Gametogenesis

• Gametogenesis is the process of gamete formation
• Male gametes form inside the anther via microsporogenesis and microgametogenesis
• Female gametes form inside ovules via megasporogenesis and megagametogenesis

Structures

• Microsporangium (pollen sac) has four walls: epidermis, endothecium, middle layers, and tapetum
• Pollen grains are formed in the microsporangium
• Each microsporangium has four pollen sacs
• The center of each sac contains sporogenous tissues
• Ovules are located at the bottom of the carpel, a vase-like structure
• The carpel includes a neck called the style and the opening called the stigma at the top
• Pollen grains vary in size with a double wall
• The inner wall (endospore) is made of cellulose
• The outer wall is made of sporopollenin
• Anther is a bi-lobed structure with two lobes attached to a sterile strip
• Stamen includes a stalk called the filament connected to the petal or thalamus.

Formation of Male Gametes

Microsporogenesis

• Microsporogenesis is the development of microspores/pollen grains in the microsporangium (pollen sac)
• Diploid pollen mother cells undergo meiosis to produce four haploid microspores
• Each microspore develops into a pollen grain

Microgametogenesis

• Microgametogenesis is the formation of the male gametophyte from the pollen grain
• Pollen grain undergoes mitosis, forming a small generative cell and a large vegetative cell
• Pollination occurs at this stage
• Generative cells produce two male gametes
• Vegetative cells produce the pollen tube