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Respiration and Concentration of Water Soluble Carbohydrate in Plant Parts of Contrasting Tall Fescue Genotypes¹

Little information is available concerning genotypic differences in dark respiration (R_D) of plant tissues. The objectives of these studies were to determine if a gradient of R_D (0₂ uptake) existed along the leaf blade and to compare maintenance respiration, growth respiration, and concentration of water-soluble carbohydrate (WSC) leaf blades, terminal meristems areas, and root tips of seven genotypes of tall rescue (Festuca arundinacea Schreb.). Three genotypes had been selected for contrasting yield/tiller, and four genotypes had been selected for contrasting CO₂ exchange rate (CER)-yield relationships.

Center portions of mature leaf blades had the highest rate of R_D and were used in subsequent leaf studies. Dark respiration of mature leaf blades probably reflected maintenance respiration since it was independent of measured carbohydrate levels and leaf growth had ceased. Rates of R_D 3 hours after the photoperiod began were similar to those measured after 48 hours of darkness in elongating leaves and terminal meristems. Concentrations of WSC in these tissues were decreased during the dark period, but probably not enough to stop respiration associated with the growth component. Respiration of root tips was not significantly different among genotypes selected for contrasting yield/tiller, but was decreased to about 44% of the original rate by the 48-hour dark treatment. That rate may have represented the maintenance component. Rates of R_D of mature blades and terminal meristems of low, medium, and high yield/tiller genotypes corresponded to their yield/tiller classification. Conversely, among the four genotypes selected for their differential CER-yield relationship, the low CER-Iow yield genotype had the highest R_D of mature leaf blades and terminal meristems.

In general, concentrations of WSC within tissues did not differ significantly among genotypes. Terminal meristems had a significantly higher concentration of WSC than did other plant tissues studied, and weights of WSC per terminal meristem were significantly different among genotypes. These data showed that genetic variation for R_D existed in tall rescue, that R_D was different for tissues within a plant, and that 48 hours in darkness was insufficient to decrease WSC enough to clearly separate the growth and maintenance components of R_D in tall fescue.

Key Words: Maintenance respiration • Growth respiration • Yield component • Festuca arundinacea Schreb • Root tips • Terminal meristems • Leaf blades

² Graduate assistant (currently assistant professor of agronomy and plant genetics, Univ. of Minnesota, St. Paul, MN 55108), and professor of agronomy, respectively, Univ. of Missouri, Columbia, MO 65211.

Received for publication August 7, 1978.

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