The role of the light harvesting complex and photosystem II in thylakoid stacking in thechlorina-f2 barley mutant

Abstract

The stacking behaviour of isolated thylakoids ofthe chlorophyll b-less barley mutant chlorina-f2, which is highly deficient in the light harvesting complex (LHCII), was investigated using electron microscopy. Pre-treatment with EDTA prevented thylakoid vesiculation during de-stacking, and was essential for the induction of re-stacking, which required a higher Mg ~* concentration (25 mM) than for wild type (5 mM). The stability of re-stacked chlorina-f2 thylakoids allowed their fractionation into photosystem I and photosystem II by treatment with Triton X-100 or [~-octyl glucoside, demonstrating thylakoid lateral heterogeneity in the absence of LHCII. An Mg'*-dependent aggregation of detergent-solubilized photosystem II from chlorina-f2 occurred at the same concentration (25 mM) as the one needed for the re-stacking of isolated thylakoids. We propose that thylakoid stacking and lateral heterogeneity in chlorina-f2 is not mediated by residual LHCII polypeptides, but by a component of photosystem [I. This mechanism may also be involved in stacking of wild type thylakoids. A simple method is described for the one-step isolation from chlorina-f2 of pure photosystem I and photosystem II preparations free of their respective chlorophyll b-containing light harvesting antenna proteins.

Ultraviolet B Exposure of Whole Leaves of Barley Affects Structure and Functional Organization of Photosystem II

“…Treatment with ultraviolet B light apparently brought about general swelling of thylakoid membranes, which, in some cases (emphasized by arrows in the 3-h irradiated samples, but clearly visible also after 6 h), could be considered as partial destacking of the membrane. We interpret this phenomenon as the consequence of the dismantling of a fraction of those PSII cores that are involved in membrane stacking (43)(44)(45). This interpretation is supported by the observation that this phenomenon was even more pronounced when the chlorophyll b-less mutant chlorina f2 was treated in the same way with ultraviolet B light (panels D-F).…”

“…Ultraviolet B degradation of proteins D1 and D2 may be the origin of the partial destacking of granum regions. Accordingly, data from the chlorophyll b-less mutant chlorina f2, where granum stacking is maintained essentially by PSII cores (since LHCII proteins are present only in residual amounts) (20,43), show that the effect of ultraviolet B light on thylakoid ultrastructure is dramatic. In this case, a low number of grana with a smaller number of thylakoids per granum are found after irradiation with ultraviolet B, 2 confirming that damage to PSII can actually affect the stability of the grana.…”

“…This interpretation is supported by the observation that this phenomenon was even more pronounced when the chlorophyll b-less mutant chlorina f2 was treated in the same way with ultraviolet B light (panels D-F). In this mutant, stacking of thylakoids is thought to be maintained mainly by PSII (43) and only marginally by residual LHCII (43,44). Thus, in view of this result, we interpret the increase in LHCII observed in the digitonin-derived stroma-exposed membranes of the wild type as the result of more extensive solubilization of membranes, produced by the detergent because of partial destacking linked to PSII degradation rather than to actual lateral migration of antenna proteins.…”

Global spectral–kinetic analysis of room temperature chlorophyll a fluorescence from light-harvesting antenna mutants of barley

“…The anomalous in vivo PS II £uorescence lifetimes in clo f 2 clearly are physically related to the well-known Mg 2+ e¡ects on isolated clo f 2 thylakoids, with respect to stacking and PS II versus PS I emission (Bassi et al 1985). Isolated clo f 2 thylakoids, compared to the wt and clo f104, are quite labile with respect to stacking and require high Mg 2+ and chelating agents to induce and retain stacking in vitro.…”

Genetic analysis and plastid ultrastructure of three chlorophyll lethal mutants in winter rye (Secale cerealeL.)

“…Betula pubescens (V ALANNE 1975), Cucumis sativus (PALCZEWSKA et al 1983), Hordeum sp. (WETISTEIN 1958(WETISTEIN , 1961BAsSI et al 1985), Lycopersicon esculentum (BoYNTON 1966), Scindapsus aureus (.ARAus et al 1986), Zea mays (BACHMANN et al 1967;MILLERD et a/. 1969).…”