4 - Sucrose concentration & pollen tube growth

What is the pollen tube?

• A path digested through the stigma of a plant by hydrolytic enzymes, so the pollen grain can travel down the stigma & through the micropyle to the embyro sac & eventually to the ovum for fertilisation

• The production of these enzymes is catalysed by the pollen tube nucleus in the pollen grain

What equipment is needed for this practical?

• 2M stock sucrose solution

• Mineral salt culture medium

• Light microscope & stage micrometer

• Filter paper & petri dishes

• Flowering plants & distilled water

• Measuring cylinder

• Stop clock & balance

• Scissors & forceps

• Mounted needle & pipette

What is the method for this practical?

1. Dilute the stock sucrose solution to several set concentrations (e.g. 0.1M, 0.3M, 0.5M, 0.7M, 0.9M)

2. Place a moist piece of filter paper into a petri dish to form a humid chamber (prevents pollen grains from drying out)

3. Add a few drops of sucrose solution & an equal volume of mineral salt medium onto a microscope slide

4. Use a mounted needle to rub the anther of the flowers, so they shed some pollen onto the microscope slide (don’t add a coverslip to prevent conditions becoming anoxic)

5. Place the slides into the petri dish until it’s time to observe them

6. Start the stop clock. Place the slides under a microscope & use a calibrated eyepiece graticule to measure the pollen tube growth

What are the control variables in this experiment?

• Environment (humid chamber)

• Volume & content of nutrient salt solution

• Volume of sucrose solution

• Time allowed for growth

What is the risk, safety precaution & in emergency for the hazard: biohazard

Risk:

• allergies, soil bacteria & contamination

Safety precaution:

• wash hands after practical

In emergency:

• seek assistance

What is the risk, safety precaution & in emergency for the hazard: scalpel

Risk:

• cuts from sharp objects

Safety precaution:

• cut away from fingers

• use forceps to hold sample whilst cutting

In emergency:

• elevate cuts & apply pressure

• seek medical assistance

What graph should be plotted for this practical?

Sucrose concentration (x-axis) against pollen tube growth (y-axis)

What is the conclusion from this practical?

• As the sucrose concentration increases, the mean pollen tube growth increases up to an optimum (after this point, the mean pollen tube growth decreases)

• This is due to the osmotic effects of increasing concentrations of sucrose