The relative absorption cross-sections of Photosystem I and Photosystem II in chloroplasts from three types of Nicotiana tabacum

Characterization of the functional organization of the photochemical apparatus in the light sensitive chlorophyll b-deficient oil yellow-yellow green (OY-YG) mutant of maize (Zea mays) is presented. Spectrophotometric and kinetic analysis revealed substantially lower amounts of the light harvesting complex of photosystem II (LHCII-peripheral) MATERIALS AND METHODSPlant Growth and Chloroplast Isolation. Maize (Zea mays) leaves of both wild type and Chl b-deficient mutant OY-YG (15) were harvested from 2 to 3 week old seedlings grown in the greenhouse. The leaves were deveined and ground for 15 s in a Waring blender at 0°C in 50 mm Tricine buffer (pH 7.8), containing 0.4 M sucrose, 10 mM NaCl, and 5 mm MgCl2. The homogenate was filtered through 4 layers of nylon mesh. Chloroplasts were pelleted at 6000g for 10 min and resuspended in the same buffer at a Chl concentration of 1 mm.

Section: Resultssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 84%

Compensatory Alterations in the Photochemical Apparatus of a Photoregulatory, Chlorophyll b-Deficient Mutant of Maize

Greene¹,

Staehelin²,

Melis³

1988

“…Similar results were obtained earlier for the tobacco mutants, Su/su and Su/su var aurea (21), although the decrease in antenna size and the increase in PSII units were larger than that for the sugar beet mutant. In the chlorina f-2 mutant of barley where there was a complete lack of LHCP, PS11, units predominated (27 …”

Section: Discussionsupporting

confidence: 90%

Photochemical Apparatus Organization in the Chloroplasts of Two Beta vulgaris Genotypes

Abadı́a¹,

Glick²,

Taylor³

et al. 1985

The composition and structural orpnization of thylakoid membranes of a low chlorophyll mutant of Beta rulgaris was investigated using spectroscopic, kinetic and electrophoretic techniques. The data obtained were compared with those of a standard Fl hybrid of the same species. The mutant was depleted in chlorophyll b relative to the hybrid and it had a higher photosystem II/photosystem I reaction center (Q/P7") (1,12,17,26).Investigation of the effects of mutations of genes coding for specific components of the thylakoid membrane permit greater precision in the interpretation of the structural/functional role of that component than would be possible for many environmental perturbations of thylakoid structure. In our laboratory (N. T.) we are studying currently a low Chl sugar beet mutant which exhibits high rates ofphotosynthesis and electron transport per unit Chl similar to those described by Miles (23): the mutation apparently affects some specific polypeptides of the LHCP.3 Here, we characterize the structural organization of thylakoid membranes of the low Chl mutant by combining spectroscopic analysis with gel electrophoresis. The mutant genotype is compared with the standard sugar beet genotype (an Fl hybrid) used in this laboratory, for which a large amount of biochemical and physiological data is available. Spectroscopic estimates of the amounts of Chl associated with PSII and PSI, and of the stoichiometries of the reaction centers of the two photosystems were compared with those obtained using three different gel electrophoresis systems. MATERIALS AND METHODS

“…This notion was supported both by spectrophotometric (16,18,28) and by O flash yield measurements (7,23,24). Of particular interest is the observation that environmental light conditions and mutations may have a significant effect both in the chloroplast ultrastructure and in the ratio of PSII/PSI reaction centers (18,22). The determination of the physical antenna size of chloroplast PS in situ is more difficult to establish.…”

mentioning

confidence: 99%

Photosystem Electron-Transport Capacity and Light-Harvesting Antenna Size in Maize Chloroplasts

Ghirardi¹,

Melis²

1984

Spectrophotometric and kinetic measurements were applied to yield photosystem (PS) stoichiometries and the functional antenna size of PSI, PSII,,, and PSIIO in Zea mays chloroplasts in situ. Concentrations of PSII and PSI reaction centers were determined from the amplitude of the light-induced absorbance change at 320 and 700 nm, which reflect the photoreduction of the primary electron acceptor Q of PSII and the photooxidation of the reaction center P700 of PSI, respectively. Determination of the functional chlorophyll antenna size (N) for each photosystem was obtained from the measurement of the rate of light absorption by the respective reaction center. Under the experimental conditions employed, the rate of light absorption by each reaction center was directly proportional to the number of light-harvesting chlorophyll molecules associated with the respective photosystem. We determined Npm = 195, N, = 230, N, = 50 for the number of chlorophyll molecules in the lightharvesting antenna of PSI, PSII,, and PSII,,, respectively. The above values were used to estimate the PSII/PSI electron-transport capacity ratio (C) in maize chloroplasts. In mesophyll chloroplasts C > 1.4, indicating that, under green actinic excitation when Chl a and Chi b molecules absorb nearly equal amounts of excitation, PSII has a capacity to turn over electrons faster than PSI. In bundle sheath chloroplasts C < 1, suggesting that such chloroplasts are not optimally poised for linear electron transport and reductant generation.Under light-limiting conditions, the measured rate of PSI and PSII electron transport in chloroplasts is a function of the rate of excitation transfer to the reaction center and the number of reaction centers in the thylakoid membrane. The rate of excitation transfer to the reaction center of a photosystem (K) depends on three parameters: the intensity of the actinic excitation (I), the effective absorption cross-section of the light-harvesting pigments of that PS2 (a) (12) have employed an O2 flash yield method by which they determined the absorption cross-section of PSII in Chlorella vulgaris.A method developed in this laboratory, based on the steady-state kinetic measurements of Q photoreduction and P700 photooxidation, has permitted the estimation of the antenna size of both PSI and PSII in situ (15,22,28).In the present work we applied spectrophotometric and kinetic measurements to obtain PS stoichiometries and the functional antenna size of PSI, PSII,,, and PSII, in maize chloroplasts. We also present a quantitative evaluation of the overall electron transport capacity (C) of maize chloroplast PS, and compare it to the values reported for C3 plants. MATERIALS AND METHODSLeaves from 2-to 3-week-old Zea mays L. plants, grown under controlled conditions in the greenhouse, were cut in small pieces and ground for 40 s in a Waring Blendor at 0C, in 50 mm Tricine buffer, pH 7.9, which contained 0.4 M sucrose, 10 mM NaCl, and 5 mm MgClI. The slurry was filtered through 8 layers of cheesecloth; cell debris were r...