Accumulation of amyloplasts on the bottom of normal and inverted rhizome tips of Caulerpa prolifera (Forsskål) Lamouroux.

Caulerpa prolifera (Chlorophyta) exhibits a gravimorphogenetic response to inversion by switching the site of new rhizoid initiations to correspond with the new direction of the gravity stimulus. When plants were fixed at 6 and 24 h after being held in either a normal or an inverted position the switch in the site of organ differentiation, upon inversion, was found to be preceded by the accumulation of starch-containing amyloplasts on the bottom of the rhizome. Approximately 1.5-2.0 times as many amyloplasts were found at the bottom of normal or inverted rhizomes as compared with the top in a region extending from 200 to 1,000 μm behind the rhizome tip. All new rhizoid initials were located in the region of amyloplast accumulation and each rhizoid initial contained numerous amyloplasts.