Benzoylcellulose derivatives as chiral stationary phases for open tubular column chromatography

The application of cellulose-based stationary phases for chiral separations has been extended to open tubular column chromatography. Efficient columns were obtained by coating the capillaries with mixtures of chiral cellulose materials and conventional achiral stationary phases for gas chromatography. In this study, various siloxane and polyethylene glycol polymers were used as achiral components and mixed with different substituted benzoylcellulose derivatives as chiral components. Systematic investigations were carried out to determine the optimal ratio for the components of the stationary phase. Depending on the chromatographic mode—gas chromatography (GC) or supercritical fluid chromatography (SFC)—the stationary phases were found to behave differently. The applicability of the technique was demonstrated by the resolution of various racemic compounds. © 1993 Wiley-Liss, Inc.     

GRAVITY-INDUCED EFFECTS ON MATERIAL PROPERTIES AND SIZE OF LEAVES ON HORIZONTAL SHOOTS OF ACER SACCHARUM (ACERACEAE)

The influence of gravity on the size and mechanical properties of mature leaves on horizontal shoots and etiolated seedlings of Acer saccharum Marsh. (Aceraceae) was examined. Leaves were grouped into three categories regarding their location on shoots (dorsal or “top” T, lateral or “left/right” L/R, and ventral or “bottom” B). Young's modulus E, petiole length L, lamina surface area A and weight P, and the cross-sectional areas of different tissues within petioles were measured for each leaf and were found to be correlated with leaf location (T, L/R, and B): T leaves were smaller and had lower E than their B counterparts; the size and material properties of L/R leaves were intermediate between those of T and B leaves. In general, A, P, and E decreased from the base to the tip of shoots. In addition to anisophylly, the influence of gravity induced petiole bending and torsion and resulted in the horizontal planation of laminae. This was observed for field-grown mature plants and etiolated seedlings. Petiole bending and torsion were interpreted as gravimorphogenetic phenomena. Anatomically, L, E, and petiole deflection angle Fv measured from the vertical were highly correlated with the combined cross-sectional areas of phloem fibers and xylem in petioles of B leaves and when data from all leaves were pooled. It is tentatively advanced that the correlation of E with the transverse areas of phloem fibers and xylem is evidence that either the pattern or the extent of lignification of petiole tissues is influenced by petiole position with respect to gravity.     

LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEXES OF THE ULVOPHYCEAE (CHLOROPHYTA):CHARACTERIZATION AND PHYLOGENETIC SIGNIFICANCE1

Photosystem II light-harvesting complexes were isolated from a number of ulvophycean algae. Some of these light-harvesting complexes displayed unusual features, most notably a high apparent molecular weight (ca. 58,000) when isolated by lithium doderyl sulfate polyarrylamide gel electrophoresis. Other ulvophycean light-harvesting complexes had a low-molecular weight (ca. 30,000). The distribution of the high-molecular weight complex was limited to certain members of the Caulerpales and Blastophysa rhizopus (Siphanocladales). Within the Caulerpales, there were also spectral differences between the high-molecular weight and low-molecular weight light-harvesting complex types. The differences in light-harvesting complexes in the Ulvophyceae suggest that there are two lines of evolution in the Caulerpales and that Blastophysa may be an intermediate between the Siphon-ocladales and the Caulerpales.     

Synthesis and AT2 receptor-binding properties of angiotensin II analogues.

The present study investigates the importance of the amino acid side chains in the octapeptide angiotensin II (Ang II) for binding to the AT2 receptor. A Gly scan was performed where each amino acid in Ang II was substituted one-by-one with glycine. The resulting set of peptides was tested for affinity to the AT2 receptor (porcine myometrial membranes). For a comparison, the peptides were also tested for affinity to the AT1 receptor (rat liver membranes). Only the substitution of Arg2 reduced affinity to the AT2 receptor considerably (92-fold when compared with Ang II). For the other Gly-substituted analogues the affinity to the AT2 receptor was only moderately affected. To further investigate the role of the Arg2 side chain for receptor binding, we synthesized some N-terminally modified Ang II analogues. According to these studies a positive charge in the N-terminal end of angiotensin III [Ang II (2-8)] is not required for high AT2 receptor affinity but seems to be more important in Ang II. With respect to the AT1 receptor, [Gly2]Ang II and [Gly8]Ang II lacked binding affinity (Ki > 10 microM). Replacement of the Val3 or Ile5 residues with Gly produced only a slight decrease in affinity. Interestingly, substitution of Tyr4 or His6, which are known to be very important for AT1 receptor binding, resulted in only 48 and 14 times reduction in affinity, respectively.     

Characterization of a 46 kda insect chitinase from transgenic tobacco

A 46 kDa Manduca sexta (tobacco hornworm) chitinase was isolated from leaves of transgenic tobacco plants containing a recombinant insect chitinase cDNA, characterized, and tested for insecticidal activity. The enzyme was purified by ammonium sulfate fractionation, Q-Sepharose anion-exchange chromatography and mono-S cation-exchange chromatography. Although the gene for the chitinase encoded the 85 kDa full-length chitinase as previously reported by Kramer et al. [Insect Biochem. Molec. Biol. 23, 691–701 (1993)], the enzyme is produced in tobacco as a 46 kDa protein that is approximately four-fold less active than the 85 kDa chitinase. The N-terminal amino acid sequence of the 46 kDa chitinase is identical to that of the 85 kDa chitinase. The former enzyme is not glycosylated, whereas the latter contains approximately 25% carbohydrate. The pH and temperature optima of the 46 kDa chitinaseare similar to those of the 85 kDa chitinase. The former enzyme is more basic than the latter. The 46 kDa chitinase likely consists of the N-terminal catalytic domain of the 85 kDa chitinase and lacks the C-terminal domain that contains several potential sites for glycosylation. The 46 kDa chitinase is expressed in a number of plant organs, including leaves, flowers, stems and roots. Enzyme levels are higher in leaves and flowers than in stems and roots, and leaves from the middle portion of the plant have more chitinase than leaves from the top and bottom portions. Little or no enzyme is secreted outside of the plant cells because it remains in the intracellular space, even though its transit sequence is processed. When fed at a 2% dietary level, the 46 kDa chitinase caused 100% larval mortality of the merchant grain beetle, Oryzaephilis mercator. The results of this study support the hypothesis that insect chitinase is a biopesticidal protein for insect pests feeding on insect chitinase gene-containing transgenic plants.     

Assessing the impact of ozone on photosynthesis of European beech (Fergus sylvatica L.) in environmental chambers

An exposure — response study with proportionalto-ambient ozone levels was conducted in closed chambers on 3-year-old European beech (Fagus sylvatica L.) of montane origin. The fumigation started in April 1990 and lasted for a single growing season. Climate data and ozone concentrations monitored at an experimental station of the Institute for Applied Plant Biology, Schönenbuch, Switzerland were simulated in the exposure chambers 12 days later (1*O₃). To test exposure-response relations three additional treatments were applied, subambient (0.2*O₃) and two proportionally increased ozone treatments (1.5*O₃ and 2*O₃). The photosynthetic behaviour of the trees in August revealed the light reactions to be less affected than parameters which are related to the dark reactions of photosynthesis. Assimilation (A₃₅₀), apparent carboxylation efficiency (CE), and maximum photosynthetic capacity (A₂₅₀₀) were reduced with increasing ozone concentration. For the ozone response of CE and A₂₅₀₀ Critical Levels were calculated.     

Response of rice varieties to soil salinity and air humidity: A possible involvement of root-borne ABA

In a phytotron experiment four rice varieties (Pokkali, IR 28, IR 50, IR 31785-58-1-2-3-3) grown in individual pots were subjected to low (40/55% day/night) and high (75/90%) air humidity (RH), while soil salinity was gradually increased by injecting 0, 30, 60 or 120 mM NaCl solutions every two days. Bulk root and stem base water potential (SWP), abscisic acid (ABA) content of the xylem sap and stomatal resistance (rs) of the youngest fully expanded leaf were determined two days after each salt application. The SWP decreased and xylem ABA and rs increased throughout the 8 days of treatment. The effects were amplified by low RH. A chain of physiological events was hypothesized in which high soil electric conductivity (EC) reduces SWP, followed by release of root-borne ABA to the xylem and eventually resulting in stomatal closure. To explain varietal differences in stomatal reaction, supposed cause and effect variables were compared by linear regression. This revealed strong differences in physiological reactions to the RH and salt treatments among the test varieties. Under salt stress roots of IR 31785-58-1-2-3-3 produced much ABA under low RH, but no additional effect of low RH on rs could be found. By contrast, Pokkali produced little ABA, but rs was strongly affected by RH. RH did not affect the relationships EC vs. SWP and SWP vs. ABA in Pokkali, IR 28, and IR 50, but the relationship ABA vs. rs was strongly affected by RH. In IR 31785-58-1-2-3-3 RH strongly affected the relationship SWP vs. ABA, but had no effect on ABA vs. rs and EC vs. rs. The results are discussed regarding possible differences in varietal stomatal sensitivity to ABA and their implications for varietal salt tolerance.     

Growth responses of some soil fungi to spatially heterogeneous nutrients

Abstract The natural nutritional environments of most fungi are spatially non-uniform, yet the majority of studies of fungal growth take no account of this fact. An experimental system is described which permits the growth responses of eucarpic fungi to heterogeneously distributed nutrient resources to be studied. The system comprises tesselations of agar tiles of contrasting nutrient status separated by air gaps. Growth responses in such systems of Alternaria alternata, Mucor sp., Phoma foveata , Rhizoctonia solani and Trichoderma viride are described. Generally, the growth of the fungi reflected the nutrient status of the underlying substrate. There was evidence for growth in low-nutrient tiles being greater when high-nutrient tiles were included in the tessellation. Reproductive structures tended to be formed only in low nutrient tiles with Trichoderma and Rhizoctonia and only high nutrient tiles with Alternaria . Growth responses of Rhizoctonia were strongly asymmetric in nutritionally symmetric, but heterogeneous, tesselations. The consequences of the observations for fungal growth in heterogeneous environments such as soil is discussed.     

Insulin-like growth factor-1 stimulates amino acid uptake by the cultured human placental trophoblast

Amino acid uptake by the human placenta is known to occur via several transport mechanisms. However, regulation by extracellular factors has received relatively little attention. A recent report by this laboratory characterized the uptake of α-aminoisobutyric acid (AIB) stimulated by insulin in the cultured human placental trophoblast The current study evaluated the effect of insulin-like growth factor-1 (IGF-1) on AIB uptake in cultured human placental trophoblasts. Na⁺-dependent AIB uptake was significantly stimulated by IGF-l in a time-dependent manner, as early as 30 min after hormone exposure. The maximum effect was at 2–4 hr of continuous exposure to IGF-l and the stimulation was dependent upon IGF-1 concentration approaching maximal stimulation at 50 ng.ml^?1. AIB uptake was inhibited by increasing concentrations of α-(methylamino)isobtyric acid (MeAIB). Approximately 75% of basal (unstimulated) Na⁺-dependent AIB uptake was inhibited by MeAIB. The IGF-1-stimulated increment above basal AIB uptake was completely inhibited by MeAIB. IGF-1 increased the maximum uptake yelocity but not Km. Using equimolar concentrations, stimulation was greater with IGF-1 then with IGF-2. Stimulation by IGF-1, but not insulin, was inhibited by anit-IGF-1 receptor antibody, indicating mediation via the IGF-1 receptor. H7, a nonspecific inhibitor of serine-threonine kinase, inhibited IGF-1-dependent stimulation of AIB uptake. In addition, calphostin C (a specific inhibitor of protein kinase C), but not H89 (a specific inhibitor of protein kinase A), inhibited the IGF-1 action. This study further characterizes regulated amino acid uptake by the human placental trophoblasts and demonstrates that the Na⁺-dependent component of AIB uptake is stimulated by physiologic concentrations of IGF-1. © 1995 Wiley-Liss Inc.     

Determination of apoplastic K+ in intact leaves by ratio imaging of PBFI fluorescence

The tetraammonium salt of the K⁺ binding fluorescent dye benzofuranisophthalate (PBFI) was used to investigate the influence ofpotassium nutrition (0.1–2.1 mol m^–3) on apoplasticK⁺ inVicia faba leaves by means of ratio imaging. As a referencethe infiltration-centrifugation method was used. Both methodsreflected the influence of K⁺ supply on apoplastic K⁺ concentration.The abaxial leaf side revealed significantly higher K⁺ concentrations(20-25 mol m^–3) than the adaxial side (5–8 mol m^–3).Application of CCCP led to an immediate increase in apoplasticK⁺ demonstrating the reliability of the PBFI method. Key words: Vicia faba, leaf, apoplast, K⁺, PBFI, ratio imaging, ratiometric fluorescence microscopy