ORIGINAL ARTICLE Arabidopsis sulfurtransferases: investigation of their function during senescence and in cyanide detoxification Received: 14 August 2002 / Accepted: 25 November 2002 / Published online: 7 February 2003 Ó Springer-Verlag 2003 Abstract Sulfurtransferases (STs) and b-cyano-L-alanine synthase (CAS) are suggested to be involved in cyanide detoxification. Therefore, the accumulation of ST1 and CAS RNAs, and the ST and CAS protein levels and enzyme activities were determined in Arabidopsis thali- ana Heynh. plants grown under different conditions. Senescence-associated processes were successfully in- duced by natural aging, by jasmonate methyl ester and by darkness in whole plants and detached leaves, as demonstrated by the expression of the senescence marker genes SAG12 and SAG13. However, the changes in RNA accumulation and protein levels of ST and CAS did not correlate with the expression of these senescence marker genes; the specific ST and CAS activities either decreased (ST) or increased (CAS). In another experi- ment, Arabidopsis plants were sprayed with cyanide to investigate the role of ST and CAS in cyanide detoxifi- cation. The expression of ST and CAS at the RNA and protein levels, and also the enzyme activities, remained equal in cyanide-treated and control plants. Incubation with 1-aminocyclopropane-1-carboxylic acid, the pre- cursor of ethylene, increased while fumigation with ethylene decreased expression and activity of ST and CAS. In summary, cyanide does not induce the expres- sion or enhance the activity of ST and CAS in Arabid- opsis. For both proteins the evidence for a role in cyanide detoxification or induced senescence is low. Keywords Arabidopsis Æ Cyanide detoxification Æ Ethylene Æ Jasmonate Æ 3-Mercaptopyruvate Æ Senescence Abbreviations ACC: 1-aminocyclopropane-1-carboxylic acid Æ CAS: b-cyano-L-alanine synthase Æ MeJA: jasmonate methyl ester Æ 3-MP: 3-mercaptopyruvate Æ MST: 3-mercaptopyruvate sulfurtransferase Æ SAG: senescence-associated gene Æ ST: sulfurtransferase Introduction Sulfurtransferases (STs) comprise a group of enzymes widely distributed in plants, animals, and bacteria that catalyze the transfer of a sulfur atom from a donor molecule to a thiophilic acceptor substrate. Members of the ST family, thiosulfate:cyanide ST (rhodanese, EC 2.8.1.1), 3-mercaptopyruvate:(di)thiol ST (EC 2.8.1.2), thiosulfate:thiol ST (EC 2.8.1.3), and thiosulfate:dithiol ST (EC 2.8.1.5) are closely related, both in the type of reaction catalyzed, and also in their primary amino acid sequence. Several physiological roles have been pro- posed for these enzymes, including cyanide detoxifica- tion (Westley 1973; Vennesland et al. 1982), management of the cytotoxicity of reactive oxygen spe- cies in aerobic tissues (Nandi et al. 2000), sulfur me- tabolism (Westley 1973, 1981), and mobilization of sulfur for Fe–S cluster biosynthesis or repair (Bonomi et al. 1977; Pagani et al. 1984). Since it was also shown that the expression and the enzyme activity of STs increased with increasing age of Arabidopsis plants (Papenbrock and Schmidt 2000b), one could postulate that STs might also play a role in mobilizing sulfur from senescent leaves into growing leaves, fruits and seeds. Leaf senescence is a genetically controlled and highly regulated process (Quirino et al. 2000). To study gene expression during senescence processes under controlled conditions, many factors have been chosen to mimic naturally occurring senescence: the transfer of leaves or whole plants into darkness, osmotic stress, extreme temperatures, wounding, ozone, pathogens, and plant hormones such as abscisic acid, ethylene and jasmonic acid (Gan and Amasino 1997; Quirino et al. 2000). However, differences in gene expression between natural and artificially induced senescence were observed (Becker and Apel 1993). So-called senescence-associated genes (SAGs) from Arabidopsis showed differential Planta (2003) 217: 1–10 DOI 10.1007/s00425-002-0964-5 Tanja Meyer Æ Meike Burow Æ Michael Bauer Jutta Papenbrock T. Meyer Æ M. Burow Æ M. Bauer Æ J. Papenbrock (&) Institute for Botany, University of Hannover, Herrenha¨userstr. 2, 30419, Hannover, Germany E-mail: jutta.papenbrock@botanik.uni-hannover.de Fax: +49-511-7623992