Preface
The articles in this issue were invited contributions from participants of the session, Sulphur metabolism in plants—integrating complexity, which took place as part of the Society for Experimental Biology Annual Meeting held at Heriot Watt University in Edinburgh, UK, between 29 March and 2 April 2004.
Acquisition and assimilation of sulphur comprises a complex, well-organized and highly regulated set of processes. Assimilated S is an essential component of many compounds, which results in many branch points of the pathways involved with competing sinks. Interactions with other nutrient assimilation pathways and areas of metabolism involved in growth and development result in a complex web of cellular and molecular processes associated with plant sulphur. The goal of this meeting was to highlight this complexity.
Substantial progress has been made over the past decade (it was in 1993 that David Clarkson organized the previous Sulphur Session at the SEB). Genes for components of the transport systems and the assimilatory and associated pathways have been cloned and characterized for many species, and especially in Arabidopsis. A surprise was the size of some of the gene families and the clear indication of cell and compartment specificity (see papers by Buchner et al.; Kopriva and Koprivova; Wirtz et al.; Klein and Papenbrock). We are now in a phase where the genes, knock-out mutants, and various reporter constructs are being utilized to tease out the details of the basic pathways and their regulation. For example, information on sulphur-responsive cis elements is becoming available. Identification of the transcription factors involved in regulation of gene expression should be the next step. A useful approach is the application of promoter–GFP fusions (Maruyama-Nakashita et al.). Links between gene expression and metabolites sometimes seem clear, but direct connections remain elusive. One approach to probing this problem is to provide hydrogen sulphide as a sulphur source. Surprisingly this seems to by-pass much of the regulation (Durenkamp and De Kok). Sulphur assimilation is intimately interconnected with N and C and crosstalk between these pathways may involve a number of compounds, but definitive signalling pathways are still undefined (Kopriva and Rennenberg). In some cases, S-containing compounds still have uncertain roles, for example, DMSP (Otte et al.). Plant health is dependent upon S. One well-known compound believed to have multiple roles in stress resistance is glutathione (Tausz et al.). Manipulation of the pathways of cysteine and glutathione biosynthesis may be possible for enhanced resistance to stress (Sirko et al.). In addition to its role in stress tolerance, glutathione undoubtedly has roles in signalling, perhaps involving calcium (Gomez et al.).
Transcriptome and metabolome studies have further underlined that there is a vast network of interacting pathways within the plant. Perturb one aspect and a cascade of responses may be expected (Nikiforova et al.; Hirai and Saito). In addition, the complexity of plant sulphur nutrition extends beyond the plant when interactions with microbes involved in S-cycling within the soil are considered (Kertesz and Mirleau). The soil environment will also affect sulphate and selenate acquisition, inextricably linked as both are taken up by common transporters. Whilst selenate is a required micro-nutrient it is toxic to plants and animals in excess (White et al.).
S-nutrition has always been recognized as an important component of crop nutrition, contributing not just to yield but also essential quality traits including flavour components (Jones et al.). Improving the content of S-containing amino acids is a specific target of crop biotechnologists which could be of great benefit to human and animal nutrition (Hesse et al.; Chiaiese et al.). Adequate S-nutrition has often been suggested to be important for resistance to pathogens and a specific example is the production and deposition of elemental S in vascular tissues (Cooper and Williams).
I would like to thank all of the contributors to the session and to this issue for their timely and stimulating input. I would like to thank the Plant Metabolism Group of the SEB and the Journal of Experimental Botany for their generous financial assistance and the editorial office for their help in bringing this volume to fruition.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||