Table of Contents
- In this funaria plant life cycle post we have briefly explained vegetative reproduction, and sexual reproduction of funaria.
Funaria Plant Life Cycle
- In this article we will discuss about the gametophytic phase, reproduction and sporophytic phase in the life cycle of Funaria. The genus Funaria contains approximately 117 species that are cosmopolitan in nature. They are known as common moss, cord moss, or green moss. It grows in velvety tufts on moist ground, rocks, tree trunks, and in the shade, among other places. Funaria reproduction happens by two types of life cycle vegetative and sexual methods.
- On germination, Funaria spores form a branched, filamentous, multicellular structure. It’s known as primary protonema. Intercalary divisions form certain colourless separation cells in it. These cells die and fragment the protonema into single cell or multicellular fragments. These fragments develop into new protonemata, which produce buds. Every bud grows into a leafy gametophore.
- When protonema is developed by other than the germination of spore, it is called secondary protonema. It can form from any detached living part of the gametophyte, including the ‘stem,’ ‘leaves,’ antheridium, archegonium paraphysis, sterile cells of the capsule, seta, or when the rhizoids are exposed to sunlight in a moist environment. It develops into a leafy gametophore, similar to primary protonema.
- Under unfavourable situations, the terminal cells of the protonemal branches divide transversely and longitudinally, forming green multicellular bodies of 10-30 cells. These are known as gemmae. Gemmae mature to a slightly reddish brown colour. When favourable conditions return, gemmae germinate and form new plants.
- When such gemmae-like structures form on rhizoids within the substratum, they are referred to as bulbils. These lack chloroplasts but can develop into leafy individuals under favourable conditions.
- Apospory is the development of a gametophyte from a sporophyte without the formation of spores. Any sporophyte vegetative cell can form green protonemal filaments with lateral buds. These buds eventually mature into leafy gametophores. The resulting gametophores are diploid. Sexual reproduction in such gametophores produces a tetraploid (4n) zygote. Tetraploid sporophytes are sterile because they are unable to produce spores.
- Sexual reproduction is oogamous. Male reproductive structure is known as antheridium and female as archegonium. Funaria is monoecious (having male and female sex organs on the same thallus) and autoicous (antheridia and archegonia develop on separate branches of the same thallus).
- Sex organs are borne on leafy gametophores in terminal clusters. The main shoot of the leafy gametophore bears antheridia and act as male branch. Female branch develops as a lateral outgrowth from the base of the male branch and bears archegonia. It grows higher than the male branch. Funaria is protandrous (antheridia mature before the archegonia). It ensures the cross fertilization.
Spore germination and Protonema
- The first cell of gametophytic generation is the spore. A Funaria meiospore germinates into a protonema, a filamentous green alga-like structure, in a suitable damp habitat. Green epiterranean chloronemal branches (chlornema) and non-green subterranean rhizoidal branches characterise Protonema (caulonema). Each chloronemal branch produces a number of buds, each of which develops into a leafy gametophore.
Life Cycle of Funaria: A) Spore, B) Different stages of spore germination.
- It is a long 1-3 cm in height and differentiated into rhizoids, axis (stem) and leaves.
- Multicellular, colourless root-like structures with oblique septa. They help in anchorage and absorption.
- It grows to a height of 1-3 cm and is branched. The spirally arranged leaves cover the axis and its branches. While the tip of the axis contains densely packed young leases that form a bud-like structure. The activity of a pyramidal apical cell causes the axis to grow.
- Leaves are sessile, ovate and green. Sessile, ovate, and green leaves. Each leaf has a mid-rib with a single layered wing on both sides.
- Male and female sex organs develop at the tips of separate shoots of the same gametophore in adult gametophore, which is monoecious and autoecious.
Funaria: A) Unbranched Gametophyte, B) branched Gametophyte.
1. Anthridia (Male sex organs)
- The main axis is known as a male shoot or an antheridiophore. The tip of the male shoot has a convex disc or receptacle on which a cluster of club-shaped antheridia intermingled with similar capitates paraphysis forms.
- A rosette of perigonial leaves surrounds the receptacle. Each mature antheridium has a short talk and a jacketed body in the shape of a dub. Inside the jacket, there is a swarm of androcyte mother cells, each of which divides diagonally into two androcytes. Each androcyte eventually becomes a biflagellate antherozoid.
2. Archegonia (Female sex organs)
- Archegonial branch or archegoniophore is the female shoot that grows from the base of the male shoot. The female receptacle is the apex of a fem ale shoot from which a cluster of archegonia emerges intermixed with non-capitate paraphysis. Furthermore, perichaetial leaves surround the female receptacle (perichaetium). Each archegonium is made up of a stalk, a flask-shaped venter, and a neck. A basal egg cell (oosphere) and an upper smaller venter canal cell are enclosed by the venter. The neck is made up of 6 or more neck canal cells.
Dehiscence of sex organs
- When the moss plant’s surface is wet, the mature antheridia absorb water and burst, releasing male gametes (antherozoids). The male gametes swim in the direction of archegonia. Neck canal cells and ventral canal cells degenerate to form mucilage in each mature archegonium. The mucilage swells and opens the tip, allowing a passage up to the egg. Sucrose, which is present in the mucilage, attracts male gametes (chemotactic).
Funaria: A) L.S antheridial head, B) An antheridium, C) An antherozoid.
- Funaria is protandrous, which means that the male sex organs mature first. As a result, cross-fertilization occurs. Water is required for fertilisation. During heavy rains, antherozoids reach the archegonial neck and swim down to the ventral. Any antherozoid can fuse with an egg to form a zygote (2n). Soon after, the zygote secretes a cell wall and develops into an oospore. To form an embryo, the oospore divides and redivides. The embryo eventually develops into a sporophyte or sporogonium. Thus, the first cell of sporophyte generation is the zygote or oospore.
- Funaria sporogonium is photosynthetic, making it semi-parasitic on gametophore. It is divided into three parts: the foot, the seta, and the capsule. The foot is embedded in the female receptacle, where it absorbs inorganic nutrients. Seta is a tall stalk with a pear-shaped capsule at the tip. The capsule is made up of three parts: the basal apophysis, the central theca, and the terminal operculum.
Archegonical head of funaria. A) L.S. of archegonical shoot, B) An archegonium.
- Annulus is a ring-like cell that separates the operculum from the Theca. From the centre to the outside, the middle fertile theca is made up of a sterile columella surrounded by a barrel-shaped spore sac, a cylindrical air space with trabeculae, hypodermis, and epidermis. As the sporogonium grows, so does the ventr, which takes the form of a protective covering called calytra. Later, the calyptra ruptures and remains attached to the capsule like a cap. Calyptrais is haploid because it develops from the ventriloquine wall.
Dehiscence of capsule and dispersal of spores
Funaria A) L.S. of capsule, B) Mature capsile with operculum removed during spore dispersal, C) inner and outer perisomal teeth.
- When the capsule dries up, the Operculum is thrown off, revealing the peristome, which is made up of two overlapping rings of periostomial teeth. Each peristome ring contains 16 teeth. The teeth of the outer ring (exostome) are conspicuous, red, and have thick transverse bands, whereas the teeth of the inner ring (endostome) are small, colourless, and soft. Spore dispersal is caused by hygroscopic movements (movement caused by moisture content of the atmosphere) of the exostome of peristomial teeth. The inner ring of peristomial teeth does not move due to hygroscopic forces.
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