Cell cycle activity during seed priming is not essential for germination advancement in tomato

Seed priming is a technique of controlled hydration and drying that results in more rapid germination when the seeds are reimbibed, Advancement of rad icle meristem cells into the S and G(2) phases of the cell cycle, increasin g the percentage of nuclei having a 4C DNA content, has been reported to oc cur during priming. It has been suggested that the efficiency of priming is related to the accumulation of 4C nuclei in the radicle meristem, but the extent of cell cycle activity varied among different treatments and seed lo ts. A wide range of priming treatments across temperatures, water potential s and durations can be compared on a common basis using the hydrothermal pr iming time model. Flow cytometry was used to monitor cell cycle activity in a number of tomato (Lycopersicon esculentum Mill.) seed lots during primin g in relation to the accumulation of hydrothermal priming time and the subs equent germination rate response. In some seed lots, the percentage of 4C n uclei in the radicle meristems prior to emergence increased in proportion t o accumulated hydrothermal priming time, while in other lots, no increase i n nuclear DNA content was detected. All lots, however, demonstrated rapid r adicle emergence following priming. Thus, replicative DNA synthesis in radi cle meristem nuclei often occurred during seed priming, but an increase in the percentage of 4C nuclei was not essential for germination advancement.