Chlorophyll species

Commercially available stable green metallo-chlorophyU colorants could be produced and in 1984 Segner et al. patented the process to preserve the green color in canned vegetables under the Veri-Green trade name. Some years later, the formation and stability of these complexes were found to be dependent on the type of metal, pH, ionic concentration, temperature, and chlorophyll species — which could explain the unpredictable color changes observed in the beginning. ... 

The bleaching of P-700 upon illumination corresponds to the production of an oxidized species that has been proposed to be a chlorophyll a dimer. The same bleaching can be obtained by chemical oxidation and titrates with a midpoint potential of about 0.45 V [49,50). The total differential spectrum of P-700 photooxidation presents, in addition to a major band at about 700 nm, a minor band at 685 nm and another in the Soret region at 435 nm. This spectrum has been attributed to chlorophyll a [51], although the presence of a new chlorophyll species in P-700-enriched preparations has been claimed [52]. 

DR Klug, LB Giorgi, B Crystal, J Barber and G Porter (1989) Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer. Photosynthesis Res 22 277-284... 

The first steps of the plant photosystem I (PSI) primary reactions are believed to be P q AqA —hiL i p AqA P qqAqAj P700 and Aq are chlorophyll species and Aj is a quinone-like molecule. (1) The initial suggestions that Aq and A act as electron acceptors in sequence prior to the acceptor X were based on EPR experiments which showed that two electron acceptors are photoaccumulated at low redox potential. (2,3) Support for this suggestion came from following the triplet state found in PSI as a function of the photoaccumulation of the proposed Aq and A, and interpretations of the transient electron spin polarized (esp) signal believed to be due to PyqqAJ which has been observed by time resolved EPR experiments. 

The data in fig.l ( ) indicate that transfer to PSII RCs is a function of the absorption wavelength, with maximal transfer occurring from antenna absorbing around 683nm. To analyse energy transfer to RCs in terms of the spectroscopic chlorophyll species, the Fv/Fo values have been related to the fractional absorptance of each chi form (fig.2). By appropriate selection of Fv/Fo intervals (the three areas indicated by the broken lines), it is possible to establish the following indipendent sequences of energy transfer efficiency to RCs ... 

In the context of the "antitrap" model It Is Interesting to note that chib In PSII antenna displays a Qy transition dipole strength weaker than that of chla (10), In analogy with the situation In organic solvents (19). This low Qy absorption "efficiency", difficult to understand In terms of the light harvesting economy, can be rationalised by the "antitrap" hypothesis. In this case the low chib Qy transition dipole strength would considerably enhance the "antitrap" properties of this chlorophyll species. 

The presented data, however, cannot exclude that the chlorine enters the molecule during extraction when the natural surroundings of the chromophores are destroyed. Neveirtheless Chi RC I must then derive from another chlorophyll species than the bulk Chi a, as it could be shown that increasing amounts of Chi a being present during extraction did not increase the isolated Chi RC I amount. The amount depended only on the type of organism or particle used for the determination. Thus we conclude that Chi RC I can on the one hand be present in vivo in the proposed structural form or on the other hand is an isolation artefact v ich derives from an vivo very reactive Chi species in the reaction centre of PS I. 

In this way, the near-linear chlorophyll-phosphorus relationship in lakes depends upon the outcome of a large number of interactive processes occurring in each one of the component systems in the model. One of the most intriguing aspects of those components is that the chlorophyll models do not need to take account of the species composition of the phytoplankton in which chlorophyll is a constituent. The development of blooms of potentially toxic cyanobacteria is associated with eutrophication and phosphorus concentration, yet it is not apparent that the yield of cyanobacterial biomass requires any more mass-specific contribution from phosphorus. The explanation for this paradox is not well understood, but it is extremely important to understand that it is a matter of dynamics. The bloom-forming cyanobacteria are among the slowest-growing and most light-sensitive members of the phytoplankton. ... 

Fungi Simple vegetative bodies from which reproductive structures are elaborated. The fungi contain no chlorophyll and therefore require sources of complex organic molecules. Many species grow on dead organic materials and others live as parasites. 

Although /3-oxidation is universally important, there are some instances in which it cannot operate effectively. For example, branched-chain fatty acids with alkyl branches at odd-numbered carbons are not effective substrates for /3-oxidation. For such species, a-oxidation is a useful alternative. Consider phy-tol, a breakdown product of chlorophyll that occurs in the fat of ruminant animals such as sheep and cows and also in dairy products. Ruminants oxidize phytol to phytanic acid, and digestion of phytanic acid in dairy products is thus an important dietary consideration for humans. The methyl group at C-3 will block /3-oxidation, but, as shown in Figure 24.26, phytanic acid a-hydroxylase places an —OFI group at the a-carbon, and phytanic acid a-oxidase decar-boxylates it to yield pristanie add. The CoA ester of this metabolite can undergo /3-oxidation in the normal manner. The terminal product, isobutyryl-CoA, can be sent into the TCA cycle by conversion to succinyl-CoA. 

Measured end points are photosynthesis as the incorporation of radiolabelled H C03 ( C) and bacterial activity as the incorporation of radiolabelled thymidine (thym) fluorometric measurements basal fluorescence (Fo) and photon yield (Y) chlorophyll-a concentration (chl-a) species composition (spp) and the biovolume of algae obtained after algal counting (biovolume)... 

In a similar way, microalgal biomass on the sediment surface can be estimated by measuring the chlorophyll contents in benthic microalgae, which are single-celled microscopic plants that inhabit the top 0 to 3 cm of a sediment surface and are sometimes referred to as microphytobenthos. These organisms are the primary food resources of benthic grazers such as shellfish and numerous finfish species. 

As can be seen in these reactions, carotenoids may protect photosynthetic bacteria at various levels by quenching the singlet-excited state of O2 or the tiiplet-excited state of chlorophyll. The ground states of oxygen would be 3O2 and for CHL the triplet state. The carotenoids may be the preferred substrates for oxidation or may act in quenching reactive species. ... 

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