bluuebunny/crossref_metadata_2025 huggingface dataset:
THE EFFECT OF GROWTH REGULATORS, LIGHT AND TEMPERATURE ON FLAVOUR PRODUCTION IN CELERY TISSUE CULTURES
Authors: WATTS M. J. , GALPIN I. J. , COLLIN H. A.
Published: May 2006

Summary

Cell suspensions of celery (Apium graveolens L.) were subcultured on media containing a range of auxins and antiauxins to replace 2,4‐dichlorophenoxyacetic acid (2,4‐D). Where the cultures showed a low growth rate and became green, the cells and media contained flavour compounds, the phthalides (3‐butyl phthalide and sedanenolide) and other terpenoid compounds. Maximum secondary product synthesis and greening was in media which contained 3,5‐dichlorophenoxy‐acetic acid (3,5‐D). In order to stimulate flavour synthesis in cultures in a medium containing 2,4‐D, the cultures were exposed to different fight and temperature regimes for varying periods during their growth cycle. Although growth was reduced in darkness and at high (30 °C) and intermediate (20 °C) temperatures, no stimulation of phthalide and terpenoid synthesis occurred. However, when the cultures were maintained at 4 °C for the first 5 d of the growth cycle and then transferred to 25 °C, phthalides and other terpenoids, particularly limonene, were released into the medium. An analysis of aggregated and finely dispersed cells on a 2,4‐D medium showed the aggregates contained phthalides and terpenoids, but these were not present in the dispersed cells. It is suggested that the altered internal cell environment in the green, aggregated or temperature stressed cells contributed to the ability of the cells to synthesize secondary products.
CYTOGENETIC VARIATION IN THE BRITISH FLORA: ORIGINS AND SIGNIFICANCE
Authors: ELKINGTON T. T.
Published: May 2006

Summary

Cytogenetic variation in the British flora is discussed in relation to the taxonomy and evolution of species and to their distribution and past history. In polyploids there may be two or more cytotypes in Britain with different distributions and ecology, e.g. Empetrum nigrum and Hippocrepis comosa; alternatively only one cytotype is present in Britain, but it forms part of a wider polyploid pattern, the study of which may clarify past patterns of migration, e.g. Potentilla fruticosa and Sisyrinchium bermudiana. The study of polyploids may also have taxonomic significance, e.g. Cochlearia, Symphytum and Mentha. In some situations gene flow between polyploid levels takes place and may be in both directions. In other polyploid groups sexually sterile cytotypes may be maintained by vegetative reproduction, e.g. Ranunculus ficaria and Holcus mollis or by gametophytic apomixis. In some cases a polyploid and aneuploid series may be maintained in which all the components are fertile; this situation is discussed in relation to the genus Erophila. There has been considerable emphasis in the past in attempting to identify the genomic ancestors of allopolyploids; two British species, Spartina anglica and Senecio cambrensis are among the few examples of recent allopolyploids of known origin; in both cases formation has depended on the establishment of an introduced species as one parent.

The significance of B chromosomes is discussed; although a range of British species contain B chromosomes it has only been possible to investigate their adaptive significance in one case. Interchanges exist in British species either in the heterozygous form, e.g. in Alopecurus species, where they can be identified by their meiotic consequences, or in the homozygous form, e.g. Epilobium sect. Epilobium species, where they can be identified by meiotic analysis of hybrids.

The use of modern cytogenetic techniques including chromosome banding and in‐situ hybridization and the investigation of characteristics such as infra‐species variation in DNA amounts are discussed in relation to future cytogenetic investigations of the British flora.
THE EFFECT OF THE FUNGUS ATKINSONELLA HYPOXYLON (CLAVICIPITACEAE)ON THE REPRODUCTIVE SYSTEM AND DEMOGRAPHY OF THE GRASS DANTHONIA SPICATA
Authors: CLAY K.
Published: May 2006

Summary

The Balansiae (Clavicipitaceae, Ascomycetes) consists of five genera of fungi that parasitize grasses, sedges and rushes. Most or all species produce alkaloids that are toxic to mammalian and insect herbivores. Previous reports suggest that infected grasses are more vigorous than uninfected grasses and that the proportion of infected individuals is greater in older populations. In this study individual plants or genotypes of the grass Danthonia spicata (L.) Beauv. Infected by the fungus Atkinsonella hypoxylon (Peck) Diehl. were compared with uninfected genotypes from the same population. Danthonia spicata typically bears dimorphic chasmogamous and cleistogamous flowers but in the study population infected plants were partially sterilized, producing only cleistogamous flowers; uninfected plants produced chasmogamous and cleistogamous flowers. Two experimental comparisons were conducted by propagating infected and uninfected genotypes into clones, or ramets, which were then planted back into their native site. Infected ramets had higher survival and growth rates, but lower flower production, than uninfected ramets both in random field transects and in field competition studies between D. spicata and the grass Anthoxanthum odoratum L. The results indicate infected individuals have higher survival and growth rates but reduced fecundity compared to uninfected individuals.
ROOT AERATION IN UNSATURATED SOIL: A MULTI‐SHELLED MATHEMATICAL MODEL OF OXYGEN DIFFUSION AND DISTRIBUTION WITH AND WITHOUT SECTORAL WET‐SOIL BLOCKING OF THE DIFFUSION PATH
Authors: ARMSTRONG W. , BECKETT P. M.
Published: May 2006

Summary

Treating the root as a homogeneous cylinder with respect to oxygen diffusivity and respiratory demand is a mathematically convenient assumption that has long been an inherent weakness and potential source of error in modelling the oxygen relations of soil‐aerated roots. The two models described here render such assumptions unnecessary: radial differences in oxygen diffusivity and respiratory demand between stele, cortex, wall layers and rhizosphere film have been accommodated by modelling the root: rhizosphere system as a multicylindrical unit. The models were designed to examine the influence of radial and circumferential cortical gas‐phase diffusion on oxygen concentrations and, also, to supplement recent theoretical studies into the effects of a sectoral blocking of the radial diffusion path for oxygen by circumferential contact between root and wet soil. Model I treats symmetrical surroundings assuming uniformity in the rhizosphere and accommodates the formation of an anoxic region within the root. Model II allows for the probability of partial blocking of the root's circumference, but only holds for fully aerobic roots.

As expected the results reveal markedly contrasting oxygen profiles between those roots having significant cortical gas‐phase diffusion (porous roots) and those without such diffusion (non‐porous). A stepped oxygen profile, the result of a shallow gradient in the cortex, characterizes the porous roots; in non‐porous roots a smooth profile is predicted. It is also predicted that as a consequence of cortical gas‐phase diffusion the maximum oxygen deficit (MOD) in porous roots ought normally to be confined to the stele and, with a deterioration in the soil oxygen supply, the stele will be first to experience anoxia. More adverse conditions accompany a high level of circumferential blocking and a second anoxic zone (in a part of the wall) should arise prior to the development of more widespread anoxia. In the examples shown, extensive blocking was required to create some stelar anoxia in porous roots but the apparent resistance to diffusion in the wall layer(s) and rhizosphere film in the unblocked sector was greatly enhanced by the effects of blocking elsewhere. It is shown that in the partially blocked porous root oxygen should mostly move circumferentially in the cortex of the blocked sector; movement in the stele should be largely radial. In non‐porous roots, blocking quickly shifts the MOD to the wall layers adjoining the blockage centre and the examples chosen indicated a wedge of anoxia spreading from the wall into cortex and stele when blocking exceeded 20%. Wall thickness was however of no particular significance. Annular contours, which indicate radial transport, are quickly lost as blocking progresses around non‐porous roots and eventually transport is approximately unidirectional across most of the root.
RECOVERY OF COBALT‐DEFICIENT ROOT NODULES IN LUPINUS ANGUSTIFOLIUS L.
Authors: RILEY IAN T. , DILWORTH M. J.
Published: May 2006

Summary

The capacity of cobalt‐deficient nodules of Lupinus angustifolius L. cv. Uniharvest to respond to delayed addition of cobalt was examined in a glasshouse. Plant and nodule mass, bacteroid concentration and acetylene reduction activity were measured at each of three harvests. A favourable response to cobalt addition was evident in all parameters measured. However, the degree of this response declined with increasing age of the nodule tissue. The contribution of this recovery in nodule cobalt to the overall recovery of cobalt‐deficient L. angustifolius is discussed.
NUCLEAR DNA CONTENTS, SHOOT PHENOLOGY AND SPECIES CO‐EXISTENCE IN A LIMESTONE GRASSLAND COMMUNITY
Authors: GRIME J. P. , SHACKLOCK J. M. L. , BAND S. R.
Published: May 2006

Summary

Within a species‐rich limestone grassland community in Northern England a correlation has been established between nuclear DNA content and the timing and rate of leaf extension in the spring. The data support the hypothesis that natural selection has operated upon nuclear DNA content through the differential sensitivity of cell division and cell expansion to low temperature. It is suggested that measurements of nuclear DNA content may provide an index of temporal niche differentiation in plant communities.
EFFICACY OF ENDOMYCORRHIZAL‐FUNGUS ISOLATES AND INOCULUM QUANTITIES REQUIRED FOR GROWTH RESPONSE*
Authors: HAAS JERRY H. , KRIKUN J.
Published: May 2006

Summary

Isolates of Glomus macroncarpum Tul. & Tul. grown in soil cultures from single spores were tested at known numbers of propagules ml−1 soil for their efficacy in promoting growth of bell pepper (Capsicum annuum L.) seedlings. The soil cultures, propagated under similar growth conditions, had from 0.02 to 25 propagules ml−1 as measured by the most probable number technique. Seven cultures with similar levels of inoculum density (a median of 7 propagules ml−1) were used undiluted, and at 10−1 and at 10−2 dilutions to test efficacy of the isolates. Also, cultures with originally dissimilar propagule levels (0.02 to 15 ml−1) were diluted to uniform inoculum density levels and tested for efficacy.

Large intra‐species variation in efficacy occurred in isolates collected from different soils and in those isolated from the same soil. Differences in the growth enhancement ability of isolates were evident from four weeks after seeding until harvest. The best isolates were superior at all inoculum levels tested but the ranking of isolates differed with the inoculum density.

A significant positive correlation was found between initial G. macrocarpum propagules ml−1 soil and all plant height and weight parameters measured. Growth of mycorrhizal plants was significantly greater than that of non‐mycorrhizal plants when more than 0.5 propagule ml−1 was present. With more than 5 ml−1, 70% of the isolates were effective. A minimum level of 1 propagule ml−1 is suggested for infestation of pepper seed beds; greater benefits can be expected from higher levels up to at least 10 to 15 propagules ml−1.
IRON TOXICITY TO PLANTS IN BASE‐RICH WETLANDS: COMPARATIVE EFFECTS ON THE DISTRIBUTION AND GROWTH OF EPILOBIUM HIRSUTUM L. AND JUNCUS SUBNODULOSUS SCHRANK
Authors: WHEELER B. D. , AL‐FARRAJ M. M. , COOK R. E. D.
Published: May 2006

Summary

The distribution of two common species of base‐rich wetlands, Epilobium hirsutum L. and funcus subnodulosus Schrank, as dominant species within a small, spring‐fed fen is correlated with high concentrations of iron present in the areas marked by superficial precipitated iron ochre. E. hirsutum was confined to the less iron‐rich parts. Other chemical variables (including P) showed little relationship to Epilobium distribution. In laboratory conditions, growth of E. hirsutum seedlings on waterlogged substrata from the same fen was much less on iron‐rich than lower‐iron soil, but J. subnodulosus seedlings showed no differential response. Growth of E. hirsutum on iron‐rich soil was slightly ameliorated by addition of P but remained low relative to that on low‐iron soil. Growth of J. subnodulosus was not increased by P addition.

Growth of E. hirsutum was substantially increased by maintaining the iron‐rich soil at 80% field capacity (F.C) rather than in waterlogged condition, though on low‐iron soils greatest growth was found in waterlogged conditions. At 80% F.C. both iron and P were less available than when soil was waterlogged. Growth of J. subnodulosus seedlings was consistently greatest in waterlogged conditions. In solution culture, Epilobium hirsutum seedlings showed poor growth, ill health and death at high iron concentrations (> 50 mg l−1) whilst, although growth of J. subnodulosus seedlings was also reduced, they remained visually healthy. High iron concentrations caused rapid blackening and ultimate flaccidity and necrosis of E. hirsutum roots; such symptoms were absent from J. subnodulosus. These data suggest that high iron concentrations are detrimental to E. hirsutum, both in the field and laboratory, and that this is not just an indirect effect of iron upon other aspects of mineral nutrition. The significance of this to possible mechanisms of iron toxicity and waterlogging tolerance is discussed.
PRE‐LAST GLACIATION MAXIMUM VEGETATION HISTORY AT HENTY BRIDGE, WESTERN TASMANIA
Authors: COLHOUN ERIC A.
Published: May 2006

Summary

Lake sediments dated to between about 28000 and 20000 years B.P. in the temperate rainforests of western Tasmania show that subalpine to alpine shrub, wet heath and herb communities occurred within 115 m of present sea level before the maximum of the last glaciation (20000 to 18000 years B.P.). The high herb, especially grass, values and charcoal content after about 22000 years B.P. may be related to the advent of aborigines.
TANSLEY REVIEW No 1.
Authors: COCKBURN W.
Published: May 2006

Summary

The term, photosynthetic acid metabolism (PAM), encompasses processes which involve four‐carbon (C4) acids as carbon‐carrying intermediates between the carboxylations catalysed by phosphoenolpyruvate (PEP) carboxylase and ribulose biphosphate (RuBP) carboxylase. These carboxylations may be separated either spatially, as in C4 photosynthesis which is not covered here, or temporally. Separation in time is referred to as diel PAM (DPAM) and the variations on this particular theme are the subject of this review. DPAM includes stomatal and astomatal types. The former types, usually described as crassulacean acid metabolism (CAM), are referred to here as stomatal CAM (SCAM). Astomatal PAM includes both aquatic and terrestrial forms; aquatic acid metabolism (AAM) and terrestrial astomatal acid metabolism (TAAM). Physiological, biochemical, structural, ecological and evolutionary aspects of these mechanisms of acquisition of carbon dioxide are reviewed.

CONTENTS

Summary
3

I.
General Introduction to Photosynthetic Acid Metabolism (PAM)
4

II.
Stomatal Crassulacean (Diel Photosynthetic) Acid Metabolism (SCAM)
5

III.
Astomatal Photosynthetic Acid Metabolism
13

IV.
Idling
18

V.
Structural Variation in Plants Exhibiting Diel PAM (DPAM)
18

VI.
The Mechanism of the Switch between C3 Photosynthesis and DPAM
19

VII.
The Cost of DPAM
19

VIII.
The Evolution of DPAM
20

IX.
Concluding Comment
22

Acknowledgements
22

References
22
THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA
Authors: SCOTT MARTHA G. , LARSON DOUGLAS W.
Published: May 2006

Summary

Two lichen species of the genus Umbilicaria were transplanted into each other's habitat in order to determine the role of winter field conditions in regulating distribution patterns. U. vellea (L.) Ach., which normally grows in a steeply inclined, snow free habitat, was transplated into the level‐ground, snow‐covered habitat of U. deusta (L.) Baum. The opposite was done for U. deusta. Suitable controls to test the effect of transplanting were also run for both species. The reciprocal transplantation was done in each of two years, one of which had a normal snow load, the other which had almost no snow cover.

The effect of reciprocal transplantation was to reduce significantly the carbon fixing ability in U. vellea in the year with the normal snow‐load. Transplantation had no effect on U. deusta. The effects on CO2 exchange were only slight for U. vellea in the year with the lesser snow‐load. It is therefore concluded that existing winter field conditions, and especially the nature of the snow cover, maintain the existing distribution pattern of the lichens in the field.
MYCORRHIZAL INFECTION OF BETULA PENDULA AND ACER PSEUDOPLATANUS: RELATIONSHIPS WITH SEEDLING GROWTH AND SOIL FACTORS
Authors: FRANKLAND JULIET C. , HARRISON A. F.
Published: May 2006

Summary

Mycorrhizal infection of two‐year‐old seedlings of Betula pendula Roth, and Acer pseudoplatanus L. was examined in a pot experiment, in relation to several soil variables (pH, organic matter, N, P, K, Ca, Fe, and phosphatase activity), host uptake of 32P, and plant performance (height and weight), in 25 Cumbrian soils from natural and semi‐natural habitats (such as woodland, carr and upland heath). Soils were used in a fresh state to maintain indigenous mycofloras and seedlings were raised from several seed‐lots to include possible ecotypic variation. Infection (incidence and intensity) of both ‘immature’ and ‘mature’ mycorrhizas was estimated.

Most plants were mycorrhizal, ectomycorrhizas occuring on Betula and vesicular‐arbuscular (VA) endophytes in Acer. Differences in the degree of infection between soils, but not between seed‐lots, were highly significant. Infection of one or both species was highly correlated with several soil factors (pH, organic matter, phosphorus and iron), and with all the plant variables. In Betula, evidence for most of these relationships was obtained only from ‘immature’ mycorrhizas, suggesting early physiological activity. Mycorrhizas accounted for a small but significant proportion of the variation in growth of both hosts, and soil properties accounted for a high proportion of the variation in both the plant growth and mycorrhizal infection, as shown by multiple regression analyses. Growth of Acer appeared to have a greater influence than soil factors on the variation in VA infection. ‘Beading’ of Acer roots was negatively correlated with plant weight and soil phosphorus, suggesting a morphological response to P‐ deficiency. Possible causal relationships between hosts, fungal symbionts and soils are discussed.
CRITICAL LEAF CONCENTRATIONS FOR DEFICIENCIES OF NITROGEN, POTASSIUM, PHOSPHORUS, SULPHUR, AND MAGNESIUM IN PERENNIAL RYEGRASS
Authors: SMITH G. S. , CORNFORTH I. S. , HENDERSON H. V.
Published: May 2006

Summary

Critical leaf concentrations for deficiency of nitrogen, potassium, phosphorus, sulphur, and magnesium were estimated for perennial ryegrass (Lolium perenne L.) grown in sand culture. The values associated with a 10% reduction in dry matter yield were as follows (all results expressed as g kg−1 DM except for the nitrate‐nitrogen value which appears as μg−1 DM): Kjeldahl‐nitrogen 32; nitrate‐nitrogen 500; potassium 28; phosphorus 2.1; sulphur 1.8; and magnesium 0.7. A major difference between the critical leaf concentrations estimated in this study and the tentative values published elsewhere was for potassium. Concentrations required in the shoot for near maximum growth were higher than previously reported. Differences in the nitrogen status of the plants probably account for this result. The depressing effect of potassium on the absorption of magnesium and calcium is discussed in relation to plant and animal nutrition. Sulphur was found to be inefficiently absorbed by phosphorus deficient plants despite non‐limiting amounts of sulphur applied in the nutrient solution. A possible explanation for this effect may be linked to the observation that the transport of sulphate into the chloroplast was coupled with that of phosphate. The concentration of macroelements required in the nutrient solution to produce maximum shoot growth of perennial ryegrass was very much greater than that generally applied to plants grown in sand culture.
PHENYLALANINE AMMONIA LYASE AND PEROXIDASE ACTIVITY IN MYCORRHIZAL AND NONMYCORRHIZAL SHORT ROOTS OF SCOTS PINE, PINUS SYLVESTRIS L.
Authors: RONALD PAMELA , SÖDERHÄLL KENNETH
Published: May 2006

Summary

Phenylalanine ammonia lyase was characterized in roots of Pinus sylvestris L. The Km for the pine root enzyme with phenylalanine as a substrate was l.2 ± 0.4 X 10−4 M. The enzyme had a pH activity optimum of 9 and the subunit molecular weight was 70 to 72 kD as determined by Western blotting. Enzyme activity could be inhibited by D,L‐2‐aminooxy 3 phenylpropionic acid at 1 μ. Treatments with zymosan, pectinase, light or kinetin and naphthylacetic acid did not induce higher phenylalanine ammonia lyase or peroxidase activity in pine roots. No significant differences were observed in phenylalanine ammonia lyase or peroxidase activity in mycorrhizal and nonmycorrhizal short roots in the P. sylvestris‐L. laccata symbiosis 15 weeks after cultivation.
ULTRASTRUCTURE OF THE FUSION CELL IN GRACILARIA VERRUCOSA (HUDS.) PAPENFUSS (RHODOPHYTA, GIGARTINALES)
Authors: DELIVOPOULOS STYLIANOS G. , TSEKOS IOANNES
Published: May 2006

Summary

The fusion cell in Gracilaria verrucosa (Huds.) Papenfuss is large, multinucleate and irregularly shaped. It originates from cytoplasmic fusions of haploid and diploid cells, and expands continuously by incorporating adjacent vegetative cells. Plastids are arrested in their development remaining in a proplastid state. Mitochondria possess ring‐like structures. Dictyosome activity is limited to forming the first wall layer. Large mucilage sacs, formed from ER, discharge their contents, thereby contributing to the formation of a second wall layer. Copious amounts of floridean starch as well as crystalline inclusions and osmiophilic granules are present in the cytoplasm. Numerous cisternae of endoplasmic reticulum occur in concentric stacked aggregations. Dark‐staining, spherical masses in the cytoplasm may represent condensed, inactivated haploid chromatin. Ultrastructural features of the fusion cell indicate that it has a nutritive function.
THE EFFECT OF REMOVAL OF EXTRARADICAL HYPHAE ON WATER UPTAKE BY VESICULAR‐ARBUSCULAR MYCORRHIZAL PLANTS
Authors: HARDIE KAY
Published: May 2006

Summary

Results from experiments on clover (Trifolium pratense L.) and leek (Allium porrum L.) revealed that removal of extraradical hyphae from vesicular‐arbuscular mycorrhizal (VAM) plants had a detrimental effect on transpiration flux. The advantage of comparisons between VAM plants with and without extraradical hyphae rather than between VAM and non‐mycorrhizal plants is discussed in relation to this type of investigation. It is suggested that extraradical hyphae increase the root absorptive‐surface area, independently of an enhanced nutrient status.
INFLUENCE OF AGE OF ROOTS ON THE PATTERN OF VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION IN LEEK AND CLOVER
Authors: HEPPER CHRISTINE M.
Published: May 2006

Summary

The effect of the age of roots on their susceptibility to infection by a vesicular‐arbuscular mycorrhizal fungus was compared in leek (Allium porrum L.) and clover (Trifolium parviflorum Ehrh.). Plants were grown in soil lacking mycorrhizal fungi for up to 21 d (clover) or 32 d (leek) and then transplanted into soil infested with Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe. The pattern of infection which occurred was compared with that in plants grown continuously in infested soil.

Leek roots up to 32 d old retained their susceptibility to infection whereas clover roots as young as 5 d old had become almost completely immune to penetration by G. mosseae and those which were 21 d old did not become infected at all. The most proximal part of the roots (9 mm in leek and 21 mm in the main root of clover) always remained uninvaded.

A difference between leek and clover was also observed in the distance of the most distal entry point from the root tip (10 and 1 mm, respectively). Some examples of host resistance to infection are described. One clover plant was not colonized by G. mosseae despite the formation of many entry points.
THE CELL CYCLES OF CHLAMYDOMONAS AND CHLORELLA
Authors: DONNAN LORRAINE , CARVILL EILEEN P. , GILLILAND TREVOR J. , JOHN PETER C. L.
Published: May 2006

Summary

In Chlorella and Chlamydomonas two periods of relatively constant duration determine total cell cycle length and cell size is stabilised by control of whether 2, 4, 8 or 16 daughter cells are formed. A timer runs through G1 phase and leads to the attainment just before S phase of a commitment to divide without further requirement for growth. The commitment timer requires growth for its continuation, is stabilized against a raising or lowering of temperature between 20 and 30°C but it is only partly stabilized against slow growth due to low energy supply. In Chlamydomonas 137c, at 25°C when growth is limited by light energy, the period between the beginning of growth in fully formed daughter cells and the attainment of first commitment to divide approximates to 5 + 0.75 × doubling time (h), at protein doubling times between 5 and 25 h. Under the same conditions division processes occurring in the period after first commitment also confer time properties since they are completed in 6 h. Postcommitment events are extended in the first cycle following a temperature reduction but develop temperature compensation in the second cell cycle. The mean generation time of Chlamydomonas 137c approximates to 11 + 0.75 × mass doubling time (h).

In both algae cell size is stabilized by an influence of mother cell mass on the number of successive further commitments that can occur following first commitment to divide. Each commitment is to perform a single further round of DNA replication and achieve a further doubling of cell number without further requirement for growth. Comparison of cells of different size when growing at the same rate shows that time, not size, controls the start of division events, and that size and not growth rate determines division number. In Chlamydomonas, division numbers provide a constant mean apportionment of 20 pg Lowry positive material to committed daughter cells at the time of final commitment. It is proposed that commitments continue until the mass available for further apportionment falls below a critical minimum of 27 pg, therefore, the minimum apportionment will be 13.5 pg and the maximum 27 pg per committed daughter ceDs. This predicted twofold range of cell sizes is confirmed by cell size frequency measurements made by microscopy and by fluorescence‐activated cell sorting. Size frequency measurements made after growth intermediate between 2, 4 or 8 in a cell cycle are consistent with increments of commitment under size control. Multiple fission cell cycles are compared with others.
FLUXES OF CARBON IN ROOTS OF BARLEY PLANTS
Authors: FARRAR J. F.
Published: May 2006

Summary

Sucrose entering barley roots is unloaded symplastically from the phloem, as indicated by anatomical considerations, the unexchangeability of [14C]sucrose of shoot origin, and the characteristics of uptake of exogenous sucrose. It then enters a cytoplasmic sucrose pool which, together with an apoplastic pool exchanging rapidly with it, accounts for 40 to 50% of sucrose in the root. The remainder is in vacuoles, from which it is released with a half‐time of 8 h. Storage polysaccharides have a half‐time of about 17 h. About one‐quarter of all sucrose leaving the cytoplasmic plus apoplastic pool is temporarily stored as sucrose or polysaccharide. The net flux of carbon to growth of structure is about 55% of that entering the root; over 40% is lost in respiration. On root excision, the flux of sucrose out of the vacuole rose but the breakdown of storage carbohydrate did not.
SELF‐COMPATIBILITY IN DISTYLOUS CRYPTANTHA FLAVA (BORAGINACEAE)
Authors: CASPER BRENDA B.
Published: May 2006

Summary

The seed production of hand pollinated flowers indicates that distylous Cryptantha flava (A. Nels.) Payson is both intramorph and self‐compatible. In addition, there is no inhibition of pollen tube growth following either intramorph or self‐pollinations. Despite the potential for crosses between individuals of the same style length and thus the production of unequal morph ratios, pins and thrums occur in equal numbers in natural populations.
TERATOLOGY AND METAMERIC PLANT CONSTRUCTION
Authors: van GROENENDAEL J. M.
Published: May 2006

Summary

The growth of Plantago lanceolata L. has been described using metamers as construction units. The growth of each unit has been broken down into a sequence of four simple building instructions, two of which incorporate two or three alternatives. The resulting conceptual model has been tested against a variety of teratologies known to exist in Plantago lanceolata. All of these malformations could be explained in terms of either wrong steps, or wrong sequences, or both. There seems to be a certain hierarchy of control such that more malformations tend to occur at tertiary meristems than at primary meristems. For at least some of the teratologies, the nature of the control seems genetic.
EFFECT OF CATIONS ON UPTAKE, TRANSLOCATION AND REDUCTION OF NITRATE IN WHEAT SEEDLINGS
Authors: BARNEIX ATILIO J. , BRETELER HANS
Published: May 2006

Summary

The effect of Ca2+, K+ and Na+ on uptake, transport and reduction of NO3− was studied in 10‐day‐old plants of Triticum aestivum L. cv. Sicco grown in water culture in relation to the ion balance in plant, medium and xylem exudate.

When Ca2+ (0.25 mM) was the only nutrient cation, NO3− uptake and accumulation of NO3− in the leaves were low as compared to treatments with K+ or Na+ (0.5 mM). With Na+, the uptake of NO3− was similar to that with K+, but virtually no Na+ and 75 % less NO3− accumulated in the leaves.

Medium pH dropped initially with 0.5 mM KNO3 but rose immediately when Ca2+ was the only cation. The carboxylate content rose in roots and leaves of K+ plants and, to a lesser extent, in Na+ plants. Roots of Ca(NO3)2 plants showed negative ash alkalinity indicating the presence of acidity.

The pH of the xylem exudate increased with the cation/NO3− ratio in the exudate and was about one unit higher with Ca(NO3)2 than with NaNO3 or KNO3.

We conclude that roots of plants grown in the absence of monovalent cations have serious pH problems because of a high rate of alkalinity release to the medium in exchange for NO3− uptake, and the secretion of alkalinity into the xylem.
EFFECTS OF SO2 AND OTHER AIR POLLUTANTS ON THE MORPHOLOGY OF EPICUTICULAR WAXES ON NEEDLES OF PINUS STROBUS AND PINUS BANKSIANA
Authors: RIDING R. T. , PERCY K. E.
Published: May 2006

Summary

Exposure of elongating needles of Pinus strobus L. to SO2 and other unidentified air pollutants delayed wax deposition in the epistomatal chambers. Following completion of wax deposition, the wax rodlets fused, forming plate like sheets. Needle wettability appeared to be increased as a result of modification of the epicuticular waxes, potentially increasing their sensitivity to acid rain‐induced injury. This occurred without alteration of the structure of the stomatal complex itself. No alteration of wax form was evident on needles of P. banksiana Lamb., even under conditions which led to acute SO2 foliar injury.
ECTOMYCORRHIZAS AFFECT IONIC BALANCE DURING AMMONIUM UPTAKE BY DOUGLAS‐FIR ROOTS
Authors: BLEDSOE CAROLINE S. , RYGIEWICZ PAUL T.
Published: May 2006

Mycorrhizas have been shown to alter ion fluxes for many nutrients. Experiments were done to determine the extent to which ectomycorrhizas alter the ionic balance of roots of Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings mycorrhizal with Hebeloma crustuliniforme (Bull, ex St. Amans) Qúel. exposed to solutions containing either 16N ammonium sulphate or 16N ammonium chloride. Net fluxes of ammonium, hydrogen, potassium, calcium, sodium, bicarbonate, sulphate and chloride were measured. The mycorrhizal association altered ion fluxes, primarily decreasing sodium uptake and potassium release rates (both anion treatments) and increasing bicarbonate release during exposure to ammonium chloride. Rates of carboxylate accumulation in the tissue were inferred from the net flux data; mycorrhizal seedlings may produce more cation‐carboxylate complexes compared with nonmycorrhizal seedlings. When compared with agricultural plants exposed to ammonium, Douglas‐fir took up a considerably greater number of cations for each ammonium ion absorbed, which may account for the greater number of carboxylate anions also produced by Douglas‐fir. These findings were discussed in terms of ecological significance for growth of Douglas‐fir.
RESPONSE OF SO2‐SENSITIVE AND RESISTANT GENOTYPES OF RYEGRASS (LOLIUM PERENNE L.) TO PROLONGED EXPOSURE TO SO2
Authors: KOZIOŁ M. J. , SHELVEY J. D. , LOCKYER D. R. , WHATLEY F. R.
Published: May 2006

Two genotypes of perennial ryegrass (Loliutn perenne L.), one (S23) sensitive to SO2 and the other (BR) reported to be resistant, were exposed to 0, 50 or 150 ni SO2 1−1 (0, 133 or 398 μg SO2 m−3 at STP) for four weeks under conditions that gave ‘slow’, ‘medium’ or ‘fast’ rates of growth. These treatments allowed comparisons of the responses between genotypes over a range of conditions within which plants could be expected to exhibit maximum and minimum sensitivities to SO2. Significant effects on growth from exposure to SO2 were observed primarily when growth was slow, when the plants were expected to be most sensitive. Although exposure to 150 nl SO2 1−1 significantly increased stomatal resistance two‐fold in both genotypes during slow growth, there was no accompanying diminution in leaf sulphur content, implying that a two‐fold increase in stomatal resistance is not sufficient to be considered an avoidance mechanism to SO2.

Compared with the sensitive S23 gentoype under control (SO2‐free conditions, the resistant BR genotype shows slightly greater stomatal resistance, reduced absorption of sulphate through the roots, and reduced dry matter production. Reduced dry matter production in BR may be attributed to its peculiar isoenzyme of ribulose‐1,5‐bisphosphate carboxylase, which shows a greater resistance to inhibition by sulphite but lower carboxylation rates than ribulose‐1,5‐bisphosphate carboxylase from S23.
PHOSPHOLIPID CATABOLISM AND SENESCENCE OF PEA FOLIAGE MEMBRANES: PARAMETERS OF Ca2+:CALMODULIN:PHOSPHOLIPASE A2−INDUCED CHANGES
Authors: SRIDHARA SAMPATH , LESHEM YA'ACOV Y.
Published: May 2006

With progress of normal senescence of pea (Pisum sativum) foliage membranes free fatty acid: sterol ratios increase, this reflecting increment of phospholipolytic activity. The effect is simulated by exogenous application of phospholipase A2 in the presence of Ca2+ and calmodulin and inhibited by the calmodulin inhibitor fluphenazine. This trend is accompanied by an increase in membrane microviscosity and transition temperatures and, as evidenced by wide angle X‐ray diffraction data, indicates a change from the liquid crystalline phase to a solid gel lipid bilayer configuration. Ethylene production, associated with plant senescence, closely follows the above biophysical changes. Membranes also manifest lipoxygenase activity, increasing with age and upon application of Ca2, calmodulin and phospholipase A2 the increment being inhibited by the more specific calmodulin inhibitor calmidazolium. Moreover, the polyunsatu‐rated linolenic acid enhanced phospholipase A2‐induced ethylene production, whereas the saturated stearic acid was ineffective. Results are interpreted as a Ca2+‐triggered and calmodulin mediated phospholipase A2 activation whereby membrane integrity is impaired by the release of the 2‐situated polyunsaturated fatty acids which in the freed form induce lipoxygenase and specific Ca2+ ionophoretic activity during the process of which an ethylene forming mechanism is activated.
CALCIUM ACCUMULATION BY TWO STRAINS, CALCICOLE AND CALCIFUGE, OF THE MYCORRHIZAL FUNGUS PAXILLUS INVOLUTUS
Authors: LAPEYRIE F. F. , BRUCHET G.
Published: May 2006

Patterns of calcium accumulation have been compared between two strains of the ectomycorrhizal fungus Paxillus involutes (Batsch. ex Fr.) Fr. Calcium accumulation during a period of growth on a substrate containing calcium paralleled that found in higher plants, with the calcifuge strain accumulating higher levels of calcium than the calcicole strain, especially in the older parts of the mycelium. In short‐term uptake experiments, using mycelia grown on calcium free medium then placed for 3 h in various calcium solutions, this order was usually reversed with the calcicole strain accumulating higher levels than the calcifuge strain. Accumulation in relation to calcium concentration was biphasic, and was generally higher at 4 °C than at 24 °C. This is inconsistent with an equilibrium model based on passive mechanisms but is consistent with a model which has active calcium efflux balancing a large passive influx. The operation of this mechanism in mycorrhizal fungi could serve to protect calcifuge plants in calcareous situations.
FLOWERING BEHAVIOUR OF THE MONOCARPIC PERENNIAL CYNOGLOSSUM OFFICINALE L.
Authors: JONG TOM J. , KLINKHAMER PETER G. L. , PRINS ADRIANA H.
Published: May 2006

Flowering in Cynoglossum officinale L. is strongly size‐dependent. The probability of flowering increases with the size of the plant. Also, a critical size exists below which the plants do not flower. Plants above this size develop flower primordia during a cold period. During winter it is determined which plants will flower in the following spring and which plants will not. The probability of flowering is not affected by nitrogen concentration in the plant or light intensity, when these factors are separated from their effects on the dry weight of the plant. Delay of flowering is a common phenomenon in natural populations of Cynoglossum officinale on coastal sand‐dunes at Meijendel (near The Hague, The Netherlands). Over a seven‐year period the percentage flowering of rosettes varied between 2 and 25 %. The proportion of rosettes flowering was positively correlated with rainfall in the previous year and was reduced after a very cold winter.
EXPERIMENTAL ANALYSIS OF FLUORIDE SUSCEPTIBILITY OF GRAPEVINE (VITIS VINIFERA L.): LEAF DEVELOPMENT DURING FOUR SUCCESSIVE SEASONS OF FUMIGATION
Authors: DOLEY D.
Published: May 2006

Leaf development was studied in potted specimens of grape vine (Vitis vinifera L., varieties Chardonnay, Gordo and Traminer) that were exposed to hydrogen fluoride in controlled environment cabinets during four successive growing seasons. The duration of exposures varied from 54 d in the second season to 159 d in the fourth. There was no significant or consistent effect of fluoride on the numbers of leaves produced on major or lateral shoots in any variety. Leaf size during the first growth flush of a season was not influenced by the present or previous exposure of plants to ambient fluoride concentrations up to 1.5μm F m−3. Mature leaf size during the middle or latter portion of the fourth season of fumigation was significantly reduced in the Chardonnay and Traminer varieties as a result of exposure to fluoride concentrations of 0.64μg m−3 or more. Leaf size in the variety Gordo was not affected by ambient fluoride concentrations up to 1.5μg F m−3. Stomatal frequency and size in the variety Chardonnay, and leaf water vapour conductance in all varieties were not affected by ambient fluoride concentrations up to 1.05μg F m−3. The work demonstrates variations in response of grape vine leaves to ambient conditions at different stages of the growing season.
A PAPER‐SANDWICH TECHNIQUE FOR RAPID SYNTHESIS OF ECTOMYCORRHIZAS
Authors: CHILVERS G. A. , DOUGLASS P. A. , LAPEYRIE F. F.
Published: May 2006

In the basic pure‐culture technique, fungus for inoculum is grown on stiff absorbent paper card over Potato Dextrose Agar, then this paper is removed aseptically and laid, fungus‐side down, on to a two‐dimensional array of roots of seedlings grown axenically on filter paper over a mineral salts agar medium. With the high inoculum potential achieved by this technique, ectomycorrhizas have been formed within one week of inoculating Pisolithus tinctorius Coker & Couch or Paxillus involutus (Batsch. ex Fr.) Fr. on to Eucalyptus globulins Subsp. bicostata (Maid, et al.) Kirkp., and over 50% of root apices were converted to ectomycorrhizas within two weeks. The paper‐based inoculum has also been applied successfully to convert peripheral roots of seedlings grown in peat‐moss within clay pots.
CELLULAR READJUSTMENT OF BARLEY SEEDLINGS TO SIMULATED ACID RAIN
Authors: WOLFENDEN JENNIFER , WELLBURN A. R.
Published: May 2006

No changes in buffer capacity at any range of pH were detected in either the shoots or roots of 9 d old hydroponically‐grown barley seedlings which had been grown in dilute acid (pH 3 or 4) for the last 4 days of growth. Similar lack of change in buffer capacity was observed in barley which had been intermittently sprayed with acidic mists (pH 3 or 4) as compared to those sprayed with pH 56 media for the last 2 or 4 d of growth. Acidic treatments, especially growth in acidic media or 2 d of occasional spraying, caused significant increases in the levels of plastidic sulphate, as measured by high performance ion chromatography but no changes in the plastidic concentrations of other anions occurred. High field 31P‐NMR spectroscopy of barley shoot tissue showed that the vacuolar pH levels (as revealed by the pH‐dependent orthophosphate signals) of those tissues which had been sprayed with acidic solutions (pH 3 or 4) for 2 d were significantly lower than in those similarly sprayed with pH 5.6 solutions. This may mean that ATP‐dependent H+‐pumps in the tonoplast are involved in cellular readjustments to the imposed acidity. No growth reductions or visible injury were detected over these short term treatments but these changes of vacuolar pH and plastidic sulphate content may indicate that homeostatic adjustments have an energetic cost which may ultimately account for reductions in plant growth attributed elsewhere to acidic precipitation.
THE NAME OF THE ROSE: A REVIEW OF IDEAS ON THE EUROPEAN BIAS IN ANGIOSPERM CLASSIFICATION
Authors: WALTERS S. M.
Published: May 2006

This ‘Tansley Review’ paper takes as its starting point a paper of mine published in 1961, which explored the shape and size of modern Angiosperm families and genera as a product of taxonomic practice over centuries. It considers how far the conclusion ‐ that our existing scientific classification, based on Linnaeus' masterly standardization in the eighteenth century, is very markedly ‘Eurocentric’– has been criticized, accepted or modified by subsequent writers. In particular, it assesses the important contribution made in recent years by ethnobiologists using expert knowledge from social anthropology, linguistics and other disciplines. Finally, the paper considers briefly the broader aspects of current controversies about the nature and purpose of taxonomic activity, including the argument about its relevance to evolutionary knowledge and speculation. It concludes that, to a remarkable degree, practising taxonomists ignore conceptual or philosophical difficulties and are able to co‐operate, although their leisurely and arcane procedures may not measure up to the‘information explosion’.

Contents

Summary
527

I.
Introduction
528

II.
The age and size of Angiosperm families and genera
530

III.
Recognition of the European bias in classification
539

IV.
Conclusions
542

References
544
THE APPARENT WIDTH OF THE RHIZOSPHERE OF TRIFOLIUM SUBTERRANEUM L. FOR VESICULAR‐ARBUSCULAR MYCORRHIZAL NFECTION: EFFECTS OF TIME AND OTHER FACTORS
Authors: SMITH S. E. , WALKER N. A. , TESTER M.
Published: May 2006

We use the mathematical model developed by Ferriss (1981) for the study of plant pathogens to calculate the apparent width of the rhizosphere (W) of Trifolium subterraneum L. for infection by propagules of vesicular‐arbuscular mycorrhizal fungi in soil, examining the effects of wetting the soil for different times before planting and of harvesting at different times. The reasons for choosing this model rather than that of Gilligan (1979) are given. Propagule densities were determined by the most probable number (MPN) method at 28 d using the same host species as the test plant, thus including a factor in the calculations which is the product of the efficiency of the propagules to infect and the susceptibility of the roots.

Values for W at 10 to 12 d were between 2.5 and 6.5 mm for mixed soil inoculum and between 8.9 and 13.2 mm for Glomus mosseae (Nicol & Gerd.) Gerdeman & Trappe. W increased with time, associated with an increase in the number of infections formed. Factors contributing to this include progressive germination of propagules following wetting the soil, growth of hyphae from greater distances to the root and formation of secondary infections. Wetting the soil before planting had the greatest effect on W in 4 d old plants. By 10 d, there was no effect, supporting the idea that most propagules are likely to have germinated by that time. The contribution of secondary infections is harder to determine, but is likely to be important from about 10 d onwards, resulting in overestimation of W. By 12 to 16 d, in experiments in which six plants were grown in 210 or 222 cm3 soil, the apparent volume of the rhizosphere plus root exceeded the volume of soil. Values of the apparent width of the rhizosphere in our experiments are therefore most reliable before the plants are 10 d old.

If the MPN method is used to determine propagule densities at the same harvest times and under the same conditions as those used to collect other data, then the equations can be used to compare different fungi and environmental conditions with respect to infection of young plants.
WATER RELATIONS OF XERIC GRASSES IN THE FIELD: INTERACTIONS OF MYCORRHIZAS AND COMPETITION
Authors: ALLEN E. B. , ALLEN M. F.
Published: May 2006

The effects of vesicular‐arbuscular mycorrhizal inoculum and competition from non‐mycorrhizal annual plants were tested on Agropyron smithii Rydb. and Agropyron dasystachyum (Hook.) Scribn. growing in an inoculum‐poor soil. Mycorrhizal A. smithii decreased stomatal resistance (rs) and increased leaf water potential compared to the non‐inoculated plants, but only during the driest portion of the growing season. The presence of annuals caused increased rs of A. smithii, but only of non‐inoculated plants. Mycorrhizal plants had the same rs with or without annuals, indicating that mycorrhizas may alleviate the detrimental effects of competition on rs of A. smithii. By contrast, neither inoculation nor annuals significantly affected water relations of A. dasystachyum. Mycorrhizas also did not increase N and P concentrations or percentage cover of either grass, but both had delayed phenology when mycorrhizal. This research was done during a wet year when the effects of mycorrhizas may be subtle. Long‐term observations are necessary to determine the importance of mycorrhizas under field conditions.