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  • 1
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The CAM vine Hoya australis and three C3 vines, Smilax australis, Ipomoea pes-caprae and Kennedta rubicunda, were studied at a site on the coast of northeastern New South Wales, Australia. The level of CAM activity (nocturnal acid accumulation) was comparable in H. australis growing in full sunlight and in deep shade. Acclimation to shade by H. australis was indicated by thinner leaves, increased chlorophyll content, decreased chlorophyll a/b ratios, lower dark respiration rates, and lower light compensation points. When growing in full sunlight H. australis exhibited reductions in photochemical efficiency, as indicated by reduced quantum yields and Fv/Fm fluorescence from PS II as well as low rates of photosynthesis at high light. Sun leaves of H. australis experienced a massive quenching of fluorescence from PS II during normal exposure to midday irradiance which was rapidly reversible under low irradiance conditions in the late afternoon. This quenching indicated a reduction in photochemical efficiency, part of which could be accounted for by an increase in non-radiative energy dissipation, while part of it was due to one or more processes not yet identified. Changes in PS II fluorescence from shade H. australis exposed to full sunlight suggest a decrease in the rate constant for photochemistry indicative of damage to the reaction centre, as well as an increase in non-radiative energy dissipation. The C3 vine S. australis was also shade tolerant, but exhibited little evidence of photoinhibition when growing in full sunlight. Ipomoea pescaprae and K. rubicunda, both of which were apparently shade intolerant (being found only in full sunlight), possessed high quantum yields and much higher photosynthetic capacities than either H. australis or S. australis. From this study, and several others, it appears that plants possessing CAM experience photoinhibition to a greater degree than do C3 species in full sunlight under natural conditions, which is probably exacerbated by some degree of CAM-idling.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2048
    Keywords: Chloroplast solutes ; Mesembryanthemum ; Salt tolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Concentrations of four major solutes (Na+, K+, Cl-, proline) were determined in isolated, intact chloroplasts from the halophyte Mesembryanthemum crystallinum L. following long-term exposure of plants to three levels of NaCl salinity in the rooting medium. Chloroplasts were obtained by gentle rupture of leaf protoplasts. There was either no or only small leakage of inorganic ions from the chloroplasts to the medium during three rapidly performed washing steps involving precipitation and re-suspension of chloroplast pellets. Increasing NaCl salinity of the rooting medium resulted in a rise of Na+ und Cl- in the total leaf sap, up to approximately 500 and 400 mM, respectively, for plants grown at 400 mM NaCl. However, chloroplast levels of Na+ und Cl- did not exceed 160–230 and 40–60 mM, respectively, based upon a chloroplast osmotic volume of 20–30 μl per mg chlorophyll. At 20 mM NaCl in the rooting medium, the Na+/K+ ratio of the chloroplasts was about 1; at 400 mM NaCl the ratio was about 5. Growth at 400 mM NaCl led to markedly increased concentrations of proline in the leaf sap (8 mM) compared with the leaf sap of plants grown in culture solution without added NaCl (proline 0.25 mM). Although proline was fivefold more concentrated in the chloroplasts than in the total leaf sap of plants treated with 400 mM NaCl, the overall contribution of proline to the osmotic adjustment of chloroplasts was small. The capacity to limit chloroplast Cl- concentrations under conditions of high external salinity was in contrast to an apparent affinity of chloroplasts for Cl- under conditions of low Cl- availability.
    Type of Medium: Electronic Resource
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