Transcript Slide 1
Unit 6: Vegetative Growth and Plant Propagation Chapters 15 &16 Unit 6: Vegetative Growth and Plant Propagation Unit 6 Objectives Understand how stems, leaves, and roots grow, and the coordinated efforts of the plant to make this happen Stages of development, and factors affecting plant growth Discuss seed germination Understand sexual vs. asexual reproduction, and self-fertilization vs. cross-fertilization Unit 6: Vegetative Growth and Plant Propagation Growth Increase in volume and wt. Increase cell numbers and size Primary Growth Occurs in young, herbaceous organs Increases length of shoots and roots Monocots and herbaceous dicots Secondary Growth Increased girth Layers of woody tissue Unit 6: Vegetative Growth and Plant Propagation Occurs at the apical meristem Seed Germination Life in a seed is virtually undetectable Seed will die if it is not allowed to germinate Time to germination varies with species Six steps to germination Water presence Enzyme activation Hydrolysis & catabolism of storage compounds Unit 6: Vegetative Growth and Plant Propagation Initiation of embryo growth Anabolism and formation of new cell structures Emergence 4 environmental factors affecting germination Water Absorption of water is first step in germination A sufficient amount of available water must be present at germination, and must continue to be present after growth begins Medium for transport, activates enzymes that initiate metabolic function, Unit 6: Vegetative Growth and Plant Propagation Light Can stimulate or inhibit germination, depending on the species Oxygen Respiration is taking place in all viable seed Medium where seed is placed should be loose enough for oxygen to permeate through the soil Reduced oxygen supply can reduce or inhibit germination Heat Affects the rate and percentage of germination Temperature needs for germination also vary w/ species Usually 65-75º is optimal for most plants Unit 6: Vegetative Growth and Plant Propagation Germination begins when: Mature embryo in the seed Large enough endosperm to sustain growth Sufficient growth regulators to initiate the process Seeds Lacking True Dormancy Common vegetable seeds Ready to sprout after planting All they need is proper moisture and temperature Seeds w/ True Dormant Embryos Thick seed coat Restricts water access to the seed Scarification – allows thick coated seeds to germinate, usually occurs naturally (How?) Unit 6: Vegetative Growth and Plant Propagation Thin Seed Coat No barrier to water Dormancy is controlled by another factor (light) Insufficient Development Embryo may have to fully mature before germination can occur Embryo often has to feed on something else to foster germination Usually not viable for long periods of time Inhibitors Chemical factors that inhibit germination Seed must eliminate these chemicals for germination to occur Unit 6: Vegetative Growth and Plant Propagation Abscisic Acid – compound present that restricts a seed from germinating through winter, seed spends entire winter breaking down the acid Phenolic Compounds – protect seed until proper moisture is present for germination – common in dry regions The Germination Process of Corn Kernel absorbs water Seed swells as chemical processes begin to prepare for growth Activation of enzymes to break down food reserves needed for growth Endosperm starch is converted to sugars Unit 6: Vegetative Growth and Plant Propagation Radicle elongates and breaks through the seed coat Grows in the direction the kernel is pointed (except up) Coleoptile emerges from the seed 2-5 seminal roots emerge Can occur in 4-5d under optimal conditions Crown area found 1-1.5” beneath soil surface Permanent roots develop If seed is planted deeper the mesocotyl is responsible for pushing coleoptile through the soil surface First leaves emerge from the coleoptile after it emerges Unit 6: Vegetative Growth and Plant Propagation Time from planting to emergence is most affected by temperature 1 wk. under optimal conditions May be 2-3 wks in cool conditions What other factors can influence emergence? The Seedling 1st leaf blade has a rounded tip Leaves begin photosynthesis and the plant no longer depends on the seed for survival Crown root system begins to take control from the seed roots Unit 6: Vegetative Growth and Plant Propagation Apical meristem initiates new leaf formation Point is below ground until the internodes elongate Aboveground leaves can be destroyed, and additional leaves can still form Unless disease occurs Hypogeal emergence Growing point remains beneath soil surface for a period of time after emergence Epigeal emergence Growing point is above soil surface at the time of emergence Unit 6: Vegetative Growth and Plant Propagation Roots 4 functions Anchor Absorb water and nutrients Conduct water and nutrients Store food materials Root and shoot system tends to stay balanced to meet plant needs Unit 6: Vegetative Growth and Plant Propagation Shoot Growth Determinate growth Flowering occurs after a certain period of vegetative growth Most shoot elongation stops Common in vegetables Indeterminate growth Flower clusters form laterally along the stem Shoots remain actively growing until stopped by senescence or something else Ex. grapevines Unit 6: Vegetative Growth and Plant Propagation Growth Patterns 3 classifications: Annuals Complete life cycle in less than 1 yr. Shoot growth in continual until senescence Flowering, fruit, and seed production occurs in the summer Herbaceous Biennials Life cycle in two growing seasons, longer than 1 yr but not necessarily 2 yrs Stored energy from 1st yr used in reproduction in 2nd yr Unit 6: Vegetative Growth and Plant Propagation Ex. Celery, asparagus, sugar beets Limited stem growth in first season Dormant winter period Flowering, fruit, and seed production during second season Senescence and death follow soon after production Herbaceous Perennials Continue growth for 2+ yrs Vegetative growth during and after reproductive phase Ex. Bermuda grass, shrubs, trees Shoot growth resumes each spring Herbaceous or woody Unit 6: Vegetative Growth and Plant Propagation Phase Changes Juvenility Plant may have a different appearance Inability to form flowers during this phase Length varies from days to years Most crops vary amount of days Trees can have 30-40 yr juvenile stages Maturity Able to produce flowers, fruit, and seeds May have different appearance May last days to years Unit 6: Vegetative Growth and Plant Propagation Flowering Days to flowering varies w/ species Can be induced by environmental controls Pollination and fertilization follow Senescence & Death Terminal, irreversible deteriorating change Results in cell breakdown and death Obvious period of physical decline Can also occur in leaves, seeds, flowers, or fruits Exhibited in different ways Total plant death Top plant death Unit 6: Vegetative Growth and Plant Propagation Usually a natural occurrence, but can be induced by disease or stress Can be postponed by removing dead flowers Abscission Losing leaves or fruit Involves abscisic acid Fruits Maturation process of fruit Should be picked at ripening to prevent senescence Unit 6: Vegetative Growth and Plant Propagation Sexual Reproduction Requires formation of flowers in order to get pollination and fertilization Flower Induction Perfect flowers – both stamen & pistil What do the parts of the flower do? Houses gametes, attract pollinators Unit 6: Vegetative Growth and Plant Propagation Pollination & Fertilization Pollination – transfer of pollen from anther to stigma What is self-pollination? Ex. Soybean & tomato What is cross pollination? Ex. Corn & pine trees How can this occur? Fertilization occurs when a small tube from the pollen grain grows through an opening in the ovary (micropyle) Unit 6: Vegetative Growth and Plant Propagation Results in: Formation of the zygote or seed Endosperm Fruit Development & Maturation Ovary begins to develop into a fruit after fertilization Fruit aids in the dispersal of seeds What are some adaptations to fruits that aid in dispersal? Seeds Three main parts of seeds: Seed coat Protects embryo Unit 6: Vegetative Growth and Plant Propagation Stored food supply Endosperm or cotyledons Feed the embryo until it can make its own food Embryo The new plant Plumule – young shoot Hypocotyl – stem Radicle – root Dormancy Seeds will not germinate during dormancy Aids in protection of the embryo through unfit environmental conditions Unit 6: Vegetative Growth and Plant Propagation Can force seeds out of dormancy if we manipulate the environment, or the seed Asexual Reproduction Ensures an exact replicate of the parent plant Enables plants to reproduce even if they don’t produce seeds (Banana) 8 common types of Asexual Reproduction Cuttings Grafting Budding Unit 6: Vegetative Growth and Plant Propagation Layering Division Rhizomes Stolons Tillers/suckers Plant Improvement Deliberate attempt to change genetic architecture of a plant Unit 6: Vegetative Growth and Plant Propagation Modern Practices What is the most common criterion for selection? Tends to affect all other functions of the plant What are some other genetic selections? Research has allowed farmers to produce more food from the same amount of land Basic Genetics Offspring tend to be very similar to the parent, but might not be identical Ex. Soybeans will be almost identical, Apple trees may be very different Unit 6: Vegetative Growth and Plant Propagation Related to the amount of genetic variation New variations can suddenly appear (mutation) Geneticists use these methods to create new/improved varieties Phenotype vs. Genotype Homozygous vs. Heterozygous Dominant vs. Recessive & Incomplete Dominance Self-pollination Produces virtual clones of the parent Unit 6: Vegetative Growth and Plant Propagation Cross-pollination Gametes originate from different plants More chance for genetic variation How does this affect plant breeding and propagation of new varieties? Hybrids Obtained by crossing two or more true-breeding parents Can produce true-breeding corn lines with continual self-pollination helps provide uniform parents and seedstock Unit 6: Vegetative Growth and Plant Propagation Hybrids tend to be more vigorous and productive Produced from two inbred parent lines Easy in corn Hard in soybeans because they are self-pollinating – must force cross-pollination Remove some reproductive parts of the flower to ensure desired cross Pollen collection and pollination must be done manually Mutations Sudden change in genetic expression Most are undesirable Can produce a desirable change Unit 6: Vegetative Growth and Plant Propagation Sometimes tough to replicate to due gene interactions Easier in asexually propagated plants