The cytosolic and chloroplastic isoforms of glucose-6-phosphate dehydrogenase (G6PDH) were separated and purified from barley leaves (Hordeum vulgare L.). In etiolated leaves, only the cytosolic isoform was expressed. The molecular mass of the cytosolic enzyme, G6PDH1, was 112±8 kDa and that of the chloroplast enzyme, G6PDH2, was 136±7 kDa. The Km values for glucose-6-phosphate and NADP were 0.133 and 0.041 mM for G6PDH1, and 0.275 and 0.062 mM for G6PDH2, respectively. The pH optimum was 8.2 for G6PDH1 and 7.8 for G6PDH2. The enzyme is absolutely specific for NADP. NADPH is a competitive inhibitor of the G6PDH1 in respect to glucose-6-phosphate (G6P) and NADP (Ki = 0.050 and 0.025 mM, respectively). NADPH is a competitive inhibitor of the G6PDH2 in respect to NADP (Ki = 0.010 mM), but a non-competitive inhibitor in respect to the G6P. ADP, AMP, UTP, NAD, and NADH had no effect on the activity of G6PDH. ATP inhibited the G6PDH2 activity. and A. Semenihina ... [et al.].
A traditional method is reported for purification of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) from leaves of Amaranthus hypochondriacus L. with a high yield of 50 %, 135-fold purification, and specific activity of 900 mmol kg-1(protein) s-1. PEPC was purified from light-adapted leaves of A. hypochondriacus, involving 40-60 % ammonium sulphate fractionation, followed by chromatography on columns of DEAE-Sepharose, hydroxylapatite (HAP), and Seralose 6-B. The enzyme appeared as a single band on 10 % SDS-PAGE, with a molecular mass of about 100 kDa. Kinetic studies with purified enzyme confirmed the PEPC to be the light-form of the enzyme. Glycerol generally increased the stability of PEPC. The stability and storage of the purified enzyme was studied at temperatures of 4 °C, -20 °C, and liquid nitrogen. PEPC maintained its activity for up to 3 months upon storage with 50 % (v/v) glycerol in liquid nitrogen. and J. Gayathri, K. Parvathi, A. S. Raghavendra.
Etiolated oat mesophyll protoplasts and etioplasts released from etiolated protoplasts were able to perform protochlorophyliide (PChlide) reduction but showed a high amount of inactive P633/628» compared with intact leaves. In špite of this, the anabolic reduction charge (ARC, NAPDH+H+/NADP+ + NADPF1+H+) was maintained at 0.66 - 0.77 up to 30 min of irradiation with weak "white light" (10 W m‘2). This indicated a high buffering capacity of the isolated systém to provide NADPF1+H+, only at the expense of intemal reserves. A change in the redox statě of the NADP+/NADPH+H^ couple during protochlorophyliide reduction was not observed in etioplasts. The resulting redox potential was in the range of -330 mV optimal for protochlorophyliide reduction.
Binding kinetics of some photosystem 2 (PS 2)-directed ínhibitors to isolated pea thylakoids during photoinUbition were studied. Changes in the herbicide binding activity were overshadowed by the redox statě of the plastoquinone (PQ) pool. After extraction of the PQ pool from the thylakoids, a correlation between the decline of herbicide binding activity and the electron transfer activity during strong irradiation was found in the presence of oxygen; in anaerobiosis this correlation was absent. The opposite was observed for the binding kinetics of the electron transfer acceptor 2,6-dichlorophenol indophenol, that was affected faster under anaerobic conditions. Following irradiation, a movement of damaged Dj-protein products from the appressed to the non-appressed regions of the membrane was observed. This observation was correlated to the fínding of an increased level of atrazine bound to the non-appressed regions of irradiated membranes.
LED lamps with various combinations of red (R) and blue (B) wavelengths were used to supplement sunlight for the growth of a heat-resistant (HR) and heat-sensitive (HS) recombinant inbred lines (RIL) of lettuce. The RB-LED ratios were 100R:0B (0B), 92R:8B (8B), 84R:16B (16B), and 76R:24B (24B) with an equal PPFD of 100 μmol m-2 s-1. The greatest leaf expansion rates were observed at 8B for both genotypes. All HR-RILs had similar values of growth parameters and specific leaf area (SLA). However, higher values of growth parameters were observed in HS-RIL with 0B, 8B, and 16B than that under 24B and sunlight. Furthermore, HS-RIL had higher SLA under 0B compared to other conditions. Photosynthetic light-use efficiency and maximal oxygen evolution rate were the lowest under 8B for both genotypes. The quality of LED lighting, if provided, seemed to implicate genotype dependence, probably as a result of their different sensitivities to heat stress., T. W. Choong, J. He, L. Qin, S. K. Lee., and Obsahuje bibliografii
In this study, we presented a new approach for quantification of bicarbonate (HCO3-) molecules bound to PSII. Our method, which is based on a combination of membrane-inlet mass spectrometry (MIMS) and 18O-labelling, excludes the possibility of "non-accounted" HCO3- by avoiding (1) the employment of formate for removal of HCO3- from PSII, and (2) the extremely low concentrations of HCO3-/CO2 during online MIMS measurements. By equilibration of PSII sample to ambient CO2 concentration of dissolved CO2/HCO3-, the method ensures that all physiological binding sites are saturated before analysis. With this approach, we determined that in spinach PSII membrane fragments 1.1 ± 0.1 HCO3- are bound per PSII reaction center, while none was bound to isolated PsbO protein. Our present results confirmed that PSII binds one HCO3- molecule as ligand to the non-heme iron of PSII, while unbound HCO3- optimizes the water-splitting reactions by acting as a mobile proton shuttle., K. Tikhonov, D. Shevela, V. V. Klimov, J. Messinger., and Obsahuje bibliografické odkazy
A portable open gas-exchange system (Li-6400, Li-Cor, Inc., Lincoln, NE, USA) has been widely used for the measurement of net gas exchanges and calibration/parameterization of leaf models. Measurement errors due to diffusive leakage rates of water vapor (LW) and CO2 (LC) between inside and outside of the leaf chamber, and the inward dark transpiration rate (DW) and dark respiration rate (DC) released from the leaf under the gasket, can be significant. Rigorous model-based approaches were developed for estimating leakage coefficients of water vapor (KW) and CO2 (KC) and correcting for the combination of these errors. Models were based on mass balance equations and the Dusty Gas Model for a ternary gas mixture of water vapor, CO2, and dry air. Experiments were conducted using two Li-6400 systems with potato and soybean leaves. Results indicated that models were reliable for estimating KW and KC, and the values varied with instrument, chamber size, gasket condition, and leaf structure. A thermally killed leaf should be used for this determination. Measurement error effects on parameterization of the Farquhar et al. (1980) model as determined by PN/C i curves were substantial and each parameter had its own sensitivity to measurement errors. Results also indicated that all four error sources should be accounted for when correcting measurements., Q. Wang ... [et al.]., and Obsahuje bibliografii a dodatky
On the basis of values from literature it was established that photosynthetically used radiation (PUR) amounts to 6 % of absorbed radiant energy in cabbage (producer of high yields), 3.5 % in sugar beet leaves, and 2.6 % in tobacco leaves. PUR of these species did not depend on irradiance in a wide range from 22 to 287 W m-2.
Potential daily biomass production of jutě was calculated from the conversion of measured incident photosynthetic photon flux (PPF) during the jutě growing season (Apríl - August) of Indo-Bangladesh sub-continent and evaluating the average respirátory loss over the same period. Taking an average incident PPF of 39.87 mol(photon) m-2 d’*, the potential daily rate of dry matter production of 49.77 g m'2 was estimated with a photosynthetic efficiency of 1.25 g mol'^ Considering the daily production rate as proportional to the amount of radiant energy interception by the crop at different stages of growth, a maximum jutě biomass production capacity of 4.081 kg m'2 (40.81 t ha'*) was estimated. This value was little more than two times the average production obtained from the field experiment under similar conditions. Radiation use efficiency of a dosed jutě canopy (3.5 g MJ**), however, appears to háve reached that for any field crop.