Reduction State of Q and Nonradiative Energy Dissipation during Photosynthesis in Leaves of a Crassulacean Acid Metabolism Plant, Kalanchoë daigremontiana Hamet et Perr

Abstract

Fluorescence was measured in leaves of the CAM plant Kalanchoe daigremontiana using a pulse modulation technique at room temperature. During a 12-h light period at 500 micromole photons per square meter per second (400-700 nanometers) in air containing 350 microbar CO2, the component of fluorescence quenching related to the reduction state of Q, the primary electron transport acceptor of PSII, remained fairly constant and showed that only 20% of Q were in the reduced form. The reduction state was slightly increased at the onset and at the end of the light period. By contrast, the nonphotochemical component of fluorescence quenching which is a measure of the fraction of nonradiative deexcitation underwent marked diurnal changes. Nonradiative energy conversion was low during the phase of most active malic acid decarboxylation in the middle of the light period when uptake of atmospheric CO2 was negligible, and when internal CO2 partial pressures were higher than in air, this allowed for high rates of CO2 reduction in the chloroplasts.Nonradiative energy conversion was high during the early and the late light period when atmospheric CO2 was taken up and internal CO2 partial pressures were below air level. Manipulation of the internal CO2 partial pressure during the late light period by increasing or decreasing the external CO2 partial pressure to 1710 and 105 microbar, respectively, led to changes in the magnitude of energy dependent fluorescence quenching which were consistent with the relationship between nonradiative energy dissipation and internal CO2 partial pressure observed during the diurnal cycle. Again, the reduction state of Q was hardly affected by these treatments. Thus, changes in electron transport rate during the diurnal CAM cycle at a given photon flux density lead primarily to alterations in the rate of nonradiative energy dissipation, with the reduction state of Q being maintained at a relatively low and constant level. Conditions are described under which nonphotochemical dissipation of excitation energy reaches a maximum value and the reduction state of Q is increased.When leaves are illuminated, the excitation energy of Chl can be dissipated by photosynthesis, as heat or, to a very small extent, as fluorescence. Simultaneous measurements of fluorescence yield and of gas exchange provide information about the partitioning of excitation energy between photochemical and nonphotochemical processes (11,21). Fluorescence emitted at room temperature emanates predominantly from Chl a of PSII and depends on the redox state of the primary electron acceptor of ' Supported by the Deutsche Forschungsgemeinschaft. PSII, Q.2 If, for example, a large percentage of Q is kept oxidized by electron flow to sustain reduction of C02, photochemical quenching, qp, will be high and fluorescence will be low. Nonphotochemical quenching processes, designated qE, relate, first, to the establishment of a proton gradient across the thylakoid membrane and, thereby, to ATP consumption in photosynthesis (12,13). Low ra...

Daily Changes in CO2 and Water Vapor Exchange, Chlorophyll Fluorescence, and Leaf Water Relations in the Halophyte Mesembryanthemum crystallinum during the Induction of Crassulacean Acid Metabolism in Response to High NaCl Salinity

“…Further, the transient decline in the rate of electron transport in the middle of the light period after 3 d at 400 mM NaCl, as indicated by measurements ofChl a fluorescence, is consistent with the conclusion that the relationship between changes in A, g, and pi during midday is different from that in normal CAM. If the midday depression in net CO2 assimilation rate and stomatal conductance were the consequence of a rise in pi, due to decarboxylation of malic acid, rates of electron transport would have increased rather than decreased (35,38). These diurnal alterations in pi (Fig.…”

“…Procedures were as described previously (35,38). The photon-use efficiency of noncyclic electron transport was obtained as (Fm-Fs)/F2 (17) where Fs is the steady state fluorescence yield in the light (with the PPFD incident on leaves in the gas-exchange chamber during photoperiods) and Fi, is the fluorescence yield in a pulse of saturating light.…”

Zeaxanthin and the Induction and Relaxation Kinetics of the Dissipation of Excess Excitation Energy in Leaves in 2% O2, 0% CO2

“…[1988] Plant Physiol 87: [17][18][19][20][21][22][23][24]. These findings suggest that the same dissipation process may be induced by very different treatments and that this particular dissipation process can have widely different relaxation kinetics.…”

High Photosynthetic Capacity in a Shade-Tolerant Crassulacean Acid Metabolism Plant (Implications for Sunfleck Use, Nonphotochemical Energy Dissipation, and Susceptibility to Photoinhibition)

“…Studies of -1eaf photosynthesis by conventional gas-exchange techniques are of limited use in CAM plants due to stomatal closure during phase I11 (Osmond, 1978; the daytime de-acidification portion of the CAM cycle). Modern chlorophyll fluorescence methods (reviewed by Schreiber et al, 1994) have proven to be of great use in CAM research (Winter and Demmig, 1987;Winter et al, 1990;Keiller et al, 1994;Adams and DemmigAdams, 1996) and were used in this study to examine photosynthetic responses to various environmental and physiological factors in A. magdalenae and associated C, species. Specific objectives were (a) to investigate the proposal that a high photosynthetic capacity in A. magdalenae enables this species to use sun flecks more efficiently for daytime CO, fixation than co-occurring C, shade plants; (b) to explore the influence of growth irradiance and time of day (as a proxy of CAM phase) on photochemical efficiency and nonphotochemical quenching, and (c) to assess the influence of current ambient light leve1 and the growth irradiance history on the daytime CAM cycle dynamics and the susceptibility to photoinhibition in A. magdalenae.…”