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Inhibition of Chlorophyll Synthesis by Pseudomonas glycinea¹

Soybean (Glycine max L.) cotyledons treated with toxin extracted from culture filtrates of Pseudomonas glycinea formed significantly less chlorophyll and aminolevulinic acid (ALA), a precursor of chlorophyll, than control cotyledons. The toxin induced a comparable reduction in the percentage of ALA and chlorophyll, which suggests that chlorosis produced by P. glycinea toxin results from an inhibition of some step at, or prior to, ALA synthesis.

Toxemia-affected trifoliate leaves of infected soybean plants were chlorotic and smaller than similar leaves of control plants. The toxin-affected leaves did not differ significantly from control leaves in percentage of pheophytin, a chlorophyll degradation product, nor in the chlorophyll a:b ratio. Thus, chlorosis in toxemia-affected leaves appears to be due to an inhibition of chlorophyll synthesis rather than an accelerated rate of chlorophyll degradation.

Key Words: Glycine max L. • Bacterial blight • Systemic toxemia • Pigment analysis • Pheophytin

² Former graduate assistant (now research pathologist, USDA-SEA-AR, Walster Hall, North Dakota State Univ., Fargo, ND 58105); plant pathologist, USDA-SEA-ARa, nd professor, Dep. of Botany and Plant Pathology, Iowa State Unix., Ames, IA50011.

Received for publication August 14, 1978.