Gametophytic development and fertilization in Macrocystis integrifolia

Abstract

A cytological investigation of gametophytic development and fertilization was conducted on cultured gametophytes of Macrocystis integrifolia. Most developmental characteristics are similar to those previously reported for other members of the order Laminariales, although some modifications were noted in the production of antheridia and spermatozoids. One of the most significant contributions of this study concerned the nuclear cytology of the egg during fertilization. There appear to be two fertilization phases: sperm penetration and nuclear activity within the egg. After penetration of the egg by one spermatozoid, the male nucleus remains in the peripheral cytoplasm while the egg nucleus undergoes mitosis, producing two daughter nuclei, one of which degenerates. The male nucleus then enters prophase and migrates to the remaining female nucleus, which is also in prophase. Karyogamy occurs while both nuclei are in prophase.