Unit 6: Vegetative Growth and Plant Propagation

1. Unit 6: Vegetative Growth and Plant Propagation Chapters 15 &16

2. 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

3. 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

4. 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

5. 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,

6. 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

7. 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?)

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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)

22. 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

23. 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

24. 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

25. Unit 6: Vegetative Growth and Plant Propagation • Layering • Division • Rhizomes • Stolons • Tillers/suckers • Plant Improvement • Deliberate attempt to change genetic architecture of a plant

26. 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

27. 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

28. 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

29. 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

30. Unit 6: Vegetative Growth and Plant Propagation • Sometimes tough to replicate to due gene interactions • Easier in asexually propagated plants