On the electron-scattering power of protein structures in the spinach chloroplast

The relative electron-scattering power of chromidia and interchromidia in protein structures of the spinach chloroplast was examined with the aid of the electron microscope. It has been demonstrated that: 1. 1. The technique of Marton and Schiff holds for WO3 crystals and silica films too. 2. 2. The mean electron-scattering constant of the chromidia amounts to about 1.34 times that of the interchromidia in preparations treated with acetone. After lipoid removal with lipase this value is 1.56. This indicates that the constitution of the chromidia is different from that of the interchromidia

Temperature dependence of absorption and fluorescence spectra of bacteriochlorophylls in vivo and in vitro

The “short wave” far-red absorption bands (795–825 nm) of bacteriochlorophyll in photosynthetic red bacteria are sharpened but not shifted upon cooling, the “long wave” far-red bands (840–890 nm) are sharpened less but shifted appreciably towards longer wavelengths. The fluorescence bands are shifted about as much as the corresponding “long wave” absorption bands. Warming results in changes in the opposite direction. The temperature effects are reversible. With bacteriochlorophyll dissolved in a number of polar solvents, the temperature-induced shift of the yellow band is more pronounced than that of the far-red band; with colloidal and adsorbed bacteriochlorophyll, the 840-nm red band upon cooling shifts, by a similar amount as the 850-nm band in some, though not all, measured bacterial species, while the shift of the 780 nm and yellow band is small. The possible interference of temperature effects with the interpretation of results on absorption in terms of photochemical activity is discussed

Fluorescence bands and chlorophyll a forms

Fluorescence spectra were determined at temperatures between 20° and −196° for a number of photosynthetic organisms. Below −90° the single fluorescence maximum around 685 mμ was replaced by a system of three bands, at 686, 696 and 717–720 mμ in algal cells. Cooling usually resulted in a decrease of the 685-mμ band. In young cultures of blue-green and red algae the three bands were of about equal intensity; in old cultures and in green algae the 717-mμ band was dominant, while in the latter the 696-mμ bans was weak. In green leaves and chloroplast also, three bands were present at low temperatures, at 686, 696 and 735–740 mμ. Here too, the 740-mμ band was by far the major one. During cooling of both diluted and concentrated chlorophyll a solutions and chlorphyll adsorbed to filter paper, the height of the 677-mμ fluorescence band and the 730-mμ vibrational level were increased by a factor of about two, provided no increased reabsorption due to increased scattering could occur. In concentrated chlorophyll a solutions no extra bands could be detected. The three fluorescence bands measured in vivo at low temperatures are assumed to belong to three chlorophyll a forms: Ca 670-F 686; Ca 695-F 717 in algal cells. Apart from an increase in intrinsic fluorescence yield of Ca 695, the marked increase in 717-mμ fluorescence during cooling is suggested to be due to increased energy transfer from Ca 670 and Ca 680 to Ca 695 as a result of shrinkage, when the temperature is lowered

Investigations on bacteriochlorophyll in organic solutions

Various spectral and photochemical properties of bacteriochlorophyll were studied. It was found that the spectral shift of the second absorption band of this pigment in polar solvents is nearly absent in the magnesium-free pigment. The quantum yield of irreversible bleaching was determined with respect to the type of solvent and the purity of the pigment. A difference of a factor of 100 was found to occur between the values in methanol and those in ether. The quantum-yield values were found to be slightly higher at lower temperatures. Addition of quinone resulted in a strong decrease of the quantum yield of bleaching. The absorption spectrum was determined for photo-bleached bacteriochlorophyll in different solvents. Furthermore, the effect of reversibility of photo-bleaching was studied as a function of temperature. A reversible “chemical” bleaching was found to occut after addition of ferric salts, iodine, or potassium permanganate. The absorption spectrum was found to be analogous to that of chlorophyll a under similar conditions. This reversible “bleaching” proved to occur not only in methanol, but also in acetone or ether. Fluorescence spectra were determined before and after bleaching of “pure” and “crude” bacteriochlorophyll solutions. The quenching of fluorescence after addition of quinone and the effect of this addition on the degree of polarisation for bacteriochlorophyll and chlorophyll a was also investigated

Effect of changes in chlorophyll concentration on photosynthetic properties I. Fluorescence and absorption of greening bean leaves

In order to obtain new information about the way of functioning of chlorophyll in vivo a study was made of optical properties and photosynthesis under condition of a low chlorophyll content in the leave. It was found that the fluorescence yeild of greening bean leaves decreased from a value approximating the yield of chlorophyll in organic solution to that of chlorophyll measured in a green leave. No transfer of absorbed light energy from carotenoids to chlorophyll a was found immediately after transformation of protochlorophyll. In the early stages of greening a relatively inefficient energy transfer developed. The light intensity at which fluorescence induction phenomena appear was studied and found to decrease during greening. Measuring measurements performed during greening showed the appearance of severeal shifts of absorption maxima thus confirming, at least partly, earlier measurements of Shibata. The effect of high light intensity and of freezing on the different chlorophyll forms was investigated

Energy transfer from carotenoids to chlorophyll in blue-green, red and green algae and greening bean leaves

From fluorescence action spectra, fluorescence spectra and absorption spectra measured at room temperature and at 77 °K of light petroleum (b.p. 40–60°)-treated and normal chloroplasts, it is concluded that: 1. 1. In blue-green and red algae energy transfer from β-carotene to chlorophyll occurs in Photosystem I exclusively. 2. 2. In green algae and greening bean leaves energy transfer from β-carotene to chlorophyll occurs in both Photosystem I and II. 3. 3. Light absorbed by β-carotene is transferred to chlorophyll with nearly 100% efficiency. 4. 4. Light energy absorbed by xanthophylls is not transferred to chlorophyll

Orientation of the pigment molecules in the chloroplast

Dichroism, absorption anisotropy, and anomal dispersion of birefringence were measured in the big lamellate chloroplasts of Mougeotia. The results of these measurements indicate a certain orientation of the chlorophyll molecules, and to a smaller extent, of the carotenoids in the chloroplast. In species like Funaria, containing relatively small grana-bearing chloroplasts, absorption measurements in polarised light were too unreliable to detect a weak dichroism. However, the anomal dispersion of birefringence was found to be a common phenomenon for all chloroplasts measured. It may be assumed from these results that a certain orientation of the pigment molecules occurs in all chloroplasts studied

A cooperation of two pigment systems and respiration in photosynthetic luminescence

Luminescence kinetics of photosynthesizing cells were investigated. This was done by measuring afterglow as a function of intensity and wavelength of actinic light as well as of temperature. In order to explain the chromatic transients, induction effects, and various other aspects of luminescence, the presence of a chloroplast respiratory “r” system was postulated. A “feedback” of products formed by photochemical “p” and “q” systems, described earlier, into the dark “r” system is believed to affect the state of reduction of cytochrome and, with it, luminescence. The relation of luminescence to gas-exchange measurements and a possible explanation of various aspects of photosynthesis by interaction of the “p”, “q” and “r” systems is discussed

A cooperation of two pigment systems and respiration in photosynthetic luminescence

Luminescence kinetics of photosynthesizing cells were investigated. This was done by measuring afterglow as a function of intensity and wavelength of actinic light as well as of temperature. In order to explain the chromatic transients, induction effects, and various other aspects of luminescence, the presence of a chloroplast respiratory “r” system was postulated. A “feedback” of products formed by photochemical “p” and “q” systems, described earlier, into the dark “r” system is believed to affect the state of reduction of cytochrome and, with it, luminescence. The relation of luminescence to gas-exchange measurements and a possible explanation of various aspects of photosynthesis by interaction of the “p”, “q” and “r” systems is discussed