The relationship between developmental stages of zygotic embryos at explanting and embryogenic frequency on hickory ( Carya cathayensis Sarg.)

In recent years, more attention has been paid than previous to clonally propagating hickory via methods of tissue culture. However, most of such methods have failed. Somatic embryogenesis is an alternative system that includes the simultaneous production of both an organized root and a shoot axis. Abscisic acid (ABA) plays a key role in zygotic embryo development at each stage, in both a stimulatory and an inhibitory manner. Thus the influences of the development stages of immature zygotic embryo on somatic embryogenesis was studied. ABA concentration of immature zygotic embryos was also detected. Immature embryos were microscopically visible at 8-9 weeks postpollination with pale yellow liquid endosperm. Cotyledons expanded rapidly at 10-12 weeks postpollination. The immature embryos were actively growing and cotyledons were fully elongated at weeks 14 weeks post-pollination. Cotyledons were filled with of kernel, and endosperm was utilized at 15-16 weeks post-pollination. The concentration of ABA ranged from 29.1 to 166.8 ngg(-1) FW within the development of zygotic embryos. The ABA content levels at 8-9 weeks and 16 weeks postpollination were significantly lower and higher, respectively, than ABA contents at all otherdevelopmental stages. For callus induction, the frequency gradually increased with the development of the zygotic embryos from 8 to 10 weeks post-pollination followed by a decrease from 10 weeks to 16 weeks post-pollination. The highest frequency (66.67%) of embryogenic callus formation was obtained at the stage of 10 weeks post-pollination, with low levels obtained before or after this period. For direct somatic embryogenesis, frequency increased with the development of zygotic embryos from 8 to 11 weeks post-pollination followed by a decrease from 11 to 16 weeks post-pollination. The highest frequency of somatic embryogenesis was 46.67%, obtained with explants collected 11 weeks postpollination. (C) 2012 Elsevier B.V. All rights reserved.