Cell growth analysis during steady and non-steady growth in leaves of perennial ryegrass (Lolium perenne L.) subject to defoliation

The effect of defoliation on leaf elongation rate (LER) and on the spatial distribution of epidermal cell lengths in the leaf growth zone was studied in vegetative main tillers of perennial ryegrass (Lolium perenne L. cv Modu s) grown in a controlled environment. A new material approach was used to a nalyse the responses of epidermal cell expansion and production during the initial, non-steady growth phase following defoliation. The analysis involv ed assigning an identity to individual expanding cells, assessing the displ acement and estimating the expansion of cells with assigned identity during day 1 and day 2 after defoliation. LER decreased by 34% during the first 2 d after defoliation and did not recover to the pre-defoliation rate within the 14 day regrowth period. Decreased LER on day 1 and day 2 after defolia tion was associated with (i) a decrease in the length of the leaf growth zo ne; (ii) a decrease in the length at which epidermal cells stopped expandin g; (iii) a reduced expansion of cells at intermediate growth stages; and (i v) a reduction in cell production (i.e. division) and an associated decreas e in the number of expanding cells in the growth zone. However, defoliation had no effect on the expansion of cells located in the proximal part of th e growth zone. Reduced LER at 14 d after defoliation was associated with a reduced cell production rate (27% lower than the pre-defoliation rate) and decreased final cell size (-28%).