Development of Photosystem II in dark grown Chlamydomonas reinhardtii. A light-dependent conversion of PS II?, QB-nonreducing centers to the PS II?, QB-reducing form

Abstract

The green alga Chlamydomonas reinhardtii is a facultative heterotroph and, when cultured in the presence of acetate, will synthesize chlorophyll (Chl) and photosystem (PS) components in the dark. Analysis of the thylakoid membrane composition and function in dark grown C. reinhardtii revealed that photochemically competent PS II complexes were synthesized and assembled in the thylakoid membrane. These PS II centers were impaired in the electron-transport reaction from the primary-quinone electron acceptor, QA, to the secondary-quinone electron acceptor, QB (QB-nonreducing centers). Both complements of the PS II Chl a-b light harvesting antenna (LHC II-inner and LHC II-peripheral) were synthesized and assembled in the thylakoid membrane of dark grown C. reinhardtii cells. However, the LHC II-peripheral was energetically uncoupled from the PS II reaction center. Thus, PS II units in dark grown cells had a β-type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS IIβ units lack LHC II-peripheral). Illumination of dark grown C. reinhardtii caused pronounced changes in the organization and function of PS II. With a half-time of about 30 min, PS II centers were converted froma QB-nonreducing form in the dark, to a QB-reducing form in the light. Concomitant with this change, PS IIβ units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS IIα form. The functional antenna of the latter contained more than 250 Chl(a+b) molecules. The results are discussed in terms of a light-dependent activation of the QA-QB electron-transfer reaction which is followed by association of the PS IIβ unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS IIα) in the membrane of the grana partition region.

Photoinhibition and light-dependent turnover of the D1 reaction-centre polypeptide of photosystem II are enhanced by mineral-stress conditions

“…These centers seemed to be transformed into active QB-reducing centers, either belonging to ampf or Table 2, and are for control (e), pH 3-grown (v), Mg-deficient (rn) and Mg/S-deficient (zx) spinach plants. Fo was determined by applying the measuring light; Fm was determined from the fluorescence yield achieved by the single turnover flash ampm, as has already been found by Guenther et al (1990). In the pH 3-grown plants, ampf was slightly lower than in the control, with a value of only 1.43-t-0.33 in the dark-adpated leaves and 1.55_+0.06 in the illuminated leaves (Table 2).…”

Photosystem II heterogeneity: the acceptor side

“…Recently, Guenther et al (1990), also using OIDP fluorescence transient, have shown that a light-dependent conversion of PS 118, non-Q B centers to PS II a , QB centers occurs in dark grown Chlamydomonas reinhardtii; the ratio of OID to DP phase was found to drastically decrease within an hour of illumination.…”

Photoproduction of hydrogen by sulfur-deprived C. reinhardtii mutants with impaired Photosystem II photochemical activity

“…The ratio of Q B -reducing to Q B -non-reducing centers determines the actual capacity of PSII centers to provide electrons to the photosynthetic electron transport chain (Guenther et al 1990). Analysis of the fluorescence induction kinetics recorded with dark-adapted cells can give information about this ratio in the mutants (Krause and Weis 1991;Lazar 1999).…”