I. LIFE CYCLE OF SEEDLING PLANT

          Life cycle = Vegetative growth + reproductive development
                                (biomass)                    (flowering, fruiting)

    A. Annual       ---- completes a life cycle in one growing season and dies

    B. Biennial      ---- completes a life cycle in two growing seasons and dies
                                            1st year --- grows vegetatively; gets vernalized in winter
                                            2nd year --- flowers and sets seeds and dies

    C. Perennials   ---- live more than two years, repeating the vegetative-reproductive
                                  cycle each year

           Herbaceous perennials - shoots die back during winter; underground structures (rhizomes, bulbs, corms, crown)
                                                        become dormant
           Woody perennials - plant size increases each year by lateral growth of cambium
 

II. FLOWERING

    - occurs during reproductive phase
    - flower bud induction
            "florigen"--- an elusive hormone
            phytochrome is involved
            gene activation ---- secret is being unlocked (i.e. Arabidopsis)
    - requires an inductive cold period (vernalization) for perennials
    - phase change
            annuals ----- weeks to months
            bamboo ---- several decades
           Agaveamericana (century plant) --- 100 years?
            apple, pear -- 5-8 years (3-4 yrs for dwarf apples)

III. POLLINATION AND FERTILIZATION
 

IV. EMBRYO AND SEED DEVELOPMENT

    A. Morphological Development
            STAGE 1
                - pericarp expansion to form a fruit shape
                - nucellus enlarges by cell division (maternal tissue)
                - endosperm still microscopic
                - zygote develops into a small proembryo attached to suspensor
                        ESM = Embryonal-Suspenor mass
                - embryo undergoes development

            STAGE 2
                - cessation of seed (ovule) and fruit (pericarp) development
                - growth of endosperm (translucent) within the nucellus
                - enlargement of embro into cotyledon
 

            STAGE 3
                - further enlargement and ripening of fruit and seed
                - fruit color development
                - dry weight increase and accumulatio of certain storage compounds

    B. Ability to Germination
            EMBRYOGENESIS-
                -Development of zygote into embryo- involves polariztion of embro axis and cotyledons
                -Time dependent development of secondary embryo and secondary cotyledons

    C. Accumulation of Storage Compounds
            -Carbohydrates, fats, oils, proteins
            -Stored in cotyledons, endosperm, nucellus
            -Translocation via funiculus and difusion

IV. SEED MATURATION AND PRIMARY DORMANCY

    A. Embryo Maturation
            -Morphological (size increase) maturity followed by
              physiological    (conditioning) maturity
                i.e. desiccation-sensitive---->desiccation-resistant
            -Abscisic Acid (ABA) is involved
                prevents precocious germination*
                induces embryo maturation by moisture regulation

                *vivipary - seed germination inside of fruit while still on plant
                        i.e. - Citrus, mangrove, pecan, barley

    B. Primary Dormancy
            (survival mechanism for a given species)
            -INHIBITORS    -naturally occurring chemicals (i.e. ABA)
                                        -present internally in embryo for many species
                                        -present externally in flesh or fruit tissue (tomato, strawberry) ABA, Coumarin
                                        -responsible for physicla dormancy
            -SEED COATS   -hard, fibrous, mucilaginous
                                        -often impervious to water and gas
                                           (cutins, macrosclereid cells in legume seeds)
                                           sunflower seed - fibrous
                                        -some seed coats are semi-permeable
                                        -responsible for physical dormancy

V. SEED RIPENING AND DISSEMINATION
    - Ripening reduces moisture content
            most species prefer drying
          *recalcitrant seeds do not germinate when moisture content is reduces
                    maple (36-40%), oak, citrus)
    - Dissemination by wind, animals, water

VI. THE MATURE SEED

       seed -a matured ovule enclosed within the mature ovary or fruit
                -consists of embryo, food storage tissue, seed covering
                            (wheat germ(cotyledons, endosperm) (nut shell)

    A. Embryo
            -Consists of embryo axis, root and shoot primordia, cotyledons

    B. Storage Tissue
            -Cotyledons in nonendospermic seeds (pear, pumkin)

    C. Seed Coverings
            -Consist of seed coats (testa), remains of pericarp and nucellus and endosperm tissues
            -Seed coat thickness and morphology vary by species
                Testa- formed by integuments of ovule

VII. POLYEMBRYONY AND APOMIXIS

    A. Polyembyony*
            -multiple embryos within a seed
            -adventitious nucellar embrogenesis
            -polyembryogenesis by polyembro at ESM stage

    B. Apomixis
                Asexual seed production via a zygote without meiosis and fertilization
            -Obligate apomicts-----producing only apomictic embryos (asexual)
            -Facultative apomicts---producing both apomictic and sexual embros (asexual, sexual) ex. grasses

            Adventitious Embryony (Citrus)
                    embryos formed by nucellar tissue
           Recurrent Apomixis
                    -seeds develop by embryo sac directly from egg mother cell (EMC) without complete meiosis
                    -ends up with 2n seeds (genotype same as mother)
                        i.e. Tarxacum (dandelion), poa (bluegrass), Allium
                             parthenium (guayule), some apple species
           Nonrecurrent Apomixis
                    -embryo develops from egg nuclesus without fertiliztion
                    -results in 1n (haploid) seed
            Vegetative Apomixis
                    -vegetative buds or bulbils formed in flowerheads (Allium, poa, agave, onion)

VIII. SPORE DEVELOPMENT

    - Produced in ferns
    - Alternation of sporangium and gametophytic generations
    - Haploid spores from sporangium, from the underside of fronds, germinate and become prothallus

        ----> Archegonia (female) and Antheridia (male) produce egg cell and sperm cell, respectively, on the same plant
                    zygotes are produced when water caries sperm cells to the egg cells and fertilization occurs------> rhizomous plants