Investigations on the Reaction Pattern of Photosystem II in Leaves from Arabidopsis thaliana Wild Type Plants and Mutants with Genetically Modified Lipid Content

Abstract

The role of digalactosyldiacylglycerol (DGDG) for the functional competence of photosystem II (PS II) has been analyzed in leaves of Arabidopsis thaliana plants where the lipid composition was selectively modified by genetic mutations. Measurements with a newly developed laser flash fluorometer and data evaluation within the framework of an extended "3-quencher" model lead to the following results: (i) the normalized fluorescence transients F(t)/F(0) induced by an actinic laser flash in dark adapted leaves are virtually the same in wild type (WT) and mutants with diminished (about 50%) monogalactosyldiacylglycerol (MGDG) content (mgd1 mutant); (ii) significant changes of the F(t)/F(0) curves are observed in mutants with a severely reduced DGDG content; (iii) in mutants dgd1 and dgd1 dgd2-1 with DGDG contents of 1/15 of the control and below the detection limit, respectively, the probability of the dissipative recombination reaction between P680(+)(*) and Q(A)(-) increases by factors of about two and four, respectively; (iv) the acceptor side reactions are only slightly affected; (v) excitation with actinic laser flash energies above the saturation level of photosynthesis gives rise to elevated carotenoid triplet formation in mutants dgd1 and dgd1 dgd2-1; and (vi) the relationship between DGDG content and functional effect(s) on PS II is strikingly nonlinear. A small fraction of DGDG molecules of the total pool is inferred to be specifically bound to PS II as an essential constituent for its functional competence.

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. IV. Temperature-induced modulation of fatty acid regiochemistry as observed by electrospray ionization/mass spectrometry

“…DGDG has also been shown to contribute to the stability of photosystem I (PSI) in Arabidopsis thaliana (Guo et al, 2005). Furthermore, in Arabidopsis, a dgd1 mutant with greatly reduced DGDG production was inhibited in photosynthetic activity compared with wild-type plants when grown at a warm temperature (Hendrickson et al, 2006); a study by Steffen et al (2005) reached similar conclusions, and a study by Chen et al (2006) observed similar results on the importance of DGDG in maintaining Arabidopsis thermotolerance. It should be noted that the direct association of DGDG with PSII has not been established in dinoflagellates.…”

Galactolipid synthesis in chloroplast inner envelope is essential for proper thylakoid biogenesis, photosynthesis, and embryogenesis

“…Another chloroplast galactolipid, DGDG, has also been found in the crystallized PSII complex and in LHCII (5,15). Analyses of a dgd1 mutant in which DGDG content is significantly depleted indicated that DGDG plays a crucial role in PSII activity and the stabilization of trimeric LHCII (16)(17)(18). The dgd1 mutant also demonstrated the importance of DGDG for the stability and activity of the PSI complex (19,20).…”

Digalactosyldiacylglycerol Is Required for Stabilization of the Oxygen-Evolving Complex in Photosystem II

“…Although subsequent analyses are required to investigate the function of Sll1398, it is assumed that Sll1398 has an important function in the assembly of subunits in PSII. Recently, Steffen et al (2005) conducted spectroscopic analyses of a DGDG-deficient mutant of Arabidopsis using a flash laser fluorometer. They showed that the DGDG-deficient mutant exhibited Chl fluorescence that differed from the wild type and could be caused by the defect on the donor side of PSII.…”

“…In higher plants, DGDG-deficient mutants have been isolated from Arabidopsis as mentioned above (Dörmann et al, 1995;Härtel et al, 1997;Kelly et al, 2003). Analysis of the double mutant (dgd1 dgd2) with a newly developed laser flash fluorometer indicated that the lack of DGDG affected the donor side of PSII, namely, the oxygen-evolving complex (Steffen et al, 2005). However, a direct interaction between DGDG molecules and the oxygenevolving complex was not found in the crystal structure of the cyanobacterial PSII complex (Loll et al, 2005).…”