GEORGE B. JOHNSON Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display PowerPoint ® Lectures prepared by Johnny El-Rady 27 Plant Reproduction and Growth Essentials of The Living World First Edition

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.1 Angiosperm Reproduction In asexual reproduction, an individual inherits all of its chromosomes from a single parent Offspring and parent are genetically identical In a stable environment, asexual reproduction is more advantageous than sexual reproduction It has a lower investment of energy

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Runners Long, slender stems that grow along the soil surface Rhizomes Underground horizontal stems that create a network underground Vegetative reproduction occurs when new individuals are cloned from parts of the parent Fig “Maternity plant” Suckers Sprouts produced by roots give rise to new plants Adventitious plantlets New plants arise from notches along the leaves

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sexual reproduction in plants is characterized by an alteration of generations Diploid sporophyte  haploid gametophyte Male gametophytes are pollen grains Develop from microspores Female gametophyte is the embryo sac Develops from a megaspore Angiosperms have different structures for producing male and female gametes These are not permanent parts of the adult individual

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Flowers contain male parts (stamens) and female parts (carpels) Dioecious plants Contain flowers that produce only ovules or only pollen Monoecious plants Contain male and female parts in separate flowers, but in the same plant Often flowers contain both parts, but there are exceptions Fig a

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Pollen grains develop from microspores formed in pollen sacs located in the anther Eggs develop in ovules, each of which contains a megaspore mother cell Fig Fig. 27.2

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The process by which pollen is transferred to stigma Self-pollination occurs when a flower’s anther pollinates the same flower’s stigma This can lead to self-fertilization Other plants are adapted to outcrossing Crossing between two different plants Some plants exhibit self-incompatibility Genetic relatedness blocks flower fertilization Pollination

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In angiosperms, pollen is carried from flower to flower by insects and other animals These pollinators are drawn to the flower’s nectar In certain angiosperms and all gymnosperms, pollen is wind-blown and reaches the stigma passively Wind-pollinated plants grow in dense strands Fig Yellow flowers attract bees Long proboscis gets deep nectar supply

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Pollen adheres to stigma and begins to grow a pollen tube Pollen tube pierces the style and eventually reaches the ovule Two sperm cells are released Fertilization One fertilizes the egg cell to form the zygote (2n) The other fuses with two polar nuclei to form the endosperm (3n) Double fertilization

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.2 Seeds Development is the entire series of events that occur between fertilization and maturity The first stage is the formation of the embryo Early in development, the angiosperm embryo stops developing and becomes dormant because of drying Outermost covering of ovule develops into seed coat enclosing dormant embryo and a stored food source Most of embryo’s metabolic activities cease Germination is the resumption of metabolic activities leading to growth of the mature plant Occurs when conditions are favorable for plant’s survival

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig Development in an angiosperm embryo Polar nuclei Micropyle Sperm Pollen tube Egg (n) Triploid endosperm mother cell Zygote (2n) First cell division Endosperm Suspensor Basal cell (3n) Globular proembryo Cotyledon Ground meristem Procambium Cotyledons Protoderm Root apex (radicle) Endosperm Shoot apical meristem Hypocotyl Root apical meristem Cotyledons

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.3 Fruit During seed formation, the flower ovary begins to develop into fruit Fruits can be fleshy or dry and hard There are three main kinds of fleshy fruit BerriesDrupesPomes Fig. 27.5

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fleshy fruit are normally dispersed by animals Animals eat the fruit and excrete the seeds as solid wastes Dry fruits are dispersed by several mechanisms Mangroves Coconuts By windBy waterBy attaching to animals Fig. 27.5e Dandelion Fig. 27.5f Burgrass

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.4 Germination Germination is the resumption of a seed’s growth and reproduction It is triggered by water The seed coat ruptures and the plant begins to send out roots and shoots Oxygen is required for active growth Endosperm or cotyledons provide the food source

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig Development of angiosperms Dicot: Soybean Cotyledons emerge from the underground Monocot: Corn Cotyledon stays underground

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.5 Plant Hormones Differentiation in plants, unlike that in animals, is largely reversible In the 1950s, F.C. Steward was able to regenerate a fertile carrot plant from bits of phloem tissue Fig. 27.7

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Following germination, further plant development depends on the activity of meristematic tissues And the interaction with the environment Fig Stages of plant differentiation

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Differentiation results from the activation or suppression of key genes This gene expression is controlled by hormones Plant hormones are produced in non-specialized tissues Five major types of hormones Auxins Gibberellins Cytokinins Ethylene Abscisic acid

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display TABLE 27.1

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display TABLE 27.1

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.6 Auxin Charles Darwin and his son Francis published a book called The Power of Movement in Plants (1881) In it, they describe the phenomenon of phototropism Growing plants bending toward light The Darwins concluded that, in response to light, an “influence” arises at the tip of the shoot It is then transmitted downward causing the shoot to bend

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig The Darwins’ experiment with phototropism

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In 1926, Frits Went identified the hormone involved in phototropism Fig He called it auxin (from the Gr. word, “to increase”)

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Phototropism can be explained as such Auxin contents on the two sides of shoot differ The side that is in the shade has more auxin Cells elongate more than those on the lighted side Auxin appears to act by increasing the stretchability of the plant cell wall Fig

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Synthetic auxins are routinely used to control weeds When treated, the weeds literally “grow to death” 2,4-dichlorophenoxyaceticacid Known as 2,4-D Affects only broad-leaved dicots 2,4,5-trichlorophenoxyaceticacid Known as 2,4,5-T Kills woody seedlings and weeds Notorious as the Agent Orange of the Vietnam War Easily contaminated with dioxin An endocrine disruptor

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.7 Other Plant Hormones Gibberellins Also hasten seed germination A large class of over 100 hormones Play major role in stem elongation Promote elongation between the node regions Fig Defective in gibberellin production

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.7 Other Plant Hormones Cytokinins Stimulate cell division Determine the course of differentiation Promote growth of lateral buds Inhibit formation of lateral roots Fig Apical meristem intact Auxin inhibits lateral buds Cytokinins stimulate lateral buds

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.7 Other Plant Hormones Ethylene Gas that hastens fruit ripening Fig Accelerates abscission of leaves or fruits damaged by various stress agents Holly twig

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.7 Other Plant Hormones Abscisic Acid (ABA) Fig May cause synthesis of ethylene Plays a role in the dormancy of seeds May also function in transpiration Opening/closing of stomata ABA causes efflux of K + out of guard cells

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.8 Photoperiodism and Dormancy Photoperiodism is the physiological response of organisms to changes in the length of day and night Angiosperm flower production Long-day plants Initiate flowers when nights become shorter than a certain length Short-day plants Initiate flowers when nights become longer than a certain length Day-neutral plants Produce flowers without regard to day length

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig How photoperiodism works in plants

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Plants contain a pigment called phytochrome It exists in two forms converted by darkness P r (inactive) P fr (active) Fig To this day, the existence of a flowering hormone remains strictly hypothetical

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Plants respond to their external environment largely by changes in growth rate When conditions are not favorable, they become dormant They stop growing altogether In temperate regions, dormancy is generally associated with winter Dormancy

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27.9 Tropisms Tropisms are directional and irreversible growth responses of plants to external stimuli Phototropism Growth toward sources of light Gravitropism Growth in response to gravity Stems grow upward and roots downward Thigmotropism Growth in response to touch

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig Tropism guides plant growth Phototropism Gravitropism Thigmotropism