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Plant and Cell Physiology, 1986, Vol. 27, No. 2 233-242
© 1986

Article

Rhythmic Oscillations in Starch Concentration and Activities of Amylolytic Enzymes and Invertase in Medicago sativa Nodules

Cynthia A. Henson1, Stanley H. Duke1 and Willard L. Koukkari2

1Department of Agronomy, University of Wisconsin Madison, WI 53706, U.S.A.
2Department of Botany, University of Minnesota St. Paul, MN 55108, U.S.A.

Alfalfa (Medicago sativa L.) nodule amylase, starch phosphorylase and invertase activities and concentrations of starch and protein were determined every 4 h for 44 h to determine if daily fluctuations occur. Plants experienced 12 h light: 12 h dark (LD) during entrainment and the first 24 h of the experiment. The last 20 h were under continuous darkness (DD). Temperature (21°C) and relative humidity (72%) were always constant. Data were analyzed by the cosinor method to determine probabilities of sinusoidal rhythms with periods between 12.0 and 30.0 h. Under LD conditions, significant 12.1 h rhythms were found for activities of amylase and starch phosphorylase and for starch content. Rhythms in amylase activities and starch content were inversely correlated whereas rhythms of starch content and starch phosphorylase activity were positively correlated. These data indicate that nodule starch can be rapidly turned over and that amylases may be responsible for the degradation. None of these rhythms persisted under DD conditions. In contrast, invertase activity was rhythmic under LD (24 h period) and DD conditions (30 h period). No significant rhythmic variations were detected in protein levels throughout the entire experiment.

(Received August 12, 1985; Accepted November 22, 1985)
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