The hepatic removal of the glutathione conjugate of bromosulfophthalein (BSPGSH) was studied in the single-pass perfused rat liver with the multiple indicator dilution (MID) technique against various background concentrations of BSPGSH (20 to 214 mumol/L) over which nonlinear binding to both plasma (albumin) and tissue proteins with two classes of binding sites was found. A bolus containing 51Cr-labeled red blood cell (a vascular reference), [125I]albumin and [14C]sucrose (large and small molecular weight interstitial references, respectively), D2O (a cellular space reference), and [3H]BSPGSH was injected into the portal vein during steady-state. The eliminated fraction of dose, obtained by subtracting the survival fraction of [3H]BSPGSH in plasma from one, corresponded to the steady state extraction ratio (E) with bulk data, which declined from 0.74 +/- 0.04 to 0.27 +/- 0.01 with concentration. The major portion of the tracer outflow profile was a throughput component, which is the proportion of tracer that did not enter liver cells during its transit through the liver. The influx, efflux, and sequestration coefficients, evaluated with previously developed barrier-limited models, provided the corresponding influx (k1), efflux (k-1) and excretion (kseq) rate constants. Concentration-dependent influx (Vmax = 83 nmol min-1 g-1 and Km = 3.7 mumol/L), efflux (Vmax = 15 nmol min-1 g-1 and Km = 1.8 mumol/L), and excretion (Vmax = 94 nmol min-1 g-1 and Km = 1.8 mumol/L) were obtained for BSPGSH, when Km values are expressed in terms of the unbound concentrations. In these calculations, the observed unbound tissue concentration was not used for estimation of the Vmax and Km for efflux and excretion because of overestimation, because of the presence of highly concentrated BSPGSH in ductular elements present in liver homogenates; rather, the unbound tissue concentration was calculated from the influx, efflux, and removal rate coefficients. Because of carrier-mediated entry, the unbound tissue concentration does not equal the unbound plasma concentration, and kinetic parameters for BSPGSH excretion could be alternately estimated when the rate of excretion or net rate of loss of BSPGSH from plasma was regressed against the estimated tissue unbound concentration. This yielded a Vmax of 97 nmol min-1 g-1 and a Km of 3.6 mumol/L, values similar to those obtained from MID.(ABSTRACT TRUNCATED AT 400 WORDS)

Background Chitosan (CTS), a natural polysaccharide, exhibits multiple functions of stress adaptation regulation in plants. However, effects and mechanism of CTS on alleviating salt stress damage are still not fully understood. Objectives of this study were to investigate the function of CTS on improving salt tolerance associated with metabolic balance, polyamine (PAs) accumulation, and Na+ transport in creeping bentgrass (Agrostis stolonifera). Results CTS pretreatment significantly alleviated declines in relative water content, photosynthesis, photochemical efficiency, and water use efficiency in leaves under salt stress. Exogenous CTS increased endogenous PAs accumulation, antioxidant enzyme (SOD, POD, and CAT) activities, and sucrose accumulation and metabolism through the activation of sucrose synthase and pyruvate kinase activities, and inhibition of invertase activity. The CTS also improved total amino acids, glutamic acid, and γ-aminobutyric acid (GABA) accumulation. In addition, CTS-pretreated plants exhibited significantly higher Na+ content in roots and lower Na+ accumulation in leaves then untreated plants in response to salt stress. However, CTS had no significant effects on K+/Na+ ratio. Importantly, CTS enhanced salt overly sensitive (SOS) pathways and also up-regulated the expression of AsHKT1 and genes (AsNHX4, AsNHX5, and AsNHX6) encoding Na+/H+ exchangers under salt stress. Conclusions The application of CTS increased antioxidant enzyme activities, thereby reducing oxidative damage to roots and leaves. CTS-induced increases in sucrose and GABA accumulation and metabolism played important roles in osmotic adjustment and energy metabolism during salt stress. The CTS also enhanced SOS pathway associated with Na+ excretion from cytosol into rhizosphere, increased AsHKT1 expression inhibiting Na+ transport to the photosynthetic tissues, and also up-regulated the expression of AsNHX4, AsNHX5, and AsNHX6 promoting the capacity of Na+ compartmentalization in roots and leaves under salt stress. In addition, CTS-induced PAs accumulation could be an important regulatory mechanism contributing to enhanced salt tolerance. These findings reveal new functions of CTS on regulating Na+ transport, enhancing sugars and amino acids metabolism for osmotic adjustment and energy supply, and increasing PAs accumulation when creeping bentgrass responds to salt stress.

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Drought is a serious outcome of climate change reducing the productivity of forage species under arid and semi-arid conditions worldwide. Diethyl aminoethyl hexanoate (DA-6), a novel plant growth regulator, has proven to be involved in the amelioration of critical physiological functions in many agricultural crops under various abiotic stresses, but the role of the DA-6 in improving seed germination has never been investigated under drought stress. The present study was carried out to elucidate the impact of the DA-6 priming on seeds germination of white clover under drought stress. Results showed that seed priming with the DA-6 significantly mitigated the drought-induced reduction in germination percentage, germination vigor, germination index, seed vigor index, root length, shoot length, and fresh weight after 7 days of seed germination. The DA-6 significantly increased the endogenous indole-3-acetic acid, gibberellin, and cytokinin content with marked reduction in abscisic acid content in seedlings under drought stress. In addition, the DA-6 significantly accelerated starch catabolism by enhancing the activities of hydrolases contributing toward enhanced soluble sugars, proline content and ameliorated the antioxidant defense system to enhance the ability of reactive oxygen species scavenging under drought stress. Furthermore, exogenous DA-6 application significantly increased dehydrins accumulation and upregulated transcript levels of genes encoding dehydrins (SK2, Y2SK, or DHNb) during seeds germination under water deficient condition. These findings suggested that the DA-6 mediated seeds germination and drought tolerance associated with changes in endogenous phytohormones resulting in increased starch degradation, osmotic adjustment, antioxidants activity, and dehydrins accumulation during seed germination under water deficient condition.

Concentration-dependent changes in the hepatic extraction ratio E and tissue accumulation of drugs were examined in a simulation study, wherein plasma protein binding, flow, and mode of entry were altered. A tubular flow model that described carrier-mediated (influx: Kml = 20 microM, Vmax1 = 1000 nmol min-1; efflux, Km2 = 200 microM, Vmax2 = 250 nmol min-1), flow-limited (influx clearance CLin = efflux clearance CLef = 50 ml min-1), or diffusion-limited (CLin = CLef = 0.1 ml min-1) hepatocytic entry was employed; drug removal was solely via biliary excretion (Km3 = 100 microM, Vmax3 = 1500 nmol min-1). Other parameter space and the combination of carrier-mediated transport and passive diffusion were also explored. Increased plasma protein binding reduced the hepatic extraction of the substrate, and in some instances, constituted the rate-controlling factor, especially at lower input concentrations for which tighter binding existed. Increased flow rate also brought about a reduction in E, affecting E almost inversely when values of E were low (e.g., for the diffusion-limited case or at higher input concentration). Tissue accumulation patterns and the apparent tissue distribution equilibrium ratio, i.e., tissue to plasma unbound concentration ratio Kp, differed among the systems. The behavior of Kp may be used as an identifier for the mode of drug transport: A declining (concave-down) Kp curve or a parabolic Kp that approached unity with input concentration (Cln) is associated with carrier-mediated entry; a rising Kp curve that approaches unity with Cln suggests flow limitation; and a waning concave-up Kp curve of very low magnitude represents diffusion limitation. Since the unbound tissue concentration (Ct) differs from the logarithmic average of the unbound input and output concentrations in plasma (Cu) for carrier-mediated and diffusion-limited systems, excretion parameters may be obtained only upon fitting of the overall excretion rate vs. Ct in the Michaelis-Menten equation; whereas when data are fitted with Cu, the rate-limiting step, influx, or deviations of influx, efflux, and excretion, will be obtained. When Ct equals Cu, as in flow-limited systems, accurate excretion parameters will be provided with the fitting of data against either Ct or Cu.