Formation Of Chl Research Articles

Adaptation processes in Halomicronema hongdechloris, an example of the light-induced optimization of the photosynthetic apparatus on hierarchical time scales.

Oxygenic photosynthesis in Halomicronema hongdechloris, one of a series of cyanobacteria producing red-shifted Chl f, is adapted to varying light conditions by a range of diverse processes acting over largely different time scales. Acclimation to far-red light (FRL) above 700 nm over several days is mirrored by reversible changes in the Chl f content. In several cyanobacteria that undergo FRL photoacclimation, Chl d and Chl f are directly involved in excitation energy transfer in the antenna system, form the primary donor in photosystem I (PSI), and are also involved in electron transfer within photosystem II (PSII), most probably at the ChlD1 position, with efficient charge transfer happening with comparable kinetics to reaction centers containing Chl a. In H. hongdechloris, the formation of Chl f under FRL comes along with slow adaptive proteomic shifts like the rebuilding of the D1 complex on the time scale of days. On shorter time scales, much faster adaptation mechanisms exist involving the phycobilisomes (PBSs), which mainly contain allophycocyanin upon adaptation to FRL. Short illumination with white, blue, or red light leads to reactive oxygen species-driven mobilization of the PBSs on the time scale of seconds, in effect recoupling the PBSs with Chl f-containing PSII to re-establish efficient excitation energy transfer within minutes. In summary, H. hongdechloris reorganizes PSII to act as a molecular heat pump lifting excited states from Chl f to Chl a on the picosecond time scale in combination with a light-driven PBS reorganization acting on the time scale of seconds to minutes depending on the actual light conditions. Thus, structure-function relationships in photosynthetic energy and electron transport in H. hongdechloris including long-term adaptation processes cover 10-12 to 106 seconds, i.e., 18 orders of magnitude in time.

Primary reaction intermediates of Type-I photosensitized lipid oxidation as revealed by time-resolved optical spectroscopies

Chlorophyll a (Chl a) as a lipophilic photosensitizer can induce biomembrane destruction via Type-II reaction involving singlet oxygen (1O2) as a primary initiator. Type-I oxidation by an excited-state photosensitizer reacting directly with lipid substrate also contributes but the primary intermediate remains to be verified experimentally. We have investigated the reaction dynamics initiated by Chl a-photosensitization involving oxygen and the -C=C- moieties of lipids in the membranes of small unilamellar vesicles (SUVs) prepared from phospholipids of different degree of unsaturation (0, 1 or 2). Under anaerobic condition, femtosecond time resolved absorption (fs-TA) combined with spectroelectrochemical spectroscopies validated the formation of Chl a− in subpicoseconds, and time resolved fluorescence spectroscopy revealed the rapid quenching of 1Chl a* with a rate constant of (28 ns)−1. These ultrafast processes, independent of oxygen, are ascribed to the electron transfer reaction from a -C=C- moiety to 1Chl a* as an initiation step of Type-I reaction. On longer timescales, ns-TA spectroscopy unraveled the drastic quenching of 3Chl a* by either -C=C- or O2, and the quenching by O2 was found to be 20 times more efficient. This together with the 1O2-luminesence analysis prove the involvement of both types of photosensitization. In addition, HPLC-MS spectroscopy confirmed the ketonic, the alcoholic and the core-aldehyde products of lipid oxidation. Moreover, the oxygen dependent partition between Type-I and Type-II reactions is discussed on a detailed kinetics basis, showing that the two mechanisms of lipid oxidation are equally important under an oxygen concentration of 1.3×10−5 M at room temperature.

Minor and trace element variations in chromite from the Songshugou dunites, North Qinling Orogen: Evidence for amphibolite-facies metamorphism

The Songshugou dunites are part of the ultramafic sequence of the Songshugou ophiolite within the Qinling Group metamorphic rocks, which are distributed in the northern part of the Shang–Dan Suture Zone (SDSZ) in central China. The dunites include lenses of coarse- and medium-grained dunite set in a fine-grained dunite host. Disseminated chromite within these dunites can be classified into three microstructural types: (1) partly altered chromite with primary cores surrounded by porous chromite rims; (2) porous chromite with abundant pores that are filled with chlorite; and (3) homogeneous chromite. The primary magmatic cores of the partly altered chromite (Chr) is depleted in Cr and enriched in Al and Mg. Porous chromite includes Cr-rich Chr and ferritchromite (Fe-Chr) that is enriched in Fe2+ but depleted in Al. Homogeneous chromite is mainly Cr-magnetite (Cr-Mag) that is enriched in Fe3+ and extremely depleted in Al. The primary Cr-poor chromite was gradually transformed to porous Cr-rich Chr and/or by Fe-Chr during metamorphism. Reaction of Cr-poor Chr with olivine (Ol) produces chlorite (Chl) and secondary Chr enriched in Cr and Fe2+. Mg and Al diffuse away from primary Chr, leaving a residual Al- and Mg-depleted, Cr-rich Chr and Fe-Chr. Porous Chr is enriched in Zn, Co, Mn, but depleted in Ga, Ni, and Sc, due to the fluid-assisted formation of Chl within the pores of porous chromite. Zn, Co, and Mn from the metamorphic fluids diffuse toward the cores of chromite. The elements Sc, Ti, V, and Ni diffuse from Cr-poor Chr core to Cr-mag rim with increasing Fe3+/(Fe3+ + Fe2+). Late precipitation of Cr-mag occurred under oxidizing and hydrous conditions. The infiltration of fluid produced non-porous Fe3+-rich Chr or Cr-mag along grain boundaries or fractures within chromite. These fluids further promoted the reordering of octahedral sites, enhancing higher mobilization and enrichment of Ga, Ni, Sc, V, and Ti. The infiltration of high oxygen fugacity fluids promoted diffusion of Ga, Ni, Sc, and Ti toward the rims, and diffusion of Zn, Co, and Mn toward the cores. All chromite grains from the Songshugou dunites have low Mg# [molar 100 × Mg/(Mg + Fe2+)] values, and high Cr# [molar 100 × Cr/(Cr + Al)] and Fe3+/(Cr + Al + Fe3+), similar to metamorphic chromite formed under amphibolite-facies conditions. The observed positive Zn–Co–Mn anomalies and negative Ga–Ni–Sc anomalies in chromite, and the crystallization of Chl, are fingerprints of amphibolite-facies metamorphism. The compositions of chromite, the inferred mineral assemblage in which it occurs, and mineral equilibria modeling of the assemblage all suggest amphibolite-facies metamorphic temperatures ranging from 600 °C to 700 °C.

How Does the β-ionone Effect the Spectra of Chlorophyll and the Excitation Energy Transfer in Solution

This paper presents the excitation spectra and fluorescence spectra of mixed solution containing chlorophyll a(Chla), chlorophyll b(Chlb) and β ionone of different concentration, investigates the spectral changes of Chla and Chlb caused by β ionone through optimizing the frontier orbital of Chl β ionone com pound, and calculates the energy transfer rate between Chla and Chlb by means of the fluorescence Gauss decomposition. The results show that the β ionone interacts with Chl mainly via the connection between the magnesium atom in Chl molecule and the carbonyl in β ionone molecule. The formation of Chl β ionone compound changes the charge distribution of Chl so greatly that it leads to the red shift of the excitation spec tra and blue shift of the fluorescence spectra of Chls. Also in the compound the electronic energy located on carbon double bond of β ionone can be transferred to Chl molecule by the Mg...O bond, which enhances the fluorescence intensity greatly. The calculation of the excitation energy transfer (EET) rate indicates that a small amount of β ionone can promote the EET between Chla and Chlb. DOI: 10.1134/S0030400X14100154 CONDENSED MATTER SPECTROSCOPY

CHLOROPHYLL b FORMATION IN DARKNESS AFTER PHOTOTRANSFORMATION OF PROTOCHLOROPHYLLIDE AND DURING A PERIOD OF INTERMITTENT LIGHT

ABSTRACT Chlorophyll (Chl) b formation in leaves of wheat (Triticum aestivum L. cv. Starke II Weibull) after a short light pulse was followed for 5 h in darkness. Prior to this the leaves were kept in darkness or in continuous far-red light. The far-red light used activated the phytochrome system but did not cause any phototransformation of the protochlorophyllide present. The Chl b/a ratio increased faster in dark-grown leaves than in far-red pretreated ones, i.e. Chl b formation was slower in the latter. Thus, continuous far-red light appears to counteract Chl b formation. When comparing 5- and 7-day-old leaves the Chl b formation was faster in the younger leaves during the first hours after phototransformation. Formation of Chl b in darkness continues for several hours after the initial photo transformation has taken place. Formation of Chl b in wheat in this phase does not seem to depend on the level of chlorophyllide (Chlide), as Chl b formation continues long after Chlide could be detected. Chl b fo...

PHEOPHYTIN FORMATION WITH SENESCENCE IN STORED JAPANESE BUNCHING ONION

18 The shelf life of Japanese bunching onion (Allium fistulosum L.; JBO genome 19 FF) leaves diminished with yellowing as a consequence of chlorophyll (Chl) degradation, 20 which seems to be the main factor in yellowing of stored JBO leaves. The aim of this 21 study was to investigate pheophytin (Phy) formation as a Chl derivative during Chl 22 degradation in stored JBO leaves. A series of alien monosomic addition lines (AMALs, 23 FF+1A to FF+8A) of JBO, with extra chromosomes from shallot (A. cepa L., 24 Aggregatum group; genome AA) was used as supportive materials to study the 25 formation of Chl a derivatives and the activity of Chl-degrading enzymes during 26 storage. Chl contents in FF+3A and FF+5A decreased greatly during storage at 25°C, 27 whereas in FF+4A the reduction in Chl content was the lowest compared to the control, 28 FF. In JBO leaves, during Chl degradation, the presence of Phy a was prominent as Chl 29 derivatives, which was not recorded in other horticultural crops. Moreover, the 30 activities of Chl-degrading enzymes, especially Mg-dechelation, also progressively 31 increased during storage at 25 o C. The formation of Phy a in stored JBO leaves was 32 further investigated. By incubating the reaction mixture of crude enzyme extract and 33 Chl a, Phy a was formed by Mg-dechelating action. Especial significant was the greater 34 formation of Phy a in FF+3A than FF and FF+4A. Electron microscopic observation 35 elucidated the formation of plastoglobules (Pgs) in chloroplasts and its movement from 36 chloroplast to vacuole in JBO. A large number of Pgs in vacuole of FF+3A might relate 37 to the high Phy a formation with Chl degradation. These findings suggest that Chl a 38 could be degraded in part, through Phy a, and the vacuole along with the chloroplast 39 might be important sites for Chl degradation in JBO during storage. 40 41

Presence of Pheophytin and its Formation as a Chlorophyll Derivative in Selected Crop Species

Most of the green leaf vegetable and fruits lose their postharvest quality mainly due to yellowing as a consequence of chlorophyll (Chl) degradation. The study of Chl degradation of many plants have been revealed that the Chl degradation mainly progress through formation of chlorophyllide (Chlide) a. Recent studies have revealed that the Chl degradation could be progressing through formation of pheophytin (Phy) a as a Chl derivative. Present study was conducted to investigate the presence and formation of Phy a as Chl a derivative in selected stored plant species. Green tea leaves, bell pepper, parsley and Japanese bunching onion were used in the study. Presence of Chl a derivatives of 80% acetone extract of green tea leaves and Japanese bunching onion were detected using HPLC at the wave length of 663nm. Formation of Chl a derivatives were studied by incubating crude enzyme extract of bellpepper, parsley and bunching onion with Chl a and buffer solution. After one hour of incubation reaction was stopped by adding 80% acetone. Chl a derivatives were studied using HPLC at 663nm. Phy a level of processed green tea leaves was very high when compared to other plants. In parsley, bellpepper and Japanese bunching onion formation of Phy a was prominent. All these indicated that early studies of Chl degradation need further study to elucidate the mechanism of Chl degradation in green plants. The Journal of Agricultural Sciences, 2012, vol.7, no3, page 127-134 DOI: http://dx.doi.org/10.4038/jas.v7i3.4876

Processes responsible for the formation and maintenance of sub-surface chlorophyll maxima in the Gulf of Finland

Vertical cross-sections of temperature, salinity and Chl a fluorescence distributions in the Gulf of Finland were mapped on 11, 19–20 and 25 July 2006. The sub-surface Chl a maximum layers with thickness varying between 1.5 and 9 m and intensity up to 7.6 μg l −1 were observed in the lower part of the seasonal thermocline within the depth range of 14.5–35 m. Nutrient (PO4 3−, NO2 − + NO3 −) analyses of water samples collected from the thermocline revealed the coincidence of the location of Chl a maxima and nutriclines. We suggest that the observed Chl a maxima were formed by dinoflagellate Heterocapsa triquetra capable for vertical migration and nutrient uptake in dark. The upward flux of nutrients caused by estuarine circulation and vertical turbulent mixing created favourable conditions for the formation and maintenance of sub-surface Chl a maxima. We explain the observed horizontal patchiness of sub-surface Chl a maxima by meso-scale processes – by the accumulation of phytoplankton along the depressed isopycnals at the base of anti-cyclonic circulation cells and by the horizontal convergence of waters in the downwelling area.

Mutations in a gene encoding a midbody kelch protein in familial and sporadic classical Hodgkin lymphoma lead to binucleated cells

Classical Hodgkin lymphoma (cHL) is a malignancy of B-cell origin in which the neoplastic cells, known as "Reed-Sternberg" (RS) cells, are characteristically binucleated. Here we describe a family where multiple individuals developing cHL have inherited a reciprocal translocation between chromosomes 2 and 3. The translocation disrupts KLHDC8B, an uncharacterized gene from a region (3p21.31) previously implicated in lymphoma and related malignancies, resulting in its loss of expression. We tested KLHDC8B as a candidate gene for cHL and found that a 5'-UTR polymorphism responsible for decreasing its translational expression is associated with cHL in probands from other families with cHL and segregates with disease in those pedigrees. In one of three informative sporadic cases of cHL, we detected loss of heterozygosity (LOH) for KLHDC8B in RS cells, but not reactive T lymphocytes, purified from a malignant lymph node. KLHDC8B encodes a protein predicted to contain seven kelch repeat domains. KLHDC8B is expressed during mitosis, where it localizes to the midbody structure connecting cells about to separate during cytokinesis, and it is degraded after cell division. Depletion of KLHDC8B through RNA interference leads to an increase in binucleated cells, implicating its reduced expression in the formation of cHL's signature RS cell.

Characterization of the secondary electron-transfer pathway intermediates of photosystem II containing low-potential cytochrome b 559

Beta-carotene (Car) and chlorophyll (Chl) function as secondary electron donors in photosystem II (PS II) under conditions, such as low temperature, when electron donation from the O(2)-evolving complex is inhibited. In prior studies of the formation and decay of Car(*+) and Chl(*+) species at low temperatures, cytochrome b(559) (Cyt b(559)) was chemically oxidized prior to freezing the sample. In this study, the photochemical formation of Car(*+) and Chl(*+) is characterized at low temperature in O(2)-evolving Synechocystis PS II treated with ascorbate to reduce most of the Cyt b(559). Not all of the Cyt b(559) is reduced by ascorbate; the remainder of the PS II reaction centers, containing oxidized low-potential Cyt b(559), give rise to Car(*+) and Chl(*+) species after illumination at low temperature that are characterized by near-IR spectroscopy. These data are compared to the measurements on ferricyanide-treated O(2)-evolving Synechocystis PS II in which the Car(*+) and Chl(*+) species are generated in PS II centers containing mostly high- and intermediate-potential Cyt b(559). Spectral differences observed in the ascorbate-reduced PS II samples include decreased intensity of the Chl(*+) and Car(*+) absorbance peaks, shifts in the Car(*+) absorbance maxima, and lack of formation of a 750 nm species that is assigned to a Car neutral radical. These results suggest that different spectral forms of Car are oxidized in PS II samples containing different redox forms of Cyt b(559), which implies that different secondary electron donors are favored depending on the redox form of Cytb(559) in PS II.

Using Allium alien monosomic addition lines to study chlorophyll degradation in stored Japanese bunching onion

SummaryChlorophyll (Chl) degradation and the formation of Chl derivatives in stored leaves of Japanese bunching onion (JBO; Allium fistulosum L., genome FF) were determined to elucidate the mechanism of Chl degradation by using alien monosomic addition lines (AMALs; FF+1A to FF+8A) of JBO from shallot (A. cepa L. Aggregatum group, genome AA). Year-round changes in Chl content in JBO and in the AMALs were also detected over 2 years. The Chl content in FF was significantly influenced by the alien chromosomes from shallot. In particular, the Chl contents of FF+4A or FF+5A, were higher in Winter than in FF, which suggests that chromosomes 4A and 5A from shallot had a larger influence on the formation of Chl than the other chromosomes. Chl contents in FF+3A and FF+5A decreased greatly in the leaves of AMALs and JBO during storage at 25°C, whereas in FF+4A the Chl content was the lowest compared to the control, FF. Chlorophyllide (Chlide) a, C132-hydroxychlorophyll (OHChl) a, pheophorbide a, and pheophytin (Phy) a, as derivatives of Chl a, were present mainly during storage of JBO and the AMALs. Phy alevels increased with Chl degradation, especially in FF+3A, while OHChl alevels in FF and FF+3A showed a decline during storage. In addition, Chlide alevels in all lines diminished during storage.Thus, Chl amay be degraded, in part, through Phy a, as well as Chlide aand OHChl a, in JBO and the AMALs during storage.

Structural Mechanism and Photoprotective Function of Water-soluble Chlorophyll-binding Protein

A water-soluble chlorophyll-binding protein (WSCP) is the single known instance of a putative chlorophyll (Chl) carrier in green plants. Recently the photoprotective function of WSCP has been demonstrated by EPR measurements; the light-induced singlet-oxygen formation of Chl in the WSCP tetramer is about four times lower than that of unbound Chl. This paper describes the crystal structure of the WSCP-Chl complex purified from leaves of Lepidium virginicum (Virginia pepperweed) to clarify the mechanism of its photoprotective function. The WSCP-Chl complex is a homotetramer comprising four protein chains of 180 amino acids and four Chl molecules. At the center of the complex one hydrophobic cavity is formed in which all of the four Chl molecules are tightly packed and isolated from bulk solvent. With reference to the novel Chl-binding mode, we propose that the photoprotection mechanism may be based on the inhibition of physical contact between the Chl molecules and molecular oxygen.

パパインによるChl a → Chl d 変換

パパインによるChl a → Chl d 変換

3P281 パパインによるChl aからChl d変換の発見(光生物 B) 光合成))

3P281 パパインによるChl aからChl d変換の発見(光生物 B) 光合成))

Recent advances in chlorophyll biosynthesis and breakdown in higher plants

Chlorophyll (Chl) has unique and essential roles in photosynthetic light-harvesting and energy transduction, but its biosynthesis, accumulation and degradation is also associated with chloroplast development, photomorphogenesis and chloroplast-nuclear signaling. Biochemical analyses of the enzymatic steps paved the way to the identification of their encoding genes. Thus, important progress has been made in the recent elucidation of almost all genes involved in Chl biosynthesis and breakdown. In addition, analysis of mutants mainly in Arabidopsis , genetically engineered plants and the application of photo-reactive herbicides contributed to the genetic and regulatory characterization of the formation and breakdown of Chl. This review highlights recent progress in Chl metabolism indicating highly regulated pathways from the synthesis of precursors to Chl and its degradation to intermediates, which are not longer photochemically active.

Recombinant water-soluble chlorophyll protein from Brassica oleracea var. Botrys binds various chlorophyll derivatives.

A gene coding for water-soluble chlorophyll-binding protein (WSCP) from Brassica oleracea var. Botrys has been used to express the protein, extended by a hexahistidyl tag, in Escherichia coli. The protein has been refolded in vitro to study its pigment binding behavior. Recombinant WSCP was found to bind two chlorophylls (Chls) per tetrameric protein complex but no carotenoids in accordance with previous observations with the native protein [Satoh, H., Nakayama, K., Okada, M. (1998) J. Biol. Chem. 273, 30568-30575]. WSCP binds Chl a, Chl b, bacteriochlorophyll a, and the Zn derivative of Chl a but not pheophytin a, indicating that the central metal ion in Chl is essential for binding. WSCP also binds chlorophyllides a and b and even the more distant Chl precursor Mg-protoporphyrin IX; however, these pigments fail to induce oligomerization of the protein. We conclude that the phytol group in bound Chl plays a role in the formation of tetrameric WSCP complexes. If WSCP in fact binds Chl or its derivative(s) in vivo, the lack of carotenoids in pigmented WSCP raises the question of how photooxidation, mediated by triplet-excited Chl and singlet oxygen, is prohibited. We show by spin-trap electron-paramagnetic resonance that the light-induced singlet-oxygen formation of WSCP-bound Chl is lower by a factor of about 4 than that of unbound Chl. This as-yet-unknown mechanism of WSCP to protect its bound Chl against photooxidation supports the notion that WSCP may function as a transient carrier of Chl or its derivatives.

A new pathway of chlorophyll biosynthesis from long-wavelength protochlorophyllide Pchlide 686/676 in juvenile etiolated plants.

By spectral methods, the final stages of chlorophyll formation from protochlorophyllide were studied using etiolated pea, bean, barley, wheat and maize plants in early stages (4 days) of growth. For these juvenile plants, along with the reaction chain known for mature (7-9-day-old) plants, a new reaction chain was found, which started with phototransformation of the long-wavelength form Pchlide 686/676(440) into Pchlide 653/648(440). (Pchlide 653/648(440) differs from the main known precursor form Pchlide 655/650(448)). The subsequent photoreduction of Pchlide 653/648(440) leads to the formation of Chlide 684/676(440), which is transformed into Chl 688/680(440) in the course of a dark reaction. After completion of this reaction, fast (20-30 s) quenching of the low-temperature fluorescence of the reaction product is observed with the formation of non-fluorescent Chl 680. The reaction accompanied by pigment fluorescence quenching is absent in pea mutants with depressed function of Photosystem II reaction centers. This suggests that the newly found reaction chain leads to the formation of chlorophyll of the Photosystem II core.

Spectroscopic analysis of desiccation-induced alterations of the chlorophyllide transformation pathway in etiolated barley leaves.

Effects of water deficit on the chlorophyllide (Chlide) transformation pathway were studied in etiolated barley (Hordeum vulgare) leaves by analyzing absorption spectra and 77-K fluorescence spectra deconvoluted in components. Chlide transformations were examined in dehydrated leaves exposed to a 35-ms saturating flash triggering protochlorophyllide (Pchlide) and Chlide transformation processes. During the 90 min following the flash, we found that dehydration induced modifications of Chlide transformations, but no effect on Pchlide phototransformation into Chlide was observed. During this time, content of NADPH-Pchlide oxydoreductase in leaves did not change. Chlide transformation process in dehydrated leaves was characterized by the alteration of the Shibata shift process, by the appearance of a new Chlide species emitting at 692 nm, and by the favored formation of Chl(ide) A(668)F(676). The formation of Chl(ide) A(668)F(676), so-called "free Chlide," was probably induced by disaggregation of highly aggregated Chlide complexes. Here, we offer evidence for the alteration of photoactive Pchlide regeneration process, which may be caused by the desiccation-induced inhibition of Pchlide synthesis.

Biosynthesis of chlorophyll of photosystem II reaction centers in plant leaves in early stages of etiolation.

Spectral methods were used to study the sequences of chlorophyll biosynthesis reactions in etiolated pea, bean, and maize plants in early stages (3-4 days) of growth. For these juvenile plants, along with the reaction chain known for mature (7-9 day-old) plants, a new reaction chain was found which started with phototransformation of the long-wavelength form PChld 686/676 into PChld 653/648. (PChld 653/648 differs from the main known precursor form PChld 655/650). The subsequent photoreduction of PChld 653/648 leads to the formation of Chld 684/676, which is transformed into Chl 688/680 in the course of a dark reaction. After completion of this reaction, fast (20-30 sec) quenching of the fluorescence of the reaction product is observed with the formation of non-fluorescent Chl 680. The reaction accompanied by pigment fluorescence quenching is absent in pea mutants with depressed function of Photosystem II reaction centers. This suggests that the newly found reaction chain leads to the formation of chlorophyll of the Photosystem II reaction center.

More on the catalysis of internal conversion in chlorophyll a by an adjacent carotenoid in light-harvesting complex (Chl a/ b LHCII) of higher plants: time-resolved triplet-minus-singlet spectra of detergent-perturbed complexes

Wavelength-selective photo-excitation of samples containing a detergent and LHCII (the main light-harvesting complex pertaining to photosystem II of green plants) is used for recording time-resolved triplet-minus-singlet (TmS) difference spectra, with a view to probing interactions between chlorophyll a (Chl a) and chlorophyll b (Chl b), and between Chl a and lutein (Lut). Once the detergent concentration ( C D) exceeds a threshold, C ©, the TmS spectrum becomes sensitive to λ ⊗, the wavelength of excitation, and to t, the delay between excitation and observation. Each increment in C D brings about a diminution in the efficiency of a †→ x † transfer (triplet–triplet transfer from Chl a to Lut) and a rise in both the triplet formation yield and the fluorescence yield of Chl a. What is more, b*→ a* transfer (singlet–singlet transfer from Chl b to Chl a) slackens to such an extent that Chl b*→Chl b † intersystem crossing, negligible when C D is below C ©, begins to vie with transfer, for the deactivation of Chl b* (in the foregoing an asterisk/dagger denotes singlet/triplet excitation). The reduction in the efficiencies of the two transfers is easily understood by: (i) invoking the Kühlbrandt–Wang–Fujiyoshi model of LHCII, which posits each Chl b in contact with a Chl a and each Chl a in contact with a Lut, and (ii) assuming that the detergent severs contact between adjacent chromophores. That a growth in the triplet yield of Chl a* accompanies the detergent-induced decrease in the efficiency of a †→ x † transfer becomes intelligible if one assumes, further, that internal conversion in Chla * is faster than that in Chla * , where under or over lining betokens the presence or absence of a carotenoid neighbour. When C D is close to C ©, most Chl a molecules are adjacent to a Lut, internal conversion dominates, and the overall triplet yield is low. As C D is gradually raised the Chla → Chla transformation sets in, causing concomitant drops in the efficiencies of a †→ x † transfer and internal conversion, and a consequent rise in the overall yields of Chl a fluorescence and formation of Chl a triplets.