Chemical studies on plant movement

Many plants close their leaves in the evening, as if to sleep, and open them early in the morning. Such a circadian rhythm has been known to be controlled by their internal clock. Since Ricca's ingenious experiments suggested that some chemicals play an important role in the leaf-movement of Mimosa pudica, many biologists and chemists have attempted to locate the leaf - closing substances, and a number of compounds have been obtained, particularly, by Schidknecht et al. Recently, we were also able to isolate a small amount of a stimulant (activity: ca. 10^-8 ~ 10^-9 M) from the same plant, which consists of three different components (potassium L-malate; magnesium trans-acconitate; dimethylammonium salt). Further extensive study on other nyctinastic plants led to the isolation of a variety of leaf- closing substances. On the other hand, indole-3-acetic acid (IAA) has been reported to be effective for Mimosa pudica as a leaf-opening factor. Three leaf-opening substance named potassium lespedezate, cis-p-coumaroylagmatine, and calcium 4-O-β-D-glucopyranoyl-cis-p-coumarate have been isolated from Lespedeia cuneate G. Don, Albizzia julibrissin D. and Cassia mimosoides, respectively. Based on our experiments using the leaf-opening and -closing substances, the circadian rhythm of these plants must be controlled by their internal clock which regulates a balance of concentration between the leaf- opening and closing substances.