Exercise 03

Principle: Pollen grains germinate and form pollen tubes after they get deposited by the process of pollination on compatible stigma. Pollen tube, made up of cellulose, is an extension of the inner wall of pollen grain (intine). It emerges through one of the germ pore and passes through tissues of stigma and style to reach the ovule. The growing pollen tube is observed by staining with cotton blue.

Requirement: 5–6 excised styles with stigma of Petunia/grass/maize/sunflower/Abelmoschus (Lady's finger), beaker, water, slides, cover slips, cotton blue stain, microscope, brush, needle.

Procedure:

(i) Place the stigmas in boiling water in a beaker for softening the tissues for 5–10 minutes.

(ii) Stain with cotton blue for 3–5 minutes and wash with water to remove excess stain.

(iii) Mount one stigma in a drop of glycerine on a slide. Place a cover slip on the stigma and gently

press the cover slip on the material. Observe the slide under a microscope.

(iv) If you fail to observe pollen tubes mount another stigma.

Observation:

Look for long blue-coloured tubular structures traversing through the tissues of stigma and style.

Discussion:

Pollen tubes are seen amidst the stylar tissue. Many pollen tubes may be seen. Trace the origin of pollen tubes to the pollen grains present around the surface of the stigma.

Questions:

1. Can pollen grains of one plant species germinate on stigma of other species? Give reasons.

2. Do all pollen tubes reach the ovules?

3. Are all the pollen tubes of equal length? If not, why?