bluuebunny/crossref_metadata_2025 huggingface dataset:
Chlorophyll breakdown in senescent cotyledons of rape, Brassica napus L.: Enzymatic cleavage of phaeophorbide a in vitro
Authors: HÖRTENSTEINER STEFAN , VICENTINI FABRIZIO , MATILE PHILIPPE
Published: April 2006

Solubilization of senescent thylakoids from rape cotyledons in the presence of Triton X‐100 was employed to establish an in vitro system that allowed the assessment of enzymatic conversion of phaeophorbide a into an uncoloured fluorescent chlorophyll catabolite, Bn‐FCC‐2. The action of the putative dioxygenase responsible for the cleavage of the porphyrin macrocycle depends on reduced ferredoxin as reductant. Apart from this thylakoidal catalyst, stromal protein is also required for the production of FCC‐2 in vitro. The cleavage reaction does not occur with phaeophorbide b as substrate. Saturation kinetics with phaeophorbide a as substrate yielded an apparent Km‐value of c. 200 μ. The enzyme contains iron as suggested by inhibitory effects of appropriate chelators. Enzyme activity lost upon treatment with bipyridyl was partly restored in the presence of Fe‐ions; other metal ions such as Cu, Zn and Co were ineffective. The enzyme is absent in the thylakoids of mature green cotyledons. It appears upon the induction of foliar senescence and reaches the highest levels towards the end of the yellowing process.
Chlorophyll breakdown in senescent leaves identification of the biochemical lesion in a stay‐green genotype of Festuca pratensis Huds.
Authors: VICENTINI FABRIZIO , HÖRTENSTEINER STEFAN , SCHELLENBERG MAYA , THOMAS HOWARD , MATILE PHILIPPE
Published: April 2006

Chlorophyll breakdown in senescent leaves proceeds in essentially three steps: dephytylation by the action of chlorophyllase; conversion of chlorophyllide to phaeophorbide by Mg‐dechelatase; and oxygenolytic cleavage of the chlorine‐macrocycle by a newly discovered dioxygenase. The metabolic lesion responsible for high retention of chlorophyll during foliar senescence in a mutant genotype of meadow fescue (Festuca pratensis Huds.) was located in the third step of the breakdown pathway. Senescent leaves of both the normally yellowing reference genotype, c.v Rossa, and the non‐yellowing mutant Bf993 were shown to be competent with regard to chlorophyllase and Mg‐dechelatase. On the other hand, thylakoids isolated from senescent leaves of cv. Rossa were able to carry out oxygenolysis of phaeophorbide into a colourless fluorescent catabolite in vitro, whereas Bf993 thylakoids were deficient in this activity. It is concluded that the Sid locus, a mutant allele of which is responsible for the stay‐green character, encodes or regulates the gene for, phaeophorbide a dioxygenase.
A study of the hydration process of isolated cuticular membranes
Authors: LUQUE PATRICIA , GAVARA RAFAEL , HEREDIA ANTONIO
Published: April 2006

Water sorption by isolated tomato fruit cuticular membranes was measured over the whole range of relative humidities. Using the water sorption isotherm, the strength of water binding and the number of binding sites were estimated. Water clustering was predicted from the isotherm analysis and data obtained by differential scanning calorimetry suggested that the water does not plasticize the tomato fruit cuticle. Water sorption characteristics reflect the hydrophobic character of this biopolymer.
Interaction between Aspergillus niger van Tiegh. and Glomus mosseae. (Nicol. & Gerd.) Gerd. & Trappe
Authors: McALLISTER C. B. , GARCIA‐ROMERA I. , MARTIN J. , GODEAS A. , OCAMPO J. A.
Published: April 2006

Percent germination and length of hyphae of germinated Glomus mosseae spores, cultivated on water agar, decreased significantly in the presence of Aspergillus niger; this decrease was independent of any change in pH of the medium. Soluble and volatile compounds produced by A. niger significantly decreased percentage spore germination and the hyphal length of G. mosseae on water agar. The decrease caused by volatile compounds was significantly greater when A. niger was grown on malt extract agar. Shoot dry weights of maize and lettuce plants cultivated in soil in pots, and percentage arbuscular mycorrhizal (AM) root colonization of plants grown either in sand: vermiculite tubes inoculated with G. mosseae spores or in soil in pots with soil inoculum, were unaffected by A. niger when this saprobe was inoculated 2 wk after G. mosseae. Shoot dry weights and percentage AM colonization of plants decreased when the saprobic fungus was inoculated at the same time or 2 wk before G. mosseae. However, the metabolic activity resulting from AM colonization, measured as the percentage of mycelium showing succinate dehydrogenase activity, decreased in all treatments. The population of A. niger decreased when inoculated to the rhizosphere of plants at the same time as, or 2 wk after, G. mosseae, but not when it was inoculated 2 wk before G. mosseae. Our results show that G. mosseae decreases the saprobic fungal population through its effect on the plant, whereas A. niger, by the production of soluble or volatile substances, inhibits G. mosseae in its extramatrical stage.
Root‐induced solubilization of phosphate in the rhizosphere of lowland rice
Authors: SALEQUE M. A. , KIRK G. J. D.
Published: April 2006

Lowland rice (Oryza sativa L., cv IR74) was grown in cylinders of a P‐deficient reduced Ultisol separated into upper and lower cells by a fine nylon mesh so that the roots formed a planar layer above the mesh. This enabled changes in soil P fractions and other root‐induced changes in the soil near the root plane to be measured. In both P‐fertilized and unfertilized soil, the quantity of readily plant‐available P was negligible in comparison with the quantity of P extracted by the plants, and the plants therefore necessarily induced changes in the soil so as to solubilize P. After 6 wk of growth, 90 % of the P taken up was drawn from acid‐soluble pools. The remainder was from an alkali‐soluble inorganic pool which was on balance depleted, although its concentration profile contained zones of accumulation corresponding to zones of Fe(III) accumulation. There was also a small accumulation of alkali‐soluble organic P. There were no changes in the more recalcitrant soil P pools. The zone of P depletion was 4–6 mm wide, increasing with P addition, and coincided with a zone of acidification in which the pH fell from near 6 in the soil bulk to less than 4 near the roots. The acidification was due to H+ generated in oxidation of Fe2+ by root‐released O2, and to H+ released from the roots to balance excess intake of cations over anions. With increasing P deficiency there were increases in the ratio of root: shoot d. wt; the ratio of shoot d. wt to total P in the plant; the excess intake of cations over anions per unit plant d. wt and corresponding release of H+ to the soil; and the quantity of Fe oxidized per unit plant d. wt and corresponding release of H+ to the soil. Independent, in vitro measurements confirmed that acid addition increased the P concentration in the soil solution and the quantity of P that could be desorbed per gram of soil. A mathematical model of the diffusion of acid away from the roots, acid reaction with the soil in solubilizing P, and the diffusion of P back to the absorbing roots showed that, under the conditions of the root‐plane experiments, solubilization by acidification accounted for at least 80% of the P taken up in both P‐fertilized and unfertilized soil, but that less than 50% of the P solubilized could be taken up by the roots.
Cuticular water permeance of European trees and shrubs grown in polluted and unpolluted atmospheres, and its relation to stomatal response to humidity in beech (Fagus sylvatica L.)
Authors: KERSTIENS GERHARD
Published: April 2006

Cuticular water permeance (P) of astomatous adaxial surfaces of intact leaves was determined in Acer pseudoplatanus L., Betula pubescens Ehrh., Corylus avellana L., Fagus sylvatica L. and Prunus avium L. Water evaporating from the stomata‐bearing abaxial leaf surface could not reach the moisture analyzer and the values of P presented here are therefore free from errors that often arise from unintentional inclusion of residual stomatal transpiration. Plants were exposed from before bud‐break for several months to 20–50 ppb SO2(Fagus), a combination of 50–60 ppb SO2 and 50–60 ppb NO2(Betula), 300–400 ppb NO (Acer, Corylus, Fagus), regular ozone episodes of up to 120 ppb (Fagus, Pnunus), or an elevated level of CO2 (600 ppm for 2 yr; Acer, Fagus). Permeances were in the range 0.6–2.9 × 10‐5 m s‐1 and were unaffected by most treatments. In Prunus, P increased slightly but significantly in the NO treatment. In Corylus and Fagus, P was sometimes found to be reduced by fumigation with NO, but not always. Betula leaves grown under elevated SO2 and NO2 showed higher values of P only if they were visibly damaged. Minimum conductances (gmin) estimated from water loss rates of both sides of detached hypo stomatous leaves were higher than P, and were more strongly affected by treatments. In these cases, the most probable explanation is some damage to stomatal function resulting in a reduced ability to close after leaf excision. Effects of growing conditions and time of year on P were found, which allowed a hypothetical interaction between P and stomatal sensitivity to air humidity to be tested in beech. No unambiguous indication of such a relationship was found.
Comparisons of early root cortical senescence between barley cultivars, Triticum species and other cereals
Authors: LILJEROTH ERLAND
Published: April 2006

The natural rate of root cortical death (RCD) in seminal roots was investigated in different cereals by staining the roots with acridine orange. In all cereals investigated the part of the cortex having stainable nuclei gradually decreased with increased age of the root. Wheat differed from barley, oats and rye in having a much faster rate of RCD In 15‐d‐old root regions of wheat grown in soil, only 10–20% of the radius of the root had stainable nuclei. In barley, oats and rye the amount of cortex with stainable nuclei varied between 65 and 80% Minor differences in RCD were found between different barley cultivars or accessions. Large variation in RCD was found between different Triticum species: T. monococcum, T. dicoccum and different Aegilops species had much slower RCD than did hexaploid wheat. These results are discussed in relation to microbial colonization of roots and susceptibility to root pathogens.
Growth patterns of the lateral roots of young oak (Quercus robur) tree seedlings Relationship with apical diameter
Authors: PAGES LOÏC
Published: April 2006

The growth patterns of the first‐order lateral roots of young oak (Quercus robur L.) tree seedlings were studied and related to variation in apical diameter. Seven seedlings were grown in root observation boxes and monitored daily for 6 wk. Apical diameters were measured daily on a sample of 48 lateral roots. A principal component analysis performed on the data set for 479 lateral roots showed that growth patterns were characterized by two major features. First, they could be described by a general growth potential (first factorial, 80% of the total variability) which was related to growth rate and growth duration. Second, but much less important (second factorial axis, 15% of the total variability), there was a distinction between early‐growing roots (growing fast just after emergence and stopping early), and late‐growing roots (having a low growth rate at emergence and a higher growth rate later). This growth pattern typology was related to the time‐dependent variation in apical diameter. On almost all the roots, the apical diameter tended to decrease after emergence. On short roots (with a low growth potential) the initial apical diameter was low and its decrease was steep. Conversely, long roots had a greater initial diameter and tended to maintain it at a higher level. The so‐called late‐growing roots had a large apical diameter but a low growth rate in the early stages, possibly because of the between root competition for growth factors. The interest of the apical diameter as a morphological marker of sink strength, and the interactive relationships between growth rate, apical diameter and sucrose supply are discussed.
Physiological responses of Atherosperma moschatum to day length, night length and photosynthetic photon fluence rate
Authors: OLESEN T.
Published: April 2006

Young, non–reproductive plants of Atherosperma moschatum Labill, were conditioned to a range of day lengths, night lengths and photosynthetic photon fluence rates (PPFRs). The plants conditioned to the shorter of the two day lengths grew more slowly. On protein specific bases, the leaves of these plants had greater PPFR–saturated CO2 exchange rates (CERs), steeper initial slopes to the CER–PPFR plots, and greater chlorophyll concentrations than did the leaves of the long day length plants. The rates of leaf respiration, and the rates of leaf carbon export and /or incorporation into structural leaf products (E+ I) were similar under the two day lengths. The plants conditioned to the shorter of the two night lengths grew more quickly. The leaves ot these plants had smaller PPFR–saturated CERs, shallower initial slopes to the CER–PPFR plots and smaller chlorophyll concentrations than did the leaves of the long night length plants, but greater rates of leaf respiration and E + I. In a separate experiment A. moschatum was shown to be vegetatively sensitive to night breaks of far–red irradiation. The plants conditioned to the higher of the two PPFRs grew more quickly. The leaves of these plants had greater PPFR–saturated CERs, greater rates of leaf respiration, and greater rates of E+I than did the leaves of the lower PPFR plants, but shallower initial slopes to the CER–PPFR plots, and smaller chlorophyll concentrations. Acclimation to photosynthetic period (day length/night length) can be as marked as that to PPFR, and is quite different in character.
Water relations in lichens at subzero temperatures: structural changes and carbon dioxide exchange in the lichen Umbilicaria aprina from continental Antarctica
Authors: SCHROETER BURKHARD , SCHEIDEGGER CHRISTOPH
Published: April 2006

Photosynthetic activity and structural changes at subzero temperatures were monitored in the foliose lichen Umbilicaria aprina Nyl. from continental Antarctica. Carbon dioxide gas exchange measurements revealed that net photosynthesis and dark respiration occurred at subzero temperatures regardless of whether a lichen thallus saturated with liquid water was exposed to subzero temperatures, or if a dry thallus was re‐hydrated only from snow at subzero temperatures. When water‐saturated thalli of U. aprina were slowly cooled at subzero temperatures ice nucleation activity could be detected at — 5·4 °C, indicating extracellular freezing of water. Using low‐temperature scanning electron microscopy (LTSEM) it was demonstrated that extracellular ice formation leads to cytorrhysis in the photobiont cells and to cavitation in the mycobiont cells. Both processes were reversible if the lichen thallus was re‐warmed. When dry lichen thalli were covered with snow at subzero temperatures a substantial re‐hydration from snow could be observed in LTSEM micrographs and measured gravimetrically. The final thallus water content was strongly dependent on the temperature regime and gave water contents between 20% d. wt at — 21 °C and 56% d. wt at —4·5 °C after 16 h exposure. Carbon dioxide gas exchange measurements revealed that metabolic activity was initiated during re‐hydration from snow at subzero temperatures. It is proposed that water uptake from snow at subzero temperatures occurs in the gaseous phase and depends only on the temperature‐related differences in water potential between the cell contents and the surrounding atmosphere in equilibrium with snow. Photosynthetic activity and re‐hydration from snow at subzero temperatures are of great ecological importance for primary production in extreme environments such as Antarctica where metabolic activity is severely limited by water availability and low temperatures.
A cytological study of compatible and incompatible interactions between Sorghum bicolor and Colletotrichum sublineolum
Authors: WHARTON P. S. , JULIAN A. M.
Published: April 2006

summary

Cytological and physiological studies were conducted on the infection process of Colietotrichum sublineolum P. Henn. Kabat et Bub. on susceptible and resistant cultivars of Sorghum bicolor (L.) Moench. Compatible interactions were characterized by an early biotrophic phase lasting c. 24 h, during which intracellular infection vesicles and primary hyphae colonized epidermal cells. Thinner secondary hyphae were first observed branching out from primary hyphae after 66 h. These hyphae proliferated throughout the epidermis and into underlying mesophyll cells. Secondary hyphae were associated with host cell death and the onset of a necrotrophic phase. Pigmented cytoplasmic inclusions, thought to represent the host defence response, were also first observed at 66 h, although there was little apparent effect on subsequent fungal colonization of tissue. By 90 h, secondary hyphae had proliferated throughout the leaf sheath, with production of necrotic lesions and acervuli. In incompatible interactions, infection vesicles formed inside epidermal cells within 42 h of inoculation but there was no evidence for a biotrophic interaction as penetrated cells appeared dead and fungal development was restricted to single epidermal cells. Host defence responses were observed earlier than in compatible interactions: heavily pigmented (dark red) cytoplasmic inclusions were distributed throughout penetrated cells at 42 h. By 66 h, these cytoplasmic inclusions had disintegrated and dark red pigment had spread throughout the cell. Concurrent with the disintegration of the cytoplasmic inclusions was the disruption of the cytoplasm of both the host cell and the fungus. Further fungal development was restricted. These observations are discussed in relation to the importance of the initial biotrophic phase in the successful colonization of S. bicolor by C. sublineolum and the role of the host defence response in preventing colonization.
Drought enhances chilling tolerance in a chilling‐sensitive maize (Zea mays) variety
Authors: IRIGOYEN JUAN J. , DE JUAN JAVIER PEREZ , SANCHEZ‐DIAZ MANUEL
Published: April 2006

summary

We investigated the effectiveness of pre‐drought treatment to acclimate a chilling‐sensitive variety of maize (Errazu) against chilling injury. We tested two methods of applying drought: (a) withholding water during 17 d in perlite culture, and (b) suppressing water by keeping plants out of the nutrient solution at time intervals (2, 4, 6, 8 and 10 h) on five successive days in hydroponic culture. Drought treatments were applied to maize seedlings either in perlite or hydroponic culture before chilling (5 d at 5°C and 150 μmol m−2 s−1 photosynthetic photon fluence rate and then 5 d of recovery at 25°C). Both experiments were carried out under low irradiance to avoid photo‐oxidation damage during chilling. Plant growth (relative growth rate, RGB; net assimilation rate, NAR; leaf area ratio, LAR; specific leaf area, SLA; and leaf weight ratio, LWR), percentage of necrotic leaf area, leaf relative water content (RWC), leaf water (Ψleaf) and osmotic (Ψs) potentials, specific plant transpiration, total water absorption and CO2 exchange rate (CER) were examined in drought‐treated and non‐treated maize seedlings during chilling and after a 5 d recovery period, RGR and NAR of droughted maize seedlings were higher than those of non‐droughted seedlings during recovery, irrespective of the growth medium (perlite or hydroponic). Chilling‐induced leaf necrosis was significantly lower in droughted than in non‐droughted seedlings. Droughted plants had higher water status (higher leaf RWC, Ψleaf and Ψs) after 5 d of chilling, mainly owing to stomatal closure induced by drought. The CER declined to a similar extent in droughted and non‐droughted maize seedlings on chilling, but during recovery droughted seedlings showed significantly higher CO2 fixation rate than non‐droughted seedlings. Leaf conductance of water vapour (g) and CO2 intercellular concentration (C2) analysis led to the conclusion that chilling‐induced CER inhibition was not due to a stomatal limitation. Droughted seedlings of maize had a better water use efficiency of photosynthesis (WUEph) than non‐droughted plants. We conclude that pre‐drought treatment hardened the chilling sensitive variety of maize Errazu against chilling injury.
Regulatory effects of zinc on corn root plasma membrane H+‐ATPase
Authors: KASTRUP VERENA , STEIGER SABINE , LÜTTGE ULRICH , FISCHER‐SCHLIEBS ELKE
Published: April 2006

summary

Effects of divalent metal ions (Zn, Mg, Mn), metal‐ATP complexes, and pH on the activity of the plasma membrane H+‐ATPase were investigated. Both native vesicles, isolated by sucrose gradient centrifugation, and solubilized H+‐ATPase, purified by linear glycerol gradient centrifugation were used. Zn, as well as Mg and Mn, stimulates the activity of H+‐ATPase. Computer calculations of equilibrium concentrations have been used to separate the effects of individual ion complexes and free ionic forms on the enzyme activity. The calculations indicated that Zn as ZnATP+ serves as a substrate of the plasma membrane H+‐ATPase. The possibility of serving as substrate depends on the Zn/ATP ratio and the pH of the medium. The native H+‐ATPase was activated by divalent metal ions in the order of Mg > Mn > Zn at pH 6.5 and in the order of Zn > Mn > Mg at pH 5.5 for total metal ion concentrations not higher than 3.0 mM. A Zn: ATP ratio of 0.6 at pH 5.5 gave more than 100% of the Mg‐dependent ATPase activity (Mg: ATP ratio of 1, pH 5.5). By contrast, free Zn2+ is an effective inhibitor of ATP hydrolysis and H+ transport with a strong dependence upon the pH of the medium. At pH 55 a total ZnSO4 concentration of 1 mM induced no inhibition of ATP hydrolysis, whereas at pH 6.5 the same Zn concentration decreased the activity of the native and purified H+‐ATPase to 49% and 34% (control activity: Mg: ATP ratio of 1, no ZnSO4), respectively. We show that both activation by ZnATP2− and inhibition by free Zn2+ of the native plasma membrane H+‐ATPase and the partially purified enzyme were strongly affected by the pH of the medium. The results provide evidence that Zn, in combination with the pH of the cytoplasm could play a role in regulating the plasma membrane H+‐ATPase and thus in nutrient uptake of plant systems.
A comparison of the extracellular enzyme activities of two ectomycorrhizal and a leaf‐saprotrophic basidiomycete colonizing beech leaf litter
Authors: COLPAERT JAN V. , VAN LAERE ANDRÉ
Published: April 2006

summary

Activities of extracellular enzymes were determined in beech (Fagus sylvatica L.) leaf litter colonized by the litter decomposer Lepista nuda (Bull.: Fr.) Cooke or by vegetative mycelium from the mycorrhizal fungi Thelephora terrestris Ehrh.: Fr. or Suillus bovinus (L.: Fr.) O. Kuntze. Organic matter (OM) was buried for up to 6 months in plant containers in which mycorrhizal or non‐mycorrhizal Pinus sylvestris L. seedlings were cultivated at a low rate of nutrient addition. After different periods of colonization the activities of phosphomonoesterase and protease, two enzymes involved in nitrogen and phosphorus mobilization, were determined in colonized and uncolonized litter. The activities of cellulase, β‐xylosidase, β‐glucosidase and polyphenol oxidase were investigated as indicators of the decomposition capacity of the fungi in the litter. Low activities of all enzymes tested were found in the uncolonized beech leaves. Phosphomonoesterase activity was high in litter colonized with L. nuda or S. bovinus, and was intermediate in the T. terrestris treatment. For all other enzymes the activities in the OM inoculated with the white‐rot litter decomposer were considerably larger than those detected in litter colonized by ectomycorrhizal basidiomycetes. Cellulase activity was low in the control as well as in the mycorrhizal treatments. β‐Xylosidase and β‐glucosidase were detected in the litter with mycorrhizal mycelium, whereas polyphenol oxidase activity was only clearly increased in the S. bovinus treatment. These results demonstrate the low lignocellulase activity of both mycorrhizal fungi. This feature reduces the capacity of the mycorrhizal fungi to exploit fresh beech leaf litter, whose endogenous nitrogen is associated with or shielded by refractory compounds. The results are discussed in relation to the role of ectomycorrhizal fungi in nutrient cycling processes m temperate forest ecosystems.
Sulphite and pH effects on CO2 evolution by fungi growing on decomposing coniferous needles
Authors: DURSUN S. , FRANKLAND JULIET C. , BODDY LYNNE , INESON P.
Published: April 2006

summary

The relative sensitivities of Mycena galopus (Pers.) Kummer, Phoma exigua (Desm.), Cladosporium clodosporioides (Fres.) de Vries and Aureobasidium pullulans (de Bary) Arnaud to low concentrations (12.5–100.0 μM) of sulphite (SO2−3) when growing on decomposing needles of Picea sitchensis (Bongard) Carrière (Sitka spruce) and Pinus sylvestris L. (Scots pine) were assessed. Carbon dioxide evolution from the decomposing needles was strongly inhibited by SO32− at pH 3.0–4.5 P. exigua was the most sensitive of the species tested in the mycelial state, and C. cladosporioides was the most sensitive species tested as spores. Mycelium was consistently less sensitive than spores. The inhibitory effect of SO32− on CO2, evolution was increased by increasing the SO32− concentration or decreasing the pH. The concentrations shown to exert toxicity were similar to those which have been measured in rainfall in the UK, and the results provide evidence that SO32− can be toxic to litter fungi at environmentally realistic concentrations.
Effect of phosphorus deficiency on growth angle of basal roots in Phaseolus vulgaris
Authors: BONSER AMY M. , LYNCH JONATHAN , SNAPP SIEGLINDE
Published: April 2006

summary

Root architectural plasticity might be an important factor in the acquisition by plants of immobile nutrients such as phosphorus (P). In this study, we examined the effect of P availability on the orientation of basal roots with respect to gravity, and thereby on the growth angle of these roots of common bean (Phaseolus vulgaris L.). In one set of studies the growth angle of basal roots of bean seedlings was measured over time. Sixteen bean genotypes were examined; six showed a decrease in root orientation with respect to gravity m low P media, one increased orientation, and nine showed no difference within 5 d of basal root emergenece. Bean taproots also showed decreased root orientation with respect to gravity in law P. Growth angle after 5 d was correlated with field performance of contrasting genotypes to low P tropical soils. Mineral deficiencies other than P did not cause changes in root angle. In a. split pouch system that provided high or low P solution to different parts of the root system, the decrease in root angle in low P was found to be a response to globat P availability, and not local to the portion of the root system in low P, Effects of P availability on root angle were associated with reduced shoot P concentration, but preceded effects on plant biomass accumulation and leaf area expansion. Results from growth pouches for genotype G 19833 were confirmed using a solid‐phase buffered sand‐culture system supplying P at three levels. Pea (Pisum sativum), soybean (Glycine max Williams), chickpea Cicer arietinum), lima bean (Phaseolus lunatus), and lentil (Lens culinaris) were grown with and without P; soybean and pea also showed decreased basal rout angles m low P.
Nitrite assimilation by the yeast Candida nitratophila
Authors: AL KUBISI ADNAN , ALI ABID H. , HIPKIN CHARLES R.
Published: April 2006

summary

Nitrite uptake in the nitrate‐assimilating yeast, Candida nitratophila, was inhibited completely by addition of nitrate or ammonium to cultures at pH 8.0). Nitrite assimilation in these cultures was also completely dependent on the availability of a suitable carbon source (glucose), In cultures at pH 5.0, neither nitrate nor ammonium inhibited nitrite uptake completely. In these cultures, some nitrite was assimilated in the absence of a carbon source. Carbon‐deficient cultures at pH 5.0 were able to reduce nitrite to ammonium but excreted this ammonium without further assimilation, Evidence for the uptake of nitrite by passive diffusion and by active transport via the nitrate uptake system is discussed.
Effects of elevated CO2, nitrogen form and concentration on growth and photosynthesis of a fast‐ and slow‐growing grass
Authors: BOWLER JOHN M. , PRESS MALCOLM C.
Published: April 2006

summary

Growth and photosynthesis of Agrostis capillaris L. and Nardus stricta L. were measured for plants grown under ambient and elevated concentrations of CO2(340 and 550 μl CO2 l−1 respectively) and a range of nitrogen concentrations (0.01, 0.1, 1 and 5 mg N l−1) supplied as either ammonium sulphate or sodium nitrate. After 42 d of growth for A. capillaris and 49 d of growth for N. stricta, the higher nitrogen concentrations resulted in stimulation of growth. The form of nitrogen did not affect the total dry weight attained by A. capillaris. However, ammonium‐grown N. stricta attained a greater total dry weight than did nitrate‐grown plants. Nitrogen form influenced leaf area ratio, which was greater in nitrate‐grown A. capillaris and in ammonium‐grown N. stricta. At the two lowest nitrogen concentrations there was no effect of elevated CO2 on total dry weight in either species, whilst at the two highest nitrogen concentrations positive growth responses to elevated C02 were observed. Photosynthetic capacity and carboxylation efficiency were lower in plants grown in elevated CO2 at the two lowest nitrogen concentrations, and were associated with greater leaf soluble carbohydrate content and lower foliar nitrogen concentrations. By contrast, the CO2 treatment did not affect these parameters at the two highest nitrogen concentrations employed.
Regional and local patterns in the spatial distribution of the flower‐infecting smut fungus Sporisorium amphilophis in natural populations of its host Bothriochloa macra
Authors: GARCÍA‐GUZMÁN GRACIELA , BURDON JEREMY J. , ASH JULIAN E. , CUNNINGHAM ROSS B.
Published: April 2006

summary

Regional variation in the incidence of the systemic floral‐smut fungus Sparisorium amphilophis (Syd.) Langdon & Fullerton an the perennial grass Bothriochloa macra (Steud.) S. T. Blake was investigated through three surveys over a 12 yr period (1981–93). In all three surveys a marked north‐south trend in percentage of infection was detected with a greater proportion of plants in northerly populations being infected than in populations located to the south. The incidence of disease in populations was negatively correlated with the frequency of days with temperatures <0°C in winter. Detailed exploration of local variation in a subset of five populations showed that the incidence of S. amphilophis was density‐dependent and was greater in the edge areas of host populations than in the less disturbed core areas. Smut prevented seed production and negatively affected different aspects of the morphology of the plants, such as the height and basal diameter. Infection also significantly increased the number of inflorescences per plant. These field results were complemented by glasshouse‐based competition experiments which indicated that, despite causing reductions in size, S. amphilophis only affected the competitive ability of infected plants grown under sub‐optimal conditions. The results of this study indicate that an interplay between physical and biotic aspects of the environment determines regional and local levels of disease.
Influence of xylem vascular architecture on the translocation of phosphorus from nodal roots in a genotype of Trifolium repens during undisturbed growth
Authors: HAY M. J. M. , HAMILTON N. R. SACKVILLE
Published: April 2006

summary

Our objective was to establish whether the xylem vascular connections (architecture) of a genotype of Trifolium repens L. had implications for the intraplant allocation of recently assimilated phosphorus (P). One nodal root of each plan! was isolated and fed 32P‐labelled nutrient solution for 24 h. The fed root was either on the parent axis (11–12 nodes proximal CO the apex) or on a branch at the third or fourth node along the branch when counting from the junction with the parent stolon. Allocation patterns were obtained by dissecting plants and assaying each dissected component for 32P.

Under conditions of undisturbed growth in a controlled environment xylem architecture was found to have an important influence on the intraplant distribution of 32P from nodal roots. Allocation patterns of 32P were consistent with those predicted from knowledge of the xylem vascular architecture of the genotype and a predominantly acropetal direction of the transpiration stream. For instance, very little 32P (< 1 % of exported 32P from the fed root) was found in branches on the opposite side of the stolon to the fed root, and the strong acropetal direction of the transpiration stream resulted in little allocation of 32P to leaves that had traces that arose from axial bundles at positions proximal to that of the fed root (the leaf subtending the fed root and the next distal leaf had low 32P content), to all plant organs proximal to the fed root (< 6%) and to all other roots (<4%).

The high allocation of 32P to the branch arising at the same node as the fed root (64%) reflects the numerous links that the‐ fed root has to vascular bundles in the branch (3–6, of which two are axial bundles) against the single connection it has to the adjacent lower axial bundle in the parent stolon. Allocation of 32P to the leaf and axillary bud at each node along the branch strongly favoured nodes on the adaxial side, a result consistent with the fact that the root connections are to the upper and lower axial bundles on the adaxial side of the branch. Allocation to a particular node along the branch was also influenced by its nodal position relative to the fed root and the sink strength of its tissues for the transpiration stream.
Monoclonal antibodies as tools to quantify mycelium of aquatic hyphomycetes
Authors: BERMINGHAM S. , MALTBY L. , DEWEY F. M.
Published: April 2006

summary

Quantitative ELISAs have been developed to determine the biomass of two aquatic hyphomycetes in natural mixed assemblages. These assays employ a species specific rat monoclonal antibody (MAb) raised to Alatospora acuminata and a genus‐specific murine MAb raised to Tetracladium marchalianum. The respective antigens are produced constitutively and their production is not affected by a range‐ of culture conditions. The MAbs can also be used to study the spatial distribution of these fungi using Immunofluorescence. Both antibodies recognize carbohydrate epitopes and belong to the immunoglobulin class IgM. The potential applications of these immunoassays are discussed.
Development of water‐conducting cells in the antipodal liverwort Symphyogyna brasiliensis (Metzgeriales)
Authors: LIGRONE ROBERTO , DUCKETT JEFFREY G.
Published: April 2006

summary

The thallus of the metzgerialean liverwort Symphyogyna brasiliensis Nets contains a strand of dead thick‐walled tells with helicoidally‐arranged pits that arc presumably involved in water transport. During the first phase of differentiation these cells undergo a 13–16‐fold elongation while remaining thin‐walled and almost unchanged in diameter. During subsequent maturation the walls become strongly thickened by deposition of highly electron‐opaque material on extraplasmodesmal areas and of transparent material forming collars around plasmodesmata. Whilst the growing wall shows an ordered microribrillar texture and is strongly reactive to PATAg staining for carbohydrates, the material associated with plasmodesmata is amorphous and PATAg‐negative. A dense cortical array of microtobules (MTs) overlies the growing wall except in proximity to plasmodesmata, which are closely associated with tubular endoplasmic reticulum (ER). During cellular maturation plasmodesmata undergo extensive secondary elongation by incorporation of cortical ER supposedly continuous with desmotubules. Quantitative analysis of plasmodesmal frequencies in relation to cellular elongation and wall thickness indicates that there is no de novo formation of plasmodesmata. Cortical MTs, wall microfibrils and secondarily‐modified plasmodesmata are consistently co‐aligned, all forming helices of about 45°. During maturation the Golgi apparatus proliferates and a vast number of vesicles containing PATAg‐positive material are produced from a membrane domain interpreted as trans Golgi network, whilst PATAg‐negative vesicles are formed along the fenestrated margins of C& and media) dictyosomal cisternae. Exocytosis of PATAg‐positive vesicles is confined to extraplasmodesmal areas. In ageing cells abundant fibrillar material, also positive to PATAg‐test, accumulates within pleomorphic membrane‐bounded tubules. Final cytoplasmic dissolution involves the lysis of all cellular membranes and the liberation of the membrane‐bounded fibrillar material, that is subsequently deposited onto the walls. The eventual dissolution of the plugs of amorphous electron‐transport material results in the formation of open pits. Similarities in the cytological mechanisms underlying pore development in water‐conducting cells of Symphyogyna and in the sieve elements of angiosperms are discussed.
Photosynthetic responses of a moss, Tortula ruralis, ssp. ruralis, and the lichens Cladonia convoluta and C. furcata to water deficit and short periods of desiccation, and their ecophysiological significance: a baseline study at present‐day CO2 concentration
Authors: TUBA ZOLTAN , CSINTALAN ZSOLT , PROCTOR MICHAEL C. F.
Published: April 2006

summary

We report the changes in CO2 assimilation, potential photochemical activity (as measured by slow fluorescence), photosynthetic pigment concentrations, and dark respiration of two desiccation‐tolerant (DT) lichens (Cladonia convoluta (Lam.) P. Cout. and C. furcata (Huds.) Schrad.), and a DT moss (Tortula ruralis (Hedw.) Gaertn. ssp. ruralis) during slow drying, and on rehydration following a 12 h period of desiccation. Initially there was a two to fourfold increase in net CO., assimilation due to reduction of CO2‐diffusion resistance by elimination of excess water. Optimum water content for photosynthesis was 100–150 % of dry mass (DM) in C. convoluta, c. 100 % DM in C. furcata, and 120–200 % DM in T. ruralis. The intensity of maximum and steady‐state slow fluorescence showed little change above water contents of 56%, DM in the lichens and 73 % DM in T. ruralis (corresponding to c. 30–40 % cell relative water content), but fell sharply at lower water content. The variable duorophyll‐fluorescence decrease ratio (Rfd) at 690 nm peaked at 56 % DM water content in the two lichens, and at 45% DM in T. ruralis. Photochemical activity ceased at the same point in the experiments as CO, assimilation; dark respiration ceased only when desiccation was complete. In all three species, the photosynthetic apparatus remained in a fully and quickly recoverable state. Chlorophyll and carotenoid concentrations remained substantially unaltered throughout. On rehydration, chlorophyll fluorescence parameters returned within 30 min to pre‐desiccation levels, and photosynthesis recovered fully and rapidly (< 1 h). All three species attained a positive carbon balance within 20 min of re‐moistening, in spite of high rates of dark respiration. The results confirm the significance of extracellularly‐stored water to poikilohydric DT lichens and bryophytes. The measurements, in conjunction with published data on the full‐turgor water content of similar mosses and lichens, show that the cell‐physiological response of photosynthesis to water deficit is not greatly different from that of either normal or DT vascular plants. Small plant size and small cell volume in DT lichens and mosses, together with rapid recovery of photosynthesis after desiccation, allow the plants to utilize the small amounts of intermittently available water from brief showers or dew.
Structure of fructan polymers from tuberous roots of Gomphrena macrocephala (Amaranthaceae) from the cerrado
Authors: SHIOMI NORIO , ONODERA SHUICHI , VIEIRA CANDIDA C. J. , FIGUEIREDO‐RIBEIRO RITA C. L.
Published: April 2006

summary

Two fructo‐polysaccharides, FP‐I and FP‐II, were separated from a soluble extract from tuberous roots of Gomphrena macrocephala St.‐Hil. by gel permeation chromatography on Toyopearl HW‐40S. FP‐I and FP‐II were mixtures of saccharides with a wide‐ranging degree of polymerization; their acid hydrolysis products were fructose and glucose. The ratios of fructose to glucose in the hydrolysates of FP‐I and FP‐II were 38 and 60, respectively. The average molecular weights of FP‐I and FP‐II were estimated to be 5500 and 10000 respectively, by gel permeation HPLC. The structural confirmation of FP‐I and FP‐II was made by 13C‐NMR analysis. Intense signals corresponding to carbon‐1 (C1), C2, C3, C4, C5 and C6 of fructose residues in FP‐I and FP‐II were observed at δ 60.60, 104.93, 76.99, 75.91, 81.02 and 64.11, respectively. These chemical shifts coincided with those of timothy and bacterial levans. The less intense resonances were tentatively assigned to carbons of terminal fructosyl residues and a fructosyl residue linked to a glucose residue by a β‐2,1 bond in FP‐I and FP‐II. Also, weak signals attributed to carbons of the glucose residue in both polysaccharides were separated from those of other glycosyl residues. These findings were supported by GLC analysis of methanolysate from permethylated FP‐I and FP‐II. Thus FP‐I and FP‐II comprise fructose residues with β‐2,6 linkages, and a terminal glucose bound with fructose residues at position C1, although both polysaccharides possibly contained a non‐terminal glucose residue in the molecule.
Microcystin‐LR inhibits photosynthesis ofPhaseolus vulgarisprimary leaves: implications for current spray irrigation practice
Authors: ABE TOSHIHIKO , LAWSON TRACY , WEYERS JONATHAN D. B. , CODD GEOFFREY A.
Published: April 2006

summary

Photosynthesis ofPhaseolus vulgarisL. leaves was measured after treatment with microcystin‐LR (MC‐LR), a potent cyanobacterial toxin and inhibitor of protein phosphatases 1 and 2A. The net photosynthetic rate fell by over 50% within 8 h of dipping leaves in MC‐LR solution. This inhibitory effect was observed when leaves were treated once with concentrations above 10−2mol m−3. At 10−2mol m−3, the inhibition caused by MC‐LR was transient, and net photosynthesis rates essentially recovered after 5 d, whereas at 10−1mol m−3, the net photosynthesis rate in treated leaves was still 42% of controls after 8 d. Necrosis was observed at the higher concentration, but not usually below 10−2mol m−3. Analysis of net photosynthetic rate as a function of internal CO2concentration and photosynthetically active photon flux density indicated that both the CO2‐saturated rate of photosynthesis and the carboxylation efficiency were lowered when MC‐LR‐treated leaves were exposed to photosynthetically‐saturating light. When the leaves were exposed to 2.0 × 10−5mol m−3MC‐LR solution repeatedly, the photosynthetic rate was significantly reduced after 7 d, suggesting that intermittent exposure ofP. vulgarisleaves to low concentrations of MC‐LR brings about an effect on photosynthesis more inhibitory than that of a single exposure to high concentrations of MC‐LR. These results indicate that relatively low concentrations of MC‐LR cause damage to the photosynthetic apparatus ofP. vulgaris in situ.We discuss the significance of these findings in relation to current spray irrigation practice for crop plants involving the use 6f water containing cyanobacterial blooms and microcystins.
Ultrastructure of the interaction between Fusarium oxysporum f. sp. lycopersici and cultured tomato mutant cells selected for altered response to the pathogen
Authors: MORASSI BONZI LAURA , ADELE PANCANI MARIA , PAOLETTI CINZIA , GABBRIELLI ROBERTO , STORTI EMANUELA , BUIATTI MARCELLO
Published: April 2006

summary

Tomato cell clones selected for high and low (F+ and F−) response to heat‐released cell wall components from Fusarium oxysporum f. sp. lycopersici were analysed ultrastructurally with particular regard to cell wall and membrane modifications in a synchronous dual culture in vitro system which avoided direct contact between the two partners of the interaction. Constitutive differences in cell shape were observed between F+, F− and parental cultivar cells by TEM and SEM. Quantitative morphological analyses, and biochemical determinations showed differences in cell wall thickness and polysaccharide content between cells of the F+ and F− clones. A temporal study revealed differences between the cell clones in (1) the rate of resistance to degradation by fungal polysaccharide hydrolytic enzymes, (2) protoplast destruction, (3) formation of paramural bodies, (4) cell wall appositions (papillae), and (5) mitochondrial alterations. The data are discussed with respect to a possible correlation between cell wall structure and the course of events during the host‐parasite interaction on the one hand and, on the other, active responses to the pathogen as suggested by the literature.
Sequential encounter of wood resources by mycelial cords of Phanerochaete velutina: effect on growth patterns and phosphorus allocation
Authors: HUGHES C. L. , BODDY LYNNE
Published: April 2006

summary

The effect of sequential encounter with wood resources (1 cm3 and 2 cm3‘baits’ in various combinations) by mycelial cords of Phanerochaete velutina (DC.: Pers.) Parmasto growing from 1 cm3 wood inocula was investigated in model soil systems in the laboratory. Encountering large wood baits (8 cm3), either next to the inoculum or after encounter of another bait, resulted in cessation of mycelial extension and regression of mycelium from the inoculum and small baits. Small wood baits had no effect on mycelial extension rates, even when encountered in rapid succession. All systems maintained a general polarity when growing out from a bait, but later often curved around the bait, extending over soil which had previously been explored. Allocation of 32P (taken up by the inoculum) between the three resource units (inoculum and two sequentially encountered baits) was investigated; significantly (P≤ 0.05) more 32P was allocated to the large wood baits (whether encountered first or second) than to the other bait; but the inoculum was usually allocated most. Wood inocula decayed more rapidly than baits. The significance of the results is discussed in relation to foraging.
Ensnaring microbes: the components of plant disease resistance
Authors: HAMMOND‐KOSACK KIM E. , JONES DAVID A. , JONES JONATHAN D. G.
Published: April 2006

Plants activate an array of co‐ordinated defence responses to restrict microbial attack. Timely perception of foreign molecules appears to be critical for the success of these defences. However, the nature of the molecular events required for resistance is largely unknown. Recent isolation of disease resistance (R) genes, has revealed that R gene products have several features in common. This finding suggests that plants have evolved several common or similar signal transduction pathways to activate resistance to a range of unrelated microbes. R gene isolation and the genetic identification of other loci required for R function permits analysis of the structure and evolution of microbe‐perception mechanisms. Numerous types of activated defence responses are recognized. A requirement for salicylic acid in resistance has been established in some systems. Roles for other events, like reactive oxygen species and the hypersensitive (host cell death) response, remain enigmatic. A thorough understanding of the components leading to pathogen recognition and the expression of resistance should permit the design of novel strategies to engineer broad‐spectrum and durable plant disease control.