Abstract
The aim of the present study was to estimate the endogenous abscisic acid (ABA) content in tulip ‘Apeldoorn’ torpedo and mature somatic embryos. Moreover, the effect of exogenous ABA and/or its inhibitor fluridone on somatic embryo maturation and conversion into plantlets was investigated. Torpedo-stage somatic embryos were subcultured on media containing 5 μM of picloram and 1 μM of 6-benzyl-aminopurine (BAP)—control, and combinations of ABA (0 or 10 μM) and/or fluridone (0 or 30 μM) for 1 week. Then, the torpedo embryos were transferred to a maturation medium containing 0.25 μM of α-naphthaleneacetic acid (NAA) and 2.5 μM of BAP, without ABA and fluridone treatment, and cultivated under darkness or light for ten weeks. Endogenous ABA content (first time measured in tulip somatic embryos) was evaluated by ELISA test. The obtained results revealed that the highest level of endogenous ABA, at 17.45 nmol g−1 dry weight (DW), was recorded in torpedo-stage of tulip embryo development, only after 1 week of ABA treatment, and was nearly 10 times higher in comparison with the control. Simultaneous addition of ABA and fluridone to the medium resulted in the lowering of the ABA concentration to 9.58 nmol g−1 DW. During ten weeks of maturation of the embryos, the endogenous ABA content in mature tissue of tulip somatic embryo considerably decreased to an amount 0.87–1.33 nmol g−1 DW (irrespective of ABA and fluridone treatment) and did not differ significantly from control (0.59 nmol g−1 DW). Exogenous ABA and fluridone significantly decreased the growth value of fresh weight (FW) of the tulip torpedo-shaped and mature embryos under light conditions. Percentage of the DW of the torpedo embryos treated with exogenous ABA was significantly higher (15.43–17.02) in comparison with the control (10.87). Three to three and a half times more malformed mature embryos were noted under light conditions than in darkness, irrespective of ABA and fluridone treatment. The highest percentage of mature embryos forming shoots (conversion) was observed under light conditions in the control and after fluridone treatment (26 and 20%, respectively).
Highlights
The traditional, vegetative way of new tulip cultivars propagation is very time consuming (Eijk et al 1991; Rees 1992; De Hertogh and Le Nard 1993; Custers et al 1997)
The length of all the embryos was favourably affected by light (Fig. 1c–f), significant differences between the means were noted only in the case of tulip mature embryos treated with abscisic acid (ABA) and fluridone (Table 2)
The analyses revealed that the highest level of ABA, at 17.45 nmol g-1 dry weight (DW), was recorded after one week of ABA treatment of torpedo embryos and was nearly ten times higher in comparison with control (1.82 nmol g-1 DW)
Summary
The traditional, vegetative way of new tulip cultivars propagation is very time consuming (Eijk et al 1991; Rees 1992; De Hertogh and Le Nard 1993; Custers et al 1997). The culture medium is supplemented mainly with an auxin, which determines the initiation of somatic embryos (Zimmerman 1993; Dodeman et al 1997; Gude and Dijkema 1997; Raghavan 1997, Bach and Ptak 2001). For proper maturation and conversion, somatic embryos must first achieve morphological maturity and —by undergoing a desiccation period—physiological maturity (Stasolla and Yeung 2003) For this purpose, they are subcultured on maturation media containing lower levels of growth regulators, or on a hormone-free MS (Murashige and Skoog 1962) medium (Gude and Dijkema 1997; Raghavan 1997; Bakhshaie et al 2010)
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