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1.
《Aquatic Botany》2005,82(4):269-283
Seeds from mature fruits of the Mediterranean seagrass Posidonia oceanica deposited in the intertidal zone by sea surface currents revealed an advanced state of embryo development. The fruit dehisces by three longitudinal openings, which originate from the base or point of fruit attachment. Within the fruit the seed is positioned with its radical end at the fruit base, and the apical or plumular end protected until the seed is completely released. Structural observations of the collected mature seeds suggest the possible onset of germination. The mature seed is characterized by an enlarged hypocotyl with abundant starch reserves, a well-defined vascular system with a predominant central vascular strand to mobilize those reserves, a well-developed plumule, and root system initials, which will assure anchorage to the sea floor. Thus, within the dispersal unit, the future plant organs and growing points are well established and the carbohydrate-rich endosperm will assure the availability of sufficient nutrient supplies for short-term development of the seedling.  相似文献   

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The accumulation is described of N, P, K, S, Ca, Mg, Na, Fe,Zn, Mn and Cu in the developing pericarp and seed of two speciesof seagrass. Both species showed essentially the same patterns,which resemble those of herbaceous terrestrial plants. Therewas a close relation between dry matter and nutrient accumulation.N, P, K, Fe, Zn, Mn and Cu accumulated in the fruit againstlarge concentration gradients, with discrimination against Na.Seeds accumulated N, P and trace elements to a greater extentthan pericarps and other plant parts; P was apparently retrievedfrom pericarps to a greater extent than other elements. Calculationswere made of the losses of these elements from seagrass meadowsin shed fruits. Posidonia spp., seagrass, nutrient accumulation in fruits  相似文献   

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C4 photosynthesis is nature’s most efficient answer to the dual activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the resulting loss of CO2 by photorespiration. Gly decarboxylase (GDC) is the key component of photorespiratory CO2 release in plants and is active in all photosynthetic tissues of C3 plants, but only in the bundle sheath cells of C4 plants. The restriction of GDC to the bundle sheath is assumed to be an essential and early step in the evolution of C4 photosynthesis, leading to a photorespiratory CO2 concentrating mechanism. In this study, we analyzed how the P-protein of GDC (GLDP) became restricted to the bundle sheath during the transition from C3 to C4 photosynthesis in the genus Flaveria. We found that C3 Flaveria species already contain a bundle sheath–expressed GLDP gene in addition to a ubiquitously expressed second gene, which became a pseudogene in C4 Flaveria species. Analyses of C3-C4 intermediate Flaveria species revealed that the photorespiratory CO2 pump was not established in one single step, but gradually. The knowledge gained by this study sheds light on the early steps in C4 evolution.  相似文献   

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Photosynthesis is an ancient process on Earth. Chemical evidence and recent fossil finds indicate that cyanobacteria existed 2.5-2.6 billion years (Ga) ago, and these were certainly preceded by a variety of forms of anoxygenic photosynthetic bacteria. Carbon isotope data suggest autotrophic carbon fixation was taking place at least a billion years earlier. However, the nature of the earliest photosynthetic organisms is not well understood. The major elements of the photosynthetic apparatus are the reaction centers, antenna complexes, electron transfer complexes and carbon fixation machinery. These parts almost certainly have not had the same evolutionary history in all organisms, so that the photosynthetic apparatus is best viewed as a mosaic made up of a number of substructures each with its own unique evolutionary history. There are two schools of thought concerning the origin of reaction centers and photosynthesis. One school pictures the evolution of reaction centers beginning in the prebiotic phase while the other school sees reaction centers evolving later from cytochrome b in bacteria. Two models have been put forth for the subsequent evolution of reaction centers in proteobacteria, green filamentous (non-sulfur) bacteria, cyanobacteria, heliobacteria and green sulfur bacteria. In the selective loss model the most recent common ancestor of all subsequent photosynthetic systems is postulated to have contained both RC1 and RC2. The evolution of reaction centers in proteobacteria and green filamentous bacteria resulted from the loss of RC1, while the evolution of reaction centers in heliobacteria and green sulfur bacteria resulted from the loss of RC2. Both RC1 and RC2 were retained in the cyanobacteria. In the fusion model the most recent common ancestor is postulated to have given rise to two lines, one containing RC1 and the other containing RC2. The RC1 line gave rise to the reaction centers of heliobacteria and green sulfur bacteria, and the RC2 line led to the reaction centers of proteobacteria and green filamentous bacteria. The two reaction centers of cyanobacteria were the result of a genetic fusion of an organism containing RC1 and an organism containing RC2. The evolutionary histories of the various classes of antenna/light-harvesting complexes appear to be completely independent. The transition from anoxygenic to oxygenic photosynthesis took place when the cyanobacteria learned how to use water as an electron donor for carbon dioxide reduction. Before that time hydrogen peroxide may have served as a transitional donor, and before that, ferrous iron may have been the original source of reducing power.  相似文献   

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Abel KM 《Plant physiology》1984,76(3):776-781
Photosynthetic carbon uptake of the tropical seagrass Thalassia hemprichii (Ehrenb.) Aschers was studied by several methods. Photosynthesis in buffered seawater in media in the range of pH 6 to pH 9 showed an exponentially increasing rate with decreasing pH, thus indicating that free CO2 was a photosynthetic substrate. However, these experiments were unable to determine whether photosynthesis at alkaline pH also contained some component due to HCO3 uptake. This aspect was further investigated by studying photosynthetic rates in a number of media of varying pH (7.8-8.61) and total inorganic carbon (0.75-13.17 millimolar). In these media, photosynthetic rate was correlated with free CO2 concentration and was independent of the HCO3 concentration in the medium. Short time-course experiments were conducted during equilibration of free CO2 and HCO3 after injection of 14C labeled solution at acid or alkaline pH. High initial photosynthetic rates were observed when acidic solutions (largely free CO2) were used but not with alkaline solutions. The concentration of free CO2 was found to be a limiting factor for photosynthesis in this plant.  相似文献   

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Abstract: Three Coffea species (C. arabica cv. Icatu, C. canephora cv. Apoatã and C. dewevrei) were tested in order to identify and study the mechanisms of tolerance to low, non‐freezing temperatures. Several photosynthesis‐related parameters were monitored during a 20‐day period of gradual temperature decrease, from 25/20 °C (day/night) down to 15/10 °C, during chilling treatments (15/4 °C), and upon rewarming (25/20 °C). Differences were found among species, both during low temperature exposure and during rewarming. In general, Coffea species showed cold‐induced photoinhibition of photosynthesis, which was attributable to biochemical (in vivo ribulose‐1,5‐bisphosphate carboxylase/oxygenase activity and carbohydrate synthesis) and biophysical (antennae functioning, photosystem II efficiency and linear electron transport) inactivation, rather than to stomatal constraints. The moderately low temperature of 15/10 °C was enough to cause a negative impact on net photosynthesis (A), mostly due to low (initial) rubisco activity in all species. However, C. arabica cv. Icatu showed a higher tolerance to chilling and recovered quickly and completely upon rewarming, as assessed from the impacts on the photosynthetic machinery (e.g. Amax, Fo, Fv/Fm, Fv′/Fm′, qP, ?e, rubisco activity) and on carbohydrate metabolism. Such lesser effects are likely to be related to the strong increases and higher contents of zeaxanthin, lutein and β‐carotene that presumably increased the ability to dissipate excitation energy and contributed to protect the photosynthetic apparatus. During cold exposure, a significant reduction of the α/β carotene ratio, which is considered an acclimation feature, was observed solely in C. arabica cv. Icatu. However, C. canephora cv. Apoatã and, especially, C. dewevrei showed to be highly cold‐sensitive. In these latter species, the photoinhibitory impairments to photosynthesis were stronger, probably due to the lower contents of protecting pigments during chilling conditions that lead to a higher vulnerability to excess excitation energy. Moreover, the mesophyll impairments (e.g. Amax, Fv/Fm, ?e) became significant even at moderately low temperatures of 15/10 °C, and a lower ability to recover after chilling exposure was observed. The limitation of in vivo rubisco activity and Amax may have been due to substrate limitation, but disturbances in sugar metabolism could also play an important role in the expression of chilling sensitivity in C. canephora cv. Apoatã and C. dewevrei.  相似文献   

11.
五味子属种子形态及其分类学意义   总被引:4,自引:1,他引:4  
用光学显微镜及扫描电镜对五味子属(Schisandra)10种96号样品的种子宏观形态和种皮的微观形态特征进行观察,首次对该属的种皮微观形态特征进行系统报道,并编排有分种检索表。研究结果表明:该属的种子宏观形态呈现平滑、细皱纹或瘤状突起,并认为五味子属种子形态可有从平滑到有细皱纹再到有瘤状突起的演化趋势;该属种皮表面微观形态可分为疣状突起型和网纹型。结合其它性状,本文认为网纹型所代表的两种植物应与本属中其它植物建立并列的分类单元。五味子属植物在种子形态特征上存在一定的差异,可为属以下、种以上的分类提供依据,并为探讨该属的系统演化提供有价值的参考资料。  相似文献   

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We investigated the impact of fish farm biodeposition on benthic bacteria, thraustochytrid protists, and heterotrophic protozoa (nanoflagellates and ciliates) in an oligotrophic area of the Mediterranean Sea. The fish farm impact was investigated both on a seagrass (Posidonia oceanica) bed and on soft bottom sediments. In both systems, sediment samples were collected with a multicontrol sampling strategy (i.e., beneath the fish farm and at three control sites per system). The uneaten food pellets supplied to the fish determined the accumulation of sediment organic matter and the enhancement of protein content in impacted sediments (both seagrass bed and soft sediments). In both systems, the abundance and biomass of heterotrophic protists increased significantly beneath the fish farm, but the structure of the protist assemblages responded differently in vegetated and unvegetated sediments. Thraustochytrid abundance increased significantly in impacted seagrass. These results provide evidence that the structure of protist assemblages respond significantly to fish farm biodeposition and indicate that the monitoring of these benthic components provides complementary information for the assessment of the fish farm impact on the benthic systems.  相似文献   

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槭属的系统演化与地理分布   总被引:20,自引:3,他引:20  
槭属(AcerL)属槭树科(Aceraceae),200种,分布于亚、欧、北美和非洲北缘。本文研究了槭属的系统演化、地理分布、起源与扩散。认为:(1)槭树科与无患子科关系密切,槭属是槭树科2属中较进化的类群。(2)在原始而典型的槭属植物的基础上,槭属沿花的各部减少,有的器官甚至向完全退化的方向演化,但也有少数向增加数目的方向特化。(3)讨论了槭属4亚属23组的演化趋势,并绘制出其系统演化图。(4)槭属起源于侏罗纪的中国四川东部、湖北、湖南及其邻近地区,并向西、东北和南方扩散而进入西亚、欧洲、非洲北缘、北美洲和马来半岛至印尼。  相似文献   

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Life History Evolution in the Genus Trillium   总被引:1,自引:0,他引:1  
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SDS-polyacrylamide gel electrophoresis of total seed extracts revealed the presence of legumin-like polypeptides ranging in molecular weight from 42 kD to 89 kD in Lathyrus sativus and L. odoratus. The polypeptides of higher mol wt were however, absent in L. aphaca. Vicilin-like polypepides of mol wt 76, 54, 36, 33, 31, 20 and 17 kD were seen in L. sativus and L. odoratus and of mol wt 72, 58, 54, 52, 36, 33 and 20 kD in L. aphaca. Analysis of various seed protein fractions of L. sativus revealed the presence of a large number of albumin polypeptides varyingin mol wt range from 12.5 to 95 kD, when as glutelin (mol wt 18 to 80 kD) and prolamin (mol wt 25.5 and 26 kD) fraction polypeptides were relatively fewer. On the basis of similarities in seed polypeptide profiles, L. sativus and L. odoratus seem to be closely related, whereas L. aphaca appears to be distantly related.  相似文献   

17.
Posidonia oceanica, a seagrass endemic to the Mediterranean forms extended and extremely persistent meadows. It is a clonal plant with an apparently irregular pattern of flowering events. An extensive bibliographic review allowed the reconstruction of past flowering events of this species around the Mediterranean, with a high degree of confidence for the last 30 years. The data series on annual flowering prevalence (FP, flowering records per total records) and flowering intensity (FI, fraction of flowering shoots) produced have been compared with four series on Sea Surface annual Temperature maxima (SSTmax) obtained for the NW Mediterranean (averaged from the local data series of l'Estartit and Villefranche: 1957–2005) and for the Eastern, Western basin and the whole Mediterranean sea (extracted from NCEP Reynolds interpolated SST maps: 1982–2005). Significant warming trends are detected in the Mediterranean SSTmax series, at a rate of (mean+SE) 0.04±0.01°C yr−1 (R2=0.24, P<0.01, N=24 years), in the Eastern basin series (0.06±0.01°C yr−1, R2=0.43, P<0.001, N=24 years) and in the long SSTmax series of the NW Mediterranean (0.02±0.01 C yr−1, R2=0.12, P<0.02, N=49 years). The magnitudes of the SSTmax anomalies around the absolute warming trend do not increase with time in any SSTmax series. Peaks of FP and FI in the Mediterranean seem to occur each 9–11 years, and coincide with peaks of annual SSTmax. Annual FP and FI increase with the residuals of annual SSTmax warming trend in all Mediterranean basins (FPMED: R2=0.27, P<0.01, N=23; FPNW: R2=0.34, P<0.01, N=31; FPE: R2=0.20; P<0.10, N=23). An outstanding event of P. oceanica flowering across the Mediterranean has been registered in Autumn 2003; 1 month after the highest annual SSTmax recorded in the series. The hypothesis of flowering induction by thermal stress as the possible cause of this relationship is discussed, as well as the potential use of P. oceanica flowering record as early indicator of biological change induced by global sea warming in Mediterranean marine ecosystems.  相似文献   

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ABSTRACT. Immunoblotting tests involving cytoskeletal protein arrays and fluorescence microscopical examinations of whole cells using monoclonal antibody 424A8 gave substantially different results in three evolutionary subgroups within the genus Tetrahymena. These responses are described and some implications of the evolutionary divergence indicated in this ciliated protozoan are discussed.  相似文献   

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