The ups and downs of auxin

1. The ups and downs of auxin A presentation on the action of auxin prepared by GTAC staff

2. Hormones signal cells to divide, elongate and differentiate to form tissues in plants Meristem = zone of actively dividing cells In dicots, the meristem is found at root and shoot tips Different in monocots (grasses). Where is the meristem? • Does grass continue to grow even after mowing? • Do you think the zone of division is in the tip or lower in grasses? Dicotyledonous plant

3. Plant tumours Henri-Louis Duhamel (1700–1782) French agriculturalist and tree expert Hmmm….. The wound has filled with cells forming a tumour This discovery forms the basis of plant tissue culture

4. Establishing a tissue culture Using sterile technique a piece Of plant is cut = explant This mass of dividing cells forms a callus. Cells in the callus are totipotent – they can differentiate into any sort of plant tissue depending upon the signal we give them. Small wound area. How can we increase the wound area? Make a longitudinal cut MS medium – contains all of the salts and organic molecules that plants need to grow

5. Effect of hormones on plant cell differentiation What will I be? Observe the tissue cultured cells on the following slide to determine the effects auxin can induce in cells Auxin(IAA) Cytokinin(kinetin) Totipotent cell Callus

6. How auxin affects plant cells Complete Q. 1 - 3

7. Gravitropism Plants responding to gravity View and complete Q 4

8. How shoots respond to gravity Statoliths are heavy organelles that sediment at the base of cells in response to gravity. This is how a plant knows which way is down.

9. Auxin enters and leaves cells through channels Auxin efflux channel Auxin influx channel

10. A pathway for auxin accumulation in shoot tissue 1. Statoliths fall to bottom of cell 2. The enzyme, Phospholipase, is activated to snip off some lipid heads 3. Lipid head second messengers stimulate auxin efflux channels to move to base of cell Enzyme

11. Auxin leaves cells through efflux transporters and accumulates at base of shoot tissues Complete Q. 5

12. Plant shoot bends upwards in response In response to gravity, auxin accumulates in cells on lower side of shoot Complete Q. 6

13. Formulate a hypothesis • For a shoot to bend upwards it needs to grow longer on the lower side. • What can happen to make one side grow longer? • Is Auxin giving these cells a message to divide? • OR • B. Is Auxin giving these cells a message to elongate? A B Complete Q. 7

14. Cut 10 mm section here Design an experiment to explore action of auxin on oat shoots Complete Q. 8 Design your experiment Treatment 1 Treatment 2 Incubate for 18 hours then find out average length of shoots in each treatment Complete Q. 9 - 11

15. Preparing a thin longitudinal section of coleoptile cells Use a scalpel to slice thin length-wise sections of a coleoptile that was immersed in water and one that was immersed in auxin. Add 2 drops of methylene blue stain onto a slide. Place a coleoptile section from each treatment on each drop, and label treatments W and A. Lower a coverslip onto the slide and view under the microscope at 100X. Methylene blue Slide Coleoptile section Cover slip W A Complete Q. 12 - 15

16. What’s happening in the roots? Where is auxin accumulating? Complete Q. 14 Is the effect of auxin on root cells the same as the effect on shoot cells? Complete Q. 16 & 17

17. Complete Q. 18 & 19 Auxin These proteins Inhibit cell elongation These proteins promote cell elongation Auxin transporter Root-specific proteins Degradation complex Shoot-specific proteins Auxin receptor Gene regulator + inhibitor Shoot-specific genes Root-specific genes Shoot-specific genes Root-specific genes Nucleus Nucleus Cytoplasm Cytoplasm Shoot cell Root cell