Autotrophe photoautotrophe

Prokaryotes Autotrophs Chemoautotrophs Photoautotrophs Aerobes Energy from energised minerals Energy from oxidised sources, Fe3+, S()42, NO s Energy from light, Mg, Mn Tolerate and use 02 from moderate to high atmospheric levels Use of Mg2+, Fe2+, Mo(W)... 

Fig. 5. Influence of DCMU concentration on elongation rate of growing points of photo-autotrophic pak-bung hairy roots The hairy roots were cultivated in the sucrose-free medium using Petri dishes illuminated at 1= 11 W nr2, o photoautotrophic hairy roots, A heterotro-phic hairy roots...

Autotrophic microorganisms synthesize organic substances from carbon dioxide through a process known as carbon dioxide fixation. They are important in nature because carbon dioxide fixation works as a precursor for the organic substrates that form the basis of the food chain for other organisms. Autotrophic bacteria include those that obtain their energy from light (photoautotrophs) and those that obtain it from the oxidation of chemical bonds (chemoau-totrophs). 

As one component of the decade-long VERTEX program, an oceanic time-series station (33°N, 139°W) was occupied for an 18-month period from October 1986 to May 1988. During this observation period, the site was visited on 7 occasions ( 90-day interval) for approximately 1 week per expedition to retrieve and redeploy a free-drifting sediment trap array, to collect water samples and to conduct experiments relevant to C- and N-cycle processes (Harrison et al., 1992 Knauer et al., 1990). The uptake and assimilation of NOa and NH4 substrates were measured during incubation experiments that were designed to assess, and correct for, isotope dilution of the added tracers. Photoautotrophic N assimilation was measured using the into protein method, described later in this section. Measurements were also made of the concentrations of NOs , NH4, DON, PON, total microbial biomass, autotrophic biomass, heterotrophic biomass, primary productivity and the export of particulate matter (Harrison et al, 1992). In many ways this was, at that time, the most comprehensive study of the marine N-cycle ever conducted in the North Pacific trades biome. 

The most abundant autotrophs on Earth are, not surprisingly, oxygenic photoautotrophs, as there is almost an unlimited amount of energy available to support the carbon fixation and biosynthesis, and a limitless supply of the electron donor, water. In contrast, lithotrophs are limited both by the fact that the free energy available from the energy-yielding reactions is small, and the availability of the reduced species is often limited and confined to anaerobic (subsurface) environments. Thus, both lithotrophs and anoxygenic phototrophs are often confined to areas isolated from the oxic atmosphere, where their electron donors are stable and available. 

The synthesis of reduced (i.e., organic) carbon and the oxidized form of the electron donor permits a photo autotroph to use respiratory metabolism, but operate them in reverse. However, not all of the reduced carbon and oxidants remain accessible to the photoautotrophs. In the oceans, cells tend to sink, carrying with them organic carbon. The oxidation of Fe forms insoluble Fe " " salts that precipitate. The sedimentation and subsequent burial of organic carbon and Fe ... 

When we subtract the costs of all other metabolic processes by the chemoautotrophs and photoautotrophs, the organic carbon that remains is available for the growth and metabolic costs of heterotrophs. This remaining carbon is called net primary production (NPP) (Lindeman, 1942). From biogeochemical and ecological perspectives, NPP provides an upper bound for all other metabolic demands in an ecosystem. If NPP is greater than all respiratory consumption of the ecosystem, the ecosystem is said to be net autotrophic. Conversely, if NPP is less than all respiratory consumption, the system must either import organic matter from outside its bounds, or it will slowly mn down—it is net heterotrophic. 

Organisms that use CO2 as the principal carbon source are defined as autotrophic organisms that use organic compounds as the principal carbon source are defined as heterotrophic. A combination ofthese two criteria leads to the establishment of four principal categories (i) photoautotrophic, (ii) photoheterotrophic, (Hi) chemoautotrophic and (iv) chemoheterotrophic organisms. 

In the plant, the enzymes of the vindoline pathway, DAT (236,247) and NMT (242), are only found in the aerial parts, and in particular the leaves, the site of vindoline biosynthesis. In C. roseus cell cultures these enzymes cannot be detected, either after elicitation or in photoautotrophic or hormone autotrophic cultures (242). However, two enzymes of the early steps of the vindoline pathway, TllH and 11-O-methyltransferase are also present in cell cultures although at lower levels than in the plant (241). In the plant, the highest TllH levels are found in young leaves, whereas it is absent in stems and old leaves. 

Yang C, Hua Q, Shimizu K Energetics and carbon metabolism during growth of microalgal cells under photoautotrophic, mixotrophic and cyclic fight-autotrophic/dark-heterotrophic conditions, Biochem EngJ 6 87—102, 2000. 

Most callus cultures excised from higher plants turn green under proper physico-chemical, nutritional and hormonal regimes. Some of these cultures are reported to have mixotrophic and autotrophic mode of nutrition(l-3). Photoautotrophic cell cultures provide a system for studying the physiological and biochemical aspects of photosynthesis at cellular level. There has been considerable speculation about the connection between "Kranz" anatomy and physiology of C. plants. 

Photoautotrophic plant cell cultures provide a useful material for studies on the metabolism and physiology of autotrophic cells and can also be Important for the knowledge of the metabolic pathways of the synthesis of natural products. 

Photoautotroph An autotroph that obtains energy from light. 

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