Occurrence of Polyploidy in Plants Examples

A survey of the chromosome number in the plant kingdom has shown that polyploidy is a natural occurrence in flowering plants. The occurrence of polyploidy in plants examples are the most valuable crops like oats, cotton, wheat, potato, tobacco, banana, etc are polyploids.

It has been shown that more than half of the flowering plants have polyploids of natural origin. Eg. Solanum nigrum has 12 chromosomes. S. muricitium has 24 chromosomes, and S. tuberosum has 48. Thus, different species of Solanum have multiples of 12 chromosomes. 

Occurrence of Polyploidy in Plants Examples

Polyploidy may arise due to irregularities in cell division, ie, during mitosis and meiosis. The irregularities in mitosis are seen in the vegetative tissue. It is called somatic doubling. Failure to form a cell wall after the division of the nucleus leads to the doubling of chromosomes. If this takes place at the first division of the embryo, the whole plant will be a polyploid. 

Sometimes, it only occurs in some particular regions. Then only a portion of the plant will be polyploid, and the remaining portion will have diploid cells. A mixture of genetically diverse tissues on the same shoot or organ is called a chimaera. Chimera tissues are observed in many plants. 

When the plants are injured, the wounds are readily healed in the course of rapid cell division. During this fact, cell division to heal the wound, also, irregularities may step in, ie, cells may be formed without walls in between. Sometimes the spindle mechanism may fail to separate the daughter chromosomes to the opposite poles. This also results in chromosome doubling. 

Polyploidy may arise during meiosis as well. Sometimes, during meiosis II, fusion of the spindles may take place. That will result in the production of diploid gametes. Sometimes, meiosis may not take place during gamete formation, resulting in diploid gametes. Very rarely, a triploid may also be produced by dispermy- a single haploid egg getting fertilized by two haploid male gametes. 

Effects of Polyploidy

Polyploidy in nature is associated with interspecific or intergenetic hybridization. While polyploidy results in meristematic cells that are larger in size. However, the formation of larger organs or tissues depends on cell elongation and the number of eventual cells produced. 

• The increase in individual cell size increases the water content in the cell, which lowers the osmotic tension. 
• Polyploidy causes a slower growth rate in some plants. Eg. Some autotetraploids usually flower later. 
• Some polyploids have reduced branching. 
• In grass, some plants suffer reduced basal shoots, which causes a reduced size of the plant. Eg. Stipa lepida. 
• Some plants show increased thickness in their leaves and appendages. 
• Reduction in pollen grains and seed fertility is another effect of some polyploidy. 
• Many autopolyploids end up being sterile. 
• Polyploidy in self-incompatible plants causes incompatibility relationships. The presence of self-incompatibility in diploids is likely to be increased when they become an autotetraploid. 
• Autopolyploids are difficult to cross with the F1 generation, causing an interspecific barrier.

References

• Agarwal, P. V. |. V. (2004). Cell biology, Genetics, Molecular Biology, Evolution, and Ecology: Evolution and Ecology. S. Chand Publishing.
• https://courses.botany.wisc.edu/botany_940/15Stebbins/Chapters/Chapt8.pdf

Additional Reading

• Polyploidy and Evolution
• Types of Polyploidy
• Artificial Induction Of Polyploidy