Taurolithocholate-induced inhibition of biliary lipid and protein excretion in the rat.

Taurolithocholate (TLC), a natural bile salt, induces selective impairment on canalicular membrane of the hepatocyte, which seems to be a major determinant of its cholestatic effect in experimental animals. In order to extend existing studies about the effects of TLC on bile secretion, we examined in TLC-treated rats the biliary excretion of compounds that are transported to canalicular membrane via vesicles, such as lipids and proteins. The single intravenous injection of TLC (3 mumol/100 g body wt.) inhibited transiently the biliary bile salt excretion, while the biliary excretion of lipids (i.e., cholesterol and phospholipids) and proteins remained inhibited even though the biliary excretion and composition of bile salts were normalized. Under such a condition, TLC also inhibited the transcellular vesicular pathway to the exogenous protein horseradish peroxidase entry into bile, without altering the paracellular biliary access of the protein. The hepatic uptake of horseradish peroxidase was unaffected by TLC-treatment. The results indicate that TLC can inhibit the biliary excretion of compounds that reach the canaliculus via a vesicular pathway, such as lipids and proteins, by a mechanism not related to a defective bile salt excretion. Possible explanations for these findings are discussed.     

Comparison of hepatic, renal and intestinal bilirubin UDP-glucuronyl transferase activities in rat microsomes

1. Bilirubin UDP-glucuronyltransferase activity and its dependence on substrate concentrations in rat liver, renal cortex and intestinal mucosa microsomes were studied. 2. Bilirubin monoglucuronide synthesis from unconjugated bilirubin was a higher capacity, lower affinity step in comparison with bilirubin diglucuronide formation in the three tissues tested. 3. Bilirubin glucuronide formation in liver microsomes showed a higher capacity but a lower affinity than extrahepatic ones. Renal cortex and intestinal mucosa exhibited similar kinetics parameters. 4. In vitro bilirubin glucuronidation in renal cortex and intestinal mucosa was quantitatively important as compared with the hepatic one.     

Needle CO2 exchange, structure and defense traits in relation to needle age in Pinus heldreichii Christ – a relict of Tertiary flora

 Pinus heldreichii Christ is a long-lived, slow-growing Tertiary relict from the Balkans. In this study we evaluated the physiological characteristics of eight needle-age classes of P. heldreichii grown at the Arboretum of the Institute of Dendrology in Kórnik, Poland. At the end of the growing season, current-year foliage had the highest rates of mass-based light-saturated net photosynthesis (A_sat) of 33.5 nmol CO₂· g^–1· s^–1. A_sat decreased with needle age, but older needle classes retained from approximately 62 to 26% of the current needles’ rate. The relationship between leaf N and chlorophyll a concentration among all needle-age classes was highly significant (r = 0.96, P = 0.0006). The variation in A_sat of 1- to 7-year-old needles was linearly related to needle N concentration (r = 0.98, P = 0.0001). Needle dark respiration rates among these needle age classes ranged from 0.8 to 2.2 nmol · g^–1· s^–1 and decreased with needle age and nitrogen concentration. Total phenols and glucose concentrations increased linearly with needle age. A similar pattern was observed in acid buffering capacity and the pH of tissue homogenates. The water content ranged from 62% for the current needles to 51% for the 6-year-old needles. Greater investment in leaf structural tissue and increased chemical defense is associated with higher structural cost of older needles and may reduce their photosynthetic activity. Significant declines in water and nitrogen content with needle age and an increase in content of phenolics is most likely a defense adaptation of P. heldreichii related to the species’ long-lived leaves. Received: 8 January 1997 / Accepted: 4 March 1997     

Stomatal density in Pinus sylvestris as an indicator of temperature rather than CO2: Evidence from a pan-European transect

The commonly observed negative relationship between stomatal density (SD) and atmospheric CO₂ has led to SD being proposed as an indicator of atmospheric CO₂ concentration. The use of SD as a proxy for CO₂, however, has been hampered by an insufficient understanding of the intraspecific variation of this trait. We hypothesized that SD in Pinus sylvestris, a widely distributed conifer, varies geographically and that this variation is determined by major climatic variables. By sampling needles from naturally growing trees along a latitudinal range of 32.25°, equivalent to 13.7°C gradient of mean annual temperature (MAT) across Europe, we found that SD decreased from the warmest southern sites to the coldest sites in the north at a rate of 4 stomata per mm² for each 1°C, with MAT explaining 44% of the variation. Additionally, samples from a provenance trial exhibited a positive relationship between SD and the MAT of the original localities, suggesting that high SD is an adaptation to warm temperature. Our study revealed one of the strongest intraspecific relationships between SD and climate in any woody species, supporting the utility of SD as a temperature, rather than direct CO₂, proxy. In addition, our results predict the response of SD to climate warming.     

Anatomical acclimation of mature leaves to increased irradiance in sycamore maple (Acer pseudoplatanus L.)

Photosynthesis Research - Trees regenerating in the understory respond to increased availability of light caused by gap formation by undergoing a range of morphological and physiological...     

Mechanistic insights into the global response to phenol in the phenol-biodegrading strain Pseudomonas sp. M1 revealed by quantitative proteomics

Quantitative proteomics was used to gain insights into the global adaptive response to phenol in the phenol-biodegrading strain Pseudomonas sp. M1 when an alternative carbon source (pyruvate or succinate) is present. A phylogenetic analysis indicated Pseudomonas citronellolis as the closest species to the environmental strain M1, while P. aeruginosa is the closest species with the genome sequence available. After two-dimensional gel electrophoresis (2-DE) separation, protein identification by MS/MS ion search allowed the assignment of 87 out of 136 selected protein spots, 56 of which matched P. aeruginosa proteins present in databases. Coordinate induction of six enzymes of the phenol catabolic pathway in cells grown in pyruvate and phenol was revealed by expression proteomics. When succinate was the alternative carbon source (C-source), these catabolic proteins were not expressed. The global response of Pseudomonas sp. M1 to phenol-induced stress involved, among others, proteins of the energy metabolism, stress response proteins, and transport proteins. Quantitative and/or qualitative differences were registered in M1 response to different phenol concentrations or to identical phenol concentrations when cells were grown in pyruvate or succinate medium. They were attributed to differences observed in the specific growth rate, in the expression of phenol catabolism, and in resistance to phenol of Pseudomonas sp. M1 grown under different conditions.