Morphometric procedures were used to examine peroxisome number and di-stribution in pea (<em>Pisum sativum</em> L.) root nodules under NaCl (50 mM) or HgCl<sub>2</sub> (7.3 µM) treatment. Peroxisomes were visualized cytochemically in meristem, invasion zone and prefixing zone of pea root nodules by catalase (EC 1.11.1.6) activity. The observations using light and electron microscopy revealed that the peroxisomes were predominantly spherical in shape and showed catalase activity. In nitrogen fixation zone, catalase active peroxisomes were observed occasionally. Bacteroids of nitrogen fixing zone showed enhanced cata-lase activity probably as a response to higher level of oxidative stress. Fluorescence microscopy investigations revealed enhanced level of (homo)glutathione in prefixing and nitrogen-fixing zone of NaCl- and Hg<sup>2+</sup>treated nodules, which served as an indicator of antioxidative response. Morphometric measurements revealed that during differentiation of meristematic cells into central tissue (bacteroidal tissue) cells an increase in peroxisome number was observed in unstressed nodules. Peroxisomes located in meristem, invasion zone and prefixing zone of NaCl- and Hg<sup>2+</sup>-treated nodules outnumbered that in control nodules. A substantial enlargement of peroxisome profiles was detected in NaCl- and Hg<sup>2+</sup>treated nodules. Peroxisome divisions observed in meristematic and infection thread penetration zone were responsible for an increase in peroxisome number.
Development of the nitrogen-fixing and protein-synthesizing apparatus of bacteroids in pea root nodules