Reaction centres: the structure and evolution of biological solar power

Reaction centres are complexes of pigment and protein that convert the electromagnetic energy of sunlight into chemical potential energy. They are found in plants, algae and a variety of bacterial species, and vary greatly in their composition and complexity. New structural information has highlighted features that are common to the different types of reaction centre and has provided insights into some of the key differences between reaction centres from different sources. New ideas have also emerged on how contemporary reaction centres might have evolved and on the possible origin of the first chlorophyll-protein complexes to harness the power of sunlight.     

Floristic variation and willow carr development within a southwest England wetland

Abstract. Woodland colonization on wetlands is considered to have a detrimental effect on their ecological value, even though detailed analysis of this process is lacking. This paper provides an evaluation of the ecological changes resulting from succession of poor fen (base‐poor mire) to willow wet woodland on Goss Moor NNR in Cornwall, UK. Different ages of willow carr were associated with eight understorey communities. During willow colonization, in the ground flora, there was a progressive decrease in poor fen species and an associated increase in woodland species, which appeared to be related to an increase in canopy cover and therefore shade. The most diverse community was found to be the most recent willow and was dominated by poor fen species. The oldest willow was the second most diverse and was associated with a reduction in poor fen species and an increase in woodland species. Architectural features were used successfully to assess the general condition and structure of willow. Tree height and DBH were identified as useful parameters to accurately assess willow age in the field. The implications of active intervention to remove willow in order to conserve the full range of communities within the hydrosere are discussed.     

Efficacy of tricyclic drugs in treating child and adolescent depression: a meta-analysis.

OBJECTIVE--To examine whether tricyclic antidepressants are superior to placebo in the treatment of child and adolescent depression. DESIGN--Meta-analysis of 12 randomised controlled trials comparing the efficacy of tricyclic antidepressants with placebo in depressed subjects aged 6-18 years. MAIN OUTCOME MEASURES--Most studies employed several depression rating scales. For each study the "best available" measure was chosen by using objective criteria, and individual and pooled effect sizes were calculated as the number of standard deviations by which the change scores for the treatment groups exceeded those for the control groups. Where authors had reported numbers "responding" to treatment we calculated individual and pooled ratios for the odds of improvement in treated compared with control subjects. RESULTS--From the six studies presenting data which enabled an estimation of effect size the pooled effect size was 0.35 standard deviations (95% confidence interval of -0.16 to 0.86) indicating no significant benefit of treatment. From the five studies presenting data on the number of "responders" in each group, the ratio of the odds of a response in the treated compared with the control subjects was calculated and the pooled odds ratio was 1.08 (95% confidence interval of 0.53 to 2.17); again indicating no significant benefit of treatment. The pooled sample had more than an 80% chance of detecting a treatment effect of 0.5 standard deviations or greater. There was an inverse relation between study quality and estimated treatment effect. CONCLUSIONS--Tricyclic antidepressants appear to be no more effective than placebo in the treatment of depression in children and adolescents.     

Studies on the assembly of the rat lens capsule. Biosynthesis of a cross-linked collagenous component of high molecular weight.

1. Intact rat lenses in tissue culture synthesize hydroxy[3H]proline-containing polypeptides of apparent mol.wt. approx. 180000, which become assembled into aggregates of higher molecular weight with time. 2. Both the 180000-mol.wt. species and the aggregates are components of the deoxycholate-insoluble base-membrane matrix. 3. Formation of the high-molecular-weight aggregate is accompanied by the biosynthesis of the reducible hydroxylysine-derived cross-link hydroxylysino-5-oxo-norleucine. 4. Hydroxylysino-5-oxonorleucine and dehydrohydroxylysinonorleucine are the major reducible cross-links present in intact foetal and 1-month-old calf lens capsules.     

Biosynthesis of sulphated macromolecules by rabbit lens epithelium. II. Relationship to basement membrane formation

Rabbit lens epithelial cells display a similar "cobblestone" morphology and produce the same complement of sulphated macromolecules (also see Heathcote, J.G., and R.W. Orkin, 1984, J. Cell Biol., 99:852-860) whether grown on plastic or glass, dried films of gelatin or type IV collagen with laminin, or on gels of type I collagen. There was no evidence of basement membrane formation by these cells when they were grown on plastic, glass, or dried films. In contrast, cultures that had been grown on gels deposited a discrete basement membrane that followed the contours of the basal surfaces of the cells and in addition, they secreted amorphous basement membrane-like material that diffused into the interstices of the gel and associated with the collagen fibrils of the gel. A significant proportion (approximately 70%) of the heparan sulphate proteoglycan fraction that was secreted into the culture medium (fraction MI) when the cells were grown on plastic became associated with the cell-gel layer in the gel cultures. Further, when basement membrane was isolated by detergent extraction, greater than 90% of the 35S-labeled material present was in this heparan sulphate proteoglycan.     

Gravitropic responses of the Avena coleoptile in space and on clinostats. IV. The clinostat as a substitute for space experiments

Gravitropic responses of dark grown oat coleoptiles were measured in weightlessness and under clinorotation on earth. The tests in microgravity were conducted in Spacelab during the IML-1 mission and those on clinostats were conducted in laboratories on earth. The same apparatus was used for both kinds of tests. In both cases autotropism and gravitropic responsiveness were determined. This allowed a quantitative comparison between the plants' responses after receiving the same tropistic stimulations either in weightlessness or on clinostats.
Autotropism was observed with oat coleoptiles responding in weightlessness but it did not occur on clinostats. Gravitropic responsiveness was measured as the ratio between the incremental bending response (degrees curvature) and the corresponding incremental g-dose (stimulus intensity times duration for which it was applied). Plants were tested at either of two stages of coleoptile development (i.e. different coleoptile lengths). From a total of six different kinds of critical comparisons that could be made from our tests that provided data for clinorotated vs weightless plants, three showed no significant difference between responses in simulated vs authentic weightlessness. Three other comparisons showed highly significant differences. Therefore, the validity of clinorotation as a general substitute for space flight was not supported by these results.