Plant Reproduction and Hormonal Functions Explained

Reproduction in Ferns (Pteridophyta)

Ferns exhibit a diplohaplontic life cycle, where the diploid sporophyte phase is predominant. The visible fern plant is the sporophyte. On the underside of the leaves, sori are formed, containing sporangia. Within these, stem cells produce spores via meiosis. These spores give rise to a tiny, heart-shaped prothallus.

The prothallus uses rhizoids to absorb nutrients from the soil. It develops antheridia, which produce flagellated antherozoids. These require water to swim toward the archegonium, where the oosphere is located. Fertilization occurs, forming a diploid zygote that develops into a new sporophyte.

Reproduction in Mosses (Bryophytes)

Mosses remain dependent on an aqueous medium for reproduction. Their life cycle is dominated by the visible gametophyte phase. The moss plant itself is the gametophyte, which develops sexual organs:

• Antheridia: Club-shaped structures that produce biflagellate antherozoids.
• Archegonia: Female organs, each containing a single oosphere.

When the antheridia rupture, the sperm are released and swim through water to reach the archegonia. Once a sperm fertilizes the oosphere, a sporophyte is formed. This sporophyte produces spores through meiosis, resulting in four haploid (n) spores.

Functions of Plant Hormones

Auxins

• Involved in cell elongation and tropisms.
• Determine the growth of axillary buds; apical dominance favors longitudinal growth.
• Activate the cambium, promoting secondary (thickness) growth.
• Involved in root development in stem cuttings.
• Facilitate fruit set.

Cytokinins

• Promote cell growth.
• Encourage the development of new shoots.
• Prevent leaf abscission (fall).
• Slow the aging and senescence of plant tissues.

Gibberellins

• Stimulate stem elongation.
• Promote the formation of flowers and fruits.
• Induce cambial activity in temperate trees.
• Increase the size of leaves and flowers.
• Synthesized in seeds to stimulate germination.

Abscisic Acid

• Acts as a primary inhibitor of plant growth.
• Inhibits seed germination.
• Inhibits bud development.
• Regulates the opening and closing of stomata.

Ethylene

• Acts as a growth inhibitor.
• Promotes the abscission of leaves, flowers, and fruits.
• Accelerates fruit ripening.