• Energy Research
• Plant Science Letters close

Abstract Soybean ( Glycine max L. Merr.) cells grown in suspension culture under continuous illumination in the presence of glucose show chloroplast biogenesis (green cells), which is absent in cells cultured in the dark (white cells). In both white and green cells the total amount of adenine nucleotides and the amount of ATP sharply increased during the lag phase, followed by a continuous decrease during subsequent growth. The ADP/ATP ratio and the energy charge in both kinds of cells were equal from the 2nd through the 5th day of culture. From the 6th day in green cells the ADP/ATP ratio increased and the energy charge decreased, while in white cells both parameters remained relatively constant, leading to significant differences between white and green cells. The failure of green cells to maintain the equilibrium between energy-requiring and -generating processes might be related to the energy demands of the continued development of the internal membrane system of the chloroplasts beyond the 5th day of culture.

Abstract The two forms of glutamine synthetase (GS-I, GS-II) isolated from etiolated soybean hypocotyls had similar molecular weights, but different elution properties from DEAE-cellulose, different apparent Km-values for glutamine and had different responses to inhibitors of GS. Alanine, the most inhibitory amino acid, resulted in a 35% inhibition at 1 mM (GS-I). Serine was a non-competitive inhibitor with respect to glutamine for GS-I. Increased phosphorylation of adenine nucleotides resulted in increased inhibition with ATP the most inhibitory (50% at 1 mM). CTP interacted with ATP synergistically and exhibited non-competitive inhibition with respect to glutamine for GS-II. Cumulative feedback inhibition was evident with amino acids and nucleotides for both enzymes. Pyrophosphate (5 mM) produced almost total inhibition of both activities with GS-II slightly more sensitive. These results indicate the involvement of amino acids and nucleotides in the feedback control of GS activity in soybean in a cumulative manner and the possible involvement of an energy charge system of regulation.

Abstract A study of the energy state and the pattern of adenosine phosphates was conducted in the developing and germinating rice embryos. After 16 days of pollination, a peak value of adenylate energy pool was obtained which then showed a gradual decline and the energy charge (EC) varied between 0.7 and 0.8. Total energy pool was maximum after 24-h germination of embryos and ATP level increased 14-fold compared to the initial value of the dry embryo. But the maximum value of ADP and AMP was obtained after 72 h of germination and EC value fluctuated from 0.5 to 0.9 during the germination period.

Abstract Ammonia, methylamine and other uncouplers of photosynthetic phosphorylation promote in vivo the reversible conversion of the oxidized active form of Chlorella fusca nitrate reductase into its reduced inactive form. Concomitantly with the in vivo inactivation of the enzyme by the uncoupler, there occurs an increase in the cellular levels of the reduced forms of nicotinamide nucleotides and of the uncharged forms of adenine nucleotides. A general view of the regulation of photosynthesis by reducing power and energy charge is discyssed.

Abstract Phosphoglycerate (PGA) kinase was purified from spinach chloroplasts. Its activity was determined in a single enzymatic reaction without any coupling with the glyceraldehyde-3-phosphate dehydrogenase. With respect to ATP it exhibits non-Michaelis kinetics and behaves like an allosteric enzyme. The Hill coefficient is 1.35 and the calculated Km(ATP) is 2 mM. Ribulose-5-phosphate (Ru5P) kinase was purified from spinach leaves. It exhibits Michaelis kinetics with respect to ATP. The Km(ATP) is 0.42 mM. Both kinases from spinach chloroplasts are controlled by the adenylate energy charge.

Abstract Nitrate and ammonium utilization in cell suspension of the acidophilic thermophilic non-vacuolate alga Cyanidium caldarium and the related pH variations in the external medium, were measured using ion specific electrodes. Nitrate absorption and pH variations were also monitored. The acidophilic C. caldarium allowed experimentation under acidic conditions where CO 2 exchange did not affect pH measurements. Both ammonium and nitrate assimilation occured in dark and light conditions; however, the rate of assimilation was higher in the light than in the dark. The presence of oxygen was an absolute requirement. It is suggested that the uptake of both nitrate and ammonium are mediated by active mechanisms dependent on the energy charge of the cell. The assimilation of nitrate and ammonium was accompanied by an increase and a decrease, respectively, of the external medium pH. Under steady-state conditions, for each equivalent of ammonium incorporated there were 0.8–1 equiv. of protons released into the external medium and for each equivalent of nitrate absorbed there were 1–1.2 equiv. of protons absorbed from the external medium.