Etiolation of `Royal Gala' apple (Malus×domestica Borkh.) shoots promotes high-frequency shoot organogenesis and enhanced ,-glucuronidase expression from stem internodes
Internodal explants from etiolated `Royal Gala' apple shoots were compared with those from non-etiolated shoots for frequency of shoot organogenesis and for efficiency of β-glucuronidase (GUS) expression after cocultivation of explants with Agrobacterium tumefaciens strain EHA105 (p35SGUSint). First (youngest) internodal explants from etiolated shoots produced 2-, 8- and 73-fold numbers of shoots compared to second, third, and fourth internodal explants, respectively. Moreover, these explants produced sevenfold the number of shoots as similar explants from non-etiolated shoots. All first internodes from etiolated shoots exhibited GUS-expressing zones and yielded fourfold as many GUS-expressing zones as commonly used leaf explants from non-etiolated shoots, which exhibited GUS-expressing zones in only 63% of the explants. An average of 9.8 GUS expressing calli per explant were observed on first internodes from etiolated shoots 2 weeks after cocultivation with A. tumefaciens.
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