Carbohydrate Metabolism in Leaf Meristems of Tall Fescue

Abstract

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arwmdiaacea Schreb.). Dark respiration rates, concentrations of nonstuc l carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kiloams per hectare) resulted in 140% higher leaf elngtion rate when compared to plants receiving low nitrogen (22 kilms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5A and 2.9 microliters 02 consumed per milligram strcturl dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and tdastase- soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructura! carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstucturl carbohydrate could be consumed per day in high- and low- nitrogen 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 trans- port to leaf intercalary meristems may not limit leaf growth of these genotypes.