Pigment, photodestructible

To enable the utilization of the full spectral range for classification also in carotenoid-rich species, we propose a method for photodestruction of carotenoid pigments in pollen using 633 nm light. In initial experiments that were conducted at 633 nm excitation, we observed that the bands ascribed to carotenoid molecules were not stable but diminished steadily, even at relatively low excitation intensities of 10 mW. Figure 4.6 displays spectra of horse-chestnut pollen excited with 633 nm as a function of exposure time to the laser. The irreversible decrease of the intensities of the typical carotenoid bands suggests the photodestruction of these molecules (see arrows in Fig. 4.6) [72-74]. With excitation at 785 nm, the spectra of the pollen remained unal-... 

Top Photooxidation of LHC-bound Chl-a induced by three 10-min periods of white light at average photon flux density of 2800 pE m s" was examined. Between the light periods, absorbance spectra were monitored and Chl-a destruction was determined from the absorbance decrease in the red maximum of LHC (676 nm for LHC + fatty acid 674 nm for LHC + Triton). Under anaerobic conditions (50 mM glucose + 0.3 mg/ml glucose oxidase) no photodestruction of the LHC-bound pigments was observed at either condition (not shown). 

Illumination of RC I under photobleaching conditions induces a rapid decrease of pigment content (4). After prolonged photodestruction a complex with a stable pigment composition of approximately 20 molecules chlorophyll a (chi a), Z - 3 B-carotene and 1 chi a per reaction centre is found, indicating a close spatial and functional relationship between these pigments (Tab. 2). 

Pigments used for PO fibers must have some technical characteristics, such as efficient thermal stability light fastness adequate for the intended uses of the finished articles no migration (blooming nor contact bleed) compatibility with other additives (stabilizers, etc.) and lack of photodestructive effect on polymer and lack of negative influence on the fiber s mechanical properties. 

Since the consistently greater stability of lutein over all other carotenoids is not the result of different physical properties of the chro-mophore (cf. Krinsky, 1979), we conclude that lutein must be situated in a different environment than the other polyenes. The function of lutein is probably not to protect chi against photodestruction but to stabilize the structure of the pigment-protein complexes. 

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