Annals of Botany

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Hunting for herbicide action: all systems negative

In searching for new herbicides, there are several key factors to consider. These include long-term effects in the environment and the possible susceptibility of non-target organisms. In respect of the latter, an obvious route to follow is to look for compounds that affect plant-specific processes, thus avoiding ‘collateral damage’. One aspect of plant biology that provides several such processes is the biochemistry and physiology of the cell wall, especially in light of the knowledge gained over the past 30 years of the structure, synthesis and modification of the wall. Indeed, as stated by O’Looney and Fry (Edinburgh University, UK, pp. 1097–1107), the cell wall is ‘a large untapped resource of potential herbicide action’. Further, the taxonomic variation in cell wall biochemistry raises the possibility of selective action. It was therefore of interest that a new herbicide, oxaziclomefone, inhibits cell expansion without affecting cell turgor, strongly suggesting that the mode of action involves an effect on cell wall extensibility. However, extensibility involves several mechanisms. Accordingly, the authors have conducted a systematic evaluation of the effects of oxaziclomefone on each of these in maize (Zea mays) cell cultures. Their research ‘covered all bases’ in studying known processes involved in cell wall synthesis, modification, loosening and tightening. However, the herbicide had no effect at all on any of the processes they studied. It is often disappointing to obtain an array of essentially negative results but there is a positive side to this situation. The clear effect of the herbicide on cell expansion, taken with the lack of any effect on processes known to be involved in cell expansion, indicates that there must be a mechanism or process, essential for cell expansion, that remains to be identified. Thus, a negative set of results will lead to the search for a completely novel aspect of plant growth and development.