Poster: Seed Biology

Abs # 548: Cellular and ultra cellular level characterization of programmed cell death (PCD) in developing caryopsis of maize.

Presenter:	Chamusco, Karen C., kchamusco@ifas.ufl.edu
Authors	Chamusco, Karen C. (A)   Chourey, Prem S. (A) (B)
Affiliations:	(A): Plant Molecular and Cellular Biology program, University of Florida (B): United States Department of Agriculture (USDA)-Agricultural Research Service (ARS)

We describe cellular and ultra cellular level changes attributable to PCD in developing caryopsis of maize. We examined placento-chalazal (PC) cell layer in the pedicel, located beneath basal endosperm transfer cells(BETC). Although a maternal tissue, the cellular level changes seen by DAPI and TUNEL stains were fertilization-dependent, and the entire process of PC-enucleation was completed during 4 to 12 days after pollination (Kladnik et al., submitted). Surprisingly, there were very few or no detectable TUNEL-positive cells preceding or during this phase of enucleation. We analyzed the PC in detail by transmission electron micrscopy (TEM) to better understand the PCD in these cells. TEM micrographs confirmed the DAPI data. TEM revealed that PC cells appeared healthy till 5DAP; the nuclei were intact and cellular contents and organelles appeared normal. By 7DAP the cells most proximal to the BETC were emptying and the nuclei in the cells just below began chromatin condensation. At 9DAP, the cells below the BETC were completely empty. Progressing basipetally the cells showed a gradation in the degree of degeneration, including the loss of plasmodesmata in the cells immediately subtending the BETC. We also examined PCD in developing endosperm during the storage phase, reported by Young et al (1997). At 24 DAP, we observed both a spatial and temporal gradient in enucleation that paralleled the maturation gradient in the endosperm. In contrast with the PC region, the enucleation in endosperm cells was tightly coupled with TUNEL activity. In addition, chromatin condensation at the nuclear membrane gave it a beaded appearance, a hallmark of PCD. Overall, there are at least two pathways to PCD in developing caryopsis; possible significance of these results will be discussed.