The age dependence of the photosynthetic performance, chlorophyll fluorescence and chloroplast ultrastructure of green form and Chl ft-deficient form (aurea) of tobacco Su/su mutant were compared. The most pronounced differences between the aurea and green tobacco found in young leaves diminished with leaf age. Slower accumulation of the photosynthetic pigments during the development of aurea leaves was accompanied by a slower accumulation of LHC antennae of both photosystems, particularly that of PS2, and by retention of an increase in the capacity of PS2 photochemistry, measured as Fy/FM The ratio Fv/Fm, however, increased rapidly during maturation of aurea leaves, and fmally the mature aurea leaves exhibited higher values of this ratio than the green ones. Rates of photosynthesis at saturating irradiance (Epiax) saturating CO2 concentration (/’sat) decreased with leaf age for both aurea and green tobacco, being always higher in aurea leaves than in leaves of green tobacco of comparable age. AU these characteristics indicated retarded development of aurea leaves. Also the chloroplast ultrastructure, particularly grana formation, exhibited slower development. The decrease in /Wx and with leaf age in both tobacco forms and retardation in the development of aurea leaves can explain higher value of usually found in aurea tobacco.
The photochemical activity of native Central Siberian Scots pine trees (Pinus sylvestris L) was estimated from the middle of February to the middle of March 2001. We measured chlorophyll (Chl) fluorescence in attached intact needles from trees located approx. 30 km west of the Yenisey river (60°44'N, 89°09'E) near the village of Zotino. In this period, the air temperature varied between -39 °C and +7 °C. At temperatures below -10 °C, P. sylvestris needles did not exhibit any variable Chl fluorescence during the daylight period. During the night, however, the effective quantum yield of photosystem 2 (PS2) photochemistry, Φ2 [Φ2 = (Fm' - Ft)/Fm'), increased from values near zero to values between 0.05 and 0.20 depending on the needle temperature and sample investigated. The increase started soon after dusk and lasted for 3-6 h depending on the temperature. A faster increase of Φ2 was found for temperatures around -16 °C, and lower rates occurred at lower temperatures. Irrespective of the temperature, Φ2 decreased rapidly to near zero values at dawn, when the photosynthetic photon flux density increased to about 1-5 µmol m-2 s-1, and remained near zero throughout the day. At temperatures higher than -10 °C, the diurnal decrease and the nocturnal increase of Φ2 were less distinct or disappeared completely. Hence the winter-adapted Scots pine maintains some photochemical activity of PS2 even at extremely cold temperatures. The capacity of photochemical reactions below -10 °C is, however, very limited and PS2 photochemistry is saturated by an extremely low irradiance (less than 5 µmol m-2 s-1). and P. Šiffel, J. Šantrůček.
Distinct crystalloids were found in chloroplasts of transgenic Pssu-ipt tobacco (Nicotiana tabacum L. cv. Petit Havana SR1) overproducing endogenous cytokinins. They were present both in rooted (T) and grafted (TC) transgenic plants contrary to control tobacco (C). The fractions enriched by crystalloids were isolated from chloroplasts using a continuous or a discontinuous Percoll gradient. Chlorophyll (Chl) fluorescence emission spectra at 77 K indicated the presence of aggregates of light-harvesting complex proteins (LHC2) that was not connected to reaction centres of photosystem 2 both in isolated chloroplasts and in the fraction of 80 % Percoll gradient from both types of transgenic tobacco. Further analyses, i.e. pigment contents, polypeptide composition by SDS-PAGE, and immunoblotting support our hypothesis that crystalloids inside chloroplasts of transgenic tobacco are formed by LHC2 aggregates. Treatment with two distinct detergents, chosen with respect to their effects (i.e. β-dodecyl maltoside or Triton X-100), resulted in different degree of disintegration of Chl a/b proteins in transgenic plants compared to the control. Electron microscopic observations and immunogold labelling with specific LHC2 antibodies carried on the resin embedded leaf sections or free suspensions of chloroplasts showed that gold particles were bound preferentially on the outer surface of crystalloids. Three-dimensional reconstruction of chloroplasts and crystalloids proved that paracrystalline structures varied moderately in their size and took up a significant portion of total chloroplast volume. and H. Synková ... [et al.].
The dark-adapted cells of the green alga Spongiochloris sp. were exposed to "white light" of 1000 µmol(photon) m-2 s-1 for 2 h and then dark adapted for 1.5 h. Changes of photochemical activities during photoadaptation were followed by measurement of chlorophyll (Chl) fluorescence kinetics, 77 K emission spectra, photosynthetic oxygen evolution, and pigment composition. We observed a build-up of slowly-relaxing non-photochemical quenching which led to a decrease of the Fv/Fm parameter and the connectivity. In contrast to the depression of Fv/Fm (35 %) and the rise of non-photochemical quenching (∼ 1.6), we observed an increase in effective absorption cross-section (20 %), Hill reaction (30 %), photosynthetic oxygen evolution (80 %), and electron transport rate estimated from the Chl fluorescence analysis (80 %). We showed an inconsistency in the presently used interpretation schemes, and ascribe the discrepancy between the increase of effective absorption cross-section and the photosynthetic activities on one side and the effective non-photochemical quenching on the other side to the build-up of a quenching mechanism which dissipates energy in closed reaction centres. Such a type of quenching changes the ratio between thermal dissipation and fluorescence without any effect on photochemical yield. In this case the Fv/Fm ratio cannot be used as a measure of the maximum photochemical yield of PS2. and M. Koblížek ... [et al.].
Differences between photosynthetic characteristics of chlorophyll (Chl) 6-deficient aurea mutant (Su/su) and the green (su/su) variety of Nicotiana tabacum were tested. Fully mature leaves of 3-5-month-old plants grown in potted soil were investigated. Main differences were found as follows: Respective Chl a and b contents were 3 and 5 times lower in aurea plants, while xanthophylls and carotenes contents per unit of Chl were higher. The content of light-harvesting complex (LHC) was lower and LHC composition differed in aurea mutant. PS 1 activity calculated per unit of Chl content was higher in aurea mutant. The green variety showed the lower photosynthetic rates (Pn) at saturating irradiances whether calculated on the Chl or leaf area basis. At excessive light declined with green plants. Carboxylation efficiency (CE) (CO2 response slope of Pjj at low CO2 concentrations) was higher for aurea mutant. Time- integrated intercellular CO2 concentrations derived from ^^C discrimination were higher for aurea mutant (304 cm^ m'^) than for green plants (283 cm^ m'^), which together with higher mean stomatal conductance in aurea matched CE differences.
Charactenstícs of the pigment apparatus were studied in plants grown from tubers of the oř 3’’^ doně generation of two cultivars of potato (Solanum tuberosum L) transformed with Agrobacterium tumefaciens strains. The cv. Zvíkov carries pRiA4b T-DNA of A. rhizogenes and the vector plasmid pGA472 T-DNA carrying the gene for kanamycin resistance. The cv. Kamýk carries the vector plasmid pCB1339 which contains the kanamycin resistance gene and the cytokinin synthesis gene. In the field experiments, the plant dry matter, the relative water content, the chlorophyll (Chl) a and b contents, the Chl a/b ratio and the course of slow Chl fluorescence induction curves were not signifícantly different in transformed and control plants. The amoímt of the Chl-protein complexes of the reaction centres of both photosystems separated by electrophoresis was similar for both transformed and control plants. Howevér, the content of oligomeric light-harvesting complex was significantly higher in both the transformants.
Experiments were performed to distinguish some of the proposed mechanisms by which thylakoid membranes regulate the performance of photosynthetic apparatus in relation to non-photochemical quenching, qN. Aliphatic diamines were used as uncouplers of transmembrane H+ gradient as they can be transported across the membrane at the expense of hydrogen cations. Diamines did not induce changes in low-temperature fluorescence emission but induced different changes in membrane ultrastructure. Positively charged peptides did not affect membrane ultrastructure but blocked qN. In addition, they caused an increase of low temperature fluorescence emission between 710 and 720 nm. For control peptide, the maximal fluorescence increase was found at 715 nm. Fragments of light-harvesting complex 2 in their phosphorylated and non-phosphorylated form shifted the position of this increase. We believe that peptides bind to membrane surface and reduce the mobility of membrane components whose migration is needed for observation of qN. Phosphorylated and non-phosphophorylated LHC2 fragments bind to different binding sites for corresponding forms of the protein. and D. Štys ... [et al.].