High-frequency oscillations and circadian rhythm of the membrane potential in Spinach leaves.

The microelectrode technique was used to follow oscillations in membrane potential in mesophyll cells of spinach (Spinacia oleracea L.) during exposure do different photoperiodic conditions. Both high-frequency oscillations and circadian variations were observed. The circadian rhythm was imposed on the period of high-frequency oscillation during short days as well as in continuous light: The free-running period was 25.2 h. The average period of high-frequency oscillation increased from 7.64 min in the dark to 19.95 min in the light within several minutes after dark to light transition. This period length coincides with the established period length for oscillations in the redox potential in the chloroplast suspensions of spinach.