Figure 7.

Model of auxin influence on marginal-meristem formation and regeneration. Hypothetical auxin gradients are represented by intensity of indigo color. 4-dpp gametophytes have not specified a marginal meristem and have an intermediate concentration of auxin between the apex and base of the prothallus, optimum for marginal meristem formation. 5-dpp gametophytes select one side to specify the marginal meristem, which becomes a site of auxin biosynthesis. The region between the original meristem and basal end has an intermediate concentration of auxin, which is optimum for regeneration. 8-dpp gametophytes experiencing normal growth continue to exhibit a similar auxin gradient pattern as the 5-dpp ones. Gametophytes ablated at 5-dpp regenerate a new meristem in the region with optimum auxin levels, most frequently between the ablation site and basal end. Gametophytes ablated and treated with 10 μM IAA experience a higher concentration of IAA throughout the gametophyte, which raises the auxin levels in the basal end beyond the level which promotes regeneration. Therefore, the apex of the gametophyte becomes optimum for regeneration after some delay.