Christina Ottander

Seasonal changes in photosystem II organisation and pigment composition in Pinus sylvestris

Conifers of the boreal zone encounter considerable combined stress of low temperature and high light during winter, when photosynthetic consumption of excitation energy is blocked. In the evergreen Pinus sylvestris L. these stresses coincided with major seasonal changes in photosystem II (PSII) organisation and pigment composition. The earliest changes occurred in September, before any freezing stress, with initial losses of chlorophyll, the D1-protein of the PSII reaction centre and of PSII light-harvesting-complex (LHC II) proteins. In October there was a transient increase in F0, resulting from detachment of the light-harvesting antennae as reaction centres lost D1. The D1-protein content eventually decreased to 90%, reaching a minimum by December, but PSII photochemical efficiency [variable fluorescence (Fv)/maximum fluorescence (Fm)] did not reach the winter minimum until mid-February. The carotenoid composition varied seasonally with a twofold increase in lutein and the carotenoids of the xanthophyll cycle during winter, while the epoxidation state of the xanthophylls decreased from 0.9 to 0.1 from October to January. The loss of chlorophyll was complete by October and during winter much of the remaining chlorophyll was reorganised in aggregates of specific polypeptide composition, which apparently efficiently quench excitation energy through non-radiative dissipation. The timing of the autumn and winter changes indicated that xanthophyll de-epoxidation correlates with winter quenching of chlorophyll fluorescence while the drop in photochemical efficiency relates more to loss of D1-protein. In April and May recovery of the photochemistry of PSII, protein synthesis, pigment rearrangements and zeaxanthin epoxidation occurred concomitantly. Indoor recovery of photosynthesis in winter-stressed branches under favourable conditions was completed within 3 d, with rapid increases in F0, the epoxidation state of the xanthophylls and in light-harvesting polypeptides, followed by recovery of D1-protein content and Fv/Fm, all without net increase in chlorophyll. The fall and winter reorganisation allow Pinus sylvestris to maintain a large stock of chlorophyll in a quenched, photoprotected state, allowing rapid recovery of photosynthesis in spring.

Cold acclimation and photoinhibition of photosynthesis in Scots pine

Cold acclimation of Scots pine did not affect the susceptibility of photosynthesis to photoinhibition. Cold acclimation did however cause a suppression of the rate of CO2 uptake, and at given light and temperature conditions a larger fraction of the photosystem II reaction centres were closed in cold-acclimated than in nonacclimated pine. Therefore, when assayed at the level of photosystem II reaction centres, i.e. in relation to the degree of photosystem closure, cold acclimation caused a significant increase in resistance to photoinhibition; at given levels of photosystem II closure the resistance to photoinhibition was higher after cold acclimation. This was particularly evident in measurements at 20° C. The amounts and activities of the majority of analyzed active oxygen scavengers were higher after cold acclimation. We suggest that this increase in protective enzymes and compounds, particularly Superoxide dismutase, ascorbate peroxidase, glutathione reductase and ascorbate of the chloroplasts, enables Scots pine to avoid excessive photoinhibition of photosynthesis despite partial suppression of photosynthesis upon cold acclimation. An increased capacity for light-induced de-epoxidation of violaxanthin to zeaxanthin upon cold acclimation may also be of significance.

Photosystem II reaction centres stay intact during low temperature photoinhibition

Photoinhibition of photosynthesis was studied in intact barley leaves at 5 and 20°C, to reveal if Photosystem II becomes predisposed to photoinhibition at low temperature by 1) creation of excessive excitation of Photosystem II or, 2) inhibition of the repair process of Photosystem II. The light and temperature dependence of the reduction state of QA was measured by modulated fluorescence. Photon flux densities giving 60% of QA in a reduced state at steady-state photosynthesis (300 μmol m−2s−1 at 5°C and 1200 μmol m−2s−1 at 20°C) resulted in a depression of the photochemical efficiency of Photosystem II (Fv/Fm) at both 5 and 20°C. Inhibition of Fv/Fm occurred with initially similar kinetics at the two temperatures. After 6h, Fv/Fm was inhibited by 30% and had reached steady-state at 20°C. However, at 5°C, Fv/Fm continued to decrease and after 10h, Fv/Fm was depressed to 55% of control. The light response of the reduction state of QA did not change during photoinhibition at 20°C, whereas after photoinhibition at 5°C, the proportion of closed reaction centres at a given photon flux density was 10–20% lower than before photoinhibition.Changes in the D1-content were measured by immunoblotting and by the atrazine binding capacity during photoinhibition at high and low temperatures, with and without the addition of chloramphenicol to block chloroplast encoded protein synthesis. At 20°C, there was a close correlation between the amount of D1-protein and the photochemical efficiency of photosystem II, both in the presence or in the absence of an active repair cycle. At 5°C, an accumulation of inactive reaction centres occurred, since the photochemical efficiency of Photosystem II was much more depressed than the loss of D1-protein. Furthermore, at 5°C the repair cycle was largely inhibited as concluded from the finding that blockage of chloroplast encoded protein synthesis did not enhance the susceptibility to photoinhibition at 5°C.It is concluded that, the kinetics of the initial decrease of Fv/Fm was determined by the reduction state of the primary electron acceptor QA, at both temperatures. However, the further suppression of Fv/Fm at 5°C after several hours of photoinhibition implies that the inhibited repair cycle started to have an effect in determining the photochemical efficiency of Photosystem II.

Laboratory work: the teachers' perspective

We describe a case study of an in-service professional development project with four experienced biology teachers in two upper secondary schools. The objective was to better understand the role of laboratory work (labwork) in science education with a special emphasis on assessment. Research questions include the following: 1. What does the teacher want to achieve with the labwork and how do the students perceive it? 2. How do biology teachers assess labwork? 3. How did the in-service project motivate teachers to change their assessment methods? 4. Are the assessment criteria in the Swedish national syllabus applicable to labwork? Data were collected during a semester-long in-service project. Laboratory instruction sheets were collected and analysed both with respect to intended learning outcome and assessment skills. Questionnaires to teachers and students about the intended learning outcome were carried out after different experiments. Finally, teachers were interviewed concerning the role of labwork and their assessment methods and also their reflections on the results of the in-service project. The teachers realised that their assessment methods require more transparency to become effective. The interpretation of intended learning outcomes of experimental work differs between students and teachers.

The Conflict within the Role: A Longitudinal Study of Preschool Student Teachers' Developing Competence in and Attitudes towards Science Teaching in Relation to Developing a Professional Role.

The aim of this exploratory, longitudinal study was to describe an overall picture of how perceptions of the teacher role and attitudes toward science and science teaching develop and interact during preschool teacher education, and how this in turn influences behavior when students are engaged in teaching science. Sixty-five students enrolled in a preschool teacher education program at a Swedish university were followed throughout their teacher education. The study used a phenomenographic approach within a theoretical framework of sociocultural and situated learning perspective. Questionnaires with open and closed questions were combined with interviews. The results show that in spite of growing competence and confidence, many of the students still found science activities to be awkward in preschool, mainly due to a wish to protect the children from school culture. The results have implications for teacher education and the preschool community, showing a need to problematize the purpose of teaching science in preschool and the meaning of pedagogical content knowledge in this context.

Emotions and values - a case study of meaning-making in ESE

Abstract With an interest in the role of emotions and values in students’ meaning-making in Environmental and Sustainability Education a case study was carried out in a Swedish school-class with students, 12 years of age. During a six-week thematic group-work focusing environmental and sustainability issues related to food, the students were observed and interviewed in their daily school practice. The results are presented here through narrative reporting, and analysed with the use of Dewey’s theoretical perspectives on experience, distinguishing three phases in a process: a start, an activity phase and a closure. Martha Nussbaum’s theory of emotions is used to assist in the understanding of emotions and values. The study reports on active and independent meaning-making processes in students’ group work. The results provide examples of students’ meaning-making experiences and the role of emotions and values in them, indicating that more of values are formed and expressed in the concluding phase.

Young students’ aesthetic experiences and meaning-making processes in an outdoor environmental school practice

ABSTRACT This study uses John Dewey’s theoretical concept of ‘aesthetic experience’ in empirically exploring expressions of cognition and emotion in students’ meaning-making processes. A case study was conducted in one class of Grade 6 students during a single school semester. This article reports results from five outdoor days. The empirical material consists of observations, field notes, logbook entries, interviews and students’ written reflections. The students’ meaning-making processes were analyzed through the Deweyan theory of an initial phase involving anticipation, an activity phase with courses of actions and a concluding phase with reflections that serve as fulfillments. Expressions of aesthetic experience were identified in four important components of the students’ meaning-making processes: prior personal experiences; responses to environments and artifacts; social interaction; and situations allowing for responsibility, trust and independence. A more in-depth process-oriented analysis revealed that aesthetic experiences are vital in continuous meaning-making processes.

Opportunities for and obstacles to science in preschools : views from a community perspective

ABSTRACT In this study, Activity Theory (AT) is used to analyse general patterns for how cultural and historical factors interact with the shaping of science activities in preschools. Data was produced from field notes, video observations, video stimulated recall group discussions and individual interviews with preschool teachers at fourteen preschool units, where science activities were described as a common feature of the practice. Two factors were found to be particularly important for how and whether science learning opportunities were afforded the children: the structure of the preschool community and the type of educational culture within it. In communities characterised by weak mutual commitment and without joint understanding of the purpose of the activities, the science learning objects of the activity often became fragmented and thereby elusive. This was also true for strong communities, with a shared approach and a joint understanding of the purpose of the science activities, but with educational cultures where science learning was not actively supported. In contrast, a strong community combined with an educational culture that allowed teachers to lead and intentionally frame the science content, offered child-centred science activities with clear science learning objects.

Utvikling av naturvitenskapelig talent og kreativitet - et nordisk perspektiv

De nordiske utdannings- og forskningsministre onsker a fremme kreativitet, innovasjon og entreprenorskap i utdannelsene. Dette var bakgrunnen for at ministrene i april 2009 besluttet ...