Summary: Published online 18 December 2002
The discussion presented below results from papers presented at The Royal Society Discussion Meeting.
J. F. Allen (Plant Biochemistry, Lund University, Lund, Sweden). Session 1 was called `Symbiosis and genome func-
tion'. There were talks by John Raven, Angela Douglas, Tom Cavalier-Smith and myself. The chairman was Chris
Leaver. Do you feel, Professor Raven, your case was adequately addressed in subsequent discussions in the meeting?
Your talk on the roles of cyanobacteria and proteobacteria in symbioses with eukaryotes?
J. A. Raven (School of Biological Sciences, University of Dundee, Dundee, UK). Yes.
J. F. Allen. Good. I thought so, too, actually. There might be a general issue about what extant symbioses have
to tell us about the dark and mysterious goings on two billion years ago, between organisms of which we can guess
and argue and speculate on; clearly symbiosis is a very popular way of doing things and is not the wild and improb-
able and unlikely way of introducing genetic innovation in evolution. But what about the specifics? I mean, is the
cyanobacterium actually a good model for the proto-chloroplast?
J. A. Raven. It seems to be the best we have. Do you have any others?
J. F. Allen. Is it possible the cyanobacterium brought into the deal the possibility to fix nitrogen, which the host
cell could not? We all think about photosynthesis and ATP synthesis.
J. A. Raven (Department of Biological Sciences, University of Dundee, Dundee, UK). This was something I hedged on;
obviously, I have thought about this before. I have got a couple of papers coming out soon that go into this in
perhaps a little more detail, without coming to any particular conclusion, really, as to whether the plastid ancestor
or ancestors were diazotrophs, and if they were, why the diazotrophy was lost. As far as today goes, of course we