Plant Reproduction Floral architecture Plant Reproduction Plant Reproduction Details of male gametophyte development Meiosis always produces Generative cell will form four cells two sperm At maturity contained within tube cell Tube cell forms pollen tube during fertilization Spore wall exterior surface of pollen deposited by sporophyte parent Plant Reproduction Details of female gametophyte development Only 1 of the 4 megaspores survive after meiosis Megaspore nucleus divides by mitosis 3 times without cytokinesis 8 nuclei Membranes then partition off egg cell 2 synergids and 3 antipodal cells 2 polar nuclei remain in center Plant Reproduction Pollination 20 use wind dispersal Wind pollinated species tend to make a lot of pollen 80 rely upon an animal Mostly insects Birds mammals too Plant Reproduction Angiosperm fertilization in detail Upon initiation of pollen tube growth generative cell divides by mitosis to form two sperm cells still surrounded entirely by tube cell Plant Reproduction Angiosperm fertilization in detail Pollen tube growth is guided by chemicals produced by synergid cells Plant Reproduction Angiosperm fertilization in detail Sperm cells discharged Double fertilization ensues Plant Reproduction After fertilization Ovule develops into a seed Ovary develops into a fruit generally Plant Reproduction After fertilization Endosperm development typically occurs first The triploid 3n endosperm nucleus undergoes several divisions without cytokinesis make a multinucleate milky supercell Cytokinesis forming of cell membranes around each endosperm nucleus occurs later Often but not always these cells then produce cell walls and become stiffer Plant Reproduction After fertilization In some eudicots the nutrients in the endosperm are taken up by the cotyledons before the seed is mature no endosperm left in mature seed In some eudicots and most monocots the endosperm remains distinct from the embryo cotyledon s in the mature seed Plant Reproduction Development of a eudicot embryo First cell division is asymmetric produces a basal cell and a terminal cell Basal cell divisions create a chain of cells termed the suspensor The suspensor serves to attach the embryo to parental tissue and also transfers nutrients from endosperm to embryo Plant Reproduction Development of a eudicot embryo First cell division is asymmetric produces a basal cell and a terminal cell Basal cell divisions create a chain of cells termed the suspensor The suspensor serves to attach the embryo to parental tissue and also transfers nutrients from endosperm to embryo Plant Reproduction Development of a eudicot embryo Terminal Cell gives rise to most of the embryo Initially creates a globular ball of cells the proembryo The proembryo differentiates into a heart shaped embryo bumps of hearts are the cotyledons Plant Reproduction Development of a eudicot embryo Terminal Cell gives rise to most of the embryo Initially creates a globular ball of cells the proembryo The proembryo differentiates into a heart shaped embryo bumps of hearts are the cotyledons Plant Reproduction Development of a eudicot embryo The root apical meristem and the shoot apical meristem can first be distinguished at the heart shaped stage of embryonic development Plant Reproduction Development of a eudicot embryo Growth of the embryo elongates the apical basal axis Plant Reproduction Development of a eudicot embryo At maturity both apical meristems are readily apparent Plant Reproduction Seed maturation Desiccation Dormancy Seed coat Hard protective coat formed from the integuments which surrounded the ovule Plant Reproduction Fruit development Ovule Seed Ovary Fruit mostly Plant Reproduction Simple fruits Develop from a single carpel Plant Reproduction Aggregate fruits Actually a cluster of fruits which each developed from a separate carpel Plant Reproduction Multiple fruits from multiple carpels borne on multiple separate flowers Inflorescence group of flowers tightly clustered together Plant Reproduction Accessory fruits Tissues besides the ovary contribute major portions Apples shown strawberries Plant Reproduction Diversity of seed dispersal adaptations Wind maple dandelion Plant Reproduction Diversity of seed dispersal adaptations Animals Does a bear x in the woods Plant Reproduction Diversity of seed dispersal adaptations Animals Acorns and hoarding behaviors Plant Reproduction Morphology of a bean Cotyledons absorb endosperm material no endosperm at maturity swollen cotyledons Plant Reproduction Morphology of a bean Radicle embryonic root Hypocotyl Embronic stem Below cotyledons Plant Reproduction Morphology of a bean Epicotyl portion of embryo above the cotyledons Plant Reproduction Morphology of a castor bean Endosperm still present at maturity Plant Reproduction Morphology of a maize seed kernel Endosperm still present at maturity Scutellum Cotyledon specialized for absorbing nutrition from endosperm during germination Plant Reproduction Morphology of a maize seed kernel Coleoptile and Coleorhiza Protective structures Plant Reproduction Dormancy dormant Seeds maintain a very low metabolic rate while There are many species specific cues which break dormancy and trigger germination Long period of cold weather Fire Copious rainfall Digestion Seed bank The reservoir of dormant seeds present in the environment Plant Reproduction Germination Imbibition Uptake of water by dried seeds Triggers a rapid re starting of metabolism Enzymes which mobilize stored energy sources become active Malted barley Allow germination Complex carbohydrates starches others broken down by seed enzymes into simple sugars Roast the germinated seedlings Boil extract sugars ferment enjoy Plant Reproduction Germination Often the hypocotyl forms a hook for protection of the shoot apical meristem during germination Plant Reproduction The problem with being a hermaprhodite Self fertilization is inbreeding Inbreeding reduces genetic diversity Nonetheless some plants are predominantly selfers Often weeds which are under selection for rapid reproduction Arabidopsis thaliana Plant Reproduction Not all flowers are complete Some lack one or more whorls Some are sterile absence or non functionality of both stamens and carpels Some are unisexual each individual flower is either staminate or pistillate staminate flowers lack female parts pistillate flowers lack male parts Plant Reproduction Species with unisexual flowers are either Monoecious or Dioecious Monoecious An