Fluorescence induction characteristics of Anacystis nidulans during recovery from iron deficiency

Cultures of the cyanobacterium, Anacystis nidulans, were grown in iron deficient medium and examined for fluorescence emission at room temperature. Iron deficiency induced several alterations in fluorescence emission kinetics which were reversed when iron was restored. When excited by 450 nm light (absorbed by chlorophyll), iron stressed cells showed an enhanced maximum fluorescence yield (Fm), due in large part to an increase in original fluorescence (Fo) and a depressed variable fluorescence. Both Fm and Fo declined during the early stages of recovery from iron deficiency. Inhibitors of chlorophyll biosynthesis (such as levulinic acid and gabaculine) had little influence on these early stages of recovery suggesting that newly synthesized chlorophyll is not responsible for the decline in Fm. In contrast, when excited by 550 or 600 nm light (absorbed by phycocyanin), iron deficient cells showed no increase in Fm. A fast rise fluorescence transient was observed which was absent in both normal or fully recovered cells. This transient was attenuated by preillumination (600 nm light), and recovered in darkness with a half time of 2–4 minutes. These results suggest that the reoxidation of acceptors on the oxidizing side of PS II is considerably slower in iron deficient cells.     

Plasma citrulline and arginine kinetics in juvenile channel catfish, Ictalurus punctatus, given oral gabaculine

Experiments with young mammals have indicated that renal arginine synthesis is a major endogenous source of this amino acid. The kidney readily synthesizes arginine from intestinally derived citrulline, which is produced from glutamate, the so-called intestinal-renal axis. The present experiment was conducted to ascertain whether or not citrulline and arginine are synthesized in channel catfish via this pathway by administering gabaculine, an effective inhibitor of ornithine aminotransferase, and then monitoring circulating levels of arginine, citrulline, glutamate and ornithine. A conditioning diet was fed to apparent satiation to triplicate groups of channel catfish initially averaging 150 g/fish. After 2 weeks of acclimation, fish were lightly anesthetized with MS-222 and were intubated with a gelatin capsule containing gabaculine (3 mg/kg body weight) in one dose. Then, 24 and 48 h after gabaculine treatment, blood plasma was obtained and analyzed for amino acids via HPLC. Oral gabaculine administration significantly (p < 0.05) decreased plasma concentrations of citrulline (–41.8%) and arginine (–8.9%). It also increased (p < 0.05) plasma glutamine (+17.5%) and ornithine (+256.6%). A reasonable explanation for the increase in plasma glutamine and the decrease in citrulline and arginine is offered by the inhibition of glutamine degradation and a decrease in synthesis of citrulline caused by gabaculine. Results of this experiment suggest that endogenous synthesis of citrulline occurs in channel catfish, most likely at the small intestine, and it may serve as a de novo source of arginine. Therefore, the physiological needs of fish tissues and organs for arginine appear to be met via both dietary arginine and the endogenous synthesis of this amino acid.