Involvement of epidermal cells in stomata movement: The effect of ABA

ABA affected K⁺ and solute transport between guard cells and epidermal cells as indicated by K⁺ staining and plasmolysis. ABA enhanced K⁺ (⁸⁶Rb) uptake into epidermal cells. To find out whether the ABA enhanced accumulation of K⁺ (⁸⁶Rb) in epidermal cells is active, uptake in the presence of exogenous ATP was studied. These studies hinted that K⁺ (⁸⁶Rb) uptake by epidermal cells is a passive process, while its release is an active one. This was verified by applying iodoacetate, which interferes with energy supply. The epidermal cells thus seem to play a role in stomatal movement.     

Stimulation of prostaglandin E2(PGE2) secretion by benzylpenicilloyl (BPO) carrier conjugates in human peripheral blood lymphocytes

The conjugates of the main determinant of penicillin, benzylpenicilloyl (BPO), with various protein carriers can stimulate mononuclear cells from human peripheral blood lymphocytes (PBL) to increase PGE₂ secretion. Thus, BPO bound to either human γ-globulin (BPO-HGG), bovine γ-globulin (BPO-BGG), and keyhole limpet menocyanin (BPO-KLH) increased the PGE₂ level 8–20 times above the level produced by stimulation with the carriers alone. Since in previous studies it was shown that preincubation with BPO-HGG can suppress the thymidine uptake after subsequent stimulation with BPO-KLH, we investigated if the induction of this unresponsiveness could be caused by PGE₂. The results of this study show that: (a) although the amount of PGE₂ secreted by the stimulation of BPO-HGG was 20-fold greater than the basic level, this amount is not sufficient to suppress significantly the thymidine uptake; (b) preincubation of PBL with higher than physiological concentration of externally added PGE₂ caused significant suppression of thymidine uptake after stimulation with BPO-KLH, but the addition of physiological concentration of PGE₂ did not show the same effect; (c) preincubation with BPO-HGG had no effect on PGE₂ level after subsequent challenge with BPO-KLH; and (d) inhibitor of PGE fails to influence the suppression of BPO-KLH proliferation induced by BPO-KLH.     

Inhibition or acceleration of tumor growth by subpopulations of thymus cells separable by a peanut lectin.

The effect of different lymphocytes subpopulations on tumor growth in mice was investigated using an in vivo adoptive neutralization test (Winn test). Thymocytes from non-tumor-bearing mice accelerated the growth of the tumors tested [Lewis lung carcinoma (3LL), thymoma 40-127-299 and fibrosarcoma P-14] when injected into syngeneic or F₁ mice in a mixture with the tumor cells. The thymocytes were separated with the aid of peanut agglutinin into immunologically mature and immature subpopulations (Reisner Y., Linker-Israeli and Sharon N., Cell. Immunol. 25, 129, 1976). The immature thymocytes accelerated tumor growth to an extent similar to that of the unfractionated cells, whereas the mature subpopulation exhibited pronounced inhibitory activity. Our findings demonstrate that the murine thymus contains two thymocyte subpopulations with opposite activities on tumor growth and that the mature thymocytes have an inhibitory effect on tumor growth similar to that of spleen cells.     

New backbone cyclic substance P analogs

Summary Structure-activity relationships of cyclic substance P (SP) analogs were extensively studied in our laboratories utilizing the new concept of backbone cyclization. Employing the C-terminal hexapeptide SP_6–11, we examined the influence of chemical changes in peptides containing backbone-to-amino-end cyclization. These changes in the ring have significant influence on activity, and should be carefully designed in order to optimize pharmacological feature.     

ALLOCATION OF CYSTEINE FOR GLUTATHIONE PRODUCTION IN CATERPILLARS WITH DIFFERENT ANTIOXIDANT DEFENSE STRATEGIES: A COMPARISON OF Lymantria dispar AND Malacosoma disstria

Sulfur amino acids [cysteine (Cys) and methionine (Met)] play two major roles during animal development: protein synthesis for growth and glutathione synthesis for defense. For caterpillars, the levels of sulfur amino acids found in foliar protein can be especially low relative to their nutritional needs. Previous work has measured concentrations of glutathione (GSH; containing Cys) in specific animal tissues, but has not examined whole‐body levels to ascertain the costliness of this defense in terms of Cys allocation. This study examined whether the production of GSH varies between species and within individuals in accordance with an insect's need for antioxidant defense. Secondly, we quantified the allocation of total Cys (peptide‐bound plus free Cys) to GSH in caterpillars as an estimate of its cost. Two contrasting species were compared: Lymantria dispar (Lymantriidae), a species that is highly defended, and Malacosoma disstria (Lasiocampidae), a species that is less defended. As expected, GSH levels were significantly higher in L. dispar than in M. disstria. Consistent with the function of the midgut as a first line of defense against ingested toxins, GSH levels were significantly higher in these tissues than in the whole bodies of both species. A major finding in this study was that a large fraction of total Cys is used to produce GSH: GSH in the midguts of L. dispar and M. disstria contained 23 and 21%, respectively, of the total Cys in these tissues, and the GSH in their remaining body tissues contained 19 and 17% of the total Cys in these tissues. Levels of total Cys in caterpillar tissues followed the same pattern of distribution as did GSH, producing a strong association between GSH and total Cys (R² = 0.794). We conclude that GSH is a costly defense, especially in generalist tree‐feeding species such as L. dispar. These results further suggest that the large allocation of Cys to GSH in highly defended species might produce a tradeoff by limiting the amount of Cys available for rapid growth.     

The Role of Aquaporins in pH-Dependent Germination of Rhizopus delemar Spores

Rhizopus delemar and associated species attack a wide range of fruit and vegetables after harvest. Host nutrients and acidic pH are required for optimal germination of R. delemar, and we studied how this process is triggered. Glucose induced spore swelling in an acidic environment, expressed by an up to 3-fold increase in spore diameter, whereas spore diameter was smaller in a neutral environment. When suspended in an acidic environment, the spores started to float, indicating a change in their density. Treatment of the spores with HgCl₂, an aquaporin blocker, prevented floating and inhibited spore swelling and germ-tube emergence, indicating the importance of water uptake at the early stages of germination. Two putative candidate aquaporin-encoding genes—RdAQP1 and RdAQP2—were identified in the R. delemar genome. Both presented the conserved NPA motif and six-transmembrane domain topology. Expressing RdAQP1 and RdAQP2 in Arabidopsis protoplasts increased the cells'' osmotic water permeability coefficient (P_f) compared to controls, indicating their role as water channels. A decrease in R. delemar aquaporin activity with increasing external pH suggested pH regulation of these proteins. Substitution of two histidine (His) residues, positioned on two loops facing the outer side of the cell, with alanine eliminated the pH sensing resulting in similar P_f values under acidic and basic conditions. Since hydration is critical for spore switching from the resting to activate state, we suggest that pH regulation of the aquaporins can regulate the initial phase of R. delemar spore germination, followed by germ-tube elongation and host-tissue infection.     

The Interaction of FABP with Kapα

Gene-activating lipophilic compounds are carried into the nucleus when loaded on fatty-acid-binding proteins (FABP). Some of these proteins are recognized by the α-Karyopherin (Kapα) through its nuclear localization signal (NLS) consisting of three positive residues that are not in a continuous sequence. The Importin system can distinguish between FABP loaded with activating and non-activating compounds. In the present study, we introduced molecular dynamics as a tool for clarifying the mechanism by which FABP4, loaded with activating ligand (linoleate) is recognized by Kapα. In the first phase, we simulated the complex between Kapα^ΔIBB (termed “Armadillo”) that was crystallized with two NLS hepta-peptides. The trajectory revealed that the crystal-structure orientation of the peptides is rapidly lost and new interactions dominate. Though, the NLS sequence of FABP4 is cryptic, since the functional residues are not in direct sequence, implicating more than one possible conformation. Therefore, four possible docked conformations were generated, in which the NLS of FABP4 is interacting with either the major or the minor sites of Kapα, and the N → C vectors are parallel or anti-parallel. Out of these four basic starting positions, only the FABP4-minor site complex exhibited a large number of contact points. In this complex, the FABP interacts with the minor and the major sites, suppressing the self-inhibitory interaction of the Kapα, rendering it free to react with Kapβ. Finally, we propose that the transportable conformation generated an extended hydrophobic domain which expanded out of the boundary of the FABP4, allowing the loaded linoleate to partially migrate out of the FABP into a joint complex in which the Kapα contributes part of a combined binding pocket.