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  • 1
    Electronic Resource
    Electronic Resource
    Stem photosynthesis in a desert ephemeral, Eriogonum inflatum (1987)
    Springer
    Oecologia 72 (1987), S. 542-549 
    Details
    ISSN: 1432-1939
    Keywords: Eriogonum inflatum ; Internal CO2 concentration ; Stem photosynthesis ; Water-use efficiency ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gas exchange characteristics of photosynthetic tissues of leaves and stems of Eriogonum inflatum are described. Inflated stems were found to contain extraordinarily high internal CO2 concentrations (to 14000 μbar), but fixation of this internal CO2 was 6–10 times slower than fixation of atmospheric CO2 by these stems. Although the pool of CO2 is a trivial source of CO2 for stem photosynthesis, it may result in higher water-use efficiency of stem tissues. Leaf and stem photosynthetic activities were compared by means of CO2 fixation in CO2 response curves, light and temperature response curves in IRGA systems, and by means of O2 exchange at CO2 saturation in a leaf disc O2 electrode system. On an area basis leaves contain about twice the chlorophyll and nitrogen as stems, and are capable of up to 4-times the absolute CO2 and O2 exchange rates. However, the stem shape is such that lighting of the shaded side leads to a substantial increase in overall stem photosynthesis on a projected area basis, to about half the leaf rate in air. Stem conductance is lower than leaf conductance under most conditions and is less sensitive to high temperature or high VPD. Under most conditions, the ratio C i /C a is lower in stems than in leaves and stems show greater water-use efficiency (higher ratio assimilation/transpiration) as a function of VPD. This potential advantage of stem photosynthesis in a water limited environment may be offset by the higher VPD conditions in the hotter, drier part of the year when stems are active after leaves have senesced. Stem and leaf photosynthesis were similarly affected by decreasing plant water potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378980
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  • 2
    Electronic Resource
    Electronic Resource
    Stem photosynthesis in a desert ephemeral, Eriogonum inflatum (1987)
    Springer
    Oecologia 72 (1987), S. 533-541 
    Details
    ISSN: 1432-1939
    Keywords: δ13C ; Eriogonum inflatum ; Great Basin ; Mojave ; Photosynthetic morphology ; Stem photosynthesis ; Water-use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Seasonal patterns in plant morphology, phenology, and physiology were monitored in several populations of Eriogonum inflatum, a desert ephemeral which produces a large photosynthetic inflorescence above a basal leaf rosette. Green stems accounted for 66–77% of whole plant photosynthetic surface area when integrated over a developmental cycle, whereas only 40–67% of the yearly transpirational water loss could be attributed to stems. Stems were found to have lower nitrogen and chlorophyll contents than leaves, and lower stomatal conductance under all physiological conditions encountered. However, because stems occur later in the year than leaves, comparison of physiological patterns was complicated by the two structures being exposed to different climatic regimes during their developmental cycles. Stems exhibited higher δ13C values than leaves, indicating that stems operated at higher water-use efficiencies than leaves, at least during periods when both leaves and stems were present. Higher water-use efficiency in stems of E. inflatum is attributed to both more conservative water use patterns and to their vertical orientation, allowing stems to remain photosynthetically active longer into the dry season after senescence of the horizontal leaf rosette.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378979
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  • 3
    Electronic Resource
    Electronic Resource
    Photosynthetic response of Ulva rotundata to light and temperature during emersion on an intertidal sand flat (1992)
    Springer
    Oecologia 89 (1992), S. 516-523 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00317158
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  • 4
    Electronic Resource
    Electronic Resource
    Photoacclimation and photoinhibition in Ulva rotundata as influenced by nitrogen availability (1991)
    Springer
    Planta 184 (1991), S. 235-243 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Growth rate ; Nitrogen and photosynthesis ; Photoacclimation ; Photoinhibition of photosynthesis ; Photosynthesis and N supply ; Quantum yield ; Ulva
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Clonal tissue of the marine chlorophyte macroalga, Ulva rotundata Blid., was transferred from 100 to 1700 μmol photons · m−2 · s−1 under limiting (1.5 μM NH 4 + maximum, N/P=2) and sufficient (15 μM NH 4 + maximum, N/P=20) nitrogen supply at 18° C and 11 h light-13 h darkness daily. Photoinhibition was assayed by light-response curves (photosynthetic O2 exchange), and chlorophyll fluorescence at 77 K and room temperature. Daily surface-area growth rate (μSA) in N-sufficient plants increased sixfold over 3 d and was sustained at that level. During this period, respiration (R d) doubled and light-saturated net photosynthesis capacity (P m) increased by nearly 50%, indicating acclimation to high light. Quantum yield (ϕ) decreased by 25% on the first day, but recovered completely within one week. The ratio of variable to maximum fluorescence (F v/F m) also decreased markedly on the first day, because of an increase in initial fluorescence (F o) and a decrease in F m, and partially recovered over several days. Under the added stress of N deficiency, μSA accelerated fivefold over 4 d, despite chronic photoinhibition, then declined along with tissue-N. Respiration doubled, but P m decreased by 50% over one week, indicating inability to acclimate to high light. Both ϕ and F v/F m decreased markedly on the first day and did not significantly recover. Changes in F o, F m and xanthophyll-cycle components indicate concurrent photodamage to photosystem II (PSII) and photoprotection by thermal deexcitation in the antenna pigments. Increasing μSA coincided with photoinhibition of PSII. Insufficient diel-carbon balance because of elevated R d and declining P m and tissue-N, rather than photochemical damage per se, was the apparent proximate cause of decelerating growth rate and subsequent tissue degeneration under N deficiency in U. rotundata.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197952
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  • 5
    Electronic Resource
    Electronic Resource
    Fluorescence quenching during photosynthesis and photoinhibition of Ulva rotundata blid. (1993)
    Springer
    Planta 190 (1993), S. 97-106 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Photoinhibition ; Photoprotection ; Ulva (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationships between photoinhibition and photoprotection in high and low-light-grown Ulva were examined by a combination of chlorophyll-fluorescence-monitoring techniques. Tissues were exposed to a computer-controlled sequence of 5-min exposures to red light, followed by 5-min darkness, with stepwise increases in photon flux. Coefficients of chlorophyll fluorescence quenching (1−qP and NPQ) were calculated following a saturating pulse of white light near the end of each 5-min light treatment. Dark-adapted chlorophyll fluorescence parameters (F0 and FV/FM) were calculated from a saturating pulse at the end of each 5-min dark period. Low-light-grown Ulva showed consistently higher 1−qP, i.e. higher reduction status of Q (high primary acceptor of photosystem II), and lower capacity for nonphotochemical quenching (NPQ) at saturating light than did high-light-grown plants. Consequently, low-light plants rapidly displayed photoinhibitory damage (increased F0) at light saturation in seawater. Removal of dissolved inorganic carbon from seawater also led to photoinhibitory damage of high-light-grown Ulva at light saturation, and addition of saturating amounts of dissolved inorganic carbon protected low-light-grown plants against photoinhibitory damage. A large part of NPQ was abolished by treatment with 3 mM dithiothreitol and the processes so inhibited were evidently photoprotective, because dithiothreitol treatment accelerated photoinhibitory damage in both low- and high-light-grown Ulva. The extent of photoinhibitory damage in Ulva was exacerbated by treatment with chloramphenicol (1 mM) without much effect on chlorophyll-quenching parameters, evidently because this inhibitor of chloroplast protein synthesis reduced the rate of repair processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195680
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  • 6
    Electronic Resource
    Electronic Resource
    Photoacclimation and photoinhibition inUlva rotundata as influenced by nitrogen availability (1991)
    Springer
    Planta 184 (1991), S. 235-243 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Growth rate ; Nitrogen and photosynthesis ; Photoacclimation ; Photoinhibition of photosynthesis ; Photosynthesis and N supply ; Quantum yield ; Ulva
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Clonal tissue of the marine chlorophyte macroalga,Ulva rotundata Blid., was transferred from 100 to 1700 μmol photons · m−2 · s−1 under limiting (1.5 μM NH 4 + maximum, N/P=2) and sufficient (15 μM NH 4 + maximum, N/P=20) nitrogen supply at 18° C and 11 h light-13 h darkness daily. Photoinhibition was assayed by light-response curves (photosynthetic O2 exchange), and chlorophyll fluorescence at 77 K and room temperature. Daily surface-area growth rate (μSA) in N-sufficient plants increased sixfold over 3 d and was sustained at that level. During this period, respiration (R d) doubled and light-saturated net photosynthesis capacity (P m) increased by nearly 50%, indicating acclimation to high light. Quantum yield (ϕ) decreased by 25% on the first day, but recovered completely within one week. The ratio of variable to maximum fluorescence (F v/F m) also decreased markedly on the first day, because of an increase in initial fluorescence (F o) and a decrease inF m, and partially recovered over several days. Under the added stress ofN deficiency, μSA accelerated fivefold over 4 d, despite chronic photoinhibition, then declined along with tissue-N. Respiration doubled, butP m decreased by 50% over one week, indicating inability to acclimate to high light. Bothϕ andF v/F m decreased markedly on the first day and did not significantly recover. Changes inF o,F m and xanthophyll-cycle components indicate concurrent photodamage to photosystem II (PSII) and photoprotection by thermal deexcitation in the antenna pigments. Increasing μSA coincided with photoinhibition of PSII. Insufficient diel-carbon balance because of elevatedR d and decliningP m and tissue-N, rather than photochemical damage per se, was the apparent proximate cause of decelerating growth rate and subsequent tissue degeneration under N deficiency inU. rotundata.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01102423
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  • 7
    Electronic Resource
    Electronic Resource
    Chlorophyll fluorescence in the resurrection plant Selaginella lepidophylla (Hook. & Grev.) Spring during high-light and desiccation stress, and evidence for zeaxanthin-associated photoprotection (1993)
    Springer
    Planta 189 (1993), S. 30-38 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Desiccation tolerance ; Fluorescence quenching (non-photochemical, photochemical) ; Photoprotection ; Selaginella ; Zeaxanthin (xanthophyll cycle)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The function of photosystem (PS)II during desiccation and exposure to high photon flux density (PFD) was investigated via analysis of chlorophyll fluorescence in the desert resurrection plant Selaginella lepidophylla (Hook. and Grev.) Spring. Exposure of hydrated, physiologically competent stems to 2000 μmol · m−2 · s−1 PFD caused significant reductions in both intrinsic fluorescence yield (FO) and photochemical efficiency of PSII (FV/FM) but recovery to pre-exposure values was rapid under low PFD. Desiccation under low PFD also affected fluorescence characteristics. Both FV/FM and photochemical fluorescence quenching remained high until about 40% relative water content and both then decreased rapidly as plants approached 0% relative water content. In contrast, the maximum fluorescence yield (FM) decreased and non-photochemical fluorescence quenching increased early during desiccation. In plants dried at high PFD, the decrease in FV/FM was accentuated and FO was reduced, however, fluorescence characteristics returned to near pre-exposure values after 24-h of rehydration and recovery at low PFD. Pretreatment of stems with dithiothreitol, an inhibitor of zeaxanthin synthesis, accelerated the decline in FV/FM and significantly increased FO relative to controls at 925 μmol · m−2 · s−1 PFD, and the differences persisted over a 3-h low-PFD recovery period. Pretreatment with dithiothreitol also significantly decreased non-photochemical fluorescence quenching, increased the reduction state of QA, the primary electron acceptor of PSII, and prevented the synthesis of zeaxanthin relative to controls when stems were exposed to PFDs in excess of 250 μmol · m−2 · s−1. These results indicate that a zeaxanthin-associated mechanism of photoprotection exists in this desert pteridophyte that may help to prevent photoinhibitory damage in the fully hydrated state and which may play an additional role in protecting PSII as thylakoid membranes undergo water loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201340
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