seeds and fruits1

Seeds and Seed Germination Seeds and seed germination  Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development Mature seed Seeds are for propagation  The biological function of seeds is for propagation of the species  How does seeds help in propagation of the species? Diversity among seeds  Seeds are very diverse in term of size: Thousands of Begonia seeds – Begonia seed weigh 10-20 micrograms – Coconuts weigh more than a kilogram Diversity among seeds In terms of adaptation to survive various environments until conditions are favorable for germination In terms of method of dispersal Seeds are for propagation  Protect the zygote against physically injury  Store foods for seedling before it becomes independent  Remain dormant to survive harsh environment  Disperse the seeds to capitalize on their genetic variability  Respond to environment cues and germinate at the right time and place Seeds are alive!  To function in propagation, seeds must be alive  Seeds respire, albeit slowly – consume O2, produce CO2 and H2O  Seeds have a finite lifespan  they cannot be stored indefinitely  Which kind of seeds can remain viable longer? Seeds of tropical plant or temperate plant? Seeds are alive!  Seeds of many tropical plants remain viable for only a short time, a few days – Tropical plants grow in environments that not have a winter season through which seeds must survive before the favorable growing conditions of spring arrive General features of seeds Embryo – Root and shoot, in a miniature form Food reserves – Allow seedling to grow before it is capable of performing photosynthesis Seed coat – Provides protection from the environment Monocots and Dicots  Flowering plants (angiosperms):  Dicotyledonous plants with two seed leaves Monocotyledonous plants with one seed leaf  Dicots Angiosperms flowering plants 200,000 species Monocots 50,000 species includes beans, roses, cacti, melons, citrus includes grasses, lilies, orchids, palms Seedling establishment  Growth of the seedling can be measured in many ways – Length Increases after seed imbibes – Fresh weight  Increases as seedling grows – Dry weight  Declines initially as stored reserves are consumed by respiration, increases once photosynthesis is established  Conclusions Seeds are alive but dormant  Comprise an embryonic plant and stored reserves  Germination requires  – Water - for imbibition – Oxygen - for respiration – Suitable temperature  Outcome of successful germination is a seedling capable of independent growth TYPES GERMINATION • • Radicle will emerge first from the seed Next, the shoot tip breaks through the soil surface • Types of germination: i epigeal - cotyledons appear above the ground { hypocotyl forms a hook and pushes aboveground, raising the cotyledons } ii hypogeal - cotyledons remain underground { epicotyl forms a hook and shoot tip is lifted out of the soil } …TYPES GERMINATION …TYPES GERMINATION Aggregate fruits Receptacle is the fruit [...]... Endospermous and nonEndospermous seeds    Takes place in the fruit on the parent plant Endospermous seeds: Retain the endosperm tissue, and is surrounded by a layer of living cells, the aleurone layer Non-endospermous seeds: The endosperm tissue is absorbed by the cotyledons The cotyledons then become the food reserve for the seed Endospermous or nonEndospermous seeds? Endospermous and nonEndospermous seeds. .. seeds natural environment Seeds that require light involves a receptor protein, phytochrome Seeds that need a period of low temperature The requirement for alternating temperatures The requirement for fire is particularly important for small, winddispersed weed seeds the cold winter may cause the parent plant to die, and thus remove competition for space in the spring will prevent germination of seeds. .. because the latter dampens the day/night temperature fluctuations; these seeds will germinate only when there is little vegetation cover, again reducing competition with established plants CHAPTER : GROWTH Dormancy mechanism is related to the seeds natural environment Seeds that require light involves a receptor protein, phytochrome Seeds that need a period of low temperature The requirement for alternating... physical state rehydration Production of growth promoters Seed Germination: Emergence of Radicle through Seed Coat To break dormancy seeds need: Water Warm Temperature So if you want to store seeds what are the conditions? Dry Cold Dormant seeds need more than moisture and warmth: Dormancy is caused by: Thick Seed Coat Thin Seed Coat Insufficient Development Inhibitor: Abscisic Acid Is overcome by:...  Triggering factors for germination Light, chilling or water (rain) trigger the inactivation of ABA, which makes dormant seeds able to germinate ABA ABA ABA GA After seeds take up water, GA is released from the embryo to signal aleurone GA The aleurone responds by synthesizing and secreting digestive enzymes (α-amylase) to hydrolyze stored nutrients in the endosperm α-amylase Nutrients (ex sugars)... (testa) is waxy = waterproof and impermeable to oxygen  Physical state – dehydrated  Chemical inhibitors present e.g salts, mustard oils, organic acids, alkaloids  Growth promoters absent  The breaking of dormancy Break down of barriers Abrasion of seed coat (soil particles) Decomposition of seed coat (soil microbes, gut enzymes) Cracking of seed coat (fire) Destruction and dilution of inhibitors... nonEndospermous seeds? Endospermous and nonEndospermous seeds A LS of maize grain / fruit SEED DORMANCY • It is a phenomenon in certain seeds in which they would not germinate if given an optimal condition ( water, oxygen, optimum temperature ) • Dormancy can be seen in seeds ( eg: legumes ), buds, spore & food storage organs ( tubers ) • Due to many factors include: Lack of oxygen Dryness Presence of... of root and shoot axis Transport of materials from food stores to growing Stages leading to cell division Mitchondria reconstituted Respiration Initially anaerobic Later ATP aerobic Soluble sugars RNA activated Protein synthesis (0.5h) Enzymes (proteins) DNA synthesis (45h) http://www.rbgsyd.nsw.gov.au/ Mitosis (70h) Mobilization of food reserves Control by growth promotors such as gibberellin and growth... the starch in an amyloplast is hydrolysed the enzyme stops work Therefore the release of the stored food is adjusted to suite the demand  The mobilisation of food reserves Carbohydra tes Proteins Lipids Starches (amylopectin & amylose) e.g Zein Oils Amylases Maltose and glucose Proteases Amino acids Lipases Fatty acids & glycerol The food reserves are stored as large insoluble macromolecules  They... of these seeds may be broken by one or more of the following: (1)light, sunlight being the most effective; (2)low temperatures (1 to 5 degrees Celsius [33.8 to 41 degrees Fahrenheit]) for several weeks; (3)day/night fluctuating temperatures of 1 to 10 degrees Celsius (41 to 50 degrees Fahrenheit); (4)chemicals, such as nitrate in the soil, or applied hormones (gibberellins) in the laboratory; and (5)fire ... function of seeds is for propagation of the species  How does seeds help in propagation of the species? Diversity among seeds  Seeds are very diverse in term of size: Thousands of Begonia seeds –... seeds to capitalize on their genetic variability  Respond to environment cues and germinate at the right time and place Seeds are alive!  To function in propagation, seeds must be alive  Seeds. .. CO2 and H2O  Seeds have a finite lifespan  they cannot be stored indefinitely  Which kind of seeds can remain viable longer? Seeds of tropical plant or temperate plant? Seeds are alive!  Seeds