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

Phototrophism

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.

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

Phototrophism - Fritz Went’s Experiment

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

Phototrophism

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”

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

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

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

Other Normal Effects of Auxins in Plants 6. Apical Dominance

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

Other Normal Effects of Auxins in Plants 7. Leaf Abscission

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

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

Trypophan-dependent Biosynthesis of IAA

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

Gibberellins Gibberellic Acid 125 forms of Gibberellins

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

Gibberellins

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

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

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

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

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

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

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

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

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.

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.

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”

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

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

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

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

Cytokinins “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 Play an antagonistic role with auxins in apical dominance.

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

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

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

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)

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

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.

Ethylene Causes hypocotyl hook & plumular arch.

Ethylene Signal Transduction Pathway Arabidopsis mutants Silver Thiosulfate

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

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

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

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

Abscisic Acid Isolated from dormant buds in the 1930’s. Growth inhibitor in seeds. Causes stomatal closure. (Response to chloroplast membrane changes during water stress.)

Brassinosteroids Found in Brassica rapus. Isolated from most tissues. Polyhydrated Sterol

Brassinosteroids Found in Brassica napus. Isolated from most tissues. Stimulates shoot elongation, ethylene production; inhibits root growth and development.

Polyamines First observed as crystals in human semen by Van Leeuwenhooke in the 1600’s. Ubiquitous in living tissue. Common biochemical pathway in all organisms.

Polyamines First observed as crystals in human semen by Van Leeuwenhooke in the 1600’s. Ubiquitous in living tissue. Investigated by plant physiologists beginning in the 1970’s. Effect on macromolecules and membranes discovered. Role in normal cell functioning in both prokaryotic and eukaryotic cells. Growth factor.

Phytohormones, Senescence and Fall Color Change in Deciduous Trees