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  • 1
    Electronic Resource
    Electronic Resource
    High susceptibility to photoinhibition of young leaves of tropical forest trees (1995)
    Springer
    Planta 197 (1995), S. 583-591 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Photoinhibition (photosynthesis) ; Photosynthetic gas exchange ; Photo-system II ; Tropical forest species ; Xanthophyll cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinhibition of photosynthesis was studied in young (but almost fully expanded) and mature canopy sun leaves of several tropical forest tree species, both under controlled conditions (exposure of detached leaves to about 1.8 mmol photons·m-2·s-1) and in the field. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence emission (FV/FM) and also by gas-exchange measurements. For investigations in situ, young and mature leaves with similar exposure to sunlight were compared. The results show a consistently higher degree of photoinhibition in the young leaves. In low light, fast recovery was observed in both types of leaves in situ, as well as in the laboratory. The fluorescence parameter 1 — FS/F′M (where FS = stationary fluorescence and f′M = maximum fluorescence during illumination) was followed in situ during the course of the day in order to test its suitability as a measure of the photosynthetic yield of photosystem II (PSII). Electron-transport rates were calculated from these fluorescence signals and compared with rates of net CO2 assimilation. Measurements of diurnal changes in PSII ‘yield’ confirmed the increased susceptibility of young leaves to photoinhibition. Calculated electron transport qualitatively reflected net CO2 uptake in situ during the course of the day. Photosynthetic pigments were analyzed in darkened and illuminated leaves. Young and mature leaves showed the same Chl a/b ratio, but young leaves contained about 50% less Chl a + b per unit leaf area. The capacity of photosynthetic O2 evolution per unit leaf area was decreased to a similar extent in young leaves. On a Chl basis, young leaves contained more α-carotene, more xanthophyll cycle pigments and, under strong illumination, more zeaxanthin than mature leaves. The high degree of reversible photoinhibition observed in these young sun leaves probably represents a dynamic regulatory process protecting the photosynthetic apparatus from severe damage by excess light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191564
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of elevated CO2 on growth and crassulacean-acid-metabolism activity of Kalanchoë pinnata under tropical conditions (1997)
    Springer
    Planta 201 (1997), S. 389-396 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Carbohydrate metabolism ; CO2 exchange ; Crassulacean acid metabolism (elevated CO2) ; Kalanchoë (elevated CO2) ; Organic acid metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  Kalanchoë pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO2 treatments. However, under elevated CO2, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050081
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  • 3
    Electronic Resource
    Electronic Resource
    Xanthophyll-cycle pigments and photosynthetic capacity in tropical forest species: a comparative field study on canopy, gap and understory plants (1995)
    Springer
    Oecologia 104 (1995), S. 280-290 
    Details
    ISSN: 1432-1939
    Keywords: Photoinhibition ; Photosynthesis ; Tropical forest ; Xanthophyll-cycle pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Xanthophyll-cycle pigments and photosynthetic capacity (PSmax) were analyzed in 25 species from different light environments (canopy, gap, understory) within a Panamanian tropical forest. (1) Sun-exposed leaves of canopy tree species showed the highest photosynthetic capacities and largest xanthophyll-cycle pools (violaxanthin, antheraxanthin, zeaxanthin) of about 87 mmol mol-1 chlorophyll with only small amounts of α-carotene [about 7 mmol mol-1 chlorophyll = 8% of total (α+β) carotene pool]. Under high natural photon flux densities (PFDs) canopy leaves rapidly converted up to 96% of the xanthophyll-cycle pool into zeaxanthin. The back reaction to violaxanthin occurred much faster in low light than in complete darkness. At the end of the night, zeaxanthin still accounted for, on average, 14% of the total xanthophyll-cycle pigments. (2) Leaves of gap plants had intermediate values of PSmax and a 43% lower total carotenoid content than canopy leaves. The average size of the xanthophyll-cycle pool was 35 mmol mol-1 chlorophyll, and α-carotene accounted for up to 66% of the total (α+β) carotene pool. Under high light conditions gap plants converted, on average, 86% of the xanthophyll-cycle pigments into zeaxanthin. The back reaction, following a decrease in ambient PFD, was slower than the forward reaction. At the end of the night, zeaxanthin accounted for, on average, 7% of the xanthophyll-cycle pigments in gap plants. (3) Understory plants showed the lowest values of PSmax and the smallest xanthophyll-cycle pool of about 22 mmol mol-1 chlorophyll. α-Carotene accounted for up to 70% of total carotene. The conversion of xanthophyll-cycle pigments into zeaxanthin was negligible during short sunflecks of 1–2 min duration and PFDs up to about 400 μmol m-2 s-1. At predawn, leaves of understory plants rarely contained any detectable zeaxanthin. Aechmea magdalenae, an understory CAM plant, showed exceptionally high rates of PSmax per unit leaf area compared to sympatric C3 understory species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328362
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    Paper (German National Licenses)
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