The synthesis and accumulation of reserve proteins in seeds require a large supply of reduced nitrogen. Generally, the transport of nitrogen from other parts of the plant involves a few specific compounds, the nature of which depends on the species and growth conditions. The fixation of N 2 by Rhizobium in symbiotic association with soybeans, cultivated in the absence of mineral nitrogen, leads to the incorporation of atmospheric nitrogen in ureides (allantoin and allantoic acid). These compounds form the main nitrogenous components found in the transport stream of nodulated soybeans. On the other hand, soybeans grown in the absence of Rhizobium and with NO3 nitrogen source, contain asparagine as the predominant as transport form of nitrogen. The accumulation of protein in the fruits of such plants will depend, therefore, on their ability to utilize these compounds for the synthesis of amino acids. The objectives of the present study were: first, demonstrate the presence of the enzymes presumed to be involved in the utilization of these compounds (i.e. allantoinase and asparaginase). Second, determine the effect of this drastic change in the transport of nitrogen from mainly ureides (nodulated plants) to asparagine (non-nodulated plants) on the appearance of these enzymes during fruit ontogeny specifically in the pods, cotyledons and teguments Asparaginase was assayed by a radiometric method, involving the separation of the product by chromatograpy. Allantoin was assayed by measuring the formation of the product by a differential method. Activity of both enzymes was found in all tissues of the fruit, except in the pod where no asparaginase activity was detected. Both allantoinase and asparaginase presented low activities in the tegument, producing only a small peak near the and of seed development, both for modulated and non-nodulated plants, In pods and cotyledons higher levels of allantoinase were found, especially during the phase of most active protein accumulation. It is noteworthy that the activity in the cotyledon was well above the rate of nitrogen accumulation. Asparaginase activity was also higher over this period of cotyledon development, although the level of activity was lower, being similar to the rate of nitrogen accumulation. A comparison of the activity patterns nodulated and non-nodulated plants reveals little difference except for a tendency for allantoinase to remain high (pod and cotyledons) over a longer period in nodulated plants. This occurred in spite of a shorter maturation period for fruits of nodulated plants. On the other, asparaginase (cotyledon) maintained high activity over a longer period in the non-nodulated plants. The possible significance of this effect was discussed in terms of the supply of ureides and asparagine to the fruits. As to the levels of ureides and amino acids in the various fruits tissues, the data show that the ureides, despite their association with nodule activity, were present in levels above that expected for non-nodulated plants. Of the fruit only the pods presented a high level of ureides (200 x) in nodulated plants compared to non-nodulated since low but similar levels were found ín the cotyledons and teguments of both plant types. It is notworthy that the level of free amino acids was generally the inverse of that for ureides, since higher levels were found in fruits of non-nodulated plants.
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