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Mutant says ‘ello’ to sucrose
The shape and size of plant organs is dependent on cell division and growth, on the polarity of division and growth, and on cell differentiation. These processes are partially regulated by hormones and other growth factors and may also be modified by environmental and nutritional signals. All this is very well illustrated by the work of Falcone et al. (Calabria, Spain; Ghent, Belgium and Adelaide, Australia, pp. 261–220) working with the elo1 mutant of Arabidopsis thaliana. The mutation itself affects the activity of the histone acetyl transferase Elongator complex; the most obvious feature of the phenotype being narrow leaves caused by a reduction in palisade cell number and a change in the pattern of their expansion. Further, as now shown by the authors, there are sub-cellular changes including less-stacked grana and (under control conditions) many more starch grains in the chloroplasts, a hypotonic vacuole, more plamodesmata, larger Golgi bodies with more active exocytosis and a larger primary cell wall. The authors also studied the interaction between the expression of the mutant phenotype and the metabolism of sucrose, which is both a metabolite and a signalling molecule. There is a clear connection between the elo1 mutation and sucrose availability. This is partly shown by the effects of the mutation on the expression of genes involved in sucrose synthesis and transport. This was also seen when the effects of adding sucrose were studied. For example, addition of sucrose to the growth medium stimulated the germination of mutant but not of wild-type seeds. By contrast, leaf cell expansion was inhibited by sucrose in the mutants but stimulated in the wild-type. These results and others presented by the authors in this intriguing paper lead to very interesting suggestion that the elo1mutation has a major effect on sucrose sensing which, in turn, perturbates the regulation of cell division and cell growth.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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