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The weird and wonderful ways plants reproduce A Plant’s Life Cycle Seed production Seed germination Juvenile vegetative growth Flower formation Mature vegetative growth The result is offspring with genetic diversity that can adapt to new or changing environments. A Plant’s Life Cycle Plantlets form rather than seeds Apomixis Seed production Seed germination Juvenile vegetative growth Flower formation Cleistogamy Precocious germination Mature vegetative growth Modified stems Clonal maintenance of juvenile form Plantlets on leaves and roots The result is offspring with reduced genetic diversity (clonal) or adaptations that allow colonization of specialized niches. A Plant’s Life Cycle Precocious germination Seed production Seed germination Juvenile vegetative growth Flower formation Mature vegetative growth Precocious germination Seeds complete development and are dry when shed from the plant and in many cases dormant. Precocious germination Premature germination Generally undesirable Genetic mutation in response to ABA Tomato Zinnia Precocious germination Precocious germination is the normal type of seed and seedling development in species from over 25 genera. Most grows along the edge of waterways, in swamps or wet forests. In mangrove (Rhizophora mangle), the seed germinates while still on the plant. Precocious germination A Plant’s Life Cycle Precocious germination Seed production Seed germination Juvenile vegetative growth Flower formation Mature vegetative growth Clonal maintenance of juvenile form Juvenile form Bamboo is an example of a monocarpic plant with delayed maturation. It spreads by rhizomes until it flowers, sets seeds and dies. Juvenile form Juvenility Phase of development where the plant can not flower even when the environment is inductive for flowering. Mature Juvenile Hedera helix (English ivy) Juvenile form Foliar dimorphism Pseudopanax Pinus A Plant’s Life Cycle Precocious germination Seed production Seed germination Juvenile vegetative growth Flower formation Mature vegetative growth Plantlets on leaves, and roots Clonal maintenance of juvenile form Adventitious plantlet formation Terminology Apogamy – without gametes Vegetative apomixis Vivipary – also used for precocious germination Gemmae Plantlets on leaves Gemmae are clonal plant fragments produced on the leaf margin or in specialized cups of several bryophytes like mosses and liverworts. Gemmae cups on the leaves of the liverwort (Marchantia) Plantlets on leaves Mother-of-thousands (Bryophyllum daigremontianum) Plantlets on leaves Bryophyllum delagoense Bryophyllum crenatodaigremontianum Plantlets on leaves Piggy-back plant (Tolmiea menziesii) Plantlets on leaves This is most likely due to the over production of cytokinin in portions of the leaf. Piggy-back begonia (Begonia hispida cucullifera) Plantlets on leaves Hen and chickens fern (Asplenium bulbiferum ) Plantlets on leaves Button fern (Tectaria cicutaria ) Plantlets on leaves Walking fern (Camptosorus rhizophyllus ) Plantlets on leaves Walking fern (Camptosorus rhizophyllus ) Plantlets on leaves Walking fern (Camptosorus rhizophyllus ) Plantlets on leaves Leaf cuttings Plantlets on leaves Micropropagation Plantlets on roots Root suckers Paw paw (Asimina triloba) Plantlets on roots Root cuttings Sassafras A Plant’s Life Cycle Precocious germination Seed production Seed germination Juvenile vegetative growth Flower formation Mature vegetative growth Modified stems Plantlets on leaves, and roots Clonal maintenance of juvenile form Modified stems Stolons Runners Aspen (Populus tremuloides) populations can have over 1000 clonal offspring (ramets) from a single dominant mother plant (genet) covering over 30 acres. Modified stems Geophytic structures Bulbs Corms Tubers Rhizomes Modified stems Dropper – a new bulb that forms at the end of a stolon. Agnes Robertson. 1906. The ‘Droppers’ of Tulipa and Erythronium. Annals of Botany20:429-440. Modified stems Dropper – a new bulb that forms at the end of a stolon. Agnes Robertson. 1906. The ‘Droppers’ of Tulipa and Erythronium. Annals of Botany20:429-440. Modified stems Dropper – a new bulb that forms at the end of a stolon. Trout lily (Erythronium) Modified stems Trout lilies are colonizing plants. They produce many single and a few double-leaved plants. Only double leaved plants flower. A flowering plant can have over 100 ovules, but a capsule rarely has 8 seeds. Trout lily (Erythronium) Modified stems The Minnesota trout lily (E. propullans) appears to only reproduce by droppers. Trout lily (Erythronium) It is endangered and restricted to two counties in Minnesota. Modified stems Geophytes - Lilium Arial bulbils Bulb scale cutting Modified stems European bittercress (Dentaria bulbifera) Modified stems Small aerial tubers produced on the stem or leaves are often called tubercles. Hardy begonia (Begonia evansiana) String-of-hearts (Ceropegia woodii) Devil’s tongue Amorphophallus bulbifera Modified stems All plants are clones reproduced by tubercles. Hardy begonia (Begonia evansiana) Modified stems Cultivated forms of air potato are edible, while wild forms can be invasive and poisonous. Air potato (Dioscorea bulbifera ) A Plant’s Life Cycle Precocious germination Seed production Seed germination Juvenile vegetative growth Flower formation Cleistogamy Mature vegetative growth Modified stems Plantlets on leaves, and roots Clonal maintenance of juvenile form Cleistogamy Chasmogamous flowers open prior to pollination and may be self or cross pollinated. Cleistogamous flowers do not open and are selfpollinated. Cleistogamy is found in over 200 (mostly herbaceous) species. The reproductive effort invested in the cleistogamous flowers is smaller than in the chasmogamous ones. Cleistogamy Arial chasmogamous flowers. Subterranean cleistogamous flowers. Flower Fruit Violet (Viola odorata) Flower Fruit Seeds A Plant’s Life Cycle Precocious germination Apomixis Seed production Seed germination Juvenile vegetative growth Flower formation Cleistogamy Mature vegetative growth Modified stems Plantlets on leaves, and roots Clonal maintenance of juvenile form Apomixis Apomixis is the production of an embryo that bypasses the usual process of meiosis and fertilization. The genotype of the embryo and resulting plant will be the same as the seed parent. This is clonal seed production! Apomixis Apomixis occurs in over 300 species from at least 35 plant families. It is most common in the Asteraceae, Graminaceae, Rosaceae, and Rutaceae. Goat’s beard (Tragopogon) Apomixis Only a few economically important food crops exhibit apomixis. These include Citrus, Mango (Mangifera), and Mangosteen (Garcinia). Several grass species and cultivars are apomicts including Kentucky blue grass. Orange (Citrus) Apomixis Types of apomixis include: 1. Diplospory 2. Apospory 3. Adventive embryony Apple (Malus) Apomixis Sexual development Megaspore Mother Cell Nucellus Meiosis Egg Sac Apomixis Diplospory Normal Meiosis Diplospory = Diplo (two) and spory (spore). Egg Sac Megaspore Mother Cell Nucellus 1n Megaspore mother cell does not finish or initiate meiosis. Egg sac organizes normally but cells are diploid. Diplospory 2n Apomixis Diplospory Normal Meiosis Embryo initiates development without being fertilized. Egg Sac Megaspore Mother Cell Nucellus 1n Diplospory 2n Endosperm also develops either with or without fertilization from the polar nuclei. Apomixis Diplospory In some cases (Poa), fertilization is required for endosperm formation. The egg does not get fertilized because it is already growing. Common in grasses and Asteraceae. Eastern gamagrass (Tripsacum dactyloides) Apomixis Adventive embryony Normal Megaspore Mother Cell Nucellus Adventive embryony Meiosis Egg Sac The megaspore mother cell undergoes normal meiosis and forms a normal sexual embryo sac. These cells are fertilized by male sperm cells as in normal embryogenesis. Apomixis Adventive embryony Normal Megaspore Mother Cell Nucellus Adventive embryony Meiosis Egg Sac However, cells in the nucellus begin forming multiple embryos in the micropylar region of the ovule. Apomixis Adventive embryony Nucellus Adventive embryos Julius von Sachs – Lectures on the physiology of plants, 1887. Apomixis Adventive embryony Apomixis Adventive embryony These asexual embryos do not produce their own embryo sac but grow into the embryo sac of the sexual embryo. Endosperm must be fertilized. Common in tropical fruit trees like citrus and mango. Apomixis Adventive embryony Multiple seedlings (polyembryony) from a single seed in Citrus. One of the seedlings will be sexual and the others will be clones. Apomixis Somatic embryogenesis A Plant’s Life Cycle Plantlets form rather than seeds Precocious germination Apomixis Seed production Seed germination Juvenile vegetative growth Flower formation Cleistogamy Mature vegetative growth Modified stems Plantlets on leaves, and roots Clonal maintenance of juvenile form Plantlets in place of seeds Wild onion Allium vineale Plantlets in place of seeds Plantlets in place of seeds Alpine bistort (Polygonum viviparum) Plantlets in place of seeds Meadow grass (Poa bulbosa) Plantlets in place of seeds Spiderplant (Chlorophytum comosum) Plantlets in place of seeds Walking iris Neomarica caerulea Plantlets in place of seeds Century plant (Agave americana) These agave plants are monocarpic. They take decades to flower, then the mother plant dies. Plantlets in place of seeds Century plant (Agave americana) A Plant’s Life Cycle Plantlets form rather than seeds Precocious germination Apomixis Seed production Seed germination Juvenile vegetative growth Flower formation Cleistogamy Mature vegetative growth Modified stems Plantlets on leaves, and roots Clonal maintenance of juvenile form The weird and wonderful ways plants reproduce