How do sweet potatoes protect themselves?
By Chelsie Vandaveer
October 24, 2001
killerPlants Tendrils: ~~1~~2~~3~~4~~5~~
Suggested Reading—>Click here.
Sweet potatoes, like most other plants, protect themselves with chemicals. The primary anti-herbivory device in a sweet potato plant is a trypsin inhibitor. This inhibitor prevents the enzyme from functioning and without active trypsin, proteins are not digested. A caterpillar chowing down on a sweet potato leaf is not getting all the nutrition in the leaf. The trypsin inhibitor is preventing the insect from benefiting from the proteins. Without the proteins, the insect will not develop correctly and may never be able to reproduce. Eventually the insect will die.
Cellulose and chitin [kite' in] are two ubiquitous polymers, long repetitive chain chemicals. They are built of chemical rings closely associated to sugars. The rings are connected with an oxygen atom in a configuration called a beta 1-4 bond. Most people do not really notice these polymers or at least do not think of them in terms of chemistry.
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Cellulose is manufactured by plants and chitin by fungi, insects, and crustaceans. Both materials provide support and protection. A block of wood, mostly cellulose, and an insect's exoskeleton, mostly chitin, appear to be different things, but chemically the two are very closely related.
When sweet potatoes are attacked by chewing insects, they increase their chemical warfare. The attacked leaves produce greater amounts of the trypsin inhibitor. More of the inhibitor encourages the insect to look elsewhere for food.
The plants also start manufacturing chitinase. Chitinase is an enzyme that breaks the chemical (beta 1-4) bonds holding the links of the chain together. Without that bond, chitin is just a bunch of chemical rings called glucosamines.
Chitinase probably does not have much effect on the exoskeleton of insects, but it does benefit the sweet potato plant. Chewed leaves are wounded leaves. Any open wound is an entry point for fungal spores and bacteria. The chitinase prevents fungi from developing and invading the plant tissues. The fungus cannot build the chitin cell walls, the cells cannot function without walls. The chitinase also damages the cell wall of bacteria causing the bacteria to burst. Even though chitin and cellulose are almost identical, the chitinase is specific to fungi and bacteria and does no damage to the sweet potato's cells.
The Crab Street Journal : Kidzone has a brief, clearly written explanation of chitin and drawings of chitin and cellulose. To learn more about chitin and cellulose, click on the link:
http://www.crabstreetjournal.com/kidzone/StudyIt/Calcium/Chitin/
killerPlants Tendrils: ~~1~~2~~3~~4~~5~~
Suggested Reading:
What twelve plants supply most of the food...? Plants that Changed History - Aug 21, 2001
Why should potatoes be stored in the dark? Herbal Folklore - October 8, 2001
What slave food is more valuable than Inca gold? Plants that Changed History - October 9, 2001
What is a hairy potato? Renfield's Garden - October 10, 2001
What is so odd about the color of the petunia? Weird Plants - October 11, 2001
What was the great Potato War? What's in a Name? - October 12, 2001
What common food plant was used for hunting? Herbal Folklore - October 15, 2001
What toxic plant feeds 500 million people? Plants that Changed History - October 16, 2001
What plant was blamed for the deaths of children? Herbal Folklore - October 22, 2001
What Ice Age morning glory feeds millions of people? Plants that Changed History - Oct 23, 2001
Of witches, werewolves, and UFOs Herbal Folklore - October 29, 2001
Why is the banana like a mule? Weird Plants - November 29, 2001
What canna is edible? Weird Plants - September 19, 2002
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