Role of cyclic electron transport in photosynthesis as measured by the photoinduced turnover of P700 in vivo

Abstract

The light-induced turnover of P700 was measured spectrophotometrically in a wide variety of algae and some photosynthetic mutants. Analysis of the postillumination recovery of P700+ revealed that the apparent first-order rate constant for reduction via the cyclic pathway was much lower that that via the noncyclic pathway. After activation of photosystems 1 and 2 the half-time for reduction of P700+ was 5-20 ms, whereas after activation of primarily photosystem 1 a longer half-time of ca. 150 ms was observed. The extent of the photooxidation of P700 was the same in both regimes of illumination. The longer half-time was also noted after inhibition of photosystem 2 by 3-(3,4-dichlorophenyl)-1,1-dimethylurea or mild heat shock and in mutant algae known to lack a functional photosystem 2. No signal was observed in mutants lacking P700 itself but those strains lacking either plastocyanin or cytochrome f were capable of a very slow turnover (reduction t 1/2 greater than 500 ms at room temperature). This very slow turnover was not affected by carbonyl cyanide m-chlorophenylhydrazone or the plastoquinone antagonist, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, indicating that the pathway for reduction of P700+ in these mutants is not energy linked and does not utilize the intersystem electron transport chain. The slow, 150 ms, reduction of P700+ due to cyclic flow was not observed when cells were engaged in photosynthesis at high-light intensities. The data are interpreted as evidence for the involvement of the total functional pool of P700 in both electron transport pathways, and we suggest that cyclic electron transport does not contribute to photosynthesis in oxygen-evolving autotrophs.

The chloroplast Ndh complex mediates the dark reduction of the plastoquinone pool in response to heat stress in tobacco leaves

“…This type of assay gives a measure of the rate of PSII-independent reduction of PSI and is comprised of both cyclic electron transfer around PSI and electron donation to the intersystem electron transfer chain by stromal reductant [8,12]. Fig.…”

Cyclic Electron Flow around Photosystem I in C3 Plants. In Vivo Control by the Redox State of Chloroplasts and Involvement of the NADH-Dehydrogenase Complex

“…Cyclic and linear electron transfers share a common sequence of electron carriers, namely the plastoquinone (PQ) pool, cytochrome b 6 /f complex, and plastocyanin (for review, see Fork and Herbert, 1993;Bendall and Manasse, 1995). This alternative electron flow has been shown to occur in vivo in cyanobacteria (Carpentier et al, 1984), in algae (Maxwell and Biggins, 1976;Ravenel et al, 1994), and in bundle sheath cells of C 4 plants (Herbert et al, 1990;Asada et al, 1993). In cyanobacteria, cyclic electron flow around PS I has been shown to provide extra ATP for different cellular processes, e.g.…”

“…It was observed that this rate measured in leaves of C 3 plants (e.g. Burrows et al, 1998) was considerably much slower than that measured in the green alga Chlamydomonas reinhardtii (Maxwell and Biggins, 1976;Ravenel et al, 1994) or in cyanobacteria (Mi et al, 1992), suggesting a very slow recycling of electrons around PS I in vivo. The existence of cyclic electron transport in vivo in C 3 plants has also been questioned by photoacoustic measurements in far-red light (Herbert et al, 1990), which allow a direct and quantitative measure of energy storage (ES) by cyclic electron flow around PS I (for review, see Malkin and Canaani, 1994).…”

“…It was observed that this rate measured in leaves of C 3 plants (e.g. Burrows et al, 1998) was considerably much slower than that measured in the green alga Chlamydomonas reinhardtii (Maxwell and Biggins, 1976; Ravenel et al, 1994) or in * Corresponding author; e-mail michel.havaux@cea.fr; fax 33-4 -42256265.…”

“…In intact leaves, PS I-mediated cyclic electron flow in far-red light was analyzed indirectly by measuring the light-scattering signal at 535 nm, which reflects changes in the trans-thylakoid pH gradient (Heber et al., 1992(Heber et al., , 1995 Cornic et al, 2000). Cyclic electron transport around PS I can also be estimated indirectly by measuring the re-reduction rate of the oxidized primary electron donor in PS I (P 700 ϩ ) after switching off the far-red light (Maxwell and Biggins, 1976;Asada et al, 1992). It was observed that this rate measured in leaves of C 3 plants (e.g.…”