Temperature-dependent changes of membrane potentials in cells of thermonastic tepals of Eranthis hyemalis (L.) Salisb.

The effect of temperature upon the bioelectric potential across the plasma membrane in cells of tepals of Eranthis hyemalis (L.) Salisb. (Winter aconite) is described. Rapid warming of an intact tepal resulted in a transient small increase in the magnitude of transmembrane potential difference followed by a substantial long-lasting depolarization which is considered as an "anomalous" response. Upon rapid cooling the reverse response occurred: a small transient depolarization was followed by a substantial hyperpolarization (also an anomalous response). The anomalous responses were more pronounced in the epidermis on the abaxial side of the tepal than in that on the adaxial side, indicating an electrophysiological dorsiventrality of the tepals. The anomalous responses were much less apparent in cells of isolated tissues than in cells of intact tepals. This difference does not appear to result from wounding or bringing a tissue into direct contact with the external solution because in segments of tepals devoid of the abaxial epidermis only, the PD of the parenchyma behaved in a way similar to that of the intact tepals. It is suggested that the occurrence of the anomalous responses is modulated by the tissue stresses. The functional importance of the responses for thermonastic movements is discussed.