GEN BIO 1 | Seeds

Seeds

matured ovule that has embryo and endosperm within a seed coat

Endosperm development

develops before embryo; the central nuclei divide into a multinucleate supercell with a milky consistency

examples of liquid endosperm is coconut milk and solid endosperm is coconut meat

Monocot endosperms

occupies bulk of kernel and is the main energy reserve for the development of the young seedling as it stores the bulk of its energy in the endosperm; has one cotyledon

Dicot Endosperms

lack endosperms upon maturity, food reserves are completely transferred to the embryo; stores food in its to cotyledon

Embryo

young plant

Endosperm

stored food for embryo

Seed Coat

encases the seed

Radicle

embryonic root

Epicotyl

embryonic shoot

Hypocotyl

junction between roots and shoots

Cotyledon

seed leaf

Embryo Development

zygote undergoes mitotic division and gives rise to terminal and basal cell

Basal Cell

gives rise to suspensor which attaches to parent plant and helps transfer nutrients to embryo

Terminal cell

gives rise to most of embryo, divides several times and forms into proembryo, cotyledons form and embryo elongates for the shoot and root apex to appear

Seed Dormancy

seed delay germination until its in the right environmental conditions for seedling growth and development, usually after environmental disruptions like heavy rainfall, fire, harsh winters.

Lettuce break dormancy in shallow soil and ample sunlight

Seed Germination

• Imbibition causes the seed to rupture and expand the coat

• enzymes digest stored food in endosperm and cotyledons

• nutrients are transferred into growing embryo

• Young roots grow downward in response to gravity

• Shoots grow upwards towards light and produce leaves

• First leaves begin photosynthesis

• Seeds buried too deep in soil will not emerge

Dicot Germination

Radicle emerges first and hook forms in hypocotyl and growth pushes it above ground. The hypocotyl straightens, the cotyledons separate and the epicotyl spreads its first true leaves

Monocot Germination

shoot tip grows through the coleoptile/sheath once it has pushed through the surface of the soil; cotyledon remains below

Seed Size

Due to natural selection, some seeds are larger for better support while smaller seeds have a better chance for wider dispersal