Endopolyploidization of mesocotyls in Nebraska maize populations selected for cold tolerance

Germination and emergence in cold conditions (12-15 [degrees] C) is important for obtaining improved maize (Zea mays L.) yields in low and no-tillage production systems. The mesocotyl plays a decisive role in determining the ability of seedlings to emerge under adverse conditions such as deep planting or cold soils. The major factor involved in elongation of the mesocotyl is somatic polyploidy, referred to as endopolyploidization. Endopolyploidy of the mesocotyl tissue was determined by flow cytometry during 1992. Nuclei were isolated from mesocotyls of various maize populations grown at 23 and 15 [degrees] C. Endopolyploidy of populations selected for cold tolerance was compared with endopolyploidy of their original unselected populations. The populations selected for cold tolerance had an endopolyploid distribution similar to their original unselected populations at both temperatures. Only the NA population was observed to have a different distribution of endopolyploidization in the selected population as compared with the original unselected population. The response was speculated to be the result of different mechanisms of cold tolerance in the NA vs. the NB and NS populations. Endopolyploidization was not affected by cold tolerance per se, but may be associated with freeze tolerance. A significant difference with respect to temperature was observed. At 15 [degrees] C, the number of the highest ploid nuclei (8C) were reduced, while the number of 2C nuclei increased. This change reflects the slowing of cell division at cooler temperatures.