Plants in our Ecosystem. Demystifying Plants: Botany for Gardeners. When scientists study plants, what do they study? Horticulture = Botany applied

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1 Demystifying Plants: Botany for Gardeners Plants in our Ecosystem Capture sun s energy Food source Replenish atmospheric oxygen Participate in water cycle Moderate world climate Provide shelter Source of numerous raw materials Support a myriad of other living things When scientists study plants, what do they study? The way plants grow and function (plant morphology and physiology) The way plants are genetically related to each other (plant taxonomy) How plants interact with their natural environment (plant ecology) How plants evolve and adapt to the environment at a gene and molecular level (plant genetics) Horticulture = Botany applied Identify plants Grow & propagate plants Influence flowering & fruit production Control unwanted growth Maintain plant health Modify plant features through breeding and selection 1

2 Horticulture is the study of useful plant oddities In disturbed, reorganized, and coddled landscapes Variegated Norway maple 2

3 Plants don t live in isolation Physical environment (soils, climate, moisture, etc.) The living environment (other plants, people, animals, insects, fungi, etc.) Plant communities are always changing This is called plant succession Examples from native landscapes Examples from gardening 3

4 Horticultural plant classifications Sun or shade Acid or neutral or alkaline soils Drainage preference Growth habit (woody vs. herbaceous; tree vs. shrub; evergreen vs. deciduous; etc.) Cold hardiness Reproductive strategy: annual, biennial, perennial. Plant family How do plants get through winter? Climate zones define the average low winter temperatures for large areas. Your property may be in a microclimate that differs (either warmer or colder) from the general cold winter pattern for your region. 4

5 The importance of life cycles Winter annuals Annuals winter summer Biennials Perennials Herbaceous Woody deciduous evergreen Spread exclusively by seeds that germinate in the fall/winter and go to seed in the spring to early summer and die. Some, in this climate, grow year round Examples: chickweed, groundsel, red dead nettle Groundsel Senecio vulgaris Also spread by seed that germinate in the spring and summer Flower and seed by fall and die Compete with vegetable crops Examples: pigweed, lambsquarter, and Summer annuals Purslane Biennials Spread by seed that germinate in spring-fall Overwinter as a rosette Flower and seed next year in the late springsummer and die Bull thistle Cirsium vulgare 5

6 Herbaceous perennials Tops die back New shoots each spring from roots/crown Spread by seed and vegetative pieces and don t die Hedge bindweed Calystegia sepium aka Morning glory Tend to spread by seeds. Some vegetative spread with some species e.g. ivy, & root suckers on some trees. We propagate by seed, cuttings, grafting, etc Don t die Woody perennials Classifying plants into families Why do we care? What are the key botanical characteristics used? Why? Why flowers? 6

7 Linnean classification of plants Lower vs. higher plants Gymnosperms (conifers and others) and Angiosperms Monocots and dicots Family: Aceracea Genus: Acer Species: rubrum Cultivar: Autumn Blaze Summary of differences, monocots & dicots Chloroplasts capture light energy CO2 + H20 + light energy = sugars + O2 7

8 What are the requirements for plant growth? Light energy Heat (some) Stored energy Water Carbon, hydrogen, oxygen Mineral elements A few other important concepts Meristems Plant hormones Areas of actively dividing cells that develop into plant tissues and organs Meristems 8

9 Plant hormones aka plant growth regulators Chemicals present in tiny quantities that affect plant development and response to environment including dormancy, growth rate, fruit, flowering, etc. Plants have to start from something Dr. B. Rathinasabapathi - U. Florida 9

10 Seed Anatomy Embryo - miniature plant in an arrested state of development Endosperm - food supply (can be comprised of proteins, carbohydrates, fats) Seed coat - hard outer covering that protects from disease and insects; also repels water Temperate seeds measure winter temperatures Seed is a dicot with two seed leaves Root apex at lower left Root connected to hypocotyl where cotyledons are attached Seed coat Endospeerm Cut away seed Seeds and Seedlings Seed germination requirements Activation of embryo within seed. Preceded by water penetrating seed coat Oxygen, favorable temperature cycle, and (in some species) light required Other cues 10

11 Other germination factors Dicot Monocot Cotyledons = modified leaves first true leaves cotyledons bean dicot seed = 2 cotyledons monocot seed = 1 cotyledon 11

12 Vascular system ( plumbing ) Anchors the plant Absorbs water and minerals Stores food Reproductive organ Compete with other plants for water and minerals Root functions Root Structure Lateral Root Zone of Primary Root Maturation Root Hairs Root Tip Zone of Elongation Root Cap Meristematic Zone 12

13 Zone of Elongation Meristematic Zone Root Tip Root Cap Photo: Source Unknown Tap Root Fibrous Root Modified roots Tuberous root sweet potato Storage root of beet Dicots Monocot Tuberous root, dahlia Storage root carrot 13

14 Root Anatomy What s inside a root? Epidermis Cortex Endodermis The vascular system is in the center Xylem Phloem buttercup Photo: Botany for Gardeners, Capon What s inside a root? Root Tissues xylem cambium in woody roots phloem cortex Xylem - conduct water & nutrients Phloem - carry sugars & starches Endodermis - contain vascular tissues Cortex - primary tissue surrounding vascular bundle Epidermis - outermost layer of plant tissues, protective layer buttercup 14

15 Unique to roots! Origin of lateral roots root cap - located at root tip & protects growing point Notice the root cap on the lateral root cut away section Root hairs on a radish seedling Root hairs absorb most of the water a plant gets very tiny Root hair cross-section delicate thin-walled room for lots of water has lower water pressure than the outside soil 15

16 Let s review Mycorrhizae = fungal partners on/in higher plant roots Mycorrhizal fungus How much water do these plants move? Which partner gets what? Corn Big leaf maple 16

17 Factors influencing root growth Light captured Gravity Temperature Soil texture Oxygen Moisture Minerals Salt Storms happen and so do shallow roots 17

18 Root spread Issues: construction, covering & stability certain herbicides problems yard invasion and suckering other problems What does a stem do? Physically support leaves, buds, flowers & fruits Transport water, minerals & sugars and other compounds Provides storage in some plants 18

19 corn What s inside the stem? vascular bundles cortex cells add structural strength to the stem Xylem Phloem Vascular bundle arrangement herbaceous dicot (sunflower) Vascular bundle Phloem transports photosynthetic products to areas of the plants needing energy Vascular cambium cells make more xylem and phloem Xylem is like tiny straws and transports water and minerals from the soil to other parts of the plant and out through the leaves Vascular cambium Cambium is a meristematic tissue, meaning it divides to produce new tissues Cambium divides to produce xylem: to the inside (heartwood, pith) phloem: to the outside (part of bark) Responsible for girth growth, or increased stem diameter in woody plants 19

20 Stem cross-section Stem cross-sections Herbaceous monocot (corn) phloem Herbaceous dicot (clover) Herbaceous monocot (corn) Woody dicot (maple tree) xylem Notice the relative position of the xylem, phloem, and cambium! cambium Xylem cells Carry H 2 O & dissolved nutrients Cells are: long, open-ended, connected end to end have thick cell walls resemble straws P. Dahiya: Nature Cell Biology Xylem cells are really strong. Why? 20

21 Phloem cells Transport actively photosynthetic products from leaves to roots, stems, flowers & fruits Cells are: long and tube-like without extra cell wall thickening vascular cambium phloem xylem bark What s this area? Heartwood - nonfunctional xylem Sapwood - functional xylem Woody Stem Anatomy Outer Bark Inner Bark (phloem) Vascular Cambium? What is bark? Answer. Bark is the outer layer of cells on a tree containing cambium, compressed phloem, and sometimes, cork. 21

22 Stems evolve in response to selection pressure Stems selected by humans for storage Thorns for defense (rose) Corky extensions (Euonymus alata) Photosynthetic stems (Blueberry and Christmas cactus) Stems evolved for vegetative propagation External parts of the stem node = place where leaf is (or was) attached to the stem internode = distance between nodes 22

23 Node Internode Node Node Terminal Bud Axillary or Lateral Bud Bud Scale Scar Lenticel (breathing pore) Leaf Scar Lateral or axillary buds Located in the angle where the leaf attaches to the stem Apical dominance Apical (apex = top) dominance Lateral buds kept dormant due to plant hormone (auxin) cascading from top downwards until auxin source removed Auxin= plant growth regulator or hormone 23

24 Auxin and fruit trees Axillary bud May produce lateral shoot or branch less auxin effect further from the apex due to dilution Phototropism another auxin effect 24

25 Auxin Phototropism Buds and vegetative dormancy what triggers the dormancy process and what brings them out of dormancy? Winter chilling requirement hours below 45 degrees 25

26 Leaf Functions Use sunlight to make sugars photosynthesis Use sugars to make energy and other compounds respiration Move water from roots throughout the plant - transpiration Major leaf parts Modified leaves lamina (leaf blade) - highly variable in size and shape petiole - stalk at base of leaf that attaches leaf blade to stem catching insects 26

27 More modified leaves Leaves modified for storage floating scales spines tendrils Succulence Remember monocots & dicots? leaf blade Monocot or Dicot? petiole dicots monocot 27

28 Leaf arrangement on a stem opposite alternate whorled These characteristics are important in identifying plants What are the leaf arrangements of these plants? Compound vs. Simple leaves bedstraw snowberry Japanese knotweed 28

29 Compound leaves Simple leaf leaflet Buds are in the axils between leaf and stem pinnately compound palmately compound What s going on inside the leaf and plant? What is photosynthesis? Photosynthesis Respiration Transpiration Balancing act 29

30 Chloroplasts capture light energy Mid-rib cross-section upper epidermis central vein or mid-rib lower epidermis CO2 + H20 + light energy = sugars + O2 Epidermis May have special adaptations like hairs or waxy layer that help with drought tolerance Other adaptions on the epidermis? stinging nettle 30

31 Leaf cut-away Stomata mesophyll Stomatal cycle Factors that affect photosynthetic rate Carbon dioxide availability Water Light (quality, amount, quantity) Temperature 31

32 What is transpiration? Transpiration is water loss (as vapor) from a plant Transpiration rate is controlled by opening and closing of the stomates, which is influenced by humidity, temperature, and time of day. Functions of transpiration Cool plant Transport minerals Move sugars & plant chemicals around Maintain turgor What is turgor? 32

33 Transpiration requires soil moisture functional root system functional stem & branch plumbing functional leaves Transpiration Rate Transpiration rate is controlled by stomatal aperture in response to relative humidity temperature light wind under constraint of water availability plant nutrition How does water get from the soil to the top of a tree? Root hairs (often with the help of mycorrhizae) absorb water from the soil Xylem cells transport water via capillary action and cohesive force of water Stomates control evaporation 33

34 What is respiration? Respiration is the opposite of photosynthesis In respiration, sugars, water, and oxygen are used to create energy to drive biochemical reactions and carbon dioxide and water are released. Factors affecting respiration rate Temperature Oxygen Soil condition Sugars + oxygen = chemical energy + CO 2 + H 2 O A Comparison Plant Processes in Balance Photosynthesis produces food stores energy uses water uses carbon dioxide releases oxygen occurs in sunlight Respiration uses food releases energy produces water releases carbon dioxide uses oxygen occurs in dark and light Water Uptake vs Transpiration Photosynthesis vs Respiration Carbohydrate allocation Nutrient allocation Growth vs Storage vs Reproduction vs Defense 34

35 . How plants reproduce (or are propagated by clever gardeners) Divisions Cuttings Layering Vegetative (asexual) propagation Grafting/Budding Tissue culture Cuttings 35

36 Responses involving auxin Layering Formation of adventitious roots Grafting Grafting Scion Rootstock 36

37 Tissue culture Cytokinin and auxin & tissue culture Flowers and sexual propagation Flowers facilitate pollination. If fertilization occurs, seeds are produced and carried in cones (conifers) or fruits (flowering plants) 37

38 The flowering response Juvenility and flowering - apples 38

39 Parts of a flower Lily Flower parts anther stigma 39

40 Complete Has all floral parts present (sepals, petals, stamens, pistils) Incomplete -flower lacks 1 or more of the 4 parts Flower Types Flower Types, Continued Perfect Has both stamens and pistils (male and female parts) Imperfect Lacks either stamens or pistils Complete or Incomplete? Perfect or Imperfect? Imperfect flowers can be either monoecious (on the same plant) or dioecious (on different plants) male flower (staminate) female flower (pistillate) 40

41 Holly: dioecious Walnut: monoecious Male and female trees Pollination Method: wind, insects, bats, lizards, etc. Incompatibility: What is it and why it has evolutionary value? Hybrids: Mostly man-made but not always Pollination vs. fertilization 41

42 big leaf maple willow cape fuchsia beetles wind hummingbirds yarrow skunk cabbage cat s ear butterflies flies bees 42

43 Dranuculus vulgaris? Can you think of any modified flowers? Hint: think veggies! Carrion beetles Fertilization pollen grains pollen tube ovary ovule 43

44 Seed dispersal Fruit: Facilitates seed dispersal Wind Water Animals Insects Others Seeds release hormones that cause cells to divide and expand. When seeds are only on one side lopsided fruit results. Very incomplete pollination = fruit drop

45 Fruit ripening Ethylene Five plant growth regulators Auxins Gibberellins Abscisic acid Cytokinins Ethylene Auxin Apical dominance Phototropism 45

46 Gibberellic acid Stimulate cell division and elongation Speeds seed germination Breaks seed dormancy Abscisic acid Induce and maintain dormancy Control stomatal closure Leaf abscision Cytokinins Stimulate cell division Delay senescence Ethylene Stress response: epinasty and leaf drop Fruit ripening 46

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