Abstract
The physiological bases for genetic differences in leaf growth rates were examined in two genotypes of tall fescue (Festuca arundinacea Schreb.) selected for a 50% difference in leaf elongation rate. Genotypes had similar dark respiration rates and concentrations of carbohydrate fractions in the leaf meristem and in each daily growth segment above the meristem. Dark respiration rates and concentrations of nonreducing sugars, fructans, and takadiastase-soluble carbohydrates were highest in leaf intercalary meristems and declined acropetally with tissue age. Concentrations of reducing sugars were 1.0% of dry weight in leaf meristems, 3.7% of dry weight in tissue adjacent to the meristem, then decreased progressively with distance from the meristem. Glucose, fructose, and myo-inositol comprised over 90% of the monosaccharides present in leaf meristems. Soluble protein concentration was 9.7 milligrams per gram fresh weight in leaf meristems, 5.5 milligrams per gram in tissues immediately above the meristem and, thereafter, increased linearly with distance from the meristem.Leaf meristems of the genotype exhibiting rapid leaf elongation contained 30% more soluble protein than those of the genotype selected for slow leaf elongation. The 4-fold difference in size of the leaf meristem appeared to be more important in influencing leaf elongation than were other characteristics examined.