Zygote implantation to cultured ovules leads to direct embryogenesis and plant regeneration of wheat

Abstract

Direct embryogenesis and plant regeneration were obtained by implantation of individual wheat (Triticum aestivum L.) zygotes into cultured ovules of wheat or barley. The zygotes were isolated mechanically from emasculated spikes, 3–9 h after hand‐pollination. In 13 independent experiments, a total of 186 zygotes were implanted into excised ovules obtained from emasculated spikes which had been treated previously with 2,4‐dichlorophenoxyacetic acid to induce parthenocarpic, embryoless ovary development. On average, 17.2% of the implanted zygotes gave rise to dorsiventrally differentiated embryos. The embryos resembled those growing in planta with no obvious deviation from the zygotic embryogenesis pathway. In contrast to previously described regeneration systems from individual zygotes of higher plants, this is the first study in which direct embryo formation is reproducibly obtained without intermediate tissue dedifferentiation. Most embryos germinated when transferred to regeneration medium, and later formed phenotypically normal, fully fertile plants. Regenerants were confirmed to be derived from the implanted zygotes by means of AFLP and/or morphological analyses. Although zygote implantation has long been established as a useful method in sexual animal reproduction, an equivalent technique for plants is described here for the first time. Since the zygotes enter the embryogenic pathway directly, the genome is presumably as stable as during embryogenesis in planta. With this new approach, isolated wheat zygotes are accessible to micromanipulation without affecting their subsequent embryonic development.