Wall-Less Prokaryotes of Plants

Abstract

The first mention of an association between wall-less prokaryotes and plants was published by Doi et al (53) in Japanese in 1967 in a work entitled, Mycoplasma or PLT:group-like microorganisms found in the phloem ele­ ments of plants infected with mulberry dwarf, potato witches' broom, aster yellows, or paulownia witches' broom.J Similar microorganisms had been seen at about the same time in rice infected with yellow dwarf disease (121). When plants containing the newly discovered microorganisms were given tetracycline treatments, symptom remission occurred as long as the antibiotic application lasted, and the observed microorganisms disappeared temporarily from the phloem of these plants (76, 121). Penicillin treatments had no effect. These results have been amply confirmed (108, 153). Because mycoplasmas were known to be sensitive to tetracycline but not penicillin, whereas the PLT agents were affected by both of these antibiotics (7, 75; see also 50), the microorganisms found by the Japanese workers were considered mycoplasma­ like and not chlamydiae-like and have been called mycoplasma-like organisms (MLOs).2 Similar MLOs have since been found to be associated with more than 100 diseases in plants (103). Mycoplasmas and permanent (irreversible) L-variants (161) of bacteria have