VIEW ARTICLE

Techniques

Phloem-Limited Prokaryotes in Sieve Elements Isolated by Enzyme Treatment of Diseased Plant Tissues. I. -M. Lee, Department of Botany, University of Maryland, College Park 20742; R. E. Davis, Plant Virology Laboratory, ARS, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 73:1540-1543. Accepted for publication 31 May 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-1540.

Sieve elements of periwinkle plants (Catharanthus roseus L.) infected with Spiroplasma citri, mycoplasmalike organisms (MLO), or clover club leaf (CCL) agent were separated from other cell types by partial digestion of plant tissue with macerating enzymes and viewed by dark-field microscopy. Sieve elements separated from plants infected with S. citri contained minute helical, motile filamentous microorganisms typical of spiroplasmas. In sieve elements from plants infected with the MLO associated with pear decline, aster yellows, or tomato big bud disease, no helical spiroplasmas were seen, but pleomorphic microorganisms with predominantly filamentous, usually branched, form were present. Sieve elements from CCL-diseased periwinkle contained numerous slender rod-shaped bacteria. Morphology of these phloem-limited prokaryotes could be studied further when the microorganisms were released from the isolated sieve elements by slight osmotic shock. Sieve elements separated from healthy periwinkle plants contained a few organelles but no structures resembling spiroplasmas, MLO, or phloem-limited bacteria. The method offers a means for studying the morphology and other properties of viable cells of uncultivated as well as cultivable pathogens in sieve elements.