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Model leaves – and shoots
Thinking about the dependence of human nutrition on fruit, seeds and their products leads to a realization of the importance of the regulation of flowering. Rightly then, the transition from the vegetative to the flowering state continues to attract attention. However, the floral transition is not just about forming flowers, as is illustrated by the work of Cookson et al. (Montpellier, France, pp. 703–711). Their subject of study was the favourite ‘model’ long-day plant, Arabidopsis thaliana. Plants were grown under five different day-length regimes; in all other respects treatments were identical. We concentrate here mainly on comparing the effects of 20-h and 10-h days on the ‘Landsberg’ erecta ecotype. Under short days, more rosette leaves were formed than under long days because the length of the leaf initiation phase was lengthened. However, when comparing leaves at the same position, the leaves on the long-day plants had a greater leaf area than those on the short-day plants. This resulted from greater absolute and relative leaf expansion rates. The number of epidermal cells was also significantly greater under long days but the effect of this was partly negated by the smaller area of the epidermal cells. Thus, the conditions that induce or inhibit flowering also affect leaf development but are the two developmental processes connected? Transferring plants from 10-h to 20-h days induced flowering and inhibited initiation of rosette leaves, consistent with the earlier experiments. To study the effects of flowering delay, the authors grew plants under 14-h days (in which flowering does occur) but then removed the flower buds. The results presented are confined to epidermal cell dynamics: predictably, the epidermal cell area was increased by this treatment but, perhaps unexpectedly, epidermal cell numbers were also increased. Nevertheless, the overall picture is clear: there are whole-plant mechanisms associated with flowering that contribute to the control of leaf development.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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