O'Neill, S.D., Roberts, J.A. Plant reproduction. Annual plant reviews vol. 6

This is the sixth volume of these periodic reviews, collected together on this occasion by two members of the Editorial Board. This is not a ‘Symposium Volume’ in the sense that it does not celebrate a meeting or a festschrift. If the reviewer seeks some alternative rationale, or even apologium, for the production of a multi‐authored assemblage of this kind, he does so in vain. In the absence of any preface, commentary or general discussion, it is hard to discern the aims of the editorial panel when this book was planned, or the extent to which the contributors fulfilled its objectives. Potentially, ‘plant reproduction’ is a massive arena, but we find, in practice, that each of the stand‐alone articles targets a circumscribed topic relating to sexual reproduction in flowering plants. The development of ovules, pollen, embryos, endosperm, ovules and mating systems are each discussed in turn, while these key central chapters are flanked by two rather similar introductory chapters on the control of flowering, and of flowering time, and a final chapter on senescence and dehiscence, so that the whole is given a semblance of symmetry. It is also possible to detect a theme to the extent that most chapters concentrate on recent accounts of the molecular control of their subject area, although it is unclear whether this emphasis results directly from editorial planning, or indirectly from the hiring of didactic followers of fashion. I find that the general usefulness of each of the articles is affected by this lightness of the editorial touch, for all lack a summary, while such concluding paragraphs as survive have been variously entitled ‘Conclusions’, ‘Summary’, Outlook’, ‘Perspectives’, ‘Prospects’, and in two cases are missing completely. A further failing, commonly found in similar volumes in recent years, is the separation of the authors’ addresses and the article contents pages from the article itself, which is infuriating for the general user. Despite the absence of any overt editorial input, the contributions of a distinguished and international cast (UK, USA, Australia, Belgium, Switzerland) hang together moderately well, and provide a useful summary of recent progress in their respective fields. On occasion, such insights as we are granted seem, at best, distorted. ‘The labyrinthine system of control of flowering time is probably critical for the successful reproduction of plants in the contrasting and unpredictable environments that have been experienced through evolution’ (Perilleux and Bernier) may have lost something in translation. All living things struggle with the ghosts of previously adaptive but now redundant genetic systems, parts of which may have been cobbled together and commandeered back into active service as part of a fresh evolutionary initiative. Perhaps this has also contributed to the equally labyrinthine operation of gametophytic self‐incompatibility systems of plants which, unlike sporophytic systems, still harbour many secrets, not least the inexplicable apparent lack of homology between different plant families (Li and Newbigin). I turned to the contribution from Koltunow, Vivian‐Smith, Tucker and Paech on apomixis and parthenocarpy with a sense of anticipation, this being a former interest with which I had rather lost touch. This area poses problems for which we have known for many decades that there will not be single answers, for apomixis has evolved on many occasions and each case is different. I received the disappointing impression that the ‘Holy Grail’ of a single apomixis gene is still being sought in some quarters. If matters have moved on to the point at which in the inhibition of reproductive development (in sex) becomes the unifying theory to explain apomixis, does that account for the adventitious production of embryo sacs, or embryos from non‐archesporial tissue which drives most apomixis? The latter case (adventitious embryony) MIGHT really be that Holy Grail, but currently no‐one seems to be interested in it. Although it feeds the world, endosperm has, until recently, attracted very little interest, so I was delighted to find a chapter dedicated to that Cinderella of plant tissues (Brown, Lemmon and Nguyen). This was not at all what I had expected. I had anticipated an analysis of developmental interplays between the embryo and endosperm (discordances between maternal and paternal dose control of developmental rate; the role of the endosperm in apomixis, and successful embryogenesis in the absence of endosperm), and that would indeed have made an absorbing chapter. Instead, I was treated to an account of the developmental architecture of endosperm, a topic of which I knew nothing and found fascinating. Beautiful pictures, reminiscent of 1960s wallpapers, are not displayed to their best advantage here. At the heart of the book, perhaps, lies Perez‐Grau’s account of embryogenesis, and this review is characteristic of the style of the volume, encapsulating its merits and limitations. My generation was raised on a diet of stultifyingly tedious, but worthy accounts of embryology, typically very badly printed on what appeared to be rice paper. We have moved on to an era in which developmental biology is characterized by a collection of mutants, minutely characterized and often cloned and sequenced, but which often do little more to explain the mysteries of differentiation than did the original descriptive accounts. To this outsider, embryology remains a subject for the future that has yet to explode into real life. Finally to the longest review, and the one that this reviewer found the most rewarding, on the developmental biology of pollen (Twell). The potential spin‐offs of a full molecular analysis of the products expressed by the haploid male gametophyte are far‐ranging, from a better understanding of pollen allergies, to the functioning of incompatibility systems, both intra‐ and inter‐specific. We have hardly started to guess at the importance of gametophytic selection on recessives in the haploid condition on rates of evolution, selection for tolerance of environmental extremes, the reduction of damaging linkage and the minimization of genetic load, so allowing co‐sexual plants to tolerate selfing and differ so strikingly from animals in their reproductive systems. This review may help to kick‐start a major research area for the coming decades.