Phototrophism

1. Phototrophism • First investigated by Charles and Frances Darwin (1881) • canary grass Phalaris canariensis L. • The Power of Movement in Plants (1881) • Seedlings • coleoptile • plumules

2. Phototrophism

3. Phototrophism - Darwins’ Experiment • Conclusion: • Some chemical is produced in the tip and transmitted down the stem to somehow produce bending. • There is a growth-promoting messenger.

4. Phototrophism - Fritz Went’s Experiment • Dutch Plant Physiologist 1929 • Oat seedlings • Diffusion of phytohormone from growing tip in agar blocks • Agar blocks placed on oat seedlings

5. Phototrophism - Fritz Went’s Experiment

6. Phototrophism - Fritz Went’s Experiment • Conclusion: • A growth substance (phytohormone) must be (1) produced in the tip; (2) transmitted down the stem; and somehow (3) accumulate on the side away from the light. • “Auxin” (to increase, by Went) • Either • H.1: is destroyed on the lighted side • or • H.2: migrates to the dark side

7. Phototrophism

8. Synthetic Auxins (precursors) • 2, 4-D and 2,4,5-T are herbicides for broad-leaved plants at very low concentrations. • Widely used commercially for 30 years - defoliant in Viet Nam. • Contaminant of 2,4,5-T • tetrachlorobenzo-para-dioxin “dioxin”

9. Other Normal Effects of Auxins in Plants • 1. Phototropism • ------ • 2. Cell Elongation • causes polysaccharide cross-bridges to break and reform

10. Other Normal Effects of Auxins in Plants • 1. Phototropism • ------ • 2. Cell Elongation

11. Other Normal Effects of Auxins in Plants • 1. Phototropism • ------ • 2. Cell Elongation • 3. Geotropism (Gravitropism) • 4. Initiation of adventitious root growth in cuttings • 5. Promotes stem elongation and inhibits root elongation

12. Other Normal Effects of Auxins in Plants • 6. Apical Dominance

13. Other Normal Effects of Auxins in Plants • 6. Apical Dominance • 7. Leaf Abscission - Abscission Layer - pectin & • cellulose • ethylene -> • pectinase & • cellulase

14. Other Normal Effects of Auxins in Plants • 7. Leaf Abscission

15. Other Normal Effects of Auxins in Plants • 1. Phototropism • 2. Cell Elongation • 3. Geotropism (Gravitropism) • 4. Initiation of adventitious root growth in cuttings • 5. Promotes stem elongation and inhibits root elongation • 6. Apical Dominance • 7. Leaf Abscission • 8. Maintains chlorophyll in the leaf • 9. Seedling Growth • 10. Fruit Growth (after fertilization) • 11. Parthenocarpic development

16. Auxins • Work at very small concentrations (500 ppm) • Action Spectrum: primarily blue • Tryptophan is the primary precursor • Auxins must be inactivated at some point by forming conjugates or by enzymatic break down by enzymes such as IAA oxidase

17. Trypophan-dependent Biosynthesis of IAA

18. Gibberellins • Isolated from a fungal disease of rice - • “Foolish Seedling Disease” • Gibberella fugikuroa • Isolated in the 1930’s Japan • Gibberellic Acid (GA)

19. Gibberellins • Gibberellic Acid • 125 forms of Gibberellins

20. Gibberellins • Produced mainly in apical meristems (leaves and embryos). Are considered terpenes (from isoprene).

21. Gibberellins

22. Gibberellins • Produced mainly in apical meristems (leaves and embryos).

23. Gibberellins • Low concentration required for normal stem elongation. • Can produce parthenocarpic fruits (apples, pears …)

24. Gibberellins • Low concentration required for normal stem elongation. • Can produce parthenocarpic fruits (apples, pears …) • Important in seedling development. • breaking dormancy • early germination

25. Gibberellins • Low concentration required for normal stem elongation. • Can produce parthenocarpic fruits (apples, pears …) • Important in seedling development.

26. Gibberellins • Important in seedling development. • Controls the mobilization of food reserves in grasses.

27. Gibberellins • Important in seedling development. • Controls the mobilization of food reserves in grasses. • - cereal grains

28. Gibberellins • Important in seedling development. • Controls the mobilization of food reserves in grasses.

29. Gibberellins • Controls bolting in rosette-type plants. • Lettuce, cabbage (photoperiod) • Queen Ann’s lace, Mullein (cold treatment) • premature bolting

30. Gibberellins • Controls bolting in rosette-type plants. • Important factor in bud break. • Promotes cell elongation and cell division. • Antisenescent. • Transported in both the phloem and xylem. • Application of GA to imperfect flowers causes male flower production. (monoecious, dioecious) • Probably function by gene regulation and gene expression.

31. Gibberellins • Application of GA to imperfect flowers causes male flower production. (monoecious, dioecious) • Probably function by gene regulation and gene expression. • Promotes flower and fruit development. • “juvenile stage” --> “ripe to flower” • The juvenile stage for most conifers lasts 10 - 20 years. Exogenous application of GA can cause precocious cones.

32. Cytokinins • Discovered during the early days of tissue culture. • Stewart 1930’s • carrot phloem cells + coconut milk --> whole plant • Skoog 1940’s • tobacco pith cells + auxin & coconut medium --> whole plant • “CYTOKININ”

33. Cytokinins • ZEATIN - most abundant cytokinin in plants. • Adenine is the basic building block.

34. Terpene Biosynthesis - cytokinin(Can be made from isoprene via the melvonic acid pathway.) • Produced mainly in apical root meristems.

35. Cytokinins • Transported “up” the plant in the xylem tissue. • Mainly affects cell division. • “Witches’ Broom” • mistletoe; bacterial, viral or fungal infection

36. Cytokinins • “Witches’ Broom” • mistletoe; bacterial, viral or fungal infection

37. “Crown Gall” a neoplasic growth due to infection by Agrobacterium tumifaciens. A. tumifaciens carries the genes for production of cytokinin and auxins on a plasmid. Plasmid genes become a part of host cell genome. Cytokinins

38. Cytokinins • Play an antagonistic role with auxins in apicaldominance.

39. Cytokinins • Promotes leaf expansion. • Prevents senescence. • Promotes seed germination in some plants. • Both cytokinins and auxins are needed for plant tissue cultures.

40. Cytokinins • Both cytokinins and auxins are needed for plant tissue cultures. (Skoog and others…) • Cell Initiation Medium (CIM) • Approximately equal amounts of cytokinin and auxins will proliferate the production of undifferentiated callus. • EXPLANT ----> CIM

41. Cytokinins • Both cytokinins and auxins are needed for plant tissue cultures. (Skoog and others…) • Cell Initiation Medium (CIM) • Root Growth Medium (RIM) • Shoot Growth medium (SIM) • High cytokinin:auxin ratio

42. Ethylene • A gas produced in various parts of the plant. • (CH2=CH2) • Production promoted by various types of stress - water stress, temperature, wounding & auxins. • Can be made from the amino acid methionine (S)

43. Ethylene • Can be made from the amino acid methionine (S) • Promotes leaf curling (epinasty).

44. Ethylene • Can be made from the amino acid methionine (S) • Promotes leaf curling (epinasty). • Promotes senescence. • Promotes fruit ripening. • Promotes etioloation & hypocotyl hook. • Is autocatalitic. • Promotes bud dormancy. • Inhibits cell elongation.

45. Ethylene • Causes hypocotyl hook & plumular arch.

46. Ethylene Signal Transduction Pathway • Arabidopsis mutants • Silver Thiosulfate

47. Abscisic Acid • Produced mainly in leaves (chloroplasts) and transported through the phloem.

48. Terpene Biosynthesis - Abscisic Acid(Can be made from isoprene via the melvonic acid pathway.)

49. Abscisic Acid • Isolated from dormant buds in the 1930’s. • Promotes “winter’ and “summer dormancy”.

50. Abscisic Acid • Isolated from dormant buds in the 1930’s. • Growth inhibitor in seeds. • ABA -----------------------> ABA-glucoside cold water stress • (may wash out)