Megagametocytes

Megagametocytes are large cells found in the life cycles of certain organisms, most notably plants and some protozoa like Plasmodium, the parasite that causes malaria. In plants, the megagametocyte is the female gamete precursor cell within the ovule. It undergoes meiosis to produce megaspores, one of which typically develops into the megagametophyte, the female gametophyte generation. This megagametophyte, often referred to as the embryo sac in angiosperms, eventually contains the egg cell, which fuses with the male gamete during fertilization.

In the life cycle of Plasmodium, the megagametocyte is the sexual stage of the parasite that develops in the blood of a vertebrate host. These cells are taken up by the definitive host, a mosquito, during a blood meal. Within the mosquito's gut, the megagametocyte matures into a macrogamete, the female gamete. This macrogamete then fuses with a microgamete (derived from a microgametocyte) to form a zygote, initiating the sporogonic cycle. The distinction between megagametocyte and macrogamete can sometimes be subtle, with the megagametocyte being the precursor that undergoes maturation into the functional female gamete.