bluuebunny/crossref_metadata_2025_split 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

SUMMARYSolubilization 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

SUMMARYChlorophyll 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

SUMMARYWater 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

SUMMARYPercent 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

SUMMARYLowland 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

SUMMARYCuticular 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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYYoung, 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

SUMMARYPhotosynthetic 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

summaryCytological 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

summaryWe 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

summaryEffects 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.