Effects of univalent cations on the formation of nitrate reductase and nitrite reductase in rice seedlings

An investigation was made to determine the effects of univalentcations as activators on the formation of nitrate reductaseand nitrite reductase in rice seedlings. K⁺ functioned moreeffectively as a univalent cation activator than did other univalentcations examined. Substitution of Rb⁺ for K⁺ resulted in stimulationof nitrate reductase formation at about half the rate obtainedwith K⁺. There was no effect on nitrite reductase formation.Na⁺ could be partially substituted for K⁺ in the formation ofboth enzymes. NH₄⁺ slightly inhibited formation of the enzymes.In the absence of univalent cations, enzyme formation proceededat a slower rate during the initial 15-hr period, but thereafterproceeded at a higher rate. This delayed formation was not observedin the presence of K⁺. Results from inhibitor experiments suggestthat K⁺ stimulates the formation of nitrate reductase and nitritereductase. In conclusion, when nitrate nitrogen is supplied to rice plantsutilization of the nitrogen may be accelerated by increasedformation of enzymes involved in nitrate assimilation in thepresence of K⁺. (Received February 21, 1969; )     

Flavine nucleotide nitrate reductase from broad bean leaves

Hydrosulfite-reduced FMN served as an electron donor for nitratereductase purified from broad bean leaves. FMN was successfullyreplaced with BV. The flavine nucleotide nitrate reductase hadits pH optima at about 7.8 with phosphate buffer and at about7.4 with Tris-HCl buffer. The Km's for nitrate and FMN were3.7 ? 10^–4 M and 3.7 ? 10^–5 M, respectively. NADH₂: nitrate reductase activity was completely inhibited by0.1 mM p-CMB, whereas FMNH₂: nitrate reductase activity wasnot. Inhibited activity was restored by the addition of cysteine.A sulfhydryl enzyme is involved in the NADH₂: nitrate reductasesystem but not in the FMNH₂ : nitrate reductase system. NADH₂and FMNH₂ probably feed electrons into the electron transportchain at different sites. The nitrate reductase preparationhad an NADH₂-specific diaphorase activity which was almost completelyinhibited by 0.1 mM p-CMB. The NADH₂-specific diaphorase mayform the sulfhydryl enzyme which mediates electron transferbetween NADH₂ and nitrate. (Received May 6, 1969; )     

Skeletal variation related to arm regeneration in Metacrinus and Saracrinus, Recent stalked crinoids

Variations in the number of skeletal elements in the proximal portion of the arms (primibrachials) of Metacrinus rotundus Carpenter and Saracrinus nobilis (Carpenter) are compared. Older specimens of Metacrinus rotundus show increased variation in number of elements along with a tendency toward reduction, whereas the number of elements remains nearly constant in Saracrinus nobilis. The variation in Metacrinus rotundus is attributed to inaccurate arm regeneration following autotomy. Separation of Saracrinus from Metacrinus on the basis of number of skeletal elements is therefore possible, but caution must be used in the application of taxonomic characters which might be influenced by regeneration.     

Rapid synthesis of glutamine during the initial period of ammonia assimilation in roots of barley plants

After 1 hr of ammonia assimilation in barley plants, glutaminecontent in the roots increased 20 fold its original content,whereas contents of glutamic and aspartic acid decreased toa remarkable extent. These findings indicate a rapid synthesisof glutamine during the initial period of ammonia assimilationin roots. Results also suggest that glutamine synthesis fromglutamic acid initially occurring in the roots, is a primaryreaction of ammonia assimilation (Received May 11, 1971; )