* Author for correspondence Onwimol, D., Chanprame, S. and Thongket, T. (2012), Seed Sci. & Technol., 40, 238-247 Arrest of cell cycle associated with delayed radicle emergence in deteriorated cucumber seed D. ONWIMOL 1,2,3 , S. CHANPRAME 1,2,3,4 AND T. THONGKET 1,2,3,4 * 1 Center for Agricultural Biotechnology, Kasetsart University, Kamphaeng Saen Campus, Nakhon Pathom 73140, Thailand 2 Center of Excellence on Agricultural Biotechnology: (AG-BIO/PERDO-CHE), Bangkok 10900, Thailand 3 Center of Advanced Studies for Agriculture and Food, KU Institute for Advanced Studies, Kasetsart University, Bangkok 10900, Thailand 4 Department of Horticulture, Faculty of Agriculture at Kamphaeng-Saen, Kasetsart University, Nakhon Pathom 73140, Thailand (E-mail: agrtst@ku.ac.th or thammasak.t@ku.ac.th) (Accepted May 2012) Summary The objective of this experiment was to study germination parameters and cell cycle activity of radical tip cells during imbibition of cucumber seeds using flow cytometry. Samples from a uniform cucumber seed lot were subjected to one of two ageing treatments prior to imbibition; non-aged seeds were used as a control. Radicle emergence was delayed in seeds subjected to an ageing treatment. Control seeds exhibited normal cell cycle activity, with radicle emergence at 24 hours of imbibition, whereas the cell cycles of the deteriorated seeds were slower and radicle emergence delayed. The length of the delay was related to the severity of the ageing treatment. A single arrest at the G 1 phase was found during 6-18 hours of imbibition in seeds that had been treated for 96 hours at 45°C, and two arrests at both G 1 and S phases were found during 6-18 hours and 24-42 hours for seeds that had been treated for 96 hours at 50°C. This suggests that the initial physiological age of the seeds needs to be taken into consideration prior to the application of flow cytometry for monitoring cucumber seed germination advancement during the seed priming process. Introduction Seed priming – imbibing seed to initiate germination, followed by dehydration to halt germination prior to radical protrusion – enhances seed quality. Upon planting, primed seeds germinate (radical protrusion) faster and with greater uniformity compared with non- primed seeds. The efficiency of seed priming depends on the extent of advancement of the germination process (Lanteri et al., 1996). Since it is difficult to identify the stage of germination by morphological examination, reliable physical or biochemical markers to determine the stage of germination during seed priming could improve the efficiency of the process. Sliwinska et al. (2009) proposed that cell cycle activity in seed somatic cells could be a cellular marker to detect both seed maturity and progression of the germination process, and hence might be used in both seed production and seed priming. The normal 238 D. ONWIMOL, S. CHANPRAME AND T. THONGKET