MORPHOGENESIS AND EXPERIMENTAL ASPECTS OF GROWTH AND DEVELOPMENT OF THE MALE GAMETOPHYTE OF GINKGO BILOBA IN VITRO

Morphogenesis in the morphologically complex male gametophyte of the seed plant Ginkgo biloba was investigated in vitro. These studies reveal that although development in vitro is far more variable than in vivo, it is still characterized by the sequential expression of three distinct patterns of growth: initial diffuse growth of the tube cell, initiation and establishment of tip growth (which may be accompanied by branching), and radial swelling of the gametophyte. Time lapse photography shows that branching of the male gametophyte results from two distinct types of initiation events: one apical (“primary branching”), and the other subapical (“secondary branching”). Experimental manipulation of the growth medium indicates that exogenous sucrose levels strongly influence the likelihood of expression of normal morphogenetic processes. High levels of sucrose tend to inhibit both the initiation of tip growth following initial diffuse growth, as well as branching of the gametophyte. Low sucrose levels appear to promote a normal pattern of early establishment of tip growth and subsequent branching of the gametophyte, similar to development of the gametophyte in vivo.