Effect ofPseudomonas syringaepv.tagetisInfection on Sunflower Leaf Photosynthetic and Ascorbic Acid Relations

Abstract

Studies were conducted to assess the role of photosynthesis and dark respiration in maintaining daily foliar ascorbate levels. Seven‐day‐old sunflower plants were inoculated with a tagetitoxin‐producing or nontoxigenic (control) strain of Pseudomonas syringae pv. tagetis. After 10 d, tagetitoxin‐affected leaves were so severely chlorotic that they were white. Tagetitoxin‐affected leaves had 99% less chlorophyll per unit fresh mass than control plant leaves. Electron microscopy of sections of chlorotic (toxin‐affected) sunflower leaf cells revealed that leaf palisade and spongy parenchyma cells possessed few chloroplasts and that those present contained disorganized thylakoids and grana and no apparent starch grains. Rates of photosynthetic CO2 assimilation per unit leaf area in toxin‐affected leaves were significantly lower than in control leaves. Compared to leaves of the control plants, the leaves of toxin‐affected plants had significantly less free glucose, and less glucose was incorporated into sucros...