bluuebunny/crossref_metadata_2025 huggingface dataset:
Respiration and photosynthesis in oats exhibiting different levels of partial resistance to Erysiphe graminis D.c. ex Merat f. sp. avenae Marchal
Authors: HAIGH G. R. , CARVER T. L. W. , GAY A. P. , Farrar J. F.
Published: April 2006

summary

Rates of photosynthesis and respiration were measured by two methods, oxygen electrode and infrared gas analysis (IRGA), in infected and control, seedling and adult leaves of oat genotypes exhibiting different levels of partial resistance. Measurements were carried out up to 9 d after inoculation, sporulation commencing on day 5. There was no decrease in the rate of photosynthesis, except in the second leaves of one genotype, and no decrease in any of the fifth leaves relative to controls. The two methods of measuring respiration gave different results, with no consistent differences being found. Measurements by oxygen electrode, up to 6 d after inoculation, revealed that disease treatment had a significant effect on respiration in only two cases; the susceptible first leaf of one genotype and the resistant fifth leaf of another. Measurements by IRGA, up to 9 d after inoculation, did not confirm these differences, but did reveal a significant increase in respiration in the diseased fifth leaf of another resistant genotype. SHAM inhibited respiration, indicating the presence of the alternative oxidase, but there was no significant difference in its activity between diseased and control plants. Thus changes in photosynthesis and respiration previously associated with powdery mildew infection are either delayed or compensated for in oats. Photosynthetic and respiratory responses do not appear to be involved in partial resistance of oats to powdery mildew.
Photosynthesis of tropical tree seedlings in relation to light and nutrient supply
Authors: RIDDOCH I. , LEHTO T. , GRACE J.
Published: April 2006

summary

The photosynthetic performances of two tropical tree species, a pioneerNauclea diderrichii(De Wilde.) Merrill, and a climax speciesEntandrophragma angolense(Welw.) C. DC., both from West Africa, were compared. Young plants were grown in controlled environments where photon flux density and nutrient supply were varied.A/C1curves of the two species were very similar, both showing an increased initial slope and maximal rate of photosynthesis when the leaves had been grown at high photon flux density. Nutrient supply had a similar, but smaller, influence. However, the pioneerNaucleashowed a greater increase in initial slope in relation to both light and nutrient supply. It also showed greater anatomical response to light, developing a second layer of palisade mesophyll when grown at high photon flux density. Light response curves of photosynthesis were also determined. The apparent quantum efficiency was insensitive to growing conditions, but the carboxylation rate, dark respiration and tight‐saturated photosynthetic rate were sensitive to the light climate of growth. The pioneerNaucleadisplayed an increase in assimilation rate as the photosynthetic photon flux density was increased beyond 300 μmol m−2s−1, butEntandrophragmadid not, and often showed a decline.
Conservation of the British National Begonia Collection by micropropagation
Authors: BOWES B. G. , CURTIS E. W.
Published: April 2006

summary

Regeneration was investigated in non‐sterile leaf explants taken from 87 Begonia lines after culturing for up to 10 weeks in vitro on Knop's mineral salts agar medium with no exogenous growth substances present. For many lines, only very limited supplies of leaf samples were available; nevertheless, in 66 lines de novo regeneration of roots and buds occurred and potted plants were recovered from 49 lines. Additionally in 13 Begonia lines, buds were excised from stock plants and cultured under non‐sterile conditions on Knap's agar. In seven of these the buds rooted and gave rise to potted plants. In six lines organogenic cultures (derived from sterile leaf explants) have been established in long‐term culture on Murashige & Skoog medium supplemented with growth substances and potted plants have been recovered. Sterile explants from a further 12 lines showed regeneration and have been sub‐cultured. The establishment of such sterile cultures, with continued regenerative capacity, is a significant step in the development of a programme for the conservation of rare and endangered begonias.
Apoplastic and symplastic pathways in the leaf of the grey mangrove Avicennia marina (Forsk.) Vierh.
Authors: FITZGERALD MELISSA A. , ALLAWAY WILLIAM G.
Published: April 2006

summary

Pathways for water and salts were traced from the vein endings to their sites of exit in leaves of Avicennia marina (Forsk.) Vierh. Investigations were conducted to determine whether the water and solutes separate at any point in the transpiration stream, and to identify their subsequent pathways. Leaves were placed with their cut petioles in solution containing one of two fluorochromes chosen to trace the transpiration stream. The apoplastic tracer was B‐hydroxypyrene‐1, 3, 6‐trisulphonic acid (PTS), and the symplastic tracer was riboflavin buffered to pH 6.8. Leaf pieces were freeze‐substituted with special care to keep the specimens dry to prevent redistribution of the water‐soluble fluorochromes. Stages of the technique were sensitive to atmospheric moisture, so sections were cut in a room dried to 30% relative humidity, and they were stored in a sealed box containing desiccant. Riboflavin was never seen in the apoplast, and was inside the abaxtal (lower) glands within 30 min indicating a low resistance pathway through the symplast to the gland. The veins terminate in heavily pitted xylem vessels, and at the ends of these pits, the junction between the vein ending and the apoplast of the surrounding mesophyll, were high concentrations of PTS indicating regions of separation of the fluorochrome from water – places where the water crosses from the apoplast to the symplast. PTS diffused slowly in cell walls (measured diffusivity: 4.7 × 10−10 cm2 s−1 reaching the abaxial epidermis after 8 h, which was sufficient time for four complete changes of leaf water. It was concluded that the transpiration stream, probably containing the salt destined for secretion, moved symplastically from the xylem vein endings.
The influence of substrate pH on carbon translocation in ectomycorrhizal and non‐mycorrhizal pine seedlings
Authors: ERLAND SUSANNE , FINLAY ROGER , SÖDERSTRÖM BENGT
Published: April 2006

summary

The effects of changed substrate pH on translocation and partitioning of14C‐labeled plant assimilates were examined in laboratory microcosms containing mycorrhizal (unidentified fungal isolate ‘Pink FMT 87:2’) and non‐mycorrhizal seedlings ofPinus sylvestrisL. andPinus contortaDougl. ex Loud. The mycorrhizal plants had intact mycelial systems at different developmental stages, and microcosms contained non‐sterile peat (pH 3.8) or peat adjusted to different pH values with CaO. In systems with mycorrhizal mycelium which had just started to colonize the peat no significant differences in14C assimilation were found, either with respect to substrate pH or mycorrhizal status of the plant. Loss of activity from the mycorrhizal plants was more rapid, however, probably mainly as a result of increased respiration from the infected root systems. After 8 wk growth in peat at pH 3.8 and 5.2 shoot weights of all seedlings were the same, whereas non‐mycorrhizal plants had root systems twice the size of the mycorrhizal ones. In plants with well developed extramatrical mycelia translocation of labeled carbon to the mycelium growing at pH 3.8 was faster than that to mycelium growing at pH 5.2. After 4 d incubation, however, the percentage of the originally supplied carbon present in the mycelium was 5% regardless of substrate pH. Activity found in the peat surrounding non‐mycorrhizal plants rarely exceeded 0.3%.
Effects of ozone and ammonium sulphate on carbon partitioning to mycorrhizal roots of juvenile Douglas fir
Authors: GORISSEN A. , JOOSTEN N. N. , JANSEN A. E.
Published: April 2006

summary

In this study the impact of two components of air pollution, i.e., ozone and ammonium sulphate, on carbon transport to mycorrhizal roots of Douglas fir was investigated. Juvenile Douglas fir (Pseudulsuga menziesii [Mirb.] Franco) were inoculated with Rhizopogon vinicolor A. H. Smith and Lactarius rufus (Scop.: Fr.) Fr., and allowed to grow outdoors for a period of four months. Subsequently, they were transferred to a phytotron and treated with 0 or 200μg m−3 ozone for 28 days. During these treatments, they were watered with a solution of ammonium sulphate of concentrations corresponding to 5, SO and 200 kg N ha−1 yr−1, During the last three days, the trees were pulse‐labelled with 14CO2. Ozone increased the amounts of 14C recovered in the new needle fraction, whereas the amounts recovered in the roots and root/soil respiration tended to decrease. Mycorrhizal frequency tended to increase during ozone treatment. Ammonium sulphate did not affect the distribution pattern of 14C over the trees, but seemed to stimulate the activity of the root system and mycorrhizal frequency at the intermediate nitrogen level.
Seasonal changes in the pigments of Norway spruce, Picea abies (L.) Karst, and the influence of summer ozone exposures
Authors: ROBINSON DEBORAH C. , WELLBURN ALAN R.
Published: April 2006

summary

There are always significant pigment changes in Norway spruce [Picea abies (L.) Karst.] needles with time in different year classes, even through the winter, but no significant changes in current year needles occur either during summer exposure due to ozone (70 nl i−1) or in the winter following. Effects of summer ozone fumigation on pigment levels, however, are very evident in 1‐ (and 2‐)yr‐old needles. These include significant decreases of total amounts of chlorophyll a and b, violaxanthin, antheraxanthin, and lutein. The only increase in pigment of 1‐yr‐old needles in the summer caused by ozone is that of 5, 6‐epoxy‐lutein; consequently, the 5, 6‐epoxy‐lutein/lutein ratio rises. Although traces of 5, 6‐epoxy‐lutein also occur in the winter afterwards, they are not significant but significant decreases in levels of chlorophylls, vioiaxanthin, antheraxanthin, lutein and β‐carotene persist. The fall in chlorophyll a levels are greater than those of chlorophyll b so a significant fall in the chlorophyll a/b ratio also occurs. Similarly, the declines in amount of β‐carotene are not as great as those of chlorophyll a and therefore significant increases in the ratio of β‐carotene to chlorophyll a are observed. No time x treatment interactions occur after ozone fumigation of 1‐yr‐old needles has been stopped but time x ozone interactions are observed during fumigation in both chlorophyll a/b and violaxanthin/antheraxanthin ratios. Most pigment changes in 2‐yr‐old needles due to summer ozone exposure are complementary to those which occurred in 1‐yr‐old needles in response to ozone the summer before.
Responses of three arid zone grass species to varying Na/Ca ratios in saline sand culture
Authors: ASHRAF M. , NAQVI M. I.
Published: April 2006

summary

The effects on three grass species, Cenchrus pennisetiformis Hochst. & Steud., Leptnchloa fusca (L.) Kunth. and Panicum turgidum Forssk., of decreasing Ca2+ concentration in a saline growth medium were assessed after 7 weeks growth in sand culture. The different Na/Ca ratios of the salt treatment were 24, 49, 99, and 199, at a constant concentration of 200 mol m−3.

Leptuchloa fusca produced the highest fresh and dry biomass, and was able to maintain Na+ and Cl− Concentrations in the shoots and roots almost constant at varying external Na/Ca ratios, except that the shoot Na+ concentration increased significantly at the highest Na/Ca ratio. In C, pennisetiformis the shoot Na+ decreased, whereas the shoot Cl− concentration increased at the highest external Na/Ca ratio. But the root Na+ and Cl− concentrations in this species remained unchanged at varying Na/Ca ratios. C. pennisetiformis and L. fusca maintained almost constant K+ and Ca2+ concentrations in both shoots and roots at varying Na/Ca ratios. In P. turgidum the shoot K+ and shoot and root Ca2+ remained almost unchanged at all Na/Ca ratios, whereas the root K+ concentration decreased significantly but uniformly at the three, higher Na/Ca ratios. No consistent pattern of increase or decrease was observed in the shoot and root Na/K and Na/Ca ratios of all the species. The shoot selectivity (Sk + na) increased consistently in C pennisetiformis with the increase in Na/Ca ratios and it decreased in L. fusca only at the highest Na/Ca ratio in the growth medium

It was established that L. fusca was tolerant, C. penni‐setiformis intermediate and P. turgidum relatively sensitive to low Ca2+ concentrations of the saline growth medium.
Biotransformation of nicotine to nornicotine by cell suspensions of Nicotiana tabacum L. cv. Wisconsin‐38
Authors: HOBBS MICHAEL C. , YEOMAN MICHAEL M.
Published: April 2006

summary

Plant cell suspension cultures of Nicotiana tabacum cv. Wisconsin‐38 accumulate nornicotine as the major alkaloid, unlike the parent plant where nicotine predominates. Nicotine was added to cultures of this cultivar, grown with differing degrees of dependence on photosynthesis for the provision of organic constituents, and also to cultures grown on medium that was optimised for alkaloid accumulation. Under optimal conditions nicotine was converted to nornicotine at an efficiency close to 100% over 10 d. Conversion appeared to he intracellular, with nicotine being taken up from the medium, demethylated to nornicotine and the product released. Illumination of cultures caused a slight decrease in conversion but, when cultures were partially photosynthetic, both growth and the degree of biotransformation were decreased by approximately 40%. As well as the four main tobacco alkaloids several minor alkaloids were detected in cultures after incubation with added nicotine.
Fructan exohydrolase activity in leaves of Lolium temulentum L.
Authors: SIMPSON R. J. , WALKER R. P. , POLLOCK C. J.
Published: April 2006

summary

Crude extracts from leaves of Lolium temulentum L. exhibited invertase activity and activity capable of releasing fructost from fructans (fructan exohydrolase; FEH), The optimum pH for FEH activity was between pH 4.8 and 5.5. When shoots of 10‐d‐old seedlings were induced to accumulate fructans by cooling their roots to 5 °C and exposing them to continuous light, FEH activity declined by at least 50 %, FEH activity increased when the shoots were induced to mobilize the fructans by warming the roots to the ambient temperature (20°C) and darkening the plants. Declining activity coincided with loss of one of at least two FEH isoforms observed after starch gel electrophoresis. Partially purified FEH from leaves of L. temulentum was inhibited when assayed in the presence of 10 HIM sucrose.
Fructan metabolism in leaves of Lolium rigidum Gaudin
Authors: SMOUTER HENK , SIMPSON RICHARD J.
Published: April 2006

summary

Accumulation of water‐soluble carbohydrates (WSC) in leaves of intact seedlings of annual ryegrass (Lolium rigidum Gaudin cv. Wimmera) was studied using a novel model system. The roots and leaf bases of intact seedlings, grown in nutrient solution, were cooled to 5°C to reduce sink activity and the production of photosynthates was enhanced by continuous illumination of the plants. This resulted in accumulation of WSC in the shoots. Thin‐layer chromatography showed the presence of a complex series of fructans, distinct from those found in tubers of Helianthus tuberosus. Two trisaccharides, 1‐kestose and neokestose, were present in various proportions, but no 6‐kestose was detected in the shoots. After feeding 14CO2 to the seedlings in a pulse‐chase experiment, high specific radioactivity was measured in monosaccharides, sucrose and fructan oligosaccharide fractions to DP 5 within 1 hr. These fructan pools were rapidly turned over without significant accumulation of fructans during the first 16 h of the accumulation phase. Neokestose and 1‐kestose contained equally high specific radioactivity, 1 h after feeding. These results indicated that neokestose was possibly as important as 1‐kestose as a possible precursor for synthesis of fructan. Concentrations of WSC increased linearly from 2 to 14 mg g−1 f. Wt of the leaves after 16 h and reached a concentration of 30 mg g−1 f. wt after 64 h. Sucrose, glucose and fructose were the first sugars to be accumulated and reached concentrations of 10, 3.5 and 2.5 mg g−1 f. wt, respectively. Tri‐ and tetrasaccharide accumulated to measurable concentrations after approximately 16 h of treatment and reached concentrations of 2.5 and 2.0 mg g−1 f. wt, respectively. The appearance of these oligosaccharides occurred when sucrose and monosaccharides reached stable concentrations in the leaves, The WSC concentration declined at a rate of about 0.8 mg g−1 f. wt h−1, when the root temperature was raised to 24°C after 64 h and plants were darkened. The decline in WSC concentration was accompanied by a 70% decline in sucrose concentration and a decline in all other fructan concentrations, white the concentration of fructose increased 2‐fold.
Carbohydrates on the surface of urediniospore‐ and basidiospore‐derived infection structures of heteroecious and autoecious rust fungi
Authors: FREYTAG S. , MENDGEN K.
Published: April 2006

summary

Nine flucirescein isothiocyanate‐labelled lectins with affinity towards different carbohydrates were used to probe the surface carbohydrates of infection structures in vitro, derived from urediniospores and basidiospores of an autoecious rust species, Uromyces viciae‐fabae (Pers. J Schroet., and of a heteroecious rust species, Uromyces rumicis (Schum.) Wint. Lectin binding was quantified by measuring fluorescence photometrically.

All lectins bound in a characteristic pattern to the infection structures of the respective spore types of each rust fungus. Differences were especially obvious between those infection structures normally produced inside leaf tissue, namely the urediniospore‐derived substomatal vesicles with infection hyphae, and the basidiospore‐derived intraepidermal vesicles. The dikaryotic stage and the monokaryotic stage of the heteroecious fungus differed mainly in their affinity for the leotins from Bandeira simplicifolin and Lotus tetragonulobus.

A statistical analysis comparing the binding of the lectins to infection structures of Two rust fungi suggested that cell surface composition is determined by nuclear condition. The monokaryotic stages of both rust fungi have a higher degree of similarity than the dikaryotic and monokaryotic stages of the same rust fungus.
Effect of root‐zone salinity on growth and chemical composition of Acacia ampliceps B. R. Maslin, A. auriculiformis A. Cunn. ex Benth. and A. mangium Willd at two nitrogen levels
Authors: MARCAR NICO E. , DART PETER , SWEENEY COLLEEN
Published: April 2006

summary

Acacia ampliceps B. R. Maslin, A. auriculiformis A. Cunn. ex Benth. and A. mangium Willd. differ in their salt tolerance. Four‐month‐old seedlings were treated with 100 (S1), 200 (S2) and 400 (S3) mol m−3 NaCl in sand culture. Two months prior to NaCl application the seedlings had been pretreated with either 1 mol m−3 N (low N: LN) or 5 mol m−3 N (high N:HN) as ammonium nitrate. LN seedlings were inoculated with a suspension of Rhizobium.

HN plants were considerably larger than inoculated plants at each NaCl concentration. Survival, damage symptoms and relative growth reduction under NaCl were generally similar for both N treatments. There was also no effect of N level on shoot water relations and stomatal conductance of youngest expanded phyllodes. However, at S1 and S2, HN plants had significantly lower concentrations of shoot Na+ and Cl− concentrations than LN plants.

There were differences in nodule number and weight per plant between species receiving the LN treatment. Nodule dry weight and nitrogenase (acetylene reduction) activity was more sensitive than plant dry weight to NaCl imposition.

Ranking of species for salt tolerance, based on relative decline in dry weight of shoot, whole plant and nodules under NaCl addition, was in the order A. ampliceps > A. aurtculiformsis > A. mangium. The greater salt tolerance of A. ampliceps was associated with relatively low shoot Na+ and Cl− concentrations (dry weight basis) and high phyllode succulence.
Terrestrial rhizophytes and H+ currents circulating over at least a millimetre: an obligate relationship?
Authors: RAVEN JOHN A.
Published: April 2006

summary

Circulating ionic currents are apparently ubiquitous in growing and differentiating eukaryotes. In many the current is carried by H+, in which case the medium around the apex of growing organs is alkalinized while the medium adjacent to subapical portions is acidified. These two zones may help in, respectively, molybdenum acquisition and reduction of aluminium toxicity, and phosphorus and iron acquisition, by rhizophytic plants. An analysis of the taxonomic distribution of H+‐borne circulating current shows that all rhizophytes (terrestrial, freshwater and, probably, marine) except those in the green algal class Ulvophyceae have such currents; the Ulvophyceae have circulating currents carried by Cl−. The Ulvophyceae do not seem to have any alternative means of causing pH zonation in the rhizosphere. Their marine habitat, with the possibility of molybdenum acquisition from the alkaline bulk water phase, may mean that the Ulvophyceae are not disadvantaged by the absence of rhizosphere acid‐alkaline zonation as would be a land plant; similarly, they are less likely to suffer aluminium toxicity to the growing zone of rhizoids. Ulvophyceae do not occur as terrestrial plants; this may relate not only to the absence of rhizosphere pH zonation in these organisms but also to mechanical problems related to their coenocytic habit, which in turn results from their inability to produce plasmodesmata.
Towards an understanding of the differences between the blepharoplasts of mosses and liverworts, and comparisons with hornworts, biflagellate lycopods and charophytes: a numerical analysis
Authors: RENZAGLIA KAREN S. , DUCKETT JEFFREY G.
Published: April 2006

summary

Numerical analysis of the lengths and positions of the two basal bodies (BBs), lamellar strip (LS) and anterior mitochondrion (AM) relative to each other in mid‐ and late‐stage spermatids of mosses and liverworts reveals the existence of several well denned, but previously unrecognized, features which clearly distinguish the blepharoplasts of the two groups. The ten possible quotients were calculated from measurements of anterior BB lengths, posterior BB lengths, LS lengths, distances between the anterior tips of the BBs and distances between the transition regions of the BBs in mid‐stage spermatids of 9 mosses and 16 hepatics. These critical data may be quickly compiled from a small number of electron micrographs. A Mann‐Whitney rank order t test showed highly significant differences in 6 of the 10 quotients between the moss and liverwort taxa. The primary data for late‐stage spermatids (4 mosses, 6 liverworts) also included the length of the AM. A Wilcoxon signed rank procedure revealed that the relationship between the AM and other blepharoplast components changed significantly between mid‐ and late‐stage spermatids in mosses but not in liverworts. The clear‐cut numerical differences between the blepharoplast components in each group are related to different patterns of development namely (1) bidirectional assembly of the LS in young spermatids of liverworts versus unidirectional (anterior) elongation at the same stage in mosses (2) elongation of the posterior BB over the nucleus in mid‐stage spermatids of mosses and (3) maturational elongation of the AM in mosses. Since the differences between the blepharoplasts of mosses and liverworts become apparent only during the later stages in ontogeny and since the mode of development of basal body stagger, involving the same precisely defined patterns of proximal triplet microtubule extension, is unique to mosses and liverworts, we suggest that the two groups share a common ancestry.

The blepharoplasts of all the taxa used in the calculations are illustrated in a simplified form and the ‘average’ blepharoplast for mid‐ and late‐stage spermatids of both mosses and liverworts is reconstructed from all the data presently available on the two groups. The same analysis of the blepharoplasts of hornworts, birlagellate lycopods, and charophytes highlights the differences between these groups and mosses and liverworts. Most striking is the side‐by‐side orientation of the basal bodies in hornworts and charophytes compared with the staggered arrangement in mosses, liverworts and the lycopods.
Continuity of chloroplast and endoplasmic reticulum membranes in Phaseolus vulgaris
Authors: WHATLEY J. M. , McLEAN B. , JUNIPER B. E.
Published: April 2006

summary

In cells of young primary leaves of Phaseolus vulgaris, the ER briefly, but regularly, forms a partial sheath around the plastids or lies in dose proximity to them. We have shown previously that, when ER encircles the chloroplasts in the lower vascular plant Equisetum telmateia, the ER membrane can become continuous with the outer membrane of the plastid envelope. It is now apparent that similar membrane continuity can become established between the ER and plastids in the angiosperm, Phaseolus vulgaris, though the period of organelle association is of much shorter duration than in Equisetum and it is characteristic only of the earlier stages of amyloplast development. A comparison is made of the relative timings of association of ER with protein bodies and mitochondria as well as with plastids.
Development and structure of resin glands on tissues of Betula pendula Roth, during growth
Authors: LAPINJOKI SEPPO P. , ELO HEIKKI A. , TAIPALE HANNU T.
Published: April 2006

summary

Betula pendula Roth, and a number of other species of the genus are known to excrete resinous chemicals on juvenile shoots and twigs as deterrents against herbivores. The present studies show that the resin is produced by specific multi cellular glands that are of the same ontogenetic origin as the glands covering developing tissues in buds during winter dormancy. It was possible to deduce from observations over a season that the resin production may be regulated at two levels. Density of the glands on the shoot surface is determined at the time of tissue differentiation in the beginning of primary growth, and the excretory activity is related at least in part to gland size. Towards the end of the growth period the cores of glands were gradually filled with bark cells and the interior of the columnar excretory cells of their epidermis appeared pale and hollow instead of the dense blue in younger glands, when stained with haematoxylin. The excretion of resin by B. pendula appears to be a primary defence mechanism that is active during that part of the season, when apical growth of a juvenile shoot takes place.
Nitrogen transfer from nodulating soybean [Glycine max (L.) Merr.], to corn (Zea mays L.) and non‐nodulating soybean in intercrops: direct 15N labelling methods
Authors: MARTIN R. C. , VOLDENG H. D. , SMITH D. L.
Published: April 2006

summary

In order to test for N transfer to com (Zea mays L.) or to non‐nodulating soybean [Glycine max [L.] Merr.), nitrogen enriched in 15N was directly applied to a petiole or to secondary roots of adjacent nodulating soybean. In the field in 1988, 15N applied directly to a petiole of nodulating soybean was detected at significantly higher levels in adjacent corn plants than when un enriched N was similarly applied. Applications of enriched N and un enriched N to nodulating soybean roots did not result in significant differences in %15N an adjacent corn plants. However, in greenhouse experiments, enriched N applied in split‐root systems to secondary roots of nodulating soybean, was detected at higher levels in associated corn and non‐nodulating soybean than when un enriched N was similarly applied.
Starch synthesis in developing pea embryos
Authors: SMITH ALISON M. , DENYER KAY
Published: April 2006

summary

The pea embryo stores about half of its carbon as starch and has proved to be an excellent system on which to study the nature and regulation of the pathway of starch synthesis. The developing embryo receives its carbon as sucrose, which is metabolized via glycolysis in the cytosol of cotyledonary cells. Glucose 6‐phosphate enters the amyloplast – probably via a phosphate‐exchange translocator – where it is converted to ADPglucose via phosphoglucomutase and ADPglucose pyrophosphorylase. ADPglucose pyrophosphorylase is the site of action of a mutation at therblocus, which reduces activity by more than 90 % and the rate of starch synthesis by about 50 %. Study of mutant and wildtype embryos reveals that one of four putative subunits of the enzyme is eliminated by the mutation. Three distinct isoforms of starch synthase catalyze the incorporation of the glucosyl moiety of ADPglucose into starch. Two of these are probably active in the soluble phase of the amyloplast and become incorporated into the granule as it grows, while the third is almost exclusively granule‐bound. Analysis of cDNA clones for starch synthases shows that the exclusively granule‐bound form is very similar to the ‘waxy’ gene product believed to be responsible for amylose synthesis in cereal endosperms. The soluble starch synthases show some similarities to the ‘waxy’ proteins, but clearly belong to a different and previously undescribed class of starch synthases. The pea embryo contains two forms of starch branching enzyme, which are encoded by different genes, are maximally expressed at different times in development, and have different kinetic properties. It is likely that they play different roles in the synthesis of the granule. A mutation at therlocus, which reduces the rate of starch synthesis by about 50% and increases the amylose content of the starch from 30% to 70%, consists of a transposon‐like insertion in the gene encoding starch‐branching enzyme I. Activity of this isoform is abolished by the mutation.

CONTENTSSummary21I.Introduction21II.The supply of sucrose to the embryo22III.The timing and location of starch synthesis23IV.The supply of carbon to the amyloplast23V.Mutations affecting the committed pathway of starch synthesis26VI.The committed pathway28Acknowledgements31References31
Cytokinins in the xylem sap of desert‐grown almond (Prunus dulcis†) trees: Daily courses and their possible interactions with abscisic acid and leaf conductance
Authors: Fußeder A. , Wartinger A. , Hartung W. , Schulze E.‐D. , Heilmeier H.
Published: April 2006

summary

Xylem sap samples were obtained from one‐ to four‐year‐old almond trees [Prunus dulcis (Miller) D. A. Webb] that had been grown in lysimeters of different volumes with different amounts of available water and subjected to an annual drying cycle. The samples were analyzed for cytokinin patterns by ELISA during the growing season. Free bases, ribosides and nucleotides of the N6‐(Δ2‐isopentenyl) adenine (iP) and the zeatin (Z) type could be identified and quantified. Z‐type cytokinins were always predominant. In many cases the concentrations of the cytokinin fractions were rather constant during the day. In a limited number of days, however, Z‐type cytokinins showed peak concentrations in the morning and a rapid decrease in the afternoon. A correlation between water status of the trees and the concentrations of cytokinins or their daily variations in the xylem sap could not be established. When the concentration of abscisic acid in the xylem sap was not limiting leaf conductance, daily‐variation of a cytokinin fraction preceded daily variation in leaf conductance. We conclude that in almond trees, cytokinins may affect stomatal behaviour on a short‐term basis. This is an outcome of changes in their xylem sap concentrations during the course of a day. Abscisic acid, on the other hand, acts as an opposing signal, the size of which reflects long‐term water deficit.
Effects of ozone and acidic fog on red spruce needle epicuticular wax production, chemical composition, cuticular membrane ultrastructure and needle wettability
Authors: PERCY K. E. , JENSEN K. F. , McQUATTIE C. J.
Published: April 2006

summary

One‐year‐old red spruce (Picea rubens Sarg.) seedlings were exposed, from bud break, to ozone (O3) and acidic fog for 14, 42 or 77 days. Ozone was more damaging than acidic fog to epicuticular wax. Wax quantity on needles exposed to charcoal‐filtered air (CFA) and pH 4.2 fog (control) increased from 14 to 42 days, but decreased by 77 days. Exposure of elongating needles to 70 ppb O3 and pH 4.2 fog reduced the rate of de novo wax synthesis. Red spruce wax is composed of secondary alcohols (50%), nonacosane diols (25%), alkyl esters (12%), primary alcohols (6 %), estolides (2 %), fatty acids (3 %), and hydroxy‐fatty acids (2 %). Wax chemical composition varied temporally. Needles exposed to O3 had significantly less secondary alcohols, diols, alkyl esters, fatty acids, and hydroxy‐fatty acids than needles exposed to CFA. Production of secondary alcohols was significantly reduced following needle exposure to fog at pH 3.0. Cuticular membrane thickness increased significantly following needle exposure to O3. The increase in thickness at 250 ppb O3 was due to a new amorphous layer which appeared above the reticulate layer. Contact angles on needles exposed to CFA and pH 4.2 fog increased from 92° after 14 days to 96° after 42 days, then declined to 77° after 77 days. Needle exposure to O3 for 42 or 77 days significantly decreased contact angles.
Effects of long‐term ozone exposure and drought on the photosynthetic capacity of ponderosa pine (Pinus ponderosaLaws.)
Authors: BEYERS JAN L. , RIECHERS GEORGE H. , TEMPLE PATRICK J.
Published: April 2006

summary

Seedlings of ponderosa pine (Pinus ponderosaLaws.) were grown for three years under three atmospheric ozone concentrations – clean air (CF), ambient ozone (NF), and 15 times ambient ozone (NF150)–at a moderately‐polluted site in the Sierra Nevada, under either well‐watered or drought‐stressed conditions. When the trees were 5 years old, photosynthetic capacities of 2‐year‐old, 1‐year‐old, and current‐year needles were measured during August and September of the 3rd season of exposure. Current‐year needles of NF150 trees had higher photosynthetic capacity than NF and CF trees during late summer, an effect due to greatly enhanced photosynthesis in well‐watered plants that had lost older needles as a result of ozone damage. This photosynthetic compensation in well‐watered NF150 seedlings was related to higher tissue nitrogen concentration in the current‐year foliage and possibly to increased inorganic phosphate cycling, both responses to the loss of older needles. Drought‐stressed NF150 seedlings were partially protected from ozone damage by decreased stomatal conductance and did not exhibit the same degree of photosynthetic compensation. No differences in photosynthetic rate were found between CF and NF seedlings or between well‐watered and drought‐stressed seedlings (across ozone treatments) in any needle age class.
Effects of dry‐deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter III. Decomposition rates and fungal respiration
Authors: NEWSHAM K. K. , BODDY LYNNE , FRANKLAND JULIET C. , INESON P.
Published: April 2006

summary

Ash (Fraxinus excelsiorL.), birch (Betulaspp.), hazel (Corylus avellanaL.), sessile oak [Quercus petraea(Mattuschka) Liebl.] and sycamore (Acer pseudoplatanusL.) leaf litters from a virtually non‐polluted and a heavily sulphur dioxide (SO2)‐polluted woodland were fumigated with environmentally‐realistic concentrations (0.010–0.030μl l−1) of SO2for 16–68 wk in an open‐air field‐fumigation experiment. Fumigation inhibited the respiration (CO2evolution) and decomposition rates of the leaf litters. However, there were few differences in the responses between leaf litters from the two woodlands.

In addition, pure cultures of four saprotrophic fungi were grown individually on irradiated hazel litter and exposed toc.0.030μl l−1of gaseous SO2, for 28 d in the laboratory. The gas inhibited the respiration ofPhoma exiguaDesm. andPhoma macrostomaMont, but not the respiration ofCladosporium cladosporioides(Fres.) de Vries orConiothyrium quercinumSacc. var.glandicolaGrove. These results in part substantiated findings of previous experiments examining the effects of SO2on the structures of saprotrophic fungal communities. The effects of SO2on fungal decomposition of angiosperm tree leaf litter as possible causes of forest decline are discussed.
Distribution of VA mycorrhizal entry points near the root apex: Is there an uninfectible zone at the root tip of leek or clover?
Authors: SMITH S. E. , DICKSON S. , WALKER N. A.
Published: April 2006

summary

This paper re‐examines the question of the susceptibility of plant roots to infection by vesicular‐arbuscular mycorrhizal fungi, particularly near the root apex. The cumulative distributions of the observed distance between the root apex and the most apical mycorrhizal entry points are compared with expected distributions based on (i) a random distribution of successful encounters between hypha and root and (ii) an uninfectible apical region (of length Zo). Data for both Allium porrum L. (leek) and Trifolium subterraneum L. (clover) are well fitted by the expected distributions and in the majority of cases (17/31) the best fit is obtained with zero Zo, with 8 additional cases being best fitted by values of Zo of 1 mm or less. Even where the best fits are obtained with values of Zo greater than zero, the distribution using Zo= 0 is still within the confidence limits for the data. These findings indicate that in neither species is there clear evidence for a subapical region that is immune to infection. The fact that there are short uninfected lengths immediately behind the apex is interpreted as representing a delay between an encounter and a detectable infection. Other consistent deviations of the data from the theoretical distributions are discussed.

Fitting the distributions yields values for the frequency of infection (A). These are compared for the two host plants at different propagule densities. The values for leek are much lower than for clover. In both species there are increases in A with increases in propagule density which are consistent with earlier findings.
Influence of NH3 and SO2 on the growth and competitive ability of Arnica montana L. and Viola canina L
Authors: DUECK TH. A. , ELDERSON J.
Published: April 2006

summary

The effects of atmospheric NH3 and SO2 separately and in combination on the growth and competitive ability of three species of the Violion caninae alliance were investigated. Growth and nutrient concentrations of Viola canina and Arnica montana in mixed culture with Agrostis capillaris were examined in relation to that in monoculture. Seedlings were transplanted into heathland topsoil in pots and placed in open‐top chambers for 9 months from autumn to summer, where they were exposed to ambient air, 90 μ m−3 SO2, 50 μg m−3 NH3 and to the combination of NH2 and SO2. In the NH3+ SO2 treatment, a more‐than‐additive increase in nitrogen and sulphur concentrations was observed indicating co‐deposition. NH3 influenced the nutritional status of V. canina the most, increasing the nitrogen, phosphorus, and magnesium concentrations and reducing those of potassium and calcium. NH3 fumigation significantly stimulated shoot growth of all three species and root growth of A. capillaris, while SO2 reduced only the root growth of A. capillaris. The relative yield of V. canina was reduced by 20–30% in the presence of the air pollutants. The relative yield of A. montana was stimulated by 30–40% in treatments including SO2 compared with that in ambient air or NH3 alone. The competitive ability of both dicotyledons in mixed culture with A. capillaris was strongly reduced by NH3 and was unaffected by SO2. The consequences of exposure to NH3 and SO2 for the survival and maintenance of threatened species in heathland vegetation are discussed.
Stolon growth and branching in Glechoma hederacea L.: an application of a plastochron index
Authors: BIRCH C. P. D. , HUTCHINGS M. J.
Published: April 2006

summary

Stolon growth and branching in Glechoma hederacea L. was analyzed, using a plastochron index based on the number of ramets on each stolon and internode growth. New methods, employing this index, were used to detect fluctuations in the rate of stolon extension, and to analyse the development of secondary stolons. The plastochron index had a strong linear correlation with time, with a new primary ramet appearing every 3.5 d. The overall stolon extension rate fluctuated between 1.9 and 2.9 cm d−1 through each plastochron cycle. The age at which each node produced secondary stolons was related to its position on the plant, but the initial rates of secondary stolon development differed little between nodes. Rate of development of secondary stolons was strongly correlated with the time at which they started to grow. Thus, later developing secondary stolons grew more slowly than those developing earlier from nodes in equivalent positions.
Nuclear magnetic resonance (NMR) micro‐imaging of ripening red raspberry fruits
Authors: WILLIAMSON B. , GOODMAN B. A. , CHUDEK J. A.
Published: April 2006

summary

Red raspberry (Rubus idaeus) fruits were subjected to nuclear magnetic resonance (NMR) micro‐imaging to study the changes in spatial distribution of mobile protons (1H) during a 3‐day ripening period while the fruit was still attached to the receptacle. All imaging measurements were made using the protons from a single absorption peak at 4.6 ppm, which corresponds to water, and data were collected by pulsed gradient spin‐echo and gradient‐echo methods with voxel dimensions of 70 × 70 × 500 μm. Individual drupelets were clearly visible by this non‐invasive histological method in distal transverse ‘slices’ of a newly harvested red ripe fruit viewed by spin‐echo; highest mobile proton densities were found at the lines of contact between drupelets. The mesocarp tissues of each drupelet showed intermediate grey tones with some evidence of radial striations. In more proximal ‘slices’ the surface of the receptacle and its central vascular cylinder had the highest mobile proton densities. The seeds produced black images in all ‘slices’, indicative of low mobile proton densities or long relaxation times.

After 3 days the proximal ring of drupelets separated from the receptacle, the spaces between drupelets enlarged slightly and the boundaries between drupelets were less pronounced. Vascular bundles in the receptacle lost their whitish radiating pattern in proximal ‘slices’ almost completely, indicating that mobile protons were less abundant after abscission of drupelets.

The same ‘slices’ viewed by gradient echo were less discriminating for localization of Seeds and pronounced tangential wave patterns, often overlaying radial striations, presented more complex images than those seen by spin echo.
Effects of simulated nitrogen rich and acid rain on the nitrogen‐fixing lichen Peltigera aphthosa (L.) Willd.
Authors: HALLINGBÄCK TOMAS , KELLNER OLLE
Published: April 2006

summary

The nitrogen‐fixing lichen Pettigera aphthosa (L.) Willd. was treated under semi‐natural conditions with simulated rain containing different combinations of ammonium, nitrate and sulphuric acid. Nitrogen in neutral solution had no negative effect on the nitrogen fixation rate. Sulphuric acid had a negative effect on nitrogen fixation rate, especially in combination with ammonium. The results could suggest an explanation for the sudden decline of P. aphthosa in southern Sweden.
Utilization of organic and inorganic nitrogen sources by ectomycorrhizal fungi in pure culture and in symbiosis with Pinus contorta Dougl. ex Loud.
Authors: FINLAY R. D. , FROSTEGÅRD Å. , SONNERFELDT A.‐M.
Published: April 2006

summary

The growth of ten species of ectomycorrhizal fungi was measured in liquid media containing different organic and inorganic nitrogen sources. All fungi grew well on ammonium. Growth on nitrate was generally lower, although there was considerable variation between different isolates of the same species. Suillus variegatus, Piloderma croceum, Paxillus involutus, Hebeloma crustuliniforme and unidentified pink and white isolates often grew as well on organic nitrogen sources as on ammonium. Growth of the other species was more variable. Isolates of Thelephora terrestris and Lactarius rufus varied in their ability to use bovine serum albumen (BSA) but two Laccaria species were poor at using the protein as a nitrogen source. The ability of mycorrhizal and non‐mycorrhizal Pinus contorta Dougl. ex Loud, plants to utilize BSA was also examined. Non‐mycorrhizal plants and mycorrhizal plants infected with either T. terrestris or the unidentified pink ectomycorrhizal symbiont were supplied either with ammonium or with BSA. Growth of plants supplied with BSA was significantly increased by mycorrhizal infection with the pink symbiont and not significantly different from that of plants supplied with ammonium, but non‐mycorrhizal plants were unable to use the protein as a nitrogen source and had significantly lower yields and nitrogen contents than infected plants. In contrast, mycorrhizal infection with T. terrestris had no effect on growth or nitrogen contents of plants supplied with protein. The results are discussed in relation to possible physiological differences between ectomycorrhizal fungi occurring at different successional stages of forest development.
Electron transport in thylakoids isolated from barley leaves infected by the powdery mildew fungus (Erysiphe graminis DC. ex Merat f.sp. hordei Marchal)
Authors: HOLLOWAY PETER J. , MACLEAN D. J. , SCOTT K. J.
Published: April 2006

summary

Barley leaves infected with powdery mildew fungus (Erysiphe graminis DC. ex Merat f.sp. hordei Marchal) show an accelerated loss of chloroplast photochemical activities and electron transport components, compared to the losses which occur during senescence of non‐infected controls. Concentrations of electron earners and rates of light‐saturated photochemical activities were measured at selected times after inoculation, in an endeavour to identify rate‐limiting components of the electron transport chain in infected leaves. It has previously been demonstrated that the rate‐limiting step in non‐infected leaves is the transfer of electrons from PQ to the cyt f/b6 complex.

When compared on a fresh weight basis, the concentration of all electron carriers (P700, cyt f, cyt b559 H.P., and the photoreducible pool of PQ), and all photochemical activities (H2O → PS2 → PS1, H2O → PS2, DONOR → PS1), decreased more rapidly in infected leaves, when compared with non‐inoculated controls of the same age, starting from 4 d after inoculation. When expressed on a chlorophyll basis, concentrations of the electron carriers and rates of the photochemical activities were identical for infected and control leaves of the same age.

These data suggest that the rate‐limiting step of non‐cyclic electron transport is the same in both infected and control leaves (PQ→cyt b6/f complex). It is proposed that in infected leaves, superimposed on normal chloroplast senescence, there is an accelerated loss of electron carriers and associated photochemical activities resulting from the breakdown of whole regions of thylakoid membranes.