Poster: Organelle Biogenesis

Abs # 1143: Arabidopsis mutants affecting plastid development in embryo-derived cells

Presenter:	Ruppel, Nicholas J., nruppel@bio.indiana.edu
Authors	Ruppel, Nicholas J. (A)   Logsdon, Charles  (A)   Hangarter, Roger P. (A)
Affiliations:	(A): Indiana University

Arabidopsis embryonic cells contain functional chloroplasts with developed thylakoid membranes and starch grains. During embryo maturation and deposition of seed storage reserves, the chloroplasts dedifferentiate into eioplasts by losing their chlorophyll, thylakoid membranes, and starch. In seeds containing normal embryos, the eioplasts will redevelop into mature plastids when the seedling germinates. For example, cotyledon cells will form green chloroplasts for photosynthesis and hypocotyl endodermal and root cap cells will form amyloplasts for gravisensing. Photosynthesis and gravisensing are critical functions for seedling establishment. We have identified a novel class of Arabidopsis mutants that affect plastid development in embryonic cells. These mutants exhibit white cotyledons upon germination, whereas leaves derived from the apical meristem after germination appear to have normal chloroplasts. The mutations have been named spd, for seedling plastid development. One of these mutants (spd1) is defective in both chloroplast and amyloplast development. The remaining spd mutants specifically affect chloroplast development. spd embryos precociously germinated prior to maturation yield green seedlings, but seedlings grown from fully developed embryos have white cotyledons. Thus, the SPD genes appear to function during the early stages of embryo maturation. We will present a detailed characterization of the development and physiology of two mutants, spd1 and spd2. Molecular and genetic analysis for both mutants is forthcoming. The spd mutations offer unique insights into fundamental mechanisms controlling plastid development and genes that function specifically during embryogenesis and/or early germination.