Nitrogen effects on leaf anatomy within the intercalary meristems of tall fescue leaf blades

Longitudinal elongation contributes most to leaf area expansion of grasses and its rate is known to be strongly affected by N. Our objective was to de termine the effect of two N regimes (N-0 and N+) on the gradient of leaf ti ssue formation in meristems of two contrasting tall fescue (Festuca arundin acea Schreb.) genotypes. Proportions of epidermal, mesophyll and vascular t issue as well as intercellular air space were determined throughout the bas e of actively elongating leaves. The area of leaf transverse sections nearl y doubled between the ligule and the distal end of the growth zone (about 3 0 min), and was mainly associated with lateral epidermal and mesophyll cell division in the proximal 5.0-7.5 min. Further increase in transverse area was due to the formation of intercellular airspace and transverse expansion of epidermal cells. Depending on genotype and N treatment the mesophyll, e pidermis, vascular bundles and air space comprised 45-54 %, 20-28 %, 6-9 %, and 17-21 %, respectively, of transverse leaf area ill the distal part of the growth zone. After a slight increase close to the leaf base, the area o f vascular tissue remained constant throughout the growth zone. The proport ion of air space to mesophyll space was higher at N-0 than at N+ because me sophyll area was enhanced by N+ to a greater degree than by N,. In the geno type with slow leaf elongation, the increase in cross-sectional leaf area w as due to an increase in both leaf width and leaf thickness, In the genotyp e which had faster leaf elongation and wider leaves, only leaf thickness wa s enhanced by N+.