Effect of osmotic stress on the growth of epicotyls of Cicer arietinum in relation to changes in the autolytic process and glycanhydrolytic cell wall enzymes

Simulation of drought by polyethylene glycol (PEG) inhibited elongation of epicotyls of Cicer arietinum L. cv. Castellana but had no effect on growth capacity since growth was restored once the inhibitory condition had been removed. The amount of proteins in the cell wall was correlated with the elongation of the epicotyls and decreased when elongation was inhibited. PEG-induced inhibition of elongation had different effects on the various glycanhydrolytic cell wall enzymes. Only α-galactosidase (EC 3. 2. 1. 22) seemed related to the lack of elongation, increasing its activity when elongation was inhibited. The β-galactosidase (EC 3. 2. 1. 23) and β-glucosidase (EC 3. 2. 1. 21) studied did not show changes in their specific activities during the inhibition of elongation. β-Galactosidase is responsible for the autolytic process in Cicer arietinum . This enzyme hydrolyzes specified linkages in the cell wall, releasing sugar constituents. Our present results show that β-galactosidase is not directly related with elongation because no changes could be observed during inhibition of elongation. The autolytic process is related with chemical processes taking place in the cell wall and preceding elongation of the epicotyls, i. e. the loosening process. Cell wall loosening is necessary for elongation to take place but elongation does not necessarily follow loosening if the osmotic conditions are unfavorable     

Characterization of a cell wall β-galactosidase of Cicer arietinum epicotyls involved in cell wall autolysis

β-Galactosidase (EC 3.2.1.23) has been established as the main enzyme involved in the autolytic process. The enzyme extracted from cell walls of epicotyls of Cicer arietinum L. cv. Castellana with 3 M LiCl is a 45 kDa protein composed of a single subunit, having an optimum pH of 4; an optimum temperature of 45°C and K_m and V_max of 1.72 m M and 18.5 nkat (mg protein)^–1 respectively, as evaluated against p -nitrophenyl-β- d -galactopyranoside. The enzyme is inhibited by Hg²⁺, d -galactono-1,4-lactone and galactose, substances that also inhibit the autolytic process. Ca²⁺ and EDTA, which do not affect the activity of the β-gaiactosidase, do however modify the hydrolysis of the cell wall mediated by the enzyme, and they also inhibit the autolytic process. Ca²⁺ decreased both processes, whereas EDTA increased them; and when both substances were added together, their individual effects were neutralized. The effects of both agents is probably due to modifications in the cell wall that prevent access of the enzyme to its substrate.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Effect of Metalaxyl on the incidence and severity of Pearl millet downy mildew disease in Northern Nigeria

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.     

Effect of temperature on the saccharide composition obtained after alpha-amylolysis of starch

The hydrolysis of starch to low-molecular-weight products (normally characterised by their dextrose equivalent (DE), which is directly related to the number-average molecular mass) was studied at different temperatures. Amylopectin potato starch, lacking amylose, was selected because of its low tendency towards retrogradation at lower temperatures. Bacillus licheniformis alpha-amylase was added to 10% [w/w] gelatinised starch solutions. The hydrolysis experiments were done at 50, 70, and 90 degrees C. Samples were taken at defined DE values and these were analysed with respect to their saccharide composition. At the same DE the oligosaccharide composition depended on the hydrolysis temperature. This implies that at the same net number of bonds hydrolysed by the enzyme, the saccharide composition was different. The hydrolysis temperature also influenced the initial overall molecular-weight distribution. Higher temperatures led to a more homogenous molecular weight distribution. Similar effects were observed for alpha-amylases from other microbial sources such as Bacillus amyloliquefaciens and Bacillus stearothermophilus. Varying the pH (5.1, 6.2, and 7.6) at 70 degrees C did not significantly influence the saccharide composition obtained during B. licheniformis alpha-amylase hydrolysis. The underlying mechanisms for B. licheniformis alpha-amylase were studied using pure linear oligosaccharides, ranging from maltotriose to maltoheptaose as substrates. Activation energies for the hydrolysis of individual oligosaccharides were calculated from Arrhenius plots at 60, 70, 80, and 90 degrees C. Oligosaccharides with a degree of polymerisation exceeding that of the substrate could be detected. The contribution of these oligosaccharides increased as the degree of polymerisation of the substrate decreased and the temperature of hydrolysis increased. The product specificity decreased with increasing temperature of hydrolysis, which led to a more equal distribution between the possible products formed. Calculations with the subsite map as determined for the closely related alpha-amylase from B. amyloliquefaciens reconfirmed this finding of a decreased substrate specificity with increased temperature of hydrolysis. Copyright 1999 John Wiley & Sons, Inc.     

Natural bile acids and synthetic analogues modulate large conductance Ca2+-activated K+ (BKCa) channel activity in smooth muscle cells

Bile acids have been reported to produce relaxation of smooth muscle both in vitro and in vivo. The cellular mechanisms underlying bile acid-induced relaxation are largely unknown. Here we demonstrate, using patch-clamp techniques, that natural bile acids and synthetic analogues reversibly increase BK(Ca) channel activity in rabbit mesenteric artery smooth muscle cells. In excised inside-out patches bile acid-induced increases in channel activity are characterized by a parallel leftward shift in the activity-voltage relationship. This increase in BK(Ca) channel activity is not due to Ca(2+)-dependent mechanism(s) or changes in freely diffusible messengers, but to a direct action of the bile acid on the channel protein itself or some closely associated component in the cell membrane. For naturally occurring bile acids, the magnitude of bile acid-induced increase in BK(Ca) channel activity is inversely related to the number of hydroxyl groups in the bile acid molecule. By using synthetic analogues, we demonstrate that such increase in activity is not affected by several chemical modifications in the lateral chain of the molecule, but is markedly favored by polar groups in the side of the steroid rings opposite to the side where the methyl groups are located, which stresses the importance of the planar polarity of the molecule. Bile acid-induced increases in BK(Ca) channel activity are also observed in smooth muscle cells freshly dissociated from rabbit main pulmonary artery and gallbladder, raising the possibility that a direct activation of BK(Ca) channels by these planar steroids is a widespread phenomenon in many smooth muscle cell types. Bile acid concentrations that increase BK(Ca) channel activity in mesenteric artery smooth muscle cells are found in the systemic circulation under a variety of human pathophysiological conditions, and their ability to enhance BK(Ca) channel activity may explain their relaxing effect on smooth muscle.