Seed Structures, Germination, and Dormancy

Flashcards covering the essential structures of angiosperm seeds, the steps involved in seed germination, different seedling emergence patterns (epigeal and hypogeal), and the distinctions between seed dormancy and quiescence.

Angiosperm Seed

A seed from the angiosperm class, characterized by three essential parts: Seed Coat (Testa), Endosperm, and Embryo.

Testa (Seed Coat)

The protective outer layer of a seed, derived from the ovule wall; it is impervious to water when mature and provides protection through Sclerenchyma tissue.

Endosperm

A nutritive tissue within the seed that supplies starches, oils, and proteins to feed the embryo upon germination. It is absorbed by the embryo in dicots and is the largest structure in monocots, composed of Parenchyma tissue.

Embryo (Germ)

The immature plant contained within a seed, consisting of parts like cotyledons, plumule, radicle, hypocotyl (dicots), and mesocotyl (monocots), waiting to grow into a seedling.

Cotyledons (Dicot)

The 'seed leaves' of a dicot embryo; they are the first leaves to emerge above ground, green, and responsible for initiating photosynthesis to help the plant produce its own food.

Plumule (Dicot)

The embryonic shoot in a dicot seed, comprising the Apical Meristem and True leaves; it is the first set of true leaves that grow above the cotyledon, protecting the growing point.

Radicle (Dicot)

The embryonic root in a dicot seed, which initially grows upwards then dives down into the soil to establish the root system.

Hypocotyl (Dicot)

The stem axis of a dicot embryo that elongates to pull the cotyledons above the ground during germination.

Cotyledon (Monocot)

The seed leaf of a monocot embryo that typically remains below ground but provides the necessary stored food function for the seedling.

Plumule (Monocot)

The embryonic shoot in a monocot seed, including the Apical Meristem and the first true leaf, protected by the Coleoptile until it emerges above ground.

Radicle (Monocot)

The initial root in a monocot seed (seminal root) which rapidly branches into adventitious roots.

Mesocotyl (Monocot)

The stem axis of a monocot embryo that elongates to push the coleoptile (and thus the plumule) above the ground during germination.

Coleoptile

A protective sheath that encloses the plumule and first true leaf of a monocot seedling, protecting them until they emerge above the soil surface.

Micropyle

A small pore or opening in the seed coat, often visible near the hilum, which allows for the absorption of water into the seed.

Hilum

A scar or mark on the seed coat that indicates where the seed was attached to the ovary wall or funicle.

Pericarp/Fruit Coat (Wheat)

The outermost layer of a wheat kernel, which is technically the wall of the fruit (ovary).

Aleurone Layer

A layer of cells in the endosperm of cereal grains like wheat, rich in proteins and enzymes, important for digestion of stored starch during germination.

Starchy Endosperm (Wheat)

The primary storage tissue in a wheat kernel, rich in starch, which constitutes the main component of flour.

Germination

The process by which a seed absorbs water, reactivates metabolic processes, and develops into a seedling.

Imbibition

The initial absorption of water by a seed, causing it to swell and initiating the germination process.

Gibberellic Acid (GA)

A plant growth hormone released from the embryo during germination, essential for activating enzymes that break down stored food reserves.

Meristems

Regions of actively dividing cells in the embryo (and later the plant), where growth occurs, driven by sugars, amino acids, and growth hormones during germination.

Mitosis

The process of cell division that, along with cell elongation, is crucial for the radicle to burst through the testa and anchor the seedling to the soil during germination.

Emergence Patterns

The different ways a seedling emerges from the soil after germination, primarily classified as epigeal and hypogeal.

Epigeal Emergence

An emergence pattern where the hypocotyl elongates, pulling the cotyledons and plumule above the ground.

Hypogeal Emergence

An emergence pattern where the epicotyl or mesocotyl elongates, allowing the plumule to emerge while the cotyledons remain below the ground.

Dormancy

A state of inactivity in a seed, even when conditions like water and oxygen are present, due to internal physiological or physical barriers such as hard testa, growth inhibitors, or an immature embryo.

Scarification

A process (mechanical or chemical) that breaks down a hard seed coat to allow water absorption, thus overcoming mechanical dormancy and promoting germination.

Quiescence

A state of inactivity in a seed that is directly caused by the absence of favorable environmental conditions, such as lack of water or oxygen. The seed will germinate readily once these conditions become available.