MEGASPOROGENESIS

MUHAMMED SADIQ

MEGASPORES•Megaspores also called macrospores are a type of

spore found in heterosporous plants

•Megaspores which germinates into a female gametophyte which produces egg cells

• These are fertilized by the male gametophyte developing from the microspore

MEGASPOROGENESIS

•Megasporogenesis is the formation of megaspores

•Megaspores are formed inside the ovule of seed plants

• A diploid cell in the ovule called megasporocyte

• Megaspore mothercell undergoes meiosis and give raise to four haploid megaspores

• In most plants only one of the megaspores develop into megagametophyte and other 3 disintegrates

• In gymnosperms and flowering plants the megaspore is produced inside the nucellus of the ovule

• Angiosperms exhibit three patterns of megasporogenesis , monosporic, bisporic,and tetrasporic.

• The megasporocyte enlarges and its cytoplasm become very dense, the nucleus enlarges in preparation for meiosis.

• The integuments develops from the ovule epidermis

• These envalops the megagametophyte and it become incomplete and leave a micropyle through which pollen tubes enters later.

• Two haploid nucei are then created.

• These divide again to produce a cell with four nuclei.

• The four haploid nuclei divide again to produce a cell with eight nuclei this process is called free nuclear division

• Following nuclear migrations and cell formation , the mature megagametophyte ie, embryo sac id formed

• It is typically composed of an egg apparatus ( egg+2synergids) at the micropylar end of the megagametophyte.

• Three antipodals are found at the chalazal end of the megagametophyte