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  • 1
    Electronic Resource
    Electronic Resource
    Loss of the precise control of photosynthesis and increased yield of non-radiative dissipation of excitation energy after mild heat treatment of barley leaves (1998)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 104 (1998), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The after effects of a short exposure of intact barley leaves to moderately elevated temperature (40°C, 5 min) on the induction transients and the irradiance dependencies of photosynthesis and chlorophyll fluorescence are presented. This mild heat treatment strongly reduced the oscillations in the rate of photosynthesis and in the yield of chlorophyll fluorescence. However, only a 25% irreversible inhibition of maximum photosynthetic capacity of photosystem II (PSII) measured by oxygen evolution was produced and the intrinsic quantum yield of PSII measured by the chlorophyll fluorescence ratio (Fm- Fo)/Fm decreased by only 15%. In contrast, the above treatment increased radiationless dissipation processes in PSII by a factor of two. In heat-treated leaves, photosynthesis was not saturated even by strong light. Both ΔpH-dependent quenching of excitons in PSII (including formation of zeaxanthin) and state 1/state 2 transition were found to be stimulated. Heat exposure enhanced the control of PSII activity by PSI, as evidenced by a significant increase in the quenching effect of far-red light on the maximum yield of chlorophyll fluorescence. It was deduced that after mild heat treatment, the photosynthetic apparatus in leaves lacks the precise coordinating control of electron transport and carbon metabolism owing to the inability of PSII to support electron transport at a level adequate for carbon metabolism. This effect was not related to the small irreversible thermal damage to PSII, but was rather due to a significant increase in non-photochemical quenching of excitation energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1040407.x
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  • 2
    Electronic Resource
    Electronic Resource
    Blue, red and blue plus red light control of chlorophyll content and CO2 gas exchange in barley leaves: Quantitative description of the effects of light quality and fluence rate (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 85 (1992), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The dependence of the Chl content and the rate of CO2 gas exchange (RGE) on both blue and red quanta fluence rates have been studied in primary leaves of barley (Hordeum vulgare L. cv. Viner). Empirical equations connecting the two photosynthetic indices with fluence rates of blue or red light were developed. These equations consist of 3 (Chl content) or 2 (RGE) terms, each reflecting the involvement of a specific reaction in the long-term light control of the development of the photosynthetic apparatus. On the basis of the equations the effects of mixed blue plus red light on both the Chl content and RGE were calculated. An additive mode of the co-action of blue and red light in the range of high PFDs (10–170 μmol m−2 s−1) becomes evident from the comparison of the experimental results and calculated data. The results indicate the involvement of phytochrome, cryptochrome and chlorophyll in the long-term regulation of the Chl content and RGE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1992.tb04765.x
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of dark-relaxation kinetics of variable fluorescence in intact leaves (1992)
    Springer
    Planta 187 (1992), S. 122-127 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence (variable, dark decay) ; Dolichos ; Electron transport ; Leaf (photosynthesis) ; Photosystem I, II ; Pisum (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dark-relaxation kinetics of variable fluorescence, Fv, in intact green leaves of Pisum stativum L. and Dolichos lablab L. were analyzed using modulated fluorometers. Fast (t1/2 = 1 s) and slow (t1/2 = 7–8 s) phases in fv dark-decay kinetics were observed; the rate and the relative contribution of each phase in total relaxation depended upon the fluence rate of the actinic light and the point in the induction curve at which the actinic light was switched off. The rate of the slow phase was accelerated markedly by illumination with far-red light; the slow phase was abolished by methyl viologen. The halftime of the fast phase of Fv dark decay decreased from 250 ms in dark-adapted leaves to 12–15 ms upon adaptation to red light which is absorbed by PSII. The analysis of the effect of far-red light, which is absorbed mainly by PSI, on Fv dark decay indicates that the slow phase develops when a fraction of QA − (the primary stable electron acceptor of PSII) cannot transfer electrons to PSI because of limitation on the availability of P700+ (the primary electron donor of PSI). After prolonged illumination of dark-adapted leaves in red (PSII-absorbed) light, a transient. Fv rise appears which is prevented by far-red (PSI-absorbed) light. This transient fv rise reflects the accumulation of QA − in the dark. The observation of this transient Fv rise even in the presence of the uncoupler carbonylcyanide m-chlorophenyl hydrazone (CCCP) indicates that a mechanism other than ATP-driven back-transfer of electrons to QA may be responsible for the phenomenon. It is suggested that the fast phase in Fv dark-decay kinetics represents the reoxidation of QA − by the electron-transport chain to PSI, whereas the slow phase is likely to be related to the interaction of QA − with the donor side of PSII.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201633
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  • 4
    Electronic Resource
    Electronic Resource
    Long-term effects of blue or red light on ATP and ADP contents in primary barley leaves (1995)
    Springer
    Planta 196 (1995), S. 211-216 
    Details
    ISSN: 1432-2048
    Keywords: Adenylate content ; Carbon dioxide fixation ; Chlorophyll ; Hordeum ; Light (intensity, quality)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Levels of ATP and ADP were studied in primary leaves of barley (Hordeum vulgare L. cv. Viner) seedlings grown under blue (BL) or red light (RL) of various irradiances. In mature leaf segments, BL stimulated a greater accumulation of adenylates than RL. Transfer of barley seedlings from RL to BL for 48 h caused about a twofold increase in the content of adenylates, probably due to de-novo synthesis of adenine nucleotides. Weak BL was found to stimulate an increase in the adenylate content and a higher irradiance enhanced the stimulatory effect. The adenylate content increased markedly from the base towards the tip of barley leaves grown under BL but not in those grown under RL. However, the adenylate content was higher in the basalmost segment of barley leaves grown under RL, indicating that the action of RL on adenylate content proceeded more rapidly than that of BL. The same conclusion could be drawn from the results of experiments with de-etiolated leaves. A linear relationship was established between the maximum rate of CO2 fixation and the ATP or ADP content in mature segments of primary barley leaves. The possible involvement of two photoreceptors, phytochrome and cryptochrome, in the long-term light regulation of the total content of adenylates in primary barley leaves is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201376
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of chlorophyll a fluoresence changes in weak light in heat treated Amaranthus chloroplasts (1990)
    Springer
    Photosynthesis research 23 (1990), S. 81-87 
    Details
    ISSN: 1573-5079
    Keywords: Amaranthus chloroplast ; chlorophyll a fluorescence ; high temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract After preheating of Amaranthus chloroplasts at elevated temperatures (up to 45°C), the chlorophyll a fluorescence level under low excitation light rises as compared to control (unheated) as observed earlier in other chloroplasts (Schreiber U and Armond PA (1978) Biochim Biophys Acta 502: 138–151). This elevation of heat induced fluorescence yield is quenched by addition of 0.1 mM potassium ferricyanide, suggesting that with mild heat stress the primary electron acceptor of photosystem II is more easily reduced than the unheated samples. Furthermore, the level of fluorescence attained after illumination of dithionite-treated samples is independent of preheating (up to 45°C). Thus, these experiments indicate that the heat induced rise of fluorescence level at low light can not be due to changes in the elevation in the true constant F0 level, that must by definition, be independent of the concentration of QA. It is supposed that the increase in the fluorescence level by weak modulated light is either partly associated with dark reduction of QA due to exposure of chloroplasts to elevated temperature or due to temperature induced fluorescence rise in the so called inactive photosystem II centre where QA are not connected to plastoquinone pool. In the presence of dichlorophenyldimethylurea the fluorescence level triggered by weak modulated light increases at alkaline pH, both in control and heat stressed chloroplasts. This result suggests that the alkaline pH accelerates electron donation from secondary electron donor of photosystem II to QA both in control and heat stressed samples. Thus the increase in fluorescence level probed by weak modulated light due to preheating is not solely linked to increase in true F0 level, but largely associated with the shift in the redox state of QA, the primary stable electron acceptor of photosystem II.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00030066
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