Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2005
Publication Date: 12/9/2005
Citation: Kladnik, A., Chourey, P.S., Pring, D.R., Dermastia, M. 2005. Development of the endosperm of sorghum bicolor during the endoreduplication-associated growth phase. Journal of Cereal Science. 43:209-215. Interpretive Summary: Cereal endosperm in a seed is a major storage site for carbohydrates (starch), proteins and oils. These nutritional compounds, the major source of food and feed for mankind, are synthesized and deposited in a short span of time in a highly coordinated fashion during seed development. How a tissue becomes a metabolic factory with a massive increase in gene expression and the associated increases in numerous proteins and enzymes is unknown. Here in this report a team of international scientists from Crop Genetics & Environmental Research Unit, CMAVE, the University of Florida in Gainesville, FL, and the University of Ljubljana, Ljubljana, Slovenia, show greatly increased amount of DNA (endoreduplication), as much as approx. 100-fold, in certain endosperm cells during starch synthesis in developing seeds of sorghum. Increased level of DNA is also associated with increased cell size (ultimately, more storage room) and higher levels of gene expression. These results provide a possible molecular basis through which an endosperm cell undergoes a metabolic switch and synthesizes massive amounts of storage compounds. A better understanding of the phenomenon of increased DNA per cell can lead to its possible manipulation toward increased crop productivity.
Technical Abstract: Endoreduplication, a special variant of cell cycle resulting in endopolyploidy, is common in differentiated plant tissues. We investigated the temporal and spatial occurrence of endoreduplication in the sorghum caryopsis. The level of nuclear endopolyploidy was measured with image densitometry using the interphase-peak method in Feulgen-stained median sections of caryopses, thus providing in situ cytometrical data on tissue sections and preserving tissue structure. First endopolyploid nuclei in the endosperm were detected as early as 5 DAP (days after pollination). Progressively higher levels of endopolyploidy occurred, however the highest levels were spatially found only in the central region of endosperm. The onset of starch deposition in the endosperm coincided with highly endopolyploid nuclei. The highest level of endopolyploidy in the endosperm, 96C (1C represents the nuclear DNA content of a non-replicated haploid genome), was first observed 10 DAP. Cells with non-endopolyploid nuclei (3C and 6C) were found exclusively in the peripheral layers of the endosperm. No starch was observed in the basal part of the endosperm where the highest level of endopolyploidy was 24C. Endosperm cell volume showed positive correlation with the level of endopolyploidy.