Histological and endogenous plant growth regulators changes associated with adventitious shoot regeneration from in vitro leaf explants of strawberry (Fragaria x ananassa cv. 'Honeoye')

Few studies have been conducted on the links between histological and hormonal variation during shoot regeneration. Therefore, we investigated this link in strawberry (Fragaria x ananassa cv. 'Honeoye'). Main plant growth regulators were measured using reverse-phase liquid chromatography-tandem mass spectrometry. Histological observations were conducted to understand the pattern of adventitious shoot regeneration from the leaf segments. After 14 days of dark culture, a mean shoot regeneration frequency of 94.7 % was obtained on MS medium supplemented with 2.0 mg L-1 thidiazuron, 30 g L-1 sucrose, and 6 g L-1 agar (pH 5.9). During shoot regeneration, indole acetic acid (IAA) concentrations increased, abscisic acid (ABA) decreased, and gibberellic acid (GA(3)) and zeatin showed peaks. The results could be correlated with the cell division and differentiation that occurred during shoot regeneration. Histological observation showed that the adventitious shoots were derived from subepidermal cells and the epidermal cells of the midrib near the cut. The meristemoids, primordia and shoots were formed sequentially on day 6, day 12, and day 18 after culture. During the meristemoids formation on day 6 after culture, IAA rapidly increased from 1.49 to 1.72 ng g(-1) fresh weight (Fw), ABA rapidly decreased from 52.61 to 13.47 ng g(-1) Fw, and zeatin increased from 1.68 to 5.98 ng g(-1) Fw. During primordia formation on day 12 after culture, IAA rapidly increased to 1.88 ng g(-1) Fw, ABA rapidly decreased to 2.69 ng g(-1) Fw, GA(3) peaked at 73.91 ng g(-1) Fw, and zeatin peaked at 7.69 ng g(-1) Fw. Our results suggested that the histological variations were consistent with the plant hormonal changes during shoot regeneration, and that changes in hormone concentration could be used as a reference to characterize the mode of shoot regeneration.