Immobilized and Free Apoplastic Pectinmethylesterases in Mung Bean Hypocotyl

The nature and the action pattern of apoplastic pectinmethylesterase (PME) isoforms were investigated in mung bean [Vigna radiata (L.) Wilzeck] hypocotyls. Successive extractions of neutral and alkaline PME isoforms present in hypocotyl native cell walls (referred to as PE1, PE2, PE3, PE4, with increasingly basic isoelectric points) revealed that solubilization of PE1, PE2, and PE4 did not induce any significant decrease in the cell-wall-bound PME activity. The in vitro de-esterification occurring when isolated cell walls were incubated with pectin resulted, then, from the activity of PE3. In addition, pH control of PME activity was shown to be much stronger for enzymes bound to cell walls, in their native state or reintroduced after solubilization, than for enzymes in solution. Mature cell walls showed much more activity than young cell walls, and were relatively enriched in two acidic PME isoforms missing in young cell walls. One acidic PME was also detected in the extracellular fluid. The acidic and neutral isoforms that could be easily transferred from their binding sites to their substrate might be those involved in the demethylation process developing along the mung bean hypocotyl.     

Effects of 3,5-Dibromo-4-Hydroxybenzonitrile (Bromoxynil) on Bioenergetics of Higher Plant Mitochondria (Pisum sativum)

The herbicide bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) was tested on mitochondria from etiolated pea (Pisum sativum L. cv Alaska) stems. This compound when used at micromolar concentrations ([almost equal to]20 [mu]M) inhibited malate- and succinate-dependent respiration by intact mitochondria but not oxidation of exogenously added NADH. Bromoxynil did not affect the activities of the succinic and the internal NADH dehydrogenases. Analyses of the effects induced by this herbicide on the membrane potential, [delta]pH, matrix Ca2+ movements, and dicarboxylate transport demonstrated that bromoxynil is likely to act as an inhibitor of the dicarboxylate carrier. In addition, bromoxynil caused a mild membrane uncoupling at concentrations [greater than or equal to]20 [mu]M. No effect on the ATPase activity was observed.     

Regulation of Sterol Content in Membranes by Subcellular Compartmentation of Steryl-Esters Accumulating in a Sterol-Overproducing Tobacco Mutant

The study of sterol overproduction in tissues of LAB 1-4 mutant tobacco (Nicotiana tabacum L. cv Xanthi) (P. Maillot-Vernier, H. Schaller, P. Benveniste, G. Belliard [1989] Biochem Biophys Res Commun 165: 125-130) over several generations showed that the overproduction phenotype is stable in calli, with a 10-fold stimulation of sterol content when compared with wild-type calli. However, leaves of LAB 1-4 plants obtained after two steps of self-fertilization were characterized by a mere 3-fold stimulation, whereas calli obtained from these plants retained a typical sterol-overproducing mutant phenotype (i.e. a 10-fold increase of sterol content). These results suggest that the expression of the LAB 1-4 phenotype is dependent on the differentiation state of cells. Most of the sterols accumulating in the mutant tissues were present as steryl-esters, which were minor species in wild-type tissues. Subcellular fractionation showed that in both mutant and wild-type tissues, free sterols were associated mainly with microsomal membranes. In contrast, the bulk of steryl-esters present in mutant tissues was found in the soluble fraction of cells. Numerous lipid droplets were detected in the hyaloplasm of LAB 1-4 cells by cytochemical and cytological techniques. After isolation, these lipid granules were shown to contain steryl-esters. These results show that the overproduced sterols of mutant tissues accumulate as steryl-esters in hyaloplasmic bodies. The esterification process thus allows regulation of the amount of free sterols in membranes by subcellular compartmentation.     

Neurogenic inflammation of Guinea-pig bladder

Capsaicin, substance P, and ovalbumin, instilled into the bladders of naive and ovalbumin (OVA) sensitized guineapigs caused inflammation, as indicated by increased vascular permeability. Histological changes after exposure to these compounds progressed with time from intense vasodilatation to marginalization of granulocytes followed by interstitial migration of leukocytes. In vitro incubation of guinea-pig bladder tissue with substance P and ovalbumin stimulated release of prostaglandin D(2) and leukotrienes. In vitro incubation of bladder tissue with capsaicin, OVA, prostaglandin D(2), leukotriene C(4), histamine, or calcium ionophore A-23587 all stimulated substance P release. These data suggest that bladder inflammation initiated by a variety of stimuli could lead to a cyclic pattern of release of inflammatory mediators and neuropeptides, which could result in amplification and persistence of cystitis after the inciting cause has subsided.     

Inhaled Nitric Oxide Counterbalances ET-1 Dependent Pulmonary Hypertension and Bronchoconstriction in the Pig

In anaesthetized, paralysed, ventilated pigs the ability of inhaled nitric oxide (80 ppm in 0(2)) to reduce the haemodynamic and respiratory effects of endothelin-1 administration (200 pmol/kg, i.v.) was evaluated. The mechanical properties of the respiratory system were evaluated by the rapid airway occlusion technique. The overall respiratory resistance, the interrupter resistance and the additional resistance that reflects the viscoelastic properties of tissues and the inequality of the time constant within the system were also evaluated. The results show that inhaled nitric oxide can act as a selective pulmonary vasodilator and as a bronchodilator to counteract the vasoconstrictor and bronchoconstrictor activity of endothelin-1. In the pig, nitric oxide inhaled at 80 ppm for 6 mitt reduced the changes in respiratory-, interrupter- and additional resistance due to endothelin-1 administration without significantly changing the static and dynamic elastance of the respiratory system.     

Conditioning of Parsley (Petroselinum crispum L.) Suspension Cells Increases Elicitor-Induced Incorporation of Cell Wall Phenolics

The elicitor-induced incorporation of phenylpropanoid derivatives into the cell wall and the secretion of soluble coumarin derivatives (phytoalexins) by parsley (Petroselinum crispum L.) suspension cultures can be potentiated by pretreatment of the cultures with 2,6-dichloroisonicotinic acid or derivatives of salicylic acid. To investigate this phenomenon further, the cell walls and an extracellular soluble polymer were isolated from control cells or cells treated with an elicitor from Phytophthora megasperma f. sp. glycinea. After alkaline hydrolysis, both fractions from elicited cells showed a greatly increased content of 4-coumaric, ferulic, and 4-hydroxybenzoic acid, as well as 4-hydroxybenzaldehyde and vanillin. Two minor peaks were identified as tyrosol and methoxytyrosol. The pretreatment effect is most pronounced at a low elicitor concentration. Its specificity was elaborated for coumarin secretion. When the parsley suspension cultures were preincubated for 1 d with 2,6-dichloroisonicotinic, 4- or 5-chlorosalicylic, or 3,5- dichlorosalicylic acid, the cells exhibited a greatly increased elicitor response. Pretreatment with isonicotinic, salicylic, acetylsalicylic, or 2,6-dihydroxybenzoic acid was less efficient in enhancing the response, and some other isomers were inactive. This increase in elicitor response was also observed for the above-mentioned monomeric phenolics, which were liberated from cell walls upon alkaline hydrolysis and for "lignin-like" cell wall polymers determined by the thioglycolic acid method. It was shown for 5-chlorosalicylic acid that conditioning most likely improves the signal transduction leading to the activation of genes encoding phenylalanine ammonia lyase and 4-coumarate: coenzyme A ligase. The conditioning thus sensitizes the parsley suspension cells to respond to lower elicitor concentrations. If a similar mechanism were to apply to whole plants treated with 2,6-dichloroisonicotinic acid, a known inducer of systemic acquired resistance, one can hypothesize that fungal pathogens might be recognized more readily and effectively.     

Chitinase: a novel target for blocking parasite transmission?

In many species of blood-sucking arthropod, the internal tissues are covered by chitinous material that may hinder parasite invasion. To circumvent this potential barrier, therefore, parasites have developed mechanisms that involve the enzyme chitinase. In this review, Mohammed Shohobuddin and David C. Kaslow examine the relationship between chitinase and parasite transmission.     

Female control of paternity

Of the two components of sexual selection, female choice is much less obvious than male-male competition, and hence has always been considered to be of secondary importance. However, recent field observations and new theory have brought about a radical change of emphasis. It now appears that although a female's choice of who fathers her offspring often occurs in a subtle manner, it may be widespread and take place through a variety of behavioural and physiological mechanisms, including the manipulation of male behaviour and the selection of sperm within the female reproductive tract.