Flow-cytometric analysis was carried out to determine the effect of low temperature on the changes in proportion of 2C:4C complement of DNA in root cells from three different zones (meristem apex, elongation and differentiation) in seedlings of Medicago sativa cv. Sitel. 2C:4C complement of DNA in cells were estimated after the treatments of the roots at control temperature of 24�C, elevated temperatures of 26�C, 30�C, 37�C and low temperatures � 10�C and 5�C (in three different periods of duration 15, 38, 45 days). The observed results showed that at control temperature percentage of nuclei 2C:4C in meristem apex is 65:35, in elongation zone 50:50 and in differentiation zone is 40:60. The elevated temperatures (26�C, 30�C, 37�C) influenced this proportion very slightly while treatments of roots with low temperature especially in a period of 45 days changed 2C:4C complement of DNA drastically. It was found that root treated for 45 days at temperature of 10�C the 2C:4C in meristem apex is 78:22, elongation zone 74:26 and in differentiation zone is 70:30. In the case of temperature of 5�C it was 85:15 in meristem apex, 80:20 in elongation zone and 71:29 in differentiation zone. In order to visualize the impact of low temperature on cell cycle plasticity with decrease of dividing cells, roots of transgenic Medicago falcata plants were exposed at control (24�C) and low (5�C) temperatures for the period of 15 and 45 days. These plants carried gus gene under the promoters (cyc1, cyc3a) from cell cycle genes After this temperature treatment roots cells were activated for division with different treatments for 1hour. GUS assay were performed for control and pre-treated root tips. The expression of marker gene was observed in highly divided cells of pre-treated root at control temperature. GUS gene was not expressed in pre-treated roots exposed to low temperature for 45 days.