megaspores...megasporogenesis

1. MEGASPOROGENESIS
MUHAMMED SADIQ

3. 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

4. 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

6. • 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.

7. • 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

9. • 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