Figure 1.

Schematic representation of a vegetative perennial ryegrass tiller at defoliation (A) and approximately one leaf appearance interval after severe defoliation (B). The tiller is composed almost entirely of leaf tissue (1–5). Daughter tillers may be present in axils of fully expanded leaves (not shown). The TB includes the apex, nodes, and unelongated internodes of the tiller. The defoliation level marks the boundary between the exposed (grazed/mown) foliage and stubble zones. At defoliation (A) leaves 1 and 2 had reached full expansion, whereas leaves 3 and 4 were expanding (↑). Defoliation removed all lamina tissue of leaves 1 and 2 and (the exposed) part of the lamina of elongating leaf 3. Leaf 4 was not touched, because its tip had not emerged above the defoliation level. Foliage production (exposure of lamina tissue above the defoliation level) during the interval A to B was due to expansion of leaves 3 and 4. At time B leaf 3 had reached its final size. Expansion stopped shortly after the ligule was exposed above the defoliation level. Leaf 4 was still expanding at time B, and leaf 5 had started to expand. Expansion and maturation of cells takes place in a zone (IM-AE) that extends from the base of the expanding leaf to the location where leaf tissue emerges from the encircling sheaths of older leaves (at approximately defoliation level). The sheath was actively expanding in leaf 4 at time B (note position of the ligule). Leaf 5 was still completely enclosed and expanding as a function of lamina growth. At any time during refoliation, the regrowing tiller can be divided into five functionally distinct zones: the TB, the EX-AE, and the IM-AE (leaves 4 and 5 in B [shaded area]) and the EX-FE and EN-FE, which stopped to elongate after defoliation (leaf 3 in B). Leaves 1 and 2 had stopped to expand before defoliation and, hence, do not form part of the regrowing tiller, as defined here.