A comparison of the early developmental morphologies of aponogeton madagascariensis and A. Boivinianus

Aponogeton madagascariensis (Mirb.) H. Bruggen is an aquatic monocot that develops perforations in its leaves through developmentally regulated programmed cell death (PCD). Aponogeton boivinianus Baill. ex Jum. is a close relative found in comparable environments with leaves that have a similar shape with no perforations. Little is known about the early developmental morphology of the family. This study characterized and compared these two species via scanning electron microscopy (SEM) and confocal laser scanning microscopy using both fresh and fixed specimens. The shoot apical meristem (SAM) of A. madagascariensis was significantly larger than that of A. boivinianus, but there was no difference in phyllotaxy observed, as both exhibited a 2/5 spiral pattern. A novel technique using serial dissections and SEM of fresh, hydrated specimens revealed that there are 16 plastochrons before perforation formation in A. madagascariensis and 34 plastochrons until a similar developmental stage in A. boivinianus. The effects on early development of A. madagascariensis plants with supressed ethylene production were also analyzed. Ethylene inhibition alters leaf development by blocking PCD, but had no significant effect on the SAM morphology or early leaf development in A. madagascariensis.