Carbohydrate Metabolism in Leaf Meristems of Tall Fescue

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Abstract
Alterations in carbohydrate status of leaf meristems that are associated with N-induced changes in leaf elongation rates of tall fescue (F. arundinacea Schreb.) were examined. Dark respiration rates, concentrations of nonstructural carbohydrates and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The 2 genotypes used differed by 43% in leaf elongation rate. Application of high N (336 kg/ha) resulted in 140% higher leaf elongation rate when compared to plants receiving low N (22 kg/ha). Leaf meristems of plants receiving high and low N had dark respiration rates of 5.4 and 2.9 .mu.l O2 consumed/milligram structural dry weight per h, respectively. Concentrations of soluble proteins were lower: concentrations of fructan tended to be slightly higher in leaf meristems of low-N plants when compared to high-N plants. Concentrations of reducing sugars, nonreducing sugars and takadiastase-soluble carbohydrate of leaf meristems were not affected by N treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-N plants, respectively. Within the leaf meristem, .apprx. 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-N plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.