Effect of Nitrate on Peroxisome Ultrastructure and Catalase Activity in Nodules ofLupinus albusL. cv. Multolupa

Abstract

This paper reports on an ultrastructural study of peroxisomes in infected nodule cells of Lupinus albus L cv Multolupa plants grown with and without nitrate (in short-term experiments) Cytochemical localization of catalase and peroxidase was performed applying the diamino-benzidine (DAB) technique in these tissues The infected cells presented a mean of seven peroxisomes, the maximum being 16 in some cells Peroxisome shapes proved to be fairly round or egg-shaped, with maximum and minimum diameter means of 0-35 and 0 18μm, respectively They were preferentially positioned on the cell periphery. The intense osmiophilic staining obtained by applying the DAB technique indicates a strong catalase activity reaction in these microbodies The addition of nitrate (20 mol m⁻³) to the growing plants exerted a negative effect on nitrogenase activity, which diminished by 31 6% after 5 d of treatment Severe alterations in the ultrastructure of microbodies, bacteroids, and penbacteroidal membranes were observed Cytochemical data show a reduction in catalase localization in peroxisomes and an increased peroxidase activity in the cytosol Finally, leghaemoglobin (Lb) localization was studied in nitrate-grown plants, confirming our previous observation of a decrease in this protein Discussion focuses on the involvement of these results in tissue senescence of the nodules following nitrate application