Poster: Tropisms

Abs # 661: Actomyosin based signaling in root gravitropism

Presenter:	Kramer, Victoria L, chitari@yahoo.com
Authors	Kramer, Victoria L (A)   Gilroy, Simon  (A)
Affiliations:	(A): Penn State University

Gravitropism causes plant roots to grow down into the soil. The modulation of root gravitropism has implications in nutrient acquisition, such as in root partitioning for deep and shallow nutrients. However, a much more fundamental question is how plant roots perceive and respond to gravity. The primary graviperception events take place in the root cap columella cells. It is thought that statoliths, starch filled plastids susceptible to changes in the gravity vector, are coupled to an actomyosin network. Movement of these statoliths would contort this network, leading to the beginning of chemical signaling. Previous work in our lab determined pH to be involved in the graviresponse. The intracellular pH of the columella would rise in response to gravistimulation in as little as 1 minute. Likewise, the extra-cellular pH in the columella would fall. To test whether or not actomyosin is involved in graviperception and the related pH signaling events, we treated Arabidopsis thaliana roots from a line that had been stably transformed with reagents that disrupt specific cytoskeletal elements, such as the actin antagonist Latrunculin B. The dynamics of the pH response to gravity was altered by treatment with the actin depolimerizing drug Latrunculin B. At a concentration that does not inhibit root growth, Latrunculin B yielded a delayed response but extended the pH increase, similar to experiments previously conducted with caged protons. In addition, treatments aimed at altering myosin activity, such as ML-9 treatment, affected gravity-related signaling events in the columella such as amyloplast motility. These results suggest the actomyosin network is involved in gravisensing. This research was supported by grants from NSF and NASA.