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  • 1
    ISSN: 1432-2048
    Keywords: Chloroplasts ; Leaf cells ; Photoinhibition ; Photorespiration ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When isolated intact chloroplasts or cells from spinach (Spinacia oleracea L.) leaves are incubated in the light in the absence of CO2, their capacity for subsequent CO2-dependent photosynthetic oxygen evolution is drastically decreased. This inhibition is light and oxygen-dependent and can be prevented by addition of bicarbonate. It is concluded that the normal dissipation of photosynthetic energy by carbon assimilation and in processes related to photorespiration is an essential condition for the physiological stability of illuminated intact chloroplasts and cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Chlorophyll fluorescence ; Photoinhibition ; Photosynthesis ; Temperature stress ; Ulva
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have investigated the diurnal response of photosynthesis and variable photosystem II (PSII) chlorophyll fluorescence at 77 K for thalli of the chlorophyte macroalga, Ulva rotundata, grown in outdoor culture and transplanted to an intertidal sand flat in different seasons. The physiological response in summer indicated synergistic effects of high PFD and aerial exposure, the latter probably attributable to temperature, which usually increased by 8 to 10° C during midday emersion. Except at extreme emersed temperatures in summer (38° C), the light-saturated photosynthesis rate (Pm) did not decline at midday. In contrast, light-limited quantum yield of photosynthetic O2 exchange (τ) and the ratio of variable to maximum fluorescence yield (Fv/Fm) reversibly declined during midday low tides in all seasons. Shade-grown thalli exhibited a fluorescence response suggestive of greater photodamage to PSII, whereas sun-grown thalli had greater photoprotective capacity. The fluorescence decline was smaller when high tide occurred at midday, and was delayed during morning cloudiness. These results suggest that the diurnal response to PFD in this shallow water species is modified by tidal and meteorological factors. U. rotundata has a great capacity for photoprotection which allows it to tolerate and even thrive in the harsh intertidal environment.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2048
    Keywords: C3, C4 plants (H-isotope composition) ; Deuterium ; Hydrogen-isotope composition ; Leaf (H-isotope composition)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The natural abundance hydrogen-isotope composition of leaf water ( $$\delta _{\text{D}}^{{\text{H}}_{\text{2}} {\text{O}}} $$ ) and leaf organic matter (δ D org ) was measured in leaves of C3 and C4 dicotyledons and monocotyledons. The $$\delta _{\text{D}}^{{\text{H}}_{\text{2}} {\text{O}}} $$ value of leaf water showed a marked diurnal variation, greatest enrichment being observed about midday. However, this variation was greater in the more slowly transpiring C4 plants than in C3 plants under comparable environmental conditions. A model based on analogies with a constant feed pan of evaporating water was developed and the difference between C3 and C4 plants expressed in terms of either differences in kinetic enrichment or different leaf morphology. Microclimatic and morphological features of the leaves which may be associated with this factor are discussed. There was no daily excursion in the δ D org value in leaves of either C3 or C4 plants. When δ D org values were referenced to the mean $$\delta _{\text{D}}^{{\text{H}}_{\text{2}} {\text{O}}} $$ values during the period of active photosynthesis, the discrimination against deuterium during photosynthetic metabolism (ΔD) was greater in C3 plants (-117 to -121‰) than in C4 plants (-86 to -109‰). These results show that the different water use “strategies” of C3 and C4 plants are responsible for the measured difference in deuterium-isotope composition of leaf water. However, it is unlikely that these physical processes account fully for the differences in hydrogen-isotope composition of the products of C3 and C4 photosynthetic metabolism.
    Type of Medium: Electronic Resource
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