SummaryDetoxification of xenobiotic compounds and heavy metals is a pivotal capacity of organisms, in which glutathione (GSH) plays an important role. In plants, electrophilic herbicides are conjugated to the thiol group of GSH, and heavy metal ions form complexes as thiolates with GSH-derived phytochelatins (PCs). In both detoxification processes of plants, phytochelatin synthase (PCS) emerges as a key player. The enzyme is activated by heavy metal ions and catalyzes PC formation from GSH by transferring glutamylcysteinyl residues (c-EC) onto GSH. In this study with Arabidopsis, we show that PCS plays a role in the plant-specific catabolism of glutathione conjugates (GS-conjugates). In contrast to animals, breakdown of GS-conjugates in plants can be initiated by cleavage of the carboxyterminal glycine residue that leads to the generation of the corresponding c-EC-conjugate. We used the xenobiotic bimane in order to follow GS-conjugate turnover. Functional knockout of the two PCS of Arabidopsis, AtPCS1 and AtPCS2, revealed that AtPCS1 provides a major activity responsible for conversion of the fluorescent bimane-GS-conjugate (GS-bimane) into c-ECbimane. AtPCS1 deficiency resulted in a c-EC-bimane deficiency. Transfection of PCS-deficient cells with AtPCS1 recovered c-EC-bimane levels. The level of the c-EC-bimane conjugate was enhanced several-fold in the presence of Cd 2þ ions in the wild type, but not in the PCS-deficient double mutant, consistent with a PCScatalyzed GS-conjugate turnover. Thus AtPCS1 has two cellular functions: mediating both heavy metal tolerance and GS-conjugate degradation.

In vivo analysis of plastid psbA, rbcL and rpl32 UTR elements by chloroplast transformation: tobacco plastid gene expression is controlled by modulation of transcript levels and translation ef®ciency Texas A&M University, College Station, Texas, USA Summary 5¢ and 3¢ untranslated regions (UTRs) of plastid RNAs act as regulatory elements for post-transcriptional control of gene expression. Polyethylene glycol-mediated plastid transformation with UTR±GUS reporter gene fusions was used to study the function of the psbA, rbcL and rpl32 UTRs in vivo. All gene fusions were expressed from the same promoter, i.e. the promoter of the 16S-rRNA gene, such that variations in RNA and protein levels would be due to the involved UTR elements alone. Transgenic tobacco lines containing different combinations of UTRs showed ®vefold variation in the uidA±mRNA level (RNA stability) and approximately 100-fold differences in GUS activity, a measure of translation activity. The rbcL 5¢-UTR conferred greater mRNA stability than the psbA 5¢-UTR on uidA transcripts. In contrast, the psbA 5¢-UTR enhanced translation of GUS to a much greater extent compared to the rbcL 5¢-UTR. The psbA 5¢-UTR also mediated light-induced activation of translation which was not observed with other constructs. Deletion mutagenesis of an unanalysed terminal sequence element of the psbA 5¢-UTR resulted in a twofold drop in uidA-mRNA level and a fourfold decrease in translation ef®ciency. Exchange of 3¢-UTRs results in up to ®vefold changes of mRNA levels and does not signi®cantly in¯uence translation ef®ciency. The mechanical impacts of these results on plastid translation regulation are discussed.

 Axenic cultures of lichen photobionts isolated from bark-inhabiting lichen thalli of the Physcietum adscendentisOchsner were identified by light microscopy and sequence comparisons of internal transcribed spacer rDNAs to investigate principles of lichenization within a defined lichen sociological unit. The photobiont identity of eight lichen species is reported for the first time (photobiont species in square brackets) : Lecania cyrtella (Ach. . The observation that pioneer lichens without vegetative propagules, growing on smooth bark, had Trebouxia arboricola as photobiont can be explained by the assumption of a free-living population of Trebouxia arboricola. Species of photobionts from Xanthoria parietina were morphologically and genetically different from those of Physcia adscendens and Phaeophyscia orbicularis, respectively ; a finding that does not support the previous assumption that Xanthoria parietina takes over its algal partner from a Physcia species, at least at the sites investigated.)

Summary• To examine the mode of dispersal and photobiont selectivity of Fulgensia fulgida we investigated the photobionts associated with the lichens of a community related to the Toninio-Psoretum decipientis association.• Photobionts and mycobionts were analysed using morphological (light microscopy) and molecular (internal transcribed spacer (ITS) and partial large subunit (LSU) nuclear ribosomal DNA sequencing) techniques.• The thalli of the mycobiont of F. fulgida , which were identical in their ITS and partial LSU-sequence, contained two strains of Trebouxia asymmetrica , one of them also present in a thallus of Toninia sedifolia . Other co-occurring lichens, namely Squamarina lentigera , Catapyrenium michelii and Collema cristatum , were shown to have Asterochloris irregularis , Myrmecia and Nostoc as photobionts.• It is suggested that F. fulgida is selective in its photobiont choice, that dispersal of the lichen has occurred by way of ascospores and subsequent independent relichenization events and that F. fulgida and T. sedifolia share the same photobiont pool. The results also suggest possible mechanisms of relichenization and strategies for future research on the selectivity of lichen bionts.

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