Regulation of voltage-gated Ca channels by lipids

Great skepticism has surrounded the question of whether modulation of voltage-gated Ca²⁺ channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in Ca_V2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP₂), a palmitoylated accessory subunit (β_2a) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M₁ muscarinic receptors may stimulate multiple lipases to break down the PIP₂ associated with VGCCs and leave PIP₂'s freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs.     

Changes in responsiveness to ethylene and gibberellin during corolla expansion ofIpomoea nil

Corolla expansion inIpomoea nil appears to be triggered by changes in gibberellin concentration and ethylene production during development. We investigated the role of responsiveness to GA and ethylene in corolla expansion. The effects of growth regulators applied in vitro were measured as a change in area of corolla segments from younger (15–17 mm) and older (18–20 mm) whole corollas. Applied gibberellic acid (GA₃) significantly (p < 0.05) promoted growth in the younger segments but was less effective in the older segments. Moreover, applications of the GA biosynthesis inhibitors, PP333 (paclobutrazol) AMO₁₆₁₈ (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride), chlorocholine chloride, and tetcyclasis had little effect on younger segments but inhibited growth of older segments. The older corollas have apparently synthesized and accumulated enough GA-like substances to become less responsive to additional applied GA₃. The amount of growth induced by applied or endogenous GA depended on the amount of ethylene simultaneously produced in the tissue. The younger corollas rapidly produced ethylene from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and did not respond to applied ACC whereas the older corollas naturally produced much less ethylene and were significantly (p < 0.05) inhibited by applied ACC. When ethylene production was inhibited by applying aminoethoxyvinylglycine (AVG), growth was promoted in all segments. However, only the growth of the younger segments was further stimulated by simultaneously applied AVG and GA₃ over the GA₃ control. Thus the differential responses of segments from 15- to 20-mm long corollas to applied growth regulators reflect developmental changes in responsiveness of the developing corolla. The change in responsiveness is attributed in part to the changes in production of endogenous growth regulators and to the effect of one endogenous plant growth regulator (PGR) on the responsiveness of the corolla to another PGR.     

Protoplast formation and reversion in Actinomadurae

Summary The optimum conditions for efficient protoplast formation and regeneration in Actinomadura species have been determined. Effective protoplast formation in A. madurae, A. salmonea and strain 2AMI was accomplished using a growth medium containing 1.5% (w/v) glycine, harvested after 3 days growth. A combination of 3 cell wall lytic enzymes was essential for maximal conversion. Using surface spread cultures on a hypertonic regeneration medium, a high efficiency (60%) of regeneration was achieved. Cephamycin C production in strain 2AMI was unaffected.     

The levels of ecdysteroids in uninjured and leg-autotomized nymphs of Blattella germanica (L.)

The levels of ecdysteroids in control and leg-autotomized first-instar nymphs of Blattella germanica were determined by radioimmunoassay from hatching to the time of the first ecdysis. Uninjured nymphs showed a distinct release of ecdysteroids half-way through the stadium, and this resulted in the commencement of the moult cycle which formed the cuticle of the second instar. Cockroaches which had legs autotomized at 48 h after hatching (i.e. before the control ecydsteroid release) had their instar duration increased by that time period. Releases of ecdysteroids and events of the moulting cycle were also postponed by the 48 h period. The titre of ecdysteroids in injured animals was double that of controls. Nymphs were also autotomized at 96 h (i.e. after the normal release of ecdysteroids) but no changes in instar duration, ecdysteroid releases, or events of the moult cycle were recorded. The effects of injury, prothoracicotropic hormone activity and ecdysteroid release are discussed.     

Physiological Studies of Methane- and Methanol-Oxidizing Bacteria: Immunological Comparison of a Primary Alcohol Dehydrogenase from Methylococcus capsulatus and Pseudomonas sp. M27

A primary alcohol dehydrogenase was purified from cell extracts of two apparently unrelated microorganisms, namely, Pseudomonas sp. M27 and Methylococcus capsulatus. Rabbit antiserum prepared against the purified enzyme from M. capsulatus revealed distinctive antigenic determinants by quantitative and gel precipitin reactions. Rabbit antiserum to M27 enzyme detected both distinctive and shared antigenic determinants. Certain methane- and methanol-oxidizing bacteria were grouped on the basis of serological cross-reacting enzyme specificities.     

Queen substances from the abdomen of the honey bee queen

Summary The secretion of the mandibular glands of a honey bee queen enables the worker bees to react to the presence of their queen. Extirpating the mandibular glands of the queen does not prevent that she is accepted by her colony. Hitherto this was attributed to contamination of the queen's body by mandibular gland substances during or preceding the extirpation. When, however, these glands are extirpated before they have secreted any material and the queens are inseminated artificially, the colonies still accept these queens. A normal-sized retinue, the absence of emergency cell building and the absence of activation of the worker's ovaries indicate that such a queen is still able to maintain her social position. This supports Verheijen-Voogd's (1959) conclusion that the queen's influence on her workers has a behavioural basis (chemoreception) rather than a biochemical one.Laboratory experiments reveal that apart from the mandibular gland substances other queen pheromones are produced in glands on the abdomen, most probably in the glands described by Renner and Baumann (1964).     

Social Behaviour of the Carpenter Bee Xylocopa pubescens (Spinola)

The development of about 20 relatively small nests of Xylocopa pubescens was studied. After the first offspring had become adult, these nests reached a social stage in which there was only one egg-layer per nest. Freshly emerged (teneral) adults eat a lot of food, collected by a forager, before they fly out of the nest. This food appears to be of major importance to these bees in that it makes them fully agile. It seems therefore, that part of the food needed for the development of a young bee is not given at the larval stage, via the beebread, but at the teneral adult stage. As a result of this, a necessary overlap of generations is accomplished. Besides, less pollen has to be collected for the provision of a brood cell, so more cells can be constructed within a short period of time. There is a high degree of nest competition. Many nests were taken over by conspecific individuals (or by females of X. sulcatipes) that were searching for nesting sites within the study area. However, although more than 50% of the solitary nests were taken over sooner or later, strangers hardly ever intruded into social nests, with more than one adult. This illustrates how important it is for a reproducing female to tolerate the presence of nestmates which guard the nest in her absence. Although in most cases the foundress of a nest proceeded to produce new brood in the presence of her offspring, it happened that a daughter took over reproduction from her mother. In two of these cases, it could be observed that a mother started a new nest elsewhere after having been thrown out by her own daughter. At least in these cases, nest competition between mother and daughter started long before the mother had reached the end of her reproductive capacities. Since nesting possibilities are scarce, it seems a logical strategy to stay in the maternal nest and wait for a chance to become the egg-layer if the mother dies or if she loses her dominance. The occurrence of several social interactions among nestmates is discussed: — trophallaxis was observed often, not only under ‘forced’ conditions, but also as a form of ‘voluntary’ feeding; — nestmates were observed to groom each other.     

Biology of the stingless beePlebeia remota (Holmberg): observations and evolutionary implications

Summary The genusPlebeia has a special significance for the study of social evolution of stingless bees: morphologically primitive, its species display a wealth of behavioural evolution, especially with respect to the oviposition process. We comparePlebeia remota with the few other members of the genus studied so far.Related to its subtropical geographical range, brood production is seasonal (there is no brood in the colony in colder months), and adult workers occur as summer and winter bees. The nest is in tree cavities, and the involucrum is absent or restricted to the winter period. Brood cells are arranged in horizontal combs, and new cells are built completely synchronously. Each series consists of up to 50 cells, their number being mainly dependent on colony size. Construction speed is remarkably constant, allowing 4–6 batches per 24 hours. Cell building and provisioning are activities of a small group of specialized workers.The oviposition cycle follows the classical subdivisions for stingless bees. During the patrolling phase a worker may offer a trophic egg in a most remarkable way: while retreating backward from the queen she bends the abdomen under thorax and head, and lays an egg on the comb. This egg is eaten by the queen or a worker.The provisioning, oviposition and operculation of all cells occur simultaneously, each cell is provisioned by 4–9 workers. Localization of a cell by the queen may be facilitated by its characteristic guard, which defends the cell against the approaching queen. The degree of synchronization within a batch is very high: the duration per cell lasts 420–950 sec, the batch of up till 50 cells needs only 557–1160 sec. Operculation is done by a worker that was not involved in the previous steps.Males are generally produced by the queen. Several male producing cycles per year occur. In orphan colonies laying workers give rise to males, and in queenright colonies workers may occasionally reproduce as well.Division of labour follows the general pattern for stingless bees; however, cell building and provisioning are activities of a specialized group of workers.