1. Skotomorphogenesis Seed germination Genes and enzymes Embryo and Seed development Plant life cycle Photomorphogenesis Photoreceptors Phytochrome Cells and cell growth Phytochrome: regulation of light responses Photosynthesis: light reaction Photosynthesis: carbon fixation Photorespiration Fruit ripening Respiration Primary metabolism Secondary metabolism Nitrogen fixation Mineral nutrition Water transport Phloem translocation Abiotic stress Biotic stress Flowering Fertilization and embryogenesis Seed development

2. What Defines a Fruit? A fruit is a ripened ovary A seed is a ripened ovule

3. What Defines a Fruit? A fruit is a ripened ovary A seed is a ripened ovule

4. Fruit forms in higher angiosperms

5. Fruit Ripening Process Process of becoming edible Fruit becomes sweeter –(accumulation of soluble sugars) Fruit becomes softer –(more palatable) Fruit becomes less green –(accumulation of pigments/decrease of chlorophyll) Fruit becomes more acidic

6. Fruit ripening Partial digestion of cell walls and middle lamella Degradation of chlorophyll & starch Synthesis of anthocyanins and carotinoids Respiration of organic acids

7. Ethylene during ripening process

8. Changes in Cell Wall Much of the cell wall is degraded Expansins are produced to “loosen” cell wall Middle lamella can be selectively degrade to allow cells to become “unglued” from each other

9. Abscission Triple response Pathogen defense Root hair formation Fruit ripening/ Senescence Elongation inhibiation Increased Radial growth Ethylene effects

10. Ethylene: it’s a gas!! Biologically active at less than 0.1ppm Transported as ACC Synthesized in ripening fruit and senescing tissues Induced by auxin, draught, wounding, cold, stress, fruit ripening, senescence, pathogen attack 1864 illuminating gas powered street lights defoliate trees 1901 Russian Dimitry Neljubov identifies ethylene as phytohormone 1917 Doubt identifies ethylene as defoliant 1934 ethylene biosynthesis in plants detected 1935 ethylene is proposed as the “ripening hormone”

11. Ethylene: it’s a gas!! CC H H H H Biologically active at less than 0.1ppm Transported as ACC Synthesized in ripening fruit and senescing tissues Induced by auxin, draught, wounding, cold, stress, fruit ripening, senescence, pathogen attack

12. Ethylene biosynthesis from methionine H2CH2C CH 2 Ethylene O2O2 ACC-Oxidase Methionine S-Adenosyl-Methionine 1-Aminocyclopropan- 1-carbonic acid NH 3 COO - H2CH2C H2CH2C C + (ACC) (SAM) ACC-Synthase SAM Synthetase

13. Antisense-Inhibition of ACC-Oxidase stops flower senescence

14. Ethylene as a fruit ripening hormone And Ethylene the defoliant….

15. Abscission zone at base of leaf at the where it joints the stem leaf stem

16. Ethylene induces abscission

17. Auxin prevents abscission However: unphysiological auxin concentrations have herbicide effects (agent orange)

19. Ethylene: triple response Triple response: - thickening of hypocotyl, radial growth - reduction of cell elongation in hypocotyl and root - exaggerated curvature of apical hook, reduced geotropism

20. Understanding the hormone: Searching for ethylene mutants (CTR1) ctr1 Constitutive triple response air Wild-type ctr1 airethylene Recessive loss-of-function ctr1 mutations: - Constitutive activation of ethylene response - Ethylene induced genes are always “on” - Constitutive triple response CTR1 leads to inhibition of ethylene response in absense of ethylene

21. Searching for ethylene mutants etr1 ctr1 Ethylene resistant (exogenous ethylene added) Constitutive triple Response (no exogenous ethylene) Air Ethylene Wild-type

22. Understanding the hormone: Searching for ethylene mutants (ETR1) Ethylene resistant AirEthylene AirEthylene Wild-typeEtr1 etr1 Etr (ethylene resistant) Ein (ethylene insensitive) Ethylene receptors

23. Understanding the hormone: Searching for ethylene mutants (ETO1) eto1 Ethylene overproducer - Ethylene overproducer show same phenotype as ctr1 - ctr1 not reversible by inhibitors of ethylene biosynthesis - eto phenotype is reversed by ethylene synthesis inhibitors ETO1 has de-regulated ethylene biosynthesis Air Ethylene Wild-type

24. Structure of ethylene receptors GMP binding

25. Ethylene Mutants Ethylene insensitive (EIN) Ethylene resistant (ETR) Constitutive Triple Response (CTR) Ethylene Response Sensor (ERS) Ethylene Overproducer (ETO)