Catalase and sulfur in the rice rhizosphere: An ultrastructural histochemical demonstration of a symbiotic relationship.

An ultrastructural study has been made of a symbiotic association between a sulfur bacterium and the roots of the rice plant (Oryza saliva L.). This association is proposed to have useful economic consequences in ameliorating hydrogen sulfide toxicity and associated Akiochi or Straighthead disease in lowland rice cultivation. The presence of catalase (E.C. 1.11.1.6) in rice roots and in some rhizosphere bacteria has been demonstrated in ultrathin sections of field-grown rice using a catalasespecific medium. Catalase was detected in capsules surrounding the catalase-negative S-bacteria. These capsules were of a novel fibrillar structure. Two sizes of inclusion bodies were present in these large bacteria. The disappearance of the smaller inclusions during carbon disulfide treatment suggests that they are the sulfur granules. The name "thiosome" is proposed for these membrane-bound structures.