Angiosperm Reproduction Review: • Plants are characterized by an alternation of generations. • haploid (n) - gametophyte... • reproduce sperm and eggs via mitosis. Fertilization results in a diploid zygote (grows into a sporophyte) • diploid (2n) - sporophyte... • reproduces spores via meiosis producing the gametophytes
Seed formation after fertilization • Pollen from another plant meets the stigma and germinates developing into a pollen tube digesting its way toward the ovule (consisting of an egg and 2 polar nuclei) • once in the vicinity of the ovule 2 sperm are released for double fertilization • 1 sperm fuses with the egg (2n) • 1 sperm fuses with the 2 polar nuclei (3n) to form the endosperm a nutritive tissue of the seed • after fertilization the ovule forms a seed and the ovary (structure containing the ovule) grows into a fruit
most plants exhibit self-incompatibility recognizing pollen from themselves and ensuring that fertilization occurs only with genetically different plants
Structure of the mature seed • the embryonic tissue forms a cotyledon (heart shaped structure) and the embryo elongates • epicotyl contains 2 miniature leaves • radicle forms the embryonic root • the hypocotyl becomes the stem between the roots and forming leaves • the seed coat forms once the cotyledon is fully developed from the integument layer of the ovule and hardens as the structure dehydrates • the structure is now in a dormant state awaiting germination • monocots - seeds with 1 part (corn) • dicots - seeds seeds with 2 parts (legumes) • ripened fruits signal the completed development of the seed
Seed to seedling (dicot) • imbibition - process of germination • uptake of water by the seed due to low water potential • causes the seed to expand and rupture (like plasmolysis in a cell) • metabolism of the endospore begins as the nutrients are transferred to growing portions of the embryo • Growth • radicle (root) is first to emerge • the hypocotyl extends to break the soil surface and expose the epicotyl (first leaves) to the sunlight
Asexual reproduction - produces clones via mitosis • accomplished through adventitious roots • asexual production of seeds (apomixes) • fragmentation - separation of parts that grow into whole plants...