Ruth Lyttle Satter (March 8, 1923 – August 3, 1989) was an American botanist best known for her work on circadian leaf movement.

[1][3][4] While raising her children, her love of plants led her to complete the New York Botanical Garden's horticulturist training in 1951 and to serve as a horticulture instructor for the YMCA Hobby School from 1953 to 1963.

In 1968, after completion of her PhD, Satter joined the lab of Arthur W. Galston at Yale University to work first as a staff biologist and then as a research associate.

[6][7] In 1980, Satter also became a professor-in-residence at the University of Connecticut, where she discovered that the phosphatidylinositol cycle is the basic light transduction mechanism in the leaf motor cells.

The coordinated inverse rigidity changes in extensor and flexor induce extension or collapse of the pulvinus to lift and lower leaflets.

[10] Satter determined that the changes in membrane potential were too quick to be explained by the passive movement of potassium ions reported in her earlier papers.

Satter additionally unveiled the mechanisms that allow circadian leaf movements to synchronize with (entrain to) light-dark cycles.

She showed that phytochromes, a type of plant photopigment, mediate changes in membrane potential of pulvini in response to red and far-red light.

Satter and her colleagues showed that blue light leads to phase shifts in leaf movement in both Samanea saman and Albizia.

While these studies revealed that blue light could advance or delay circadian leaf movement rhythms, the photoreceptor that mediates this response would not be discovered until later.