How do changes in temperature during growth affect leaf pigment composition and photosynthesis in Zea mays genotypes differing in sensitivity to low temperature?

The changes in photosynthetic activity and composition of pigments induced by changes in temperature were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of maize (Zea mays L.). The plants were grown under a controlled environment at a photon flux density of 550 µmol m−2 s−1, a 12 h photoperiod and at a suboptimal temperature of 14/12°C (day/night) until the full expansion of the third leaf. After this treatment, the chilling-tolerant genotypes, when compared with the sensitive ones, displayed a higher photosynthetic activity, a higher content of chlorophyll (Chl) a + b, a higher Chl a/b ratio, a larger total carotenoid pool size as well as a different carotenoid composition. When temperature was subsequently increased to 24/22°C for 3 d the composition of the pigments changed, but the chilling-sensitive genotypes, while adjusting their lower Chl a/b ratio and their different carotenoid composition, were unable to adjust their lower content of chlorophyll, their smaller total carotenoid pool size or their lower photosynthetic performance. Moreover, while the chilling-tolerant genotypes converted the most part of zeaxanthin to violaxanthin in the xanthophyll cycle, the chilling-sensitive genotypes retained high amounts of zeaxanthin. The changes in pigment composition that occurred over the 3 d at 24/22°C were largely conserved when the plants were returned to 14/12°C, but photosynthetic activity decreased and zeaxanthin accumulated again. The results suggest that the capability of the chilling-tolerant genotypes, when compared with the sensitive ones, to retain high amounts of pigments and to form a competent photosynthetic apparatus at low temperature is the basis for their more vigorous growth in cool climate

Effects of anaerobiosis as probed by the polyphasic chlorophyll a fluorescence rise kinetic in pea (Pisum sativum L.)

We analysed the changes of the chlorophyll (Chl) a fluorescence rise kinetic (from 50 μs to 1 s) that occur when leaves or chloroplasts of pea ( Pisum sativum L.) are incubated under anaerobic conditions in the dark. In control leaves, Chl a fluorescence followed a typical O-J-I-P polyphasic rise [Strasser et al. (1995) Photochem Photobiol 61: 32-42]. Anaerobiosis modified the shape of the transient with the main effect being a time-dependent increase in the fluorescence yield at the J-step (2 ms). Upon prolongation of the anaerobic treatment (> 60 min), the O-J-I-P fluorescence rise was eventually transformed to an O-J (J = P) rise. A similar transformation was observed when pea leaves were treated with DCMU or sodium dithionite. Anaerobiosis resulted in a 10-20% reduction in the maximum quantum yield of the primary photochemistry of Photosystem II, as measured by the ratio of the maximal values of variable and total fluorescence (FV/FM). When the leaves were returned to the air in the dark, the shape of the fluorescence transient showed a time-dependent recovery from the anaerobiosis-induced change. The original O-J-I-P shape could also be restored by illuminating the anaerobically treated samples with far-red light but not with blue or white light. Osmotically broken chloroplasts displayed under anaerobic conditions fluorescence transients similar to those observed in anaerobically treated leaves, but only when they were incubated in a medium comprising reduced pyridine nucleotides (NADPH or NADH). As in intact leaves, illumination of the anaerobically treated chloroplasts by far-red light restored the original O-J-I-P transient, although only in the presence of methyl viologen. The results provide additional evidence for the existence of a chlororespiratory pathway in higher plant cells. Furthermore, they suggest that the J-level of the fluorescence transient is strongly determined by the redox state of the electron carriers at the PS II acceptor sid

Personality traits and psychopathology over the course of six months of outpatient psychotherapy : a prospective observational study

There is a lack of prospective studies that test pre-specified hypotheses on the role of personality traits in outpatient psychotherapy. A total of 47 patients with a broad range of psychopathological syndromes were enrolled in a prospective 6-month observational study conducted in Zurich, Switzerland. We found evidence for remarkably high differential stability in all Big Five personality traits during the first 6 months of psychotherapy. Mean-level stability was very high in agreeableness and conscientiousness, while modest changes were observed in neuroticism, extraversion and openness. Baseline scores in neuroticism and conscientiousness at the beginning of therapy predicted modest change in self-reported severity of psychopathology over 6 months, but no effect was found in association with therapist-rated functional deficits. We conclude that personality trait levels may change slightly over the course of 6 months of psychotherapy and that both neuroticism and conscientiousness may have weak associations with the self-perceived improvement in psychopathology

Mercury inhibits the non-photochemical reduction of plastoquinone by exogenous NADPH and NADH: evidence from measurements of the polyphasic chlorophyll a fluorescence rise in spinach chloroplasts

Chlorophyll a fluorescence rise kinetics (from 50 μs to 1 s) were used to investigate the non-photochemical reduction of the plastoquinone (PQ) pool in osmotically broken spinach chloroplasts (Spinacia oleracea L.). Incubation of the chloroplasts in the presence of exogenous NADPH or NADH resulted in significant changes in the shape of the fluorescence transient reflecting an NAD(P)H-dependent accumulation of reduced PQ in the dark, with an extent depending on the concentration of NAD(P)H and the availability of oxygen; the dark reduction of the PQ pool was saturated at lower NAD(P)H concentrations and reached a higher level when the incubation took place under anaerobic conditions than when it occurred under aerobic conditions. Under both conditions NADPH was more effective than NADH in reducing PQ, however only at sub-saturating concentrations. Neither antimycin A nor rotenone were found to alter the effect of NAD(P)H. The addition of mercury chloride to the chloroplast suspension decreased the NAD(P)H-dependent dark reduction of the PQ pool, with the full inhibition requiring higher mercury concentrations under anaerobic than under aerobic conditions. This is the first time that this inhibitory role of mercury is reported for higher plants. The results demonstrate that in the dark the redox state of the PQ pool is regulated by the reduction of PQ via a mercury-sensitive NAD(P)H-PQ oxidoreductase and the reoxidation of reduced PQ by an O2-dependent pathway, thus providing additional evidence for the existence of a chlororespiratory electron transport chain in higher plant chloroplast

The Role of Dyadic Teacher-Student Relationships for Primary School Teachers' Well-Being.

Teacher well-being is not only relevant for the effectiveness of individual teaching and student learning but also for general school quality and societal functioning, because teacher well-being is related to lower burnout risks and lower attrition. Previous research identified social relationships in school as a crucial source of teacher well-being. However, studies investigating the role of teacher-student relationships as a determining factor for teacher well-being are still scarce. This study takes a qualitative approach toward investigating the role of dyadic teacher-student relationships in teacher well-being. We analyzed twenty-six semi-structured interviews with Swiss primary school teachers, using a qualitative content analysis. The results showed that dyadic teacher-student relationships played an important to a very important role in the everyday life of teachers and were a source of both positive and negative emotions, cognitions, and physical sensations. The quality of the dyadic teacher-student relationship was reflected in the social-emotional competence of both teachers and students. Conflicts were not necessarily inhibiting teacher well-being. The findings of this study can be used to inform teacher-training institutions, as well as authorities, on how to support teachers in building relationships with their students and, in turn, foster their well-being

Cycling in the era of Covid-19: The effects of the pandemic and pop-up bike lanes on cycling practices

This paper addresses the effects of the pandemic and of Covid pop-up cycle lanes on cycling. A questionnaire survey was carried out in Geneva and Lausanne, Switzerland. The pandemic has strengthened the attractiveness of cycling both as a mode of transport and as a recreational activity, showing its resilience in a time of crisis. Covid cycle lanes implemented after the first lockdown have improved traffic conditions for cycling in terms of safety, directness and the overall experience. Beyond the recruitment of new cyclists, an effect of consolidating existing practices is observed through, for example, their extension to additional routes and motives. These pop-up cycle lanes have, however, been politically contested, and their reception varies in the population, depending mainly on mobility habits and political position. As both cities aim to increase their modal share of cycling, the challenge is to capitalize on the recent development of cycling, to provide suitable infrastructures, but also to find ways to deal with the controversies and to legitimate cycling as a fully-fledged means of transport