Physiological and biochemical disruptions in Phaseolus vulgaris L. induced by Pseudomonas syringae pv. phaseolicola infection

Abstract

This study examines the physiological and biochemical responses of Phaseolus vulgaris L. cv. Prince to infection by Pseudomonas syringae pv. phaseolicola Race 1 under controlled environmental conditions. Plants were inoculated with a bacterial suspension of 6 × 10⁸ cfu cm⁻³ applied to unifoliate leaves, and disease progression was assessed via microscopic examination and photography. Photosynthetic performance, chlorophyll and carotenoid concentrations, protein content, carbon assimilation, and carbohydrate metabolism were analyzed to elucidate the pathogen's impact on plant physiology. Results revealed the onset of infection symptoms, including necrosis and chlorosis, within 36 h post-inoculation, with a progressive decline in plant health, particularly in unifoliate and trifoliate leaves. Photosynthetic efficiency, measured through oxygen evolution, was significantly impaired in infected tissues, alongside a marked increase in dark respiration rates. Chlorophyll a and b, as well as carotenoid concentrations, were significantly reduced in inoculated areas. Soluble protein levels and carbon translocation, traced via ¹⁴CO₂ labeling, were also adversely affected, with inoculated plants displaying altered carbon partitioning and decreased total soluble carbohydrates, particularly near infection sites. Inoculation reduced relative growth rates and dry mass accumulation, most notably in plants with inoculated unifoliate leaves. These findings provide comprehensive insights into the deleterious effects of bacterial infection on both the structural and functional aspects of plant physiology, demonstrating significant impairments in photosynthetic capacity, protein content, and carbohydrate metabolism. This study offers a deeper understanding of the complex plant-pathogen interactions, highlighting the multifaceted impacts of P. syringae on plant growth and health.