Seed Longevity and Germination Quiz

Germination and Embryo Growth and Development

• Plant growth begins with germination and the emergence of the seedling.
• Plant growth involves stages like vegetative stage, floral initiation, flowering, pollination and zygote formation, fruit and seed maturity, and senescence.
• Senescence is a natural process where the plant deteriorates and dies. It's not dormancy, which is when normal functions are suspended to conserve energy until conditions improve.
• Germination is a sequence of events beginning with water absorption, leading to seedling growth and development.
• Water absorption, called imbibition, is crucial for germination. Cereals need roughly 50% moisture, and beans need about 75%.
• Water activates enzymes that break down stored food, and also increases respiration. This process is crucial to turn stored food into energy to build new cells.
• The level of physiological activity drastically increases during germination due to enzyme activation and synthesis.
• Enzymes break down stored food into simpler compounds to provide energy and nutrients for growth.
• For example, in cereal crops, the embryo releases a hormone (gibberellin) activating enzymes in the aleurone layer. Alpha amylase converts starches to glucose for the embryo's growth.
• Water imbibition is affected by factors including soil firmness and soil water content.
• Firm soil allows close moisture contact with the seed, making it easier to absorb.
• Large air pockets in the soil cause moisture loss to the atmosphere, affecting absorption.
• Too much or too little water inhibits germination. Waterlogged soil has insufficient oxygen for germination, which is needed for respiration.
• The rate of imbibition depends on the seed's composition. Proteins absorb more water (than starch), so the embryo absorbs more water than the endosperm.
• Some seeds have impermeable seed coats that initially resist water absorption.
• Each plant has an optimum temperature for germination and a range that will inhibit it if it goes beyond.
• Cereal crops can germinate just above freezing, and up to 37°C. The optimum temperature for cereal germination is 15°C. Warmer-season crops like corn need higher temperatures (10°C) for germination.
• Oxygen is essential for respiration, a process for using stored food to create the first leaves for photosynthesis. Insufficient oxygen due to planting too deep or waterlogged soil can inhibit germination.
• Light is not always needed for all plants to germinate. Most plants can germinate in light or dark, but some require light.
• A seed's viability (being alive and capable of germination with proper conditions) impacts successful germination.
• Seeding depth affects the availability of oxygen and moisture to the seed. Deeper planting can deplete conditions for seeds to reach the surface. Larger seeds (generally) need deeper planting than smaller ones.
• Successful germination depends on seedlings becoming self-sufficient before the seed's food stores are used.
• Dormancy is a survival mechanism for plants that delays germination until conditions improve, such as favorable temperatures or sufficient moisture.
• Seeds are viable (alive) but prevent germination in unfavorable conditions.
• Germination can be staggered in time, meaning different seeds sprout at different times for survival purposes.
• Plants have either exogenous (physical constraints like seed coat) or endogenous dormancy (physiological or embryonic conditions). Some seeds have both.
• Methods like scarification (mechanical scratching to rupture the coat), heat treatment and acid treatment can overcome exogenous dormancy.
• Strategies to cope with endogenous dormancy include stratification (exposure to low temperatures and moisture).
• Chemicals in some seeds block germination. With enough moisture, these chemicals can leach out to enable germination.
• Many crops have lost or selected against their dormancy traits for easier production and seed use.
• The loss of dormancy to allow quick germination can result in problems with sprouting in the field.
• Seed viability is the ability for germination in suitable conditions; it declines. Seed longevity is the time a seed can stay dormant and viable; it depends on factors such as plant type, growing conditions, and storage methods.

Embryo Growth and Development

• The radicle (root) and plumule (shoot) grow through cell division and enlargement, making the cells bigger.
• Food from the seed is transported to growing parts.
• The seed coat (testa) is broken, and the radicle grows down to absorb moisture and nutrients.
• The plumule gets out into sunlight and starts photosynthesis.
• The embryo becomes a seedling.

Monocot Germination

• The monocot embryo has a protective structure (coleoptile) that surrounds the plumule (shoot.)
• The radicle grows into the root system.
• The coleoptile emerges from the soil, followed by the first true leaf, emerging from the coleoptile.
• The cotyledon remains below ground in monocots.

Dicot Germination

• Dicot germination is of two types: epigeal (cotyledon emerges above ground) and hypogeal (cotyledon stays below ground)
• In epigeal germination, the hypocotyl (stem below cotyledons) pushes the cotyledons above ground, functioning as leaves until true leaves develop.
• In hypogeal germination, the cotyledon remains below ground. The epicotyl (the stem above the cotyledon) grows, bringing the plumule above ground.

Conditions to Promote Good Germination

• Seed viability, seeding depth (to facilitate moisture and oxygen), and seedling vigour impact germination.
• Seed tests can assess seed viability to improve germination outcomes.
• The depth of the seed affects oxygen and moisture availability.
• Successfully germinating seedling becomes self-sufficient before exhausting the seed's stored nutrients.

Other Factors Affecting Germination: Dormancy

• Dormancy prevents germination in unfavorable conditions.
• Dormancy may be Exogenous (physical seed coat constraint) or Endogenous (physiological constraint.)
• Methods to break exogenous dormancy include scarification (mechanical scratching, acid treatment, heat treatment). Examples are weathering, animals digestive action.
• Strategies to break endogenous dormancy include stratification (exposure to low temperatures and moisture).
• Chemicals in seeds may block germination; adequate moisture causes these chemicals to leach out, initiating germination.

Viablity and Longevity

• Viability is the ability of a seed to germinate under suitable conditions; it declines.
• Longevity is the time a seed stays dormant and viable; factors like plant species, growing conditions and storage conditions impact longevity.
• Examples show longevity differences between plant species (e.g., wheat to 32 years; wild mustard to 60 years).
• Plant age, food reserves, disease and physical damage shorten seed longevity.
• Higher temperature and moisture in storage decrease longevity due to faster seed respiration and a higher risk of disease.

Test your knowledge on the factors affecting seed longevity and the process of germination. This quiz will cover topics such as conditions for seed viability, germination types, and specific structures involved in seedling development. Perfect for students studying plant biology or seed science.