C4 Photosynthesis: Thirty or Forty Years On

Abstract

The C₄ pathway has served as a rallying point for so many creative contributions, a focus for attention from so many outstanding researchers, that any attempt to set the context 30 or 40 years on is doomed to offend the majority of one’s colleagues. However, there is one colleague whose personal research has set the standards to which we all aspire, and rarely attain; whose achievements have been applauded for more than a quarter of a century. Hal Hatch has brought great distinction to Australian plant science.

This preamble deals with what is perhaps Australia’s most significant contribution to modern plant sciences research. It is certainly one of the main reasons why plant sciences research over the last decade or so has had more influence internationally (measured by relative citation impact), than any other field of biological research in Australia (Bourke and Butler 1994; Osmond 1995). Although we may take pride in this quantitative evidence, I believe we share a deeper sense of achievement in C₄ pathway photosynthetic carbon metabolism. This deeper sense is reflected in the neatness, the comprehensiveness, that accompanied the unfolding of our understanding in this field. We can identify with Medewar (1968) that, above all else, researchers value discoveries first for their explanatory value, second for their clarifying power ‘the degree to which they resolve what has hitherto been perplexing’ and third, for the feat of originality involved, ‘the surprisingness of the solution to which it led’.

Thirty or 40 years on, it is good to reflect on where we have come from, what has been achieved and, as this Symposium has defined, where we will go next. One acknowledged starting point is an incidental observation and an inspired guess of Haberlandt (1884), whose anatomical insight provoked a more comprehensive understanding of photosynthetic carbon metabolism in all its forms. There is no question that the insights and the confidence gained through progress in C₄ photosynthesis research led to a mature view of photosynthetic carbon metabolism in C₃ and CAM plants as well. Our perception of leaf photosynthesis has been refined through the integrative philosophy, and growth of research capability, that accompanied the unfolding of the C₄ pathway. We are now presented with a plethora of well-defined new problems that tax our creativity in fields of gene expression, cell biology, ecophysiology and evolutionary biology, all arising from a desire to understand this remarkable pathway.

In a musical contribution to an early C₄ pathway conference, it was heralded that Roger Slack wanted a ‘C-through plant’ (Hatch et al. 1971). After 30 or 40 years, the essence of the C₄ pathway is so transparent that it gives insight into some of the big questions in plant biology with the promise of more to come. Looking back, it seems natural to deal with the growth of research in C₄ photosynthesis as phases of a generalised biological growth cycle.