Life Cycle of Marchantia

The life cycle of Marchantia shows that the plant is a haploid gametophyte developed from the spores. The haploid spore germinates to form protonema which will grow into an independent plant having a dorsiventral structure having chloroplast and rhizoids. 

• Marchantia gametophyte reproduces vegetatively from the decaying plant body which gets separated at the junction of dichotomy.
• The asexual reproduction in Marchantia occurs with the help of gemmae cups which grow into independent thalli.
• The main method of reproduction in Marchantia is sexual reproduction.

Development of Antheridium and Archegonium in Marchantia

Antheridium and archegonium in Marchantia develop from special branches called gametophores.

The male plant produces antheridium and the female plant produces archegonium. These gametophores are called antheridiophores and archegoniophores respectively. Since they are produced from the growing tips, gametophores are terminal in position. 

Marchantia Antheridiophore

• Antheridiophore in Marchantia is a structure on which its male sex organ antheridium grows. Each antheridiophore has a long stalk and a disc-like structure.
• The stalk is cylindrical and has a length of 3 cm. The disc has 8 lobes and each lobe is a branch. The lobes are formed by dichotomous division of each branch.
• The disc has two sides- a dorsal concave and a thick central part with thin peripheral sides. Moreover, the disc resembles the vegetative thallus.
  • On the upper side of the disc, there is the epidermal layer with air pores, assimilatory filaments, air chambers and storage regions.
  • On the ventral side of the disc, there are rhizoids and scales.
• Antheridia are formed in antheridial chambers, arranged in 4 or 8 radiating rows.
• Each row will have several antheridia arranged from younger to older ones.
• The younger ones are at the periphery and the older ones are in the centre.

Development of Antheridium

The antheridium develops from the antheridial initial cell in the antheridiophore. 

• The antheridial initial divides into upper and basal cells.
• The basal cell forms the stalk of the antheridium and is embedded in the thallus.
• Upper cell divides multiple times to form a row of 4-5 cells. The upper 2-3 cells develop the primary antheridial cells, and the other cells form a short stalk.
• The primary antheridial cell divides into 2-3 tier of 4 cells each.
• These cells form the single-layered sterile jacket and central primary androgonial cells.
• Androgonial cells divide to form androcyte mother cells.
• Each androcyte mother cell divides to form two naked androcytes which will develop into an antherozoid.
• Antherdozoid is an uninucleate coiled structure with two cilia.
• The cilia is developed from the blepharoplast.

Marchantia Archegoniophore

The archegonium is developed from the archegoniophore of the female Marchantia thallus. Each archegoniophore or carpocephalum has a disc and a stalk. A young archegoniophore is short and the distal disc portion will have 8 lobes, developing from 8 rows, coinciding with the radiating line. 

Each row will have 12-18 archegonia. They will be arranged in such a manner that the older ones are towards the centre and the younger ones towards the periphery. 

Development of Archegonium of Marchantia

As the older ones mature and enlarge, they are pushed towards the periphery and form convex in shape. The younger ones are pushed towards the stalk as the archegonia become inverted and hang from above. 

At the same time, the intervening cells grow and elongate to form sterile ray cells. They grow and become curved as if to protect the developing archegonia. 

Development of Sporophyte of Marchantia

The diploid zygote of Marchantia which is kept in the centre of archegonium develops into a sporophyte or sporogonium. 

• Initially, the archegonial stalk elongates and bulges causing the archegonia to become inverted under the disc.
• At the same time, the cells along the walls divide periclinally to form double layered calyptra.
• The cells of calyptra divide anticlinally to become enlarged.
• The tissue around the archegonium divides to form a cylindrical single-layered sheath that encloses the sporogonium.
• This sheath is called perigynium or pseudoperianth.

Sporogonium Development

The zygote divides transversely and forms an upper epibasal and a lower hypobasal cell. They divide vertically to form a quadrant and later into an octant stage. 

• The four cells from hypo basal cells form the foot and seta of the sporogonium.
• The other four cells formed from epibasal cells develop into a capsule.
• These cells divide irregularly to form an elongated globular structure.

The cells in foot, seta, and capsule are morphologically, cytologically, and physiologically different. 

The sporogenous tissue inside the capsule undergoes meiotic division to form haploid spores. These spores germinate into protonema and then into a thallus. 

Life Cycle of Marchantia

Marchantia plant is dioecious and produces antheridiophore and archegoniophore which produce antheridium and archegonium respectively. They produce male gamete antherozoid and female gamete egg. These gametes fuse to form the diploid zygote. 

The zygote forms the diploid generation in the life cycle of Marchantia. The diploid zygote divides to form proembryo and later a sporogonium. Sporogonium has a foot, seta, and a capsule. This sporogonium is completely dependent on the gametophyte for its nutrition. 

The sporogonium produces haploid spores which will grow into the next gametophytic generation. Thus the life cycle of Marchantia clearly shows alternation of generation between gametophyte and sporophyte. 

The actual plant body is independent and autotrophic while the sporophyte is dependent on the gametophyte and parasitic in nature. Both the gametophyte and sporophyte are completely different from each other. 

This life cycle of Marchantia is an example of diplohaplontic type of life cycle. 

References

• https://premabotany.blogspot.com/2018/12/marchantia-classification-structure-of.html
• Gemma Cups- Science Photo Library- https://www.sciencephoto.com/media/16726/view/liverwort-marchantia-with-gemma-cups
• Yasui, Y., Tsukamoto, S., Sugaya, T., Nishihama, R., Wang, Q., Kato, H., Yamato, K. T., Fukaki, H., Mimura, T., Kubo, H., Theres, K., Kohchi, T., & Ishizaki, K. (2019). GEMMA CUP-ASSOCIATED MYB1, an Ortholog of Axillary Meristem Regulators, Is Essential in Vegetative Reproduction in Marchantia polymorpha. Current Biology, 29(23), 3987-3995.e5. https://doi.org/10.1016/j.cub.2019.10.004

Additional Reading

• Gametophyte of Marchantia
• Vegetative Reproduction in Marchantia