Epidermal cell division and cell elongation in two Aegilops species with contrasting leaf elongation rates

The 2-fold difference in final length of leaf number three on the main stem between the fast-growing Aegilops tauschii L. and the slow-growing Aegilops caudata L. is correlated with a difference in leaf elongation rate (LER), and not in duration of leaf elongation. In this paper the cellular basis of inherent differences in LER between these species was investigated. The dynamics of abaxial epidermal cells along the growth zone of leaf number three on the main stem of both species was analysed by means of a kinematic analysis. The faster LER of Ae. tauschii compared with that of Ae. caudata was associated with (i) a larger leaf basal meristem and cell elongation-only zone, and (ii) a faster cell production rate owing to a larger number of dividing cells. Cell division rate, mature cell size and cell elongation rate did not differ between the two species. The lack of variation in cell expansion rate between the species was supported by a similar capacity of both species to extend their isolated cell walls upon acidification. These data suggest that differences in the number of dividing cells can bring about differences in the number of simultaneously elongating cells, and hence in LER.