Correct option is D
Ans. (d) Opines are a source of nitrogen for Agrobacterium cells.
Opines are compounds produced by the plant cells that have been infected by Agrobacterium tumefaciens. These compounds are a result of the transfer of T-DNA from Agrobacterium into the plant's genome. The plant then synthesizes opines, which are used by Agrobacterium as a source of carbon and nitrogen, providing a nutrient-rich environment for the bacteria to grow and multiply. This unique interaction is a key feature of the Agrobacterium-plant relationship.
Information Booster
Opines: Opines, such as nopaline and octopine, are produced by the transformed plant cells after the integration of T-DNA from Agrobacterium. These compounds are not typical of normal plant metabolism and are specifically produced as part of the bacterial infection process. Agrobacterium consumes these opines as a carbon and nitrogen source, aiding its survival and proliferation.
T-DNA integration and plant interaction: The integration of T-DNA into the plant genome is a critical step in the Agrobacterium infection process. The T-DNA carries genes that lead to the production of opines and promote tumor formation (crown gall). This integration is not limited to homologous recombination alone but may also involve other mechanisms.
Additional Information
Option (a): None of the virulence genes of Agrobacterium tumefaciens are expressed constitutively is incorrect. The virulence genes in Agrobacterium are often expressed in response to signals from the plant host. They are not constitutively expressed but are triggered by specific conditions, such as the presence of phenolic compounds released by the plant.
Option (b): Integration of T-DNA with the nuclear genome of plant cells occurs only by homologous recombination is incorrect. While homologous recombination is one mechanism for T-DNA integration, Agrobacterium-mediated T-DNA integration also involves illegitimate recombination and other processes, not just homologous recombination.
Option (c): Host plant genes do not play any role in Agrobacterium-mediated transfer of T-DNA into plant cells is incorrect. The plant's cellular machinery plays an essential role in the process of T-DNA transfer and integration, especially in recognizing and interacting with the Agrobacterium and mediating the transfer process.
