bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fructan biosynthesis in excised leaves of Lolium temulentum L.
Authors: CAIRNS ANDREW J. 
Published: April 2006

summaryAnalyses of the kinetic properties and products of fructosyl transferases from Lolium temulentum L. suggest that these enzymes are artifacts of conventional extinction and/or assay methods. An alternative approach to the investigation of fructan biosynthesis in cell‐free extracts has been developed. This approach employs the Sensitivity of radiotraeers to overcome the limitations of conventional quantitative methods for the analysis of fructan.Homogenates of leaves were prepared, which contained enzyme protein, endogenous sucrose and fructan. These extracts catalysed the rapid and efficient incorporation of radioactivity from [U‐14C]sucrose into material with a decree of polymerization greater than 2. The chromatographic pattern of these labelled products was identical to the pattern of native leaf fructan. Kestose, which does not accumulate to high concentrations in vivo but was a major product of our previous enzyme assay procedures, was not a product of these homogenates.The flux of radioactivity into oligofructan was sufficient to account for observed rates of fructan accumulation in the leaf And fructosyl transfer was observed at sucrose concentrations between 15 and 30 mol m−3, which is within the probable physiological range of substrate concentration for L. temulentum leaf cells. Extracts derived from leaves which were not actively accumulating fructan were unable to label oligofructan. Labelling of fructan was not due to non‐enzymic isotope exchange.Leal homogenates contained invertase and fructan hydrolase activities. Invertase activity was inhibited by pyridoxal HCl and pyridoxine MCI when these compounds were included in reactions at 20 mol m−3. Inhibition of invertase activity was correlated with a marked stimulation of fructosyl transfer, suggesting competition for substrate. Because this system functions at physiologically relevant sucrose concentrations and produces a pattern of labelled products identical to native leaf fructan, we suggest that it represents a more convincing starting point for studies of the enzymology of fructan biosynthesis than previous cell‐free extracts.
Distribution of photosynthetically fixed carbon within root systems of Eucalyptus pilularis plants ectomycorrhizal with Pisolithus tinctorius
Authors: CAIRNEY J. W. G. , ASHFORD A. E. , ALLAWAY W. G. 
Published: April 2006

summaryIn intact seedlings of Eucalyptus pilularis Stn. ectomycorrhizal with Pisolithus tinctorius (Pers.) Coker & Couch in growth pouches, and labelled photosynthetically with 14C4 more radioactivity was translocated into mycorrhizal than to non‐mycorrhizal roots. Results from autoradiography of intact root systems were supported by data from scintillation counting of individual root tips. Greater 14C accumulation occurred in young than in older mycorrhizas. It is proposed that individual mycorrhizal roots act most strongly as carbon sinks early in their life and that there is a progressive reduction in the amount of photosynthate translocated to them as they age.
Oxalic acid induced cytological alterations differ in beans tolerant or susceptible to white mould
Authors: TU J. C. 
Published: April 2006

summaryLeaf tissues of two white bean (Phuscolus vulgaris L.) cultivars, one susceptible and one tolerant to white mould [Sclerotinia sclerotinrum (Lib.) de Bary], were treated for different times with oxalic acid. Tissues were prepared by both thin sectioning and freeze‐fraeture techniques for electron microscopy. The plasma membrane of the resistant cultivar appeared more tolerant to damage induced by oxalic acid than that of the susceptible cultivar. At the same concentration of oxalic acid the plasma membrane and chloroplasts of the susceptible cultivar were affected more, and ruptured more quickly, than those of the tolerant one. In thin sections, the ruptured organelles were partially or completely disorganized. In replicas of freeze‐fractured preparations of the plasma membrane, increased protrusions, wrinkles, breakages and ruptures were associated with increasing exposure to oxalic acid. Damage was more severe in the plasma membrane of the susceptible cultivar than in that of the tolerant one. Measurements of the conductivity of water bathing leaf discs of the two cultivars showed that the susceptible cultivar led to a higher conductivity than the resistant one, indicating that the injury and rupturing of the plasma membrane were closely related to membrane stability.
Morphological features of pericycle cells in relation to their topographical location in onion adventitious roots
Authors: CASERO P. J. , GARCÍA‐SÁNCHEZ C. , LLORET P. G , NAVASCUÉS J. 
Published: April 2006

summaryAnalysis of cell length, cross‐sectional area and nuclear length of pericycle cells in adventitious roots of Allium cepa L. has revealed the existence of three cell types whose topographical location is related to the vascular pattern. Cells opposite the xylem are short and narrow with an elongated nucleus. The intervening cells are also short but their cross‐sectional area is much greater than that of cells at the xylem pofes, while their nucleus is relatively short. Cells opposite the phloem are long, with an elongated nucleus, and their cross‐sectional area is intermediate between that of the other two cell types. Lateral root primordia are always initiated from the population of short cells opposite the xylem. However, the different cell types appear in the pericycle before primordial initiation and not as a result of this event.
Fluxes of atmospheric hydrogen sulphide to plant shoots
Authors: DE KOK Luit J. , STAHL KLAUS , RENNENBERG HEINZ 
Published: April 2006

summaryShort‐term exposure of maize, pumpkin, spinach and spruce to various atmospheric H2S concentrations resulted in high H2S fluxes to the shoots. In all species an almost linear relation was observed between flux and H2S concentration up to around 0.3 μl −1. At higher H2S concentrations the flux reached a maximum, which was about 0.08, 0.04, 0.1 and 0.03 μmol g f. wt−1 h−1 for maize, pumpkin, spinach and spruce, respectively. The transpiration rate was not affected during H2S exposure. Up to a level of 0.3 μl 1−1, the shoot conductance for a influx of the various species varied between 61 and 92% of that predicted from shoot conductance for aqueous vapour efflux. There was no relation between the H2S flux to the shoots and the sensitivity of the species towards H2S. A 12 days' exposure of maize, pumpkin and spinach to 0.75 μl 1−1 H2S resulted in a reduction of shoot yield of 1.36 and 69%, respectively. H2S flux to the shoots of pumpkin, spinach and spruce remained rather constant during exposure for three or four days to about 0.22μl l−l H2S. Even at a concentration of about 0.8 μl 1−1H2, which reduced the growth of pumpkin and spinach, the fluxes remained nearly constant. Fluxes of H2S to the shoots did, however, vary diurnally, being high during the light and low during the dark period. The H2S flux to transpiration ratio was constant during both light and dark periods, indicating that uptake was predominantly via the stomata. Only part of the total flux of H2S to the shoots of pumpkin and spinach could be recovered in the water‐soluble non‐protein sulphydryl fraction of the shoots (maximum 34%). It is proposed that cysteine synthase is directly involved in the fixation and metabolism of atmospheric H2S by the plant.
Fluoride‐induced enhancement and inhibition of shoot growth in four taxa of Pinus
Authors: DOLEY D. 
Published: April 2006

summary Pinus elliottii Englem. Var. elliottii (PEE) and three varieties of Pinus caribaca morelet [var. caribaca barr. Et Golf. (PCC), var bahamensisi Barr. et Golf. (PCB) and var. hondurensis (PCH)] were grown at gaseous hydrogen fluoride concentrations of 0.0, 1.2, 1.8 and 4.3 μ F m−3 during a period of 200 d. Extension growth of the mainstem and lateral branches was not significantly affected by fluoride in any taxon. Overbark diameter increment at the stem base was signicantly greater at 1.2 μg F m−3 than at 0, 1.8 or 4.3 μ F m−3 in all taxa, and also near the stem apex in PEE. Only in PEE was the stem base diameter increment lower at 4.3 μ F m−3 than in control plants. Lateral branch diameter increments were not signicantly affected by ambient fluoride concentration. Stem base diameter increments in all taxa linearly related to the rates of photosynthesis I needles 4–8 weeks old.
The effect of arginine on rates of internalization of other amino acids by symbiotic Chlorella cells
Authors: McAULEY P. J. 
Published: April 2006

summaryAddition of arginine to the medium of symbiotic Chlorella freshly isolated from the European strain of green hydra increases the rate of uptake of other amino acids into the cells via a general amino acid permease. Uptake rates increase immediately upon addition of arginine, reaching a new stable level after 20–30 min. Removal of arginine causes an immediate decrease in uptake rates. Changes in the Km and Vmax of amino‐acid uptake in the presence of arginine, and the fact that cycloheximide treatment does not inhibit the arginine‐stimulated increase, suggest that arginine does not induce synthesis of new transport protein. Instead, arginine may alter properties of the cell membrane such as charge, thereby increasing the efficiency of uptake of amino acids by existing transport mechanisms. The significance of this novel effect is discussed in terms of possible control of amino acid supply to the symbiotic Chlorella.
Evidence from peroxidase polymorphism on the taxonomy and reproduction of some Sorbus populations in south‐west England
Authors: PROCTOR MICHAEL C. F. , PROCTOR MARGARET E. , GROENHOF ANDREW C. 
Published: April 2006

summaryPeroxidase isoenzymes in stem tissue were investigated by polyacrylamide gel electrophoresis in Sorbus populations mainly from Devon, south‐west England, A total of 16 bands were recognized, of which 10 were variable between individuals or populations. The sexual diploid species S. aucuparia, S. aria and S. torminalis showed individual variation within populations. Six polyploid microspecies, S. anglica, S. porrigentiformis, S. rupicola, S. vexans, S. subcuneata and S. devoniensis, and an extensive unnamed rupicola‐like population on the coast of north Devon and west Somerset, consisted of individuals of essentially identical phenotype (with a few recognizable minor variants). Every microspecies had a distinctive peroxidase phenotype but S. porrigentiformis from Devon was not identical with a specimen from Leigh Woods, Bristol. Microspecies of the S. aria group have various combinations of seven bands which occur in diploid S. aria populations. S. anglica combines ‘S. aria’ bands with a prominent band from S. aucuparia. S. subcuneata and S. devoniensis possess four or five of the ‘S. aria’ bands, together with two bands which are apparently constant in S. torminalis; S. intermedia also has a peroxidase phenotype related to these species.
Effect of oxygen supply and temperature at the root on the physiology of kiwifruit vines
Authors: SMITH G. S. , BUWALDA J. G. , GREEN T. G. A. , CLARK C. J. 
Published: April 2006

SummaryA severe leaf disorder currently affects kiwifruit vines (Actinidia deliciosa var. deliciosa) in New Zealand and a number of other countries. The symptoms, which develop in mid‐summer, include interveinal chlorosis, development of necrolic areas on the leaf and eventual leaf death. Field observations strongly indicated the involvement of the root system. The present study investigated the extent to which temperature and oxygen supply at the root influenced the physiology of kiwifruit vines.Maximum root growth occurred at 20 °C, while temperatures in excess of 25 °C reduced growth. Shoot growth was also reduced by root temperatures above 20 °C. No obvious leaf symptoms developed on the vines affected by the high temperatures. Below 20 °C there was a marked reduction in growth with little or no growth occurring at 10 °C. While soil temperature can be expected to influence root growth per se, it would appear unlikely that it directly controls the seasonal pattern of root growth or greatly influences the physiology of the leaf.This study showed kiwifruit vines are not well adapted to tolerate low concentrations of oxygen in their root zone. Growth was substantially reduced when the supply of oxygen to the roots was reduced. The extent of the reduction was proportional to the number of hours per day the vines were without aeration. Root growth was particularly affected. Distinctive leaf symptoms appeared on all oxygen‐stressed vines and included the sudden appearance of large necrotic areas on the older leaves, sometimes preceded by an interveinal chlorosis. Measurement of the porosity of the roots indicated that the average air space between the tightly packed cells accounted for 2% or less of the total root volume. There was no obvious change in root porosity with decreasing oxygen supply or difference between the solution grown vines and vines from the field.Decreasing the supply of oxygen to the roots resulted in rapid reduction in the stomatal conductance of the leaves and the virtual elimination of the diurnal pattern. Associated with the decrease m the stomatal conductance was a marked increase in the maximum daily temperature of the leaves compared to the control vines. The difference between the two treatments increased with time. An estimate of the rate of consumption of oxygen per unit length of root (9.1 × 10−10 mol m−1 s −1) suggests that a mature kiwifruit vine could deplete the oxygen supply in a well aerated soil to an anoxic condition in about 5 hours. The relatively high consumption of oxygen coupled with the low porosity of the roots ensures that even short periods of low concentrations of oxygen in the root zone will seriously affect the physiology and growth of kiwifruit vines. It was concluded that poor aeration of the root system is likely to be a major factor in the incidence of the leaf disorder currently affecting kiwifruit vines in a number of countries.
A correlation in plastid development and cytoplasmic ultrastructure with nuclear gene expression during seed ripening in soybean
Authors: SAITO G. Y. , CHANG Y. C. , WALLING L. L. , THOMSON W. W. 
Published: April 2006

SummaryWith greening of soybean embryos during seed ripening, increased granal stacking directly correlates with decreasing chlorophyll a/b ratios. However, the intergranal fret system that is normally observed in chloroplasts is minimally developed during embryogenesis. Transitions in chloroplast development were correlated with coincident transitions in cellular ultrastructure. Levels of chlorophyll a/b binding protein mRNAs decreased prior to chloroplast dedifferentiation to eoplast during seed maturation. This suggests that the availability of chlorophyll a/b binding proteins is essential for maintenance of thylakoid appression and stacking against derivative processes.
The relationship between some morphological and chemical features of Sphagnum cuspidatum Ehrh. and physical characteristics of the environment
Authors: BAKER R. G. E. , BOATMAN D. J. 
Published: April 2006

SummaryThe frequency (No. 1000 fascicles−1) of innovations (branches resembling the parent shoot) on plants of Sphagnum cuspidatum Ehrh. was determined at IX sites on or near the Silver Flowe National Nature Reserve on six occasions. The capitula were analysed for nitrogen, phosphorus and potassium.When the sites were arranged in order of increasing mean innovation frequency it was found that the frequency at ombrotrophic sites was less than that at rheotropic sites. Interfascicle length was directly related to innovation frequency but no evidence of a relationship between either interfascicle length or innovation frequency and capitulum dry weight was found. During the course of each growing season the variances of the means of interfascicle length and capitulum dry weight declined.Multiple regression analysis indicated that the capitulum dry weight and interfascicle length were negatively and positively related respectively to the nitrogen content of the capitula. The regression of innovation frequency on N, P and K in the capitula was not significant (P > 0.05).Two experiments were undertaken in which shoots of Sphagnum cuspidatum were reciprocally transplanted between a rheotrophic and an ombrotrophic site. During the course of a single growing season the mean interfascicle length, the mean capitulum dry weight and the mean concentrations of N, P and K in the capitula became much more similar to those of the controls. At the beginning of each experiment all visible innovations were removed from the plants. At the end of the experiment in 1983 innovation frequencies on the transplants were intermediate between those on the ombrotrophic and rheotrophic controls. In 1984 innovation frequencies on both controls and transplants were relatively low and an attempt is made to explain this in terms of the climatic conditions of that year.
Ultrastructure and cytochemistry of Dunaliella tertiolecta Butcher and Pavlova lutheri (Droop) Green grown on three different sources of organic nitrogen*
Authors: OLIVEIRA LUIS , HUYNH HANH 
Published: April 2006

SummaryPhototrophic growth of Dunaliella tetiolecta Butcher or Pavloca lutheri (Droop) Greet) on hypoxanthine or allantoatc produces major ultrastructural changes, by comparison with nitrate‐ and urea‐grown cultures. These are particularly noticeable during growth on hypoxanthitie and affect mainly the endoplasmic reticulum, mitochondria and vacuoles. Cytochemical tests reveal the presence of both uricaase and cataJase activities in mitochondria. Since no mierobodies are observed m cells of these trncroaluac, it appears that mitochondria participate in the oxidativc degradation of putines and their derivatives. These oryancllcs may therefore play a major role m the organic N budget oi Dunaliella tertiolecta and Pavlova lutheri.
The temporal window of germination in oospores of Chara (Charophyceae) following primary dormancy in the laboratory
Authors: STROSS R. G. 
Published: April 2006

SummaryFully ripened oospores from two clones of Chara Zeylanica Klein ex Willdenow. were harvested in October. Initially, the oospores of one clone were all dormant, those of the second clone were non‐dormant. Postharvest temperatures influenced after‐ripening and dormancy initiation respectively. The temperature effect was reflected in the amplitude of germination, which ranged from 29‐100% hut not in the duration of the dormant interval. The germination window opened independently of temperature and was maximally open 6‐2 months postharvest. After‐ripening was augmented and germination was suppressed by oscillating temperatures. Light, given as prolonged exposures, was a necessary stimulus for activation. A secondary, or ‘Haupt’, messenger, diffusing from the bactoagar substratum, obscured the light reaction and disrupted the germination window. A ‘location awareness’ is suggested by an endogenous temporal window of germinability, superimposed on which are discriminators that sense appropriate conditions of light and temperature.
Compensation in growth and photosynthesis of wheat (Triticum aestivum L.) following early inoculations with Septoria nodorum (Berk.) Berk.
Authors: ROONEY J. M. , HOAD G. V. 
Published: April 2006

SummaryInoculations of winter wheat with Septoria nodorum (Berk.) Berk, at either the three or six Leaf stage in the glasshouse identified possible mechanisms of changes in the growth of winter wheat to compensate for the damaging effects of infection. Following inoculations at the three leaf Stage there was increased photosynthesis in healthy fourth leases on inoculated plants; no equivalent increase was shown for later inoculations. There was some indication that, after third leaf inoculation, photosynthesis was stimulated in healthy areas on infected leaves but depressed in infected areas. After inoculations at the third leaf stage, the shoot/root dry weight ratio increased compared with that of controls. No significant changes in dry matter production, at anthesis or during grain‐growth, followed inoculation at the six leaf stage. At anthesis there was an increase in the proportion of dry weight partitioned to stems, and tiller and leaf area of infected plants was greater than m the control plants.
Ectomycorrhizas and putative ecto‐mycorrhizal fungi of Afzelia africana Sm and Uapaca guineensis Müll. Arg. in southern Senegal
Authors: THOEN D. , BA A. M. 
Published: April 2006

SummaryEctomycorrhizas and ectomycorrhizal fungi of Afzelia africana Sm. and Uapaca guineensis Müll. Arg. are reported in forests of southern Senegal. Ectomycorrhizas occurred in dry and wet conditions, at different soil contents of available phosphorus (0–17.5 μg g−1). U. guineensis was confined to groundwater forests. Individual trees had both ecto‐ and endomycorrhizas, A. africana grew scattered in semi‐evergreen and riverside forests, whereas in the woodland it formed larger patches and could dominate the canopy. Eighteen putative ectomycorrhizal fungi grew under U. guineensis and thirty‐one under A. africana. Only six species were common to both trees, indicating an ecological and/or taxonomical selection. The fungi belonged to the following Orders: Russulales (16), Boletales (11), Agaricales (9), Cantharellales (2), Selerodermatales (2), Hymenogastrales (1), Gautieriales (1), Aphyllophorales (11). Some of them had a wide Sudano‐Zamhezian or Guineo‐Congolian distribution and reached their northern limit in Senegal.