CP14: investigating the effect of gibberellin on production of amylase in germinating cereals using a starch agar assay

what does giberrellin do?

• during germination starch stored in endosperm is converted to glucose

• giberrelins are secreted by the embryo → activated by the absorption of water

• diffuse to aleurone layer of the endosperm which stimulate aleruone layer to produce amylase

• amylase hydrolyses the starch into glucose

method

1. dilute stock giberrellin solution to several set concentration

2. collected the required no. of seeds and pull of husks

3. cut the seeds in half (one hald should contain the embryo and the other half should contain the endosperm) - discard half w/ embryo

4. sterilise the half containing the endosperm by placing it into sodium hypochlorite solution

5. wash the seeds w/ distilled water until no smell of bleach

6. place seed halves in gibberellin solution and leave for 12 - 48 hours

7. use sterile forces to move seed halves onto a sterile petrish with starch agar

8. partially tape lids (to prevent anoxic conditions) and leave for 12 - 48 hours

9. pour potassium iodide onto the plates

10. measure zone of inhibition/clear zone around seed half

conclusion

• as giberrellin concentration increases, the amount of amylase produced by the aleruone layer increased, so area of starch from the agar around the seed half digested also increases.

• giberellin influences transcription of the amylase gene.

• iodine stains starch blue - black so the area where starch has been digested appeared as a clear area the seed half,

independent variable

concentration of gibberellin

dependent variable

the diameter of the clear zones

control variables

• time allowed to soak in gibberellin

• time left on starch agar plate source/age of seeds