Cell determination during embryogenesis in Citrus jambhiri. III. Graft formation and nonformation in embryonic tissues

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Abstract
Approach grafts were constructed using embryos in vitro with and without surface tissue removal along the root–hypocotyl axis. All embryonic stages from mid-heart through mature proved competent to graft after surface excision. Early heart-shaped embryos grafted back to themselves when a longitudinal incision was made which cut the hypocotyl in half but left the root intact. Cut globular embryos could not be maintained in position for a sufficient period to generate a graft union. Callus tissue was produced in all cut embryos by internal cells but not by surface cells neighboring the cut region. Intact embryos failed to graft or respond in any fashion. The incompetence to graft of surface tissues at all embryonic stages indicates that those tissues are determined as epidermal even in the earliest stages of embryogenesis. Internal cells of the embryo were not epidermal in response. They were able to form callus and graft with increasing ease toward older stages of embryogenesis.