Chloroplasts of Arabidopsis fhaliana move in response to blue light. Sensitivity to light and the range of fluence rates to which the chloroplasts respond were found to be comparable to those of other higher plants studied. We investigated typical chloroplast distributions in Arabidopsis grown under three different light conditions: standard-light conditions, similar to natural light intensities; weaklight intensities, close to the compensation point of photosynthesis; and strong-light intensities, close to the saturation of the lightresponse curve of photosynthesis. We observed a striking difference in chloroplast arrangement in darkness between plants grown under weak-and strong-light conditions. There was a slight difference after weak-light pretreatment, and the arrangements of chloroplasts after strong-light pretreatment in both plant groups were very similar. These results support the ecological significance of chloroplast movements.Chloroplast movement is a phenomenon commonly observed throughout the plant kingdom (see reviews: Zurzycki, 1980; Haupt and Scheurelein, 1990;Wada et al., 1993). In most plants studied so far, the movement is controlled by a blue UV-absorbing system (Zurzycki, 1980; Galland and Senger, 1980). Only in a few cases are red light and phytochrome also involved: Mougeotia (Haupt, 1959), Adiantum (Yatsuhashi et al., 1985), and Mesotaenium (Haupt and Thiele, 1961). Chloroplast rearrangements in cells are induced and maintained by irradiation and depend on light direction, wavelength, and irradiance.There are two extreme chloroplast positions: (a) face position (low fluence rate arrangement), with chloroplasts at the cell walls perpendicular to light; and (b) profile position (high fluence rate arrangement), with chloroplasts at the walls parallel to light. In D, the chloroplasts are distributed either randomly around a11 of the cell walls, or their position depends on local factors inside the cell (Haupt and Scheuerlein, 1990). These three arrangements are typical of species with multichloroplast cells like Funaria, Lemna, and Tradescantia. There are some differences in chloroplast movement in plants with cells containing one large chloroplast (e.g. Hormidium, Mougeotia, and Mesotaenium) or for coenocytes (eg. Vaucheria) (see review: Schonbohm, 1980). Although movement patterns differ in their detail in various species, the common result of these patterns is greater exposure of chloroplasts to WL and reduced exposure under SL conditions.The conventional interpretation of the ecological role of chloroplast movements is that they result in optimizing light utilization in photosynthesis. However, little is actually known about the significance of chloroplast movements, and only a few studies have been devoted to this problem. Zurzycki (1955) was the first to ask if there was a correlation between the level of photosynthesis and chloroplast response. He carried out experiments on the green alga Mougeotia sp., the moss Funaria hygrometrica, and the duckweed Lemna trisulca, a11 of which hav...

A series of laboratory experiments was performed to determine the carbon stable isotopic composition of different combustion/pyrolysis (B/P) products. Variation in the δ13C values of the products was observed, up to 4‰. The differences in the carbon isotopic compositions of the B/P products were dependent on temperature, time and wood type. Comparison of the results for fresh and fossil oak wood suggested that the δ13C differences were the effect of selective decomposition of some wood components during the fossilization process. The temperature dependence of the carbon isotopic composition was linked to variation in the carbon isotopic composition of the main wood components, which each had different levels of thermal stability. Isotopes exchange reactions in between different products can be also considered as possible source of variation of δ13C on temperature. Both these hypotheses were supported by molecular simulations of cellulose and lignin B/P. The results confirm that B/P should be treated as a continuous process, where the results depend on the degree of process development. Natural burning processes are dynamic and burning conditions change rapidly and it is necessary to take care when using combustion products as a paleoenvironmental proxy or as an isotopic characteristic for the identification of source material.

Coal and hydrocarbons have been exploited from the Carboniferous rocks of the Midland Valley for over 200 years. This work characterises organic matter from the Mississippian black shales of the Midland Valley from Wardie, Scotland. Biomarker analysis allowed the estimation of the degree of microbial transformation of organic matter, type of kerogen and thermal maturity during hydrocarbon generation. Parameters based on the biomarker indicators confirm a generally mixed type II/III kerogen. However, some samples contain mostly terrestrial organic matter, whilst others contain predominantly marine organic matter, which shows that the sedimentary environment varied greatly throughout the basin. The presence of gammacerane suggests water column stratification and anoxic conditions. Organic matter was much better protected from postdepositional alteration within the concretions, where higher TOC (total organic carbon) and TS (total sulphur) contents occur, than in the surrounding sediments. This can be induced by very early diagenetic formation of these concretions which protected organic matter from late diagenetic degradation.Estimated values of vitrinite reflectance (Rc, Rcs) show that the sedimentary rocks reached the catagenesis stage. Most samples exhibit maximum organic matter maturation temperatures of around c60-90 C. However, stable isomers of phenyldibenzo [b,d ]thiophene detected in some samples indicate that in some cases post-depositional hydrothermal activity affected maturation of organic matter increasing temperatures to as high as c174 C.

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