Circadian Electrochemical Changes in the Pulvinules of Trifolium repens L

Abstract

In pulvinules of T. repens, circadian changes were observed in the content and influx of potassium. No corresponding changes were observed for calcium or sodium, although the influx of calcium has a light-dependent component. For both adaxial and abaxial cells, potassium influx becomes high prior to cellular swelling and remains high until shortly before shrinkage, when it falls and remains low for the remainder of the cycle. Circadian changes in transmembrane potential are also observed. Swollen cells are initially hyperpolarized (H ≈ 90 mV), but depolarize (to H ≈ 70 mV) about 9 h before shrinking. The potential reverts to the more negative value about 9 h before the cells again swell. The phasing of the potassium influx, water volume and membrane potential cycles of pulvinule cells may indicate sequential steps in an oscillating feedback system which could form the basis for the circadian behaviour.