01 Reproduction in Lower and Higher Plants - part 08 - Development of Endosperm

01 Reproduction in Lower and Higher Plants - part 08 - Development of Endosperm


Development of Endosperm : 
  • The triploid primary endosperm nucleus repeatedly divides, mitotically to form nutritive tissue, called endosperm. 
  • In post-fertilization changes within the ovule, the embryo and endosperm are seen to develop simultaneously. 
  • The other cells of embryo sac disorganized sooner or later. 
  • The formation of triploid endosperm nucleus triggers cell division which leads to the formation of endosperm.
Types of endosperms [on the basis of mode of development] :
  1. Nuclear type
  2. Cellular type
  3. Helobial type 
1. Nuclear Type : 
  • It is the most common type found in 161angiospermic families. 
  • Here, the primary endosperm nucleus repeatedly dividesmitotically without wall formation to produce large number of free nuclei. 
  • A big central vacuole appears in the centre of cell pushing the nuclei towards the periphery.
  • Later, walls develop between the nuclei, hence multicellular endosperm is formed. 
  • But in several cases cell wall formation remains incomplete. e.g. wheat, sunflower and coconut.
  • Coconut has multicellular endosperm in the outer part and free nuclear as well as vacuolated endosperm in the centre. 
2. Cellular Type : 
  • In some plants, division of triploid primary endospermic nucleus is immediately followed by wall formation. 
  • So that the endosperm is cellular right from the beginning. 
  • It is mostly observed in 72 families of dicots as in members - Balsam, Petunia, Adoxa, etc.
3.Helobial Type : 
  • It occurs in the order Helobiales of monocotyledons. 
  • In this case, first divison of primary endosperm nucleus is followed by a transverse wall, which divides the cell unequally. 
  • The smaller cell is called chalazal cell and larger cell is themicropylar cell. 
  • Then the nuclei in each cell divide by free nuclear divisions and then walls develop between nuclei in micropylar chamber. 
  • It is intermediate between cellular and nuclear type endosperm e.g. Asphodelus.
Mosaic Endosperm :
  • Endosperm containing tissues of two different types is called mosaic endosperm. 
  • In plants like corn the endosperm contains patches of two different colours. 
  • It forms a sort of mosaic pattern.

Comments

Post a Comment

Popular posts from this blog

6. Biomolecules - part 01 - Carbohydrates

Image
  6. Biomolecules - part 01 - Carbohydrates Introduction : Our planet is having a wide diversity of living organisms that are classified as - unicellular  (consisting of a single cell; including bacteria and yeast) or  multicellular  having many cells (e.g. plants and animals).  living organisms have cell as the basic structural and functional unit.  The cells have protoplasm containing numerous chemical molecules, the biomolecules. Biochemistry  : Biochemistry is  biological chemistry  that provides us the idea of the chemistry of living organisms and molecular basis for changes taking place in plants, animals and microbial cells.  It develops the foundation or understanding  all biological processes  and communication within and between cells as well as chemical basis of inheritance and diseases in animals and plants. Chemical analysis of all living organisms indicates presence of the most common elements like  carbon, h...
Read more

6. Biomolecules - part 02 - Lipids

Image
  6. Biomolecules - part 02 - Lipids B. Lipids : These are group of substances with greasy consistency with  long hydrocarbon chain containing carbon, hydrogen and oxygen. In lipids, hydrogen to oxygen ratio is  greater than 2:1  (in carbohydrates it is always 2:1). Lipid is a broader term used for fatty acids and their derivatives.  They are soluble in organic solvents (non-polar solvents).  Fatty acids are organic acids which are composed of hydrocarbon chain  ending in carboxyl group (-COOH).  They can be  saturated fatty acids  with no double bonds between the carbon atoms of the hydrocarbon chain.  Palmitic and stearic acids  found in all animal and plant fats are examples of saturated fatty acids. Unsaturated Fatty Acids  are with one or more double bonds between the carbon atoms of the hydrocarbon chain.  Oleic acid  found in nearly all fats and  linoleic acid  found in many seed oils are example...
Read more

6. Biomolecules - part 05 - Enzymes

Image
  6. Biomolecules - part 05 - Enzymes Enzymes : Thousands of different chemical reactions take place automatically at a given time in a tiny living cell. The reactions take place at the body temperature.  If these enzymes were not present in the cell, either the reactions would not occur or if they occur they would occur at a  very very slow rate . Know the scientists : German chemist  Edward Buchner  discovered enzymes by accident.  Buchner discovered that living cells were not necessary but that  yeast  extract could bring about fermentation.  He then coined the term Enzyme (Gk. En = in, zyma = yeast i.e. in yeast). This term is now commonly used for all biocatalysts. Each enzyme catalyzes a small number of reactions, specifically perhaps only one. Substrate :  The substance upon which an enzyme acts is termed as the substrate.  Endo-enzymes :  The enzymes which act within the cell in which they are synthesizedare known as en...
Read more