Second Messengers in Animals and Their Possible Relevance for Plants

Abstract

My task is to review the subject of second messengers in animals and its possible relevance for plants. Implicit in this title is the hope that useful guidance will be found in the results from the relatively well-studied animal regulatory systems as we begin to probe transmembrane signalling systems that operate in plants during pathogenic and symbiotic plant-microbe interactions. Some support for this position may be taken from arguments recently set forth by Janssens (1987). He has concluded that similarities are evident in signal transduction mechanisms in vertebrates, invertebrates and eukaryotic microbes, whereas signalling mechanisms in prokaryotes appear to be significantly different. Although much of the evidence on which these comparisons are based is still very preliminary, Janssens suggests that eukaryotic transduction mechanisms, along with many other properties of the eukaryotic cell, may well have originated with eukaryotic microbes. An extension of this reasoning suggests that higher plants would share these attributes as well. On the other hand, it may be well to remember that the signal transduction pathways we are considering in animal cells are mostly concerned with the regulation of basic cellular processes and the integration of metabolic activities within multicellular organisms, whereas we are considering in this Workshop signalling processes that probably evolved at a later stage during the interaction of two different organisms. We should not be surprised to see special features of the signalling pathways that operate in these cases.