Basic Spatial and Temporal Patterns of Organ Growth Distributions

Spatial and temporal patterns of growth distributions are often intimately connected to each other, since neighboring regions of an expanding organ often consist of tissue of successive developmental stages. For monocotyle-donous leaves and for root growth zones, which are organized linearly with clearly distinguished zones of cell division and expansion, development is deterministic to a high extent. Hence, the principal distribution of growth rates along the axial direction of those organs is very similar and has been well investigated throughout the last decades. Much less attention has been directed towards distributions of growth rates in leaves of dicotyledonous plants.

The temporal sequence of cell elongation also differs strongly between root and leaf tissue. While in roots, cell elongation is typically finished within between 6 h (Arabidopsis thaliana; Beemster and Baskin 1998) and 24 h (Zea mays; Silk et al. 1989), cells of leaves typically expand for 7 d (Arabidopsis thaliana; De Veylder et al. 2001) or 14 d (Nicotiana tabacum; Walter et al. 2003b). Correspondingly, maximal relative growth rates are much higher in root cells, reaching values of up to 40% h-1, while in leaf tissue, peak values hardly ever exceed 4% h-1. Another fundamental difference between growth dynamics of roots and leaves is, that root growth activity is typically not fluctuating throughout the diel cycle (Head 1965; Iijima et al. 1998; Walter et al. 2002b; Walter and Schurr 2005), while it has long been known that leaf growth intensity is not constant throughout 24 h.

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