Ontogenetic Study of Urease in Jack Beans, Canavalia ensiformis (L.) DC.

Abstract

Urease occurs in all parts of the jack bean (Canavalia ensiformis [L.] DC.) plant. The floral parts contain 1/6-1/10 as much urease as the vegetative shoot apices and green leaves. The embryo and the seedling, excluding cotyledons containing about 1% of the total units, showed a constant amount of urease up to 10 days following the initiation of germination. Shoot apices contained 1-2 units of urease per 25 apices for a period of about 7 weeks and possibly thereafter. Studies on cotyledons of germinating seedlings showed the existence of three phases in urease activity. For the first few days, the urease content remained constant, and the specific activity increased somewhat; the second phase was characterized by a declining urease content but increasing specific activity; and in the last phase both the amount of urease and its specific activity declined. Dark-grown seedlings showed the same pattern except that the first phase was somewhat prolonged. The peak of proteolytic activity of the cotyledonary extracts was observed in the first phase around 6-7 days after germination began. Possibly, changes in the specific activity of urease may be a reflection of the prevailing proteolytic activity. Studies on cotyledons of maturing seeds showed that the increase in urease units per gram of dry wt increased with increasing dry wt of the cotyledons, and the rate of synthesis was very high in the 6-7 week post-fertilization period. A difference of 7-10 days in the age of the seeds from pods harvested in this period was reflected in the urease content. In the last few weeks of maturation of seeds, however, the rate of urease synthesis was slow, and at this stage the differences in age did not show up in the urease measurements. Small-sized fully mature seeds may possess double the specific activity of the large-sized seeds on a per-gramprotein basis. Probably, in the later part of seed maturation proteins other than urease are synthesized in greater amounts in the seeds attaining a large size than in the small ones.