Overcoming seed dormancy of Taxus baccata L. by embryo rescue leads to germination and seedling growth

Hairy roots generated by Rhizobium rhizogenes-mediated transformation of yew (Taxus spp.) is a promising approach to enhance production of Taxol^® (paclitaxel), which is one of the most effective anticancer drugs. As a prerequisite, it is pivotal to successfully produce Taxus seedlings for transformation. However, the deep dormancy of Taxus seeds leads to extreme difficulties in seed germination. Therefore, embryo rescue has been used to break the dormancy of Taxus baccata seeds, thereby producing seedlings for transformation. In the current study, a successful strategy of embryo rescue was to sterilize the surface of T. baccata seeds collected from the field at two different maturity stages (low and high). The strategy resulted in 100% germination rate, but it was worth noting that not all germinated embryos grew into fully developed plants. As a result, the present experiment introduced an innovative indicator—fully developed seedling index—to describe the growth of seedlings developed by germinated embryos. Collectively, the data revealed that 21 ± 4% of the seedlings eventually grew into fully developed plants. Regarding the development of the seedlings, the fully developed seedling index increased initially along with seedling growth, reaching a peak after 2 weeks. Subsequently, the fully developed seedling index from low maturity seeds and high maturity seeds began to decrease until it stabilized after 4 weeks and 7 weeks, respectively. Consequently, the new findings proved helpful to select T. baccata seeds with appropriate maturity, hence developing a reliable technique to produce viable seedlings for a transformation pipeline.