A V region mutation in a phosphocholine-binding monoclonal antibody results in loss of antigen binding

A V region mutant producing an antibody that had lost the ability to bind phosphocholine was isolated from a hybridoma producing a germline encoded T15 antibody. The mutation resulted in a single aspartic acid to asparagine substitution at residue 95 of the H chain V region. This confirms that the aspartic acid at residue 95 plays a major role in Ag binding. The results also suggest that somatic cell genetic techniques can be used to generate mAb with useful changes in Ag binding.     

Novel peptides derived from a region of local homology between uteroglobin and lipocortin-1 inhibit platelet aggregation and secretion

The active site for uteroglobin inhibition of phospholipase A2 has been localized to a nonapeptide (P1) which is partially homologous to a nonapeptide (P2) in lipocortin, which also inhibits phospholipase A2. P1 and P2 share an identical tetrapeptide (P4) which is required for inhibition, although P4 alone does not inhibit this enzyme. We found the mechanism of inhibition of platelet aggregation and secretion by the nonapeptides and P4 varied depending on whether platelets were thrombin- or ADP-activated. All three peptides decrease thrombin esterolytic activity and thereby inhibit thrombin-induced platelet activation. P1 decreases ADP-induced aggregation and serotonin secretion by inhibiting phospholipase A2 whereas P4 decreases only aggregation by blocking fibrinogen binding to activated platelets. The P4 sequence in P1 may affect the interaction of P1 with platelets since the presence of P4 potentiates P1 inhibition of platelet activation.     

Quality of micropropagated plants—Vitrification

Summary Vitrification-Hyperhydrous shoot development, effects the survival and quality of several micropropagated plants ex-vitro. The leaves which are the immediate organ to be affected, exhibit abnormal morphology and physiology. Leaf malfunction is apparently a stress response to very rich media and high relative humidity. The understanding of the underlying mechanism of vitrification and its control in vitro can contribute to a more efficient micropropagation. Vitrification was found to be associated with elevated ethylene production which was related to hypolignification and poor cell wall development. Liquid and low agar media induced callose formation along with reduced and disoriented cellulose biosynthesis, manifested also in non-functioning guard cells. Malfunctioning stomata, in addition to defective cuticle contributed to increased transpiration and desiccation of in vitro formed leaves. The activity of various enzymes, associated with cell wall synthesis, was low and total proteins in normal leaves was higher than in vitreous ones. Various measures were found to reduce vitrification; lowered matrix and water potential in the medium, reduction in RH, low NH ₄ ⁺ , changes in Ca⁺⁺ levels and the removal of ethylene. These measures improved leaf morphogenesis, survival and the quality of several micropropagated plant species. Presented in the Session-in-Depth Transition of Plants From Culture to Establishment In Vivo,“ at the 41st Annual Meeting of the Tissue Culture Association, Houston, Texas, June 10–13, 1990.     

In vitro corm production in the saffron crocus (Crocus sativus L.)

Means to increase the reproductive capacity of Crocus sativus L., in vitro, are described. Cytokinins and auxin were found to be essential for development of bud explants. Ethylene and ethaphon pretreatments inhibited leaf development but induced corm production. Microsurgery of the apical bud combined with ethylene pretreatment increased both sprouting and corm production.     

Dopamine-Induced Apoptosis Is Inhibited in PC12 Cells Expressing Bcl-2

1. Degeneration of nigrostriatal dopaminergic neurons is the major pathogenic substrate of Parkinson's disease (PD). It is assumed that the lethal trigger is the accumulation of oxidative reactive species generated during metabolism of the natural neurotransmitter dopamine.2. We have recently shown that dopamine is capable of inducing programmed cell death (PCD) or apoptosis in cultured postmitotic chick sympathetic neurons and rat PC12 pheochromocytoma cells.3. The bcl-2 gene encodes a protein which blocks physiological PCD in many mammalian cells. In an attempt to elucidate further the mechanism of dopamine toxicity, we examined the potential protective effect of bcl-2 in PC12 cells which were transfected with the protooncogene.4. In our experiments, Bcl-2 producing cells showed a marked resistance to dopamine toxicity. The percentage of nuclear condensation and DNA fragmentation visualized by the end-labeling method following dopamine treatment was significantly lower in bcl-2 expressing cells. Bcl-2 did not protect PC12 cells against toxicity induced by exposure to dopamine-melanin. Extracts of PC12 cells containing Bcl-2 inhibited dopamine autooxidation and formation of dopamine-melanin. Furthermore, the presence of Bcl-2 protected cells from thiol imbalance and prevented thiol loss following exposure to dopamine.5. The protective effects of Bcl-2 against dopamine toxicity may be explained, in part, by its action as an antioxidant and by its interference in the production of toxic agents. The possible protection by Bcl-2 against neuronal degeneration caused by dopamine may play a role in the pathogenesis of PD andmay provide a new direction for the development of neuroprotective therapies.     

Plant-growth regulators derived from the sweetener stevioside

A series of isosteviol derivatives such as aromatic esters and amino acid amides were synthesized. Their effects on seed germination and root elongation of the crop plants, Capsicum annuum, Lens culinaris medicus, Lycopersicon esculentum, Trifollium spp. and Triticum vulgare, were studied. The derivatives could be arranged into four groups: (1) seed germination inhibitors (2) root elongation inhibitors (3) root elongation inducers (4) general inhibitors.     

Inactivation of photosynthetic electron flow during desiccation of desert biological sand crusts and Microcoleus sp.-enriched isolates.

Filamentous cyanobacteria, the main primary producers in biological sand crusts, survive harsh environmental conditions including diurnal desiccation/rehydration cycles. Here we describe the inactivation of photosystem II during dehydration of native crusts (NC) and Microcoleus sp. isolates grown on nitrocellulose filters (NCF). The morphology of NCF cells, visualized by scanning-transmission and atomic-force microscopy, disclosed long bacterial filaments encapsulated in extracellular polysaccharides (EPS) tubes consisting of parallel fibrils (100-400 nm wide and 50-100 nm high) oriented mostly perpendicular to the tube length. Presence of empty EPS tubes indicated a gliding capability of the cells. Desiccation of NC resulted in a rapid decline of F(o) and complete loss of F(v). These changes were accompanied by a decrease of 77 K PSII fluorescence emission relative to that of PSI, when excited at 430 nm, and a significant decrease of energy transfer from phycobilisomes to PSII. Lowering the turgor pressure through the addition of 1.5 M trehalose to natural crusts, reduced F(v)/F(m) by over 50% and was accompanied by a decrease of 77 K PSI fluorescence induced by chlorophyll excitation. Excitation of phycobilisomes resulted in a downshift of the PSI emission wavelength by 8 nm, indicative of reduced energy transfer from LHCI to the core PSI. Decline of F(v)/F(m) in trehalose-incubated NCF cells did not induce significant changes in 77 K fluorescence emission. These results suggest that alterations in energy transfer from antennae to reaction centers may be part of the survival strategy of Microcoleus.