Effect of ozone on sulfhydryl groups of ribosomes in pinto bean leaves relationship with ribosome dissociation

Abstract

Summary Chloroplast ribosomes and cytoplasmic ribosomes were isolated from the primary leaves of control and ozone-treated pinto bean plants. On the basis of a unit of ribosomal protein, the levels of ribosomal sulfhydryl groups and their kinetic responses to 5,5′-dithiobis(2-nitrobenzoic acid) were assayed by Ellman's procedure in the presence of sodium dodecyl sulfate. The sedimentation profile of ribosomes was determined by sucrose density gradient. Ozone, 0.30 ppm for 20 to 50 min, decrease the levels of sulfhydryl groups in chloroplast ribosomes far more than in cytoplasmic ribosomes. Both ozone and p-chloromercuribenzoate directly dissociate polysomes and monosomes of isolated chloroplast ribosomes into smaller particles in vitro. The levels of sulfhydryl groups which react with 5,5′-dithiobis(2-nitrobenzoic acid) are higher in chloroplast ribosomes than in cytoplasmic ribosomes. The reaction with 5,5′-dithiobis(2-nitrobenzoic acid) of this higher level of sulfhydryl groups in chloroplast ribosomes goes to completion much faster than the reaction of the lower level of sulfhydryl groups in cytoplasmic ribosomes. With these data, the mechanism which is directly involved in the previous finding, ozone's preferential influence on the disintegration of chloroplast ribosomes in bean leaves is discussed.