Poster: Late and Moved Abstracts

Abs # 957: The spatial distribution of endoreduplication during early seed development in soybean.

Presenter:	Li, Songtao , sli@purdue.edu
Authors	Li, Songtao  (B)   Ritchie, Rae D (A)   Nielsen, Niels C (A) (B)
Affiliations:	(A): USDA Agricultural Research Service (B): Purdue University

Endoreduplication is an alternate form of the cell cycle in which chromosomal DNA is replicated in the absence of mitosis and is most often associated with differentiated cells that have high metabolic activity. Soybean cotyledons are storage organs in which there is a massive accumulation of oil and protein upon the onset of seed-fill. To characterize developmental events associated with the establishment of seed-fill in these cotyledons, we demonstrated that the increase in starch content in these organs was correlated with an increase in the average ploidy of nuclei isolated from seeds at progressive times during seed development. By in situ measurement of DNA content of nuclei in cotyledon sections from seeds before and after the onset of seed-fill, we demonstrated that an increase in nuclear ploidy first became evident in parenchyma cells in the adaxial region distal from the embryo and that the distribution of highly endoreduplicated cells in the adaxial region increased rapidly. In situ RT-PCR was used to demonstrate that mRNA encoding beta-conglycinin was co-localized with the highly endoreduplicated cells. To further investigate events associated with the establishment of endoreduplication in these cells, accumulation patterns of transcripts encoding various cell cycle components were monitored using real time RT-PCR and in situ RT-PCR. The mRNAs encoding cell cycle components associated with mitosis rapidly disappeared from the cotyledons upon the onset of seed-fill. Those messages that could be detected at mid-maturation were located in mostly diploid parenchyma cells that subtend the abaxial surface of the cotyledon. Conversely, mRNAs that encode ICKs were co-localized with highly endoreduplicated cells in the adaxial region of the cotyledon.