ZYGOTE IMPLANTATION TO CULTURED OVULES LEADS TO DIRECT EMBRYOGENESIS AND PLANT-REGENERATION OF WHEAT

Direct embryogenesis and plant regeneration were obtained by implantat ion of individual wheat (Triticum aestivum L.) zygotes into cultured o vules of wheat or barley. The zygotes were isolated mechanically from emasculated spikes, 3-9 h after hand-pollination. In 13 independent ex periments, a total of 186 zygotes were implanted into excised ovules o btained from emasculated spikes which had been treated previously with 2,4-dichlorophenoxyacetic acid to induce parthenocarpic, embryoless o vary 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 embryoge nesis pathway. In contrast to previously described regeneration system s from individual zygotes of higher plants, this is the first study in which direct embryo formation is reproducibly obtained without interm ediate tissue dedifferentiation. Most embryos germinated when transfer red to regeneration medium, and later formed phenotypically normal, fu lly fertile plants. Regenerants were confirmed to be derived from the implanted zygotes by means of AFLP and/or morphological analyses. Alth ough zygote implantation has long been established as a useful method in sexual animal reproduction, an equivalent technique for plants is d escribed here for the first time. Since the zygotes enter the embryoge nic pathway directly the genome is presumably as stable as during embr yogenesis in planta. With this new approach, isolated wheat zygotes ar e accessible to micromanipulation without affecting their subsequent e mbryonic development.