Using chlorophyll fluorescence to assess the fraction of absorbed light allocated to thermal dissipation of excess excitation

Abstract

In the present study we explored the possibility of assessing the allocation of photons absorbed by photosystem II (PSII) antennae to thermal energy dissipation and photosynthetic electron transport in leaves of several plant species under field conditions. Changes in chlorophyll fluorescence parameters were determined in situ over the course of an entire day in the field in sun‐exposed leaves of two species with different maximal rates of photosynthesis, Helianthus annuus (sunflower) and Vinca major. Leaves of Vinca minor (periwinkle) growing in a deeply shaded location were also monitored. We propose using diurnal changes in the efficiency of open PSII centers (F′v/F′m) in these sun and shade leaves to (a) assess diurnal changes in the allocation of absorbed light to photochemistry and thermal energy dissipation and, furthermore, (b) make an estimate of changes in the rate of thermal energy dissipation, an analogous expression to the rate of photochemistry. The fraction of light absorbed in PSII antennae that is dissipated thermally (D) is proposed to be estimated from D = 1‐F′v/F′m, in analogy to the widely used estimation of the fraction of light absorbed in PSII antennae (P) that is utilized in PSII photochemistry from P = F′v/F′m× qP (where qP is the coefficient for photochemical quenching; Genty, B., Briantais, J.‐M. & Baker, N. R. 1989. Biochim. Biophys. Acta 990: 87‐92). The rate of thermal dissipation is consequently given by D × PFD (photon flux density), again in analogy to the rate of photochemistry P × PFD, both assuming a matching behavior of photosystems I and II. Characterization of energy dissipation from the efficiency of open PSII centers allows an assessment from a single set of measurements at any time of day; this is particularly useful under field conditions where the fully relaxed reference values of variable or maximal fluorescence needed for the computation of nonphotochemical quenching may not be available. The usefulness of the assessment described above is compared with other currently used parameters to quantify nonphotochemical and photochemical chlorophyll fluorescence quenching.

The lack of LHCII proteins modulates excitation energy partitioning and PSII charge recombination in Chlorina F2 mutant of barley

“…Several models based on chlorophyll fluorescence parameters have been proposed for quantifying the partitioning of total absorbed light energy by PS II (Demmig-Adams et al, 1996;Kramer et al, 2004;Hendrickson et al, 2004). Although different approaches, i.e.…”

“…Although different approaches, i.e. pure "puddle" (Demmig-Adams et al, 1996) or "lake" antenna models of PSII (Kramer et al, 2004;Hendrickson et al, 2004) were used for estimating the fate of absorbed light energy, all models defined the sum of all energy fluxes via PSII as unity and categorized the partitioning of total absorbed energy by PS II as either photochemical or thermal dissipation processes. In addition, all three models, regardless of their underlying assumptions ("puddle" or "lake" antenna models) were able to recognize two easily distinguishable thermal dissipation processes, the major one originating from the lightharvesting antenna complexes (LHCII) and defined as regulated NPQ (Ø NPQ ) and an additional one defined as constitutive thermal dissipation Ø NO (Kramer et al, 2004;Hendrickson et al, 2004) or "excess excitation energy" (E) defined as a fraction of absorbed light neither going to photochemistry or regulated NPQ, i.e.…”

“…In addition, all three models, regardless of their underlying assumptions ("puddle" or "lake" antenna models) were able to recognize two easily distinguishable thermal dissipation processes, the major one originating from the lightharvesting antenna complexes (LHCII) and defined as regulated NPQ (Ø NPQ ) and an additional one defined as constitutive thermal dissipation Ø NO (Kramer et al, 2004;Hendrickson et al, 2004) or "excess excitation energy" (E) defined as a fraction of absorbed light neither going to photochemistry or regulated NPQ, i.e. excitation energy trapped and/or dissipated by PSII reaction centers with Q A in reduced state (Demmig-Adams et al, 1996).…”

Using Chlorophyll Fluorescence and Vegetation Indices to Predict the Timing of Nitrogen Demand in Pentas lanceolata

“…Photosynthesis is sensitive to environmental changes. Photoinhibition of photosynthesis is characterized by a reduction in the quantum yield of photochemistry and reduced ChlF, which entails both inhibition of PSII and increased thermal deexcitation of excited Chl (Demmig-Adams et al, 1996). The △F/Fm' ratio reflects the actual photochemical capacity of PSII under bright conditions, which correlates linearly with the efficiency of CO 2 fixation.…”

Photosynthetic Characteristics of Multifoliolate Alafalfa Leaves

“…2B), indicating high flexibly responses to environmental changes and higher potential to avoid stress influence of deleterious environmental factors. Such characteristics could be related to the observed low level of excess fluorescence parameter that reflects the level of damage in the photosynthetic apparatus [ 9 ]. Consequently, one of the main factors determining the retained plant productivity of MF23 line should be a better adjustment of MF23 alfalfa plants to the environment.…”