Improving Infection Efficiency of Agrobacterium to Immature Cotyledon Explants of Japanese Apricot (Prunus mume) by Sonication Treatment

Abstract

The infection efficiency of Agrobacterium to cotyledon explants of Japanese apricot ( Prunus mume ) was markedly improved by sonication treatment. The use of sGFP(S65T) reporter gene in this study enabled direct observation of transgene expression, thus allowing the evaluation of Agrobacterium infection efficiency. Immature cotyledons of different cultivars and different developmental stages were subjected to sonication treatment of durations ranging from 10 sec to 2 min. When early-stage immature cotyledons of ‘Nanko’ were subjected to sonication treatment, the transient GFP expression frequency after co-cultivation was nearly 100% and GFP fluorescence was distributed over almost the entire cotyledon surface. In contrast, when the inoculation was carried out according to the standard dipping method, transient GFP expression frequency was less than 10% and GFP fluorescence was observed only in spots. The highest frequency of somatic embryogenesis (SEG) with GFP expression was obtained from 40 sec sonication treatment of May 14 ‘Nanko’ immature cotyledons. However, with younger cotyledons, which have a higher SEG frequency, 20 sec of sonication treatment was found to be sufficient to increase the infection frequency.