No description available.

Thylakoid organization and the distribution of photosystem (PS) I and II proteins in the green alga Coleochaete scutata were analyzed by electron microscopy. Thylakoids were observed to associate in varied conformations. Extended bands of thylakoids were present, as in other algae, but numerous grana, characteristic of higher plants, were also detected. Immunolabelling experiments were conducted with two heterologous antisera raised against PS proteins in the cyanobacterium Synechococcus elongatus: one antiserurn against the 60 and 62 kDa PSI reaction centre proteins, the other against the 47 kDa PSII core antenna protein. PSI was 2.6 times more concentrated in the nonappressed membranes (NAM) than in the appressed (AM), with 62% of labelling on NAM. The concentration of PSII in AM was 1.6 times that of the NAM, accounting for 75% of PSII. Thus, in C scutata, PSI and PSII are located in both appressed and nonappressed thylakoid membranes, but with a trend towards the lateral heterogeneity of PS proteins observed in higher plants. These results support the body of ultrastructural and molecular data linking charophytes with the ancestry of higher plants.

It has been proposed that the protective systems (photorespiration, the anti-oxidant system and non-radiative energy dissipation) alleviate or reduce photoinhibitory damage under high light conditions. To investigate the role of these mechanisms in C4 photosynthetic species, nine day old Zea mays seedlings were photoinhibited (30 minutes of 2500 J,Lmol m-2 s-1 PPFD) in the presence of various concentrations of 02 or CO2; or by photoinhibiting leaves in N2 after they had been fed glycolate or phosphoglycerate via the transpiration stream. The extent of the photoinhibition and the subsequent recovery from the photoinhibitory treatments was monitored with both CO2 gas exchange and chlorophyll fluorometry. Photoinhibitory treatments resulted in both a decrease in the rate of CO2 fixation and an interruption of PSII electron transport. CO2 response curves were used to monitor the efficiency of the carboxylation processes and the level of carbon metabolism substrate cycling during recovery following photoinhibitory treatments. Both were decreased by the treatment and recovered once leaves were returned to normal conditions. Low concentrations of 02 (2%) markedly reduced the extent of the photoinhibition. This protection could not be accounted for by photorespiration, which would be inoperative at such a low 02 concentration. Leaves fed glycolate exhibited enhanced photoinhibtion. It is also unlikely that the anti-oxidant system (Mehler reaction and associated glutathione and ascorbate reactions) could utilize sufficient reductant at such low 02 concentrations to produce the observed protection. Leaves inhibited in the presence of 02 had decreased maximum fluorescence yields (Fm) and little altered initial fluorescence yields (F0)' resulting in decreased PSlI efficiency (Fv/Fm)' Photoinhibition resulted in a small increase in the slow relaxing component (60 minute) of non-radiative energy dissipation. This component became more predominant as the 02 concentration was increased. The rate constant for photochemistry was also decreased by the inhibitory treatment. Leaves supplied with CO2 at a concentration above 50 J,Lmol mol-1 exhibited little photoinihibition suggesting that the protection was not due to a quantitative utilization of energy. PGA, fed via the transpiration strea~ enhanced the photoinhibition, suggesting that more than just the Benson-Calvin cycle is required to protect C4 plants from photoinhibition. At CO2 concentrations below this, the Fv/FID ratio was decreased due to large increases in the F0 values. Fm was little altered. These changes are characteristic of a decrease in the rate constant for photochemistry. The rate constant for non-radiative energy dissipation was little altered by the photoinhibition. The protection observed in the presence of either CO2 or 02 was not due to a quantitative utilization of energy and the different responses of F0' Fm and the rate constants KD and Kp, suggest that different mechanisms were operative in the presence or absence of oxygen. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

No description available.

Bienertia sinuspersici is one of three terrestrial plants identified to perform C4 photosynthesis in a single chlorenchyma cell by compartmentation of organelles and photosynthetic enzymes. This thesis describes a study on the distribution of photosynthetic proteins and their corresponding transcripts in an attempt to understand the regulatory mechanisms underlying their differential accumulation in two types of chloroplast. The patterns of photosynthetic enzymes and transcripts accumulation in developing leaves were examined by using immunolocalization and in situ hybridization. The polypeptides of Rubisco large subunit (RbcL) and pyruvate Pi dikinase (PPDK) accumulate equally in all chloroplasts before the formation of two intracellular cytoplasmic compartments: the central (CCC) and peripheral (PCC) cytoplasmic compartment. The differential accumulation of these enzymes is not completed until the mature stage, indicating that the transition from C3 to C4 photosynthesis occurs at the very late stage of leaf development. In mature chlorenchyma cells, RbcL accumulates 20-fold more in the CCC than in the PCC while PPDK demonstrates a concentration gradient that is lowest in chloroplasts in the center of the CCC and highest in the PCC chloroplasts. The pattern of rbcL transcript accumulation follows that of its polypeptides in developing leaves, suggesting the expression of this gene is controlled at the transcriptional and/or mRNA stability level. The quantitative real-time PCR results of rbcL transcripts from isolated chloroplasts of each compartment further supported this observation. Bioinformatics tools were used to predict possible structual motifs on rbcL mRNA as an attempt to speculate on their role in its distribution and identify the presence of secondary structures in the 5??? untranslated region (UTR) that may function in the regulation of gene expression. Detailed examination of the ultrastructure of the unique intracellular organization in the single-cell C4 system showed various vesicles in close proximity to chloroplasts in both compartments in mature chlorenchyma cells of B. sinuspersici under H2O2 treatments. To further understand the biogenesis of these vesicles, imunolocalization and transient expression of green fluorescent protein (GFP) experiments were performed. These studies identified stroma-filled tubules (stromules) as the structure that participates in the formation of sequestering vesicles (autophagosomes) containing cytosol and organelles. Fluorescent microscopic analyses using autophagosome-specific and autophagic vacuole markers only showed partial overlapping of two fluorescent signals. These results suggest that the formation of autophagosome and autophagic vacuole occur independently. The contribution of stromules to autophagosome formation and the involvement of chloroplastic envelopes in this process provide another level of regulation in the compartmentation of photosynthetic enzymes in single-cell C4 system. Collectively, the findings in this thesis enhance our overall understanding on the development and function of single-cell C4 photosynthesis.

ix, 134 leaves : tables, graphs (part fold.) ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.), University of Adelaide, Dept. of Botany, 1979

Photosynthetic activity of three seagrass species, Posidonia sinuosa Cambridge et Kuo, Posidonia australis Hook. f. and Halophila ovalis (R. Br.) Hook., growing in Cockburn Sound, Western Australia, was assessed using an underwater pulse amplitude modulated fluorometer (Diving-PAM). The study aimed to determine possible causes and the extent of stress to seagrasses during transplantation, so that rehabilitation efforts can be improved by reducing stress during the transplant process. Absorptance factors for each species were determined as 0.64 ± 0.04 for P. sinuosa, 0.59 ± 0.02 for P. australis and 0.55 ± 0.02 for H. ovalis, which were substantially lower than previously reported photosynthetic absorption factors. Transmittance, reflectance and non-photosynthetic absorptance of light diverted between 35-45% of irradiance from use in photosynthesis. An investigation of potential errors during measurement of rapid light curves (RLCs) reinforced the importance of ensuring that leaves remained stationary in the Universal Sample Holder. Any movement of seagrass leaves resulted in incorrect measurements of electron transport rates (ETR). A study on seasonal photosynthetic rates of each species found that maximum ETR (ETRmax) varied seasonally and among species. The highest ETRmax for each species occurred during summer, when ambient irradiances were at a maximum, and decreased during autumn. H. ovalis had the highest overall ETRmax in summer, followed by P. australis and P. sinuosa. Effective quantum yield(ΔF/Fm′)of each species varied seasonally, changing inversely with irradiance, which agrees with previously reported studies. ETRmax for each species also showed a diurnal pattern coincident with irradiance throughout the day. The ÄF/Fm for all species demonstrated a diurnal decrease in photosynthetic efficiency coincident with the midday irradiance maximum. Large natural variation in ETR was detected in all species, indicating that the effects of external stress on ETR may be difficult to detect. Two adjacent, physically separated seagrass meadows were examined to determine if apparent visual differences between the sites were reflected by measured physical and photosynthetic characteristics. ETR, leaf area index and sediment grain size differed between sites, but ΔF/Fm, canopy height, shoot density and epiphyte biomass did not, indicating a poor connection between physical and photosynthetic characteristics at these two meadows. Therefore caution should be used when attempting to visually assess the photosynthetic activity of a site based on physical characteristics. Changes in photosynthetic activity were monitored to determine seagrass stress during transplantation, and post-transplantation recovery. Two transplantation methods, sprigs and plugs, were examined, and photosynthetic activity was compared before, during and after transplantation. ETRmax of sprigs took one to two months to increase to the same level recorded at a control meadow, primarily due to desiccation stress suffered during transport. The ΔF/Fm′ decreased below 0.2 after transplantation, but fully recovered after three months. Survival of sprigs was reduced due to strong currents and heavy epiphytic fouling. The ETRmax of transplanted plugs (5, 10 and 15 cm diameter) took up to one week to recover to the same level recorded at a control meadow. Survival of plugs was reduced due to winter swells and storms. Since the leading human-controlled cause of transplant failure was desiccation stress, future transplanting efforts should endeavour to keep seagrasses submerged at all times during the transplanting process.

Thesis (Ph.D.), University of Adelaide, Dept. of Botany, 1979.

Thesis (M.S.)--Bowling Green State University, 2008. / Document formatted into pages; contains vi, 52 p. : ill., maps. Includes bibliographical references.

Undergraduate honors paper--Mount Holyoke College, 2005. Dept. of Earth and Environment. / Includes bibliographical references (leaves 67-72).