Correct option is B
Phenylalanine ammonia-lyase (PAL) is a crucial enzyme in the phenylpropanoid pathway, which is responsible for producing lignins and other secondary metabolites, including caffeine. When PAL activity is lost due to a mutation:
Lignin Biosynthesis: PAL catalyzes the conversion of phenylalanine to cinnamic acid, which is an essential precursor for the biosynthesis of lignin in the cell walls of plants. Lignins are polymers that provide structural support and rigidity to plant cell walls, particularly in vascular tissues.
Impact of PAL Mutation: A loss of PAL function would lead to decreased production of lignins, as the pathway to synthesizing lignin is disrupted. This results in weaker, less rigid cell walls.
Caffeine Production: While PAL is involved in the synthesis of caffeine, the more direct impact of a loss-of-function mutation in PAL would be on lignin biosynthesis because lignin formation is a key role of the phenylpropanoid pathway, and it has a more prominent structural function in plant cells compared to caffeine.
Hence, the most likely consequence of a loss of function mutation in PAL is a decrease in lignins in the cell walls, leading to a reduced structural integrity in the plant.
Additional Information:
- (a) Increased levels of caffeine: Incorrect — PAL mutation does not lead to an increase in caffeine production, and in fact, caffeine production would likely decrease due to the disruption of the phenylpropanoid pathway.
- (c) Increased lignins in cell walls: Incorrect — PAL loss would result in a decrease in lignin synthesis, not an increase.
- (d) Decreased levels of caffeine: Partially correct — While caffeine levels may decrease, the more significant effect of a PAL mutation is the reduction in lignin production in the cell walls.
