Question

Can you pleasee answer these questions:

1. What are the mechanisms of tolerance used by resistant or engineered plants. Give an example.

2. What is the pesticidal crystal protein Bt.

3. What is Bt toxin mode of action, explain in detail.

Thank you in advance, I would appreciate it a lot, and I am grateful forever!!!

Answer 1

1. Tolerance is defined as the ability of the plants to mitigate the negative effects caused by various biotic factors like a pest, fungi, virus attack, and abiotic factors like heat, salt, drought, etc.

For example- Heat stress due to increased temperature affects plant growth and development. The adverse effect of heat stress can be mitigated by developing crop plants with improved thermotolerance using various genetic approaches. Heat stress affects plant growth at different developmental stages like, during seed germination, high temperature may slow down or completely inhibit termination depending on plant species and intensity of the stress. High temperatures may affect photosynthesis, respiration, membrane stability, and also levels of primary and secondary metabolites. Enhanced production of a variety of heat shock proteins and other stress-related proteins and production of reactive oxygen species (ROS) constitute major plant response to heat stress. To cope with these plants uses various mechanisms like maintenance of membrane stability, production of antioxidants, scavenging ROS, accumulation of compatible solutes, induction of mitogen-activated protein kinase(MAPK), and calcium-dependent protein kinase (CDPK).

Heat shock proteins(Hsps) and antioxidant enzymes are important in encountering the heat stress in plants.

2. Pesticidal crystal protein (CRY)are endotoxins produced by Bacillus thuringiensis and form crystal structures. These toxins have specific activities against insects, moths, etc. When insects ingest toxin crystals, the alkaline pH of their digestive tract denatures the insoluble crystals and making them soluble and thus amenable to being cut by the proteases found in the insect gut which liberate the Cry toxin from the crystal. The Cry toxin is then inserted into the gut cell membrane of the insect, paralyzing the digestive tract and forming a pore. The insect stops eating and starves to death.

The Cry protein has three domains I, II, and III. The arginine residues present in the first domain responsible for creating a pore in the gut of the insect.

3. Even though the toxin does not kill the insect immediately, and treated plant plants will not be damaged as the insect stops feeding on them. The mechanism is as follows-

Insect eats Bt crystal and spores. The toxin binds to the specific receptor in the gut of the insect and the insect stops feeding. The crystals cause the gut wall to break down allowing the spores to enter the body. The insect dies as spores proliferate in the body.

Bt action is very specific. Different strains of Bt are specific to different receptors in the insect gut wall.

The above image is taken from a research paper that shows the mechanism of action by Bt toxins in the insects. There are various genetically modified plants that express the Bt genes like rice, corn, potato, cotton.