Structure of the red fluorescence band in chloroplasts

Photochemical properties of mesophyll and bundle sheath chloroplasts of maize

Several photochemical and spectral properties of maize (Zea mays) bundle sheath and mesophyll chloroplasts are reported that provide a better understanding of the photosynthetic apparatus of C(4) plants. The difference absorption spectrum at 298 K and the fluorescence excitation and emission spectra of chlorophyll at 298 K and 77 K provide new information on the different forms of chlorophyll a in bundle sheath and mesophyll chloroplasts: the former contain, relative to short wavelength chlorophyll a forms, more long wavelength chlorophyll a form (e.g. chlorophyll a 693 and chlorophyll a 705) and less chlorophyll b than the latter. The degree of polarization of chlorophyll a fluorescence is 6% in bundle sheath and 4% in mesophyll chloroplasts. This result is consistent with the presence of relatively high amounts of oriented long wavelength forms of chlorophyll a in bundle sheath compared to mesophyll chloroplasts. The relative yield of variable, with respect to constant, chorophyll a fluorescence in mesophyll chloroplasts is more than twice that in bundle sheath chloroplast. Furthermore, the relative yield of total chlorophyll a fluorescence is 40% lower in bundle sheath compared to that in mesophyll chloroplasts. This is in agreement with the presence of the higher ratio of the weakly fluorescent pigment system I to pigment system II in bundle sheath than in mesophyll chloroplast. The efficiency of energy transfer from chlorophyll b and carotenoids to chlorophyll a are calculated to be 100 and 50%, respectively, in both types of chloroplasts. Fluorescence quenching of atebrin, reflecting high energy state of chloroplasts, is 10 times higher in mesophyll chloroplasts than in bundle sheath chloroplasts during noncyclic electron flow but is equal during cyclic flow. The entire electron transport chain is shown to be present in both types of chloroplasts, as inferred from the antagonistic effect of red (650 nm) and far red (710 nm) lights on the absorbance changes at 559 nm and 553 nm, and the photoreduction of methyl viologen from H(2)O. (The rate of methyl viologen photoreduction in bundle sheath chloroplasts was 40% of that of mesophyll chloroplasts.).

Lifetime of the excited state in vivo. I. Chlorophyll a in algae, at room and at liquid nitrogen temperatures; rate constants of radiationless deactivation and trapping

Using a mode-locked laser (lambda, 632.8 nm), fluorescence decay of chlorophyll (Chl) a in the green alga Chlorella pyrenoidosa, the red alga Porphyridium cruentum, and the blue-green alga Anacystis nidulans was measured by the phase-shift method under conditions when photosynthesis was not operative (3-(3,4-dichlorophenyl)-1,1-dimethylurea [DCMU] poisoning, or cooling to 77 degrees K). In the presence of 10(-5) M DCMU, the lifetime of Chl a fluorescence (tau) at room temperature is about 1.7 nsec in Chlorella, 1.0 nsec in Porphyridium, and 0.7 nsec in Anacystis. At 77 degrees K, tau is 1.4 nsec (for fluorescence at about 685 nm, F-685) and 2.3 nsec (for F-730) in Chlorella, 0.9 nsec (F-685) and 1.2 nsec (F-730) in Porphyridium, and 0.8 nsec (F-685 and F-730) in Anacystis. From the above measurement, and the assumption that tau(0) (the intrinsic fluorescence lifetime) for Chl a in all three algae is 15.2 nsec, we have calculated the rate constants of radiationless transition (that includes energy transfer to weakly fluorescent system I) processes competing with fluorescence at room temperature to be about 5 x 10(8) sec(-1) in Chlorella, 9 x 10(8) sec(-1) in Porphyridium, and 13 x 10(8) sec(-1) in Anacystis. At 77 degrees K, this rate constant for Chl a that fluoresces at 685 nm remains, in the first approximation, the same as at room temperature. From the tau data, the rate constant for the trapping of excitation energy is calculated to be about 1.2 x 10(9) sec(-1) for Chlorella, 2 x 10(9) sec(-1) for Porphyridium, and 2 x 10(9) sec(-1) for Anacystis. The efficiency of trapping is calculated to be about 66% (Chlorella), 68% (Porphyridium), and 60% (Anacystis). (It is recognized that variations in the above values are to be expected if algae grown under different conditions are used for experimentation.) The maximum quantum yield of Chl a fluorescence for system II (lambda, 632.8 nm), calculated from tau measurements, is about 10% in Chlorella, 6-7% in Porhyridium, and 5% in Anacystis under conditions when photosynthesis is not operative; the values at 77 degrees K appear to be very close to those with DCMU added at room temperature. ø for F-730 at 77 degrees K, however, is somewhat higher than for F-685. The predicted quantum yields of fluorescence for Chl a in intact cells (both systems I and II) at low intensities of 632.8 nm light are about 2-3, 1-2, and 1% for Chlorella, Porphyridium, and Anacystis, respectively.

The forms of native chlorophyll in Chlamydobotrys stellata and their changes during adaptation from photo-heterotrophic to autotrophic growth

Absorption and fluorescence spectra were measured for Chlamydobotrys stellata cultured either photo-heterotrophically on acetate or autotrophically on CO2 as well as during adaptation from hetero- to autotrophic conditions. Curve analyses of the absorption spectra at liquid nitrogen temperature suggest the presence of chlorophyll-a forms with their main absorption peaks at 663, 670, 678, 685, 693 and 707 nm. The proportion of the longer wavelength forms, 685, 693 and 707 nm, decreases during adaptation to autotrophic growth. The chlorophyll-b content of the photo-heterotrophic culture was very low.

Absorption and fluorescence of chlorophyll a in particle fractions from different plants

Density-gradient centrifugation of disintegrated cells from a variety of plants gave two kinds of chlorophyll particles from all except the blue-green algae. As in previous procedures using detergents, the lighter Fraction 1 particles usually had greater absorption at longer wavelengths; they always had a lower ratio of short to long wavelength fluorescence at low temperature, and a lower fluorescence yield per chlorophyll than the denser Fraction 2 particles. Although only one kind of particle fraction was found in each blue-green alga, the fine structure of the chlorophyll a absorption band differed significantly among the three species measured.

Red drop in the quantum yield of fluorescence of sonicated algae

The change of the quantum yield of fluorescence, Phi, with the frequency of exciting light, was investigated in Chlorella, Anacystis, and Porphyridium suspensions, and in sonicates from these cells prepared under aerobic and anaerobic conditions. In case of Chlorella, sonicates were made in acid and in alkaline media (pH 4.65 and 7.80). In the alkaline medium, a drop of Phi towards the longer waves was found to begin at 1.466 x 10(4) cm(-1) (682 nm) in sonicates, and in suspension. In the acid medium, the drop began at 1.471 x 10(4) cm(-1) (680 nm), 1.418 x 10(4) cm(-1) (705 nm), and 1.389 x 10(4) cm(-1) (720 nm) in suspension, anaerobic sonicate, and aerobic sonicate, respectively. The results indicate that the cause of the change in the red drop is preferential destruction of a long-wave component of chlorophyll a (such as Chl a 693). The amount of this component remaining after sonication is larger in alkaline than in acid sonicates. With Anacystis and Porphyridium, only alkaline suspensions (pH 7.80) could be used for sonication, because in acid medium, the phycobilin-chlorophyll complex is rapidly broken and phycobilin extracted from the cell. In Anacystis, the red drop begins at 1.562 x 10(4) cm(-1) (640 nm) and 1.538 x 10(4) cm(-1) (650 nm) in suspension and sonicate, respectively; in Porphyridium, it starts at 1.550 x 10(4) cm(-1) (645 nm) in both cases. These results suggest that sonication in alkaline medium (pH 7.80) destroys some Chl a 693 in Anacystis, but not in Porphyridium.

Changes in intensity and spectral distribution of fluorescence. Effect of light treatment on normal and DCMU-poisoned Anacystis nidulans

The intensity of the "steady-state" fluorescence of "aerobic" Anacystis nidulans is variable under prolonged illumination with orange (590 mmu) or blue (440 mmu) light for both normally photosynthesizing and DCMU-poisoned cells. In general, orange light illumination causes an increase of the fluorescence intensity followed by a decrease, while blue light causes an increase until a steady level is reached. Poisoned Anacystis cells show four to eight times larger changes in fluorescence intensity than the normal cells; the detailed time course of fluorescence changes is also different in poisoned and normal cells. When algae are cooled to -196 degrees C in light, the light-induced changes in the "steady-state" fluorescence disappear in both types of cells. Difference fluorescence spectra, constructed by subtracting the fluorescence spectra taken after 5-15 min of illumination from those after 60-90 min of illumination, show a doublet structure of the difference band with a major peak coinciding with the Anacystis emission maximum (685 mmu) and a minor peak located at about 693 mmu.

Transfer of the excitation energy in Anacystis nidulans grown to obtain different pigment ratios

The blue-green alga, Anacystis nidulans, was grown in lights of different colors and intensities, and its absorption and fluorescence properties were studied. Strong orange light, absorbed mainly by phycocyanin, causes reduction in the ratio of phycocyanin to chlorophyll a; strong red light, absorbed mainly by chlorophyll, causes an increase in this ratio. This confirms the earlier findings of Brody and Emerson (12) on Porphyridum, and of Jones and Myers (8) on Anacystis. Anacystis cultures grown in light of low intensity show, upon excitation of phycocyanin, emission peaks at 600 mmu and 680 mmu, due to the fluorescence of phycocyanin and chlorophyll a, respectively. Changes in the efficiency of energy transfer from phycocyanin to chlorophyll a are revealed by changes in the ratios of these two bands. A decrease in efficiency of energy transfer from phycocyanin to chlorophyll a seems to occur whenever the ratio of chlorophyll a to phycocyanin deviates from the normal. Algae grown in light of high intensity show, upon excitation of phycocyanin, only a fluorescence band at 660 mmu and no band at 680 mmu. This suggests reduced efficiency of energy transfer from phycocyanin to the strongly fluorescent form of chlorophyll a (chlorophyll a(2)) and perhaps increased transfer to the weakly fluorescent form of chlorophyll a (chlorophyll a(1)).