Pathogenesis Mechanisms, Enzymes, Toxins & Virulence Factors

• Mode of Action of Phaseolotoxin: Phaseolotoxin is a non-host-specific chlorosis-inducing phytotoxin produced by Pseudomonas syringae pv. phaseolicola (halo blight of bean):
• Inhibition of OCTase: Inside plant tissues, phaseolotoxin is cleaved into octicidin (phosphosulfamylornithine), which irreversibly inhibits the urea cycle enzyme ornithine carbamoyltransferase (OCTase).
• Accumulation of Ornithine: Blocking OCTase prevents the conversion of ornithine and carbamoyl phosphate into citrulline, resulting in a dramatic buildup of the amino acid ornithine and an arginine deficiency (Statement II is true).
• Disruption of Apical Dominance: The systemic physiological shock and hormonal imbalance cause chlorotic halos, stunted bushy growth, and loss of apical dominance in affected bean shoots (Statement I is true).
• Conclusion: Both Statement (I) and Statement (II) are true (Option 1).

Correct option: (1) Both Statement (I) and Statement (II) are true.