Leaf elongation rate (LER) of grasses depends on N supply and is expre
ssed mostly through cell production, whereas most N in mature leaf tis
sues is chloroplastic. Our objective was to evaluate a possible compet
ition for N between cell production and chloroplast development proces
ses, utilizing the gradient of cell development along the leaf growth
zone of tall fescue (Festuca arundinacea Schreb.). Under the two contr
asting N regimes, total N content was highest in the cell production z
one, declined sharply as cells elongated, and remained relatively cons
tant in more distal positions, at values close to those measured in ma
ture tissues. A similar pattern was found for N in proteins and nuclei
c acids that were not soluble in 80% ethanol. Content of N compounds s
oluble in 80% ethanol was higher in the cell production and elongation
zones than in mature parts of the leaf. NO3- N content was low in the
cell production zone and increased in the cell elongation zone for hi
gh-N plants. The deposition rate of total N in the growth zone was muc
h higher with plants in high N than in those shifted to no N. For both
N regimes, most N was deposited during cell production and early cell
elongation. Little N was deposited during cell maturation where ribul
ose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was being activel
y synthesized. This suggests that synthesis of Rubisco, and probably o
ther chloroplastic proteins, occurs largely from recycling of N that w
as previously incorporated into proteins during cell production. Thus,
Rubisco content in mature tissues is more closely associated with N d
eposited during cell production than with N deposited during its biosy
nthesis.