Contrasting physiological responses to excess heat and irradiance in two tropical savanna sedges.

Tropical hyperseasonal savannas provide a rare example of a tropical climax community dominated by graminoid species. Species living in such savannas are frequently exposed to excess heat and light, in addition to drought and waterlogging, and must possess traits to avoid or tolerate these stress factors. Here we examine the contrasting heat and light stress adaptations of two dominant savanna sedges: Lagenocarpus guianensis, which is restricted to the sheltered forest edge, and Lagenocarpus rigidus, which extends from the forest edge to the open savanna. An ecotone extending from the forest edge to the open savanna was used to assess differences in a range of physiological traits (efficiency of photosystem II, cell membrane thermostability, stomatal conductance, leaf surface reflectance and canopy temperature depression) and a range of leaf functional traits (length : width ratio, specific leaf area and degree of folding). Lagenocarpus guianensis showed significantly less canopy temperature depression than L. rigidus, which may explain why this species was restricted to the forest edge. The range of leaf temperatures measured was within the thermal tolerance of L. guianensis and allowed photosystem II to function normally, at least within the cool forest edge. The ability of L. rigidus to extend into the open savanna was associated with an ability to decouple leaf temperature from ambient temperature combined with enhanced cell membrane thermostability. The high degree of canopy temperature depression seen in L. rigidus was not explained by enhanced stomatal conductance or leaf reflectance, but was consistent with a capacity to increase specific leaf area and reduce leaf length: width ratio in the open savanna. Plasticity in leaf functional traits and in cell membrane thermostability are key factors in the ability of this savanna sedge to survive abiotic stress.

The effect of temperature shock and grain morphology on alpha-amylase in developing wheat grain.

BACKGROUND AND AIMS: The premature production of alpha-amylase without visible germination has been observed in developing grain of many cereals. The phenomenon is associated with cool temperatures in the late stages of grain growth but the mechanisms behind it are largely unknown. The aim of this study was to replicate the phenomenon under controlled conditions and investigate the possibility of a mechanistic link with grain size or endosperm cavity size. METHODS: Five wheat (Triticum aestivum) genotypes differing in their susceptibility to premature alpha-amylase were subjected to a range of temperature shocks in controlled environments. A comparison was then made with plants grown under ambient conditions but with grain size altered by using degraining to increase the assimilate supply. At maturity, alpha-amylase, grain area and endosperm cavity area were measured in individual grains. KEY RESULTS: Both cold and heat shocks were successful in inducing premature alpha-amylase in susceptible genotypes, with cold shocks the most effective. Cold shocks also increased grain area. Degraining resulted in increased grain area overall, but the larger grain did not have higher alpha-amylase. Analysis of individual grain found that instances of high alpha-amylase were not associated with differences in grain area or endosperm cavity area. CONCLUSIONS: Pre-maturity alpha-amylase is associated with temperature shocks during grain filling. In some cases this coincides with an increase in grain area, but there is no evidence of a mechanistic link between high alpha-amylase and grain or endosperm cavity area.

The effect of gibberellic acid on the response of leaf extension to low temperature.

The effect of cooling on leaf extension rate (LER) and on relative elemental growth rate (REGR) was measured in both gibberellic acid (GA)-responsive dwarf barley and in the same barley variety treated with GA. Seedlings were maintained at 20 degrees C while their leaf extension zone (LEZ) temperature was reduced either in steps to -6 degrees C in short-term cooling experiments, or to 10 degrees C for 48 h in long-term cooling experiments. Short-term cooling resulted in a biphasic response in LER, with a clear inflection point identified. Below this point, the activation energy for leaf extension becomes higher. The short-term response of LER to cooling was altered by the application of GA, which resulted in a lower base temperature (Tb), inflection point temperature and activation energy for leaf extension. Both GA-treated and untreated seedlings were less sensitive to cooling maintained for a prolonged period, with LER making a partial recover over the initial 5 h. Although long-term cooling reduced maximum REGR, it resulted in a longer LEZ and an increase in the length of mature interstomatal cells in GA-treated and untreated seedlings. These changes in overall physiology appear to enhance the ability of the leaves to continue expansion at suboptimal temperatures. In both GA-treated and cold-acclimated tissue, the occurrence of a longer LEZ was associated with a lower temperature sensitivity in LER.

Evaluation of Responding in Peaceful and Positive Ways (RIPP): a school-based prevention program for reducing violence among urban adolescents.

Evaluated Responding in Peaceful and Positive Ways (RIPP)--a 6th-grade universal violence prevention program. Classes of 6th graders at 3 urban middle schools serving predominantly African American youth were randomized to intervention (N = 321) and control groups (N = 305). Intervention effects were found on a knowledge test but not on other mediating variables. RIPP participants had fewer disciplinary violations for violent offenses and in-school suspensions at posttest compared with the control group. The reduction in suspensions was maintained at 12-month follow-up for boys but not for girls. RIPP participants also reported more frequent use of peer mediation and reductions in fight-related injuries at posttest. Intervention effects on several measures approached significance at 6-month and 12-month follow-up. The program's impact on violent behavior was more evident among those with high pretest levels of problem behavior.

Development and evaluation of school-based violence prevention programs.

Discusses key issues in developing and evaluating school-based violence prevention interventions. Schools provide a natural setting for implementing programs directed at teaching youth attitudes, knowledge, and skills to reduce their involvement in violence. Although multitudes of these programs exist, few have been rigorously evaluated. Developers of violence prevention programs need to pay particular attention to the type of violence being addressed, the target population, relevant risk and protective factors, and the target of the intervention. Conducting sound evaluations of such programs requires careful attention to the unit of randomization, treatment conditions, outcome measures, timing of data collection, and potential moderator variables. Efforts to develop effective prevention programs can be greatly facilitated by adopting an action-research strategy in which evaluation findings provide a basis for continual program refinement.

Structure of anxiety symptoms in urban children: competing factor models of the Revised Children's Manifest Anxiety Scale.

The Revised Children's Manifest Anxiety Scale (RCMAS; C. R. Reynolds & B. O. Richmond, 1985) is among the most widely used self-report measures of children's anxiety. The authors compared its current empirically derived factor structure with theory-driven models derived from 8 experts on child anxiety using concept mapping. Confirmatory factor analyses compared models using data from 898 seventh graders in an urban public school system serving a high percentage of African Americans. The most parsimonious best-fitting model was an expert-derived model with factors reflecting anxious arousal, social evaluation-oversensitivity, worry, and a higher order factor. This model was theoretically meaningful, excluded items less relevant to anxiety, and was invariant across gender. Future research with the RCMAS should consider use of these dimensions. The combination of qualitative and quantitative methodology used in this study appeared to have considerable utility for refining measures.

The structure of self-reported aggression, drug use, and delinquent behaviors during early adolescence.

Examined the structure of self-report scales designed to assess the frequency of adolescent problem behaviors. Urban (n = 988) and rural (n = 1,895) middle school students completed the Problem Behavior Frequency Scale (Farrell, Danish, & Howard, 1992a) and measures of other relevant constructs. Confirmatory factor analyses supported a model that included specific factors related to aggression, drug use, and delinquent behaviors, and a higher order problem behavior factor. Findings did not support a distinction between physical and nonphysical aggression. Results were generally consistent across settings (i.e., urban vs. rural) and gender. Other relevant constructs, including peer pressure for drug use and attitudes favoring aggression, had both specific associations with relevant first-order factors and more general associations with the second-order factor. These findings support the construction of separate scales assessing specific domains of problem behaviors in studies of adolescents' problem behaviors.

Structure of the Weinberger Adjustment Inventory Self-Restraint scale and its relation to problem behaviors in adolescence.

The authors examined the structure of the Weinberger Adjustment Inventory (WAI) Self-Restraint scale in derivation (n = 1,286) and cross-validation (n = 1,154) samples of mostly African American 6th graders in 3 urban schools. Four models were compared: (a) a 1-factor model; (b) a hierarchical model in which factors representing Impulse Control, Suppression of Aggression, Responsibility, and Consideration of Others were subsumed by a higher order factor; (c) a model that represented these 4 factors as correlated but distinct constructs; and (d) a model that excluded Consideration of Others from the higher order factor. Consistent support was found for the last model based on confirmatory factor analyses and latent-variable analyses examining the relations among self-restraint scales, drug use, delinquency, and aggression. These findings have implications for using the WAI, particularly in studies of adolescent problem behaviors.

Identification and impact of risk and protective factors for drug use among urban African American adolescents.

Identified 10 risk and 12 protective factors associated with drug use among African American 8th graders (N = 994) in an urban school system. Regression analyses identified 7 risk and 7 protective factors with minimal overlap. The total number of risk factors was significantly related to the prevalence of use for cigarettes, beer or wine, liquor, marijuana, and a composite measure of drug use. The Protective Factor Index (PFI) was a significant moderator of the relation between risk and use of beer or wine, liquor, marijuana, and the composite measure. Longitudinal analyses of data on 650 students across the transition from middle to high school indicated that the sum of risk factors predicted changes in all drug use categories except the composite. The PFI significantly predicted changes in beer or wine, liquor, and composite drug use over this 1-year period. It also moderated risk for cigarette use, but not for other drugs. Results replicated prior studies and highlighted the importance of protective factors such as adaptive functioning in school and family influences.

Development and evaluation of problem frequency scales from version 3 of the computerized assessment system for psychotherapy evaluation and research (CASPER).

A comprehensive analysis of interview items on the Computerized Assessment System for Psychotherapy Evaluation and Research (CASPER) was conducted using derivation (N = 1,168) and cross-validation samples (N = 1,158) from a university counseling center and an outpatient training clinic sample (N = 355). Nine scales were identified that demonstrated acceptable internal consistency and unidimensionality. Confirmatory factor analyses of 6 of these scales supported the presence of 6 factors, but indicated that several were highly intercorrelated. These findings were consistent across all 3 samples. Analyses relating these 6 scales to comparable scales on the Brief Symptom Inventory (BSI) obtained for the training clinic sample indicated a high degree of correspondence across instruments. In addition, significant correlations were found between global measures obtained from CASPER and the BSI.

Identification and assessment of problematic interpersonal situations for urban adolescents.

Identified and developed a scale to assess problematic interpersonal situations among urban adolescents. In Study 1, problematic situations were identified by focus groups of 6th graders (N = 43). Their relevance was verified in Study 2 by assessing their reported frequency and difficulty in a sample of 6th graders (N = 457) that included mostly African American youth from low-income families. Scales representing 3 dimensions, peer provocation, perceived injustice, and environmental stressors were verified by confirmatory factor analyses. In Study 3, the internal consistency and structure of these scales were cross-validated in a sample of 7th graders (N = 459). All 3 scales were correlated with self-reported violent behavior, drug use, and anxiety and uniquely accounted for 11% to 19% of the variance. These findings have implications for identifying youth at risk for emotional and behavioral problems and for designing more relevant interventions.

Peer influences and drug use among urban adolescents: family structure and parent-adolescent relationship as protective factors.

The moderating influences of family structure and parent-adolescent distress on the relationship between peer variables and drug use were examined in a predominantly African American sample of 630 10th graders at 9 urban high schools. Both peer pressure and peer drug use were significantly related to the reported frequency of drug use. The relationship between peer pressure and drug use was stronger among girls than boys, and also among adolescents in families without fathers or stepfathers. The association between peer pressure and drug use also increased as a function of the level of mother-adolescent distress among adolescents who were not living with fathers or stepfathers. Neither gender nor family structure moderated the relationship between peer drug models and drug use. However, the association between peer drug models and drug use increased as a function of the level of mother-adolescent distress.

The effectiveness of a school-based curriculum for reducing violence among urban sixth-grade students.

OBJECTIVES: In this study, we examine the impact of a school-based curriculum designed to reduce violence among urban sixth-grade students. METHODS: This study used a staggered implementation design in which sixth-graders in six middle schools were taught an 18-session violence-prevention curriculum during either the fall or spring semester. Outcome measures were completed at the beginning, middle, and end of the school year. RESULTS: For boys, participation in the program during the fall resulted in significant posintervention differences in the self-reported frequency of violence and several other problem behaviors. Most of these differences were maintained at the end of the school year. Girls, in contrast, did not appear to benefit from the program. CONCLUSION: These results support the use of a school-based curriculum for reducing violence among sixth-grade boys. They also underscore the importance of early intervention and the necessity of examining gender effects in evaluating such programs.

Impact of exposure to community violence on violent behavior and emotional distress among urban adolescents.

Examined the effects of witnessing community violence on emotional distress and frequency of violent behavior across three time points within a predominantly African American sample of 436 sixth-grade students in an urban public school system. A high percentage of students, particularly boys, reported witnessing a variety of violent incidents (e.g., shootings, beatings, and stabbings). Comparison of structural equation models revealed a number of significant gender differences in the effects of exposure to violence and in the measurement of violent behavior. Exposure to violence was related to subsequent changes in the frequency of violent behavior among girls, but not among boys. Exposure to violence was not related to subsequent changes in emotional distress for either boys or girls. Cross-sectional results replicated previous studies that have found relations between exposure to violence and frequency of violent behavior; however neither variable was related to emotional distress.

Richmond youth against violence: a school-based program for urban adolescents.

The Richmond Youth Against Violence Project teaches middle school students in the Richmond Public Schools knowledge, attitudes, and skills for reducing their involvement in violence. These students are primarily African Americans, many of whom come from low-income, single-parent households in neighborhoods with high rates of crime and drug use. The program, "Responding in Peaceful and Positive Ways," employs a developmentally anchored health promotion model. Its goal is to promote peaceful and positive alternatives to interpersonal and situational violence, by creating environments that teach and encourage health-enhancing behaviors and intrapersonal attributes and weakening supports for health-compromising behaviors and intrapersonal attributes. The 16-session school-based program was implemented by prevention specialists with sixth graders during the 1994-1995 school year. Students are taught a seven-step problem-solving model. Program implementation was staggered to allow an intervention group to participate during the fall semester and a control group to participate during the spring semester. Outcome measures include school data and measures completed by students. There were few significant baseline differences between the intervention and control groups. A high percentage of students, particularly boys, reported exposure to community violence; more than 92% had heard gunshots. Many have also engaged in risk behaviors; 70% of the boys and 44% of the girls reported being in a fight in the preceding 30 days. The impact of the curriculum is being examined. The program has provided valuable lessons about conducting community-based research, particularly designing, implementing, and evaluating prevention programs.

Structural equation modeling with longitudinal data: strategies for examining group differences and reciprocal relationships.

This article describes the use of structural equation modeling with latent variables to examine group differences and test competing models about cause-effect relationships in passive longitudinal designs. This approach is compared with several other statistical methods including analysis of cross-lagged panel correlations, regression analysis, and path analysis. The mechanics and advantages of structural equation modeling are illustrated using an example based on a 3-wave longitudinal study of adolescents' alcohol use. Within this example, the generalizability of the measurement model and structural model are assessed across gender and time, and competing models about the causes and consequences of adolescents' alcohol use are tested. The article concludes with a discussion of some of the strengths and limitations of using structural equation modeling with longitudinal data.

Peer drug associations and emotional restraint: causes or consequences of adolescents' drug use?

A 3-wave longitudinal design was used to examine the relationships among emotional restraint, peer drug associations, and gateway drug use in a sample of 1,256 middle school students. Structural equation modeling was used to compare 3 models: (a) One model viewed drug use as a consequence of emotional restraint and peer variables; (b) 1 viewed drug use as a cause of restraint and peer variables, and (c) 1 included reciprocal effects. All 3 models fit the data fairly well. However, the reciprocal model fit the data significantly better than either of the others. Within this model, low emotional restraint was significantly related to subsequent increases in gateway drug use among boys. In contrast, peer drug models and peer pressure were not related to subsequent changes in gateway drug use. Changes in peer drug models were, however, predicted by previous levels of gateway drug use.

Relationship between drug use and other problem behaviors in urban adolescents.

This study tested the generality of Jessor and Jessor's (1977) problem behavior theory, which states that a variety of problem behaviors constitute a behavioral syndrome in normal adolescents. Relationships among 5 adolescent problem behaviors (cigarette use, alcohol use, marijuana use, delinquency, and sexual intercourse) were examined in 7th-grade boys (n = 556) and girls (n = 715), and 9th-grade boys (n = 481) and girls (n = 485) in an urban school system in which the majority of students were African American and from low-income families. Measures of problem behavior frequency were positively correlated with each other and negatively correlated with several measures of conventional behavior. Confirmatory factor analyses replicated findings of previous studies that a single common factor underlies adolescent problem behaviors.

Risk factors for drug use in urban adolescents: identification and cross-validation.

Examined the relationship between 26 dichotomous risk factors and drug use in derivation (N = 1,352) and cross-validation (N = 1,309) samples of seventh graders in the public school system of a large southeastern city. The majority of students was African American, many came from low-income, single parent families. A total of 20 risk factors representing a variety of variables was significantly related to at least one category of drug use in both samples. Regression analyses identified a subset of 11 risk factors with minimum overlap. The simple sum of these 11 risk factors was significantly associated with prevalence of use for cigarettes, beer and wine, hard liquor, marijuana, and other drugs. The total number of risk factors also showed a curvilinear relationship with the frequency of 30-day use for each category of drug. Theoretical and practical implications of these findings are discussed.

Risk factors for drug use in rural adolescents.

This study tested the relevance of a risk factor model for predicting drug use among rural adolescents. A questionnaire battery assessing drug use and the presence/absence of twenty risk factors derived from a previous study of urban adolescents was administered to a sample of seventh graders (N = 235) in the public school system of a rural community. All but one of these risk factors were found to be significantly related to at least one category of drug use. In addition, a risk factor index based on a subset of ten risk factors was significantly associated with the prevalence and frequency of use for cigarettes, beer and wine, hard liquor, marijuana, and other drugs. These findings support the generalizability of a risk factor approach to predicting drug use, and underscore the need for increased prevention and research efforts directed at rural adolescents.