Physiological functions of PsbS-dependent and PsbS-independent NPQ under naturally fluctuating light conditions.
The PsbS protein plays an important role in dissipating excess light energy as heat in photosystem II (PSII). However, the physiological importance of PsbS under naturally fluctuating light has not been quantitatively estimated. Here we investigated energy allocation in PSII in PsbS-suppressed rice transformants (ΔpsbS) under both naturally fluctuating and constant light conditions. Under constant light, PsbS was essential for inducing the rapid formation of light-inducible thermal dissipation (Φ(NPQ)), which consequently suppressed the rapid formation of basal intrinsic decay (Φ(f,D)), while the quantum yield of electron transport (Φ(II)) did not change. In the steady state phase, the difference between the wild type (WT) and ΔpsbS was minimized. Under regularly fluctuating light, the reduced PsbS resulted in higher Φ(II) upon the transition from high light to low light and in lower Φ(II) upon the transition from low light to high light, indicating that Φ(II) was, to some extent, controlled by PsbS. Under naturally fluctuating light in a greenhouse, rapid changes in Φ(II) were compensated by Φ(NPQ) in the WT, but by Φ(f,D) in ΔpsbS. As a consequence, a significantly lower ΣNPQ integrated Φ(NPQ) over a whole day) and higher Σf,D were found in ΔpsbS. Furthermore, thermal dissipation associated with photoinhibtion was enhanced in ΔpsbS. These results suggest that PsbS plays an important role in photoprotective process at the induction phase of photosynthesis as well as under field conditions. The physiological relevance of PsbS as a photoprotection mechanism and the identities of Φ(NPQ) and Φ(f,D) are discussed.
Division of Integrated Life Sciences, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan.
Masahiro
M
Ikeuchi
Division of Integrated Life Sciences, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan.
Nozomu
N
Uebayashi
Division of Integrated Life Sciences, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan.
Fumihiko
F
Sato
Division of Integrated Life Sciences, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan tuendo@kais.kyoto-u.ac.jp.
Tsuyoshi
T
Endo
D000222:Adaptation, Physiological / Q000528:radiation effects*; D002734:Chlorophyll / Q000378:metabolism; D002940:Circadian Rhythm; D004579:Electron Transport / Q000528:radiation effects; D004734:Energy Metabolism / Q000528:radiation effects; D005453:Fluorescence; D008027:Light; D012275:Oryza / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D030821:Plants, Genetically Modified
D045332:Photosystem II Protein Complex; D002734:Chlorophyll
Energy allocation in PSII; Naturally fluctuating light; Non-photochemical quenching (NPQ); PsbS; Thermal dissipation of absorbed light energy