Difference Between Protonema and Prothallus

Main Difference – Protonema vs Prothallus

Protonema and prothallus are two structures of primitive plants. The main difference between protonema and prothallus is that protonema is the first stage of development of mosses and liverworts whereas prothallus is the gametophyte of pteridophytes. Protonema is a thread-like chain of cells whereas prothallus is a heart-shaped structure. Both protonema and prothallus are produced by the germination of spores. Both structures do not differentiate into stem, root, and leaves. Protonema is the first stage of the gametophyte generation in mosses and liverworts. Prothallus consists of male and female sex organs, which produce male and female gametes respectively.

Key Areas Covered

1. What is a Protonema
      – Definition, Characteristics, Role
2. What is a Prothallus
      – Definition, Characteristics, Role
3. What are the Similarities Between Protonema and Prothallus
      – Outline of Common Features
4. What is the Difference Between Protonema and Prothallus
      – Comparison of Key Differences

Key Terms: Caulonemata, Chloronemata, Gametophyte, Mosses, Protonema, Prothallus, Pteridophytes, Rhizoids, Spores

What is Protonema

Protonema is a thread-like cell chain, which is formed in the early development of the gametophyte of mosses and some liverworts. Protonemata is formed from the germination of spores. They contain two types of cells: chloronemata and caulonemata. Chloronemata are the first type of cells that develop from the germination of a spore. The caulonemata develop from the chloronemata. From the protonema, the leafy gametophytes are developed. Therefore, protonema can be considered as the juvenile gametophyte. A single protonema can give rise to several gametophytes. The growth of a protonema occurs by apical cell division. Buds are formed under the influence of cytokines. These buds are called gametophores.

Difference Between Protonema and Prothallus

Figure 1: A Protonema of Moss

Though the gametophyte of mosses and liverworts does not develop ‘true’ stems, roots, and leaves, it consists of stem-like structures and leaf-like structures. The root-like structures of the gametophyte are called rhizoids. A protonema of moss is shown in figure 1.

What is a Prothallus

Prothallus is the heart-shaped gametophyte of the pteridophytes or ferns. Ferns undergo the alteration of generations in which the fluctuation between diploid and haploid stages occur during the life cycle. The diploid sporophyte stage is prominent against the haploid gametophyte in ferns. The spores are produced on the underside of the leaves of the sporophyte. The germination of the spores produces the gametophyte. The gametophyte is called the prothallus. The prothallus is a 2-5 mm wide, photosynthetic structure. It attaches to the soil by rhizoids.

The structure of the prothallus is shown in figure 2.

Main Difference - Protonema vs Prothallus

Figure 2: Protothallus

Both male (antheridia) and female (archegonia) sex organs are developed in the prothallus. The flagellated sperm cells swim to the ova in the archegonia for fertilization. The fertilization forms the diploid zygote, and the zygote divides by mitosis to form the sporophyte.

Similarities Between Protonema and Prothallus

Protonema and prothallus are developed by the germination of spores.
Both protonema and prothallus are multicellular structures.
Both protonema and prothallus are haploid.
Both protonema and prothallus are green-colored structures.
Both protonema and prothallus are not differentiated into stem, root, and leaves.

Definition

Protonema: Protonema is a filamentous thalloid structure of the gametophyte in mosses and some liverworts.

Prothallus: Prothallus is the gametophyte of pteridophytes.

Shape

Protonema: Protonema is a thread-like structure.

Prothallus: Prothallus is a heart-shaped structure.

Gametophytic Stage

Protonema: Protonema is the first stage of gametophyte development in mosses and liverworts.

Prothallus: Prothallus is the gametophyte of pteridophytes.

Development

Protonema: Protonema develops leafy shoots called gametophores.

Prothallus: Prothallus develops both male and female sex organs.

Conclusion

Protonema and prothallus are haploid structures related to the gametophyte stages of primitive plants. Protonema is a filamentous structure. It is the first stage formed by the germination of spores of mosses and liverworts. The protonema develops the gametophytes of the mosses and liverworts. Prothallus is the heart-shaped gametophyte of pteridophytes. This is the main difference between protonema and prothallus.

Reference:

1. “Protonema.” Wikipedia, Wikimedia Foundation, 10 Aug. 2017, Available here. Accessed 7 Sept. 2017.
2. “Prothallium.” Wikipedia, Wikimedia Foundation, 21 Aug. 2017, Available here. Accessed 7 Sept. 2017.

Image Courtesy:

1. “Aspidium – prothallium” by Paul K (CC BY 2.0) via Flickr
2. “Physcomitrella Protonema” By Anja Martin, Labor Ralf Reski – Reski Lab, University of Freiburg (CC BY-SA 1.0) via Commons Wikimedia