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Molecular Weight and ¹⁴C Distribution of Fructosan in Timothy Stem Bases at Three Stages of Development¹

Variation in fructosan concentration in the stem base of timothy (Phleum pratense L.) at three stages of growth (initiation of stem elongation, ear emergence, and anthesis) from 1 to 168 hours after exposure to ¹⁴CO² was investigated. Molecular weight distribution of ¹⁴C-labeled fructosan was determined. From initiation of stem elongation to anthesis, fructosan concentration increased from about 13 to almost 40%. In the first two growth stages, fructosan showed a broad molecular weight distribution, ^a = 18,000 to ⁿ = 2,000. There was a tendency by 168 hours after initiation of stem elongation for the plants to accumulate primarily higher molecular weight fructosan, while by ear emergence, there was a distinct accumulation of long-chain fructosan molecules. In all growth stages, ¹⁴C-labeled fructosan appeared as early as 1 hour after exposure to ¹⁴CO² with label distributed throughout the molecular weight range. High ¹⁴C activity was found in long-chain fructosans by 168 hours after exposure at ear emergence and anthesis. Condensation of short-chain fructosans and synthesis of new fructosans using monosaccharides with high ¹⁴C activity may explain the above observation.

Key Words: Gel-filtration • Carbohydrates • Grass

² Visiting scientist and specialist, respectively, Dep. of Agronomy, Univ. of Wisconsin, Madison 53706. The senior author's permanent address is Faculty of Agriculture and Horticulture, Technical Univ. of Munich, West Germany.

Received for publication April 8, 1976.