Poster: Seed biology

Abs # 716: Programmed cell death and endoreduplication during caryopsis development in maize and sorghum

Presenter:	Dermastia, Marina , marina.dermastia@uni-lj.si
Authors	Dermastia, Marina  (A)   Kladnik, Ales  (A)   Chamusco, Karen  (B)   Sutherland, Shayna  (B)   Tang, Hoang  (C) (B)  Pring, Daryl  (C) (B)  Chourey, Prem  (C) (B)
Affiliations:	(A): University of Ljubljana, Department of Biology (B): University of Florida (C): USDA-Agricultural Research Service

Quantitative image analyses in developing caryopses of maize and sorghum show positive correlation between endoreduplication and the size of both cell and nuclei in these two crop plants that share much syntenic similarity. Spatial distribution of cells in relation to their size and endoreduplication state was determined at 12 days after pollination, which represents the final phase of endosperm endoreduplication in both maize and sorghum. Nuclei of both crop plants by 12 DAP undergo at least 5 cycles of endoreduplication with the final value of 96 C. However, volumes of nuclei and cells in sorghum endosperm were progressively smaller at the respective C-value classes as compared to maize. Positive correlation between cell volume and endoreduplication in both studied species suggested that these two cell characteristics were interdependent. We also present cumulative evidence, based on cellular and ultrastructural level studies of programmed cell death (PCD) in placento-chalazal cell layers and placental sac of maternal tissue in developing caryopses of maize and sorghum, respectively. In maize, two spatially and temporally distinctive sub-domains were identified by the TUNEL stain (diagnostic of apoptotic-like PCD), and by UV-induced autofluorescence indicating the presence of unique sets of cell wall associated phenolic acids and flavonoids. The results so far in sorghum indicate a similar developmental program of placental sac. We suggest that early wave of PCD, is of osmolytic etiology, as an adaptive strategy to provide a clear passage for rapid transport of nutrients and water to a developing sink tissue. The regulatory control of transport from maternal cells may depend on the collective forces of turgor and metabolic sensing in the basal endosperm cells.