Cryopreservation of mat rush lateral buds by air dehydration using aluminum cryo-plate

A cryopreservation protocol based on air dehydration of explants placed on aluminium cryo-plates, termed D cryo-plate, was successfully developed for <i>in vitro</i> mat rush (<i>Juncus decipiens</i> Nakai) lateral buds. The buds of line ‘Hiroshima 4gou(1)’ with basal stems were dissected from multiple shoots and precultured overnight at 25°C on solid MS medium containing 0.3 M sucrose. Precultured buds were placed on aluminium cryo-plates, each one with 10 elliptical wells (2.5 mm long, 1.5 mm wide and 0.75 mm deep) and embedded in calcium alginate gel with 0.4 M sucrose and 1 M glycerol. Osmoprotection was performed by immersing the cryo-plates with buds for 30 min at 25°C in loading solution (2 M glycerol+1.0 M sucrose). Buds were dehydrated to 26% moisture content (fresh weight) by placing the cryo-plates for 2.5 h either in the air current of a laminar flow cabinet or in Petri dishes containing silica gel. Cooling was performed by placing the cryo-plates in uncapped cryotubes, which were immersed in liquid nitrogen. For rewarming, cryo-plates were immersed in liquid medium with 1.0 M sucrose for 15 min at room temperature. Under these conditions, regrowth of cryopreserved buds of line, ‘Hiroshima 4gou (1)’ was 93% after four weeks culture. The average regrowth of 20 mat rush lines was 88%. The D cryo-plate procedure will facilitate cryostorage of mat rush germplasm.