You can use a refridgerator at 5 degrees C for 48 hours. See: Proteomics. 2007 Apr; 7(8):1293–302. Proteomic analysis of rice seedlings during cold stress.

A large polystyrene foam tray with lid and inside a bed of crushed ice can last 24+ h. These can be found as package for chemical solvents analytical grade or dry ice containers. a thermometer would monitor the treatment. A cold room like the ones for butchery is more easy to manage large batches

Grow the  rice or any crop plant before its actual time of sowing will impose the stress.

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