Cell Dynamics in Leaf Meristems of Contrasting Tall Fescue Genotypes

Leaf elongation rate is a factor associated with yield per tiller and rate of canopy development. Elucidation of the mechanism by which leaves elongate may assist plant breeders and crop managers in optimizing agronomic performance. Our objectives were to locate the leaf intercalary meristem of tall rescue (Festuca arundinacea Schreb.) and to assess the relative contribution of cell division, cell elongation rate, and mature cell length to leaf elongation rate. Both cell division and elongation occurred in an intercalary meristem located with a lignin-sensitive stain in the basal 30 mm of the elongating leaf. Growth rates within the elongation zone were ascertained by placing equispaced ink dots on the epidermis of the exposed meristem region and then measuring their displacement after 24 hours of growth. Growth occurred between dots placed 2 mm above the point of the previous leaf's attachment and those placed 13 and 26 mm above in genotypes exhibiting low (LYT) and high (HYT) yield per tiller, respectively. Maximum elongation rate occurred from 6 to 7 mm and from 9 to 14 mm above the point of the previous leaf's attachment in the LYT and HYT genotypes, respectively. In these regions, elongation rate of leaf tissue of the LYT genotype averaged 1.0 mm mm⁻¹ day ⁻¹, which was 40% higher than that of the HYT genotype. Microscopic measurement of epidermal cell lengths throughout the elongation zone, and measurement of leaf elongation rate (LER), permitted an assessment the relative contribution of both cell division and elongation. The LER of 26 mm day⁻¹ of the HYT genotype was 44% higher than that of the LYT genotype. The HYT genotype also had a 100% longer cell elongation zone and produced 185 epidermal cells day ⁻¹ cell column⁻¹ which was 24% more than that produced by the LYT genotype. The 145 µm length of mature epidermal cells of the HYT genotype was 22% longer than those of the LYT genotype. The elongation zone of the HYT genotype contained 509 epidermal cells which was 94% more than the LYT genotype, but each epidermal cell expanded at a rate that was 20% slower. This resulted in a duration of elongation of 2.8 days cell⁻¹ for the HYT genotype, which was 56% longer than that of the LYT genotype. The large number of cells and long duration of cell elongation in the HYT genotype overcame the slow rate of cell elongation. This resulted in more and larger matured cells which led to the more rapid LER and high yield per tiller characteristic of the HYT genotype in comparison with the LYT genotype.