bluuebunny/crossref_metadata_2025 huggingface dataset:
Age Differences in the Correlates of Perceived Dominance*
Authors: Wright Jack C. , Zakriski Audrey L. , Fisher Philip
Published: April 2006

Previous evidence indicates that the correlates of dominance vary over studies. We hypothesized that one source of this variability is that dominance shifts with age from being associated with aggression to being more associated with prosocial behavior and sociometric status. To test this, we examined 10 vs. 13 year‐old boys' perceptions of dominance, using a measure that assessed the perceived outcomes of dyadic agonism. In a sample consisting predominantly of lower‐ and middle‐SES boys from public schools attending a racially integrated summer program for youths with behavior problems, we examined the relation between perceived dominance, sociometric status, and measures of social behavior, including physical and verbal aggression. Perceived dominance was associated with hitting and bullying among 10 year‐olds, whereas among 13 year‐olds it was more closely associated with sociometric status. The measure of perceived dominance we present produced rigidity scores comparable to those found using behavioral measures of dominance.
Infants' Sensitivity to Manipulations of Maternal Touch During Face‐to‐Face Interactions*
Authors: Stack Dale M. , LePage Diane E.
Published: April 2006

Forty‐eight mothers and their 5.5‐month‐olds participated in a series of face‐to‐face interactions consisting of a Normal plus three still‐face (SF) periods where mothers could touch their infants (SF with touch). The primary objective was to determine whether young infants are sensitive to subtle changes in maternal touch. Variations in infants' affective and attentional responses were revealed as a function of the different periods; infants smiled more when mothers were requested to maximize their smiling using touch alone, and gaze shifted from mothers' faces in the Normal period to their hands in the SF with touch periods. Results imply that: (1) infants are sensitive to subtle changes in their mothers' touching, (2) mothers are effective in using touch to elicit specific infant responses, (3) touch‐only interactions are positive, as reflected in infants' gaze and affective displays, (4) mothers use consistent types of touch when touching specific areas of their infants' bodies during brief interactions.
Learning How to Say What One Means: A Longitudinal Study of Children's Speech Act Use*
Authors: Snow Catherine E. , Pan Barbara Alexander , Imbens‐Bailey Alison , Herman Jane
Published: April 2006

In this paper we present a set of methods for describing development in the expression of communicative intents. Studying children in interaction with a parent, we found children improved from age 14 to 32 months in the number of communicative attempts per minute they made, in the intelligibility of their attempts, as well as in the repertoire of intents they expressed. Correlations with other language measures suggest that a complete picture of language development requires a description of pragmatic skills in addition to syntactic and lexical indices. Our two‐level coding scheme revealed that the social‐interactive interchanges most commonly engaged in by the youngest children were negotiating immediate activity, discussing a joint focus of attention, and directing hearer's attention. Within these social interchanges, a small but widely shared set of communicative intents was expressed by the younger children; surprisingly, questions were quite late emerging communicative intents, as were agreeing, disagreeing, and giving reasons
A Developmental Perspective on Community Service in Adolescence
Authors: Yates Miranda , Youniss James
Published: April 2006

A substantial number of U.S. adolescents currently participate in community service and there is increased national interest in service programs. This article assesses the assumption of developmental benefits to service participants by critically reviewing 44 empirical studies. It offers a theoretical framework for understanding the findings by connecting them to identity development and delineating three pertinent concepts: agency, social relatedness, and moral‐political awareness. These concepts are applied to studies that investigate: (1) the characteristics and motivations of participants, (2) the effects of service, and (3) the process of service. The findings support the conclusion that service activities which provide opportunities for intense experiences and social interactions are often associated with prasocial development. The findings also point to the need for more studies focused on particular service programs and on relationships between service providers and those served.
Affiliative Structures in Preschool Peer Groups.
Authors: Strayer F. F. , Santos A. J.
Published: April 2006

Changes in affiliative organization of 15 age‐graded toddler and preschool play groups were examined in terms of assessed similarity in patterns of playmate association. Measures of peer association were derived from direct observation of social interaction during free play. The degree of between subject similarity in association profiles was derived using complete linkage hierarchical clustering procedures. Findings revealed distinct social subgroups in all social groups. Secondary analyses showed a linear increase in the size of affiliative subgroups as a function of age. Measures of interactive reciprocity within social subgroups suggested progressive consolidation of affiliative structures with age. Among older children, membership within affiliative subgroups was associated with more frequent preferences for subgroup members. Findings are discussed in terms of how children's insertion within the affiliative network of their peer group constrain socialization of their behavior and provide specific experiences that serve as contexts for the construction of more intimate interpersonal relationships.
The Stability of Social Groups in Childhood and Adolescence: The Role of the Classroom Social Environment.
Authors: Neckerman Holly J.
Published: April 2006

This study provides a developmental analysis of childhood and adolescent social relationships within the school context. The social groups of 220 fourth graders and 475 seventh graders were tracked over a one year interval. The initial results indicated that approximately 30% of the social groups were identified as stable in that they maintained at least 50% of their membership over the one year interval. However, the stability in group affiliations was a function of the stability of the composition of the classroom. When schools did not promote classrooms as a unit, only 6.8% of social groups were stable, as compared to 55% of groups being stable when the school did promote classrooms as a unit. This school effect in group stability was demonstrated by a high correlation (rs = .97) between classroom stability and group stability. Even in unstable classrooms, individuals were more likely to maintain affiliations when group members were assigned to the same classroom. This work suggests that stable environments promote stable relationships, which in turn, may promote greater continuity in the organization of behavioral patterns.
Social Networks and Self Enhancement in Chinese Children: A Comparison of Self Reports and Peer Reports of Group Membership*
Authors: Leung Man‐Chi
Published: April 2006

Children's self reports of social groups were compared with the social groups identified by a consensus judgment of their peers. The subjects were 138 Chinese 4th grade students (mean age = 9.91) from a primary school and 167 Chinese 7th grade students (mean age = 13.09) from a secondary school, both located in Hong Kong. Following the Social Cognitive Map (SCM) procedure, students were asked to identify the social groups within their grades, including their own groups. The subjects also rated themselves on multiple domains of competence. Their teachers rated them on the same domains. Subjects tended to be biased toward self‐enhancement when reporting their own groups: They omitted members who had low school scholastic rank and unfavorable scores on teacher ratings of competence. There was a strong effect of propinquity and gender on group membership, in that all groups were comprised of children from the same classroom and virtually all (98%) of the same sex. Members scored similarly on teacher ratings of competence. In elementary school, conventional values and academic achievement provided the behavioral bases for peer group cohesion. By early adolescence, peer‐related concerns supplemented rather than replaced conventional values as the bases for group cohesion.
Strategies for the Study of Individual Development within Naturally‐Existing Peer Groups*
Authors: Kindermann Thomas A.
Published: April 2006

The investigation of peer influences on children's development in natural settings rests squarely on appropriate methods to identify those individuals who are influential for a given child. Traditional methods of sociometric ratings or assessments of friendship choices are not intended to identify reciprocal influences in children's peer groups of social interrelationships. In the study of networks within sociology, researchers have focused on the structural properties of children's networks, instead of the psychologically meaningful characteristics of the children who comprise a target child's network. To complement these strategies, a method is presented that can reliably identify those individuals who constitute children's natural peer groups in a setting. This information is used to form composite maps that represent the psychological peer context of a given child. Strategies are outlined for analyzing processes of group selection and socialization among developing individuals and their changing peer contexts.
Development of the Distinction Among the “Desirable”, Morality, and Personal Preference
Authors: Nisan Mordecai
Published: April 2006

Israeli children of grades 1, 4, and 7 were asked, with respect to nine types of behavior, whether such behavior is bad, whether a child should be brought up to behave otherwise (and why), whether a child should be required to behave otherwise, and whether such behavior should be punished. Analysis of their responses and the reasons they provided supports the hypothesized distinction between three categories of behaviors or reasons for action—morality, “the desirable” and personal preferences—in terms of two dimensions: desirability and obligatoriness. Specifically, moral norms were perceived as both desirable and strictly obligatory, and were justified in terms of inherent goodness/badness and the welfare of others. Behaviors in the category of “the desirable” were perceived as desirable but not obligatory, and were justified in terms of self‐development and long‐term utility. Behaviors in the category of personal preferences were perceived as non‐obligatory and neither desirable nor undesirable, and were justified in terms of personal choice. This distinction was less sharp among first graders, who exhibited some tendency to view desirables and preferences, as well as moral behavior, as obligatory. In light of these findings, it is suggested that the young child's “intuitive morality” relates only to the dimension of desirability and not to that of obligatoriness, which seems to develop somewhat later.
The Semantically Reciprocating Robot: Adult Influences on Children's Early Conversational Skills
Authors: Dunham Philip , Dunham Frances
Published: April 2006

Two‐year‐old children's conversational replies were observed in two social contexts: (a) with a partner who consistently responded to each of their utterances by semantically reciprocating and commenting briefly on their topic; or (b) with a partner who also consistently replied to each of their utterances but did not semantically reciprocate their topic. Children were significantly more likely to reply to a partner who maintained their topic. Given that a child replied, the verbal responses in the semantic reciprocation group were also more likely to have a topic‐comment structure characteristic of more advanced conversational skills. These experimental data confirm previous correlational evidence suggesting that children are sensitive to semantic reciprocation during the early stages of verbal communicative development, and they support recent arguments suggesting that the adult's use of expansions scaffolds the child's tendency to use predicative, topic‐comment replies…and perhaps advances the child's understanding of the adult partner as an attentional/intentional mental agent.
Teaching Three Year‐Olds to Pass False Belief Tests: A Conversational Approach
Authors: Appleton Michele , Reddy Vasudevi
Published: April 2006

A training procedure was developed for teaching three year‐old children to pass a standard false belief task. A series of 4 video sequences was developed, in each of which a child showed surprise following the unexpected transfer of an object. A group of 23 three year‐olds who failed a standard false belief task took part in 8 discussions of the 4 video clips, over a period of two weeks, and were compared with a control group of 23 task‐failers who had 8 story reading sessions over the same time period. The training involved (a) interactive recall of the initial events in each sequence, (b) factual questioning about the events and (c) an explanation of the thoughts and actions of the video protagonists. The emphasis was on positive elaboration of children's answers rather than on negative feedback as counter evidence. The training group performed significantly better at an immediate post‐test, and at a follow‐up test two weeks later, on a similar as well as a generalisation task. Task success was unrelated to vocabulary (BPVS) score, but was significantly related to success of responses during the training. The results indicate learning in the Training group of a discursive format for talking about events useful for describing false beliefs.
THE SAP OF PLANT CELLS
Authors: MATILE PHILIPE
Published: April 2006

Summary

Recent advances in the understanding of the functional relevance of sap of mature plant cells are reviewed. The emphasis is placed on roles of vacuoles played in the temporary storage of saccharides and organic acids, in the accumulation of water soluble products of secondary metabolism and in the intracellular digestion of protein.

Contents

Summary
1

I.
Introduction
1

II.
Functions of vacuoles
2

III.
Vacuoles as pools of saccharides
3

IV.
Organic acids
7

V.
(Potentially) toxic cell saps
9

VI.
Pools of protein
14

VII.
Digestive cell saps
15

VIII.
Tonoplast, cell sap and cytoplasm
18

IX.
Cellular homeostasis
19

Acknowledgement
20

References
20
DIURNAL CHANGES IN THE PHOTOSYNTHESIS OF FIELD‐GROWN GRAPE VINES
Authors: DOWNTON W. J. S. , GRANT W. J. R. , LOVEYS B. R.
Published: April 2006

Summary

Field studies of the gas exchange of Riesling grape vines (Vitis vinifera L.) showed large diurnal changes in net photosynthesis during the period of rapid sugar accumulation by fruit. The onset of the decline in photosynthesis occurred earlier in the day for vines without fruit. Decreases in photosynthesis were approximately proportional to changes in stomatal conductance. Despite the accompanying large changes in stomatal conductance, changes in intercellular CO2 concentration were small and mathematical analysis showed that stomatal changes accounted for only 20 to 40% of the change in assimilation rate. The CO2 compensation point, oxygen enhancement of photosynthesis, light and temperature responses of the leaf did not vary throughout the day. Stimulation of photorespiration was therefore not responsible for the non‐stomatal inhibition of photosynthesis. No obvious correlation existed between the decline in leaf photosynthesis and daily changes in leaf water potential. A field study of Colombard grape vines revealed that frequently watered vines which had received irrigation 2 d prior to measurement showed little change in photosynthetic rate over the day compared with vines subjected to a more usual watering cycle, which had last been irrigated 18 d prior to measurement. Possible non‐stomatal factors responsible for the reduction in photosynthesis during the day are discussed.
PHOTOSYNTHETIC AND RESPIRATORY CHARACTERISTICS OF MALAYAN SUN AND SHADE FERNS
Authors: NASRULHAQ‐BOYCE A. , MOHAMED M. A. HAJI
Published: April 2006

Summary

A comparative study of four Malayan ferns, Christensenia aesculifolia (Bl.) Maxon, Tectaria singaporeana (Wall.) Ching, Abacopteris multilineata (Wall.) Ching and Hymenophyllum polyanthos Sw. from shady habitats and another four, Dicranopteris linearis (Burm.) Und., Lygodium scandens (L.) Sw., Blechnum orientate Linn, and Stenochlaena palustris (Burm.) Bedd. from sunlit habitats showed that the total chlorophyll content expressed on a gram fresh weight basis was greater in the shade ferns. There was little difference in the chlorophyll content between the sun and shade ferns when it was expressed on a per unit leaf area basis. The protein and protohaem content was greater in the sun ferns. Measurements of the in vitro photochemical activities of the photosystems I and II in isolated chloroplasts by means of an oxygen electrode showed higher rates in the sun ferns. As determined by spectrophotometric analysis, the photosynthetic cytochrome content from isolated chloroplasts was greater in the sun ferns. The results indicate that the sun ferns have physiological characteristics favouring greater capacity for photosynthesis. Mitochondria isolated from the sun ferns showed faster rates of electron transport using exogenous NADH as substrate.
THE ACCUMULATION OF PHOSPHORYLATED GUANOSINE NUCLEOTIDES IN ANABAENA CYLINDRICA
Authors: AKINYANJU J. , SMITH R. J.
Published: April 2006

Summary

Two highly phosphorylated guanosine derivatives accumulate in alkaline cultures of Anabaena cylindrica during the early stationary phase and in anaerobic, nitrogen‐deprived cultures. The accumulation of these nucleotides is accompanied by the suppression of the normal accumulation of ppGpp and ppGppp, nucleotides which are effectors of the stringent response in bacteria. The accumulation of the two sets of nucleotides appears to be mutually exclusive. The accumulation of the guanosine derivatives during growth inhibition and their replacement of ppGpp and pppGpp suggests that the newly discovered guanine compounds may also fulfil a regulatory role.
FACTORS AFFECTING THE KINETICS OF INTRA‐AND EXTRACELLULAR CADMIUM UPTAKE BY THE MOSS RHYTIDIADELPHUS SQUARROSUS
Authors: WELLS J. M. , BROWN D. H.
Published: April 2006

Summary

The responses of field‐grown and cultured shoots of a moss, Rhytidiadelphus squarrosus (Hedw.) Warnst, to Cd were investigated. Respiration was not affected, but photosynthesis was progressively reduced with increasing Cd uptake. Field‐grown shoots of two morphologically distinct populations differed in their photosynthetic responses to Cd. This could be related to different rates of Cd uptake by the two populations. During storage of Cd‐treated shoots, movement of extracellular Cd to an intracellular location occurred, and this was reflected in altered photosynthetic rates.

The maximum extracellular uptake capacity and affinity for Cd were identical for the two populations of field‐grown shoots. Field‐grown material from the two populations differed significantly in their intracellular Cd uptake characteristics, cation contents, gas exchange rates and dry weights per unit length. These differences were eliminated by laboratory culture. Cultured shoots had increased affinity for both intra‐ and extracellular cadmium uptake compared to field‐grown shoots. The results indicate that the activity of Cd and other divalent cations at the plasmalemma may control the affinity for and accumulation of Cd by this moss. The results are discussed in terms of the design of experiments in studies of ion uptake and tolerance in bryophytes.
THE INFLUENCE OF SIMULATED ACIDIC RAIN ON VEGETATIVE AND REPRODUCTIVE TISSUES OF CUCUMBER (CUCUMIS SATIVUS L.)
Authors: JACOBSON JAY S. , OSMELOSKI JOE , YAMADA KAREN , HELLER LAURENCE
Published: April 2006

Summary

Cucumis sativus L. plants were grown in the greenhouse and exposed 21 times to simulated acidic rain over a period of 6 weeks to compare the responses of vegetative and reproductive tissues. Chemical composition and temporal characteristics of rain were patterned according to rainfall in the growing season in the eastern US. Flowers were hand‐pollinated to promote fruit set. Foliar symptoms were the most sensitive response of all the variables measured. Necrosis was visible after exposures to simulated acidic rain at pH 2.6, 3.0, and 34 but not at 3.8, 4.2, 4.6, 5.0, or 5.4. Despite these injury symptoms, there were no significant reductions in most measures of vegetative or reproductive tissues, even at pH 2.6. When durations of exposure were increased from 80 to 160 min, there was an increase in the severity of foliar injury, a significant reduction in dry mass of stems, numbers of female flowers produced and dry mass of flowers and immature fruit. However, there still were no significant reductions in numbers or weight of fruit, even though the plants were exposed to as much as a 20‐fold greater deposition of acidity than ambient rainfall (average pH 4.0 to 4.3) in the north‐eastern US. Evidently, cucumber plants have the capacity to recover and compensate for initial decreases in foliage and flower production, and the reproductive stage is not particularly susceptible to simulated acidic rain. These findings support previous results indicating that considerable increases in acidity of ambient rain would have to occur before the yield of crops would be measurably reduced.
INTERACTION BETWEEN OZONE AND COLD SENSITIVITY IN NORWAY SPRUCE: A FACTOR CONTRIBUTING TO THE FOREST DECLINE IN CENTRAL EUROPE?
Authors: BROWN K. A. , ROBERTS T. M. , BLANK L. W.
Published: April 2006

Summary

Three‐year‐old clonal saplings of Picea abies L. Karst. were fumigated for 60 d during the summer of 1985 with four different levels of O3. Visible injury (in the form of severe, uniform brown necrosis and shedding of affected needles) occurred after a frost in November on the older needles of three of the clones which had received over 200 μg m−3 of O3 during the summer, 47 d previously. No visible injury occurred during the fumigation period or on the current (1985) year needles. It is suggested that the results provide preliminary evidence for an enhancement of frost sensitivity by O3 which may be significant in the current wave of forest decline affecting high‐altitude forests in central Europe.
THE DISTRIBUTION OF LIGNIN DERIVATIVES IN FOSSIL PLANTS
Authors: LOGAN KAREN J. , THOMAS BARRY A.
Published: April 2006

Summary

Lignin derivatives have been obtained from a range of sub‐fossil woods and fossil plant compressions by cupric oxide oxidation. Fossil woods yield essentially the same products as wood from living spermatophytes. Although some demethoxylation of the phenolic aldehydes occurs during fossilization, the overall difference between conifer and angiosperm wood is maintained. Compressions of varied plant organs yield recognizable phenolic aldehydes, though often in small amounts.
UPWASH AND DOWNWASH OF POLLEN AND SPORES IN THE UNSATURATED SURFACE LAYER OF SPHANGNUM‐DOMINATED PEAT
Authors: CLYMO R. S. , MACKAY D.
Published: April 2006

Summary

The vertical movement of Corylus and Cedrus pollen and of Lycopodium spores in Sphagnum and peat was studied in a factorial experiment with four flow regimes (no flow, downward, upward, alternate down and up), three injection depths (1, 5 and 9 cm below the surface) and three forms of packing (natural, hand‐packed at natural density, haphazard). The experiment lasted for 36 d.

The results were corrected for compaction and differential recovery of pollen and spores, but the main results were unaffected by these corrections.

Downward, upward and alternating flows moved the median pollen position by about 1.5 cm during the experiment. The flows also increased the interquartile span by 2 cm: about 25 % of grains moved at least 3 cm.

The velocity of upward flow is probably more than sufficient to overcome the rate of sinking of pollen and spores in the unsaturated zone. Reversals of flow may be of importance in dislodging grains into the main channels again.
THE INFLUENCE OF TEMPERATURE, WATER AND NUTRIENT CONDITIONS DURING GROWTH ON THE RESPONSE OF BRASSICA OLERACEA L. TO A SINGLE, SHORT TREATMENT WITH SIMULATED ACID RAIN
Authors: CAPORN SIMON J. M. , HUTCHINSON THOMAS C.
Published: April 2006

A single treatment with simulated acid rain [pH 3.0 delivered as a 30 min spray to glasshouse‐grown seedlings of cabbage (Brassica oleracea L.)] caused extensive damage to the adaxial surface of the cotyledons. The extent of this injury was compared between plants which had been grown under different environmental conditions. Seedlings which were germinated and grown out of doors during springtime at a time of low minimum temperatures (full range: 7 to 32 °C) were less injured by the acid spray than were those grown in the glasshouse under warmer conditions (18 to 36 °C). The influence of temperature alone was studied further in controlled environments. Plants grown at 10 °C showed less damage from acid sprays, in terms of visible injury and in the effect on the subsequent rate of growth, than did those grown at 20 °C. In addition to the influence of low temperature, an insufficient supply of either water or nutrients during growth also reduced the extent of visible damage to the cotyledons from simulated acid rain. Estimates of the contact angles between water droplets and cotyledon surfaces, and SEM studies of the epicuticular wax, indicated that temperature–induced changes in the sensitivity of the cotyledon to acidity were not related simply to the wettability and morphology of the surface wax. The results indicate that laboratory or indoor experiments with stimulated acid rain should be interpreted cautiously; in the natural environment the direct effect of acidity on higher plants may change seasonally and spatially according to the plants’growing conditions.
THE PROCESSES OF ANTHER DEHISCENCE AND POLLEN DISPERSAL III. THE DEHYDRATION OF THE FILAMENT TIP AND THE ANTHER IN THREE MONOCOTYLEDONOUS SPECIES
Authors: KEIJZER C. J. , HOEK I. H. S. , WILLEEMSE M. T. M.
Published: April 2006

The relationship between anther dehiscence and dehydration of the filament tip and the connective tissue were followed in Gasteria verrucosa (Mill.) H. Duval, Allium cepa L. and Lilium hybrida cv.‘Enchantment’using various microscopical techniques, including direct observations of living tissues in the SEM.

In G. verrucosa anther dehiscence immediately follows anthesis, with concomitant dehydration and shrivelling of the filament tip. In L. hybrida the filament tip dehydrates and shrivels before anthesis. The anthers start to dehisce immediately after anthesis. In A. cepa the filament tip dehydrates and shrivels slowly after anthesis and dehiscence, which may take up to several days, correlates with the rate of extension of the filament.

The attenuated period of dehiscence in A. cepa may be related to the absence of stomata on the anther. Experiments on xylem conductivity and transpiration reveal that the presence of continuously open stomata on the anthers sets the time of dehiscence after anthesis in G. verrucosa and L. hybrida.

The shrinking filament tip in all three species functions as a hinge which suspends the dangling anther after dehiscence. The uniformly thickened epidermal cell walls on the anthers opposite the filament prevent the outwardly bending locule walls from embracing the filament.
GENETIC VARIATION IN CANADIAN AND EUROPEAN POPULATIONS OF THE COLONIZING WEED SPECIES APERA SPICA‐VENTI*
Authors: WARWICK S. I. , THOMPSON B. K. , BLACK L. D.
Published: April 2006

Apera spica‐venti L., a widely distributed weed in Europe, has recently become established as a weed of winter cereals in Canada. Levels of genetic variation were compared between and within nine Canadian and six native European populations grown under uniform conditions. Both the Canadian and European populations showed high levels of variation among populations with respect to 31 life history and morphological traits. As one would have predicted, greater differences were recorded among the European populations, although only one population in each group was clearly distinct from the other populations. High levels of genetic variability in allozyme characters were also evident in both the Canadian and European populations (percentage of polymorphic loci = 57 to 62%, number of alleles per locus = 2.53 and levels of heterozygosity = 0.23). There was, however, little or no divergence in allozyme characters among populations, with all populations having very high genetic identity values (0.948 to 0.998) and only 1.0 to 2.4% of the total gene diversity allocated to the among‐population component. The extent of within‐population variation in the 31 life‐history and morphological characters were similar in both introduced and native populations. Studies of population structure in three Canadian populations indicated that most of the variation in nine morphological characters occurred among progeny within families rather than among families. Estimates of outcrossing rate (t) using allozyme markers at two loci equalled 1.0, indicating random mating. Selfing experiments indicated that the plants were predominantly self‐incompatible. The amounts and patterns of genetic variation are consistent with what one would expect in an outcrossing species and do not support the hypothesis of genetically depauperate introductions.
GAS EXCHANGE CHARACTERISTICS OF HETEROMELES ARBUTIFOLIA DURING FUMIGATION WITH SULPHUR DIOXIDE
Authors: ATKINSON CHRISTOPHER J. , WINNER WILLIAM E.
Published: April 2006

The objectives of this study were to determine the gas exchange responses of Heteromeles arbutifolia (Ait.) Roem. to a range of sulphur dioxide (SO2) concentrations applied in various sequences including possible ambient levels. Carbon dioxide and light‐response curves were used to determine the mechanisms of SO2 responses. These experiments were performed with greenhouse‐grown plants.

Net photosynthesis (A) of H. arbutifolia was shown to be depressed by SO2 concentrations ranging from 1.5 to 43.8 μmol m−3 (0.04 to 1 μl l−1). In most cases on first exposure to SO2 a larger decrease in stomatal conductance to water vapour (gH) occurred than on subsequent exposures to either the same or greater SO2 concentrations. Acclimation of gH to SO2 appeared to occur with repeated exposure.

Light‐response curves determined during exposure to 25 μmol SO2 m−3 (0.6 μl l−1) for a leaf repeatedly exposed to SO2 indicated that inefficiency of photon utilization in the primary reaction of energy transduction or reduction in photosynthetic capacity was unlikely. The maximum rates of A (Amax) determined from these curves were similar in both SO2 and SO2− free air. The limitations of gH to carbon acquisition were removed using CO2−response curves [photosynthesis expressed relative to the internal CO2 concentration (Ci)]. This analysis shows that A may have been limited during repeated exposures by reduced carboxylation efficiency. It appeared that at similar values of gH, plants exposed to SO2 would fix less carbon and water use efficiency (WUE) would decrease in polluted plants.
CHLOROPLAST AUTONOMY FOR THE BIOSYNTHESIS OF ISOPENTENYL DIPHOSPHATE IN GUAYULE (PARTHENIUM ARGENTATUM GRAY)
Authors: REDDY A. RAMACHANDRA , DAS V. S. RAMA
Published: April 2006

Purified chloroplasts (80% intact) with a photosynthetic activity of 195 μmol O2 mg chlorophyll−1 h−1 were prepared from the leaves of guayule. The activities of phosphoglyceromutase, enolase and pyruvate kinase were estimated in the purified chloroplasts and compared with those of Phaseolus radiatus Roxb. Activity of the pyruvate dehydrogenase complex (PDC) in the chloroplasts of guayule (448 nkat mg protein−1) was substantially higher than the PDC activity of Phaseolus (282 nkat mg protein−1). Incorporation of carbon from the added labelled carbon compounds, [14C]bicarbonate, [2‐14C]pyruvate and [U‐14C]‐3‐phosphoglycerate into isopentenyl diphosphate (IDP) was significant, indicating the ability of the chloroplasts to utilize Calvin cycle intermediates for IDP biosynthesis via acetyl CoA and mevalonate. DCMU inhibited the incorporation of 14CO2 and [14C]pyruvate into IDP. Acetoacetyl CoA thiolase, HMG‐CoA reductase, mevalonate kinase, phosphomevalonate kinase and pyrophosphomevalonate decarboxylase activity were localized in the isolated chloroplasts. It is believed that the chloroplasts in the leaf of guayule are autonomous for the biosynthesis of IDP and this is presumed to be dependent on photosynthetic energy and carbon flow.
DEVELOPMENT OF ‘EPIDERMAL’ GRAFTS ON CULTURED INTERNODES OF DATURA STRAMONIUM
Authors: HOLDEN M. A. , JEFFREE C. E. , YEOMAN M. M.
Published: April 2006

This paper describes a novel system of graft assembly in vitro performed on excised Datura stramonium internodes. The grafted material is a 2 × 10 mm strip of superficial tissue consisting of the epidermis plus three to seven layers of underlying tissue and the technique is therefore called ‘epidermal’ grafting. The excision of the strip of superficial tissue initiates cell division in the wounded tissue. At 10 d, control internodes, where tissue was excised but not replaced, had significantly higher cell numbers than the corresponding homografts. The assembly of the graft therefore appears to limit the cell division caused by tissue injury. Only two cell types are brought into contact during ‘epidermal’ graft assembly, thereby circumventing the problems associated with the study of the union of multiple cell types. This technique, therefore, represents a simplified system in which the cellular interactions during graft formation can be studied.
ZINC TOLERANCE IN BETULA SPP.
Authors: DENNY HILARY J. , WILKINS D. A.
Published: April 2006

Clones of zinc‐tolerant and non‐tolerant genotypes of Betula pendula Roth, and B. pubescens Ehrh. were cultured aseptically on media containing different concentrations of zinc. The location, concentration and form of zinc in root tissues of both groups of genotype were compared using various microanalytical techniques. At concentrations of zinc at which all genotypes were viable, there were no obvious differences between the tolerant and non‐tolerant genotypes. When the roots were subjected to concentrations above the lethal threshold, zinc accumulated intracellularly, at the endodermis, in the form of electron‐dense granules. This form of accumulation was symptomatic of tissue inundation with zinc. The results do not support the presence of cell wall binding or intracellular detoxification mechanisms of tolerance. The possibility that zinc tolerance, control of zinc uptake and zinc‐induced inhibition of cell extension are all linked by common events centred on the plasma membrane are discussed.
LITTLE ICE AGE DECLINE OF A COLD MARGINAL PINUS SYLVESTRIS FOREST IN THE SWEDISH SCANDES
Authors: KULLMAN LEIF
Published: April 2006

The natural decline of a virgin high‐altitude Pinus sylvestris forest during the Little Ice Age (approximately AD 1300–1850) was studied in the Swedish Scandes. Methods included 14C and cross‐dating of wood remnants, soil analyses, year‐ring chronologies and age structures. A closed pine forest started a gradual decline in the 11th century or somewhat later, which proceeded until the mid‐19th century. Long‐term failure of regeneration and premature death of trees are postulated to have caused the forest dieback, mainly owing to a negative shift of the carbon budget, including weather‐induced loss of photosynthetic tissue and root disfunction. Temperature measurements on the study site stressed its current marginality. Especially thermal conditions in and close to the ground were deduced to be decisive. The decline of the forest is considered to indicate a long‐term lowering during the Little Ice Age of the summer (June‐September) mean temperature by 1°C or more, compared with the 1931–1960 mean.
CARBON DIOXIDE AND WATER DEMAND: CRASSULACEAN ACID METABOLISM (CAM), A VERSATILE ECOLOGICAL ADAPTATION EXEMPLIFYING THE NEED FOR INTEGRATION IN ECOPHYSIOLOGICAL WORK
Authors: LÜTTGE U.
Published: April 2006

Summary

Plants having crassulacean acid metabolism (CAM) tend to occupy habitats where the prevailing environmental stress is scarcity of water. These are semi‐arid or arid regions, salinas or epiphytic sites. CAM plants manage the dilemma of desiccation or starvation by nocturnal malic acid accumulation in the vacuoles. Malic acid serves as a form of CO2 storage and as an osmoticum. In this way malic acid accumulation allows, firstly, separation of uptake and assimilation of atmospheric CO2 with water‐saving daytime stomatal closure and, secondly, osmotic acquisition of water. There is no very special trait which is specific for CAM. An array of biophysical and biochemical functional elements, which are also found in other plants, is integrated in CAM performance. This leads to a large diversity of behaviour which makes CAM plants highly versatile in their response to environmental variables. Besides CO2 dark fixation, transport of malic acid across the tonoplast is one of the key elements in CAM function. This is examined in detail at the level of membrane biophysics and biochemistry. The versatility of CAM is illustrated by examples from field work, with comparisons involving different species, seasons, modes of photosynthesis (CAM vs C3), kinds of stress and ways of stress imposition.

Contents

Summary
593

I.
Studies of CAM: an example for the ecophysiological approach
594

II.
Malic acid transport at the tonoplast
602

III.
Regulation
605

IV.
Desiccation or starvation
610

V.
Comparative autecology
614

VI.
Ecology: promise of integration
621

Acknowledgements
622

References
622
THE MINIMUM PHOTON REQUIREMENT FOR PHOTOSYNTHESIS
Authors: OSBORNE BRUCE A. , GEIDER RICHARD J.
Published: April 2006

Summary

Variations in the apparent photon requirement for photosynthesis (Φ−1co2) or (Φ−1co2) in the data of Warburg & Burk (1950) and Yuan, Evans & Daniels (1955) can be ascribed to changes in O2uptake and energy‐dependent processes which result in aberrant photon requirements in organisms subjected to non‐optimal conditions. The increase in Φ−1co2with increases in the gas exchange quotient (γ) in the observations of Yuan et al. (1955) is consistent with increases in photorespiratory production of glycollate, whilst changes in Φ−1co2and Φ−1co2in the results of Warburg & Burk (1950) can be explained by a variable Kok effect associated with nitrate assimilation at low light levels. When these O2and energy‐dependent processes are minimal, the lowest values should be observed. The minimum value obtained whenChlorellais photosynthesizing under optimal conditions is 6 mol photons mol−1O2. These results provide direct independent evidence for a photon requirement for photosynthesis of less than 8 mol photons mol−1O2. Such a value is not consistent with the Z scheme of photosynthesis.
OSMOTIC ADJUSTMENT IN MARINE EUKARYOTIC ALGAE: THE ROLE OF INORGANIC IONS, QUATERNARY AMMONIUM, TERTIARY SULPHONIUM AND CARBOHYDRATE SOLUTES
Authors: DICKSON D. M. J. , KIRST G. O.
Published: April 2006

Summary

The unicellular marine algae, Phaeodactylum tricornutum Bohlin, Cyclotella cryptica Reimann and Cyclotella meneghiniana Kützing (Bacillariophyceae) and Porphyridium aerugineum Geitler (Rhodophyceae) synthesized and accumulated glycine betaine and proline in response to increases of the NaCl concentration (150 to 1000 mol m−3NaCl) of the growth medium. C. cryptica and C. meneghiniana also synthesized and accumulated homarine (N‐methyl picolinic acid betaine). Both P. tricornutum and P. aerugineum synthesized increasing amounts of intracellular glycerol and P. aerugineum also formed the heteroside, floridoside [O‐α‐D‐galactopyranosyl (1 → 2)‐glycerol], in response to the elevated salinities. No major low molecular weight carbohydrates were found in Cyclotella. Sucrose was not detected in the algal extracts. Only P. tricornutum synthesized the tertiary sulphonium compound, β‐dimethylsulphoniopropionate (DMSP), and the quantity of this solute in the alga was dependent on the amount of NaCl in the medium. Intracellular K+concentrations in the algae were three to six times greater than those of Na+. Increases of the salinity of the media led to the uptake and accumulation of K+by the cells, and smaller increases of Na+and Cl−1and loss of intracellular NO3−. The inorganic cations Na+and K+, with their accompanying anions, and the estimated organic solutes could largely account for the osmotic balance of P. tricornutum and P. aerugineum.
OSMOTIC ADJUSTMENT IN MARINE EUKARYOTIC ALGAE: THE ROLE OF INORGANIC IONS, QUATERNARY AMMONIUM, TERTIARY SULPHONIUM AND CARBOHYDRATE SOLUTES
Authors: DICKSON D. M. J. , KIRST G. O.
Published: April 2006

Summary

The effects of steady state salinities (150 to 700 mol m−3NaCl) on the growth rates and intracellular solutes of the prasinophyte algae Tetraselmis chui Butcher and Prasinocladus Kuckuck and the prymnesiophyte algae, Prymnesium parvum Carter and Ruttnera spectabilis Geitler, are described. Maximum growth rates were reached in media approximating to the NaCl concentration of oceanic waters (about 500 mol m−3). The following intracellular organic solutes paralleled the increases of external salinity: the tertiary sulphonium compound β‐dimethylsulphoniopropionate (DMSP) in T. chui, Prasinocladus, P. parvum and R. spectabilis; the polyhydric alcohol, mannitol, in T. chui, Prasinocladus and R. spectabilis; the quaternary ammonium compounds (QACs), glycine betaine and homarine, in T. chui and Prasinocladus. QACs were not detected in P. parvum and R. spectabilis. An unknown polyol, which may be the cyclitol, 1,4/2,5 cyclohexanetetrol, was synthesized by P. parvum and R. spectabilis and in addition P. parvum contained significant concentrations of glucose. Sucrose was not detected in the algal extracts. Proline was an insignificant osmoticum in all the algae.

Increases of the media NaCl concentration led to the uptake and accumulation of K+in T. chui and Prasinocladus, with smaller increases of Na+and Cl−. The intracellular K+concentrations in the prasinophyte algae were about five times greater than those of Na+. The inorganic cations Na+and K+, and their accompanying anions, and the organic solutes found could largely account for the osmotic balance of T. chui and Prasinocladus. The inorganic ions in P. parvum and R. spectabilis were not determined.
THE INFLUENCE OF AIR POLLUTION ON THE CONCENTRATION OF ATP AND ON CHLOROPHYLL DEGRADATION IN THE LICHEN, RAMALINA DURIAEI (DE NOT.) BAGL.
Authors: KARDISH NITZA , RONEN R. , BUBRICK P. , GARTY J.
Published: April 2006

Summary

The most efficient of five methods used for the extraction of ATP from lichens was found to be the use of Tris + EDTA after acetone treatment. Changes in the concentration of ATP in transplanted Ramalina duriaei (De Not.) Bagl. reflected the influence of air pollution on this lichen. The ATP concentration remained constant at a control station in a rural site, whilst at urban stations it decreased to 10% of the control value. Changes in the concentration of ATP were compared with chlorophyll degradation, as expressed by the ratio OD 435 nm/OD 415 nm. The values of this ratio also decreased in the urban sites, but less so than the ATP.
VESICULAR‐ARBUSCULAR MYCORRHIZA IMPROVE BOTH SYMBIOTIC N2 FIXATION AND N UPTAKE FROM SOIL AS ASSESSED WITH A 15N TECHNIQUE UNDER FIELD CONDITIONS
Authors: BAREA J. M. , AZCÓN‐AGUILAR C. , AZCÓN R.
Published: April 2006

Summary

A technique using 15N‐labelled inorganic fertilizer was applied to estimate N2 fixation by the forage legume Hedysarum coronarium L. and to ascertain the role of vesicular‐arbuscular (VA) mycorrhizas in plant N nutrition throughout a growing season under field conditions. The absence of the specific Rhizobium for the forage legume in the test soil allowed us the use of 15N methodology with the same legume as reference ‘non‐fixing’ crop.

At the first harvest, mycorrhizal inoculation behaved similarly to the phosphate addition in improving the percentage (70 %) and the total amount of N derived from fixation. But thereafter, mycorrhizal inoculation not only enhanced dry matter yield, N concentration and total N yield but also the amount of N derived from soil and from fixation, as compared with either phosphate‐added or control plants. This indicated that mycorrhizas acted both by a P‐mediated mechanism to improve N2 fixation and by enhancing N uptake from soil. The latter agrees with recent findings by others that VA mycorrhizal hyphae can translocate and assimilate ammonium, a fact of physiological and ecological interest.
THE SPREAD OF MYCORRHIZAL INFECTION BY GIGASPORA CALOSPORA FROM A LOCALIZED INOCULUM
Authors: SCHELTEMA M. A. , ABBOTT L. K. , ROBSON A. D. , DE'ATH G.
Published: April 2006

Summary

The lateral spread of Gigaspora calospora (Nicol. and Gerd.) Gerdemann & Trappe was examined in Trifolium subterraneum L. (subterranean clover) grown on a steamed lateritic podsol. Plants were sown in a sward in pots 29 cm long × 12 cm wide and inoculum of G. calospora was placed at one end. Mycorrhizal infection was estimated 21, 35, 63, 91 and 119 d after sowing at points 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 and 26 cm from the inoculum. The lateral spread of Glotnusfasciculatum (Thaxter sensu Gerd.) through roots of T. subterraneum was measured 35 d after sowing.

The percentage root length infected by G. calospora declined exponentially with distance from the inoculum. In contrast, infection by G. fasciculatum spread with a distinct front and hence was best described by a Gompertz curve.

The number of spores of G. calospora recovered at increasing distances from the point of inoculation at the final harvest was correlated with the proportion of roots infected at an earlier harvest, and therefore provided a useful measure of the pattern of spread of G. calospora within roots.
PLANT SIZE AND SEED PRODUCTION IN THE MONOCARPIC PERENNIAL CYNOGLOSSUM OFFICINALE L.
Authors: KLINKHAMER PETER G. L. , DE JONG TOM J.
Published: April 2006

Summary

In a study of Cynoglossum officinale L. it was found that the number of seeds per flower increased with plant weight, and that flower production was inversely related to the number of seeds per flower. As a result, the number of seeds and total seed weight increased proportionally with plant weight. Seed size was not related to plant weight. Differences in seed size within the individual were, in part, related to the position of the seed on the cyme and not related to the number of seeds within a flower. The relationship, between plant size and female fitness found in this study is discussed in relation to life‐history theory.