Discuss About Sporophyte of Anthoceros and Its Evolutionary Significance
The sporophyte of Anthoceros is dependent on the gametophyte. At the same time, it is of highly significant from an evolutionary perspective. Here we will discuss the evolutionary significance of Anthoceros sporophyte.
It has a differentiated body with a foot, seta, and capsule. It represents the diploid generation in the life cycle of Anthoceros. The sporophyte produces haploid spores, which grow into the haploid plant body of this bryophyte.
Development of Sporophyte of Anthoceros
Sporophyte of Anthoceros develops from the diploid zygote inside the venter of the archegonium.
- The zygote enlarges and creates a wall around itself and starts germinating.
- There is no resting period for the zygote, and it straightaway proceeds to the formation og sporogonium.
- Initially, the zygote undergoes a vertical and a transverse division to form a quadrant of cells.
- These four cells divide to form an octant stage with an upper and a lower tier of cells. Further division from the octant stage differs with the species.
- In Anthoceros erectus, there is no further division. The upper tier develops the capsule and seta. The foot is developed from the cells of the lower tier.
- In A. glandulosus, A. personi, and A. himalayensis, the upper tier of cells divides to form an octant to produce a third tier of cells. The uppermost tier forms the capsule, the middle tier forms the seta, and the lower one produces the foot.
- In A. crispulus, the upper tier of cells divides twice to form a total of 4 tiers of cells. The lower two tiers form the foot and seta, while the upper two tiers form the elongated capsule.
Capsule of Anthoceros
The capsule of Anthoceros contains the embryonal cells that divide periclinally to form the outer amphithecium and inner endothecium.
- The endothecium gives rise to the columella, the special conductive tissue.
- Endothecium first divides to form four vertical rows and later divides to form 16 rows.
- Amphithecium, on the other hand, divides periclinally to form two layers.
- The outer layer forms the sterile jacket while the inner layer develops archesporium.
Sterile Jacket
The outer layer of an amphitheca divides both periclinally and anticlinally to form 4-6 layers of a sterile jacket of the capsule. The outermost layer of these functions as the epidermis, which will have a cutin layer and stomata as well. The other layers underneath are loosely packed parenchyma cells having chloroplasts.
Archesporium
The inner layer of the amphithecium develops into the dome-shaped archesporium, which covers the columella. These cells act as sporogenous cells. Depending on the species, this can be single-layered to multiple-layered.
Sporogenous Cells
The sporogenous cells produce fertile spore mother cells and sterile pseudoelater mother cells. They are mostly arranged irregularly and alternately.
- The spherical or oval spore mother cells are diploid, with dense protoplasm, a nucleus, and a chloroplast.
- These cells undergo meiotic division to form 4 haploid cells each.
The pseudoelater mother cells also divide transversely into a 4-celled structure. They unite to form a network around the spore mother cells. During meiosis, they break this network and form a sterile cover of 3-4 cells.
Maturation of Sporophyte
When the sporophyte matures, the protective cover over it is called the involucre, which covers it when young. Later, as the sporophyte matures and the capsule grows, it pierces the involucre. Thus, the involucre simply remains as a sterile collar-like structure at the base. It helps with water retention, protection, and support.
Structure of Mature Sporophyte in Anthoceros
The mature sporophyte of Anthoceros contains a bulbous foot, a short seta, and an elongated capsule.
- The foot has parenchymatous cells embedded in the gametophytic thallus.
- The cells that connect the foot to the gametophyte are elongated and are palisade-like.
- They function as haustoria and help the capsule fix to the gametophyte and absorb food.
- The matured capsule consists of central connective tissue called the columella.
- The capsule wall is multilayered.
- In between the capsule wall and columella lie the sporogenous tissues, including the spore and elater mother cells and the haploid spores.
- Columella is a mechanical tissue that supports the capsule and holds it above.
- A mature sporangium of Anthoceros looks like a cluster.
- They are slender, elongated, and curved rods that resemble horns.
- Hence, Anthoceros is called hornwort.
Evolutionary Significance of Anthoceros Sporophyte
The sporophyte of Anthoceros shows several evolutionary features that are advanced when compared to other bryophytes.
Most bryophytes have sporophytes that are parasitic on the gametophyte. However, the sporophyte of Anthoceros is independent and autotrophic. Such advanced characteristics of the Anthoceros sporophyte are listed below.
- The foot of the sporophyte is enlarged, and it superficially develops rhizoids for absorption.
- The intercalary meristem in the sporophyte is similar to cambium and can develop new cells to the growing sporophyte that help elongate the capsule. This is also similar to the vegetatively growing sporophytes of pteridophytes.
- The capsule of Anthoceros contains a multilayered wall and a layer of cutinized epidermis with stomata. The parenchyma cells here contain chloroplasts and intercellular spaces.
- The presence of a columella is similar to that of tracheids and is considered a primitive vascular cylinder.
- Amphithecial origin of archesporium is different from that of other bryophytes that have the archesporium developing from the endothecial cells. This particular characteristic makes Anthoceros close to pteridophytes.
- Moreover, the spores inside the sporogenous tissue are closer to the periphery and are not confined to the core area. This is another similarity of Anthoceros to pteridophytes.
- The alternating fertile and sterile sporogenous tissue leads to the evolution of a strobilus with sporophylls and sporangia.
Studies indicate an evolutionary connection between Anthoceros and Rhynia because the sporophytes of pteridophytes are rootless, leafless, and simple, erect, independent structures. Looking at all these features, it could be considered that Anthoceros is an advanced plant.
Possible Questions for Exams
- Why is the sporophyte of Anthoceros considered a modern plant?
- What characteristics of Anthoceros made it an advanced type of plant?
- Evolutionary features of Anthoceros sporophyte.
References
Additional Topics