Ruth Lyttle Satter

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

Biography

Ruth Lyttle Satter was born March 8, 1923, in New York City as Ruth Lyttle.

Satter received a B.A. in mathematics and physics from Barnard College in 1944. In 1946 she married Robert Satter and in 1947 she became a homemaker, devoting herself to raising her and Robert's four children, Mimi, Shoshana, Jane and Dick. 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. Additionally, in 1980, she co-authored the third edition of The Life of the Green Plant, a textbook on plant physiology and botany, with Galston and another colleague, Peter J. Davies.

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. In 1990, the Ruth Lyttle Satter Prize in Mathematics was also established in her memory, with funds donated by her sister, Joan S. Birman. The prize is given every two years and honors Satter's commitment to research and encourages women in science by awarding $5000 to a woman who has made a significant contribution to mathematics research. However, it was not until Satter's groundbreaking work that the molecular mechanisms of this phenomenon were understood.

Satter worked to decipher the structure and function of pulvini, specialized plant motor organs found at the base of leaves and leaflets which allow leaves to extend and fold down. She identified that changes in potassium and chloride ion concentrations in pulvini drive osmotic water flux, or changes in the amount of water in the cell. The pulvini contain two cell types, flexor and extensor cells. Satter's work demonstrated that as the flexor gains solutes and thus water to increase their rigidity, the extensor loses ions and water to decrease their rigidity. The coordinated inverse rigidity changes in extensor and flexor induce extension or collapse of the pulvinus to lift and lower leaflets.

Phytochromes have two interconvertible isomeric forms, Pfr and Pr. Red light converts the pulvinus phytochrome to the Pfr form which promotes leaf closing, while exposure to far-red light converts the photopigment to the Pr form and promotes leaf opening. Pfr phytochrome depolarizes the cell membrane by opening potassium ion channels and facilitating potassium ion flow while Pr hyperpolarizes the cell membrane to close the potassium ion channel and prevent ion flow. Over the course of 24 hours, the amount of red and far-red light in the environment changes, so the form of phytochrome in the pulvinus also changes over time, causing the plant leaves to open or close as a result of the environmental light cycle.

Satter also studied other methods of leaf movement entrainment including the effects of blue light. Satter and her colleagues showed that blue light leads to phase shifts in leaf movement in both Samanea saman and Albizia. Satter found that blue light exposure can affect when plant leaves extend and that the timing of blue light exposure determined whether leaves extended earlier or later than expected. 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.