Cold-induced elongation and division in radicle cells of Pirus Malus embryos

Abstract

Mitoses and elongation occurred concomitantly during the first days of germination in apple (Pirus Malus L.) radicle cells only when embryos were previously cold stimulated. The radicle cells in nonstimulated embryos did not elongate or enter the S, G2, and M phases of the cell cycle (the 2C level was estimated to 5 pg per nucleus). Accordingly, nuclear areas did not increase in the absence of cold treatment, whereas they doubled in size when embryos were cold stimulated and cultured to germinate. This increase in nuclear size can be considered a specific event in the pathway to germination. In nonstimulated embryos, nucleoli did not exhibit vacuolation and did not develop a granular component as they did in the germinating embryos after 3 days. Ultrastructural aspects of the chromatin itself were difficult to correlate with germination, since nuclei remained relatively homogeneous in structure during this process as well as during the breaking of dormancy. Key words: Radicle growth, embryo dormancy, microspectrophotometry, cell cycle, nuclear activation, ultrastructure.