Effect of Nitrate on Peroxisome Ultrastructure and Catalase Activity in Nodules of<i>Lupinus albus</i>L. cv. Multolupa

Abstract

This paper reports on an ultrastructural study of peroxisomes in infected nodule cells of &lt;it&gt;Lupinus albus&lt;/it&gt; 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