Survival and retention of infectivity of bacterial stalk rot pathogen of maize and its perpetuation on varied cropping pattern

Summary The sterilized environment prompted the maize stalk rot pathogen Erwinia carotovora f. sp. zeae Sabet to retain its infectivity for a longer period than the unsterilized one. The survival as well as infectivity potency of the pathogen present in the soil having naturally-infested or artificially-inoculated host plant as debris was superior to that in the soil or even the soil containing maize stalk tissue. ‘Maize-potato-maize’ cropping pattern effected a considerable increase in the disease incidence due to maintainance of continuity of life of the pathogen in the intervening potato crop. re]19741113     

A new colorimetric method for the estimation of resorcinol

A new, rapid, simple, and sensitive colorimetric method for the estimation of resorcinol in microgram amounts is described.     

Purification and properties of trehalase from the thermophilic fungus Humicola lanuginosa.

Trehalase (alpha,alpha-Trehalose glucohydrolase, EC 3.2.1.28) was partially solubilized from the thermophilic fungus Humicola lanuginosa RM-B, and purified 184-fold. The purified enzyme was optimally active at 50 degrees C in acetate buffer at pH 5.5. It was highly specific for alpha,alpha-trehalose and had an apparent Km = 0.4 mM at 50 degrees C. None of the other disaccharides tested either inhibited or activated the enzyme. The molecular weight of the enzyme was around 170 000. Trehalase from mycelium grown at 40 and 50 degrees C had similar properties. The purified enzyme, in contrast to that in the crude-cell free extract, was less stable. At low concentration, purified trehalase was afforded protection against heat-inactivation by "protection against heat-inactivation by "protective factor(s)" present in mycelial extracts. The "protective factor(s)" was sensitive to proteolytic digestion. It was not diffusible and was stable to boiling for at least 30 min. Bovine serum albumin and casein also protected the enzyme from heat-inactivation.     

Single channel properties of d-Leu2-gramicidin A side chain modulation of channel lifetime

The channel forming properties of synthetic gramicidin A and dLeu²-gramicidin A were compared in black lipid membranes. The most probable single channel conductance was identical for both derivatives but in each case a distribution of smaller channel sizes was observed. However, the lifetime of the channel formed by dLeu²-gramicidin A was considerably shorter than for gramicidin A. The dLeu² substitution is considered to interfere with the head to head hydrogen bonding which forms the conducting dimer, thus destabilizing the dimeric structure of the channel and reducing the lifetime. This represents the first demonstration of side-chain modulation of channel lifetime.     

Histological and ultrastructural studies of the rabbit pars intermedia in organ culture

Pars intermedia (PI) tissue from fetal, perinatal, neonatal and juvenile rabbits has been maintained in organ culture for up to nine weeks after explantation. Autoradiography showed that DNA synthesis took place for at least 22 days of culturing. PI-glandular cells and interstitial cells remain identifiable throughout this period but ACT-type cells were recognised only up to six weeks. Material from fetal and perinatal animals had a higher proportion of surviving cells than that from adult animals. The degree of differentiation achieved by PI-glandular cells in vitro appears to depend on three factors: i) the stage of development reached before explantation; ii) the original topographic position in the PI tissue before explantation; and iii) the position in the explant in relation to the gas-liquid interphase.     

Detection of ischemia-reperfusion cardiac injury by cardiac muscle chemiluminescence

Various methods have been used in the past to assess the implication of oxygen free radicals (OFR) in ischemia-reperfusion-induced cardiac injury. Luminol-enhanced tert-butyl-initiated chemiluminescence in cardiac tissue reflects oxidative stress and is a very sensitive method. It was used to elucidate the role of OFR in cardiac injury due to ischemia and reperfusion. Studies were conducted on perfused isolated rabbit hearts in three groups (n = 8 in each): I, control; II, submitted to global ischemia for 30 min; III, submitted to ischemia for 30 min followed by reperfusion for 60 min. The heart tissue was then assayed for chemiluminescence (CL); content of malondialdehyde (MDA), an indicator of OFR-induced cardiac injury; and activity of tissue levels of antioxidants [superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-Px)].The control values for left and right ventricular CL and malondialdehyde were 81.1 ± 15.4 (S.E.) and 182.4 ± 50.3 (S.E.), mv-min-mg protein^–1; and 0.024 ± 0.006 (S.E.) and 0.324 ± 0.005 (S.E.) nmoles-mg protein^–1 respectively. Ischemia produced an increase in the cardiac CL (3.3 to 4.4 fold) and MDA content (2 to 2.6 fold). Reperfusion following ischemia also produced similar changes in CL and MDA content. The control values for activity of left ventricular SOD, catalase, and GSH-Px were 45.77 ± 1.73 (S.E.) U-mg protein^–1 5.35 ± 0.51 (S.E.) K-10^–3-sec^–1-mg protein^–1, and 77.50 ± 7.70 (S.E.) nmoles NADPH-min^–1-mg protein^–1 respectively. Activities of SOD and catalase decreased during ischemia but were similar to control values in ischemic-reperfused hearts. The GSH-Px activity of left ventricle was unaffected by ischemia, and ischemia-reperfusion. GSH-Px activity of the right ventricle increased with ischemia, and ischemic-reperfusion.These results indicate that cardiac tissue chemiluminescence would be a useful and sensitive tool for the detection of oxygen free radical-induced cardiac injury.     

Reduced free radical generation during reperfusion of hypothermically arrested hearts

Several studies indicate the presence of hydroxyl radical (OH·) as well as its involvement in the myocardial reperfusion injury. A transition metal-like iron is necessary for the conversion of superoxide anion (O₂ ^–) to a highly reactive and cytotoxic hydroxyl radical (OH·). In the present study, we have examined the generation of OH· and free iron in reperfused hearts following either normothermic (37°C) or hypothermic ischemia (5°C). Employing the Langendorff technique, isolated rat hearts were subjected to global ischemia for 30 min at 37°C or 5°C and were then reperfused for 15 min at 37°C. The results of the study suggest that both the OH· generation in myocardium and free iron release into perfusate were significantly lower in hearts made ischemic at 5°C as compared to 37°C. Release of myoglobin and lactic acid dehydrogenase into perfusate also followed a similar pattern. Furthermore, in in vitro studies, chemically generated O₂ ^– at 5°C caused a significantly lower rate of oxidation of oxymyoglobin as well as generation of OH° and free iron as compared to 37°C. These results suggest that (1) reperfusion of hypothermic ischemic heart is associated with a reduction in the generation of OH· and cellular damage compared to that of normothermic ischemic heart, and (2) myoglobin, an intracellular protein, is a source of free iron and plays a role in the reperfusion injury mediated by free radicals.Abbreviations OH· hydroxyl radical - O₂ ^– superoxide anion - ODFR oxygen-derived free radicals - KHB Krebs-Henseleit buffer - LDH lactate hydrogenase - SOD superoxide dismutase     

Nitrogen contribution of cowpea green manure and residue to upland rice

Cowpea, Vigna unguiculata (L.) Walp., is well adapted to acid upland soil and can be grown for seed, green manure, and fodder production. A 2-yr field experiment was conducted on an Aeric Tropaqualf in the Philippines to determine the effect of cowpea management practice on the response of a subsequent upland rice crop to applied urea. Cowpea was grown to flowering and incorporated as a green manure or grown to maturity with either grain and pods removed or all aboveground vegetation removed before sowing rice. Cowpea green manure accumulated on average 68 kg N ha⁻¹, and aboveground residue after harvest of dry pods contained on average 46 kg N ha⁻¹. Compared with a pre-rice fallow, cowpea green manure and residue increased grain yield of upland rice by 0.7 Mg ha⁻¹ when no urea was applied to rice. Green manure and residue substituted for 66 and 70 kg urea-N ha⁻¹ on upland rice, respectively. In the absence of urea, green manure and residue increased total aboveground N in mature rice by 12 and 14 kg N ha⁻¹, respectively. These increases corresponded to plant recoveries of 13% for applied green manure N and 24% for applied residue N. At 15 d after sowing rice (DAS), 33% of the added green manure N and 16% of the added residue N was recovered as soil (nitrate + ammonium)-N. At 30 DAS, the corresponding recoveries were 20 and 37% for green manure N and residue N, respectively. Cowpea cropping with removal of all aboveground cowpea vegetation slightly increased (p<0.05) soil (nitrate + ammonium)-N at 15 DAS as compared with the pre-rice fallow, but it did not increase rice yield. Cowpea residue remaining after harvest of dry pods can be an effective N source for a subsequent upland rice crop.