The Excess Light Energy that is neither Utilized in Photosynthesis nor Dissipated by Photoprotective Mechanisms Determines the Rate of Photoinactivation in Photosystem II

Abstract

Photoinactivation of PSII is thought to be caused by the excessive light energy that is neither used for photosynthetic electron transport nor dissipated as heat. However, the relationship between the photoinactivation rate and excess energy has not been quantitatively evaluated. Chenopodium album L. plants grown under high-light and high-nitrogen (HL-HN) conditions show higher tolerance to photoinactivation and have higher photosynthetic capacity than the high-light and low-nitrogen (HL-LN)- and low-light and high-nitrogen (LL-HN)-grown plants. The rate of photoinactivation in the LL-HN plants was faster than that in the HL-LN, which was similar to that in the HL-HN plants, while the LL-HN and HL-LN plants had similar photosynthetic capacities [Kato et al. (2002b) Funct. Plant Biol. 29: 787]. We quantified partitioning of light energy between the electron transport and heat dissipation at the light intensities ranging from 300 to 1,800 micromol m(-2) s(-1). The maximum electron transport rate was highest in the HL-HN plants, heat dissipation was greatest in the HL-LN plants, and the excess energy, which was neither consumed for electron transport nor dissipated as heat, was greatest in the LL-HN plants. The first-order rate constant of the PSII photoinactivation was proportional to the magnitude of excess energy, with a single proportional constant for all the plants, irrespective of their growth conditions. Thus the excess energy primarily determines the rate of PSII photoinactivation. A large photosynthetic capacity in the HL-HN plants and a large heat dissipation capacity in the HL-LN plants both contribute to the protection of PSII against photoinactivation.

Estimating Chlorophyll Fluorescence Parameters Using the Joint Fraunhofer Line Depth and Laser-Induced Saturation Pulse (FLD-LISP) Method in Different Plant Species

“…Also under the same level of illumination, leaves with a lower photosynthetic capacity exhibit lower Φ PSII and higher NPQ. These facts have been reported previously in various ChlF studies at leaf and cell levels [1,5,[72][73][74][75][76][77][78]. The relationships between PPFD and the ChlF parameters of Φ PSII , NPQ, and ETR measured using FLD-LISP in all three plant species (Figures 4-6) were similar to the relationships obtained through the PAM measurement.…”

Arabidopsis thaliana Plants Lacking the PSI-D Subunit of Photosystem I Suffer Severe Photoinhibition, Have Unstable Photosystem I Complexes, and Altered Redox Homeostasis in the Chloroplast Stroma

“…Measurements were performed on wild-type plants and plants with 10 (29). Efficiency of PSII photochemistry was also measured in plants under growth light conditions followed by recovery in the dark for 40 min.…”

Submergence-Induced Morphological, Anatomical, and Biochemical Responses in a Terrestrial Species Affect Gas Diffusion Resistance and Photosynthetic Performance

“…q P and q N were calculated from chlorophyll fluorescence measurements (van Kooten and Snel, 1990). Partitioning of absorbed photons in PSII was calculated by dividing total absorbed energy over inherent inefficiency in dark (L 5 1 2 F v /F m ), thermal dissipation (D 5 F v /F m 2 F v #/F m #), photosynthetic electron transport (P 5 DF/F m #), and excess energy (E 5 1 2 L 2 D 2 P; Demmig- Adams et al, 1996;Kato et al, 2003).…”