Plants – Unit Overview

1. Plants – Unit Overview A basic knowledge of plant anatomy and physiology is essential for crop management. Knowing more about plants allows management decisions that enhance their growth and development, meaning better quality and larger harvests.

2. Parts of a plant- external Courtesy of University of Georgia Agriculture Education Department

3. Details of plant structure Courtesy of University of Georgia Agriculture Education Department

4. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), Plant structure – internal tissue types

6. Diagram of a stoma Courtesy of University of Georgia Agriculture Education Department

7. Stoma Courtesy of University of Georgia Agriculture Education Department

8. Xylem Illustration by Lynn Pugh

9. Phloem Illustration by Lynn Pugh

10. Plant vs Animal Cells • Plants have a cell membrane and a rigid cell wall • Plants have large fluid filled vacuoles • Plants have physical connecting strands between cells • Animals have flexible cell membrane • Animals have no vacuoles • Substances move in and out of animal cells through the membrane

11. Plant and Animal cells Animal Cell Plant cell Courtesy of University of Georgia Agriculture Education Department

12. Transpiration • Movement of water from soil • through plant to atmosphere • Root hairs take up water • Moves through xylem, one way • Movement powered by the sun, as each molecule of water evaporates, pulling the one behind it up • Only 1% of water that passes through the plant is absorbed by the plant Courtesy of University of Georgia Agriculture Education Department

13. Factors which affect transpiration • Light • Stomata open in response to light • Temperature • Increases with increasing T, until overheated • Humidity • Less water lost when humidity is high • Air movement • Air movement increases water loss • as “boundary layer” blown away

15. Courtesy of University of Georgia Agriculture Education Department

16. Movement of sugars in plant- source to sink • Sugars in the form of glucose, made by photosynthesis in the leaves move through the phloem • They move from high concentration of sugar(leaf cells) to low concentration (throughout the plant) and are stored in vacuoles • This movement can be two way • Source is leaf cells to sink which can be other parts of the plant

17. Growth RegulatorsOriginal by Libby AstrachanModified by Georgia Agriculture Education Curriculum Office- July 2004Modified by Georgia Organics 2008

18. Plant Hormones-Growth Regulators • Natural (made by plants) – also called hormones • Synthetic (man-made) • Also called PGRs (plant growth regulators) • Purposes: start growth, stop growth, modify growth & development

19. 5 Known Plant Hormones • Auxins (ox ins) • Gibberellins (jib ber ill ins) • Cytokinins (site oh kine ins) • Ethylene (eth el een) • Abscisic acid (ab sis ick) Hormones may act individually or together

20. Auxins • Stem elongation • Produced in tips of stems (“B” in photo) • Migrate from cell to cell in stems Courtesy of University of Georgia Agriculture Education Department

21. Phototropism – ability to bend towards light • Auxins - responsible for plants bending towards light. • Auxins - move down shaded side of the stem and cause cells to elongate Courtesy of University of Georgia Agriculture Education Department

22. Gravitropism (geotropism) – plant response to gravity • Auxins – responsible for plant response to gravity • Auxins – move to lowest side and cause stem tissue to elongate – stem curves upwards Courtesy of University of Georgia Agriculture Education Department

23. Apical dominance • Auxins – move down the stem from the terminal bud and inhibit growth of side shoots Courtesy of University of Georgia Agriculture Education Department

24. Pinching • Pinching - removing the terminal bud • Pinching - stops flow of auxins down the stem and allows side shoots to develop • Produces bushy, well-branched crops Courtesy of University of Georgia Agriculture Education Department

25. Root development • Auxins encourage root development in cuttings • Some plants produce plenty of auxins to make rooting cuttings easy • Other plants need synthetic auxins such as IBA Courtesy of University of Georgia Agriculture Education Department

26. Gibberellins • Cell elongation and cell division • Stimulate development of flowers (as in “gibbing” camelias) • Cause internodes to stretch • Produced in stem and root apical meristems, seed embryos, young leaves Courtesy of University of Georgia Agriculture Education Department

27. Internode Elongation • Gibberellins cause internodes to stretch in relation to light intensity. • High light intensity = no stretch • Low light intensity = long internodes. Leaves are raised to capture light Courtesy of University of Georgia Agriculture Education Department

28. Problems with Internode Elongation • Greenhouse problem – plants spaced too closely to one another • Plants shade one another – results in stretching, less compact plants, weaker stems, loss in value $$$ Courtesy of University of Georgia Agriculture Education Department

29. Cytokinins • Cell division (used in tissue culture) • Cell differentiation (used in tissue culture for plant organ formation) • Formation of callus tissue • Delay aging process in plants • Produced in roots • Transported through xylem • Still being researched Courtesy of University of Georgia Agriculture Education Department

30. Cytokinins vs. Auxins • In stems – auxins inhibit lateral shoots, cytokinins promote lateral shoots • In roots – auxins promote root branching, cytokinins inhibit root branching • Work together to control cell differentiation and cell division Courtesy of University of Georgia Agriculture Education Department

31. Ethylene Gas • Colorless gas • Produced in nodes of stems, ripening fruits, dying leaves Courtesy of University of Georgia Agriculture Education Department

32. Ethylene exposure • Thickens stems • Breaks down chlorophyll • Weakens cell membranes • Softens cell walls Courtesy of University of Georgia Agriculture Education Department

33. The Holly and the Ethylene Courtesy of University of Georgia Agriculture Education Department

34. Abscisic Acid – The Plant Stress Hormone • Growth inhibiting hormone • Responsible for seed dormancy • Responsible for closing stomata during drought Courtesy of University of Georgia Agriculture Education Department

35. Rooting compounds • Rooting Compounds – • Instead of synthetic rooting compounds, try willow water • Strip leaves and terminal stems from present year’s growth of any willow species and soak in water for 24 hours. • Soak cuttings for 24 hours in willow water before sticking in medium • Water with willow water

36. Plant/soil life relationships • Symbiotic • Mutualistic- rhizobium, mycorrhiza • Parasitic- pathogens • Commensal- spanish moss

37. Rhizobium Courtesy of USDA

38. Mycorrhiza Courtesey of USDA, Forest Service, PNW Research Station, Corvallis, Oregon

39. Summary • Plant anatomy • Structures of plant • Plant physiology • Water and sugar movements • Photosynthesis • Hormones • Relationships • Symbiotic relationships