seed dormancy, germination and establishment

1️⃣ Imbibition: Water uptake, three phases. 2️⃣ Metabolic reactivation: Gene transcription, protein translation, enzyme activation. 3️⃣ Reserve mobilization: Breakdown of starch, lipids, and proteins for energy. 4️⃣ Radicle emergence: Seed coat ruptures, radicle emerges (end of germination). 5️⃣ Seedling establishment: Shoot and root system development begins.

1️⃣ Phase I: Rapid water uptake (rehydration of dry seed). 2️⃣ Phase II: Water uptake slows; metabolic reactivation occurs (gene transcription, translation). 3️⃣ Phase III: Water uptake increases as cell division and expansion resume, leading to radicle emergence.

• Formation of three tissues: embryo, endosperm, seed coat. • Development of primary meristems (for future growth). • Formation of embryonic organs (shoot, root, cotyledons). • Accumulation of seed storage reserves (carbohydrates, lipids, proteins).

• Seed is viable and can germinate under the right conditions. • Seed becomes quiescent, with extremely slow metabolism. • Embryo desiccates, reducing water content. • Seed coat provides protection for the embryo and storage reserves. • Growth resumes once the seed is rehydrated.

• The embryo dehydrates, reducing water content. • The seed acquires desiccation tolerance, protecting the embryo. • Metabolic activity slows down. • The seed enters a quiescent (inactive) state. • Growth resumes after water uptake (imbibition) and germination begins.

• Germination begins with imbibition (water uptake) and metabolic reactivation. • The seed must be viable and non-dormant to germinate. • Radicle emergence (root tip) marks the end of germination. • Germination is followed by seedling establishment as the shoot emerges and grows.

• Dormancy: Seed fails to germinate even under ideal conditions. • Quiescence: Seed is inactive but will germinate once conditions are suitable. • Dormancy involves a temporal block in germination. • Dormancy is controlled by the balance of hormones (ABA vs. GA).

• Abscisic Acid (ABA) promotes dormancy and prevents premature germination. • Gibberellins (GA) promote germination by activating hydrolytic enzymes. • The outcome depends on the ABA:GA ratio, which changes in response to environmental signals.

1) Light: Red (R) light promotes germination, while Far Red (FR) light promotes dormancy. Light is sensed by the photoreceptor phytochrome, which controls the R/FR light response. 2) Water: Essential for seed imbibition, enzyme activation, and metabolic processes. 3) Oxygen: Required for aerobic respiration to produce energy for growth. 4) Temperature: Influences enzyme activity; optimal range depends on species.

• Gibberellins (GA) from the embryo signal the aleurone layer. • The aleurone layer produces hydrolytic enzymes (e.g., amylases) in response to GA. • Enzymes are released into the endosperm to break down starch into sugars. • Sugars fuel the growth of the embryo and radicle emergence.