| Summary: | 博士 === 國立中興大學 === 生命科學系 === 92 === Abstract
Shoot tips from in vitro-grown plantlets of papaya （Carica papaya L.） were successfully cryopreserved using the methods of desiccation and vitrification. Shoot tips were dissected from 4 to 6-week-old plantlets. In desiccation, plantlets were preculture on MS medium containing 0.5M sucrose, then shoot tips were firstly dehydrated with dry silica gel, and placed into 2 ml cryo-tubes and plunged into liquid nitrogen immediately. In vitrification, shoot tips were loaded in a 2 ml cryo-tube with a solution of 2 M glycerol and 0.4 M sucrose at 25℃ for 20 min, then dehydrated with 1 ml pre-cooled vitrification solution at 4℃ for 60 min, prior to immersing into liquid nitrogen for at least one week.
The maximal recovery rate of shoot tips by desiccation is around 38%. However, by means of vitrification, the recovery rate can be increased to over 68%. Successfully cryopreservated shoot tips can, after being warmed, resume growth within 7 days and develop shoots directly without intermediate callus formation.
The result showed that shoot tips between 0.8-1.2 mm are the ideal size for vitrification. Also, prolonged storage duration in liquid nitrogen (up to 2 years) did not affect the regeneration rate. The recovery percentages of six cultivars’ shoot tips after vitrification were between 48% to 93%, depending on the cultivars. This study had successfully developed a simple and effective protocol for cryopreservation of papaya shoot tips.
The results of TTC test and structure of papaya shoot tips observation showed that, apical meristem has an important effects to the recovery percentages of papaya after dehydration and cryopreserved.
The results of this study demonstrated that the damage effect of vitrification solution can be minimized by lowering working temperature from room temperature to 4℃. In addition, applying a loading solution pretreatment has also been proven useful in reducing harm effects during dehydration process.
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