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41.
The amounts of protochlorophyllide (P650) and protohaem were measured in ageing dark-grown barley leaves. Maximum amounts of P650 and protohaem were found in 6- to 8-day-old material after which P650 declined rapidly and protohaem more slowly. In leaves exposed to light maximum chlorophyll was produced in 6-day-old material with progressively less the older the leaves. Haem concentrations increased in seedlings of all ages exposed to light. A lag phase was observed for both chlorophyll and haem formation in leaves given a light treatment. Haem, however, showed a slight yet sig nificant decline as chlorophyll production commenced. The results indicate that chlorophyll and haem synthesis share a common pool of δ-aminolae vulinic acid (ALA). At a certain stage of development, the magnesium porphyrin pathway diverts precursors away from haem synthesis. It is only when the ALA synthesising system is well developed that the production of ALA can satisfy pathways to both haem and chlorophyll. The observed changes in haem under certain conditions suggest that, as in animal systems, haem levels may regulate porphyrin formation (chlorophylls) by controlling the supply of ALA. 相似文献
42.
Barthélemy X Bouvier G Radunz A Docquier S Schmid GH Franck F 《Photosynthesis research》2000,64(1):63-76
The localization of protochorophyllide (Pchlide) and of NADPH-protochlorophyllide oxidoreductase (POR, EC 1.6.99.1) within
(etio)chloroplasts has been investigated at selected stages of greening of barley seedlings. Pchlide pigment and POR protein
contents were evaluated in different plastid membrane fractions by fluorescence spectroscopy and immunoblot analysis using
a monospecific polyclonal antibody raised against the purified enzyme. Fluorescence analysis showed the presence of Pchlide
in both the envelope and thylakoid membranes. During greening, the Pchlide content, expressed on a total protein basis, decreased
in thylakoid membranes, whereas it increased in the envelope membranes. POR proteins were detected mainly in thylakoid membranes
at early greening stages. In contrast, the weak amount of POR proteins was associated more specifically with envelope membranes
of mature chloroplasts. Whatever the greening stage, thylakoid-bound Pchlide and POR proteins were more abundant in the thylakoid
regions which remained unsolubilized after mild Triton treatment used as standard procedure to prepare PS II particles. This
suggests the preferential association of Pchlide and POR to the appressed regions of thylakoids.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
43.
B. Schoefs 《Photosynthetica》1999,36(4):481-496
Two different pathways for protochlorophyllide a (Pchlide) reduction in photosynthetic organisms have been proved: one is strictly light-dependent whereas the second is light-independent.
Both pathways occur in all photosynthetic cells except in angiosperms which form chlorophyll only through the light-dependent
pathway. Most cells belonging to Eubacteria (i.e., the anoxygenic photosynthetic bacteria) synthesize bacteriochlorophyll through the light-independent pathway. This review
deals with the physiological, biochemical, and molecular biological features of molecules involved in both pathways of Pchlide
reduction.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
44.
Jean-Marie Briantais 《Photosynthesis research》1994,40(3):287-294
Recently, it has been suggested (Horton et al. 1992) that aggregation of the light-harvesting a-b complex (LHC II) in vitro reflects the processes which occur in vivo during fluorescence induction and related to the major non-photochemical quenching (qE). Therefore the requirement of this chlorophyll a-b containing protein complex to produce qN was investigated by comparison of two barley mutants either lacking (chlorina f2) or depressed (chlorina104) in LHC II to the wild-type and pea leaves submitted to intermittent light (IL) and during their greening in continuous light. It was observed that qN was photoinduced in the absence of LHC II, i.e. in IL grown pea leaves and the barley mutants. Nevertheless, in these leaves qN had no (IL, peas) or little (barley mutants) inhibitory effect on the photochemical efficiency of QA reduction measured by flash dosage response curves of the chlorophyll fluorescence yield increase induced by a single turn-over flash During greening in continuous light of IL pea leaves, an inhibitory effect on QA photoreduction associated to qN developed as Photosystem II antenna size increased with LHC II synthesis. Utilizing data from the literature on connectivity between PS II units versus antenna size, the following hypothesis is put forward to explain the results summarized above. qN can occur in the core antenna or Reaction Center of a fraction of PS II units and these units will not exhibit variable fluorescence. Other PS II units are quenched indirectly through PS II-PS II exciton transfer which develops as the proportion of connected PS II units increases through LHC II synthesis. 相似文献
45.
David Verbyla 《Global Ecology and Biogeography》2008,17(4):547-555
Aim To examine the trends of 1982–2003 satellite‐derived normalized difference vegetation index (NDVI) values at several spatial scales within tundra and boreal forest areas of Alaska. Location Arctic and subarctic Alaska. Methods Annual maximum NDVI data from the twice monthly Global Inventory Modelling and Mapping Studies (GIMMS) NDVI 1982–2003 data set with 64‐km2 pixels were extracted from a spatial hierarchy including three large regions: ecoregion polygons within regions, ecozone polygons within boreal ecoregions and 100‐km climate station buffers. The 1982–2003 trends of mean annual maximum NDVI values within each area, and within individual pixels, were computed using simple linear regression. The relationship between NDVI and temperature and precipitation was investigated within climate station buffers. Results At the largest spatial scale of polar, boreal and maritime regions, the strongest trend was a negative trend in NDVI within the boreal region. At a finer scale of ecoregion polygons, there was a strong positive NDVI trend in cold arctic tundra areas, and a strong negative trend in interior boreal forest areas. Within boreal ecozone polygons, the weakest negative trends were from areas with a maritime climate or colder mountainous ecozones, while the strongest negative trends were from warmer basin ecozones. The trends from climate station buffers were similar to ecoregion trends, with no significant trends from Bering tundra buffers, significant increasing trends among arctic tundra buffers and significant decreasing trends among interior boreal forest buffers. The interannual variability of NDVI among the arctic tundra buffers was related to the previous summer warmth index. The spatial pattern of increasing tundra NDVI at the pixel level was related to the west‐to‐east spatial pattern in changing climate across arctic Alaska. There was no significant relationship between interannual NDVI and precipitation or temperature among the boreal forest buffers. The decreasing NDVI trend in interior boreal forests may be due to several factors including increased insect/disease infestations, reduced photosynthesis and a change in root/leaf carbon allocation in response to warmer and drier growing season climate. Main conclusions There was a contrast in trends of 1982–2003 annual maximum NDVI, with cold arctic tundra significantly increasing in NDVI and relatively warm and dry interior boreal forest areas consistently decreasing in NDVI. The annual maximum NDVI from arctic tundra areas was strongly related to a summer warmth index, while there were no significant relationships in boreal areas between annual maximum NDVI and precipitation or temperature. Annual maximum NDVI was not related to spring NDVI in either arctic tundra or boreal buffers. 相似文献
46.
Chaya Kalcheim 《Developmental neurobiology》2010,70(12):796-812
The dorsal neural tube first generates neural crest cells that exit the neural primordium following an epithelial‐to‐mesenchymal conversion to become sympathetic ganglia, Schwann cells, dorsal root sensory ganglia, and melanocytes of the skin. Following the end of crest emigration, the dorsal midline of the neural tube becomes the roof plate, a signaling center for the organization of dorsal neuronal cell types. Recent lineage analysis performed before the onset of crest delamination revealed that the dorsal tube is a highly dynamic region sequentially traversed by fate‐restricted crest progenitors. Furthermore, prospective roof plate cells were shown to originate ventral to presumptive crest and to progressively relocate dorsalward to occupy their definitive midline position following crest delamination. These data raise important questions regarding the mechanisms of cell emigration in relation to fate acquisition, and suggest the possibility that spatial and/or temporal information in the dorsal neural tube determines initial segregation of neural crest cells into their derivatives. In addition, they emphasize the need to address what controls the end of neural crest production and consequent roof plate formation, a fundamental issue for understanding the separation between central and peripheral lineages during development of the nervous system. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 70: 796–812, 2010. 相似文献
47.
Slow response of soil organic matter to the reduction in atmospheric nitrogen deposition in a Norway spruce forest 总被引:1,自引:0,他引:1
NICOLE DÖRR KLAUS KAISER ROBERT MIKUTTA GEORG GUGGENBERGER 《Global Change Biology》2010,16(11):2990-3003
Global nitrogen (N) deposition rates in terrestrial environments have quadrupled since preindustrial times, causing structural and functional changes of ecosystems. Different emission reduction policies were therefore devised. The aim of our study was to investigate if, and over what timescale, processes of soil organic matter (OM) transformation respond to a decline in atmospheric N deposition. A N‐saturated spruce forest (current N deposition: 34 kg ha?1 yr?1; critical N load: 14 kg ha?1 yr?1), where N deposition has been reduced to 11.5 kg ha?1 yr?1 since 1991, was studied. Besides organic C and organic and inorganic N, noncellulosic carbohydrates, amino sugars and amino acids were determined. A decline in organic N in litter indicated initial effects at plant level. However, there were no changes in biomarkers upon the reduction in N deposition. In addition, inorganic N was not affected by reduced N deposition. The results showed that OM cycling and transformation processes have not responded so far. It was concluded that no direct N deposition effects have occurred due to the large amount of stored organic N, which seems to compensate for the reduction in deposited N. Obviously, the time span of atmospheric N reduction (about 14.5 years) is too short compared with the mean turnover time of litter to cause indirect effects on the composition of organic C and N compounds. It is assumed that ecological processes, such as microbial decomposition or recycling of organic N and C, react slowly, but may start within the next decade with the incorporation of the new litter. 相似文献
48.
以广东省仁化至博罗高速公路(仁化至新丰段路)为例,通过对该路段沿线乡土植物调查,运用层次分析法(AHP)对388种乡土植物的环境适应性、培植特性、功能特性和经济效应进行评价和综合分析。结果表明,在一级指标中,环境适应性权重最大(0.5476);其次是功能特性(0.2051)。在选取的14个二级指标中, 耐贫瘠权重最大(0.1642),耐旱能力和耐寒性的权重相对也比较大,分别为0.1533、0.0916。根据AHP模型,对所调查的388种乡土植物进行评价,其中评分80分以上适宜高速公路绿化的有64种。结合观赏性、耐寒性评价和市场苗木供应情况最终筛选出20种乡土植物作为仁新高速沿线绿化的建议树种。 相似文献
49.
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