Male gametophyte morphology

The pollen grains (morphology),
Pollen wall features

1. Presented by... Thakor Maitri M. M.Sc . (Botany) Department of life sciences, H.N.G.U., Patan . ❶ Male gametophyte -morphology

2. Content ❷ Introduction ☻ The pollen grains (morphology) Pollen Wall features

3. Introduction ❸ In the male gametophyte, first cell generation represent by the microspores or the pollen grains . The development of male gametophyte is remarkably uniform in angiosperms.

4. Microsporogenesis : Diploid cell of micro-spore mother cell divided by meiosis & make 4 haploid spores at the end of the process (i.e., tetrad). Each tetrad becomes the microspore . = Male gametophyte . ❹

5. Microspore - morphology ❺ The pollen grains or microspores are the male reproductive bodies of a flower, and are contained in the pollen sac or micro sporangium. They are very minute in size, and are like particles of dust. It is commonly globular in outline, though several other shapes are also found. The diameter is mostly 25 – 50 µm .

6. ❻ There is a highly resistant wall on the outside and cellular contents inside. Pollen grain’s cytoplasm is rich in starch and unsaturated oils, it protect the chromosomes from radiation damage.

7. Each pollen grain consists of a single microscopic cell, possessing two coats : a rough outer wall of cutin called the exine and an inner thin wall of cellulose and pectin substances called the intine . ❼

8. ❽ According to Erdtman the external surface of pollen is characterised by various markings such as pilate , reticulate, striate, ornate, crasssisexinous, tenuisexinous, subsaccate, tegillate, etc.

9. ❾ The exine possesses one or more thin places known germ pores .

10. Pollen wall features ❿ pollen wall is also known as sporoderm , which have highly resistant on the outside of the polllen grains. Normally the pollen wall possesses two layer : the exine and the intine . The exine is made of highly resistant fatty substance called sporopollenin ( Zelisch , 1932).

11. ⓫ The outer layer is not even degraded by any physical or biological agents like high temperature, strong acid or alkali, any enzyme, etc. Because of the sporopollenin, pollen grains are well preserved as microfossils. At places, the exine possesses proteins for enzymatic and compatibility reactions.

12. ⓬ The intine is thin and mainly consist of pectin & cellulose, so it is pecto -cellulosic in nature. ֎ The intine can be destroyed during acetolysis . At places, the intine contains enzymatic proteins ( Knox and Heslop - Harrison,1971).

13. ⓭ The tectum provides a characteristic sculpturing or designs over the surface of pollen grains, e.g., ridges, tubercles, spines, reticulations.

14. ⓮ In isect pollinated pollen grains the exine is spiny as well as covered by a yellowish, viscous sticky and oily layer called pollenkit . Pollenkit is made up of lipid, carotenoids and some proteins.

15. ⓯ At certain places the exine is thin or absent & the areas may have thickened intine or deposition of callose . It’s called germ pores (if rounded) or germinal furrows (if elongated).

16. ⓰ Pollen grains are generally tricolpate (with three germ pores) in dicots and monocolpate (with single germinal furrow) in monocots.

17. References ⓱ 1)A text book of Botany – Embryology of Angiosperms. ♣ Author :Sanjay kumar singh ♣ Edition : 1971 (First Edition) 2)College Botany ( Volume two ). ♣ Author : S. Sundara Rajan . ♣ Edition :2015 3) WWW.Slideshare.net

18. ⓲