboldii, the internal CO2transfer conductance (gi) slightly increased for 10 d after FLE but then decreased toward the later stages. Limitation of photosynthesis bygiwas only about 10% at FLE, but then increased to about 30% at around 40 d after FLE. The large limitation after FLE bygiwas probably due to the decrease in CO2concentration in the chloroplast caused by the increases in thickness of mesophyll cell walls and in Rubisco content per chloroplast surface area. These results clearly showed that: (1) inC. sieboldii, chloroplast development proceeded more slowly than mesophyll cell expansion and continued well after FLE, whereas inP. vulgaristhese processes proceeded synchronously and were completed by FLE; (2) after FLE, photosynthesis in leaves ofC. sieboldiiwas markedly limited bygi. From these results, it is suggested that, in the evergreen broad‐leaved trees, mechanical protection of mesophyll cells has priority over the efficient CO2transfer and quick construction of the chloroplasts.
Distribution of N, Rubisco and photosynthesis in Pinus pinaster and acclimation to light
Authors: Warren C. R. , Adams M. A.
Published: March 2003

The light–nitrogen hypothesis suggests canopy photosynthesis is maximized when there is a positive relationship between irradiance received by foliage, its nitrogen content (per unit area Narea), and maximum rate of photosynthesis (Amax). Relationships among relative irradiance and Narea, allocation of nitrogen within the photosynthetic apparatus to Rubisco and chlorophyll, and Amax were examined in Pinus pinaster Ait. needles up to 6 years of age. Measurements were made before bud break in August 1998, and in May 1999 after the first ‘winter’ rains. In August, Narea in P. pinaster needles decreased from 5·1 to 5·7 g m−2 in sunlit 1‐year‐old needles to 2·3 g m−2 in shaded 6‐year‐old needles. In May, Narea was 5–40% less but spatial trends were the same. At both sampling dates, Amax was less in old shaded needles compared with young sunlit needles, and was thus consistent with the light–nitrogen hypothesis. Relationships between Narea and Amax were positive at both dates yet varied in strength and form. Allocation of nitrogen within the photosynthetic apparatus was qualitatively consistent with acclimation to light (i.e. Rubisco/Chl decreased with shading), but quantitatively suboptimal with respect to photosynthesis owing to consistent over‐investment in Rubisco. This over‐investment increased with height in the canopy and was greater in May than in August.
Acclimation of leaf respiratory properties in Alocasia odora following reciprocal transfers of plants between high‐ and low‐light environments
Authors: Noguchi K. , Nakajima N. , Terashima I.
Published: March 2003

Acclimation of respiration to the light environments is important for a plant’s carbon balance. Respiratory rates of mature leaves of Alocasia odora, a typical shade‐tolerant species, were measured during the night for 14 d after reciprocal transfers between high‐ (330 µ mol m−2 s−1) and low‐light (20 µ mol m−2 s−1) environments. Following the transfer, both the rate of CO2 efflux and that of O2 uptake of A. odora leaves adjusted to the new light environments. The O2‐uptake rates changed more slowly than the CO2‐efflux rates under the new environments. Leaf mass per area also changed after the transfer. We analysed whether substrate availability or ATP‐consumption rates influence the respiratory acclimation. Since the addition of sucrose to leaf segments did not influence the O2‐uptake rates, the change of respiratory substrate availability was not responsible for the respiratory acclimation. The addition of an uncoupler induced increases in the O2‐uptake rates, and the degree of enhancement significantly decreased after the transfer from low to high irradiance. Thus, the change in ATP‐consumption rates was responsible for the changes in respiratory rates in the plants transferred from low to high light. Potential rates of O2 uptake, as measured in the presence of both the substrate and the uncoupler, changed after the transfer, and strongly correlated with the O2‐uptake rates, irrespective of the directions of transfer (r = 0·961). There was a strong correlation between maximal activities of NAD‐isocitrate dehydrogenase and the potential rates of O2 uptake (r = 0·933), but a weaker correlation between those of cytochrome c oxidase and the potential rates (r = 0·689). These data indicate that the changes of light environments altered the respiratory rates via the change of the respiratory ATP demand, and that the altered rates of respiration will induce the changes of the respiratory capacities.
Exudation of carboxylates in Australian Proteaceae: chemical composition
Authors: Roelofs R. F. R. , Rengel Z. , Cawthray G. R. , Dixon K. W. , Lambers H.
Published: March 2003

Roots of a wide range of plant species exude carboxylates, such as citrate, into the rhizosphere. In the present study, seedlings of a range of Australian Banksia, Hakea and Dryandra species (Proteaceae) were assayed for their exudation of carboxylates. All of these species (Hakea prostrata, Hakea undulata, Hakea petiolaris, Hakea baxteri, Banksia grandis, Banksia prionotes, Banksia occidentalis and Dryandra sessilis) form cluster roots when grown in nutrient solution with a low phosphate concentration. Exudation of carboxylates was studied for cluster roots and non‐cluster roots separately, and for the entire root system. Cluster roots of these Proteaceae exuded malate, malonate, lactate, acetate, maleate, citrate, fumarate, cis‐ and trans‐aconitate. The relative contributions of each of these carboxylates differed between species. Malate, malonate, lactate, citrate and trans‐aconitate, however, were invariably present in large proportions of total carboxylate exudation. Non‐cluster roots of H. prostrata exuded a spectrum of carboxylates (mainly malonate, lactate and citrate), which differed somewhat from the exudation pattern of cluster roots (mainly malate, malonate, lactate and citrate). The rate of exudation for cluster roots of the seven species was approximately 1·6 nmol g−1 FM s−1, which is considerably higher than that reported for a variety of crop and native species that do or do not form cluster roots. Contrary to what occurs in the cluster roots of Lupinus albus, which release carboxylates accompanied by protons so that the rhizosphere is acidified, the present Proteaceae exude the carboxylates as anions without concomitant proton release. The role of carboxylates in the mobilization of phosphate and other nutrients from soil is discussed.
Identification and characterization of a salt‐stress‐induced plasma membrane H+‐ATPase in tomato
Authors: Kalampanayil B. D. , Wimmers L. E.
Published: March 2003

Plant plasma membrane H+‐ATPases (PM H+‐ATPases) energize the secondary transport of Na+ from the cytosol across the plasma membrane and so may play a role in the plant response to salt stress. A PM H+‐ATPase gene in rice is closely linked to a locus responsible for increased salt resistance. PM H+‐ATPases are encoded by large gene families, including 10–12 in tomato (Lycopersicon esculentum). Salt stress stimulates the accumulation of PM H+‐ATPase transcripts in a variety of plants but the effect of salt stress on the expression of specific isoforms has not been investigated. We isolated a partial‐length cDNA clone of a novel tomato PM H+‐ATPase gene from salt‐stressed expanded leaf tissue and characterized its expression in response to salt and osmotic stress. The gene, LHA8, is a member of the subfamily including AHA1, AHA2, AHA3, AHA4, AHA9, LHA4, PHA2 and PMA4, and is most closely related to the Nicotiana plumbaginifolia gene PMA6. LHA8 transcript accumulation is induced by NaCl exposure. LHA8 is not expressed at detectable levels in roots or expanded leaves and is present at very low levels in unexpanded leaves. LHA8 expression is induced in expanded leaves, unexpanded leaves and roots. Induction appears to be specific to the ionic, rather than the osmotic, effects of NaCl because iso‐osmotic levels of polyethylene glycol do not induce message accumulation.
Multivariate analysis of intraspecific responses to UV‐B radiation in white clover (Trifolium repensL.)
Authors: Hofmann R. W. , Campbell B. D. , Fountain D. W. , Jordan B. R. , Greer D. H. , Hunt D. Y. , Hunt C. L.
Published: March 2003

White clover (Trifolium repensL.) is experiencing increased levels of ultraviolet‐B (UV‐B) radiation in temperate pastures due to the depletion of the stratospheric ozone layer. Based on 17 morphological, morphogenetic and physiological attributes, this study analysed the consequences of enhanced UV‐B on 26 white clover populations using principal components analysis (PCA). After 18 d of exposure to 13·3 kJ m−2d−1UV‐B in controlled environments, UV‐B significantly decreased above‐ground and below‐ground plant growth attributes, epidermal cell surface area and maximum quantum efficiency of photosystem II photochemistry (Fv/Fm). Aspects of cell division and cell expansion both were negatively affected by UV‐B. Stomatal density, specific leaf mass, root‐to‐shoot ratio and levels of UV‐B‐absorbing compounds increased in response to UV‐B. In the multivariate analysis, the main dimension of UV‐B sensitivity was characterized by changes in plant growth attributes. Alterations in partitioning within and between plant organs constituted a secondary tier of UV‐B responsiveness. Plant characteristics related to UV‐B tolerance included lower growth rate, smaller epidermal cell surface area and higher UV‐B‐induced levels of UV‐B‐absorbing compounds. The results suggest overall UV‐B tolerance for slower‐growing populations from less productive habitats with higher natural UV‐B irradiance.
Drought‐induced senescence is characterized by a loss of antioxidant defences in chloroplasts
Authors: Munné‐Bosch S. , Jubany‐Marí T. , Alegre L.
Published: March 2003

The relationship between drought, oxidative stress and leaf senescence was evaluated in field‐grown sage (Salvia officinalis L.), a drought‐susceptible species that shows symptoms of senescence when exposed to stress. Despite the photoprotection conferred by the xanthophyll cycle, drought‐stressed senescing leaves showed enhanced lipid peroxidation, chlorophyll loss, reduced photosynthetic activity and strong reductions of membrane‐bound chloroplastic antioxidant defences (i.e. β‐carotene and α‐tocopherol), which is indicative of oxidative stress in chloroplasts. H2O2 accumulated in drought‐stressed senescing leaves. Subcellular localization studies showed that H2O2 accumulated first in xylem vessels and the cell wall and later in the plasma membrane of mesophyll cells, but not in chloroplasts, indicating reactive oxygen species other than H2O2 as direct responsible for the oxidative stress observed in the chloroplasts of drought‐stressed senescing leaves. The strong degradation of β‐carotene and α‐tocopherol suggests an enhanced formation of singlet oxygen as the putative reactive oxygen species responsible for oxidative stress to senescing chloroplasts. This study demonstrates that oxidative stress in chloroplasts mediates drought‐induced leaf senescence in sage growing in Mediterranean field conditions.
Osmolyte accumulation: can it really help increase crop yield under drought conditions?
Authors: Serraj R. , Sinclair T. R.
Published: March 2003

Osmolyte accumulation (OA) is frequently cited as a key putative mechanism for increasing yields of crops subjected to drought conditions. The hypothesis is that OA results in a number of benefits that sustain cell and tissue activity under water‐deficit conditions. It has been proposed as an effective tolerance mechanism for water deficits, which could be enhanced in crops by traditional plant breeding, marker‐assisted selection or genetic engineering, to generate drought‐tolerant crops. However, field studies examining the association between OA and crop yield have tended to show no consistent benefit. The few, often‐cited, investigations with positive associations were obtained under severe water deficits with extremely low yields or conditions with special water‐supply scenarios when much of the benefit is plant survival. Under conditions where water deficits threaten crop survival, yields are so low that even large fractional yield gains offer little practical benefit to growers. Indeed, the often‐cited benefit of turgor maintenance in cells is likely to result in crop behaviour that is exactly opposite to what is beneficial to crops. The one clear mechanism identified in this review for beneficial yield responses to OA is in the maintenance of root development in order to reach water that may be available deeper in the soil profile.
Water uptake profile response of corn to soil moisture depletion
Authors: Li Y. , Fuchs M. , Cohen S. , Cohen Y. , Wallach R.
Published: March 2003

The effects of soil moisture distribution on water uptake of drip‐irrigated corn were investigated by simultaneously monitoring the diurnal evolution of sap flow rate in stems, of leaf water potential, and of soil moisture, during intervals between successive irrigations. The results invalidate the steady‐state resistive flow model for the continuum. High hydraulic capacitance of wet soil and low hydraulic conductivity of dry soil surrounding the roots damped significantly diurnal fluctuations of water flow from bulk soil to root surface. By contrast, sap flow responded directly to the large diurnal variation of leaf water potential. In wet soil, the relation between the diurnal courses of uptake rates and leaf water potential was linear. Water potential at the root surface remained nearly constant and uniformly distributed. The slope of the lines allowed calculating the resistance of the hydraulic path in the plant. Resistances increased in inverse relation with root length density. Soil desiccation induced a diurnal variation of water potential at the root surface, the minimum occurring in the late afternoon. The increase of root surface water potential with depth was directly linked to the soil desiccation profile. The development of a water potential gradient at the root surface implies the presence of a significant axial resistance in the root hydraulic path that explains why the desiccation of the soil upper layer induces an absolute increase of water uptake rates from the deeper wet layers.
Role of leaf apoplast in silicon‐mediated manganese tolerance of Cucumis sativus L.
Authors: Rogalla H. , Römheld V.
Published: March 2003

Silicon (Si) supplied as sodium silicate (1·8 mm) clearly decreased symptoms of manganese (Mn) toxicity in Cucumis sativus L. (cv. Chinesische Schlange) grown in nutrient solution with low to elevated Mn concentrations (0·5–1000 µm). Despite approximately the same total Mn content in the leaves, plants not treated with Si had higher Mn concentrations in the intercellular washing fluid (IWF) compared with plants treated with Si, especially in the BaCl2‐ and DTPA‐exchangeable fraction of the leaf apoplast. The Mn concentration of the IWF correlated positively with the severity of Mn‐toxicity symptoms and negatively with the Si supply. Furthermore, in Si‐treated plants less Mn was located in the symplast (< 10%) and more Mn was bound to the cell wall (> 90%) compared with non‐Si‐treated plants (about 50% in each compartment). Manganese present in Si‐treated plants is therefore less available and for this reason less toxic than in plants not treated with Si. It is concluded that Si‐mediated tolerance of Mn in C. sativus is a consequence of stronger binding of Mn to cell walls and a lowering of Mn concentration within the symplast. These results support the role of Si as an important beneficial element in plant nutrition.
Use of decreasing foliar carbon isotope discrimination during water limitation as a carbon tracer to study whole plant carbon allocation
Authors: Arndt S. K. , Wanek W.
Published: March 2003

Foliar carbon isotope discrimination (Δ) of C3 plants decreases in water‐deficit situations as discrimination by the photosynthetic primary carboxylation reaction decreases. This diminished Δ in leaves under water deficit can be used as a tracer to study whole plant carbon allocation patterns. Carbon isotope composition (δ13C value) of leaf hot water extracts or leaf tissue sap represents a short‐term integral of leaf carbon isotope discrimination and thus represents the δ13C value of source carbon that may be distributed within a plant in water‐deficit situations. By plotting the δ13C values of source carbon against the δ13C values of sink tissues, such as roots or stems, it is possible to assess carbon allocation to and incorporation into sink organs in relation to already present biomass. This natural abundance labelling method has been tested in three independent experiments, a one‐year field study with the fruit tree species Ziziphus mauritiana and peach (Prunus persica), a medium‐term drought stress experiment with Ziziphus rotundifolia trees in the glasshouse, and a short‐term drought stress experiment with soybean (Glycine max). The data show that the natural abundance labelling method can be applied to qualitatively assess carbon allocation in drought‐stressed plants. Although it is not possible to estimate exact fluxes of assimilated carbon during water deficit the method represents an easy to use tool to study integrated plant adaptations to drought stress. In addition, it is a less laborious method that can be applied in field studies as well as in controlled experiments, with plants from any developmental stage.
Characteristics and host range of tomato powdery mildew
Authors: Whipps J. M. , Budge S. P. , Fenlon J. S.
Published: March 2003

The anamorphic state of a powdery mildew, which first appeared on tomato in the UK in 1987, currently listed as Erysiphe orontii (anamorph Oidium violae), was examined microscopically on both tomato and alternative hosts. Host range studies were also carried out. In 1993–95, species and cultivars of plants from 26 of the 30 families listed as hosts of E. orontii were inoculated with tomato powdery mildew in the glasshouse and assessed for susceptibility on a 0–3 scale based on degree of sporulation and growth. Thirteen families contained species or varieties that were susceptible and a total of 80 varieties, including many economically important Cucurbitaceae and Solanaceae, supported sporulation to some extent (susceptibility score 1–3). Necrosis was not a constant feature of plants exhibiting resistance, as it could accompany sporulation on some susceptible varieties. Microscopic measurements showed that conidial size, conidiophore length, conidiophore foot‐cell length and width, and the number of cells distal to the foot‐cell were remarkably constant between samples of powdery mildew taken from tomato each year and from the various alternative hosts. Based on the production of conidia singly, the presence of nipple‐shaped to moderately lobed appressoria, and occurrence of straight conidiophores, it is concluded that this fungus on tomato should more correctly be named Oidium lycopersicum until the sexual stage is discovered. The highly polyphagous nature of this powdery mildew would suggest that it represents a potential risk to UK agriculture and horticulture, but the failure to recover any powdery mildew from 120 samples of potato, including varieties Cara and Maris Piper, on which the tomato powdery mildew could sporulate in the glasshouse, suggests that environmental factors may play a key role in preventing establishment of this powdery mildew on alternative hosts on a commercial scale in the field.
Comparative analysis of ELISA, nonradioactive molecular hybridization and PCR for the detection of prunus necrotic ringspot virus in herbaceous and Prunus hosts
Authors: Sanchez‐Navarro  , Aparicio  , Rowhani  , Pallás
Published: March 2003

Three methods were compared for the detection of prunus necrotic ringspot virus in herbaceous and woody plants: DAS‐ELISA, nonisotopic dot‐blot hybridization and reverse transcriptional polymerase chain reaction (RT‐PCR). When purified virus preparations were used, the detection limit of the RT‐PCR technique was 1.28 pg mL−1 whereas nonisotopic molecular hybridization and DAS‐ELISA allowed detection of 0.8 ng mL−1 and 4 ng mL−1, respectively. Several sample processing procedures were evaluated for virus detection by the nonisotopic molecular hybridization technique. When a very short and simple sample processing method was used, the detection limit of the nonisotopic molecular hybridization technique was 25 times higher than that of DAS‐ELISA and 625 times lower than that of RT‐PCR. A comparison of the level of virus accumulation in mature fruits and in leaf tissue showed that, on average, 125 times more virus was found in the fruits.
Pectolytic enzymes produced in vitro and during colonization of melon tissues by Didymella bryoniae
Authors: Chilosi  , Magro
Published: March 2003

Pectolytic enzymes produced by Didymella bryoniae in a liquid medium containing pectin as sole carbon source and in inoculated etiolated hypocotyls of 10 melon cultivars, as well as those constitutively expressed in spores, were studied by isoelectric focusing, quantitatively and qualitatively. Five constitutive pectin lyase (PNL) isoenzymes differing in isoelectric joint (pI), one acidic (pI 3.9) and four basic (pI 8.4, 8.9, 9.3, 9.9) were expressed in extracts from spores. The same PNL isoenzyme pattern was detected in culture filtrates and in infected tissues of all the melon cultivars tested. Polygalacturonase (PG) activity, represented by a single inducible acidic band (pI 4.6) was detected only in culture filtrates. A single constitutive basic pectin methylesterase (PME) isoenzyme (pI > 10.0) was also found in spores, culture filtrates and inoculated melon tissues. All cultivars were susceptible at the seedling growth stage, but with differences in disease severity; cultivars Amarillo Oro and Juane Canari were, respectively, the least and most susceptible. Pectin lyase activity was highly correlated with disease severity. In rotted tissues and culture filtrates, an increase in pH to values over 7.0 was recorded, values optimal for PNL activity. In this plant–pathogen interaction, PNL activity represents the principal pectolytic component and these isoenzymes were associated with the onset of disease, disease severity and an increase in pH of infected tissue.