Photoperiodic responses, light receptors and the biological clock

1. Photoperiodic responses, light receptors and the biological clock

2. Classification according to photoperiodic control of flowering Short Day Plants (SDP) Flowering requires short days (long nights) Long Day Plants (LDP) Flowering requires long days (short nights) Day Neutral Plants (DNP) Flowering is not regulated by day length

4. Photoperiodism and flowering Effect of day length on flowering and other activities (seed germination, seed dormancy, bud break, bud dormancy) in temperate regions of the northern hemisphere. Fig. 15-20, p. 252

5. How does a change in day length lead to the induction of flowering? For any biological organism to detect a change in day length, it needs: A day light detection mechanism (the photoreceptors Phy and Cry) A biological clock (set at a 24 hr cycle) as a time measuring system

6. Example of a circadian rhythm: The circadian oscillator controls the leaf movement rhythm in beans Leaf angle already starts to change before the light of day. Leaf angle changes continue their rhythm also in continuous dark. Leaf angle Leaf angle

7. Circadian rhythms allow to monitor (to visualize) the biological (circadian) clock Without light detection (mediated by Phy and Cry receptors) the period of the biological clock becomes slightly longer than 24 hrs. The 24 hr cycle of light detection allows to entrain the clock to maintain a 24 hr cycle.

8. Review

9. Absorption and transport Osmosis and hydrostatic pressure used?

10. PROTOPLAST SOLUTION (3) Hydrostatic pressure in cells Concentration 0.3 molar Concentration 0.3 molar (Isotonic) Pressure 0 megapascals Concentration 0.27 molar Concentration 0 molar (Hypotonic) Pressure 0.66 megapascals Turgor pressure is one type of hydrostatic pressure. Turgor pressure is the result of a combination of osmosis and cell wall rigidity. Concentration 0.5 molar Concentration 0.5 molar (Hypertonic) Pressure 0 megapascals Fig. 3-7 (a-c), p. 36

11. LIGHT Events leading to the opening of a stoma: The production of malate and the influx of K+ and Cl- powered by the electrical and pH gradients produced by the proton pump increase the concentration of osmotically active solutes in the guard cells. As a result, water flows into the cells by osmosis. starch malic acid malate– plasma membrane ATP H+ proton pump ADP + Pi  H+ K+ + CI K+ H+ CI Fig. 11-8a, p. 170

12. Root pressure is generated by an osmotic pump • After passing the endodermis, mineral nutrients accumulate in the stele of the root. The endodermal cells provide the differentially permeable membrane needed for osmosis. • Soil saturated with water • Water tends to enter root and stele • Builds up root pressure in xylem • Forces xylem sap up into shoot Fig. 11-13a, p. 178

13. Mechanism of Phloem Transport high pressure low pressure sieve tube sucrose sucrose H2O H2O sucrose sucrose H2O H2O glucose source sink H2O glucose CO2 + H2O sucrose H2O parenchyma parenchyma Fig. 11-14, p. 179 Sucrose is actively transported into the sieve tubes at the food source region of the plant (leaves or storage organs) and removed at the sink regions (regions of growth or storage). Water follows by osmosis, increasing the hydrostatic pressure in the sieve tubes at the source region and decreasing the pressure at the sink region. The sieve-tube contents flow en masse from high(source)- to low(sink)-pressure regions.

14. Absorption and transport Water flow through xylem compared to phloem? What are the similarities, what are the differences?

15. Absorption and transport Do plants acidify the soil they grow in? Yes: - Respiration - H+ extrusion

16. Soil Formation atmospheric gases: CO2 SO2 N2O5 rock rain acids: H2CO3 H2SO3 HNO3 wind and water erode rocks and soil freeze-thaw produces cracks roots: crack rocks through pressure, secrete acid Fig. 11-11, p. 175

17. Fig. 11-12, p. 177 Active Uptake of Minerals Into Root Cells

18. Differential Growth • What is the link between turgor pressure, cell walls and differential growth?

19. PROTOPLAST SOLUTION (3) Hydrostatic pressure in cells Concentration 0.3 molar Concentration 0.3 molar (Isotonic) Pressure 0 megapascals Concentration 0.27 molar Concentration 0 molar (Hypotonic) Pressure 0.66 megapascals Turgor pressure is one type of hydrostatic pressure. Turgor pressure is the result of a combination of osmosis and cell wall rigidity. Concentration 0.5 molar Concentration 0.5 molar (Hypertonic) Pressure 0 megapascals Fig. 3-7 (a-c), p. 36

20. Differential growth a Rate of cell elongation is higher on the a-side of the coleoptile compared to the b-side. This leads to differential growth: increased growth rate on one side of plant organ, results in curvature of the organ. b

21. Plant transformation Agrobacterium Auxin Cytokinin Dedifferentiation Differentiation

22. Transforming a plant cell by using Agrobacterium Gene to be introduced in plant cell (for example: a gene that encodes the Luciferase protein) Plant Cell Agrobacterium + Modified Ti-plasmid Nucleus Transformed Plant Cell Agrobacterium Plant cell makes luciferase protein

23. auxin cytokinin

24. Major signals that control plant growth and development • Internal signals: Plant Hormones -AUXIN - CYTOKININ - ETHYLENE - ABSCISIC ACID - GIBBERELLIC ACID The plant’s toolbox for positive and negative control of physiological and developmental processes.

25. Shade avoidance Shading of a plant by plants that grow above it leads to increased or decreased Phy activity ?

26. Absorption spectra of Chlorophyll a and b 100 chlorophyll b 80 Percent of light absorbed 60 chlorophyll a 40 20 0 400 500 600 700 Fig. 10-5, p. 152 Wavelength (nm) 660 730 The ratio of Red (660 nm) to Far Red (730 nm) light will be low underneath green leaves that absorb light between 640 and 700 nm.

28. The predicted properties of the receptor

29. The End