Suspensor, gibberellin and in vitro development of <i>Phaseolus coccineus</i> embryos
Embryos of Phaseolus coccineus in different stages of development (from 0.5 to 5 mm in length) were grown in vitro. Both intact embryos (with suspensor) and embryos deprived of suspensor were studied. It was found that removal of the suspensor has no effect on the development of embryos which have reached a length of 5 mm. With younger embryos, removal of the suspensor reduces embryo development, the negative effect being the greater the younger the embryo. It was shown that gibberellic acid (GA 3 ) concentrations of 10 -8 to 10 -6 M can replace the suspensor in heart-shaped and early cotyledonary embryos (0.5 to 1.5 mm in length), whereas they reduce the development of suspensor-deprived embryos of later stages (embryos 2 to 3 mm in length) as compared with intact embryos of similar size grown on hormone-free medium. GA 3 concentrations of 10 -5 and 10 -4 M are generally inhibitory and may stimulate callus formation in some embryos. The present data and those of Alpi et al. (1975) concur in ascribing a major role to gibberellins in characterizing the physiological function of the suspensor in early embryogenesis in Phaseolus coccineus .