Male Germ Unit (MGU) — College Notes
1. Definition
The Male Germ Unit (MGU) is a structural and functional unit in the mature pollen
grain or pollen tube, consisting of the vegetative nucleus and the two male gamete
nuclei (or generative cell before division). These components remain closely
associated during pollen tube growth and fertilization.
2. Discovery and Concept
•The concept of the Male Germ Unit was first proposed by Dumas et al. (1984).
•It is formed after the division of the generative cell into two male gametes within
the pollen tube.
•The vegetative nucleus and male gametes are interconnected by cytoplasmic
strands or microtubules, forming a coordinated unit.
•The association ensures synchronized movement during pollen tube elongation
and double fertilization.
3. Structure and Components
•(a) Vegetative Nucleus: Large, irregular in shape, and metabolically active; it
guides the growth of the pollen tube.
•(b) Generative Cell: Initially attached to the vegetative nucleus; later divides
mitotically to form two male gametes.
•(c) Male Gametes: Two small sperm cells (nuclei) formed from the generative cell;
they remain associated with the vegetative nucleus via cytoskeletal connections.
•(d) Cytoskeletal Elements: Microtubules and actin filaments connect the
vegetative nucleus and gametes, ensuring movement as one coordinated unit.
4. Formation Process
•After pollen germination, the vegetative nucleus and the generative cell migrate
into the pollen tube.
•The generative cell undergoes mitosis to form two male gametes.
•The vegetative nucleus remains associated with these gametes via cytoplasmic
strands, creating the Male Germ Unit.
•This association is maintained until the gametes are released near the embryo sac
during fertilization.
5. Functions and Significance
