Some features of secretory systems in plants

Synopsis Recent work on secretion in plants is reviewed, with emphasis on the anatomy and physiology of root cap cells in higher plants, the stalked glands ofDrosera capensis, and the secretory mechanism ofDionaea muscipula. Cells of the root cap of higher plants switch from a geo-perceptive role to one of mucilage secretion at maturation. Features of this process, the role of the Golgi and the pathway for mucilage distribution are reviewed. In contrast, the stalked glands of the leaves ofDrosera capensis are much longer lived and have a complex anatomy. The mechanisms for mucilage secretion, protein absorption and the role of the cell membranes in the internal secretion of the protein are described, using data from X-ray microscopv. The secretion of fluid and protein byDionaea is stimulated by various nitrogen-containing compounds. Uric acid, often excreted by captured insects, is particularly effective in this respect.     

A soluble CO- and NO-bindingc-type cytochrome inNeisseria meningitidis

Group BNeisseria meningitidis (SDIC) was grown aerobically in Mueller-Hinton medium to stationary phase and then broken either by sonic oscillation or high pressure extrusion from a French pressure cell. The particulate fraction (345,000×g, 3 h) contained cytochromesc, b, o, and evidence of ana-type. The supernatant fraction contained a solublec-type cytochrome (c ₅₄₉). The pyridine hemochrome derivatives of acid-acetone-extracted supernatant fractions were shown to be free of other cytochrome types. The solublec cytochrome increased during the growth cycle of the organism, reaching a maximum after cells entered stationary phase, whereas the cellular level of other cytochromes from the particulate fraction started to decline as cells progressed from log into stationary phase. Osmotic shock, as well as other treatments, failed to selectively release the solublec cytochrome from the cell. When untreated, thec ₅₄₉ in the supernatant fraction remained in a reduced form. While it was not air oxidizable, it was readily oxidizable with K₃Fe(CN)₆. In the reduced form, thec ₅₄₉ bound either CO or NO, but in the oxidized form, only NO was bound. The results obtained from this study indicate that the solublec ₅₄₉ is probably best classified as a cytochromec′.     

Recent Advances in Neuroblastoma

Neuroblastoma is one of the commoner tumors of infancy and childhood. There is great variation in the histological picture and even within one tumor. One unique feature is the apparently high rate of spontaneous regression, particularly during the first year of life. There is also a tendency for neuroblastoma to mature to the more benign ganglioneuroma and recent in vitro studies suggest that a serum factor may influence this process. Approximately 90 percent of patients with neuroblastoma excrete abnormally high quantities of various catecholamines, thus providing a useful diagnostic tool and a means for evaluating the effect of therapy.Treatment requires a multidisciplinary team approach involving a surgeon, radiotherapist and chemotherapist. Prognosis is influenced by a number of host factors and the most important of these seem to be the patient''s age at diagnosis and the extent of the disease, although some children with widespread disease appear to have a particularly good prognosis. It is difficult to evaluate the influence of chemotherapy on survival in patients with neuroblastoma but it has not been of great significance. The unique biologic characteristics of this tumor require further study in the hope of providing more effective therapy.     

Deficiencies in numerical models of anisotropic nonlinearly elastic materials

Incompressible nonlinearly hyperelastic materials are rarely simulated in finite element numerical experiments as being perfectly incompressible because of the numerical difficulties associated with globally satisfying this constraint. Most commercial finite element packages therefore assume that the material is slightly compressible. It is then further assumed that the corresponding strain-energy function can be decomposed additively into volumetric and deviatoric parts. We show that this decomposition is not physically realistic, especially for anisotropic materials, which are of particular interest for simulating the mechanical response of biological soft tissue. The most striking illustration of the shortcoming is that with this decomposition, an anisotropic cube under hydrostatic tension deforms into another cube instead of a hexahedron with non-parallel faces. Furthermore, commercial numerical codes require the specification of a ‘compressibility parameter’ (or ‘penalty factor’), which arises naturally from the flawed additive decomposition of the strain-energy function. This parameter is often linked to a ‘bulk modulus’, although this notion makes no sense for anisotropic solids; we show that it is essentially an arbitrary parameter and that infinitesimal changes to it result in significant changes in the predicted stress response. This is illustrated with numerical simulations for biaxial tension experiments of arteries, where the magnitude of the stress response is found to change by several orders of magnitude when infinitesimal changes in ‘Poisson’s ratio’ close to the perfect incompressibility limit of 1/2 are made.     

Substrate and endocrine responses during exercise at selected stages of pregnancy.

To determine whether the concomitant effects of pregnancy and exercise yield substrate and endocrine patterns different from those expected during exercise alone, we compared the responses of glucose, lactate, free fatty acids, insulin, epinephrine (EP), norepinephrine (NE), human chorionic gonadotropin (HCG), human placental lactogen (HPL), estriol, and progesterone (P) in nonpregnant women (NP; n = 7) and pregnant women in the second (TR2; n = 6) and third trimester (TR3; n = 8) of pregnancy, before, during, and after 30 min of bicycle ergometer exercise at heart rates of 130-140 beats/min. In general, all substrates and hormone concentrations increased with exercise (P less than 0.05), except insulin, which decreased (P less than 0.05), and HCG, which did not change (P = 0.08). Differences in selected hormone concentrations (P, estriol, HCG, and HPL) among groups were already present at rest because of the different stages of pregnancy. Differences among groups at rest were also found in insulin and NE (P less than 0.05). Significantly different responses to exercise (i.e., group x time interactions) were as follows. NP vs. TR2:P, estriol, HCG, HPL, EP, and NE (P less than 0.05); NP vs. TR3: glucose, EP, and NE (P less than 0.05); TR2 vs. TR3: lactate, EP, and NE (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of stilboestrol on sodium balance,cardiac state,and renin-angiotensin-aldosterone activity in prostatic carcinoma.

A prospective study examined the sequential effects of diethylstilboestrol (stilboestrol) on sodium balance, cardiac state, and renin-angiotensin-aldosterone activity in six patients with metastatic carcinoma of the prostate. Whereas metabolic balance studies did not show evidence of sodium retention during the first seven days of treatment, there was a significant and progressive increase in plasma volume after three months (mean increase 541 ml; p less than 0.01). Stilboestrol increased supine plasma renin and angiotensin II values but the response of renin-angiotensin-aldosterone activity to erect posture was progressively reduced during treatment. No significant changes in blood pressure or indices of cardiac function occurred during the three months of observation. The findings of increased basal renin-angiotensin-aldosterone activity and an increase in plasma volume suggest an important mechanism of the cardiac complications associated with oestrogen treatment.     

Characterization of epoxide hydrolase activity in shape Alternaria alternata f. sp. shape lycopersici. Possible involvement in toxin production

Using trans-diphenylpropane oxide (tDPPO) as a substrate, we measured epoxide hydrolase (EH) activity in subcellular fractions of Alternaria alternata f. sp. lycopersici (Aal), a fungus that produces host-specific toxins. The activity was mainly (>99.5%) located in the soluble fraction (100,000 × g supernatant) with the optimum pH at 7.4. An increase of toxin production between days 3 and 9 found in a Aal liquid culture over a 15 days period was concomitant with a period of high EH activity. EH activity remained constant during the same period in an Alternaria alternata culture, a fungus which does not produce toxin. In vivo treatment of Aal culture with the peroxisome proliferator clofibrate stimulated EH activity by 83% and enhanced toxin production 6.3 fold. Both 4-fluorochalcone oxide (4-FCO) and (2S,3S)-(-)-3-(4-nitrophenyl)-glycidol (SS-NPG) inhibited EH activity in vitro with a IM₅₀f 23 ± 1 μM and 72 ± 19 μM, respectively. The possible physiological substrate 9,10-epoxystearic acid was hydrolyzed more efficiently by Aal sEH than the model substrates trans- and cis-stilbene oxide (TSO and CSO) and trans- and cis-diphenylpropane oxide (tDPPO and cDPPO). This revised version was published online in June 2006 with corrections to the Cover Date.